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Sample records for polycrystalline si thin

  1. Photoluminescence from stain-etched polycrystalline Si thin films

    NASA Astrophysics Data System (ADS)

    Steckl, A. J.; Xu, J.; Mogul, H. C.

    1993-04-01

    Visible room-temperature photoluminescence has been observed from stain-etched polycrystalline Si thin films. Poly-Si thin films deposited on oxidized Si and quartz substrates became porous (PoSi) after stain-etching in a 1:3:5 solution of HF:HNO3:H2O. Under UV excitation, the stain-etched doped and undoped poly-Si films produce uniform orange-red (about 650 nm) luminescence very similar to that obtained from stain-etched crystalline Si substrates. Stained amorphous thin films did not exhibit photoluminescence. Luminescent patterns with sub-micrometer (about 0.6 micron) dimensions have been obtained for the first time from PoSi produced from poly-Si films.

  2. Effect of flash lamp annealing on electrical activation in boron-implanted polycrystalline Si thin films

    SciTech Connect

    Do, Woori; Jin, Won-Beom; Choi, Jungwan; Bae, Seung-Muk; Kim, Hyoung-June; Kim, Byung-Kuk; Park, Seungho; Hwang, Jin-Ha

    2014-10-15

    Highlights: • Intensified visible light irradiation was generated via a high-powered Xe arc lamp. • The disordered Si atomic structure absorbs the intensified visible light. • The rapid heating activates electrically boron-implanted Si thin films. • Flash lamp heating is applicable to low temperature polycrystalline Si thin films. - Abstract: Boron-implanted polycrystalline Si thin films on glass substrates were subjected to a short duration (1 ms) of intense visible light irradiation generated via a high-powered Xe arc lamp. The disordered Si atomic structure absorbs the intense visible light resulting from flash lamp annealing. The subsequent rapid heating results in the electrical activation of boron-implanted Si thin films, which is empirically observed using Hall measurements. The electrical activation is verified by the observed increase in the crystalline component of the Si structures resulting in higher transmittance. The feasibility of flash lamp annealing has also been demonstrated via a theoretical thermal prediction, indicating that the flash lamp annealing is applicable to low-temperature polycrystalline Si thin films.

  3. Polycrystalline Mg{sub 2}Si thin films: A theoretical investigation of their electronic transport properties

    SciTech Connect

    Balout, H.; Boulet, P.; Record, M.-C.

    2015-05-15

    The electronic structures and thermoelectric properties of a polycrystalline Mg{sub 2}Si thin film have been investigated by first-principle density-functional theory (DFT) and Boltzmann transport theory calculations within the constant-relaxation time approximation. The polycrystalline thin film has been simulated by assembling three types of slabs each having the orientation (001), (110) or (111) with a thickness of about 18 Å. The effect of applying the relaxation procedure to the thin film induces disorder in the structure that has been ascertained by calculating radial distribution functions. For the calculations of the thermoelectric properties, the energy gap has been fixed at the experimental value of 0.74 eV. The thermoelectric properties, namely the Seebeck coefficient, the electrical conductivity and the power factor, have been determined at three temperatures of 350 K, 600 K and 900 K with respect to both the energy levels and the p-type and n-type doping levels. The best Seebeck coefficient is obtained at 350 K: the S{sub yy} component of the tensor amounts to about ±1000 μV K{sup −1}, depending on the type of charge carriers. However, the electrical conductivity is much too small which results in low values of the figure of merit ZT. Structure–property relationship correlations based on directional radial distribution functions allow us to tentatively draw some explanations regarding the anisotropy of the electrical conductivity. Finally, the low ZT values obtained for the polycrystalline Mg{sub 2}Si thin film are paralleled with those recently reported in the literature for bulk chalcogenide glasses. - Graphical abstract: Structure of the polycrystalline thin film of Mg{sub 2}Si. - Author-Highlights: • Polycrystalline Mg{sub 2}Si film has been modelled by DFT approach. • Thermoelectric properties have been evaluated by semi-classical Boltzmann theory. • The structure was found to be slightly disordered after relaxation. • The highest

  4. Ambient condition laser writing of graphene structures on polycrystalline SiC thin film deposited on Si wafer

    SciTech Connect

    Yue, Naili; Zhang, Yong; Tsu, Raphael

    2013-02-18

    We report laser induced local conversion of polycrystalline SiC thin-films grown on Si wafers into multi-layer graphene, a process compatible with the Si based microelectronic technologies. The conversion can be achieved using a 532 nm CW laser with as little as 10 mW power, yielding {approx}1 {mu}m graphene discs without any mask. The conversion conditions are found to vary with the crystallinity of the film. More interestingly, the internal structure of the graphene disc, probed by Raman imaging, can be tuned with varying the film and illumination parameters, resembling either the fundamental or doughnut mode of a laser beam.

  5. Polycrystalline Mg2Si thin films: A theoretical investigation of their electronic transport properties

    NASA Astrophysics Data System (ADS)

    Balout, H.; Boulet, P.; Record, M.-C.

    2015-05-01

    The electronic structures and thermoelectric properties of a polycrystalline Mg2Si thin film have been investigated by first-principle density-functional theory (DFT) and Boltzmann transport theory calculations within the constant-relaxation time approximation. The polycrystalline thin film has been simulated by assembling three types of slabs each having the orientation (001), (110) or (111) with a thickness of about 18 Å. The effect of applying the relaxation procedure to the thin film induces disorder in the structure that has been ascertained by calculating radial distribution functions. For the calculations of the thermoelectric properties, the energy gap has been fixed at the experimental value of 0.74 eV. The thermoelectric properties, namely the Seebeck coefficient, the electrical conductivity and the power factor, have been determined at three temperatures of 350 K, 600 K and 900 K with respect to both the energy levels and the p-type and n-type doping levels. The best Seebeck coefficient is obtained at 350 K: the Syy component of the tensor amounts to about ±1000 μV K-1, depending on the type of charge carriers. However, the electrical conductivity is much too small which results in low values of the figure of merit ZT. Structure-property relationship correlations based on directional radial distribution functions allow us to tentatively draw some explanations regarding the anisotropy of the electrical conductivity. Finally, the low ZT values obtained for the polycrystalline Mg2Si thin film are paralleled with those recently reported in the literature for bulk chalcogenide glasses.

  6. Electrical and thermal properties of polycrystalline Si thin films with phononic crystal nanopatterning for thermoelectric applications

    NASA Astrophysics Data System (ADS)

    Nomura, Masahiro; Kage, Yuta; Müller, David; Moser, Dominik; Paul, Oliver

    2015-06-01

    Electrical and thermal properties of polycrystalline Si thin films with two-dimensional phononic patterning were investigated at room temperature. Electrical and thermal conductivities for the phononic crystal nanostructures with a variety of radii of the circular holes were measured to systematically investigate the impact of the nanopatterning. The concept of phonon-glass and electron-crystal is valid in the investigated electron and phonon transport systems with the neck size of 80 nm. The thermal conductivity is more sensitive than the electrical conductivity to the nanopatterning due to the longer mean free path of the thermal phonons than that of the charge carriers. The values of the figure of merit ZT were 0.065 and 0.035, and the enhancement factors were 2 and 4 for the p-doped and n-doped phononic crystals compared to the unpatterned thin films, respectively, when the characteristic size of the phononic crystal nanostructure is below 100 nm. The greater enhancement factor of ZT for the n-doped sample seems to result from the strong phonon scattering by heavy phosphorus atoms at the grain boundaries.

  7. Electrical and thermal properties of polycrystalline Si thin films with phononic crystal nanopatterning for thermoelectric applications

    SciTech Connect

    Nomura, Masahiro; Kage, Yuta; Müller, David; Moser, Dominik; Paul, Oliver

    2015-06-01

    Electrical and thermal properties of polycrystalline Si thin films with two-dimensional phononic patterning were investigated at room temperature. Electrical and thermal conductivities for the phononic crystal nanostructures with a variety of radii of the circular holes were measured to systematically investigate the impact of the nanopatterning. The concept of phonon-glass and electron-crystal is valid in the investigated electron and phonon transport systems with the neck size of 80 nm. The thermal conductivity is more sensitive than the electrical conductivity to the nanopatterning due to the longer mean free path of the thermal phonons than that of the charge carriers. The values of the figure of merit ZT were 0.065 and 0.035, and the enhancement factors were 2 and 4 for the p-doped and n-doped phononic crystals compared to the unpatterned thin films, respectively, when the characteristic size of the phononic crystal nanostructure is below 100 nm. The greater enhancement factor of ZT for the n-doped sample seems to result from the strong phonon scattering by heavy phosphorus atoms at the grain boundaries.

  8. Low Temperature Deposition of PECVD Polycrystalline Silicon Thin Films using SiF4 / SiH4 mixture

    NASA Astrophysics Data System (ADS)

    Syed, Moniruzzaman; Inokuma, Takao; Kurata, Yoshihiro; Hasegawa, Seiichi

    2016-03-01

    Polycrystalline silicon films with a strong (110) texture were prepared at 400°C by a plasma-enhanced chemical vapor deposition using different SiF4 flow rates ([SiF4] = 0-0.5 sccm) under a fixed SiH4 flow rate ([SiH4] = 1 or 0.15 sccm). The effects of the addition of SiF4 to SiH4 on the structural properties of the films were studied by Raman scattering, X-ray diffraction (XRD), Atomic force microscopy and stress measurements. For [SiH4] = 1 sccm, the crystallinity and the (110) XRD grain size monotonically increased with increasing [SiF4] and their respective maxima reach 90% and 900 Å. However, for [SiH4] = 0.15 sccm, both the crystallinity and the grain size decreased with [SiF4]. Mechanisms causing the change in crystallinity are discussed, and it was suggested that an improvement in the crystallinity, due to the addition of SiF4, is likely to be caused by the effect of a change in the surface morphology of the substrates along with the effect of in situ chemical cleaning.

  9. SEMICONDUCTOR DEVICES: A process simplification scheme for fabricating CMOS polycrystalline-Si thin film transistors

    NASA Astrophysics Data System (ADS)

    Miin-Horng, Juang; Chia-Wei, Chang; Der-Chih, Shye; Chuan-Chou, Hwang; Jih-Liang, Wang; Sheng-Liang, Jang

    2010-06-01

    A process simplification scheme for fabricating CMOS poly-Si thin-film transistors (TFTs) has been proposed, which employs large-angle-tilt-implantation of dopant through a gate sidewall spacer (LATITS). By this LATITS scheme, a lightly doped drain region under the oxide spacer is formed by low-dose tilt implantation of phosphorus (or boron) dopant through the spacer, and then the n+-source/drain (n+-S/D) (or p+-S/D) region is formed via using the same photo-mask layer during CMOS integration. For both n-TFT and p-TFT devices, as compared to the sample with conventional single n+-S/D (or p+-S/D) structure, the LATITS scheme can cause an obviously smaller leakage current, due to more gradual dopant distribution and thus smaller electric field. In addition, the resultant on-state currents only show slight degradation for the LATITS scheme. As a result, by the LATITS scheme, CMOS poly-Si TFT devices with an on/off current ratio well above 8 orders may be achieved without needing extra photo-mask layers during CMOS integration.

  10. Polycrystalline thin film photovoltaic technology

    SciTech Connect

    Ullal, H.S.; Zweibel, K.; Mitchell, R.L.; Noufi, R.

    1991-03-01

    Low-cost, high-efficiency thin-film modules are an exciting photovoltaic technology option for generating cost-effective electricity in 1995 and beyond. In this paper we review the significant technical progress made in the following thin films: copper indium diselenide, cadmium telluride, and polycrystalline thin silicon films. Also, the recent US DOE/SERI initiative to commercialize these emerging technologies is discussed. 6 refs., 9 figs.

  11. Comparison of ZnO thin films grown on a polycrystalline 3C-SiC buffer layer by RF magnetron sputtering and a sol-gel method

    NASA Astrophysics Data System (ADS)

    Phan, Duy-Thach; Chung, Gwiy-Sang

    2011-02-01

    Zinc oxide (ZnO) thin films were deposited on a polycrystalline (poly) 3C-SiC buffer layer using RF magnetron sputtering and a sol-gel method. The post-deposition annealing was performed on ZnO thin films prepared using both methods. The formation of ZnO piezoelectric thin films with less residual stress was due to a close lattice mismatch of the ZnO and SiC layers as obtained by the sputtering method. Nanocrystalline, porous ZnO film prepared using the sol-gel method showed strong ultraviolet UV emission at a wavelength of 380 nm. The 3C-SiC buffer layer improved the optical and piezoelectric properties of the ZnO film produced by the two deposition methods. Moreover, the different structures of the ZnO films on the 3C-SiC intermediate layer caused by the different deposition techniques were also considered and discussed.

  12. Thin film polycrystalline Si solar cells studied in transient regime by optical pump-terahertz probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Pikna, P.; Skoromets, V.; Becker, C.; Fejfar, A.; Kužel, P.

    2015-12-01

    We used time-resolved terahertz spectroscopy to study ultrafast photoconductivity of polycrystalline thin-film silicon solar cells. We selected a series of samples, which exhibited variable conversion efficiencies due to hydrogen plasma passivation under various technological conditions. The decay of the transient terahertz conductivity shows two components: the fast one is related to the charge recombination at interfaces, while the slow nanosecond one is attributed to the trapping of photocarriers by defects localized at grain boundaries or at dislocations in the polycrystalline p- layer of the structure. We observed a clear correlation between the open-circuit voltage and the nanosecond-scale decay time of the transient terahertz conductivity of the solar cells. Thus, the terahertz spectroscopy appears to be a useful contactless tool for inspecting the local photoconductivity of solar cells including, in particular, various nanostructured schemes.

  13. Polycrystalline domain structure of pentacene thin films epitaxially grown on a hydrogen-terminated Si(111) surface

    SciTech Connect

    Nishikata, S.; Sadowski, J. T.; Al-Mahboob, A.; Nishihara, T.; Fujikawa, Y.; Sakurai, T.; Nakajima, K.; Sazaki, G.; Suto, S.

    2007-10-15

    Single-monolayer high pentacene (Pn) dendrites grown on a hydrogen-terminated Si(111) surface [H-Si(111)] under ultrahigh vacuum were observed by low-energy electron microscopy and microbeam low-energy electron diffraction analyses. We determined the epitaxial structure (type I) inside a unique polycrystalline domain structure of such dendrites, each of which has six equivalent epitaxial orientations of Pn two-dimensional (2D) unit cells. There are three sets of these cells, which are rotated {+-}120 deg. relative to each other. Domain boundaries inside each dendrite were successfully observed by scanning tunneling microscopy. In addition, we found another epitaxial relation (type II): the polycrystalline domain structure and lattice parameters are similar to those of the type-I dendrite; however, the 2D unit cells of the type-II dendrite are rotated approximately 90 deg. relative to those of the type-I dendrite. These results suggest that the crystal structure of the dendrites on H-Si(111) is determined mainly by the interaction between Pn molecules. Each dendrite is composed of domains that are exclusively of type I or II. The so-called point-on-line coincidences are found between the Pn 2D lattices of types I and II, and H-Si(111). The higher commensurability of the type-I dendrites than the type-II dendrites results in a higher probability of type-I dendrite formation. Moreover, for both the type-I and type-II dendrites, we found supercell structures. We estimated the minimum interface energy between the dendrite and H-Si(111) from an island's free energy, which is necessary to reproduce the growth of a single-monolayer high dendrite.

  14. Characterization of excimer laser annealed polycrystalline Si1-xGex alloy thin films by x-ray diffraction and spectroscopic ellipsometry

    NASA Astrophysics Data System (ADS)

    Yu, Guolin; Krishna, Kalaga Murali; Shao, Chunlin; Umeno, Masayoshi; Soga, Tetsuo; Watanabe, Junji; Jimbo, Takashi

    1998-01-01

    Thin films of Si1-xGex alloys of different compositions x have been deposited, on single-crystal Si (100) surface and glass substrates, by simple ion beam sputtering, at room temperature. Crystallization of these films has been done using excimer laser annealing. Structural and optical properties of as-deposited and annealed Si1-xGex alloy films are characterized by x-ray diffraction (XRD), uv-visible spectrophotometry, spectroscopic ellipsometry (SE), and Auger electron spectroscopy (AES). The as-deposited films, both on Si and glass, have been found to be amorphous by XRD. Polycrystalline nature of laser-annealed samples has been evidenced by both x-ray and SE measurements. The results of x-ray, uv-visible, AES, and SE are compared and discussed. The poly-Si1-xGex films were oriented predominantly to (111) and the grain sizes were determined from half-width of x-ray peaks. The compositions x of Si1-xGex films have been evaluated from the SE dielectric function ɛ(ω) data, using the second-derivative technique, and are found to be 0.23 and 0.36 for two different compositions. A detailed analysis of ɛ(ω) with the effective-medium theory has demonstrated the volume fraction of crystalline Si1-xGex increases with the increasing energy of laser irradiation.

  15. Preparation of translucent Gd2Si2O7:Ce polycrystalline thin plates and their scintillation performance for α-particles

    NASA Astrophysics Data System (ADS)

    Nishikata, Mami; Ueda, Aki; Higuchi, Mikio; Kaneko, Junichi H.; Tsubota, Youichi; Ishibashi, Hiroyuki

    2015-07-01

    Translucent Gd2Si2O7:Ce (GPS:Ce) polycrystalline plates were prepared via liquid-phase sintering using SiO2 as a self-flux, and their scintillation performances for α-particles were investigated. Dense sintered compacts comprising large grains, some of which were larger than 100 μm in diameter, were successfully prepared by sintering at 1690 °C for 100 h. The best result was obtained with the powder comprising only <40 μm particles. Any combination of powders of <40 μm and <15 μm resulted in inhomogeneous structures with smaller grains of about 50 μm. A translucent GPS:Ce thin plate was fabricated by grinding the sintered compact that contained excess SiO2 of 8 mol%. Since the plate was composed of large grains, scattering at the grain boundaries was effectively suppressed and many of the grains virtually act as single crystals when the plate thickness was less than 100 μm. Therefore, the decrease in the plate thickness brought increase in the total transmission, and light yield and energy resolution were consequently improved. When the plate thickness was 50 μm, light yield was 82% as compared with that of a GPS:Ce single crystal as a reference, and energy resolution attained to 13%.

  16. Polycrystalline-thin-film thermophotovoltaic cells

    NASA Astrophysics Data System (ADS)

    Dhere, Neelkanth G.

    1996-02-01

    Thermophotovoltaic (TPV) cells convert thermal energy to electricity. Modularity, portability, silent operation, absence of moving parts, reduced air pollution, rapid start-up, high power densities, potentially high conversion efficiencies, choice of a wide range of heat sources employing fossil fuels, biomass, and even solar radiation are key advantages of TPV cells in comparison with fuel cells, thermionic and thermoelectric convertors, and heat engines. The potential applications of TPV systems include: remote electricity supplies, transportation, co-generation, electric-grid independent appliances, and space, aerospace, and military power applications. The range of bandgaps for achieving high conversion efficiencies using low temperature (1000-2000 K) black-body or selective radiators is in the 0.5-0.75 eV range. Present high efficiency convertors are based on single crystalline materials such as In1-xGaxAs, GaSb, and Ga1-xInxSb. Several polycrystalline thin films such as Hg1-xCdxTe, Sn1-xCd2xTe2, and Pb1-xCdxTe, etc., have great potential for economic large-scale applications. A small fraction of the high concentration of charge carriers generated at high fluences effectively saturates the large density of defects in polycrystalline thin films. Photovoltaic conversion efficiencies of polycrystalline thin films and PV solar cells are comparable to single crystalline Si solar cells, e.g., 17.1% for CuIn1-xGaxSe2 and 15.8% for CdTe. The best recombination-state density Nt is in the range of 10-15-10-16 cm-3 acceptable for TPV applications. Higher efficiencies may be achieved because of the higher fluences, possibility of bandgap tailoring, and use of selective emitters such as rare earth oxides (erbia, holmia, yttria) and rare earth-yttrium aluminium garnets. As compared to higher bandgap semiconductors such as CdTe, it is easier to dope the lower bandgap semiconductors. TPV cell development can benefit from the more mature PV solar cell and opto

  17. Polycrystalline thin-film solar cells and modules

    SciTech Connect

    Ullal, H.S.; Stone, J.L.; Zweibel, K.; Surek, T.; Mitchell, R.L.

    1991-12-01

    This paper describes the recent technological advances in polycrystalline thin-film solar cells and modules. Three thin film materials, namely, cadmium telluride (CdTe), copper indium diselenide (CuInSe{sub 2}, CIS) and silicon films (Si-films) have made substantial technical progress, both in device and module performance. Early stability results for modules tested outdoors by various groups worldwide are also encouraging. The major global players actively involved in the development of the these technologies are discussed. Technical issues related to these materials are elucidated. Three 20-kW polycrystalline thin-film demonstration photovoltaic (PV) systems are expected to be installed in Davis, CA in 1992 as part of the Photovoltaics for Utility-Scale Applications (PVUSA) project. This is a joint project between the US Department of Energy (DOE), Pacific Gas and Electric (PG&E), Electric Power Research Institute (EPRI), California Energy Commission (CEC), and a utility consortium.

  18. Polycrystalline thin-film solar cells and modules

    SciTech Connect

    Ullal, H.S.; Stone, J.L.; Zweibel, K.; Surek, T.; Mitchell, R.L.

    1991-12-01

    This paper describes the recent technological advances in polycrystalline thin-film solar cells and modules. Three thin film materials, namely, cadmium telluride (CdTe), copper indium diselenide (CuInSe{sub 2}, CIS) and silicon films (Si-films) have made substantial technical progress, both in device and module performance. Early stability results for modules tested outdoors by various groups worldwide are also encouraging. The major global players actively involved in the development of the these technologies are discussed. Technical issues related to these materials are elucidated. Three 20-kW polycrystalline thin-film demonstration photovoltaic (PV) systems are expected to be installed in Davis, CA in 1992 as part of the Photovoltaics for Utility-Scale Applications (PVUSA) project. This is a joint project between the US Department of Energy (DOE), Pacific Gas and Electric (PG E), Electric Power Research Institute (EPRI), California Energy Commission (CEC), and a utility consortium.

  19. Polycrystalline thin films FY 1992 project report

    SciTech Connect

    Zweibel, K.

    1993-01-01

    This report summarizes the activities and results of the Polycrystalline Thin Film Project during FY 1992. The purpose of the DOE/NREL PV (photovoltaic) Program is to facilitate the development of PV that can be used on a large enough scale to produce a significant amount of energy in the US and worldwide. The PV technologies under the Polycrystalline Thin Film project are among the most exciting ``next-generation`` options for achieving this goal. Over the last 15 years, cell-level progress has been steady, with laboratory cell efficiencies reaching levels of 15 to 16%. This progress, combined with potentially inexpensive manufacturing methods, has attracted significant commercial interest from US and international companies. The NREL/DOE program is designed to support the efforts of US companies through cost-shared subcontracts (called ``government/industry partnerships``) that we manage and fund and through collaborative technology development work among industry, universities, and our laboratory.

  20. Polycrystalline thin films FY 1992 project report

    SciTech Connect

    Zweibel, K.

    1993-01-01

    This report summarizes the activities and results of the Polycrystalline Thin Film Project during FY 1992. The purpose of the DOE/NREL PV (photovoltaic) Program is to facilitate the development of PV that can be used on a large enough scale to produce a significant amount of energy in the US and worldwide. The PV technologies under the Polycrystalline Thin Film project are among the most exciting next-generation'' options for achieving this goal. Over the last 15 years, cell-level progress has been steady, with laboratory cell efficiencies reaching levels of 15 to 16%. This progress, combined with potentially inexpensive manufacturing methods, has attracted significant commercial interest from US and international companies. The NREL/DOE program is designed to support the efforts of US companies through cost-shared subcontracts (called government/industry partnerships'') that we manage and fund and through collaborative technology development work among industry, universities, and our laboratory.

  1. Polycrystalline thin-film technology: Recent progress in photovoltaics

    SciTech Connect

    Mitchell, R.L.; Zweibel, K.; Ullal, H.S.

    1991-12-01

    Polycrystalline thin films have made significant technical progress in the past year. Three of these materials that have been studied extensively for photovoltaic (PV) power applications are copper indium diselenide (CuInSe{sub 2}), cadmium telluride (CdTe), and thin-film polycrystalline silicon (x-Si) deposited on ceramic substrates. The first of these materials, polycrystalline thin-film CuInSe{sub 2}, has made some rapid advances in terms of high efficiency and long-term reliability. For CuInSe{sub 2} power modules, a world record has been reported on a 0.4-m{sup 2} module with an aperture-area efficiency of 10.4% and a power output of 40.4 W. Additionally, outdoor reliability testing of CuInSe{sub 2} modules, under both loaded and open-circuit conditions, has resulted in only minor changes in module performance after more than 1000 days of continuous exposure to natural sunlight. CdTe module research has also resulted in several recent improvements. Module performance has been increased with device areas reaching nearly 900 cm{sup 2}. Deposition has been demonstrated by several different techniques, including electrodeposition, spraying, and screen printing. Outdoor reliability testing of CdTe modules was also carried out under both loaded and open-circuit conditions, with more than 600 days of continuous exposure to natural sunlight. These tests were also encouraging and indicated that the modules were stable within measurement error. The highest reported aperture-area module efficiency for CdTe modules is 10%; the semiconductor material was deposited by electrodeposition. A thin-film CdTe photovoltaic system with a power output of 54 W has been deployed in Saudi Arabia for water pumping. The Module Development Initiative has made significant progress in support of the Polycrystalline Thin-Film Program in the past year, and results are presented in this paper.

  2. US polycrystalline thin film solar cells program

    SciTech Connect

    Ullal, H S; Zweibel, K; Mitchell, R L

    1989-11-01

    The Polycrystalline Thin Film Solar Cells Program, part of the United States National Photovoltaic Program, performs R D on copper indium diselenide and cadmium telluride thin films. The objective of the Program is to support research to develop cells and modules that meet the US Department of Energy's long-term goals by achieving high efficiencies (15%-20%), low-cost ($50/m{sup 2}), and long-time reliability (30 years). The importance of work in this area is due to the fact that the polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells and modules have made rapid advances. They have become the leading thin films for PV in terms of efficiency and stability. The US Department of Energy has increased its funding through an initiative through the Solar Energy Research Institute in CuInSe{sub 2} and CdTe with subcontracts to start in Spring 1990. 23 refs., 5 figs.

  3. Modeling of polycrystalline thin film solar cells

    NASA Astrophysics Data System (ADS)

    Fahrenbruch, Alan L.

    1999-03-01

    This paper describes modeling polycrystalline thin-film solar cells using the program AMPS-1D1 to visualize the relationships between the many variables involved. These simulations are steps toward two dimensional modeling the effects of grain boundaries in polycrystalline cells. Although this paper describes results for the CdS/CdTe cell, the ideas presented here are applicable to copper-indium-gallium selenide (CIGS) cells as well as other types of cells. Results of these one-dimensional simulations are presented: (a) the duplication of experimentally observed cell parameters, (b) the effects of back-contact potential barrier height and its relation to stressing the cell, (c) the effects of the depletion layer width in the CdTe layer on cell parameters, and (d) the effects of CdS layer thickness on the cell parameters. Experience using the software is also described.

  4. Polycrystalline thin film materials and devices

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E. . Inst. of Energy Conversion)

    1992-10-01

    Results of Phase II of a research program on polycrystalline thin film heterojunction solar cells are presented. Relations between processing, materials properties and device performance were studied. The analysis of these solar cells explains how minority carrier recombination at the interface and at grain boundaries can be reduced by doping of windows and absorber layers, such as in high efficiency CdTe and CuInSe{sub 2} based solar cells. The additional geometric dimension introduced by the polycrystallinity must be taken into consideration. The solar cells are limited by the diode current, caused by recombination in the space charge region. J-V characteristics of CuInSe{sub 2}/(CdZn)S cells were analyzed. Current-voltage and spectral response measurements were also made on high efficiency CdTe/CdS thin film solar cells prepared by vacuum evaporation. Cu-In bilayers were reacted with Se and H{sub 2}Se gas to form CuInSe{sub 2} films; the reaction pathways and the precursor were studied. Several approaches to fabrication of these thin film solar cells in a superstrate configuration were explored. A self-consistent picture of the effects of processing on the evolution of CdTe cells was developed.

  5. Progress in polycrystalline thin-film solar cells

    SciTech Connect

    Zweibel, K; Hermann, A; Mitchell, R

    1983-07-01

    Photovoltaic devices based on several polycrystalline thin-film materials have reached near and above 10% sunlight-to-electricity conversion efficiencies. This paper examines the various polycrystalline thin-film PV materials including CuInSe/sub 2/ and CdTe in terms of their material properties, fabrication techniques, problems, and potentials.

  6. Helium irradiation effects in polycrystalline Si, silica, and single crystal Si

    SciTech Connect

    Abrams, K. J.; Greaves, G.; Berg, J. A. van den; Hinks, J. A.; Donnelly, S. E.; Pawley, C. J.; Eyidi, D.; Ward, M. B.

    2012-04-15

    Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin ({approx_equal}55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change.

  7. Polycrystalline Thin-Film Research: Cadmium Telluride (Fact Sheet)

    SciTech Connect

    Not Available

    2013-06-01

    This National Center for Photovoltaics sheet describes the capabilities of its polycrystalline thin-film research in the area of cadmium telluride. The scope and core competencies and capabilities are discussed.

  8. Polycrystalline Thin-Film Research: Cadmium Telluride (Fact Sheet)

    SciTech Connect

    Not Available

    2011-06-01

    Capabilities fact sheet that includes scope, core competencies and capabilities, and contact/web information for Polycrystalline Thin-Film Research: Cadmium Telluride at the National Center for Photovoltaics.

  9. Polycrystalline silicon thin films crystallized by green laser

    NASA Astrophysics Data System (ADS)

    Yuan, Zhijun; Lou, Qihong; Zhou, Jun; Liu, Xia; Wang, Wei; Su, Zhouping

    2008-12-01

    A top hat beam of frequency-doubled Nd: YAG laser is obtained from our beam shaping optical system. With this beam, amorphous silicon thin films deposited on glass by plasma-enhanced chemical vapor deposition (PECVD) are successfully crystallized. The surface morphology of the laser-crystallized materials is studied by atomic force microscopy (AFM). Pronounced increase in surface roughness after the laser treatment could be observed from the Microscope Photos. Raman spectra of the Si films are measured to confirm the phase transition from amorphous to polycrystalline and to investigate the silicon structural properties. Crystalline fraction evaluated from the Raman spectra are found to increase almost linearly with the laser fluence. There exists the optimized laser fluence to produce the best crystallization in the range of 400 ~1000mJ/cm2.

  10. Polycrystalline thin film materials and devices

    NASA Astrophysics Data System (ADS)

    Baron, B. N.; Birkmire, R. W.; Phillips, J. E.; Shafarman, W. N.; Hegedus, S. S.; McCandless, B. E.

    1991-11-01

    Results and conclusions of Phase 1 of a multi-year research program on polycrystalline thin film solar cells are presented. The research comprised investigation of the relationships among processing, materials properties and device performance of both CuInSe2 and CdTe solar cells. The kinetics of the formation of CuInSe2 by selenization with hydrogen selenide was investigated and a CuInSe2/Cds solar cell was fabricated. An alternative process involving the reaction of deposited copper-indium-selenium layers was used to obtain single phase CuInSe2 films and a cell efficiency of 7 percent. Detailed investigations of the open circuit voltage of CuInSe2 solar cells showed that a simple Shockley-Read-Hall recombination mechanism can not account for the limitations in open circuit voltage. Examination of the influence of CuInSe2 thickness on cell performance indicated that the back contact behavior has a significant effect when the CuInSe2 is less than 1 micron thick. CdTe/CdS solar cells with efficiencies approaching 10 percent can be repeatedly fabricated using physical vapor deposition and serial post deposition processing. The absence of moisture during post deposition was found to be critical. Improvements in short circuit current of CdTe solar cells to levels approaching 25 mA/cm(exp 2) are achievable by making the CdS window layer thinner. Further reductions in the CdS window layer thickness are presently limited by interdiffusion between the CdS and the CdTe. CdTe/CdS cells stored without protection from the atmosphere were found to degrade. The degradation was attributed to the metal contact. CdTe cells with ZnTe:Cu contacts to the CdTe were found to be more stable than cells with metal contacts. Analysis of current-voltage and spectral response of CdTe/CdS cells indicates the cell operates as a p-n heterojunction with the diode current dominated by SRH recombination in the junction region of the CdTe.

  11. Fabrication of poly-crystalline Si-based Mie resonators via amorphous Si on SiO2 dewetting

    NASA Astrophysics Data System (ADS)

    Naffouti, Meher; David, Thomas; Benkouider, Abdelmalek; Favre, Luc; Ronda, Antoine; Berbezier, Isabelle; Bidault, Sebastien; Bonod, Nicolas; Abbarchi, Marco

    2016-01-01

    We report the fabrication of Si-based dielectric Mie resonators via a low cost process based on solid-state dewetting of ultra-thin amorphous Si on SiO2. We investigate the dewetting dynamics of a few nanometer sized layers annealed at high temperature to form submicrometric Si-particles. Morphological and structural characterization reveal the polycrystalline nature of the semiconductor matrix as well as rather irregular morphologies of the dewetted islands. Optical dark field imaging and spectroscopy measurements of the single islands reveal pronounced resonant scattering at visible frequencies. The linewidth of the low-order modes can be ~20 nm in full width at half maximum, leading to a quality factor Q exceeding 25. These values reach the state-of-the-art ones obtained for monocrystalline Mie resonators. The simplicity of the dewetting process and its cost-effectiveness opens the route to exploiting it over large scales for applications in silicon-based photonics.

  12. Fabrication of poly-crystalline Si-based Mie resonators via amorphous Si on SiO2 dewetting.

    PubMed

    Naffouti, Meher; David, Thomas; Benkouider, Abdelmalek; Favre, Luc; Ronda, Antoine; Berbezier, Isabelle; Bidault, Sebastien; Bonod, Nicolas; Abbarchi, Marco

    2016-02-01

    We report the fabrication of Si-based dielectric Mie resonators via a low cost process based on solid-state dewetting of ultra-thin amorphous Si on SiO2. We investigate the dewetting dynamics of a few nanometer sized layers annealed at high temperature to form submicrometric Si-particles. Morphological and structural characterization reveal the polycrystalline nature of the semiconductor matrix as well as rather irregular morphologies of the dewetted islands. Optical dark field imaging and spectroscopy measurements of the single islands reveal pronounced resonant scattering at visible frequencies. The linewidth of the low-order modes can be ∼20 nm in full width at half maximum, leading to a quality factor Q exceeding 25. These values reach the state-of-the-art ones obtained for monocrystalline Mie resonators. The simplicity of the dewetting process and its cost-effectiveness opens the route to exploiting it over large scales for applications in silicon-based photonics.

  13. Research on polycrystalline thin-film materials, cells, and modules

    SciTech Connect

    Mitchell, R.L.; Zweibel, K.; Ullal, H.S.

    1990-11-01

    The US Department of Energy (DOE) supports research activities in polycrystalline thin films through the Polycrystalline Thin-Film Program at the Solar Energy Research Institute (SERI). This program includes research and development (R D) in both copper indium diselenide and cadmium telluride thin films for photovoltaic applications. The objective of this program is to support R D of photovoltaic cells and modules that meet the DOE long-term goals of high efficiency (15%--20%), low cost ($50/m{sup 2}), and reliability (30-year life time). Research carried out in this area is receiving increased recognition due to important advances in polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells and modules. These have become the leading thin-film materials for photovoltaics in terms of efficiency and stability. DOE has recognized this potential through a competitive initiative for the development of CuInSe{sub 2} and CdTe modules. This paper focuses on the recent progress and future directions of the Polycrystalline Thin-Film Program and the status of the subcontracted research on these promising photovoltaic materials. 26 refs., 12 figs, 1 tab.

  14. Polycrystalline silicon thin-film solar cell prepared by the solid phase crystallization (SPC) method

    SciTech Connect

    Baba, T.; Matsuyama, T.; Sawada, T.; Takahama, T.; Wakisaka, K.; Tsuda, S.; Nakano, S.

    1994-12-31

    A solid phase crystallization (SPC) method was applied to the fabrication of thin-film polycrystalline silicon (poly-Si) for solar cells for the first time. Among crystalline silicon solar cells crystallized at a low temperature of less than 600 C, the world`s highest conversion efficiency of 8.5% was achieved in a solar cell using thin-film poly-Si with only 10 {micro}m thickness prepared by the SPC method. This solar cell showed high photosensitivity in the long-wavelength region of more than 800 nm and also exhibited no light-induced degradation after light exposure.

  15. Formation and ferromagnetic properties of FeSi thin films

    SciTech Connect

    Shin, Yooleemi; Anh Tuan, Duong; Hwang, Younghun; Viet Cuong, Tran; Cho, Sunglae

    2013-05-07

    In this work, the growth and ferromagnetic properties of {epsilon}-FeSi thin film on Si(100) substrate prepared by molecular beam epitaxy are reported. The inter-diffusion of Fe layer on Si(100) substrate at 600 Degree-Sign C results in polycrystalline {epsilon}-FeSi layer. The determined activation energy was 0.044 eV. The modified magnetism from paramagnetic in bulk to ferromagnetic states in {epsilon}-FeSi thin films was observed. The saturated magnetization and coercive field of {epsilon}-FeSi film are 4.6 emu/cm{sup 3} and 29 Oe at 300 K, respectively.

  16. Thin film polycrystalline silicon: Promise and problems in displays and solar cells

    SciTech Connect

    Fonash, S.J.

    1995-08-01

    Thin film polycrystalline Si (poly-Si) with its carrier mobilities, potentially good stability, low intragrain defect density, compatibility with silicon processing, and ease of doping activation is an interesting material for {open_quotes}macroelectronics{close_quotes} applications such as TFTs for displays and solar cells. The poly-Si films needed for these applications can be ultra-thin-in the 500{Angstrom} to 1000{Angstrom} thickness range for flat panel display TFTs and in the 4{mu}m to 10{mu}m thickness range for solar cells. Because the films needed for these microelectronics applications can be so thin, an effective approach to producing the films is that of crystallizing a-Si precursor material. Unlike cast materials, poly-Si films made this way can be produced using low temperature processing. Unlike deposited poly-Si films, these crystallized poly-Si films can have grain widths that are much larger than the film thickness and almost atomically smooth surfaces. This thin film poly-Si crystallized from a-Si precursor films, and its promise and problems for TFTs and solar cells, is the focus of this discussion.

  17. Polycrystalline Thin Film Device Degradation Studies

    SciTech Connect

    Albin, D. S.; McMahon, T. J.; Pankow, J. W.; Noufi, R.; Demtsu, S. H.; Davies, A.

    2005-11-01

    Oxygen during vapor CdCl2 (VCC) treatments significantly reduced resistive shunts observed in CdS/CdTe polycrystalline devices using thinner CdS layers during 100 deg C, open-circuit, 1-sun accelerated stress testing. Cu oxidation resulting from the reduction of various trace oxides present in as-grown and VCC treated films is the proposed mechanism by which Cu diffusion, and subsequent shunts are controlled. Graphite paste layers between metallization and CdTe behave like diffusion barriers and similarly benefit device stability. Ni-based contacts form a protective Ni2Te3 intermetallic layer that reduces metal diffusion but degrades performance through increased series resistance.

  18. Dynamical electrophotoconductivity in polycrystalline thin films

    NASA Technical Reports Server (NTRS)

    Kowel, S. T.; Kornreich, P. G.

    1982-01-01

    Polycrystalline cadmium sulfide (CdS) films were deposited on lithium niobate (LiNbO3) substrates by vacuum evaporation and annealed to obtain high photosensitivity. The change in photoconductivity of these films due to the penetration of electric fields associated with elastic waves propagating on their substrates was demonstrated and studied. The relationship between the acoustic electric field and the induced change in film conductivity was found to be a nonlinear one. The fractional change in conductivity is strongly dependent on the light intensity and the film temperature, showing a prominent maximum as a function of these quantities. The largest recorded fractional change in conductivity was about 25% at electric fields of the order of 1,000 volts per centimeter. A phenomological model was developed based on the interaction between the space charge created by the electric field and the electron trapping states in the photoconductor.

  19. Flexible polycrystalline thin-film photovoltaics for space applications

    NASA Technical Reports Server (NTRS)

    Armstrong, J. H.; Lanning, B. R.; Misra, M. S.; Kapur, V. K.; Basol, B. M.

    1993-01-01

    Polycrystalline thin-film photovoltaics (PV), such as CIS and CdTe, have received considerable attention recently with respect to space power applications. Their combination of stability, efficiency, and economy from large-scale monolithic-integration of modules can have significant impact on cost and weight of PV arrays for spacecraft and planetary experiments. An added advantage, due to their minimal thickness (approximately 6 microns sans substrate), is the ability to manufacture lightweight, flexible devices (approximately 2000 W/kg) using large-volume manufacturing techniques. The photovoltaic effort at Martin Marietta and ISET is discussed, including large-area, large-volume thin-film deposition techniques such as electrodeposition and rotating cylindrical magnetron sputtering. Progress in the development of flexible polycrystalline thin-film PV is presented, including evaluation of flexible CIS cells. In addition, progress on flexible CdTe cells is presented. Finally, examples of lightweight, flexible arrays and their potential cost and weight impact is discussed.

  20. Flexible polycrystalline thin-film photovoltaics for space applications

    NASA Astrophysics Data System (ADS)

    Armstrong, J. H.; Lanning, B. R.; Misra, M. S.; Kapur, V. K.; Basol, B. M.

    1993-05-01

    Polycrystalline thin-film photovoltaics (PV), such as CIS and CdTe, have received considerable attention recently with respect to space power applications. Their combination of stability, efficiency, and economy from large-scale monolithic-integration of modules can have significant impact on cost and weight of PV arrays for spacecraft and planetary experiments. An added advantage, due to their minimal thickness (approximately 6 microns sans substrate), is the ability to manufacture lightweight, flexible devices (approximately 2000 W/kg) using large-volume manufacturing techniques. The photovoltaic effort at Martin Marietta and ISET is discussed, including large-area, large-volume thin-film deposition techniques such as electrodeposition and rotating cylindrical magnetron sputtering. Progress in the development of flexible polycrystalline thin-film PV is presented, including evaluation of flexible CIS cells. In addition, progress on flexible CdTe cells is presented. Finally, examples of lightweight, flexible arrays and their potential cost and weight impact is discussed.

  1. DOE/SERI polycrystalline thin-film photovoltaic research

    SciTech Connect

    Hermann, A; Zweibel, K; Mitchell, R

    1984-05-01

    This paper presents recent results, status, and future prospects for the US Department of Energy's (DOE's) Polycrystalline Thin Film Photovoltaic program, managed by the Solar Energy Research Institute (SERI). The devices being studied most intensively are heterojunctions based on CuInSe/sub 2/ and on CdTe. Both materials have attained over 10% efficiency in polycrystalline form. The main emphasis is on CuInSe/sub 2/, for which Boeing has reported an 11%-efficient device (AMl ELH simulation). Important work is being done on studies of the composition/electronic properties of CuInSe/sub 2/ and its response to post-deposition annealing. In the CdTe research, ohmic, stable back-contacting and control of p-type doping are being investigated. New efforts to study polycrystalline two-junction stacked cells are underway with two-terminal cells (at IEC) and with four-terminal cells (at SMU). This preliminary work is expected to be expanded, with emphasis on CdTe and other top-cell (high-bandgap) materials. These efforts introduce a number of new research areas (e.g., transparent ohmic contacts to p-CdTe and sub-bandgap light-losses in polycrystalline materials). The aim of the program is to produce stable, high-efficiency (15%), thin-film cells that can be deposited inexpensively by techniques that are scalable to large areas.

  2. Thin-film polycrystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    Ghosh, A. K.; Feng, T.; Eustace, D. J.; Maruska, H. P.

    1981-07-01

    The highest efficiencies achieved with single crystals are 14.1% for ITO/n-SI and 13.3% of SnO2/n-Si, while the corresponding values for polysilicon are 11.2% and 10.1%. For large area single crystal devices the efficiency values are 11.7% and 11.2% for ITO and SnO2 cells, respectively, while for polysilicon the corresponding values are 9.82% and 8.55%. The lower efficiency for large area devices is mainly due to lower J sub sc and FF. Results are presented to show the optimum grid spacing required. From stability studies it is shown that there are two distinct mechanisms for degradation, one optical and the other thermal. The optical degradation could be eliminated if the cells could be protected from uv light and the thermal degradation can be prevented if the cells are operated below 100 C.

  3. Creep behavior for advanced polycrystalline SiC fibers

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.; Kohyama, Akira

    1997-04-01

    A bend stress relaxation (BSR) test has been utilized to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Qualitative, S-shaped 1hr BSR curves were compared for three selected advanced SiC fiber types and standard Nicalon CG fiber. The temperature corresponding to the middle of the S-curve (where the BSR parameter m = 0.5) is a measure of a fiber`s thermal stability as well as it creep resistance. In order of decreasing thermal creep resistance, the measured transition temperatures were Nicalon S (1450{degrees}C), Sylramic (1420{degrees}C), Hi-Nicalon (1230{degrees}C) and Nicalon CG (1110{degrees}C).

  4. Progress and issues in polycrystalline thin-film PV technologies

    SciTech Connect

    Zweibel, K.; Ullal, H.S.; Roedern, B. von

    1996-05-01

    Substantial progress has occurred in polycrystalline thin-film photovoltaic technologies in the past 18 months. However, the transition to first-time manufacturing is still under way, and technical problems continue. This paper focuses on the promise and the problems of the copper indium diselenide and cadmium telluride technologies, with an emphasis on continued R&D needs for the near-term transition to manufacturing and for next-generation improvements. In addition, it highlights the joint R&D efforts being performed in the U.S. Department of Energy/National Renewable Energy Laboratory Thin-Film Photovoltaic Partnership Program.

  5. Fabrication of polycrystalline thin films by pulsed laser processing

    DOEpatents

    Mitlitsky, Fred; Truher, Joel B.; Kaschmitter, James L.; Colella, Nicholas J.

    1998-02-03

    A method for fabricating polycrystalline thin films on low-temperature (or high-temperature) substrates which uses processing temperatures that are low enough to avoid damage to the substrate, and then transiently heating select layers of the thin films with at least one pulse of a laser or other homogenized beam source. The pulse length is selected so that the layers of interest are transiently heated to a temperature which allows recrystallization and/or dopant activation while maintaining the substrate at a temperature which is sufficiently low to avoid damage to the substrate. This method is particularly applicable in the fabrication of solar cells.

  6. Fabrication of polycrystalline thin films by pulsed laser processing

    DOEpatents

    Mitlitsky, F.; Truher, J.B.; Kaschmitter, J.L.; Colella, N.J.

    1998-02-03

    A method is disclosed for fabricating polycrystalline thin films on low-temperature (or high-temperature) substrates which uses processing temperatures that are low enough to avoid damage to the substrate, and then transiently heating select layers of the thin films with at least one pulse of a laser or other homogenized beam source. The pulse length is selected so that the layers of interest are transiently heated to a temperature which allows recrystallization and/or dopant activation while maintaining the substrate at a temperature which is sufficiently low to avoid damage to the substrate. This method is particularly applicable in the fabrication of solar cells. 1 fig.

  7. Controlled nanostructuration of polycrystalline tungsten thin films

    SciTech Connect

    Girault, B.; Eyidi, D.; Goudeau, P.; Guerin, P.; Bourhis, E. Le; Renault, P.-O.; Sauvage, T.

    2013-05-07

    Nanostructured tungsten thin films have been obtained by ion beam sputtering technique stopping periodically the growing. The total thickness was maintained constant while nanostructure control was obtained using different stopping periods in order to induce film stratification. The effect of tungsten sublayers' thicknesses on film composition, residual stresses, and crystalline texture evolution has been established. Our study reveals that tungsten crystallizes in both stable {alpha}- and metastable {beta}-phases and that volume proportions evolve with deposited sublayers' thicknesses. {alpha}-W phase shows original fiber texture development with two major preferential crystallographic orientations, namely, {alpha}-W<110> and unexpectedly {alpha}-W<111> texture components. The partial pressure of oxygen and presence of carbon have been identified as critical parameters for the growth of metastable {beta}-W phase. Moreover, the texture development of {alpha}-W phase with two texture components is shown to be the result of a competition between crystallographic planes energy minimization and crystallographic orientation channeling effect maximization. Controlled grain size can be achieved for the {alpha}-W phase structure over 3 nm stratification step. Below, the {beta}-W phase structure becomes predominant.

  8. Advances in polycrystalline thin-film photovoltaics for space applications

    SciTech Connect

    Lanning, B.R.; Armstrong, J.H.; Misra, M.S.

    1994-09-01

    Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 eV and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not `reactor-specific` and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a `substrate configuration` by physical vapor deposition techniques and CdTe cells/modules are fabricated in a `superstrate configuration` by wet chemical methods.

  9. Suppressing light reflection from polycrystalline silicon thin films through surface texturing and silver nanostructures

    SciTech Connect

    Akhter, Perveen; Huang, Mengbing Kadakia, Nirag; Spratt, William; Malladi, Girish; Bakhru, Hassarum

    2014-09-21

    This work demonstrates a novel method combining ion implantation and silver nanostructures for suppressing light reflection from polycrystalline silicon thin films. Samples were implanted with 20-keV hydrogen ions to a dose of 10¹⁷/cm², and some of them received an additional argon ion implant to a dose of 5×10¹⁵ /cm² at an energy between 30 and 300 keV. Compared to the case with a single H implant, the processing involved both H and Ar implants and post-implantation annealing has created a much higher degree of surface texturing, leading to a more dramatic reduction of light reflection from polycrystalline Si films over a broadband range between 300 and 1200 nm, e.g., optical reflection from the air/Si interface in the AM1.5 sunlight condition decreasing from ~30% with an untextured surface to below 5% for a highly textured surface after post-implantation annealing at 1000°C. Formation of Ag nanostructures on these ion beam processed surfaces further reduces light reflection, and surface texturing is expected to have the benefit of diminishing light absorption losses within large-size (>100 nm) Ag nanoparticles, yielding an increased light trapping efficiency within Si as opposed to the case with Ag nanostructures on a smooth surface. A discussion of the effects of surface textures and Ag nanoparticles on light trapping within Si thin films is also presented with the aid of computer simulations.

  10. Synthesis and characterization of large-grain solid-phase crystallized polycrystalline silicon thin films

    SciTech Connect

    Kumar, Avishek E-mail: dalapatig@imre.a-star.edu.sg; Law, Felix; Widenborg, Per I.; Dalapati, Goutam K. E-mail: dalapatig@imre.a-star.edu.sg; Subramanian, Gomathy S.; Tan, Hui R.; Aberle, Armin G.

    2014-11-01

    n-type polycrystalline silicon (poly-Si) films with very large grains, exceeding 30 μm in width, and with high Hall mobility of about 71.5 cm{sup 2}/V s are successfully prepared by the solid-phase crystallization technique on glass through the control of the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio. The effect of this gas flow ratio on the electronic and structural quality of the n-type poly-Si thin film is systematically investigated using Hall effect measurements, Raman microscopy, and electron backscatter diffraction (EBSD), respectively. The poly-Si grains are found to be randomly oriented, whereby the average area weighted grain size is found to increase from 4.3 to 18 μm with increase of the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio. The stress in the poly-Si thin films is found to increase above 900 MPa when the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio is increased from 0.025 to 0.45. Finally, high-resolution transmission electron microscopy, high angle annular dark field-scanning tunneling microscopy, and EBSD are used to identify the defects and dislocations caused by the stress in the fabricated poly-Si films.

  11. Advances in polycrystalline thin-film photovoltaics for space applications

    NASA Technical Reports Server (NTRS)

    Lanning, Bruce R.; Armstrong, Joseph H.; Misra, Mohan S.

    1994-01-01

    Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 ev and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its (each step) effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not 'reactor-specific' and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a 'substrate configuration' by physical vapor deposition techniques and CdTe cells/modules are fabricated in a 'superstrate configuration' by wet chemical

  12. Advances in polycrystalline thin-film photovoltaics for space applications

    NASA Astrophysics Data System (ADS)

    Lanning, Bruce R.; Armstrong, Joseph H.; Misra, Mohan S.

    1994-09-01

    Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 ev and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its (each step) effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not 'reactor-specific' and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a 'substrate configuration' by physical vapor deposition techniques and CdTe cells/modules are fabricated in a 'superstrate configuration' by wet chemical

  13. Anisotropic thermal conductivity of thin polycrystalline oxide samples

    SciTech Connect

    Tiwari, A.; Boussois, K.; Nait-Ali, B.; Smith, D. S.; Blanchart, P.

    2013-11-15

    This paper reports about the development of a modified laser-flash technique and relation to measure the in-plane thermal diffusivity of thin polycrystalline oxide samples. Thermal conductivity is then calculated with the product of diffusivity, specific heat and density. Design and operating features for evaluating in-plane thermal conductivities are described. The technique is advantageous as thin samples are not glued together to measure in-plane thermal conductivities like earlier methods reported in literature. The approach was employed to study anisotropic thermal conductivity in alumina sheet, textured kaolin ceramics and montmorillonite. Since it is rare to find in-plane thermal conductivity values for such anisotropic thin samples in literature, this technique offers a useful variant to existing techniques.

  14. Polycrystalline silicon on glass for thin-film solar cells

    NASA Astrophysics Data System (ADS)

    Green, Martin A.

    2009-07-01

    Although most solar cell modules to date have been based on crystalline or polycrystalline wafers, these may be too material intensive and hence always too expensive to reach the very low costs required for large-scale impact of photovoltaics on the energy scene. Polycrystalline silicon on glass (CSG) solar cell technology was developed to address this difficulty as well as perceived fundamental difficulties with other thin-film technologies. The aim was to combine the advantages of standard silicon wafer-based technology, namely ruggedness, durability, good electronic properties and environmental soundness with the advantages of thin-films, specifically low material use, large monolithic construction and a desirable glass superstrate configuration. The challenge has been to match the different preferred processing temperatures of silicon and glass and to obtain strong solar absorption in notoriously weakly-absorbing silicon of only 1-2 micron thickness. A rugged, durable silicon thin-film technology has been developed with amongst the lowest manufacturing cost of these contenders and confirmed efficiency for small pilot line modules already in the 10-11% energy conversion efficiency range, on the path to 12-13%.

  15. Boron- and phosphorus-doped polycrystalline silicon thin films prepared by silver-induced layer exchange

    SciTech Connect

    Antesberger, T.; Wassner, T. A.; Jaeger, C.; Algasinger, M.; Kashani, M.; Scholz, M.; Matich, S.; Stutzmann, M.

    2013-05-27

    Intentional boron and phosphorus doping of polycrystalline silicon thin films on glass prepared by the silver-induced layer exchange is presented. A silver/(titanium) oxide/amorphous silicon stack is annealed at temperatures below the eutectic temperature of the Ag/Si system, leading to a complete layer exchange and simultaneous crystallization of the amorphous silicon. Intentional doping of the amorphous silicon prior to the exchange process results in boron- or phosphorus-doped polycrystalline silicon. Hall effect measurements show carrier concentrations between 2 Multiplication-Sign 10{sup 17} cm{sup -3} and 3 Multiplication-Sign 10{sup 20} cm{sup -3} for phosphorus and 4 Multiplication-Sign 10{sup 18} cm{sup -3} to 3 Multiplication-Sign 10{sup 19} cm{sup -3} for boron-doped layers, with carrier mobilities up to 90 cm{sup 2}/V s.

  16. Properties of boron-doped thin films of polycrystalline silicon

    SciTech Connect

    Merabet, Souad

    2013-12-16

    The properties of polycrystalline-silicon films deposited by low pressure chemical vapor deposition and doped heavily in situ boron-doped with concentration level of around 2×10{sup 20}cm{sup −3} has been studied. Their properties are analyzed using electrical and structural characterization means by four points probe resistivity measurements and X-ray diffraction spectra. The thermal-oxidation process are performed on sub-micron layers of 200nm/c-Si and 200nm/SiO{sub 2} deposited at temperatures T{sub d} ranged between 520°C and 605°C and thermally-oxidized in dry oxygen ambient at 945°C. Compared to the as-grown resistivity with silicon wafers is known to be in the following sequence <ρ{sub 200nm/c−Si}> < <ρ{sub 200nm/SiO2}> and <ρ{sub 520}> < <ρ{sub 605}>. The measure X-ray spectra is shown, that the Bragg peaks are marked according to the crystal orientation in the film deposited on bare substrates (poly/c-Si), for the second series of films deposited on bare oxidized substrates (poly/SiO{sub 2}) are clearly different.

  17. Creep behavior for advanced polycrystalline SiC fibers

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.; Kohyama, Akira

    1997-08-01

    A bend stress relaxation (BSR) test is planned to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Baseline 1 hr and 100 hr BSR thermal creep {open_quotes}m{close_quotes} curves have been obtained for five selected advanced SiC fiber types and for standard Nicalon CG fiber. The transition temperature, that temperature where the S-shaped m-curve has a value 0.5, is a measure of fiber creep resistance. In order of decreasing thermal creep resistance, with the 100 hr BSR transition temperature given in parenthesis, the fibers ranked: Sylramic (1261{degrees}C), Nicalon S (1256{degrees}C), annealed Hi Nicalon (1215{degrees}C), Hi Nicalon (1078{degrees}C), Nicalon CG (1003{degrees}C) and Tyranno E (932{degrees}C). The thermal creep for Sylramic, Nicalon S, Hi Nicalon and Nicalon CG fibers in a 5000 hr irradiation creep BSR test is projected from the temperature dependence of the m-curves determined during 1 and 100 hr BSR control tests.

  18. Polycrystalline Thin Film Photovoltaics: Research, Development, and Technologies: Preprint

    SciTech Connect

    Ullal, H. S.; Zweibel, K.; von Roedern, B.

    2002-05-01

    II-VI binary thin-film solar cells based on cadmium telluride (CdTe) and I-III-VI ternary thin-film solar cells based on copper indium diselenide (CIS) and related materials have been the subject of intense research and development in the past few years. Substantial progress has been made thus far in the area of materials research, device fabrication, and technology development, and numerous applications based on CdTe and CIS have been deployed worldwide. World record efficiency of 16.5% has been achieved by NREL scientists for a thin-film CdTe solar cell using a modified device structure. Also, NREL scientists achieved world-record efficiency of 21.1% for a thin-film CIGS solar cell under a 14X concentration and AM1.5 global spectrum. When measured under a AM1.5 direct spectrum, the efficiency increases to 21.5%. Pathways for achieving 25% efficiency for tandem polycrystalline thin-film solar cells are elucidated. R&D issues relating to CdTe and CIS are reported in this paper, such as contact stability and accelerated life testing in CdTe, and effects of moisture ingress in thin-film CIS devices. Substantial technology development is currently under way, with various groups reporting power module efficiencies in the range of 7.0% to 12.1% and power output of 40.0 to 92.5 W. A number of lessons learned during the scale-up activities of the technology development for fabrication of thin-film power modules are discussed. The major global players actively involved in the technology development and commercialization efforts using both rigid and flexible power modules are highlighted.

  19. Progress with polycrystalline silicon thin-film solar cells on glass at UNSW

    NASA Astrophysics Data System (ADS)

    Aberle, Armin G.

    2006-01-01

    Polycrystalline Si (pc-Si) thin-film solar cells on glass have long been considered a very promising approach for lowering the cost of photovoltaic (PV) solar electricity. In recent years there have been dramatic advances with this PV technology, and the first commercial modules (CSG Solar) are expected to hit the marketplace in 2006. The CSG modules are based on solid-phase crystallisation of plasma-enhanced chemical vapor deposition (PECVD) -deposited amorphous Si. Independent research in the author's group at the University of New South Wales (UNSW) during recent years has led to the development of three alternative pc-Si thin-film solar cells on glass—EVA, ALICIA and ALICE. Cell thickness is generally about 2 μm. The first two cells are made by vacuum evaporation, whereas ALICE cells can be made by either vacuum evaporation or PECVD. Evaporation has the advantage of being a fast and inexpensive Si deposition method. A crucial component of ALICIA and ALICE cells is a seed layer made on glass by metal-induced crystallisation of amorphous silicon (a-Si). The absorber layer of these cells is made by either ion-assisted Si epitaxy (ALICIA) or solid-phase epitaxy of a-Si (ALICE). This paper reports on the status of these three new thin-film PV technologies. All three solar cells seem to be capable of voltages of over 500 mV and, owing to their potentially inexpensive and scalable fabrication process, have significant industrial appeal.

  20. Activation of ion-implanted polycrystalline silicon thin films prepared on glass substrates

    SciTech Connect

    So, Byoung-Soo; Bae, Seung-Muk; You, Yil-Hwan; Kim, Young-Hwan; Hwang, Jin-Ha

    2012-10-15

    Phosphorous-implanted polycrystalline Si thin films were subjected to thermal annealing between 300 °C and 650 °C. The thermal activation was monitored electrically and structurally using Hall measurements, Raman spectroscopy, UV–visible spectrophotometry, and transmission electron microscopy. Charge transport information was correlated to the corresponding structural evolution in thermal activation. Phosphorous-implanted activation is divided into short-range ordering at low temperatures and long-range ordering at high temperatures, with the boundary between low and high temperatures set at 425 °C. Short-range ordering allows for significant increase in electronic concentration through substitution of P for Si. Higher temperatures are attributed to long-range ordering, thereby increasing electronic mobility.

  1. Noise Characterization of Polycrystalline Silicon Thin Film Transistors for X-ray Imagers Based on Active Pixel Architectures.

    PubMed

    Antonuk, L E; Koniczek, M; McDonald, J; El-Mohri, Y; Zhao, Q; Behravan, M

    2008-01-01

    An examination of the noise of polycrystalline silicon thin film transistors, in the context of flat panel x-ray imager development, is reported. The study was conducted in the spirit of exploring how the 1/f, shot and thermal noise components of poly-Si TFTs, determined from current noise power spectral density measurements, as well as through calculation, can be used to assist in the development of imagers incorporating pixel amplification circuits based on such transistors. PMID:20862269

  2. Superconductor—Insulator Transitions in Pure Polycrystalline Nb Thin Films

    NASA Astrophysics Data System (ADS)

    Couedo, F.; Crauste, O.; Bergé, L.; Dolgorouky, Y.; Marrache-Kikuchi, C.; Dumoulin, L.

    2012-12-01

    We report on a study of the transport properties of Nb thin films. By varying the thickness of the films from 263 Å to 25 Å, we observed a depression of the superconductivity. Magnetic field was also applied up to 6 T, inducing the disappearance of the superconductivity and the onset of an insulating behavior. The results were compared to those we have already obtained on a highly disordered system, a-NbxSi1-x, to understand whether the same mechanisms for the disappearance of the superconductivity could be at play in pure metallic thin films and in highly disordered systems.

  3. Poly-crystalline thin-film by aluminum induced crystallization on aluminum nitride substrate

    NASA Astrophysics Data System (ADS)

    Bhopal, Muhammad Fahad; Lee, Doo Won; Lee, Soo Hong

    2016-09-01

    Thin-film polycrystalline silicon ( pc-Si) on foreign (non-silicon) substrates has been researched by various research groups for the production of photovoltaic cells. High quality pc-Si deposition on foreign substrates with superior optical properties is considered to be the main hurdle in cell fabrication. Metal induced crystallization (MIC) is one of the renowned techniques used to produce this quality of material. In the current study, an aluminum induced crystallization (AIC) method was adopted to produce pc-Si thin-film on aluminum nitride (AlN) substrate by a seed layer approach. Aluminum and a-Si layer were deposited using an e-beam evaporator. Various annealing conditions were used in order to investigate the AIC grown pc-Si seed layers for process optimization. The effect of thermal annealing on grain size, defects preferentially crystallographic orientation of the grains were analyzed. Surface morphology was studied using an optical microscope. Poly-silicon film with a crystallinity fraction between 95-100% and an FWHM between 5-6 cm-1 is achievable at low temperatures and for short time intervals. A grain size of about 10 micron can be obtained at a low deposition rate on an AIN substrate. Similarly, Focused ion beam (FIB) also showed that at 425 °C sample B and at 400 °C sample A were fully crystallized. The crystalline quality of pc-Si was evaluated using μ-Raman spectroscopy as a function of annealed conditions and Grazing incidence X-ray diffraction (GIXRD) was used to determine the phase direction of the pc-Si layer. The current study implicates that a poly-silicon layer with good crystallographic orientation and crystallinity fraction is achievable on AIN substrate at low temperatures and short time frames.

  4. Magnetoelastic properties of thin polycrystalline Terfenol-D films

    NASA Astrophysics Data System (ADS)

    Bailly, Cecile; Su, Quanmin; Wuttig, Manfred R.

    1998-07-01

    In this paper we report on polycrystalline thin films sputter- deposited at elevated temperatures. The grain size of the films was changed by controlling the film thickness. A series of 4 samples with thicknesses ranging from 0.1 μm to 1 μm was studied. The magnetic properties of the films were characterized by vibrating sample magnetometer measurement technique. The magneto-mechanical properties of the films were determined by dynamic magneto-mechanical measurements. The coercivity of the films was found to increase linearly with decreasing film thickness. A sharp transition occurred for film thickness below 0.3 μm and the coercivity decreased to 100 Oe as the film thickness reached 0.1 μm. The saturation magnetization of the films was calculated from the magneto-mechanical measurements. The values were found to agree with those determined from the VSM measurements for all the samples but the thinnest film for which VSM and magneto-mechanical values diffracted by one order of magnitude. It is suggested that the low coercivity of the 0.1 μm film can be associated with the onset of superparamagnetism in the nanograins of the film.

  5. High-Efficiency Polycrystalline Thin Film Tandem Solar Cells.

    PubMed

    Kranz, Lukas; Abate, Antonio; Feurer, Thomas; Fu, Fan; Avancini, Enrico; Löckinger, Johannes; Reinhard, Patrick; Zakeeruddin, Shaik M; Grätzel, Michael; Buecheler, Stephan; Tiwari, Ayodhya N

    2015-07-16

    A promising way to enhance the efficiency of CIGS solar cells is by combining them with perovskite solar cells in tandem devices. However, so far, such tandem devices had limited efficiency due to challenges in developing NIR-transparent perovskite top cells, which allow photons with energy below the perovskite band gap to be transmitted to the bottom cell. Here, a process for the fabrication of NIR-transparent perovskite solar cells is presented, which enables power conversion efficiencies up to 12.1% combined with an average sub-band gap transmission of 71% for photons with wavelength between 800 and 1000 nm. The combination of a NIR-transparent perovskite top cell with a CIGS bottom cell enabled a tandem device with 19.5% efficiency, which is the highest reported efficiency for a polycrystalline thin film tandem solar cell. Future developments of perovskite/CIGS tandem devices are discussed and prospects for devices with efficiency toward and above 27% are given.

  6. Fundamentals of polycrystalline thin film materials and devices

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E. . Inst. of Energy Conversion)

    1991-01-01

    This report presents the results of a one-year research program on polycrystalline thin-film solar cells. The research was conducted to better understand the limitations and potential of solar cells using CuInSe{sub 2} and CdTe by systematically investigating the fundamental relationships linking material processing, material properties, and device behavior. By selenizing Cu and In layers, we fabricated device-quality CuInSe{sub 2} thin films and demonstrated a CuInSe{sub 2} solar cell with 7% efficiency. We added Ga, to increase the band gap of CuInSe{sub 2} devices to increase the open-circuit voltage to 0.55 V. We fabricated and analyzed Cu(InGa)Se{sub 2}/CuInSe{sub 2} devices to demonstrate the potential for combining the benefits of higher V{sub oc} while retaining the current-generating capacity of CuInSe{sub 2}. We fabricated an innovative superstrate device design with more than 5% efficiency, as well as a bifacial spectral-response technique for determining the electron diffusion length and optical absorption coefficient of CuInSe{sub 2} in an operational cell. The diffusion length was found to be greater than 1 {mu}m. We qualitatively modeled the effect of reducing heat treatments in hydrogen and oxidizing treatments in air on the I-V behavior of CuInSe{sub 2} devices. We also investigated post-deposition heat treatments and chemical processing and used them to fabricate a 9.6%-efficient CdTe/CdS solar cell using physical vapor deposition.

  7. Polycrystalline Thin-Film Research: Copper Indium Gallium Diselenide (Fact Sheet)

    SciTech Connect

    Not Available

    2011-06-01

    Capabilities fact sheet for the National Center for Photovoltaics: Polycrystalline Thin-Film Research: Copper Indium Gallium Diselenide that includes scope, core competencies and capabilities, and contact/web information.

  8. Broadening of optical transitions in polycrystalline CdS and CdTe thin films

    SciTech Connect

    Li Jian; Chen Jie; Collins, R. W.

    2010-11-01

    The dielectric functions {epsilon} of polycrystalline CdS and CdTe thin films sputter deposited onto Si wafers were measured from 0.75 to 6.5 eV by in situ spectroscopic ellipsometry. Differences in {epsilon} due to processing variations are well understood using an excited carrier scattering model. For each sample, a carrier mean free path {lambda} is defined that is found to be inversely proportional to the broadening of each of the band structure critical points (CPs) deduced from {epsilon}. The rate at which broadening occurs with {lambda}{sup -1} is different for each CP, enabling a carrier group speed {upsilon}{sub g} to be identified for the CP. With the database for {upsilon}{sub g}, {epsilon} can be analyzed to evaluate the quality of materials used in CdS/CdTe photovoltaic heterojunctions.

  9. Charge carrier transport in polycrystalline organic thin film based field effect transistors

    NASA Astrophysics Data System (ADS)

    Rani, Varsha; Sharma, Akanksha; Ghosh, Subhasis

    2016-05-01

    The charge carrier transport mechanism in polycrystalline thin film based organic field effect transistors (OFETs) has been explained using two competing models, multiple trapping and releases (MTR) model and percolation model. It has been shown that MTR model is most suitable for explaining charge carrier transport in grainy polycrystalline organic thin films. The energetic distribution of traps determined independently using Mayer-Neldel rule (MNR) is in excellent agreement with the values obtained by MTR model for copper phthalocyanine and pentacene based OFETs.

  10. Multiscale modelling framework for the fracture of thin brittle polycrystalline films: application to polysilicon

    NASA Astrophysics Data System (ADS)

    Mulay, Shantanu S.; Becker, Gauthier; Vayrette, Renaud; Raskin, Jean-Pierre; Pardoen, Thomas; Galceran, Montserrat; Godet, Stéphane; Noels, Ludovic

    2015-01-01

    Micro-electro-mechanical systems (MEMS) made of polycrystalline silicon are widely used in several engineering fields. The fracture properties of polycrystalline silicon directly affect their reliability. The effect of the orientation of grains on the fracture behaviour of polycrystalline silicon is investigated out of the several factors. This is achieved, firstly, by identifying the statistical variation of the fracture strength and critical strain energy release rate, at the nanoscopic scale, over a thin freestanding polycrystalline silicon film having mesoscopic scale dimensions. The fracture stress and strain at the mesoscopic level are found to be closely matching with uniaxial tension experimental results. Secondly, the polycrystalline silicon film is considered at the continuum MEMS scale, and its fracture behaviour is studied by incorporating the nanoscopic scale effect of grain orientation. The entire modelling and simulation of the thin film is achieved by combining the discontinuous Galerkin method and extrinsic cohesive law describing the fracture process.

  11. Investigation of Melting and Solidification of Thin Polycrystalline Silicon Films via Mixed-Phase Solidification

    NASA Astrophysics Data System (ADS)

    Wang, Ying

    Melting and solidification constitute the fundamental pathways through which a thin-film material is processed in many beam-induced crystallization methods. In this thesis, we investigate and leverage a specific beam-induced, melt-mediated crystallization approach, referred to as Mixed-Phase Solidification (MPS), to examine and scrutinize how a polycrystalline Si film undergoes the process of melting and solidification. On the one hand, we develop a more general understanding as to how such transformations can transpire in polycrystalline films. On the other hand, by investigating how the microstructure evolution is affected by the thermodynamic properties of the system, we experimentally reveal, by examining the solidified microstructure, fundamental information about such properties (i.e., the anisotropy in interfacial free energy). Specifically, the thesis consists of two primary parts: (1) conducting a thorough and extensive investigation of the MPS process itself, which includes a detailed characterization and analysis of the microstructure evolution of the film as it undergoes MPS cycles, along with additional development and refinement of a previously proposed thermodynamic model to describe the MPS melting-and-solidification process; and (2) performing MPS-based experiments that were systematically designed to reveal more information on the anisotropic nature of Si-SiO2 interfacial energy (i.e., sigma Si-SiO2). MPS is a recently developed radiative-beam-based crystallization technique capable of generating Si films with a combination of several sought-after microstructural characteristics. It was conceived, developed, and characterized within our laser crystallization laboratory at Columbia University. A preliminary thermodynamic model was also previously proposed to describe the overall melting and solidification behavior of a polycrystalline Si film during an MPS cycle, wherein the grain-orientation-dependent solid-liquid interface velocity is identified

  12. Investigation of Melting and Solidification of Thin Polycrystalline Silicon Films via Mixed-Phase Solidification

    NASA Astrophysics Data System (ADS)

    Wang, Ying

    Melting and solidification constitute the fundamental pathways through which a thin-film material is processed in many beam-induced crystallization methods. In this thesis, we investigate and leverage a specific beam-induced, melt-mediated crystallization approach, referred to as Mixed-Phase Solidification (MPS), to examine and scrutinize how a polycrystalline Si film undergoes the process of melting and solidification. On the one hand, we develop a more general understanding as to how such transformations can transpire in polycrystalline films. On the other hand, by investigating how the microstructure evolution is affected by the thermodynamic properties of the system, we experimentally reveal, by examining the solidified microstructure, fundamental information about such properties (i.e., the anisotropy in interfacial free energy). Specifically, the thesis consists of two primary parts: (1) conducting a thorough and extensive investigation of the MPS process itself, which includes a detailed characterization and analysis of the microstructure evolution of the film as it undergoes MPS cycles, along with additional development and refinement of a previously proposed thermodynamic model to describe the MPS melting-and-solidification process; and (2) performing MPS-based experiments that were systematically designed to reveal more information on the anisotropic nature of Si-SiO2 interfacial energy (i.e., sigma Si-SiO2). MPS is a recently developed radiative-beam-based crystallization technique capable of generating Si films with a combination of several sought-after microstructural characteristics. It was conceived, developed, and characterized within our laser crystallization laboratory at Columbia University. A preliminary thermodynamic model was also previously proposed to describe the overall melting and solidification behavior of a polycrystalline Si film during an MPS cycle, wherein the grain-orientation-dependent solid-liquid interface velocity is identified

  13. Research on polycrystalline thin-film photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Hermann, A. M.; Fabick, L.

    1983-05-01

    Recent results from the United States Department of Energy Polycrystalline Thin-Film Photovoltaic Device Program are presented. The program which is managed by the solar Energy Research Institute encompasses materials and device research on a variety of compound semiconductors with emphasis on II-VI compounds and II-VI ternary analogs. This paper covers preparation (emphasizing thin-film deposition) and characterization of semiconducting materials such as Cu 2- xS, Cu 2- xSe, CdTe and CuInSe 2. Photovoltaic device characteristics of these absorbers with heterojunction partners such as CdS are discussed. Excitement in the program has been generated by recent progress in the (Cd, Zn/S)/CuInSe 2 device area. An AM1 efficiency of 9.93% for a 5 μm thick 1 cm 2 cell has been verified at SERI. Unencapsulated (Cd, Zn)S/CuInSe 2 cells have been subjected to more than 6000 h of accelerated stability testing with no measureable degradation in photovoltaic performance. Other program highlights include fabrication of a hybrid CdS/Cu 2S device (evaporated CdS, sputtered Cu 2S) with a 7.2% AM1 efficiency, and a 3.9% AM1 efficiency all-sputtered CdS/Cu 2S cell. Preliminary data are presented on the achievement of intrinsically stable high-efficiency (>9%) wet-processed CdS/Cu 2S cells. Progress in the less mature research areas is outlined. A 5.3% (AM1) CVD Au/n-CdTe Schottky barrier cell is described, and AM1 cell efficiencies exceeding 4% for vacuum evaporated CdS/Cu 2Se and chemically sprayed CdS/CdTe cells are reported. Future research emphasis is discussed. One of the important technical issues which is being addressed in an increase in the open-circuit voltage of (Cd,Zn)S/CuInSe 2 cells. Technical issues being addressed in other areas include film growth and doping studies in CdTe and improvement in the doping profile of CdS/Cu 2Se junctions.

  14. Buffer layers for deposition of superconducting YBaCuO thin film on polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Beetz, Charles P.; Cui, G. J.; Lincoln, B. A.; Kirlin, Peter S.

    1992-09-01

    In an attempt to combine the properties of high temperature superconductors with the high thermal conductivity and low specific heat of diamond, we have explored the deposition of in- situ YBa(subscript 2)Cu(subscript 3)O(subscript 7-(delta) ) (YBCO) superconducting films on polycrystalline diamond thin films. We demonstrate for the first time superconducting YBCO films on diamond employing multiple layer buffer layer systems. Three different composite buffer layer systems were explored for this purpose: (1) Diamond/Zr/YSZ/YBCO, (2) Diamond/Si(subscript 3)N(subscript 4)/YSZ/YBCO, and (3) Diamond/SiO(subscript 2)/YSZ/YBCO. Adherent thin Zr films were deposited by dc sputtering on the diamond films at 450 to 820 degree(s)C. The yttria stabilized zirconia (YSZ) was deposited by reactive RF sputtering at 680 to 750 degree(s)C. The Si(subscript 3)N(subscript 4) and SiO(subscript 2) were also deposited by on-axis RF sputtering at 400 to 700 degree(s)C. YBCO films were grown on the buffer layers by off-axis RF sputtering at substrate temperatures between 690 degree(s)C and 750 degree(s)C. In all cases, the as-deposited YBCO films were superconducting above 77 K. This demonstration enables the fabrication of low heat capacity, fast response time bolometric far IR detectors and paves the way for the use of HTSC as a high frequency interconnect metallization on thick diamond film based multichip modules.

  15. Amorphous silicon/polycrystalline thin film solar cells

    SciTech Connect

    Ullal, H.S.

    1991-03-13

    An improved photovoltaic solar cell is described including a p-type amorphous silicon layer, intrinsic amorphous silicon, and an n-type polycrystalline semiconductor such as cadmium sulfide, cadmium zinc sulfide, zinc selenide, gallium phosphide, and gallium nitride. The polycrystalline semiconductor has an energy bandgap greater than that of the amorphous silicon. The solar cell can be provided as a single-junction device or a multijunction device.

  16. Progress in polycrystalline thin-film photovoltaic-device research

    NASA Astrophysics Data System (ADS)

    Hermann, A. M.; Fabick, L.; Zweibel, K.; Hardy, R. W.

    1982-09-01

    Recent results from the United States Department of Energy (DOE) Thin Film Photovoltaic Device Program are presented. The program encompasses materials and device research on highly absorbing compound semiconductors including CuInSe2, CdTe, Cu/sub 2-x/Se, Zn3P2, ZnSiAs2, and Cu2S. Excitement in the program has been generated by recent progress in the (Cd,Zn)S/CuInSe2 device area where an efficiency of 10.6% on a 5 micrometers thick device has been reported. Other highlights include deposition of a hybrid CdS/Cu2S device (evaporated CdS, sputtered Cu2S) with a 7.1% AMI efficiency, and of a 3.94% AMI efficiency all sputtered CdS/Cu2S cell. AMI efficiencies exceeding 5% are reported for CdTe Schottky barrier and heterojunction devices, and for a CdS/Cu/sub 2-x/Se heterojunction. AMI efficiencies exceeding 4% are reported for Mg/Zn3P3 Schottky barrier cells. Future research emphasis is outlined.

  17. Beta-to-alpha transformation in polycrystalline SiC. II - Interfacial energetics

    NASA Technical Reports Server (NTRS)

    Mitchell, T. E.; Ogbuji, L. U.; Heuer, A. H.

    1978-01-01

    A phenomenological analysis of the energetics of the beta-to-alpha transformation in polycrystalline SiC is presented. It is found that the extreme anisotropy of the interfacial energy between alpha- and beta-SiC can account for the rapid growth of composite grains into the beta matrix during conventional sintering or hot-pressing processes. The composite grains consist of alpha-SiC plates 'sandwiched' between well-oriented and recrystallized beta-SiC 'envelopes'. The interfaces involving the 111 plane type of beta and (0001) of alpha have much lower energies than random beta/alpha interfaces.

  18. Polycrystalline VO2 thin films via femtosecond laser processing of amorphous VO x

    NASA Astrophysics Data System (ADS)

    Charipar, N. A.; Kim, H.; Breckenfeld, E.; Charipar, K. M.; Mathews, S. A.; Piqué, A.

    2016-05-01

    Femtosecond laser processing of pulsed laser-deposited amorphous vanadium oxide thin films was investigated. Polycrystalline VO2 thin films were achieved by femtosecond laser processing in air at room temperature. The electrical transport properties, crystal structure, surface morphology, and optical properties were characterized. The laser-processed films exhibited a metal-insulator phase transition characteristic of VO2, thus presenting a pathway for the growth of crystalline vanadium dioxide films on low-temperature substrates.

  19. Technique for measuring irradiation creep in polycrystalline SiC fibers

    SciTech Connect

    Youngblood, G.E.; Hamilton, M.L.; Jones, R.H.

    1996-10-01

    A bend stress relaxation (BSR) test has been designed to examine irradiation enhanced creep in polycrystalline SiC fibers being considered for fiber reinforcement in SiC/SiC composite. Thermal creep results on Nicalon-CG and Hi-Nicalon were shown to be consistent with previously published data with Hi-Nicalon showing about a 100{degrees}C improvement in creep resistance. Preliminary data was also obtained on Nicalon-S that demonstrated that its creep resistance is greater than that of Hi-Nicalon.

  20. Ferroelectric domain switching of individual nanoscale grains in polycrystalline lead zirconate titanate thin films

    NASA Astrophysics Data System (ADS)

    Jing, Yuanyuan

    2011-12-01

    This thesis will focus on the switching behavior of nanoscale ferroelectric domains in polycrystalline thin films. Ferroelectrics are a class of dielectric materials that demonstrate spontaneous polarizations under zero applied electric field. A region with the same polarization is called a ferroelectric domain. One important attribute of ferroelectrics is the domain switching from one thermodynamically stable state to another by application of an external electric field. Ferroelectric domain switching has been intensively investigated in epitaxial thin films. However, little is known about the domain switching in polycrystalline thin films. The main reason is that each grain is differently orientated and each is in a unique local stress and electric field determined by neighboring grains. To understand and deterministically control the nanoscale domain switching in polycrystalline thin films, it's critical to experimentally identify the effect of local microstructure (grain orientation and grain boundary misorientation) on the individual grain switching behavior. In this thesis, the effect of local microstructure on domain switching has been quantitatively analyzed in a 100 nm thick polycrystalline PbZr 0.2Ti0.8O3 thin film. The ferroelectric domains are characterized by Piezoresponse Force Microscopy (PFM), with their switching behavior analyzed by Polarization Difference Maps (PDMs, an analytical technique developed in this work). The local microstructure is determined by Electron Back Scattering Diffraction (EBSD). The results are discussed in chapter 3 to 6. Chapter 3 introduces the PDMs technique that enables the rapid identification of 0o, 90o switching and 180o switching in polycrystalline thin films. By assigning different colors to different types of switching, the full nature of polarization switching can be visualized simultaneously for large number of domains or grains in one map. In chapter 4, an external electric field reversal experiment has been

  1. Magnetic properties of epitaxial and polycrystalline Fe/Si multilayers

    SciTech Connect

    Chaiken, A.; Michel, R.P.; Wang, C.T.

    1995-08-01

    Fe/Si multilayers with antiferromagnetic interlayer coupling have been grown via ion-beam sputtering on both glass and single-crystal substrates. X-ray diffraction measurements show that both sets of films have crystalline iron silicide spacer layers and a periodic composition modulation. Films grown on glass have smaller crystallite sizes than those grown on single-crystal substrates and have a significant remanent magnetization. Films grown on single-crystal substrates have a smaller remanence. The observation of magnetocrystalline anisotropy in hysteresis loops and (hkl) peaks in x-ray diffraction demonstrates that the films grown on MgO and Ge are epitaxial. The smaller remanent magnetization in Fe/Si multilayers with better crystallinity suggests that the remanence is not intrinsic.

  2. Polycrystalline SiC fibers from organosilicon polymers

    NASA Technical Reports Server (NTRS)

    Lipowitz, Jonathan; Rabe, James A.; Zank, Gregg A.

    1991-01-01

    Various organosilicon polymers have been converted into small diameter, fine-grained silicon carbide fibers by melt spinning, crosslinking, and pyrolyzing to greater than 1600 C. The high pyrolysis temperature densifies the fiber and causes CO evolution which removes nearly all oxygen. An additive prevents the loss of strength normally associated with such treatments. Silicon carbide fibres with up to 2.6 GPa (380 ksi) tensile strength, greater than 420 GPa (greater than 60 Msi) elastic modulus, and 3.1-3.2 mg/cu m density have been prepared via this process. Their microstructure consists of greater than 95 wt pct B-SiC crystallites averaging 30-40 nm diameter, with varying amounts of graphitic carbon between the SiC grains. Under inert conditions, the fibers can be thermally aged at least 12 h/1800 C with minimal change in properties.

  3. Influence of lattice distortion on phase transition properties of polycrystalline VO2 thin film

    NASA Astrophysics Data System (ADS)

    Lin, Tiegui; Wang, Langping; Wang, Xiaofeng; Zhang, Yufen; Yu, Yonghao

    2016-08-01

    In this work, high power impulse magnetron sputtering was used to control the lattice distortion in polycrystalline VO2 thin film. SEM images revealed that all the VO2 thin films had crystallite sizes of below 20 nm, and similar configurations. UV-vis-near IR transmittance spectra measured at different temperatures showed that most of the as-deposited films had a typical metal-insulator transition. Four-point probe resistivity results showed that the transition temperature of the films varied from 54.5 to 32 °C. The X-ray diffraction (XRD) patterns of the as-deposited films revealed that most were polycrystalline monoclinic VO2. The XRD results also confirmed that the lattice distortions in the as-deposited films were different, and the transition temperature decreased with the difference between the interplanar spacing of the as-deposited thin film and standard rutile VO2. Furthermore, a room temperature rutile VO2 thin film was successfully synthesized when this difference was small enough. Additionally, XRD patterns measured at varied temperatures revealed that the phase transition process of the polycrystalline VO2 thin film was a coordinative deformation between grains with different orientations. The main structural change during the phase transition was a gradual shift in interplanar spacing with temperature.

  4. Near-infrared light absorption by polycrystalline SiSn alloys grown on insulating layers

    SciTech Connect

    Kurosawa, Masashi; Kato, Motohiro; Yamaha, Takashi; Taoka, Noriyuki; Nakatsuka, Osamu; Zaima, Shigeaki

    2015-04-27

    High-Sn-content SiSn alloys are strongly desired for the next-generation near-infrared optoelectronics. A polycrystalline growth study has been conducted on amorphous SiSn layers with a Sn-content of 2%–30% deposited on either a substrate of SiO{sub 2} or SiN. Incorporating 30% Sn into Si permits the crystallization of the amorphous layers at annealing temperatures below the melting point of Sn (231.9 °C). Composition analyses indicate that approximately 20% of the Sn atoms are substituted into the Si lattice after solid-phase crystallization at 150–220 °C for 5 h. Correspondingly, the optical absorption edge is red-shifted from 1.12 eV (Si) to 0.83 eV (Si{sub 1−x}Sn{sub x} (x ≈ 0.18 ± 0.04)), and the difference between the indirect and direct band gap is significantly reduced from 3.1 eV (Si) to 0.22 eV (Si{sub 1−x}Sn{sub x} (x ≈ 0.18 ± 0.04)). These results suggest that with higher substitutional Sn content the SiSn alloys could become a direct band-gap material, which would provide benefits for Si photonics.

  5. Polycrystalline thin film materials and devices. Final subcontract report, 16 January 1990--15 January 1993

    SciTech Connect

    Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E.; Yokimcus, T.A.

    1993-08-01

    This report describes results and conclusions of the final phase (III) of a three-year research program on polycrystalline thin-film heterojunction solar cells. The research consisted of the investigation of the relationships between processing, materials properties, and device performance. This relationship was quantified by device modeling and analysis. The analysis of thin-film polycrystalline heterojunction solar cells explains how minority-carrier recombination at the metallurgical interface and at grain boundaries can be greatly reduced by the proper doping of the window and absorber layers. Additional analysis and measurements show that the present solar cells are limited by the magnitude of the diode current, which appears to be caused by recombination in the space charge region. Developing an efficient commercial-scale process for fabricating large-area polycrystalline, thin-film solar cells from a research process requires a detailed understanding of the individual steps in making the solar cell, and their relationship to device performance and reliability. The complexities involved in characterizing a process are demonstrated with results from our research program on CuInSe{sub 2}, and CdTe processes.

  6. Giant rotating magnetocaloric effect induced by highly texturing in polycrystalline DyNiSi compound.

    PubMed

    Zhang, Hu; Li, YaWei; Liu, Enke; Ke, YaJiao; Jin, JinLing; Long, Yi; Shen, BaoGen

    2015-01-01

    Large rotating magnetocaloric effect (MCE) has been observed in some single crystals due to strong magnetocrystalline anisotropy. By utilizing the rotating MCE, a new type of rotary magnetic refrigerator can be constructed, which could be more simplified and efficient than the conventional one. However, compared with polycrystalline materials, the high cost and complexity of preparation for single crystals hinder the development of this novel magnetic refrigeration technology. For the first time, here we observe giant rotating MCE in textured DyNiSi polycrystalline material, which is larger than those of most rotating magnetic refrigerants reported so far. This result suggests that DyNiSi compound could be attractive candidate of magnetic refrigerants for novel rotary magnetic refrigerator. By considering the influence of demagnetization effect on MCE, the origin of large rotating MCE in textured DyNiSi is attributed to the coexistence of strong magnetocrystalline anisotropy and highly preferred orientation. Our study on textured DyNiSi not only provides a new magnetic refrigerant with large rotating MCE for low temperature magnetic refrigeration, but also opens a new way to exploit magnetic refrigeration materials with large rotating MCE, which will be highly beneficial to the development of rotating magnetic refrigeration technology. PMID:26159558

  7. Giant rotating magnetocaloric effect induced by highly texturing in polycrystalline DyNiSi compound

    NASA Astrophysics Data System (ADS)

    Zhang, Hu; Li, Yawei; Liu, Enke; Ke, Yajiao; Jin, Jinling; Long, Yi; Shen, Baogen

    2015-07-01

    Large rotating magnetocaloric effect (MCE) has been observed in some single crystals due to strong magnetocrystalline anisotropy. By utilizing the rotating MCE, a new type of rotary magnetic refrigerator can be constructed, which could be more simplified and efficient than the conventional one. However, compared with polycrystalline materials, the high cost and complexity of preparation for single crystals hinder the development of this novel magnetic refrigeration technology. For the first time, here we observe giant rotating MCE in textured DyNiSi polycrystalline material, which is larger than those of most rotating magnetic refrigerants reported so far. This result suggests that DyNiSi compound could be attractive candidate of magnetic refrigerants for novel rotary magnetic refrigerator. By considering the influence of demagnetization effect on MCE, the origin of large rotating MCE in textured DyNiSi is attributed to the coexistence of strong magnetocrystalline anisotropy and highly preferred orientation. Our study on textured DyNiSi not only provides a new magnetic refrigerant with large rotating MCE for low temperature magnetic refrigeration, but also opens a new way to exploit magnetic refrigeration materials with large rotating MCE, which will be highly beneficial to the development of rotating magnetic refrigeration technology.

  8. Crystallization to polycrystalline silicon thin film and simultaneous inactivation of electrical defects by underwater laser annealing

    NASA Astrophysics Data System (ADS)

    Machida, Emi; Horita, Masahiro; Ishikawa, Yasuaki; Uraoka, Yukiharu; Ikenoue, Hiroshi

    2012-12-01

    We propose a low-temperature laser annealing method of a underwater laser annealing (WLA) for polycrystalline silicon (poly-Si) films. We performed crystallization to poly-Si films by laser irradiation in flowing deionized-water where KrF excimer laser was used for annealing. We demonstrated that the maximum value of maximum grain size of WLA samples was 1.5 μm, and that of the average grain size was 2.8 times larger than that of conventional laser annealing in air (LA) samples. Moreover, WLA forms poly-Si films which show lower conductivity and larger carrier life time attributed to fewer electrical defects as compared to LA poly-Si films.

  9. Crystallization to polycrystalline silicon thin film and simultaneous inactivation of electrical defects by underwater laser annealing

    SciTech Connect

    Machida, Emi; Horita, Masahiro; Ishikawa, Yasuaki; Uraoka, Yukiharu; Ikenoue, Hiroshi

    2012-12-17

    We propose a low-temperature laser annealing method of a underwater laser annealing (WLA) for polycrystalline silicon (poly-Si) films. We performed crystallization to poly-Si films by laser irradiation in flowing deionized-water where KrF excimer laser was used for annealing. We demonstrated that the maximum value of maximum grain size of WLA samples was 1.5 {mu}m, and that of the average grain size was 2.8 times larger than that of conventional laser annealing in air (LA) samples. Moreover, WLA forms poly-Si films which show lower conductivity and larger carrier life time attributed to fewer electrical defects as compared to LA poly-Si films.

  10. An inert marker study for palladium silicide formation - Si moves in polycrystalline Pd2Si

    NASA Technical Reports Server (NTRS)

    Ho, K. T.; Lien, C.-D.; Shreter, U.; Nicolet, M.-A.

    1985-01-01

    A novel use of Ti marker is introduced to investigate the moving species during Pd2Si formation on 111 and 100 line-type Si substrates. Silicide formed from amorphous Si is also studied using a W marker. Although these markers are observed to alter the silicide formation in the initial stage, the moving species can be identified once a normal growth rate is resumed. It is found that Si is the dominant moving species for all three types of Si crystallinity. However, Pd will participate in mass transport when Si motion becomes obstructed.

  11. Polycrystalline thin film materials and devices. Annual subcontract report, 16 January 1991--15 January 1992

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E.

    1992-10-01

    Results of Phase II of a research program on polycrystalline thin film heterojunction solar cells are presented. Relations between processing, materials properties and device performance were studied. The analysis of these solar cells explains how minority carrier recombination at the interface and at grain boundaries can be reduced by doping of windows and absorber layers, such as in high efficiency CdTe and CuInSe{sub 2} based solar cells. The additional geometric dimension introduced by the polycrystallinity must be taken into consideration. The solar cells are limited by the diode current, caused by recombination in the space charge region. J-V characteristics of CuInSe{sub 2}/(CdZn)S cells were analyzed. Current-voltage and spectral response measurements were also made on high efficiency CdTe/CdS thin film solar cells prepared by vacuum evaporation. Cu-In bilayers were reacted with Se and H{sub 2}Se gas to form CuInSe{sub 2} films; the reaction pathways and the precursor were studied. Several approaches to fabrication of these thin film solar cells in a superstrate configuration were explored. A self-consistent picture of the effects of processing on the evolution of CdTe cells was developed.

  12. Optical and electrical properties of polycrystalline and amorphous Al-Ti thin films

    NASA Astrophysics Data System (ADS)

    Canulescu, S.; Borca, C. N.; Rechendorff, K.; Davidsdóttir, S.; Pagh Almtoft, K.; Nielsen, L. P.; Schou, J.

    2016-04-01

    The structural, optical, and transport properties of sputter-deposited Al-Ti thin films have been investigated as a function of Ti alloying with a concentration ranging from 2% to 46%. The optical reflectivity of Al-Ti films at visible and near-infrared wavelengths decreases with increasing Ti content. X-ray absorption fine structure measurements reveal that the atomic ordering around Ti atoms increases with increasing Ti content up to 20% and then decreases as a result of a transition from a polycrystalline to amorphous structure. The transport properties of the Al-Ti films are influenced by electron scattering at the grain boundaries in the case of polycrystalline films and static defects, such as anti-site effects and vacancies in the case of the amorphous alloys. The combination of Ti having a real refractive index (n) comparable with the extinction coefficient (k) and Al with n much smaller than k allows us to explore the parameter space for the free-electron behavior in transition metal-Al alloys. The free electron model, applied for the polycrystalline Al-Ti films with Ti content up to 20%, leads to an optical reflectance at near infrared wavelengths that scales linearly with the square root of the electrical resistivity.

  13. Grain boundary diffusion of Ag through polycrystalline SiC in TRISO fuel particles

    NASA Astrophysics Data System (ADS)

    Deng, Jie; Ko, Hyunseok; Demkowicz, Paul; Morgan, Dane; Szlufarska, Izabela

    2015-12-01

    The effective diffusivity and release fraction of Ag in polycrystalline SiC are evaluated using a kinetic Monte Carlo model. The effects of various grain boundary network properties on the transport of Ag across the SiC layer have been examined, including fraction of grain boundary type, spread in grain boundary diffusivities and distribution of grain boundary types. It is shown that the effective diffusivity and release fraction of Ag can exhibit a large variability due to changes in the GB structure of SiC, and this variability is almost independent of temperature fluctuation. The present results suggest that the variation in properties of grain boundary networks in SiC may contribute to the spread in the Ag diffusivity and release fraction measured in TRISO particles. It is also found that the grain boundary diffusion alone may be insufficient to account for the Ag diffusivities and release fractions measured in integral release experiments. Additional factors such as irradiation and temperature distribution may also play an important role in Ag transport across the SiC layer.

  14. Low temperature deposition of polycrystalline silicon thin films on a flexible polymer substrate by hot wire chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lee, Sang-hoon; Jung, Jae-soo; Lee, Sung-soo; Lee, Sung-bo; Hwang, Nong-moon

    2016-11-01

    For the applications such as flexible displays and solar cells, the direct deposition of crystalline silicon films on a flexible polymer substrate has been a great issue. Here, we investigated the direct deposition of polycrystalline silicon films on a polyimide film at the substrate temperature of 200 °C. The low temperature deposition of crystalline silicon on a flexible substrate has been successfully made based on two ideas. One is that the Si-Cl-H system has a retrograde solubility of silicon in the gas phase near the substrate temperature. The other is the new concept of non-classical crystallization, where films grow by the building block of nanoparticles formed in the gas phase during hot-wire chemical vapor deposition (HWCVD). The total amount of precipitation of silicon nanoparticles decreased with increasing HCl concentration. By adding HCl, the amount and the size of silicon nanoparticles were reduced remarkably, which is related with the low temperature deposition of silicon films of highly crystalline fraction with a very thin amorphous incubation layer. The dark conductivity of the intrinsic film prepared at the flow rate ratio of RHCl=[HCl]/[SiH4]=3.61 was 1.84×10-6 Scm-1 at room temperature. The Hall mobility of the n-type silicon film prepared at RHCl=3.61 was 5.72 cm2 V-1s-1. These electrical properties of silicon films are high enough and could be used in flexible electric devices.

  15. Impact of universal mobility law on polycrystalline organic thin-film transistors

    NASA Astrophysics Data System (ADS)

    Raja, Munira; Donaghy, David; Myers, Robert; Eccleston, Bill

    2012-10-01

    We have developed novel analytical models for polycrystalline organic thin-film transistor (OTFT) by employing new concepts on the charge carrier injection to polysilicon thin-films. The models, also incorporate the effect of contact resistance associated with the poor ohmic nature of the contacts. The drain current equations of the OTFT, both in the quasi-diffusion and quasi-drift regimes, predict temperature dependencies on essential material and device parameters. Interestingly, under the drift regime, the polycrystalline OTFT model reveals similar power dependencies on the applied voltages, to those of purely disordered model developed by utilizing the universal mobility law (UML). Such similarities are not thought to be coincidental since the effect of gate voltage on surface potential is influenced by the Fermi level pinning in the grain boundary. Nonetheless, the best fits on the data of 6,13-bis(tri-isopropylsilylethynyl) OTFTs are attained with the proposed polycrystalline rather than the disordered model, particularly at low gate voltages where the diffusive component is dominant. Moreover, in order to understand the effect of grain boundaries, we devise a relationship for the dependency of the effective mobility on carrier concentration, assuming a crystalline region to be in direct contact with a disordered region. Interestingly, we find a similar dependency as the UML in purely disordered materials, which further signifies the conduction to be limited by the grain boundaries. Subsequently, an analytical model for the variation of the effective mobility with gate voltage is established. Such models are vital in assisting the development of more accurate designs of the novel organic circuits.

  16. MIS and PN junction solar cells on thin-film polycrystalline silicon

    SciTech Connect

    Ariotedjo, A.; Emery, K.; Cheek, G.; Pierce, P.; Surek, T.

    1981-05-01

    The Photovoltaic Advanced Silicon (PVAS) Branch at the Solar Energy Research Institute (SERI) has initiated a comparative study to assess the potential of MIS-type solar cells for low-cost terrestrial photovoltaic systems in terms of performance, stability, and cost-effectiveness. Several types of MIS and SIS solar cells are included in the matrix study currently underway. This approach compares the results of MIS and p/n junction solar cells on essentially identical thin-film polycrystalline silicon materials. All cell measurements and characterizations are performed using uniform testing procedures developed in the Photovoltaic Measurements and Evaluation (PV M and E) Laboratory at SERI. Some preliminary data on the different cell structures on thin-film epitaxial silicon on metallurgical-grade substrates are presented here.

  17. Compressive intrinsic stress originates in the grain boundaries of dense refractory polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Magnfält, D.; Fillon, A.; Boyd, R. D.; Helmersson, U.; Sarakinos, K.; Abadias, G.

    2016-02-01

    Intrinsic stresses in vapor deposited thin films have been a topic of considerable scientific and technological interest owing to their importance for functionality and performance of thin film devices. The origin of compressive stresses typically observed during deposition of polycrystalline metal films at conditions that result in high atomic mobility has been under debate in the literature in the course of the past decades. In this study, we contribute towards resolving this debate by investigating the grain size dependence of compressive stress magnitude in dense polycrystalline Mo films grown by magnetron sputtering. Although Mo is a refractory metal and hence exhibits an intrinsically low mobility, low energy ion bombardment is used during growth to enhance atomic mobility and densify the grain boundaries. Concurrently, the lateral grain size is controlled by using appropriate seed layers on which Mo films are grown epitaxially. The combination of in situ stress monitoring with ex situ microstructural characterization reveals a strong, seemingly linear, increase of the compressive stress magnitude on the inverse grain size and thus provides evidence that compressive stress is generated in the grain boundaries of the film. These results are consistent with models suggesting that compressive stresses in metallic films deposited at high homologous temperatures are generated by atom incorporation into and densification of grain boundaries. However, the underlying mechanisms for grain boundary densification might be different from those in the present study where atomic mobility is intrinsically low.

  18. Nucleation, growth, and control of ferroelectric-ferroelastic domains in thin polycrystalline films

    NASA Astrophysics Data System (ADS)

    Ivry, Yachin; Scott, James F.; Salje, Ekhard K. H.; Durkan, Colm

    2012-11-01

    The unique response of ferroic materials to external excitations facilitates them for diverse technologies, such as nonvolatile memory devices. The primary driving force behind this response is encoded in domain switching. In bulk ferroics, domains switch in a two-step process: nucleation and growth. For ferroelectrics, this can be explained by the Kolmogorov-Avrami-Ishibashi (KAI) model. Nevertheless, it is unclear whether domains remain correlated in finite geometries, as required by the KAI model. Moreover, although ferroelastic domains exist in many ferroelectrics, experimental limitations have hindered the study of their switching mechanisms. This uncertainty limits our understanding of domain switching and controllability, preventing thin-film and polycrystalline ferroelectrics from reaching their full technological potential. Here we used piezoresponse force microscopy to study the switching mechanisms of ferroelectric-ferroelastic domains in thin polycrystalline Pb0.7Zr0.3TiO3 films at the nanometer scale. We have found that switched biferroic domains can nucleate at multiple sites with a coherence length that may span several grains, and that nucleators merge to form mesoscale domains, in a manner consistent with that expected from the KAI model.

  19. Innovative deposition techniques for the fabrication of polycrystalline thin-film photovoltaics

    NASA Astrophysics Data System (ADS)

    Armstrong, J. H.; Lanning, B. R.; Misra, M. S.

    1992-12-01

    A key issue for photovoltaics (PV), both in terrestrial and future space applications, is producibility, particularly for applications utilizing a large volume of PV. Among the concerns for fabrication of polycrystalline thin-film photovoltaics, such as copper-indium-diselenide (CIS) and cadmium-telluride (CdTe), are production volume, which translates directly related to cost, and minimization of waste. Both the rotating cylindrical magnetron (C-MagTM) and pulsed electrodeposition have tremendous potential for the fabrication of polycrystalline thin-film photovoltaics due to scaleability, efficient utilization of source materials and inherently higher deposition rates. In the case of sputtering, the unique geometry of the C-MagTM facilitates innovative cosputtering and reactive sputtering that could lead to greater throughput, reduced health and safety risks, and ultimately lower fabrication cost. For pulsed electrodeposition, the films appear to be more tightly adherent and deposited at an enhanced rate when compared to conventional DC electrodeposition. This paper addresses Martin Marietta's investigation into innovative sputtering techniques and pulsed electrodeposition with a near-term goal of 930 cm2 (1 ft2) monolithically-integrated CIS and CdTe submodules.

  20. Innovative deposition techniques for the fabrication of polycrystalline thin-film photovoltaics

    SciTech Connect

    Armstrong, J.H.; Lanning, B.R.; Misra, M.S. )

    1992-12-01

    A key issue for photovoltaics (PV), both in terrestrial and future space applications, is [ital producibility], particularly for applications utilizing a large volume of PV. Among the concerns for fabrication of polycrystalline thin-film photovoltaics, such as copper-indium-diselenide (CIS) and cadmium-telluride (CdTe), are production volume, which translates directly related to cost, and minimization of waste. Both the rotating cylindrical magnetron (C-Mag[sup TM]) and pulsed electrodeposition have tremendous potential for the fabrication of polycrystalline thin-film photovoltaics due to scaleability, efficient utilization of source materials and inherently higher deposition rates. In the case of sputtering, the unique geometry of the C-Mag[sup TM] facilitates innovative cosputtering and reactive sputtering that could lead to greater throughput, reduced health and safety risks, and ultimately lower fabrication cost. For pulsed electrodeposition, the films appear to be more tightly adherent and deposited at an enhanced rate when compared to conventional DC electrodeposition. This paper addresses Martin Marietta's investigation into innovative sputtering techniques and pulsed electrodeposition with a near-term goal of 930 cm[sup 2] (1 ft[sup 2]) monolithically-integrated CIS and CdTe submodules.

  1. Progress towards high efficiency polycrystalline thin-film GaAs AMOS solar cells

    NASA Technical Reports Server (NTRS)

    Yeh, Y. C. M.; Ernest, F. P.; Stirn, R. J.

    1978-01-01

    Results of Ge film recrystallization using focused laser beams and GaAs film growth on such layers in the making of high efficiency thin-film AMOS solar cells are discussed. Since a conversion efficiency of 14% was obtained for an AMOS cell fabricated on sliced bulk polycrystalline GaAs, high efficiency cells are being developed by chemically vapor-depositing GaAs films on previously recrystallized evaporated Ge films to minimize the grain boundary (GB) effects. Schottky barrier solar cells made on sliced polycrystalline GaAs wafers were studied to investigate the effects of grain boundaries on cell properties and the potential efficiency of GaAs thin-film cells. Ge film recrystallization and the chemical vapor deposition (CVD) of the 2 to 3 micron thick GaAs films are described. AMOS solar cells with 100 Angstrom thick Ag metallization were made on CVD GaAs/recrystallized Ge/W substrates with an energy conversion efficiency of 8%.

  2. Mixed Al and Si doping in ferroelectric HfO{sub 2} thin films

    SciTech Connect

    Lomenzo, Patrick D.; Nishida, Toshikazu; Takmeel, Qanit; Zhou, Chuanzhen; Chung, Ching-Chang; Jones, Jacob L.; Moghaddam, Saeed

    2015-12-14

    Ferroelectric HfO{sub 2} thin films 10 nm thick are simultaneously doped with Al and Si. The arrangement of the Al and Si dopant layers within the HfO{sub 2} greatly influences the resulting ferroelectric properties of the polycrystalline thin films. Optimizing the order of the Si and Al dopant layers led to a remanent polarization of ∼20 μC/cm{sup 2} and a coercive field strength of ∼1.2 MV/cm. Post-metallization anneal temperatures from 700 °C to 900 °C were used to crystallize the Al and Si doped HfO{sub 2} thin films. Grazing incidence x-ray diffraction detected differences in peak broadening between the mixed Al and Si doped HfO{sub 2} thin films, indicating that strain may influence the formation of the ferroelectric phase with variations in the dopant layering. Endurance characteristics show that the mixed Al and Si doped HfO{sub 2} thin films exhibit a remanent polarization greater than 15 μC/cm{sup 2} up to 10{sup 8} cycles.

  3. Mixed Al and Si doping in ferroelectric HfO2 thin films

    NASA Astrophysics Data System (ADS)

    Lomenzo, Patrick D.; Takmeel, Qanit; Zhou, Chuanzhen; Chung, Ching-Chang; Moghaddam, Saeed; Jones, Jacob L.; Nishida, Toshikazu

    2015-12-01

    Ferroelectric HfO2 thin films 10 nm thick are simultaneously doped with Al and Si. The arrangement of the Al and Si dopant layers within the HfO2 greatly influences the resulting ferroelectric properties of the polycrystalline thin films. Optimizing the order of the Si and Al dopant layers led to a remanent polarization of ˜20 μC/cm2 and a coercive field strength of ˜1.2 MV/cm. Post-metallization anneal temperatures from 700 °C to 900 °C were used to crystallize the Al and Si doped HfO2 thin films. Grazing incidence x-ray diffraction detected differences in peak broadening between the mixed Al and Si doped HfO2 thin films, indicating that strain may influence the formation of the ferroelectric phase with variations in the dopant layering. Endurance characteristics show that the mixed Al and Si doped HfO2 thin films exhibit a remanent polarization greater than 15 μC/cm2 up to 108 cycles.

  4. Polycrystalline silicon thin-film transistor with nickel-titanium oxide by sol-gel spin-coating and nitrogen implantation

    NASA Astrophysics Data System (ADS)

    Wu, Shih-Chieh; Hou, Tuo-Hung; Chuang, Shiow-Huey; Chou, Hsin-Chih; Chao, Tien-Sheng; Lei, Tan-Fu

    2012-12-01

    This study demonstrates polycrystalline silicon thin-film transistors (poly-Si TFTs) integrated with a high-κ nickel-titanium oxide (NiTiO3) gate dielectric using sol-gel spin-coating and nitrogen channel implantation. This novel fabrication method of the high-κ NiTiO3 gate dielectric offers thin equivalent-oxide thickness and high gate capacitance density, favorable for increasing the current driving capability. Introducing nitrogen ions into the poly-Si using implantation effectively passivates the trap states not only in the poly-Si channel but also at the gate dielectric/poly-Si interface. The poly-Si NiTiO3 TFTs with nitrogen implantation exhibit significantly improved electrical characteristics, including lower threshold voltage, a steeper subthreshold swing, higher field-effect mobility, a larger on/off current ratio, and less threshold-voltage roll-off. Furthermore, the nitrogen implantation improves the reliability of poly-Si NiTiO3 TFTs against hot-carrier stress and positive bias temperature instability.

  5. MIS solar cells on thin polycrystalline silicon. Progress report No. 3, September 1-November 30, 1980

    SciTech Connect

    Anderson, W.A.

    1980-12-01

    The first task of this project involves electron-beam deposition of thin silicon films on low cost substrates. The goal is to obtain 20 ..mu..m thick films having 20 ..mu..m diameter crystallites which may be recrystallized to > 40 ..mu..m. Material characterization and device studies are to be included in efforts to reach a 6% conversion efficiency. The second task deals with MIS solar cell fabrication on various types of silicon including poly-Si, ribbon-Si, silicon on ceramic, and thin film silicon. Conduction mechanism studies, optimum engineering design, and modification of the fabrication process are to be used to achieve 13% efficiency on Xtal-Si and 11% efficiency on poly-Si. The third task involves more detailed test procedures and includes spectral response, interface and grain boundary effects, computer analysis, materials studies, and grain boundary passivation. Progress is detailed. (WHK)

  6. Effects of gate insulator using high pressure annealing on the characteristics of solid phase crystallized polycrystalline silicon thin-film transistors

    NASA Astrophysics Data System (ADS)

    Kim, Moojin; Jin, GuangHai

    2009-04-01

    The oxidizing ambient was built using high pressure H2O vapor at 550 °C. For the solid phase crystallization (SPC) polycrystalline silicon (poly-Si) that is annealed for 1 h at 2 MPa, the oxide thickness is about 150 Å. The oxide layer is approximately 90 Å above the original surface of the poly-Si and 60 Å below the original surface. The oxide layer is used as the first gate insulator layer of thin-film transistors (TFTs). The heating at 550 °C with 2 MPa H2O vapor increased the carrier mobility from 17.6 cm2/V s of the conventional SPC process to 30.4 cm2/V s, and it reduced the absolute value of the threshold voltage (Vth) from 4.13 to 3.62 V. The subthreshold swing also decreased from 0.72 to 0.60 V/decade. This improvement is attributed mainly to the reduction in defect density at the oxide/poly-Si interface and in the poly-Si film by the high pressure annealing (HPA) process. Since the realization of excellent performance at the oxide/poly-Si interface and in poly-Si depends on the defect density, the poly-Si having the thermal oxide formed by a combined process of SPC and HPA may be well suited for fabrication of poly-Si TFTs for flat panel displays such as active matrix organic light emitting diodes.

  7. Appropriate materials and preparation techniques for polycrystalline-thin-film thermophotovoltaic cells

    NASA Astrophysics Data System (ADS)

    Dhere, Neelkanth G.

    1997-03-01

    Polycrystalline-thin-film thermophotovoltaic (TPV) cells have excellent potential for reducing the cost of TPV generators so as to address the hitherto inaccessible and highly competitive markets such as self-powered gas-fired residential warm air furnaces and energy-efficient electric cars, etc. Recent progress in polycrystalline-thin-film solar cells have made it possible to satisfy the diffusion length and intrinsic junction rectification criteria for TPV cells operating at high fluences. Continuous ranges of direct bandgaps of the ternary and pseudoternary compounds such as Hg1-xCdxTe, Pb1-xCdxTe, Hg1-xZnxTe, and Pb1-xZnxS cover the region of interest of 0.50-0.75 eV for efficient TPV conversion. Other ternary and pseudoternary compounds which show direct bandgaps in most of or all of the 0.50-0.75 eV range are Pb1-xZnxTe, Sn1-xCd2xTe2, Pb1-xCdxSe, Pb1-xZnxSe, and Pb1-xCdxS. Hg1-xCdxTe (with x~0.21) has been studied extensively for infrared detectors. PbTe and Pb1-xSnxTe have also been studied for infrared detectors. Not much work has been carried out on Hg1-xZnxTe thin films. Hg1-xCdxTe and Pb1-xCdxTe alloys cover a wide range of cut-off wavelengths from the far infrared to the near visible. Acceptors and donors are introduced in these materials by excess non-metal (Te) and excess metal (Hg and Pb) respectively. Extrinsic acceptor impurities are Cu, Au, and As while and In and Al are donor impurities. Hg1-xCdxTe thin films have been deposited by isothermal vapor-phase epitaxy (VPE), liquid phase epitaxy (LPE), hot-wall metalorganic chemical vapor deposition (MOCVD), electrodeposition, sputtering, molecular beam epitaxy (MBE), laser-assisted evaporation, and vacuum evaporation with or without hot-wall enclosure. The challenge in the preparation of Hg1-xCdxTe is to provide excess mercury incidence rate, to optimize the deposition parameters for enhanced mercury incorporation, and to achieve the requisite stoichiometry, grain size, and doping. MBE and MOCVD

  8. Mechanical behavior of polycrystalline ceramics: Brittle fracture of SiC-Si3N4 materials

    NASA Technical Reports Server (NTRS)

    Ceipold, M. H.; Kapadia, C. M.; Kelkar, A. H.

    1972-01-01

    Research on the fracture behavior of silicon nitride and silicon carbide is reported along with the role of anion impurities in the fabrication and behavior of magnesium oxide. The results of a survey of crack propagation in SiC and Si3N4 are presented. Studies in the following areas are reported: development of a fracture toughness testing technique, constant moment beam, microcrack examination, and etching techniques.

  9. Polycrystalline Thin Film Photovoltaics: From the Laboratory to Solar Fields (Presentation)

    SciTech Connect

    von Roedern, B.; Ullal, H.; Zweibel, K.

    2006-05-01

    The conclusions of this report are that: (1) many issues how thin-film solar cells work remain unresolved, requiring further fundamental R and D effort; (2) commercial thin-film PV module production reached 29% in 2005 in the US, indicating much more rapid growth than crystalline Si PV; (3) commercial module performance is increasing based on current knowledge, more R and D will lead to further improvement; and (4) stability of thin-film modules is acceptable ({le} 1% per year power loss) if the right manufacturing processes are used for manufacturing.

  10. Tailoring of in-plane magnetic anisotropy in polycrystalline cobalt thin films by external stress

    NASA Astrophysics Data System (ADS)

    Kumar, Dileep; Singh, Sadhana; Vishawakarma, Pramod; Dev, Arun Singh; Reddy, V. R.; Gupta, Ajay

    2016-11-01

    Polycrystalline Co films of nominal thickness ~180 Å were deposited on intentionally curved Si substrates. Tensile and compressive stresses of 100 MPa and 150 MPa were induced in the films by relieving the curvature. It has been found that, within the elastic limit, presence of stress leads to an in-plane magnetic anisotropy in the film and its strength increases with increasing stress. Easy axis of magnetization in the films is found to be parallel/ transverse to the compressive /tensile stresses respectively. The origin of magnetic anisotropy in the stressed films is understood in terms of magneto- elastic coupling, where the stress try to align the magnetic moments in order to minimize the magneto-elastic as well as anisotropy energy. Tensile stress is also found to be responsible for the surface smoothening of the films, which is attributed to the movement of the atoms associated with the applied stress. The present work provides a possible way to tailor the magnetic anisotropy and its direction in polycrystalline and amorphous films using external stress.

  11. Low Temperature Polycrystalline Silicon Thin Film Transistor Pixel Circuits for Active Matrix Organic Light Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Fan, Ching-Lin; Lin, Yu-Sheng; Liu, Yan-Wei

    A new pixel design and driving method for active matrix organic light emitting diode (AMOLED) displays that use low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) with a voltage programming method are proposed and verified using the SPICE simulator. We had employed an appropriate TFT model in SPICE simulation to demonstrate the performance of the pixel circuit. The OLED anode voltage variation error rates are below 0.35% under driving TFT threshold voltage deviation (Δ Vth =± 0.33V). The OLED current non-uniformity caused by the OLED threshold voltage degradation (Δ VTO =+0.33V) is significantly reduced (below 6%). The simulation results show that the pixel design can improve the display image non-uniformity by compensating for the threshold voltage deviation in the driving TFT and the OLED threshold voltage degradation at the same time.

  12. Process for fabricating polycrystalline semiconductor thin-film solar cells, and cells produced thereby

    DOEpatents

    Wu, Xuanzhi; Sheldon, Peter

    2000-01-01

    A novel, simplified method for fabricating a thin-film semiconductor heterojunction photovoltaic device includes initial steps of depositing a layer of cadmium stannate and a layer of zinc stannate on a transparent substrate, both by radio frequency sputtering at ambient temperature, followed by the depositing of dissimilar layers of semiconductors such as cadmium sulfide and cadmium telluride, and heat treatment to convert the cadmium stannate to a substantially single-phase material of a spinel crystal structure. Preferably, the cadmium sulfide layer is also deposited by radio frequency sputtering at ambient temperature, and the cadmium telluride layer is deposited by close space sublimation at an elevated temperature effective to convert the amorphous cadmium stannate to the polycrystalline cadmium stannate with single-phase spinel structure.

  13. A simple and continuous polycrystalline silicon thin-film transistor model for SPICE implementation

    NASA Astrophysics Data System (ADS)

    Pappas, I.; Hatzopoulos, A. T.; Tassis, D. H.; Arpatzanis, N.; Siskos, S.; Dimitriadis, C. A.; Kamarinos, G.

    2006-09-01

    A simple current-voltage model for polycrystalline silicon thin-film transistors (polysilicon TFTs) is proposed, including the sixth-order polynomial function coefficients fitted to the effective mobility versus gate voltage data, the channel length modulation, and impact ionization effects. The model possesses continuity of current in the transfer characteristics from weak to strong inversion and in the output characteristics throughout the linear and saturation regions of operation. The model parameters are used as input parameters in AIM-SPICE circuit simulator for device modeling. The model has been applied in a number of long and short channel TFTs, and the statistical distributions of the model parameters have been derived which are useful for checking the functionality of TFTs circuits with AIM-SPICE.

  14. Metastable Electrical Characteristics of Polycrystalline Thin-Film Photovoltaic Modules upon Exposure and Stabilization: Preprint

    SciTech Connect

    Deline, C. A.; del Cueto, J. A.; Albin, D. S.; Rummel, S. R.

    2011-09-01

    The significant features of a series of stabilization experiments conducted at the National Renewable Energy Laboratory (NREL) between May 2009 and the present are reported. These experiments evaluated a procedure to stabilize the measured performance of thin-film polycrystalline cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) thin-film photovoltaic (PV) modules. The current-voltage (I-V) characteristics of CdTe and CIGS thin-film PV devices and modules exhibit transitory changes in electrical performance after thermal exposure in the dark and/or bias and light exposures. We present the results of our case studies of module performance versus exposure: light-soaked at 65 degrees C; exposed in the dark under forward bias at 65 degrees C; and, finally, longer-term outdoor exposure. We find that stabilization can be achieved to varying degrees using either light-soaking or dark bias methods and that the existing IEC 61646 light-soaking interval may be appropriate for CdTe and CIGS modules with one caveat: it is likely that at least three exposure intervals are required for stabilization.

  15. Controllability of self-aligned four-terminal planar embedded metal double-gate low-temperature polycrystalline-silicon thin-film transistors on a glass substrate

    NASA Astrophysics Data System (ADS)

    Ohsawa, Hiroki; Sasaki, Shun; Hara, Akito

    2016-03-01

    Self-aligned four-terminal n-channel (n-ch) and p-channel (p-ch) planar embedded metal double-gate polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) were fabricated on a glass substrate at a low temperature of 550 °C. This device includes a metal top gate (TG) and a metal bottom gate (BG), which are used as the drive and control gates or vice versa. The BG was embedded in a glass substrate, and a poly-Si channel with large lateral grains was fabricated by continuous-wave laser lateral crystallization. The threshold voltage modulation factors under various control gate voltages (γ = ΔVth/ΔVCG) were nearly equal to the theoretical predictions in both the n- and p-ch TFTs. By exploiting this high controllability, an enhancement depletion (ED) inverter was fabricated, and successful operation at 2.0 V was confirmed.

  16. Structure of Fe3Si/Al/Fe3Si thin film stacks on GaAs(001)

    NASA Astrophysics Data System (ADS)

    Jenichen, B.; Jahn, U.; Nikulin, A.; Herfort, J.; Kirmse, H.

    2015-11-01

    Fe3Si/Al/Fe3Si/GaAs(001) structures were deposited by molecular-beam epitaxy and characterized by transmission and scanning electron microscopy, and x-ray diffraction. The first Fe3Si film on GaAs(001) grew epitaxially as a (001) oriented single crystal. The subsequent Al film grew almost {111} oriented in a fibrous texture although the underlying Fe3Si is exactly (001) oriented. The growth in this orientation is triggered by a thin transition region which is formed at the Fe3Si/Al interface. In the end, after the growth of the second Fe3Si layer on top of the Al, the final properties of the whole stack depended on the substrate temperature T s during deposition of the last film. The upper Fe3Si films are mainly {110} oriented although they are poly-crystalline. At lower T s, around room temperature, all the films retain their original structural properties.

  17. Ferroelectric properties of highly a-oriented polycrystalline Bi2WO6 thin films grown on glass substrates

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Son, Jong Yeog

    2016-10-01

    Polycrystalline Bi2WO6 (BWO) thin films were deposited on Pt/Ta/glass substrates by pulsed laser deposition (PLD). In this study, we comparatively investigate the influence of oxygen partial pressure on structural and ferroelectric properties of the BWO films. In comparison with the BWO films deposited at oxygen partial pressure of 100 and 300 mTorr, the BWO film deposited at 300 mTorr exhibits a highly a-oriented crystalline structure. The highly a-oriented polycrystalline BWO thin film shows good ferroelectric properties with a remnant polarization of about 21.5 μ C /cm2 . The piezoresponse force microscope study reveals that the highly a-oriented BWO thin film possesses larger ferroelectric domain patterns due to smaller domain wall energy.

  18. Metal-induced unilaterally crystallized polycrystalline silicon thin-film transistor technology and application to flat-panel displays

    NASA Astrophysics Data System (ADS)

    Meng, Zhiguo

    High quality flat-panel displays (FPD) typically use active-matrix (AM) addressing, with the optical state of each pixel controlled by one or more active devices such as amorphous silicon (a-Si) thin film transistors (TFT). The successful examples are portable computer and liquid-crystal television (LC-TV). A high level of system on panel (SoP) electronic integration is required for versatile and compact systems. Meanwhile, many self-emitting display technologies are developing fast, active matrix for self-emitting display is typically current driven. The a-Si TFTs suffer from limited current driving capability, polycrystalline silicon (poly-Si) device technology is required. A new technology employing metal-induced unilaterally crystallization (MIUC) is presently reported. The device characteristics are obviously better than those in rapid-thermal annealed (RTA) and solid-phase crystallization (SPC) TFTs and the fabrication equipment is much cheaper than excimer laser crystallization (ELC) technology. The field effect mobility (muFE) of p- and n-channel MIUC TFTs is about 100cm2/Vs. Ion/I off is more than seven orders. Gate-induced leakage current in LT-MIUC poly-Si TFTs has been reduced by crystallization before heavy junction implantation to improve material quality and incorporating a gate-modulated lightly-doped drain (gamo-LDD) structure to reduce the electric field near the drain/channel junction region. At the same time, recrystallized (RC) MIUC TFT was researched with device characteristics improved. The 6.6cm 120 x 160 active matrix for OLED display is fabricated using LT-MIUC TFT technology on glass substrate. This display has the advantages of self-emitting, large intrinsic view angle and very fast response. At the same time, 6.6cm 120X160 AM-reflective twist nematic (RTN) display is fabricated using RC-MIUC TFT technology. This display is capable of producing 16 grade levels, 10:1 contrast and video image. The SOP display for AM-OLED were designed

  19. BiSI Micro-Rod Thin Films: Efficient Solar Absorber Electrodes?

    PubMed

    Hahn, Nathan T; Self, Jeffrey L; Mullins, C Buddie

    2012-06-01

    The development of improved solar energy conversion materials is critical to the growth of a sustainable energy infrastructure in the coming years. We report the deposition of polycrystalline BiSI thin films exhibiting promising photoelectrochemical properties on both metal foils and fluorine-doped tin-oxide-coated glass slides using a single-source chemical spray pyrolysis technique. Their strong light absorption in the visible range and well-crystallized layered structure give rise to their excellent photoelectrochemical performance through improved electron-hole generation and separation. The structure and surface composition of the films are dependent on deposition temperature, resulting in dramatic differences in performance over the temperature range studied. These results reveal the potential of n-BiSI as an alternative thin film solar energy conversion material and may stimulate further investigation into V-VI-VII compounds for these applications.

  20. Large exchange bias in polycrystalline ribbons of Ni56Mn21Al22Si1

    NASA Astrophysics Data System (ADS)

    Singh, Rohit; Ingale, Babita; Varga, Lajos K.; Khovaylo, Vladimir V.; Taskaev, S.; Chatterjee, Ratnamala

    2015-11-01

    Large exchange bias (EB) effect is demonstrated in a Ni56Mn21Al22Si1 polycrystalline ribbon that shows spin-glass behaviour below 68 K and superparamagnetic (SPM) behaviour above this temperature. The average magnetic moment μ of the SPM clusters is estimated to be considerably smaller than that reported for other Heusler alloy systems that demonstrate spin glass behaviour and EB effect. The M-H loops measured in field-cooled (FC) conditions show significant asymmetry that is observed to be strongly field and temperature dependant. The maximum EB field (HEB ~2.6 kOe at 20 kOe and 2 K) is much larger than that reported for any metallic alloy system with conventional EB effect. The dependence of HEB on temperature shows an exponential decrease. An approach towards enhancement of the EB effect in this conventional EB system can be realized via manipulation of SPM or superferromagnetic (SFM) cluster size with variation of cooling magnetic field.

  1. Significant enhancement of the thermoelectric figure of merit of polycrystalline Si films by reducing grain size

    NASA Astrophysics Data System (ADS)

    Valalaki, K.; Vouroutzis, N.; Nassiopoulou, A. G.

    2016-08-01

    The thermoelectric properties of p-type polycrystalline silicon thin films deposited by low pressure chemical vapour deposition (LPCVD) were accurately determined at room temperature and the thermoelectric figure of merit was deduced as a function of film thickness, ranging from 100 to 500 nm. The effect of film thickness on their thermoelectric performance is discussed. More than threefold increase in the thermoelectric figure of merit of the 100 nm thick polysilicon film was observed compared to the 500 nm thick film, reaching a value as high as 0.033. This enhancement is mainly the result of the smaller grain size in the thinner films. With the decrease in grain size the resistivity of the films is increased twofold and electrical conductivity decreased, however the Seebeck coefficient is increased by 30% and the thermal conductivity is decreased eightfold, being mainly at the origin of the increased figure of merit of the 100 nm film. Our experimental results were compared to known theoretical models and the possible mechanisms involved are presented and discussed.

  2. Ultrafast carrier dynamics and the role of grain boundaries in polycrystalline silicon thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Titova, Lyubov V.; Cocker, Tyler L.; Xu, Sijia; Baribeau, Jean-Marc; Wu, Xiaohua; Lockwood, David J.; Hegmann, Frank A.

    2016-10-01

    We have used time-resolved terahertz spectroscopy to study microscopic photoconductivity and ultrafast photoexcited carrier dynamics in thin, pure, non-hydrogenated silicon films grown by molecular beam epitaxy on quartz substrates at temperatures ranging from 335 °C to 572 °C. By controlling the growth temperature, thin silicon films ranging from completely amorphous to polycrystalline with minimal amorphous phase can be achieved. Film morphology, in turn, determines its photoconductive properties: in the amorphous phase, carriers are trapped in bandtail states on sub-picosecond time scales, while the carriers excited in crystalline grains remain free for tens of picoseconds. We also find that in polycrystalline silicon the photoexcited carrier mobility is carrier-density-dependent, with higher carrier densities mitigating the effects of grain boundaries on inter-grain transport. In a film grown at the highest temperature of 572 °C, the morphology changes along the growth direction from polycrystalline with needles of single crystals in the bulk of the film to small crystallites interspersed with amorphous silicon at the top of the film. Depth profiling using different excitation wavelengths shows corresponding differences in the photoconductivity: the photoexcited carrier lifetime and mobility are higher in the first 100-150 nm from the substrate, suggesting that thinner, low-temperature grown polycrystalline silicon films are preferable for photovoltaic applications.

  3. Metal-induced crystallization of a-Si thin films by nonvacuum treatments

    SciTech Connect

    Kalkan, A.K.; Fonash, S.J.

    1997-11-01

    Thin film polycrystalline Si (poly-Si) is of considerable interest today for microelectronics, flat panel displays, and photovoltaics. Low thermal budget solid-phase crystallization (SPC) of a-Si precursor films was achieved using surface treatments with metal-containing solutions. Two different treatment procedures were demonstrated. With these treatments, one based on a Pd solution and the other on a Ni solution, the SPC time at 600 C was reduced from 18 h to 10 min or less. This approach renders the usual vacuum deposition step used in metal-induced crystallization unnecessary. The authors find that the ultraviolet reflectance and Raman shift signals for the crystallized films are independent of whether the SPC-enhancing metal is applied by vacuum or solution. These characterization results do differ, however, with the metal applied.

  4. Thickness dependence of structure and piezoelectric properties at nanoscale of polycrystalline lead zirconate titanate thin films

    NASA Astrophysics Data System (ADS)

    Araújo, E. B.; Lima, E. C.; Bdikin, I. K.; Kholkin, A. L.

    2013-05-01

    Lead zirconate titanate Pb(Zr0.50Ti0.50)O3 (PZT) thin films were deposited by a polymeric chemical method on Pt(111)/Ti/SiO2/Si substrates to understand the mechanisms of phase transformations and the effect of film thickness on the structure, dielectric, and piezoelectric properties in these films. PZT films pyrolyzed at temperatures higher than 350 °C present a coexistence of pyrochlore and perovskite phases, while only perovskite phase grows in films pyrolyzed at temperatures lower than 300 °C. For pyrochlore-free PZT thin films, a small (100)-orientation tendency near the film-substrate interface was observed. Finally, we demonstrate the existence of a self-polarization effect in the studied PZT thin films. The increase of self-polarization with the film thickness increasing from 200 nm to 710 nm suggests that Schottky barriers and/or mechanical coupling near the film-substrate interface are not primarily responsible for the observed self-polarization effect in our films.

  5. High-Temperature Thermoelectric Properties of Polycrystalline Silicon Clathrate Ba8TM x Si46- x (TM = Ni, Pt)

    NASA Astrophysics Data System (ADS)

    Kikuchi, Daisuke; Fujimura, Koji; Tadokoro, Jun; Matsumoto, Miko; Yamazaki, Satoshi; Sasaki, Hirokazu; Eguchi, Tatsuhiko; Susai, Kyota

    2016-03-01

    The n-/ p-type stability of a silicon clathrate in which silicon was substituted with nickel or platinum was evaluated by density functional theory calculations. Then, Ba8Pt5Si41 and Ba8Pt1.5Ni3.5Si41 were synthesized, and their thermoelectric properties were investigated. The polycrystalline compounds, which have a type-I clathrate structure, were prepared through arc melting and spark-plasma-sintering. The crystal structures and elemental compositions of the synthesized samples were characterized via powder x-ray diffraction and electron microprobe analyses, respectively. The temperature dependence of both the electrical resistivity and the Seebeck coefficient was measured.

  6. The Effect of Grain Size and Phosphorous-doping of Polycrystalline 3C-SiC on Infrared Reflectance Spectra

    SciTech Connect

    I. J. van Rooyen; J. A. A. Engelbrecht; A. Henry; E. Janzen; J. H. Neethling; P. M. van Rooyen

    2012-03-01

    The effect of P-doping and grain size of polycrystalline 3C-SiC on the infrared reflectance spectra is reported. The relationship between grain size and full width at half maximum (FWHM) suggest that the behaviour of the 3C-SiC with the highest phosphorous doping level (of 1.2 x 10{sup 19} at. cm{sup -3}) is different from those with lower doping levels (< 6.6 x 10{sup 18} at. cm{sup -3}). It is also further demonstrated that the plasma resonance frequency (w{sub p}) is not influenced by the grain size.

  7. Recovery Act : Near-Single-Crystalline Photovoltaic Thin Films on Polycrystalline, Flexible Substrates

    SciTech Connect

    Venkat Selvamanickam; Alex Freundlich

    2010-11-29

    III-V photovoltaics have exhibited efficiencies above 40%, but have found only a limited use because of the high cost of single crystal substrates. At the other end of the spectrum, polycrystalline and amorphous thin film solar cells offer the advantage of low-cost fabrication, but have not yielded high efficiencies. Our program is based on single-crystalline-like thin film photovoltaics on polycrystalline substrates using biaxially-textured templates made by Ion Beam-Assisted Deposition (IBAD). MgO templates made by IBAD on flexible metal substrate have been successfully used for epitaxial growth of germanium films. In spite of a 4.5% lattice mismatch, heteroepitaxial growth of Ge was achieved on CeO2 that was grown on IBAD MgO template. Room temperature optical bandgap of the Ge films was identified at 0.67 eV indicating minimal residual strain. Refraction index and extinction coefficient values of the Ge films were found to match well with that measured from a reference Ge single crystal. GaAs has been successfully grown epitaxially on Ge on metal substrate by molecular beam epitaxy. RHEED patterns indicate self annihilation of antiphase boundaries and the growth of a single domain GaAs. The GaAs is found to exhibit strong photoluminescence signal and, an existence of a relatively narrow (FWHM~20 meV) band-edge excitons measured in this film indicates a good optoelectronic quality of deposited GaAs. While excellent epitaxial growth has been achieved in GaAs on flexible metal substrates, the defect density of the films as measured by High Resolution X-ray Diffraction and etch pit experiments showed a high value of 5 * 10^8 per cm^2. Cross sectional transmission electron microscopy of the multilayer architecture showed concentration of threading dislocations near the germanium-ceria interface. The defect density was found decrease as the Ge films were made thicker. The defects appear to originate from the MgO layer presumably because of large lattice mismatches

  8. 1 Tbit/in.2 Very-High-Density Recording in Mass-Productive Polycrystalline Ferroelectric Thin Film Media

    NASA Astrophysics Data System (ADS)

    Fujimoto, Kenjiro; Kawano, Takahiro; Onoe, Atsushi; Tamura, Masahiro; Umeda, Masaru; Toda, Masayuki

    2009-07-01

    We demonstrate very-high-density ferroelectric recording experiments of 1 Tbit/in.2 in polycrystalline Pb(Zr,Ti)O3 (PZT) thin film for the first time. A high-quality polycrystalline PZT thin film was successfully deposited on a silicon substrate with a SrRuO3 (SRO) electrode by metal-organic chemical vapor deposition (MOCVD). The roughness of the PZT film was reduced to less than 1 nm by chemical mechanical polishing (CMP). The PZT film has very high controllability for domain inversion. Our fabrication process also enables high productivity. Therefore, our PZT film has potential to be a mass-productive ferroelectric recording medium for high-density storage systems.

  9. Epitaxial orientation of Mg{sub 2}Si(110) thin film on Si(111) substrate

    SciTech Connect

    Wang, Y.; Wang, X. N.; Mei, Z. X.; Du, X. L.; Zou, J.; Jia, J. F.; Xue, Q. K.; Zhang, X. N.; Zhang, Z.

    2007-12-15

    Epitaxial Mg{sub 2}Si(110) thin film has been obtained on Si(111) substrate by thermally enhanced solid-phase reaction of epitaxial Mg film with underlying Si substrate. An epitaxial orientation relationship of Si(111) parallel Mg{sub 2}Si(110) and Si<110> parallel Mg{sub 2}Si<110> has been revealed by transmission electron microscopy. The formation of the unusual epitaxial orientation relationship is attributed to the strain relaxation of Mg{sub 2}Si film in a MgO/Mg{sub 2}Si/Si double heterostructure.

  10. Appropriate materials and preparation techniques for polycrystalline-thin-film thermophotovoltaic cells

    SciTech Connect

    Dhere, N.G.

    1997-03-01

    Polycrystalline-thin-film thermophotovoltaic (TPV) cells have excellent potential for reducing the cost of TPV generators so as to address the hitherto inaccessible and highly competitive markets such as self-powered gas-fired residential warm air furnaces and energy-efficient electric cars, etc. Recent progress in polycrystalline-thin-film solar cells have made it possible to satisfy the diffusion length and intrinsic junction rectification criteria for TPV cells operating at high fluences. Continuous ranges of direct bandgaps of the ternary and pseudoternary compounds such as Hg{sub 1{minus}x}Cd{sub x}Te, Pb{sub 1{minus}x}Cd{sub x}Te, Hg{sub 1{minus}x}Zn{sub x}Te, and Pb{sub 1{minus}x}Zn{sub x}S cover the region of interest of 0.50{endash}0.75 eV for efficient TPV conversion. Other ternary and pseudoternary compounds which show direct bandgaps in most of or all of the 0.50{endash}0.75 eV range are Pb{sub 1{minus}x}Zn{sub x}Te, Sn{sub 1{minus}x}Cd{sub 2x}Te{sub 2}, Pb{sub 1{minus}x}Cd{sub x}Se, Pb{sub 1{minus}x}Zn{sub x}Se, and Pb{sub 1{minus}x}Cd{sub x}S. Hg{sub 1{minus}x}Cd{sub x}Te (with x{approx}0.21) has been studied extensively for infrared detectors. PbTe and Pb{sub 1{minus}x}Sn{sub x}Te have also been studied for infrared detectors. Not much work has been carried out on Hg{sub 1{minus}x}Zn{sub x}Te thin films. Hg{sub 1{minus}x}Cd{sub x}Te and Pb{sub 1{minus}x}Cd{sub x}Te alloys cover a wide range of cut-off wavelengths from the far infrared to the near visible. Acceptors and donors are introduced in these materials by excess non-metal (Te) and excess metal (Hg and Pb) respectively. Extrinsic acceptor impurities are Cu, Au, and As while and In and Al are donor impurities. Hg{sub 1{minus}x}Cd{sub x}Te thin films have been deposited by isothermal vapor-phase epitaxy (VPE), liquid phase epitaxy (LPE), hot-wall metalorganic chemical vapor deposition (MOCVD), electrodeposition, sputtering, molecular beam epitaxy (MBE), laser-assisted evaporation, and vacuum

  11. Electrical and structural properties of semi-insulating polycrystalline silicon thin films

    NASA Astrophysics Data System (ADS)

    Lombardo, S.; Campisano, S. U.; Baroetto, F.

    1993-05-01

    Semi-insulating polycrystalline silicon layers with oxygen concentrations ranging from 2 up to 30 at. % O have been prepared by low-pressure chemical vapor deposition. After deposition, the samples were annealed at 920 °C for 30 min. Grain-size distributions, high- and low-frequency dielectric constants were measured, respectively, by transmission-electron microscopy, capacitance, and optical measurements as a function of the oxygen content. The average grain radius decreases with the oxygen content from 15 up to 2.5 nm. The current-voltage characteristics have been measured as a function of temperature in the range 80-450 K and under applied transverse electric fields up to ~=106 V/cm. In weak-transverse-field conditions, the current density as a function of temperature shows two thermally activated regions at low and high temperatures, with activation energies of ~=0.14 and ~=0.54 eV, respectively. The application of transverse electric fields of the order of ~=106 V/cm produces a current enhancement depending upon field intensity, temperature, and oxygen content. The results have been modeled by assuming thermionic emission, tunneling, and Frenkel generation in a long series of Schottky barriers formed at the boundary of the adjacent grains. The best-fit values of the model parameters indicate that for 30 at. % O a continuous SiO2 shell, two monolayers thick, surrounds each grain. For lower oxygen contents this shell is discontinuous and the carrier transport parameters change considerably.

  12. Fatigue characteristics of polycrystalline silicon thin-film membrane and its dependence on humidity

    NASA Astrophysics Data System (ADS)

    Tanemura, Tomoki; Yamashita, Shuichi; Wado, Hiroyuki; Takeuchi, Yukihiro; Tsuchiya, Toshiyuki; Tabata, Osamu

    2013-03-01

    This paper describes fatigue characteristics of a polycrystalline silicon thin-film membrane under different humidity evaluated by out-of-plane resonant vibration. The membrane, without the surface of sidewalls by patterning of photolithography and etching process, was applied to evaluate fatigue characteristics precisely against the changes in the surrounding humidity owing to narrower deviation in the fatigue lifetime. The membrane has 16 mm square-shaped multilayered films consisting of a 250 or 500 nm thick polysilicon film on silicon dioxide and silicon nitride underlying layers. A circular weight of 12 mm in diameter was placed at the center of the membrane to control the resonant frequency. Stress on the polysilicon film was generated by deforming the membrane oscillating the weight in the out-of-plane direction. The polysilicon film was fractured by fatigue damage accumulation under cyclic stress. The lifetime of the polysilicon membrane extended with lower relative humidity, especially at 5%RH. The results of the fatigue tests were well formulated with Weibull's statistics and Paris’ law. The dependence of fatigue characteristics on humidity has been quantitatively revealed for the first time. The crack growth rate indicated by the fatigue index decreased with the reduction in humidity, whereas the deviation of strength represented by the Weibull modulus was nearly constant against humidity.

  13. Local impedance imaging of boron-doped polycrystalline diamond thin films

    SciTech Connect

    Zieliński, A.; Ryl, J.; Burczyk, L.; Darowicki, K.

    2014-09-29

    Local impedance imaging (LII) was used to visualise surficial deviations of AC impedances in polycrystalline boron-doped diamond (BDD). The BDD thin film electrodes were deposited onto the highly doped silicon substrates via microwave plasma-enhanced CVD. The studied boron dopant concentrations, controlled by the [B]/[C] ratio in plasma, ranged from 1 × 10{sup 16} to 2 × 10{sup 21} atoms cm{sup −3}. The BDD films displayed microcrystalline structure, while the average size of crystallites decreased from 1 to 0.7 μm with increasing [B]/[C] ratios. The application of LII enabled a direct and high-resolution investigation of local distribution of impedance characteristics within the individual grains of BDD. Such an approach resulted in greater understanding of the microstructural control of properties at the grain level. We propose that the obtained surficial variation of impedance is correlated to the areas of high conductance which have been observed at the grain boundaries by using LII. We also postulate that the origin of high conductivity is due to either preferential boron accumulation, the presence of defects, or sp{sup 2} regions in the intragrain regions. The impedance modulus recorded by LII was in full agreement with the bulk impedance measurements. Both variables showed a decreasing trend with increasing [B]/[C] ratios, which is consistent with higher boron incorporation into BDD film.

  14. A thin-film polycrystalline photoelectrochemical cell with 8% solar conversion efficiency

    NASA Astrophysics Data System (ADS)

    Hodes, G.

    1980-05-01

    A thin-film polycrystalline CdSe(0.65)Te(0.35)/polysulfide-based photoelectrochemical solar cell with an energy conversion efficiency of up to 8% is presented. Cell electrodes were prepared by painting a slurry of sintered CdSe(0.65)Te(0.35) powder onto a Ti substrate and then annealing in an inert atmosphere and etching by various means. Solar efficiencies of the electrodes immersed in an aqueous electrolyte 1 M in KOH, Na2S and S with a counter electrode of sulfide brass gauze of up to 5% were obtained following a HCl:HNO3 etch, up to 5.5% following etching in dilute aqueous CrO3 and up to 8.0% following photoetching and K2CrO4 treatment. The spectral response of the anode in polysulfide solution exhibits a short-wavelength cutoff due to electrolyte absorption, a flat plateau region, and a fairly sharp long-wavelength cut-off indicating an effective band gap of about 1.45 eV, similar to that of CdTe. Output stability has been found to decrease with increasing output current, remaining stable for more than 21 h at a current of 20 mA/sq cm.

  15. Polycrystalline silicon thin-film solar cells with plasmonic-enhanced light-trapping.

    PubMed

    Varlamov, Sergey; Rao, Jing; Soderstrom, Thomas

    2012-01-01

    One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To compensate for lower light absorption such physically thin devices have to incorporate light-trapping which increases their optical thickness. Light scattering by textured surfaces is a common technique but it cannot be universally applied to all solar cell technologies. Some cells, for example those made of evaporated silicon, are planar as produced and they require an alternative light-trapping means suitable for planar devices. Metal nanoparticles formed on planar silicon cell surface and capable of light scattering due to surface plasmon resonance is an effective approach. The paper presents a fabrication procedure of evaporated polycrystalline silicon solar cells with plasmonic light-trapping and demonstrates how the cell quantum efficiency improves due to presence of metal nanoparticles. To fabricate the cells a film consisting of alternative boron and phosphorous doped silicon layers is deposited on glass substrate by electron beam evaporation. An Initially amorphous film is crystallised and electronic defects are mitigated by annealing and hydrogen passivation. Metal grid contacts are applied to the layers of opposite polarity to extract electricity generated by the cell. Typically, such a ~2 μm thick cell has a short-circuit current density (Jsc) of 14-16 mA/cm(2), which can be increased up to 17-18 mA/cm(2) (~25% higher) after application of a simple diffuse back reflector made of a white paint. To implement plasmonic light-trapping a silver nanoparticle array is formed on the metallised cell silicon surface. A precursor silver film is deposited on the cell by thermal evaporation and annealed at 23°C to form silver nanoparticles. Nanoparticle size and coverage, which affect plasmonic light-scattering, can be tuned for enhanced cell performance by varying the precursor film thickness and its annealing

  16. Interconnected Si nanocrystals forming thin films with controlled bandgap values

    SciTech Connect

    Nychyporuk, T.; Zakharko, Yu.; Lysenko, V.; Lemiti, M.

    2009-08-24

    Interconnected Si nanocrystals forming homogeneous thin films with controlled bandgap values from 1.2 to 2.9 eV were formed by pulsed plasma enhanced chemical vapor deposition technique under dusty plasma conditions. The chosen values of plasma duration time correspond to specific phases of the dust nanoparticle growth. Structural and optical properties of the deposited nanostructured films are described in details. These nanocrystalline Si thin films seem to be promising candidates for all-Si tandem solar cell applications.

  17. Electrically-alterable read-only-memory using Si-rich SiO2 injectors and a floating polycrystalline silicon storage layer

    NASA Astrophysics Data System (ADS)

    DiMaria, D. J.; DeMeyer, K. M.; Serrano, C. M.; Dong, D. W.

    1981-07-01

    Currently, electrically-alterable read-only-memory (EAROM) has become increasingly important for memory and logic operations. A novel EAROM device in a field-effect transistor (FET) configuration, which uses a floating polycrystalline silicon (poly-Si) layer on top of thermal SiO2 and a dual electron injector structure (DEIS) between this floating poly-Si and a control gate poly-Si contact, is described. The DEIS stack consists of sequentially chemically vapor deposited (CVD) layers of Si-rich SiO2 (46% atomic Si), SiO2, and Si-rich SiO2 (46% atomic Si) between the poly-Si layers. Electrons from either poly-Si layer can move to the other poly-Si layer biased at the higher voltage with moderate applied voltages. Thus, the floating poly-Si storage layer can be charged with electrons (''write'' operation) or with positive charge (''erase'' operation) in milliseconds with negative and positive control gate voltages, respectively. The average electric fields in the intervening CVD SiO2 layer during writing and erasing are 5-6 MV /cm and 4-5 MV/cm, respectively, and voltages from ±10 V to ±40 V can be used depending on the device configuration. The enhanced electron injection in these devices is believed to be controlled by localized electric field distortion at the Si-rich SiO2-SiO2 interface caused by the two phase (Si and SiO2) nature of the Si-rich SiO2. The electrical asymmetry of the DEIS is believed to be due to differences in the interfaces of the bottom and top Si-rich SiO2 injectors with the intervening SiO2 layer. At the low voltages used for the ''read'' operation in which the charge state of the floating poly-Si layer is sensed by the FET drain current, no read perturb effects are observed. These structures also show excellent charge retention at low voltages, characteristic of a floating poly-Si storage layer surrounded by SiO2. This excellent retention is due to a characteristic of the Si-rich SiO2 in which it builds up a reversible space-charge layer

  18. Characterization of polycrystalline VO2 thin film with low phase transition temperature fabricated by high power impulse magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Lin, Tiegui; Wang, Langping; Wang, Xiaofeng; Zhang, Yufen

    2016-04-01

    VO2 is a unique material that undergoes a reversible phase transformation around 68∘C. Currently, applications of VO2 on smart windows are limited by its high transition temperature. In order to reduce the temperature, VO2 thin film was fabricated on quartz glass substrate by high power impulse magnetron sputtering with a modulated pulsed power. The phase transition temperature has been reduced to as low as 32∘C. In addition, the VO2 film possesses a typical metal-insulator transition. X-ray diffraction and selected area electron diffraction patterns reveal that an obvious lattice distortion has been formed in the as-deposited polycrystalline VO2 thin film. X-ray photoelectron spectroscopy proves that oxygen vacancies have been formed in the as-deposited thin film, which will induce a lattice distortion in the VO2 thin film.

  19. Si oxyhydrides on stain-etched porous Si thin films and correlation with crystallinity and photoluminescence

    NASA Astrophysics Data System (ADS)

    Steckl, A. J.; Xu, J.; Mogul, H. C.; Prokes, S. M.

    1995-05-01

    Porous Si has been fabricated from amorphous and polycrystalline Si films by stain-etching in HF:HNO3:H2O. Infrared transmission measurements have revealed an absorption peak at 880-890 cm(sup - 1) only in crystalline porous Si samples. This peak is probably due to an SiH2 bending mode in the presence of oxygen. Similarly, only crystalline PoSi films exhibit visible (approximately 650-670 nm) photoluminescence under UV excitation. Amorphous PoSi samples do not luminesce even after very long etch times, in spite of greatly increased porosity. Therefore, it appears that there exists a unique correlation between the presence of crystallinity in the starting Si film and the presence of surface oxyhydrides and photoluminescence after stain-etching.

  20. Optical absorption characteristics of polycrystalline AgGaSe2 thin films

    NASA Astrophysics Data System (ADS)

    Bhuiyan, M. R. A.; Firoz Hasan, S. M.

    2006-12-01

    Silver gallium di-selenide (AgGaSe2) composite thin films have been formed onto ultrasonically and chemically cleaned glass substrates by in situ thermal annealing of the stack of successively evaporated individual elemental layers in vacuum. The structural properties of the films were ascertained by the x-ray diffraction method. The diffractogram indicated that these films were polycrystalline in nature having tetragonal structure with lattice parameters, a ap 6.00 Å and c ap 10.92 Å and average grain dimension 40 nm. The optical properties and atomic compositions of the films have been determined by UV-VIS-NIR spectrophotometry (photon wavelength ranging between 300 and 2500 nm) and energy dispersive analysis of x-ray, respectively. The typical optical absorption characteristic of the films has been critically analysed. The optical absorption coefficients vary from 103 to 105 cm-1 in the measured wavelength range of photons. The films have more than one type of fundamental electronic transitions. Direct allowed and direct forbidden transitions vary from 1.628 to 1.748 eV and 2.077 to 2.193 eV, respectively, depending on the composition of the films. The former transitions are found to have a general tendency to be symmetric around non-molecularity ΔX = 0, defined by ΔX = [(Ag/Ga)] - 1, while the latter shows no such dependence. Stoichiometric or slightly silver-deficient films show electron transition energies closer to the single crystal value. Spin-orbit splitting of the valence band becomes minimum at perfect stoichiometry.

  1. Influence of thickness on physical properties of vacuum evaporated polycrystalline CdTe thin films for solar cell applications

    NASA Astrophysics Data System (ADS)

    Chander, Subhash; Dhaka, M. S.

    2016-02-01

    This paper presents the influence of thickness on physical properties of polycrystalline CdTe thin films. The thin films of thickness 450 nm, 650 nm and 850 nm were deposited employing thermal vacuum evaporation technique on glass and indium tin oxide (ITO) coated glass substrates. The physical properties of these as-grown thin films were investigated employing the X-ray diffraction (XRD), source meter, UV-Vis spectrophotometer, scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The structural analysis reveals that the films have zinc-blende cubic structure and polycrystalline in nature with preferred orientation (111). The structural parameters like lattice constant, interplanar spacing, grain size, strain, dislocation density and number of crystallites per unit area are calculated. The average grain size and optical band gap are found in the range 15.16-21.22 nm and 1.44-1.63 eV respectively and observed to decrease with thickness. The current-voltage characteristics show that the electrical conductivity is observed to decrease with thickness. The surface morphology shows that films are free from crystal defects like pin holes and voids as well as homogeneous and uniform. The EDS patterns show the presence of cadmium and tellurium elements in the as grown films. The experimental results reveal that the film thickness plays significant role on the physical properties of as-grown CdTe thin films and higher thickness may be used as absorber layer to solar cells applications.

  2. Synthesis of (SiC){sub 3}N{sub 4} thin films by ion implantation

    SciTech Connect

    Uslu, C.; Lee, D.H.; Berta, Y.; Park, B.; Thadhani, N.N.; Poker, D.B.

    1993-12-31

    We have investigated the synthesis of carbon-silicon-nitride compounds by ion implantation. In these experiments, 100 keV nitrogen ions were implanted into polycrystalline {beta}-SiC (cubic phase) at various substrate temperatures and ion doses. These thin films were characterized by x-ray diffraction with a position-sensitive detector, transmission electron microscopy with chemical analysis, and Rutherford backscattering spectroscopy. The as-implanted samples show a buried amorphous layer at a depth of 170 nm. Peak concentration of nitrogen saturates at approximately 45 at. % with doses above {approximately} 9.0 {times} 10{sup 17} N/cm{sup 2} at 860{degree}C. These results suggest formation of a new phase by nitrogen implantation into {beta}-SiC.

  3. Exploration of maximum count rate capabilities for large-area photon counting arrays based on polycrystalline silicon thin-film transistors

    NASA Astrophysics Data System (ADS)

    Liang, Albert K.; Koniczek, Martin; Antonuk, Larry E.; El-Mohri, Youcef; Zhao, Qihua

    2016-03-01

    Pixelated photon counting detectors with energy discrimination capabilities are of increasing clinical interest for x-ray imaging. Such detectors, presently in clinical use for mammography and under development for breast tomosynthesis and spectral CT, usually employ in-pixel circuits based on crystalline silicon - a semiconductor material that is generally not well-suited for economic manufacture of large-area devices. One interesting alternative semiconductor is polycrystalline silicon (poly-Si), a thin-film technology capable of creating very large-area, monolithic devices. Similar to crystalline silicon, poly-Si allows implementation of the type of fast, complex, in-pixel circuitry required for photon counting - operating at processing speeds that are not possible with amorphous silicon (the material currently used for large-area, active matrix, flat-panel imagers). The pixel circuits of two-dimensional photon counting arrays are generally comprised of four stages: amplifier, comparator, clock generator and counter. The analog front-end (in particular, the amplifier) strongly influences performance and is therefore of interest to study. In this paper, the relationship between incident and output count rate of the analog front-end is explored under diagnostic imaging conditions for a promising poly-Si based design. The input to the amplifier is modeled in the time domain assuming a realistic input x-ray spectrum. Simulations of circuits based on poly-Si thin-film transistors are used to determine the resulting output count rate as a function of input count rate, energy discrimination threshold and operating conditions.

  4. Carrier mobility measurement across a single grain boundary in polycrystalline silicon using an organic gate thin-film transistor

    SciTech Connect

    Hashimoto, Masaki; Kanomata, Kensaku; Momiyama, Katsuaki; Kubota, Shigeru; Hirose, Fumihiko

    2012-01-09

    In this study, we developed a measurement method for field-effect-carrier mobility across a single grain boundary in polycrystalline Si (poly Si) used for solar cell production by using an organic gate field-effect transistor (FET). To prevent precipitation and the diffusion of impurities affecting the electronic characteristics of the grain boundary, all the processing temperatures during FET fabrication were held below 150 deg. C. From the grain boundary, the field-effect mobility was measured at around 21.4 cm{sup 2}/Vs at 297 K, and the temperature dependence of the field-effect mobility suggested the presence of a potential barrier of 0.22 eV at the boundary. The technique presented here is applicable for the monitoring of carrier conduction characteristics at the grain boundary in poly Si used for the production of solar cells.

  5. Epitaxially grown polycrystalline silicon thin-film solar cells on solid-phase crystallised seed layers

    NASA Astrophysics Data System (ADS)

    Li, Wei; Varlamov, Sergey; Xue, Chaowei

    2014-09-01

    This paper presents the fabrication of poly-Si thin film solar cells on glass substrates using seed layer approach. The solid-phase crystallised P-doped seed layer is not only used as the crystalline template for the epitaxial growth but also as the emitter for the solar cell structure. This paper investigates two important factors, surface cleaning and intragrain defects elimination for the seed layer, which can greatly influence the epitaxial grown solar cell performance. Shorter incubation and crystallisation time is observed using a simplified RCA cleaning than the other two wet chemical cleaning methods, indicating a cleaner seed layer surface is achieved. Cross sectional transmission microscope images confirm a crystallographic transferal of information from the simplified RCA cleaned seed layer into the epi-layer. RTA for the SPC seed layer can effectively eliminate the intragrain defects in the seed layer and improve structural quality of both of the seed layer and the epi-layer. Consequently, epitaxial grown poly-Si solar cell on the RTA treated seed layer shows better solar cell efficiency, Voc and Jsc than the one on the seed layer without RTA treatment.

  6. Selective Growth of Nanocrystalline 3C-SiC Thin Films on Si

    NASA Astrophysics Data System (ADS)

    Beke, D.; Pongrácz, A.; Battistig, G.; Josepovits, K.; Pécz, B.

    2010-11-01

    Epitaxial formation of SiC nanocrystals has been investigated on single crystal silicon surfaces. A simple and cheap method using reactive annealing in CO has been developed and patented by our group (BME AFT and MTA MFA). By this technique epitaxial 3C-SiC nanocrystals can be grown at the Si side of a SiO2/Si interface without void formation at the SiC/Si interface. CO diffusion and SiC nanocrystal formation on different silicon based systems (SiO2/Si, Si3N4/3Si and SiO2/LPCVD poly-Si) after CO treatment at 105 Pa at elevated temperatures (T>1000° C) will be presented. By optimizing the annealing time a thin continuous nanocrystalline SiC layer has been formed. Applying a patterned Si3N4 capping layer as a barrier layer against CO diffusion, SiC nanocrystal formation at the Si3N4/Si interface is inhibited. We will present the selective growth of SiC nanocrystals using the before mentioned technique.

  7. Electronic transitions in the bandgap of copper indium gallium diselenide polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Heath, Jennifer Theresa

    The electronic properties of polycrystalline copper indium gallium diselenide thin films have been investigated, with emphasis on understanding the distribution and origin of electronic states in the bandgap. The samples studied were working photovoltaic devices with the structure ZnO/CdS/CuIn1-xGa xSe2/Mo, and photovoltaic efficiencies ranging from 8 to 16%. The CdS layer and the p-type CuIn1-xGa xSe2 film create the n+- p junction at the heart of these devices. The samples were investigated using four techniques based on the electrical response of the junction: admittance spectroscopy, drive level capacitance profiling, transient photocapacitance spectroscopy, and transient photocurrent spectroscopy. From these measurements the free carrier densities, defect densities within the bandgap, spatial uniformity, and minority carrier mobilities have been deduced. The sub-bandgap response from the CuIn1-xGaxSe2 film was dominated by two defects. One exhibited a thermal transition to the valence band with an activation energy ranging between 0.1 and 0.3 eV and thermal emission prefactors obeying the Meyer-Neldel rule. The second was detected as an optical transition 0.8 eV from the valence band edge. Neither of these defects exhibited densities that varied systematically with gallium content, implying that they are not directly connected with the group III elements in these alloys. The defect densities also do not clearly correlate with the photovoltaic device performance; however, the position of the 0.8 eV defect lies nearer to mid-gap in the higher gallium, and hence higher band gap, material. This implies that it may be a more important recombination center in these devices and may be partially responsible for the reduced photovoltaic efficiencies observed when Ga/(In + Ga) > 0.4. An additional defect response was observed near mid-gap in films grown by processes known to produce lower quality devices. The influence of defects located at grain boundaries was also

  8. Polycrystalline thin film materials and devices. Annual subcontract report, 16 January 1990--15 January 1991

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E.

    1991-11-01

    Results and conclusion of Phase I of a multi-year research program on polycrystalline thin film solar cells are presented. The research comprised investigation of the relationships among processing, materials properties and device performance of both CuInSe{sub 2} and CdTe solar cells. The kinetics of the formation of CuInSe{sub 2} by selenization with hydrogen selenide was investigated and a CuInSe{sub 2}/CdS solar cell was fabricated. An alternative process involving the reaction of deposited copper-indium-selenium layers was used to obtain single phase CuInSe{sub 2} films and a cell efficiency of 7%. Detailed investigations of the open circuit voltage of CuInSe{sub 2} solar cells showed that a simple Shockley-Read-Hall recombination mechanism can not account for the limitations in open circuit voltage. Examination of the influence of CuInSe{sub 2} thickness on cell performance indicated that the back contact behavior has a significant effect when the CuInSe{sub 2} is less than 1 micron thick. CdTe/CdS solar cells with efficiencies approaching 10% can be repeatedly fabricated using physical vapor deposition and serial post deposition processing. The absence of moisture during post deposition was found to be critical. Improvements in short circuit current of CdTe solar cells to levels approaching 25 mA/cm{sup 2} are achievable by making the CdS window layer thinner. Further reductions in the CdS window layer thickness are presently limited by interdiffusion between the CdS and the CdTe. CdTe/CdS cells stored without protection from the atmosphere were found to degrade. The degradation was attributed to the metal contact. CdTe cells with ZnTe:Cu contacts to the CdTe were found to be more stable than cells with metal contacts. Analysis of current-voltage and spectral response of CdTe/CdS cells indicates the cell operates as a p-n heterojunction with the diode current dominated by SRH recombination in the junction region of the CdTe.

  9. On the effect of processing parameters in the chemical-vapor deposition of YBa2Cu3O(7-delta) thin films on polycrystalline silver

    NASA Astrophysics Data System (ADS)

    Chen, L.; Piazza, T. W.; Schmidt, B. E.; Kelsey, J. E.; Kaloyeros, A. E.; Hazelton, D. W.; Walker, M. S.; Luo, L.; Dye, R. C.; Maggiore, C. J.

    1993-06-01

    Results are presented of experimental studies which examined the effect of recrystallization of polycrystalline silver on the growth of YBa2Cu3O(7-delta) superconducting thin films and investigated optimum processing conditions for high-quality superconducting films. The samples were characterized using XRD, Rutherford backscattering, SEM, dynamic impedance, and four-point resistivity probe. The results were used to formulate a model for the underlying mechanics of film growth on polycrystalline silver substrates.

  10. Pixel structures to compensate nonuniform threshold voltage and mobility of polycrystalline silicon thin-film transistors using subthreshold current for large-size active matrix organic light-emitting diode displays

    NASA Astrophysics Data System (ADS)

    Na, Jun-Seok; Kwon, Oh-Kyong

    2014-01-01

    We propose pixel structures for large-size and high-resolution active matrix organic light-emitting diode (AMOLED) displays using a polycrystalline silicon (poly-Si) thin-film transistor (TFT) backplane. The proposed pixel structures compensate the variations of the threshold voltage and mobility of the driving TFT using the subthreshold current. The simulated results show that the emission current error of the proposed pixel structure B ranges from -2.25 to 2.02 least significant bit (LSB) when the variations of the threshold voltage and mobility of the driving TFT are ±0.5 V and ±10%, respectively.

  11. Diffusion of Si in thin CoSi2 layers

    NASA Technical Reports Server (NTRS)

    Schowengerdt, F. D.; Lin, T. L.; Fathauer, R. W.; Grunthaner, P. J.

    1989-01-01

    Evidence of silicon diffusion in 100-A CoSi2 layers grown by room-temperature codeposition and annealing on Si(111) substrates was from Auger peak height ratios, which were interpreted in terms of a Si overlayer. It was found that this layer could be removed by chemical etching and reformed by subsequent annealing. By measuring the intensity of the plasmon energy loss peak associated with the CoL23 VV Auger peak, the effective thickness of the Si overlayer was measured as a function of annealing temperature, by calibrating the plasmon loss data against known overlayer thicknesses on unannealed samples. Similar results were found for samples grown both with and without the addition of a 10-A Si cap to prevent pinhole formation in the CoSi2; moreover, Si diffusion was also observed at temperatures well below the point where pinhole formation is first found, suggesting that Si diffusion does not depend on the presence of observable pinholes.

  12. Electronic transport in highly conducting Si-doped ZnO thin films prepared by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Kuznetsov, Vladimir L.; Vai, Alex T.; Al-Mamouri, Malek; Stuart Abell, J.; Pepper, Michael; Edwards, Peter P.

    2015-12-01

    Highly conducting (ρ = 3.9 × 10-4 Ωcm) and transparent (83%) polycrystalline Si-doped ZnO (SiZO) thin films have been deposited onto borosilicate glass substrates by pulsed laser deposition from (ZnO)1-x(SiO2)x (0 ≤ x ≤ 0.05) ceramic targets prepared using a sol-gel technique. Along with their structural, chemical, and optical properties, the electronic transport within these SiZO samples has been investigated as a function of silicon doping level and temperature. Measurements made between 80 and 350 K reveal an almost temperature-independent carrier concentration consistent with degenerate metallic conduction in all of these samples. The temperature-dependent Hall mobility has been modeled by considering the varying contribution of grain boundary and electron-phonon scattering in samples with different nominal silicon concentrations.

  13. Enhanced electrical properties at boundaries including twin boundaries of polycrystalline CdTe thin-film solar cells.

    PubMed

    Li, H; Liu, X X; Lin, Y S; Yang, B; Du, Z M

    2015-05-01

    The effect of grain boundaries (GBs), in particular twin boundaries (TBs), on CdTe polycrystalline thin films is studied by conductive atomic force microscopy (C-AFM), electron-beam-induced current (EBIC), scanning Kelvin probe microscopy (SKPM), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (STEM). Four types of CdTe grains with various densities of {111} Σ3 twin boundaries (TBs) are found in Cl-treated CdTe polycrystalline thin films: (1) grains having multiple {111} Σ3 TBs with a low angle to the film surface; (2) grains having multiple {111} Σ3 TBs parallel to the film surfaces; (3) small grains on a scale of not more than 500 nm, composed of Cd, Cl, Te, and O; and (4) CdTe grains with not more than two {111} Σ3 TBs. Grain boundaries (including TBs) exhibit enhanced current transport phenomena. However, the {111} Σ3 TB is much more beneficial to micro-current transport. The enhanced current transport can be explained by the lower electron potential at GBs (including TBs) than the grain interiors (GIs). Our results open new opportunities for enhancing solar cell performances by controlling the grain boundaries, and in particular TBs.

  14. Formation, optical properties, and electronic structure of thin Yb silicide films on Si(111)

    NASA Astrophysics Data System (ADS)

    Galkin, N. G.; Maslov, A. M.; Polyarnyi, V. O.

    2005-06-01

    Continuous very thin (2.5-3.0 nm) and thin (16-18 nm) ytterbium suicide films with some pinhole density (3×107- 1×108 cm-2) have been formed on Si(111) by solid phase epitaxy (SPE) and reactive deposition epitaxy (RDE) growth methods on templates. The stoichiometric ytterbium suicide (YbSi2) formation has shown in SPE grown films by AES and EELS data. Very thin Yb suicide films grown by RDE method had the silicon enrichment in YbSi2 suicide composition. The analysis of LEED data and AFM imaging has shown that ytterbium suicide films had non-oriented blocks with the polycrystalline structure. The analysis of scanning region length dependencies of the root mean square roughness deviation (σR(L)) for grown suicide films has shown that the formation of ytterbium suicide in SPE and RDE growth methods is determined by the surface diffusion of Yb atoms during the three-dimensional growth process. Optical functions (n, k, α, ɛ1, ɛ2, Im ɛ1-1, neff, ɛeff) of ytterbium silicide films grown on Si(1 1 1) have been calculated from transmittance and reflectance spectra in the energy range of 0.1-6.2 eV. Two nearly discrete absorption bands have been observed in the electronic structure of Yb silicide films with different composition, which connected with interband transitions on divalent and trivalent Yb states. It was established that the reflection coefficient minimum in R-spectra at energies higher 4.2 eV corresponds to the state density minimum in Yb suicide between divalent and trivalent Yb states. It was shown from optical data that Yb silicide films have the semi-metallic properties with low state densities at energies less 0.4 eV and high state densities at 0.5-2.5 eV.

  15. Impact of thermal annealing on physical properties of vacuum evaporated polycrystalline CdTe thin films for solar cell applications

    NASA Astrophysics Data System (ADS)

    Chander, Subhash; Dhaka, M. S.

    2016-06-01

    A study on impact of post-deposition thermal annealing on the physical properties of CdTe thin films is undertaken in this paper. The thin films of thickness 500 nm were grown on ITO and glass substrates employing thermal vacuum evaporation followed by post-deposition thermal annealing in air atmosphere within low temperature range 150-350 °C. These films were subjected to the XRD, UV-Vis NIR spectrophotometer, source meter, SEM coupled with EDS and AFM for structural, optical, electrical and surface topographical analysis respectively. The diffraction patterns reveal that the films are having zinc-blende cubic structure with preferred orientation along (111) and polycrystalline in nature. The crystallographic parameters are calculated and discussed in detail. The optical band gap is found in the range 1.48-1.64 eV and observed to decrease with thermal annealing. The current-voltage characteristics show that the CdTe films exhibit linear ohmic behavior. The SEM studies show that the as-grown films are homogeneous, uniform and free from defects. The AFM studies reveal that the surface roughness of films is observed to increase with annealing. The experimental results reveal that the thermal annealing has significant impact on the physical properties of CdTe thin films and may be used as absorber layer to the CdTe/CdS thin films solar cells.

  16. Structural and optical analysis of 60Co gamma-irradiated thin films of polycrystalline Ga10Se85Sn5

    NASA Astrophysics Data System (ADS)

    Ahmad, Shabir; Asokan, K.; Shahid Khan, Mohd.; Zulfequar, M.

    2015-12-01

    The present study focuses on the effects of gamma irradiation on structural and optical properties of polycrystalline Ga10Se85Sn5 thin films with a thickness of ∼300 nm deposited by the thermal evaporation technique on cleaned glass substrates. X-ray diffraction patterns of the investigated thin films show that crystallite growth occurs in the orthorhombic phase structure. The surface study carried out by using the scanning electron microscope (SEM) confirms that the grain size increases with gamma irradiation. The optical parameters were estimated from optical transmission spectra data measured from a UV-vis-spectrophotometer in the wavelength range of 200-1100 nm. The refractive index dispersion data of the investigated thin films follow the single oscillator model. The estimated values of static refractive index n0, oscillator strength Ed, zero frequency dielectric constant ε0, optical conductivity σoptical and the dissipation factor increases after irradiation, while the single oscillator energy Eo decreases after irradiation. It was found that the value of the optical band gap of the investigated thin films decreases and the corresponding absorption coefficient increases continuously with an increase in the dose of gamma irradiation. This post irradiation changes in the values of optical band gap and absorption coefficient were interpreted in terms of the bond distribution model.

  17. Low-temperature atomic layer deposition of MgO thin films on Si

    NASA Astrophysics Data System (ADS)

    Vangelista, S.; Mantovan, R.; Lamperti, A.; Tallarida, G.; Kutrzeba-Kotowska, B.; Spiga, S.; Fanciulli, M.

    2013-12-01

    Magnesium oxide (MgO) films have been grown by atomic layer deposition in the wide deposition temperature window of 80-350 °C by using bis(cyclopentadienyl)magnesium and H2O precursors. MgO thin films are deposited on both HF-last Si(1 0 0) and SiO2/Si substrates at a constant growth rate of ˜0.12 nm cycle-1. The structural, morphological and chemical properties of the synthesized MgO thin films are investigated by x-ray reflectivity, grazing incidence x-ray diffraction, time-of-flight secondary ion mass spectrometry and atomic force microscopy measurements. MgO layers are characterized by sharp interface with the substrate and limited surface roughness, besides good chemical uniformity and polycrystalline structure for thickness above 7 nm. C-V measurements performed on Al/MgO/Si MOS capacitors, with MgO in the 4.6-11 nm thickness range, allow determining a dielectric constant (κ) ˜ 11. Co layers are grown by chemical vapour deposition in direct contact with MgO without vacuum-break (base pressure 10-5-10-6 Pa). The as-grown Co/MgO stacks show sharp interfaces and no elements interdiffusion among layers. C-V and I-V measurements have been conducted on Co/MgO/Si MOS capacitors. The dielectric properties of MgO are not influenced by the further process of Co deposition.

  18. Ultra-high current density thin-film Si diode

    DOEpatents

    Wang, Qi

    2008-04-22

    A combination of a thin-film .mu.c-Si and a-Si:H containing diode structure characterized by an ultra-high current density that exceeds 1000 A/cm.sup.2, comprising: a substrate; a bottom metal layer disposed on the substrate; an n-layer of .mu.c-Si deposited the bottom metal layer; an i-layer of .mu.c-Si deposited on the n-layer; a buffer layer of a-Si:H deposited on the i-layer, a p-layer of .mu.c-Si deposited on the buffer layer; and a top metal layer deposited on the p-layer.

  19. Ultrafast optical control of magnetization dynamics in polycrystalline bismuth doped iron garnet thin films

    SciTech Connect

    Deb, Marwan Vomir, Mircea; Rehspringer, Jean-Luc; Bigot, Jean-Yves

    2015-12-21

    Controlling the magnetization dynamics on the femtosecond timescale is of fundamental importance for integrated opto-spintronic devices. For industrial perspectives, it requires to develop simple growth techniques for obtaining large area magneto-optical materials having a high amplitude ultrafast Faraday or Kerr response. Here we report on optical pump probe studies of light induced spin dynamics in high quality bismuth doped iron garnet polycrystalline film prepared by the spin coating method. We demonstrate an ultrafast non-thermal optical control of the spin dynamics using both circularly and linearly polarized pulses.

  20. Fabrication of polycrystalline CdTe thin-film solar cells using carbon electrodes with carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Okamoto, Tamotsu; Hayashi, Ryoji; Ogawa, Yohei; Hosono, Aikyo; Doi, Makoto

    2015-04-01

    The effects of adding carbon nanotubes (CNTs) to carbon back electrodes in polycrystalline CdTe thin-film solar cells were investigated. The CNTs were prepared by arc discharge under atmospheric pressure. The conductivity of the obtained CNT film with a density of 1.65 g/cm3 was approximately 2.6 × 103 S/cm. In the CdTe solar cells using carbon back electrodes with CNTs, the fill factor (FF) was improved as a result of adding CNTs with a concentration of 1 to 5 wt %. The improvement of FF was mainly due to the decrease in the series resistance of the CdTe solar cell. Furthermore, the open-circuit voltage (VOC) was improved by the CNT addition. The improvement of VOC was probably due to the reduction of the back barrier at the back contact.

  1. A New Low Temperature Polycrystalline Silicon Thin Film Transistor Pixel Circuit for Active Matrix Organic Light Emitting Diode

    NASA Astrophysics Data System (ADS)

    Ching-Lin Fan,; Yi-Yan Lin,; Jyu-Yu Chang,; Bo-Jhang Sun,; Yan-Wei Liu,

    2010-06-01

    This study presents one novel compensation pixel design and driving method for active matrix organic light-emitting diode (AMOLED) displays that use low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) with a voltage feed-back method and the simulation results are proposed and verified by SPICE simulator. The measurement and simulation of LTPS TFT characteristics demonstrate the good fitting result. The proposed circuit consists of four TFTs and two capacitors with an additional signal line. The error rates of OLED anode voltage variation are below 0.3% under the threshold voltage deviation of driving TFT (Δ VTH = ± 0.33 V). The simulation results show that the pixel design can improve the display image non-uniformity by compensating the threshold voltage deviation of driving TFT and the degradation of OLED threshold voltage at the same time.

  2. A New Low Temperature Polycrystalline Silicon Thin Film Transistor Pixel Circuit for Active Matrix Organic Light Emitting Diode

    NASA Astrophysics Data System (ADS)

    Fan, Ching-Lin; Lin, Yi-Yan; Chang, Jyu-Yu; Sun, Bo-Jhang; Liu, Yan-Wei

    2010-06-01

    This study presents one novel compensation pixel design and driving method for active matrix organic light-emitting diode (AMOLED) displays that use low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) with a voltage feed-back method and the simulation results are proposed and verified by SPICE simulator. The measurement and simulation of LTPS TFT characteristics demonstrate the good fitting result. The proposed circuit consists of four TFTs and two capacitors with an additional signal line. The error rates of OLED anode voltage variation are below 0.3% under the threshold voltage deviation of driving TFT (ΔVTH = ±0.33 V). The simulation results show that the pixel design can improve the display image non-uniformity by compensating the threshold voltage deviation of driving TFT and the degradation of OLED threshold voltage at the same time.

  3. Polycrystalline thin-film, cadmium-telluride solar cells fabricated by electrodeposition cells. Final subcontract report, March 20, 1992--April 27, 1995

    SciTech Connect

    Trefny, J.U.; Mao, D.; Kim, D.

    1995-10-01

    The objective of this project was to develop improved processes for the fabrication of CdTe/CdS polycrystalline thin film solar cells. The technique we used for the formation of CdTe, electrodeposition, was a non-vacuum, low-cost technique that is attractive for economic, large-scale production. Annealing effects and electrical properties are discussed.

  4. Electron beam-physical vapor deposition of SiC/SiO 2 high emissivity thin film

    NASA Astrophysics Data System (ADS)

    Yi, Jian; He, XiaoDong; Sun, Yue; Li, Yao

    2007-02-01

    When heated by high-energy electron beam (EB), SiC can decompose into C and Si vapor. Subsequently, Si vapor reacts with metal oxide thin film on substrate surface and formats dense SiO 2 thin film at high substrate temperature. By means of the two reactions, SiC/SiO 2 composite thin film was prepared on the pre-oxidized 316 stainless steel (SS) substrate by electron beam-physical vapor deposition (EB-PVD) only using β-SiC target at 1000 °C. The thin film was examined by energy dispersive spectroscopy (EDS), grazing incidence X-ray asymmetry diffraction (GIAXD), scanning electron microscopy (SEM), atomic force microscopy (AFM), backscattered electron image (BSE), electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS) and Fourier transformed infra-red (FT-IR) spectroscopy. The analysis results show that the thin film is mainly composed of imperfect nano-crystalline phases of 3C-SiC and SiO 2, especially, SiO 2 phase is nearly amorphous. Moreover, the smooth and dense thin film surface consists of nano-sized particles, and the interface between SiC/SiO 2 composite thin film and SS substrate is perfect. At last, the emissivity of SS substrate is improved by the SiC/SiO 2 composite thin film.

  5. Characterization of ZnO thin films grown on different p-Si substrate elaborated by solgel spin-coating method

    SciTech Connect

    Chebil, W.; Fouzri, A.; Fargi, A.; Azeza, B.; Zaaboub, Z.; and others

    2015-10-15

    Highlights: • High quality ZnO thin films grown on different p-Si substrates were successful obtained by sol–gel process. • PL measurement revealed that ZnO thin film grown on porous Si has the better optical quality. • I–V characteristics for all heterojunctions exhibit successful diode formation. • The diode ZnO/PSi shows a better photovoltaic effect under illumination with a maximum {sub Voc} of 0.2 V. - Abstract: In this study, ZnO thin films are deposited by sol–gel technique on p-type crystalline silicon (Si) with [100] orientation, etched silicon and porous silicon. The structural analyses showed that the obtained thin films were polycrystalline with a hexagonal wurtzite structure and preferentially oriented along the c-axis direction. Morphological study revealed the presence of rounded and facetted grains irregularly distributed on the surface of all samples. PL spectra at room temperature revealed that ZnO thin film grown on porous Si has a strong UV emission with low defects in the visible region comparing with ZnO grown on plat Si and etched Si surface. The heterojunction parameters were evaluated from the (I–V) under dark and illumination at room temperature. The ideality factor, barrier height and series resistance of heterojunction grown on different p-Si substrates are determined by using different methods. Best electrical properties are obtained for ZnO layer deposited on porous silicon.

  6. Elastic wave speeds and moduli in polycrystalline ice Ih, si methane hydrate, and sll methane-ethane hydrate

    USGS Publications Warehouse

    Helgerud, M.B.; Waite, W.F.; Kirby, S.H.; Nur, A.

    2009-01-01

    We used ultrasonic pulse transmission to measure compressional, P, and shear, S, wave speeds in laboratory-formed polycrystalline ice Ih, si methane hydrate, and sll methane-ethane hydrate. From the wave speed's linear dependence on temperature and pressure and from the sample's calculated density, we derived expressions for bulk, shear, and compressional wave moduli and Poisson's ratio from -20 to 15??C and 22.4 to 32.8 MPa for ice Ih, -20 to 15??C and 30.5 to 97.7 MPa for si methane hydrate, and -20 to 10??C and 30.5 to 91.6 MPa for sll methane-ethane hydrate. All three materials had comparable P and S wave speeds and decreasing shear wave speeds with increasing applied pressure. Each material also showed evidence of rapid intergranular bonding, with a corresponding increase in wave speed, in response to pauses in sample deformation. There were also key differences. Resistance to uniaxial compaction, indicated by the pressure required to compact initially porous samples, was significantly lower for ice Ih than for either hydrate. The ice Ih shear modulus decreased with increasing pressure, in contrast to the increase measured in both hydrates ?? 2009.

  7. Polycrystalline ZnTe thin film on silicon synthesized by pulsed laser deposition and subsequent pulsed laser melting

    NASA Astrophysics Data System (ADS)

    Xu, Menglei; Gao, Kun; Wu, Jiada; Cai, Hua; Yuan, Ye; Prucnal, S.; Hübner, R.; Skorupa, W.; Helm, M.; Zhou, Shengqiang

    2016-03-01

    ZnTe thin films on Si substrates have been prepared by pulsed laser deposition and subsequent pulsed laser melting (PLM) treatment. The crystallization during PLM is confirmed by Raman scattering, x-ray diffraction and room temperature photoluminescence (PL) measurements. The PL results show a broad peak at 574 nm (2.16 eV), which can be assigned to the transitions from the conduction band to the acceptor level located at 0.145 eV above the valence band induced by zinc-vacancy ionization. Our work provides an applicable approach to low temperature preparation of crystalline ZnTe thin films.

  8. Ultralow thermal conductivity in polycrystalline CdSe thin films with controlled grain size.

    PubMed

    Feser, Joseph P; Chan, Emory M; Majumdar, Arun; Segalman, Rachel A; Urban, Jeffrey J

    2013-05-01

    Polycrystallinity leads to increased phonon scattering at grain boundaries and is known to be an effective method to reduce thermal conductivity in thermoelectric materials. However, the fundamental limits of this approach are not fully understood, as it is difficult to form uniform sub-20 nm grain structures. We use colloidal nanocrystals treated with functional inorganic ligands to obtain nanograined films of CdSe with controlled characteristic grain size between 3 and 6 nm. Experimental measurements demonstrate that thermal conductivity in these composites can fall beneath the prediction of the so-called minimum thermal conductivity for disordered crystals. The measurements are consistent, however, with diffuse boundary scattering of acoustic phonons. This apparent paradox can be explained by an overattribution of transport to high-energy phonons in the minimum thermal conductivity model where, in compound semiconductors, optical and zone edge phonons have low group velocity and high scattering rates.

  9. Cu2+1O coated polycrystalline Si nanoparticles as anode for lithium-ion battery.

    PubMed

    Zhang, Junying; Zhang, Chunqian; Wu, Shouming; Liu, Zhi; Zheng, Jun; Zuo, Yuhua; Xue, Chunlai; Li, Chuanbo; Cheng, Buwen

    2016-12-01

    Cu2+1O coated Si nanoparticles were prepared by simple hydrolysis and were investigated as an anode material for lithium-ion battery. The coating of Cu2+1O on the surface of Si particles remarkably improves the cycle performance of the battery than that made by the pristine Si. The battery exhibits an initial reversible capacity of 3063 mAh/g and an initial coulombic efficiency (CE) of 82.9 %. With a current density of 300 mA/g, its reversible capacity can remains 1060 mAh/g after 350 cycles, corresponding to a CE ≥ 99.8 %. It is believed that the Cu2+1O coating enhances the electrical conductivity, and the elasticity of Cu2+1O further helps buffer the volume changes during lithiation/delithiation processes. Experiment results indicate that the electrode maintained a highly integrated structure after 100 cycles and it is in favour of the formation of stable solid electrolyte interface (SEI) on the Si surface to keep the extremely high CE during long charge and discharge cycles.

  10. Structural and Thermoelectric Properties of Polycrystalline p-Type Mg2- x Li x Si

    NASA Astrophysics Data System (ADS)

    Nieroda, P.; Kolezynski, A.; Oszajca, M.; Milczarek, J.; Wojciechowski, K. T.

    2016-07-01

    The aim of this study was to determine the location of Li atoms in Mg2Si structure, and verify the influence of Li dopant on the transport properties of obtained thermoelectric materials. The results of theoretical studies of the electronic band structure (full potential linearized augmented plane wave method) in Li-doped Mg2Si are presented. Theoretical calculations indicate that only in the case when Li is located in the Mg position, the samples will have p-type conduction. To confirm the theoretical predictions, a series of samples with nominal composition Mg2- x Li x Si ( x = 0-0.5) were prepared using the spark plasma sintering (SPS) method. Structural and phase composition analyses were carried out by x-ray and neutron powder diffraction, as well as scanning electron microscopy. Neutron diffraction studies confirmed that the lithium atoms substitute magnesium in the Mg2Si structure. The investigations of the influence of Li dopant on the transport properties, i.e. electrical conductivity, the Seebeck coefficient and the thermal conductivity, were carried out in a temperature range from 340 K to 720 K. Carrier concentration was measured with Hall method. The positive values of the Seebeck coefficient and Hall coefficient indicate that all examined samples show p-type conductivity. On the basis of the experimental data, the temperature dependencies of the thermoelectric figure of merit ZT were calculated.

  11. Cu2+1O coated polycrystalline Si nanoparticles as anode for lithium-ion battery.

    PubMed

    Zhang, Junying; Zhang, Chunqian; Wu, Shouming; Liu, Zhi; Zheng, Jun; Zuo, Yuhua; Xue, Chunlai; Li, Chuanbo; Cheng, Buwen

    2016-12-01

    Cu2+1O coated Si nanoparticles were prepared by simple hydrolysis and were investigated as an anode material for lithium-ion battery. The coating of Cu2+1O on the surface of Si particles remarkably improves the cycle performance of the battery than that made by the pristine Si. The battery exhibits an initial reversible capacity of 3063 mAh/g and an initial coulombic efficiency (CE) of 82.9 %. With a current density of 300 mA/g, its reversible capacity can remains 1060 mAh/g after 350 cycles, corresponding to a CE ≥ 99.8 %. It is believed that the Cu2+1O coating enhances the electrical conductivity, and the elasticity of Cu2+1O further helps buffer the volume changes during lithiation/delithiation processes. Experiment results indicate that the electrode maintained a highly integrated structure after 100 cycles and it is in favour of the formation of stable solid electrolyte interface (SEI) on the Si surface to keep the extremely high CE during long charge and discharge cycles. PMID:27102903

  12. Cu2+1O coated polycrystalline Si nanoparticles as anode for lithium-ion battery

    NASA Astrophysics Data System (ADS)

    Zhang, Junying; Zhang, Chunqian; Wu, Shouming; Liu, Zhi; Zheng, Jun; Zuo, Yuhua; Xue, Chunlai; Li, Chuanbo; Cheng, Buwen

    2016-04-01

    Cu2+1O coated Si nanoparticles were prepared by simple hydrolysis and were investigated as an anode material for lithium-ion battery. The coating of Cu2+1O on the surface of Si particles remarkably improves the cycle performance of the battery than that made by the pristine Si. The battery exhibits an initial reversible capacity of 3063 mAh/g and an initial coulombic efficiency (CE) of 82.9 %. With a current density of 300 mA/g, its reversible capacity can remains 1060 mAh/g after 350 cycles, corresponding to a CE ≥ 99.8 %. It is believed that the Cu2+1O coating enhances the electrical conductivity, and the elasticity of Cu2+1O further helps buffer the volume changes during lithiation/delithiation processes. Experiment results indicate that the electrode maintained a highly integrated structure after 100 cycles and it is in favour of the formation of stable solid electrolyte interface (SEI) on the Si surface to keep the extremely high CE during long charge and discharge cycles.

  13. Role of Polycrystalline Thin-Film PV Technologies in Competitive PV Module Markets: Preprint

    SciTech Connect

    von Roedern, B.; Ullal, H. S.

    2008-05-01

    This paper discusses the developments in thin-film PV technologies and provides an outlook on future commercial module efficiencies achievable based on today's knowledge about champion cell performance.

  14. Phosphorus Doping Using Electron Cyclotron Resonance Plasma for Large-Area Polycrystalline Silicon Thin Film Transistors

    NASA Astrophysics Data System (ADS)

    Kakinuma, Hiroaki; Mohri, Mikio; Tsuruoka, Taiji

    1994-01-01

    We have investigated phosphorus doping using an electron cyclotron resonance (ECR) plasma, for application to the poly-Si driving circuits of liquid crystal displays or image sensors. The PH3/He was ionized and accelerated to poly-Si and c-Si substrates with a self bias of -220 V. The P concentration, as detected by secondary ion mass spectroscopy (SIMS), is ˜5×1021 cm-3 at the surface, which decayed to ˜1017 cm-3 within 50 100 nm depth. The surface is found to be etched during doping. The etching is restored by adding a small amount of SiH4 and the sheet resistance R s decreases. The optimized as-irradiated R s is ˜ 1× 105 Ω/\\Box and 1.7× 102 Ω/\\Box for poly-Si and (110) c-Si, respectively. The dependence of R s on the substrates and the anomalous diffusion constants derived from SIMS are also discussed.

  15. Active pixel imagers incorporating pixel-level amplifiers based on polycrystalline-silicon thin-film transistors.

    PubMed

    El-Mohri, Youcef; Antonuk, Larry E; Koniczek, Martin; Zhao, Qihua; Li, Yixin; Street, Robert A; Lu, Jeng-Ping

    2009-07-01

    Active matrix, flat-panel imagers (AMFPIs) employing a 2D matrix of a-Si addressing TFTs have become ubiquitous in many x-ray imaging applications due to their numerous advantages. However, under conditions of low exposures and/or high spatial resolution, their signal-to-noise performance is constrained by the modest system gain relative to the electronic additive noise. In this article, a strategy for overcoming this limitation through the incorporation of in-pixel amplification circuits, referred to as active pixel (AP) architectures, using polycrystalline-silicon (poly-Si) TFTs is reported. Compared to a-Si, poly-Si offers substantially higher mobilities, enabling higher TFT currents and the possibility of sophisticated AP designs based on both n- and p-channel TFTs. Three prototype indirect detection arrays employing poly-Si TFTs and a continuous a-Si photodiode structure were characterized. The prototypes consist of an array (PSI-1) that employs a pixel architecture with a single TFT, as well as two arrays (PSI-2 and PSI-3) that employ AP architectures based on three and five TFTs, respectively. While PSI-1 serves as a reference with a design similar to that of conventional AMFPI arrays, PSI-2 and PSI-3 incorporate additional in-pixel amplification circuitry. Compared to PSI-1, results of x-ray sensitivity demonstrate signal gains of approximately 10.7 and 20.9 for PSI-2 and PSI-3, respectively. These values are in reasonable agreement with design expectations, demonstrating that poly-Si AP circuits can be tailored to provide a desired level of signal gain. PSI-2 exhibits the same high levels of charge trapping as those observed for PSI-1 and other conventional arrays employing a continuous photodiode structure. For PSI-3, charge trapping was found to be significantly lower and largely independent of the bias voltage applied across the photodiode. MTF results indicate that the use of a continuous photodiode structure in PSI-1, PSI-2, and PSI-3 results in

  16. Active pixel imagers incorporating pixel-level amplifiers based on polycrystalline-silicon thin-film transistors

    SciTech Connect

    El-Mohri, Youcef; Antonuk, Larry E.; Koniczek, Martin; Zhao Qihua; Li Yixin; Street, Robert A.; Lu Jengping

    2009-07-15

    Active matrix, flat-panel imagers (AMFPIs) employing a 2D matrix of a-Si addressing TFTs have become ubiquitous in many x-ray imaging applications due to their numerous advantages. However, under conditions of low exposures and/or high spatial resolution, their signal-to-noise performance is constrained by the modest system gain relative to the electronic additive noise. In this article, a strategy for overcoming this limitation through the incorporation of in-pixel amplification circuits, referred to as active pixel (AP) architectures, using polycrystalline-silicon (poly-Si) TFTs is reported. Compared to a-Si, poly-Si offers substantially higher mobilities, enabling higher TFT currents and the possibility of sophisticated AP designs based on both n- and p-channel TFTs. Three prototype indirect detection arrays employing poly-Si TFTs and a continuous a-Si photodiode structure were characterized. The prototypes consist of an array (PSI-1) that employs a pixel architecture with a single TFT, as well as two arrays (PSI-2 and PSI-3) that employ AP architectures based on three and five TFTs, respectively. While PSI-1 serves as a reference with a design similar to that of conventional AMFPI arrays, PSI-2 and PSI-3 incorporate additional in-pixel amplification circuitry. Compared to PSI-1, results of x-ray sensitivity demonstrate signal gains of {approx}10.7 and 20.9 for PSI-2 and PSI-3, respectively. These values are in reasonable agreement with design expectations, demonstrating that poly-Si AP circuits can be tailored to provide a desired level of signal gain. PSI-2 exhibits the same high levels of charge trapping as those observed for PSI-1 and other conventional arrays employing a continuous photodiode structure. For PSI-3, charge trapping was found to be significantly lower and largely independent of the bias voltage applied across the photodiode. MTF results indicate that the use of a continuous photodiode structure in PSI-1, PSI-2, and PSI-3 results in optical

  17. Active pixel imagers incorporating pixel-level amplifiers based on polycrystalline-silicon thin-film transistors

    PubMed Central

    El-Mohri, Youcef; Antonuk, Larry E.; Koniczek, Martin; Zhao, Qihua; Li, Yixin; Street, Robert A.; Lu, Jeng-Ping

    2009-01-01

    Active matrix, flat-panel imagers (AMFPIs) employing a 2D matrix of a-Si addressing TFTs have become ubiquitous in many x-ray imaging applications due to their numerous advantages. However, under conditions of low exposures and∕or high spatial resolution, their signal-to-noise performance is constrained by the modest system gain relative to the electronic additive noise. In this article, a strategy for overcoming this limitation through the incorporation of in-pixel amplification circuits, referred to as active pixel (AP) architectures, using polycrystalline-silicon (poly-Si) TFTs is reported. Compared to a-Si, poly-Si offers substantially higher mobilities, enabling higher TFT currents and the possibility of sophisticated AP designs based on both n- and p-channel TFTs. Three prototype indirect detection arrays employing poly-Si TFTs and a continuous a-Si photodiode structure were characterized. The prototypes consist of an array (PSI-1) that employs a pixel architecture with a single TFT, as well as two arrays (PSI-2 and PSI-3) that employ AP architectures based on three and five TFTs, respectively. While PSI-1 serves as a reference with a design similar to that of conventional AMFPI arrays, PSI-2 and PSI-3 incorporate additional in-pixel amplification circuitry. Compared to PSI-1, results of x-ray sensitivity demonstrate signal gains of ∼10.7 and 20.9 for PSI-2 and PSI-3, respectively. These values are in reasonable agreement with design expectations, demonstrating that poly-Si AP circuits can be tailored to provide a desired level of signal gain. PSI-2 exhibits the same high levels of charge trapping as those observed for PSI-1 and other conventional arrays employing a continuous photodiode structure. For PSI-3, charge trapping was found to be significantly lower and largely independent of the bias voltage applied across the photodiode. MTF results indicate that the use of a continuous photodiode structure in PSI-1, PSI-2, and PSI-3 results in optical fill

  18. Thermal Characterization of SiC Amorphous Thin Films

    NASA Astrophysics Data System (ADS)

    Jeong, Taehee; Zhu, Jian-Gang; Mao, Sining; Pan, Tao; Tang, Yun Jun

    2012-06-01

    The cross-plane thermal conductivity of SiC amorphous films was measured employing the transient thermoreflectance technique. The SiC films were deposited on silicon substrates by RF magnetron sputtering at room temperature. The thickness of the films was varied in the range from 100 nm to 2500 nm to analyze the size effect. The results found that the thermal conductivity of the SiC thin films is significantly smaller than that of the SiC material in bulk form. The small thermal conductivity stems from the structural disorder of the films, which was confirmed by high-resolution transmission electron microscopy and X-ray diffraction. In addition, the contribution of the thermal boundary resistance to the thermal conductivity of the films is discussed.

  19. Thin film poly-crystalline silicon fabrication based on Rapid Thermal Annealing (RTA) process

    NASA Astrophysics Data System (ADS)

    Qian, Jun; Li, Jirong; Liao, Yang; Shi, Weimin; Kuang, Huahui; Ming, Xiuchun; Liu, Jin; Jin, Jing; Qin, Juan

    2013-12-01

    Rapid Thermal Annealing (RTA) process was introduced to the experiment of Aluminum-induced crystallization of a-Si, based on sputtering method, on low cost glass substrate. A stack of glass/Al (150 nm)/Si (220 nm) was deposited by sputtering sequentially. Samples were annealed under RTA process, then annealed in the tube annealing furnace at 400 °C for 5 h. The grain crystallization was inspected by optical microscopy (OM), ,Raman spectroscopy, X-ray diffraction (XRD),and energy dispersive spectroscopy (EDS). The preferential orientation (111) was observed, with a Raman Peak at 520.8cm-1, Different annealing periods were discussed.

  20. Optical properties of vacuum evaporated Cd xSn 1-xSe polycrystalline thin films: influence of composition and thickness

    NASA Astrophysics Data System (ADS)

    Padiyan, D. Pathinettam; Marikani, A.; Murali, K. R.

    2005-03-01

    Polycrystalline Cd xSn 1-xSe material is synthesized by melt growth technique for various x values and thin films are prepared by vacuum evaporation technique. Optical transmittance measurements have been made on thin films of Cd xSn 1-xSe, with x=0,0.3,0.75 and 1 for various thicknesses. The studies reveal that these thin films have a direct allowed band gap energy and the indirect band gap energy is improbable. The band gap energy increases with decrease in thickness in all the compositions and it is attributed to the quantum size effect.

  1. On the mechanism of carrier transport in metal-thin-oxide semiconductor diodes on polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Kar, S.; Panchal, K. M.; Bhattacharya, S.; Varma, S.

    1982-12-01

    The carrier transport mechanism in MOS tunnel diodes and solar cells fabricated on cast polycrystalline silicon was investigated. The direct current-voltage and 100 kHz small signal capacitance-voltage characteristics of the diodes were measured at various values of device temperature ranging between 300-420 K. Polysilicon diodes which exhibited exponential I-V characteristics were chosen for analysis, and diodes located on large angle grain boundaries and on very small grains were excluded. In addition, several diodes and cells were fabricated on single-crystal silicon by identical processing and were measured and analyzed. Results show that the density and nature of defects present in the surface barrier region of the polysilicon material seem to have a significant influence on the mechanism of carrier transport across the barrier. The dominant transport mechanism becomes multistep tunneling with increase in the number of defects such as dislocations, incoherent twin boundaries, and precipitates, while in MOS tunnel diodes on single-crystal silicon the carrier transport mechanism was an activated process such as thermionic emission or minority-carrier injection. A milder influence was produced by stacking faults and coherent twin boundaries.

  2. Device Physics of Thin-Film Polycrystalline Cells and Modules; Final Subcontract Report; 6 December 1993-15 March 1998

    SciTech Connect

    Sites, J. R.

    1999-05-03

    This report describes work performed under this subcontract by Colorado State University (CSU). The results of the subcontract effort included progress in understanding CdTe and Cu(In1-xGax)Se2-based solar cells, in developing additional measurement and analysis techniques at the module level, and in strengthening collaboration within the thin-film polycrystalline solar-cell community. A major part of the CdTe work consisted of elevated-temperature stress tests to determine fabrication and operation conditions that minimize the possibility of long-term performance changes. Other CdTe studies included analysis of the back-contact junction, complete photon accounting, and the tradeoff with thin CdS between photocurrent gain and voltage loss. The Cu(In1-xGax)Se2 studies included work on the role of sodium in enhancing performance, the conditions under which conduction-band offsets affect cell performance, the transient effects of cycling between light and dark conditions, and detailed analysis of several individual series of cells. One aspect of thin-film module analysis has been addressing the differences in approach needed for relatively large individual cells made without grids. Most work, however, focused on analysis of laser-scanning data, including defect signatures, photocurrent/shunting separation, and the effects of forward bias or high-intensity light. Collaborations with other laboratories continued on an individual basis, and starting in 1994, collaboration was through the national R&D photovoltaic teams. CSU has been heavily involved in the structure and logistics of both the CdTe and CIS teams, as well as making frequent technical contributions in both areas.

  3. Progress Toward a Stabilization and Preconditioning Protocol for Polycrystalline Thin-Film Photovoltaic Modules

    SciTech Connect

    del Cueto, J. A.; Deline, C. A.; Rummel, S. R.; Anderberg, A.

    2010-08-01

    Cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) thin-film photovoltaic (PV) modules can exhibit substantial variation in measured performance depending on prior exposure history. This study examines the metastable performance changes in these PV modules with the goal of establishing standard preconditioning or stabilization exposure procedures to mitigate measured variations prior to current-voltage (IV) measurements.

  4. Growth and characterization of copper indium diselenide polycrystalline thin films for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Engelmann, Michael G.

    The incorporation of sulfur into CuInSe2 thin films was quantitatively investigated to establish a scientific and engineering basis for the fabrication of homogeneous and compositionally graded CuIn(Se,S)2 thin films. The motivation for this work was to develop a means of controlling the band gap for this class of materials to achieve improved performance in photovoltaic devices. The approach taken was the reaction of thin film Cu/In layers and CuInSe2 thin films in H2S and/or H2Se gasses at atmospheric pressure. The reaction of Cu/In layers in a mixture of H2S and H 2Se as a function of gas phase composition was investigated to quantify the relationship between the gas and solid phase compositions in the formation of homogeneous CuIn(Se,S)2 thin films. A reaction model, accounting for mixing and the presence of oxygen, was developed and regressed to the experimental data. This work then led to the development of a phenomenological model for the inhomogeneous incorporation of sulfur into CuInSe2 thin films by a surface reaction followed by diffusion. X-ray diffraction line profiles, grain size distribution, and grain boundary width were used in conjunction with a quantitative diffusion model to estimate the bulk and grain boundary diffusion of sulfur into CuInSe2. Diffusion coefficients were determined at multiple temperatures and activation energies were estimated. The analysis was also applied to the diffusion of CdS into CdTe that occurs during the post deposition thermochemical treatments that are necessary to achieve high performance CdTe solar cells. Bulk and grain boundary diffusion coefficients and activation energies for CdS-CdTe were estimated. Based on the analysis of both equilibrium chemistry and diffusion, a well defined process for the fabrication of homogeneous and graded CuIn(Se,S) 2 thin films was developed. This process provides a method of band gap engineering that has application in both the fabrication of wide band gap devices for use in

  5. Bend stress relaxation and tensile primary creep of a polycrystalline alpha-SiC fiber

    NASA Technical Reports Server (NTRS)

    Hee Man, Yun; Goldsby, Jon C.; Morscher, Gregory N.

    1995-01-01

    Understanding the thermomechanical behavior (creep and stress relaxation) of ceramic fibers is of both practical and basic interest. On the practical level, ceramic fibers are the reinforcement for ceramic matrix composites which are being developed for use in high temperature applications. It is important to understand and model the total creep of fibers at low strain levels where creep is predominantly in the primary stage. In addition, there are many applications where the component will only be subjected to thermal strains. Therefore, the stress relaxation of composite consituents in such circumstances will be an important factor in composite design and performance. The objective of this paper is to compare and analyze bend stress relaxation and tensile creep data for alpha-SiC fibers produced by the Carborundum Co. (Niagara Falls, NY). This fiber is of current technical interest and is similar in composition to bulk alpha-SiC which has been studied under compressive creep conditions. The temperature, time, and stress dependences will be discussed for the stress relaxation and creep results. In addition, some creep and relaxation recovery experiments were performed in order to understand the complete viscoelastic behavior, i.e. both recoverable and nonrecoverable creep components of these materials. The data will be presented in order to model the deformation behavior and compare relaxation and/or creep behavior for relatively low deformation strain conditions of practical concern. Where applicable, the tensile creep results will be compared to bend stress relaxation data.

  6. Tunnel Magnetoresistance and Spin-Transfer-Torque Switching in Polycrystalline Co2FeAl Full-Heusler-Alloy Magnetic Tunnel Junctions on Amorphous Si /SiO2 Substrates

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Sukegawa, Hiroaki; Kasai, Shinya; Inomata, Koichiro; Mitani, Seiji

    2014-08-01

    We study polycrystalline B2-type Co2FeAl (CFA) full-Heusler-alloy-based magnetic tunnel junctions (MTJs) fabricated on a Si /SiO2 amorphous substrate. Polycrystalline CFA films with a (001) orientation, a high B2 ordering, and a flat surface are achieved by using a MgO buffer layer. A tunnel magnetoresistance ratio up to 175% is obtained for a MTJ with a CFA /MgO/CoFe structure on a 7.5-nm-thick MgO buffer. Spin-transfer-torque-induced magnetization switching is achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as a switching layer. By using a thermal activation model, the intrinsic critical current density (Jc0) is determined to be 8.2×106 A /cm2, which is lower than 2.9×107 A /cm2, the value for epitaxial CFA MTJs [Appl. Phys. Lett. 100, 182403 (2012), 10.1063/1.4710521]. We find that the Gilbert damping constant (α) evaluated by using ferromagnetic resonance measurements for the polycrystalline CFA film is approximately 0.015 and is almost independent of the CFA thickness (2-18 nm). The low Jc0 for the polycrystalline MTJ is mainly attributed to the low α of the CFA layer compared with the value in the epitaxial one (approximately 0.04).

  7. Anisotropic and inhomogeneous thermal conduction in suspended thin-film polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Sood, Aditya; Cho, Jungwan; Hobart, Karl D.; Feygelson, Tatyana I.; Pate, Bradford B.; Asheghi, Mehdi; Cahill, David G.; Goodson, Kenneth E.

    2016-05-01

    While there is a great wealth of data for thermal transport in synthetic diamond, there remains much to be learned about the impacts of grain structure and associated defects and impurities within a few microns of the nucleation region in films grown using chemical vapor deposition. Measurements of the inhomogeneous and anisotropic thermal conductivity in films thinner than 10 μm have previously been complicated by the presence of the substrate thermal boundary resistance. Here, we study thermal conduction in suspended films of polycrystalline diamond, with thicknesses ranging between 0.5 and 5.6 μm, using time-domain thermoreflectance. Measurements on both sides of the films facilitate extraction of the thickness-dependent in-plane ( κ r ) and through-plane ( κ z ) thermal conductivities in the vicinity of the coalescence and high-quality regions. The columnar grain structure makes the conductivity highly anisotropic, with κ z being nearly three to five times as large as κ r , a contrast higher than that reported previously for thicker films. In the vicinity of the high-quality region, κ r and κ z range from 77 ± 10 W/m-K and 210 ± 50 W/m-K for the 1 μm thick film to 130 ± 20 W/m-K and 710 ± 120 W/m-K for the 5.6 μm thick film, respectively. The data are interpreted using a model relating the anisotropy to the scattering on the boundaries of columnar grains and the evolution of the grain size considering their nucleation density and spatial rate of growth. This study aids in the reduction in the near-interfacial resistance of diamond films and efforts to fabricate diamond composites with silicon and GaN for power electronics.

  8. Hot Extruded Polycrystalline Mg2Si with Embedded XS2 Nano-particles (X: Mo, W)

    NASA Astrophysics Data System (ADS)

    Bercegol, A.; Christophe, V.; Keshavarz, M. K.; Vasilevskiy, D.; Turenne, S.; Masut, R. A.

    2016-08-01

    Due to their abundant, inexpensive and non-toxic constituent elements, magnesium silicide and related alloys are attractive for large-scale thermoelectric (TE) applications in the 500-800 K temperature range, in particular for energy conversion. In this work, we propose a hot extrusion method favorable for large-scale production, where the starting materials (Mg2Si and XS2, X: W, Mo) are milled together in a sealed vial. The MoS2 nano-particles (0.5-2 at.%) act as solid lubricant during the extrusion process, thus facilitating material densification, as confirmed by density measurements based on Archimedes' method. Scanning electron microscopy images of bulk extruded specimens show a wide distribution of grain size, covering the range from 0.1 μm to 10 μm, and energy dispersive spectroscopy shows oxygen preferentially distributed at the grain boundaries. X-ray diffraction analysis shows that the major phase is the expected cubic structure of Mg2Si. The TE properties of these extruded alloys have been measured by the Harman method between 300 K and 700 K. Resistivity values at 700 K vary between 370 μΩ m and 530 μΩ m. The ZT value reaches a maximum of 0.26 for a sample with 2 at.% MoS2. Heat conductivity is reduced for extruded samples containing MoS2, which most likely behave as scattering centers for phonons. The reason why the WS2 particles do not bring any enhancement, for either densification or heat transfer reduction, might be linked to their tendency to agglomerate. These results open the way for further investigation to optimize the processing parameters for this family of TE alloys.

  9. In-plane texturing control of Y-Ba-Cu-O thin films on polycrystalline substrates by ion-beam-modified intermediate buffer layers

    NASA Astrophysics Data System (ADS)

    Iijima, Y.; Onabe, K.; Futaki, N.; Tanabe, N.; Sadakata, N.; Kohno, O.; Ikeno, Y.

    1993-03-01

    Biaxially aligned YBCO thin films were successfully formed on polycrystalline Ni-based alloy by using ion-beam-modified yttria-stabilized-zirconia (YSZ) intermediate layers. YSZ layers were deposited by ion-beam-assisted deposition (IBAD) with concurrent off-axis ion beam bombardment. The YSZ 100-line axis was oriented normal to the substrate, and a YSZ 111-line axis was aligned to the bombarding ion beam axis. Explicit in-plane ordering was achieved on polycrystalline metallic substrates without epitaxial relationships. C-axis-oriented YBCO thin films were grown on those buffer layers, with controlled in-plane a- and b-axes, by pulsed laser deposition. At 77 K, 0 T and at 77 K, 0.6 T, 4.3 x 10 exp 5 A/sq cm and 1.1 x 10 exp 5 A/sq cm were achieved, respectively.

  10. Transport Properties of Anatase-TiO2 Polycrystalline-Thin-Film Field-Effect Transistors with Electrolyte Gate Layers

    NASA Astrophysics Data System (ADS)

    Horita, Ryohei; Ohtani, Kyosuke; Kai, Takahiro; Murao, Yusuke; Nishida, Hiroya; Toya, Taku; Seo, Kentaro; Sakai, Mio; Okuda, Tetsuji

    2013-11-01

    We have fabricated anatase-TiO2 polycrystalline-thin-film field-effect transistors (FETs) with poly(vinyl alcohol) (PVA), ion-liquid (IL), and ion-gel (IG) gate layers, and have tried to improve the response to gate voltage by varying the concentration of mobile ions in these electrolyte gate layers. The increase in the concentration of mobile ions by doping NaOH into the PVA gate layer or reducing the gelator in the IG gate layer markedly increases the drain-source current and reduces the driving gate voltage, which show that the mobile ions in the PVA, IL, and IG gate layers cause the formation of electric double layers (EDLs), which act as nanogap capacitors. In these TiO2-EDL-FETs, the slow formation of EDLs and the oxidation reaction at the interface between the surface of the TiO2 film and the electrolytes cause unideal FET properties. In the optimized IL and IG TiO2-EDL-FETs, the driving gate voltage is less than 1 V and the ON/OFF ratios of the transfer characteristics are about 1×104 at RT, and the nearly metallic state is realized at the interface purely by applying a gate voltage.

  11. A study on the optical and microstructural characteristics of quaternary Cu(In,Ga)Se2 polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Albin, D. S.; Tuttle, J. R.; Mooney, G. D.; Carapella, J. J.; Duda, A.

    The optical and microstructural properties of polycrystalline CuIn(1-y)Ga(y)Se2 (CIGS) thin films deposited by coevaporation are reported within the boundaries of an orthogonal experimental design investigating the effects of Cu flux, Ga/(Ga+In) composition, Se rate, substrate temperature, Ts, and substrate type. The optical bandgaps for near-stoichiometric CuIn(1-y)Ga(y)Se2 are smaller and exhibit bowing behavior which follows the relationship Eg = 1.011 + 0.664y + 0.249y(y-1). In comparison, Cu-poor films exhibit a linear variation with zero bowing given by Eg = 1.0032 + 0.71369y. The increase in Eg with decreasing Cu may result in part from lattice shrinkage as measured by X-ray diffraction (XRD). Optical absorption below the band edge appears to be dependent upon both Cu and Ga content. Absorption coefficients of alpha = 1000/cm or greater within this region are indicative of Cu-rich films. Absorption of 1000/cm or less may be dictated more by surface morphology and possible phase separation in films containing = 50 percent or more Ga. The magnitude of alpha varies from 20,000 near the band edge up to 100,000/cm at 1 eV above the edge for near-stoichiometric films, with the absorption in Cu-poor films being slightly less.

  12. Tunable thermal conductivity of thin films of polycrystalline AlN by structural inhomogeneity and interfacial oxidation.

    PubMed

    Jaramillo-Fernandez, J; Ordonez-Miranda, J; Ollier, E; Volz, S

    2015-03-28

    The effect of the structural inhomogeneity and oxygen defects on the thermal conductivity of polycrystalline aluminum nitride (AlN) thin films deposited on single-crystal silicon substrates is experimentally and theoretically investigated. The influence of the evolution of crystal structure, grain size, and out-of plane disorientation along the cross plane of the films on their thermal conductivity is analyzed. The impact of oxygen-related defects on thermal conduction is studied in AlN/AlN multilayered samples. Microstructure, texture, and grain size of the films were characterized by X-ray diffraction and scanning and transmission electron microscopy. The measured thermal conductivity obtained with the 3-omega technique for a single and multiple layers of AlN is in fairly good agreement with the theoretical predictions of our model, which is developed by considering a serial assembly of grain distributions. An effective thermal conductivity of 5.92 W m(-1) K(-1) is measured for a 1107.5 nm-thick multilayer structure, which represents a reduction of 20% of the thermal conductivity of an AlN monolayer with approximately the same thickness, due to oxygen impurities at the interface of AlN layers. Our results show that the reduction of the thermal conductivity as the film thickness is scaled down, is strongly determined by the structural inhomogeneities inside the sputtered films. The origin of this non-homogeneity and the effect on phonon scattering are also discussed.

  13. Structural and optical analyses of polycrystalline Zn1-xSbxSe thin films prepared by resistive heating technique

    NASA Astrophysics Data System (ADS)

    Rashid, R.; Mahmood, Arshad; Aziz, U.; Shah, A.; Ali, Zahid; Raza, Q.; Malik, Abdul; Rasheed, Muhammad Asim

    2016-01-01

    Here we report the influence of Sb doping on the structural and optical properties of Zn1-xSbxSe (0 ⩽ x ⩾ 0.15) thin films prepared by thermal evaporation technique on glass substrate. Various characterization techniques such as X-ray diffraction (XRD), EDS, Raman spectroscopy and spectroscopic ellipsometer are employed to assess the structural and optical properties of the deposited films. XRD analysis reveals the formation of polycrystalline cubic structure having preferred growth orientation along (1 1 1) plane without any evidence of secondary phases. Crystallographic parameters like grain size, micro strain, dislocation density, number of crystallites per unit area and texture coefficient point out the structural modification in ZnSe films with Sb inclusion. Raman analysis shows the existence of three 1LO, 2LO and 3LO phonon modes at 251, 511 and 745 cm-1 in pure ZnSe while 3LO mode disappears by the incorporation of Sb atoms in ZnSe matrix. Increase in FWHM of Raman peaks with Sb concentration also indicates the change in crystalline quality of ZnSe films which is in accordance with our XRD results. Spectroscopic ellipsometry results demonstrate a decreasing trend for the optical band gap energy (from 2.61 eV to 1.81 eV) with increasing Sb content.

  14. Structural and optical properties of (Ag,Cu)(In,Ga)Se{sub 2} polycrystalline thin film alloys

    SciTech Connect

    Boyle, J. H.; Shafarman, W. N.; Birkmire, R. W.; McCandless, B. E.

    2014-06-14

    The structural and optical properties of pentenary alloy (Ag,Cu)(In,Ga)Se{sub 2} polycrystalline thin films were characterized over the entire compositional range at a fixed (Cu + Ag)/(In + Ga) ratio. Films deposited at 550 °C on bare and molybdenum coated soda-lime glass by elemental co-evaporation in a single-stage process with constant incident fluxes exhibit single phase chalcopyrite structure, corresponding to 122 spacegroup (I-42d) over the entire compositional space. Unit cell refinement of the diffraction patterns show that increasing Ag substitution for Cu, the refined a{sub o} lattice constant, (Ag,Cu)-Se bond length, and anion displacement increase in accordance with the theoretical model proposed by Jaffe, Wei, and Zunger. However, the refined c{sub o} lattice constant and (In,Ga)-Se bond length deviated from theoretical expectations for films with mid-range Ag and Ga compositions and are attributed to influences from crystallographic bond chain ordering or cation electronegativity. The optical band gap, derived from transmission and reflection measurements, widened with increasing Ag and Ga content, due to influences from anion displacement and cation electronegativity, as expected from theoretical considerations for pseudo-binary chalcopyrite compounds.

  15. Metal-organic chemical vapour deposition of polycrystalline tetragonal indium sulphide (InS) thin films

    NASA Technical Reports Server (NTRS)

    Macinnes, Andrew N.; Cleaver, William M.; Barron, Andrew R.; Power, Michael B.; Hepp, Aloysius F.

    1992-01-01

    The dimeric indium thiolate /(t Bu)2In(mu-S sup t Bu)/2 has been used as a single-source precursor for the MOCVD of InS thin films. The dimeric In2S2 core is proposed to account for the formation of the nonequilibrium high-pressure tetragonal phase in the deposited films. Analysis of the deposited films has been obtained by TEM, with associated energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy.

  16. Development of tandem cells consisting of GaAs single crystal and CuInSe2/CdZnS polycrystalline thin films

    NASA Technical Reports Server (NTRS)

    Kim, Namsoo P.; Stanbery, Billy J.; Gale, Ronald P.; Mcclelland, Robert W.

    1989-01-01

    The tandem cells consisting of GaAs single crystal and CuInSe2 polycrystalline thin films are being developed under the joint program of the Boeing Co. and Kopin Corp. to meet the increasing power needs for future spacecraft. The updated status of this program is presented along with experimental results such as cell performance, and radiation resistance. Other cell characteristics including the specific power of and the interconnect options for this tandem cell approach are also discussed.

  17. A novel light trapping concept for liquid phase crystallized poly-Si thin-film solar cells on periodically nanoimprinted glass substrates

    NASA Astrophysics Data System (ADS)

    Preidel, V.; Amkreutz, D.; Sontheimer, T.; Back, F.; Rudigier-Voigt, E.; Rech, B.; Becker, C.

    2013-09-01

    Large grained polycrystalline silicon (poly-Si) absorbers were realized by electron beam induced liquid phase crystallization on 2 μm periodically patterned glass substrates and processed into a-Si:H/poly-Si heterojunction thin-film solar cells. The substrates were structured by nanoimprint lithography using a UV curable hybrid polymer sol-gel resist, resulting in a glassy high-temperature stable micro-structured surface. Structural analysis yielded high quality poly-Si material with grain sizes up to several hundred micrometers. An increase of absorption and an enhancement of the external quantum efficiency in the NIR as a consequence of light trapping due to the micro-structured poly-Si/substrate interface were observed. Up to now, only moderate solar cell parameters, a maximum open-circuit voltage of 413 mV and a short-circuit current density of 8 mA cm-2, were measured being significantly lower to what can be achieved with liquid phase crystallized poly-Si thin-film solar cells on planar glass substrates indicating that the substrate texture has impact on the electrical material quality. By reduction of the SiC interlayer thickness at the micro-structured poly- Si/substrate interface defect-related parasitic absorption was considerably minimized. This encourages the implementation of nanoimprinted tailored substrate textures for light trapping in liquid phase crystallized poly-Si thinfilm solar cells.

  18. Tutorial: Understanding residual stress in polycrystalline thin films through real-time measurements and physical models

    NASA Astrophysics Data System (ADS)

    Chason, Eric; Guduru, Pradeep R.

    2016-05-01

    Residual stress is a long-standing issue in thin film growth. Better understanding and control of film stress would lead to enhanced performance and reduced failures. In this work, we review how thin film stress is measured and interpreted. The results are used to describe a comprehensive picture that is emerging of what controls stress evolution. Examples from multiple studies are discussed to illustrate how the stress depends on key parameters (e.g., growth rate, material type, temperature, grain size, morphology, etc.). The corresponding stress-generating mechanisms that have been proposed to explain the data are also described. To develop a fuller understanding, we consider the kinetic factors that determine how much each of these processes contributes to the overall stress under different conditions. This leads to a kinetic model that can predict the dependence of the stress on multiple parameters. The model results are compared with the experiments to show how this approach can explain many features of stress evolution.

  19. High-speed and high-efficiency Si optical modulator with MOS junction, using solid-phase crystallization of polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Fujikata, Junichi; Takahashi, Masashi; Takahashi, Shigeki; Horikawa, Tsuyoshi; Nakamura, Takahiro

    2016-04-01

    We developed a high-speed and high-efficiency MOS-capacitor-type Si optical modulator (Si-MOD) by applying a low optical loss and a low resistivity of a polycrystalline silicon (poly-Si) gate with large grains. To achieve a low resistivity of a poly-Si film, a P-doped poly-Si film based on Si2H6 solid-phase crystallization (SPC) was developed, which showed a comparable resistivity to that of P-doped single-crystal Si. In addition, high-temperature annealing (HTA) after SPC was effective for realizing low optical loss. We designed the optimum Si-MOD structure and demonstrated a very high modulation efficiency of 0.3 V cm, which is very efficient among the Si-MODs developed thus far. High-speed (15 Gbps) operation was achieved with a small footprint of the 200-µm-long phase shifter and a low drive voltage of 1.5 Vpp at a low optical insertion loss of -2.2 dB and 1.55 µm wavelength.

  20. Thermally Stimulated Luminescence of hbox {Y}2{Si}{O}5{:} {Ce}^{3+} Commercial Phosphor Powder and Thin Films

    NASA Astrophysics Data System (ADS)

    Debelo, N. G.; Dejene, F. B.; Roro, Kittessa

    2016-07-01

    We report on the thermoluminescence (TL) properties of hbox {Y}2{Si}{O}5{:} {Ce}^{3+} phosphor powder and thin films. For the phosphor powder, the TL intensity increases with an increase in UV dose for up to 20 min and then decreases. The TL intensity peak shifts slightly to higher-temperature region at relatively high heating rates, but with reduced peak intensity. Important TL kinetic parameters, such as the activation energy ( E) and the frequency factor ( s), were calculated from the glow curves using a variable heating rate method, and it was found that the glow peaks obey first-order kinetics. For the films, broad TL emissions over a wide temperature range with reduced intensity relative to that of the powder were observed. The maxima of the TL glow peaks of the films deposited in oxygen ambient and vacuum shift toward higher temperature relative to the TL peak position of the film deposited in an argon environment. Vacuum environment resulted in the formation of a deep trap relative to oxygen and argon environments. Furthermore, the structure of hbox {Y}2{Si}{O}5{:} {Ce}^{3+} phosphor powder transformed from {x}2-monoclinic polycrystalline phase to {x}1-monoclinic polycrystalline phase, for deposition at low substrate temperature.

  1. Elasticity of Polycrystalline Pyrope (Mg3Al2Si3O12) to 9 GPa and 1000°C

    SciTech Connect

    Gwanmesia,G.; Zhang, J.; Darling, K.; Kung, J.; Li, B.; Wang, L.; Neuville, D.; Liebermann, R.

    2006-01-01

    Acoustic wave velocities for synthetic polycrystalline pyrope (Mg3Al2Si3O12) were measured to 9 GPa and temperatures up to 1000 C by ultrasonic interferometry combined with energy-dispersive synchrotron X-ray diffraction in a cubic-anvil DIA-type apparatus (SAM-85). Specimen lengths at high pressures (P) and temperatures (T) are directly measured by X-radiographic methods. Elastic wave travel times and X-ray diffraction data were collected after heating and cooling at high pressures to minimize effect of non-hydrostatic stress on the measurements. A linear fit to the high P and T data set yields the elastic bulk and shear moduli [KS = 175 (2) GPa; G = 91 (1) GPa] and their pressure and temperature derivatives [K'S=3.9{+-}0.3; G' = 1.7 {+-} 0.2 and ({partial_derivative}KS/{partial_derivative}T)P = -18 (2) MPa/K; ({partial_derivative}G/{partial_derivative}T)P = -10 (1) MPa/K]. In a separate analysis, the pressure-volume-temperature data collected during these acoustic experiments were fit to a high temperature Birch-Murnaghan (HTBM) equation [with K' fixed at 3.9] and to each isothermal P-V-T data yielding ({partial_derivative}KT/{partial_derivative}T)P = -22 (2) MPa/K and ({partial_derivative}KT/{partial_derivative}T)P = -20 (5) MPa/K, respectively. Comparison of Py100 data with those other Py-Mj compositions indicates that the thermo elastic properties are insensitive to majorite content in the garnet along the pyrope-majorite join.

  2. Elasticity of Polycrystalline Pyrope (Mg3Al2Si3O12) to 9 GPa and 1000 degrees C

    SciTech Connect

    Gwanmesia,G.; Zhang, J.; Darling, K.; Kung, J.; Li, B.; Wang, L.; Neuville, D.; Liebermann, R.

    2006-01-01

    Acoustic wave velocities for synthetic polycrystalline pyrope (Mg{sub 3}Al{sub 2}Si{sub 3}O{sub 12}) were measured to 9 GPa and temperatures up to 1000 degrees C by ultrasonic interferometry combined with energy-dispersive synchrotron X-ray diffraction in a cubic-anvil DIA-type apparatus (SAM-85). Specimen lengths at high pressures (P) and temperatures (T) are directly measured by X-radiographic methods. Elastic wave travel times and X-ray diffraction data were collected after heating and cooling at high pressures to minimize effect of non-hydrostatic stress on the measurements. A linear fit to the high P and T data set yields the elastic bulk and shear moduli [K{sub S} = 175 (2) GPa; G = 91 (1) GPa] and their pressure and temperature derivatives [K{prime}{sub S}=3.9{+-}0.3; G{prime} = 1.7 {+-} 0.2 and ({partial_derivative}K{sub S}/{partial_derivative}T){sub P} = -18 (2) MPa/K; ({partial_derivative}G/{partial_derivative}T){sub P} = -10 (1) MPa/K]. In a separate analysis, the pressure-volume-temperature data collected during these acoustic experiments were fit to a high temperature Birch-Murnaghan (HTBM) equation [with K{prime} fixed at 3.9] and to each isothermal P-V-T data yielding ({partial_derivative}K{sub T}/{partial_derivative}T){sub P} = -22 (2) MPa/K and ({partial_derivative}K{sub T}/{partial_derivative}T){sub P} = -20 (5) MPa/K, respectively. Comparison of Py{sub 100} data with those other Py-Mj compositions indicates that the thermo elastic properties are insensitive to majorite content in the garnet along the pyrope-majorite join.

  3. Metastability of copper indium gallium diselenide polycrystalline thin film solar cell devices

    NASA Astrophysics Data System (ADS)

    Lee, Jinwoo

    High efficiency thin film solar cells have the potential for being a world energy solution because of their cost-effectiveness. Looking to the future of solar energy, there is the opportunity and challenge for thin film solar cells. The main theme of this research is to develop a detailed understanding of electronically active defect states and their role in limiting device performance in copper indium gallium diselenide (CIGS) solar cells. Metastability in the CIGS is a good tool to manipulate electronic defect density and thus identify its effect on the device performance. Especially, this approach keeps many device parameters constant, including the chemical composition, grain size, and interface layers. Understanding metastability is likely to lead to the improvement of CIGS solar cells. We observed systematic changes in CIGS device properties as a result of the metastable changes, such as increases in sub-bandgap defect densities and decreases in hole carrier mobilities. Metastable changes were characterized using high frequency admittance spectroscopy, drive-level capacitance profiling (DLCP), and current-voltage measurements. We found two distinctive capacitance steps in the high frequency admittance spectra that correspond to (1) the thermal activation of hole carriers into/out of acceptor defect and (2) a temperature-independent dielectric relaxation freeze-out process and an equivalent circuit analysis was employed to deduce the dielectric relaxation time. Finally, hole carrier mobility was deduced once hole carrier density was determined by DLCP method. We found that metastable defect creation in CIGS films can be made either by light-soaking or with forward bias current injection. The deep acceptor density and the hole carrier density were observed to increase in a 1:1 ratio, which seems to be consistent with the theoretical model of VCu-V Se defect complex suggested by Lany and Zunger. Metastable defect creation kinetics follows a sub-linear power law

  4. In-situ investigation of thermal instabilities and solid state dewetting in polycrystalline platinum thin films via confocal laser microscopy

    SciTech Connect

    Jahangir, S.; Cheng, Xuan; Huang, H. H.; Nagarajan, V.; Ihlefeld, J.

    2014-10-28

    Solid state dewetting and the subsequent morphological changes for platinum thin films grown on zinc oxide (ZnO) buffered (001) silicon substrates (Pt/ZnO/SiO{sub 2}/(001)Si system) is investigated under vacuum conditions via a custom-designed confocal laser microscope coupled with a laser heating system. Live imaging of thin film dewetting under a range of heating and quenching vacuum ambients reveals events including hillock formation, hole formation, and hole growth that lead to formation of a network of Pt ligaments, break up of Pt ligaments to individual islands and subsequent Pt islands shape reformation, in chronological fashion. These findings are corroborated by ex-situ materials characterization and quantitative electron microscopy analysis. A secondary hole formation via blistering before film rupture is revealed to be the critical stage, after which a rapid dewetting catastrophe occurs. This process is instantaneous and cannot be captured by ex-situ methods. Finally, an intermetallic phase forms at 900 °C and alters the morphology of Pt islands, suggesting a practical limit to the thermal environments that may be used for these platinized silicon wafers in vacuum conditions.

  5. Effect of deposition temperature on electron-beam evaporated polycrystalline silicon thin-film and crystallized by diode laser

    SciTech Connect

    Yun, J. Varalmov, S.; Huang, J.; Green, M. A.; Kim, K.

    2014-06-16

    The effects of the deposition temperature on the microstructure, crystallographic orientation, and electrical properties of a 10-μm thick evaporated Si thin-film deposited on glass and crystallized using a diode laser, are investigated. The crystallization of the Si thin-film is initiated at a deposition temperature between 450 and 550 °C, and the predominant (110) orientation in the normal direction is found. Pole figure maps confirm that all films have a fiber texture and that it becomes stronger with increasing deposition temperature. Diode laser crystallization is performed, resulting in the formation of lateral grains along the laser scan direction. The laser power required to form lateral grains is higher in case of films deposited below 450 °C for all scan speeds. Pole figure maps show 75% occupancies of the (110) orientation in the normal direction when the laser crystallized film is deposited above 550 °C. A higher density of grain boundaries is obtained when the laser crystallized film is deposited below 450 °C, which limits the solar cell performance by n = 2 recombination, and a performance degradation is expected due to severe shunting.

  6. Elastic properties determination of CuInSe2 polycrystalline thin films via a dynamic method

    NASA Astrophysics Data System (ADS)

    Hadjoub, Z.; Merdes, S.; Hadjoub, I.; Doghmane, A.

    2010-11-01

    Developing and using a simulation program based on the spectrum angular model, we first determine reflectance functions and acoustic signatures for bulk as well as for different thickness of CuInSe2 films. For bulk material, it is found that the longitudinal and Rayleigh modes are excited at incidence angles of 23.4° and 47°, respectively. This result reveals the great difficulties to characterize CuInSe2 with a conventional scanning acoustic microscope that uses a lens half- opening angle of 50° and water as a coupling liquid. Hence, Freon is used as alternative coupling liquid. Consequently, the effect of thickness on reflection coefficient and acoustic signature variations are quantified for both bulk and thin material. It is shown that as the thickness increases: (i) the critical angle of mode excitation increases, (ii) the periods of acoustic signature curves decrease and (iii) the Rayleigh velocity, VR, mode shifts towards lower values. Hence, a velocity dispersion curve is established in terms of VR as a function of film thickness; it decreases initially from the velocity value of the glass substrate then saturates when it reaches that of CuInSe2. The importance of such curve lies in the possibility of velocity determination by just knowing the thickness, and vice versa. Moreover, elastic constants are straight forward deduced from such a velocity.

  7. Effect of depth of traps in ZnO polycrystalline thin films on ZnO-TFTs performance

    NASA Astrophysics Data System (ADS)

    Medina-Montes, Maria I.; Baldenegro-Perez, Leonardo A.; Sanchez-Zeferino, Raul; Rojas-Blanco, Lizeth; Becerril-Silva, Marcelino; Quevedo-Lopez, Manuel A.; Ramirez-Bon, Rafael

    2016-09-01

    ZnO thin films were processed by radio frequency magnetron sputtering at room temperature on p-Si/SiO2 substrates under pure argon (Ar:O2 = 100:0 vol.%) and argon-oxygen mixture (Ar:O2 = 99:1 vol.%) gas environment. Morphological, optical and electrical characteristics of the ZnO films are reported, and they show a clear relationship with the gas mixture employed for the sputtering process. Scanning Electron Microscopy revealed the formation of grains of 15.3 and 19.9 nm average sizes and thicknesses of 59 nm and 82 nm for films growth in pure argon and argon-oxygen, respectively. Photoluminescence measurements at room temperature showed the violet emission band (centered at 3 eV) which was only detected in the ZnO film grown under pure argon. From thermally stimulated conductivity measurements two traps with 0.27 and 0.14 eV activation energies were identified for films grown in pure argon and argon-oxygen mixture, respectively. The trap at 0.27 eV is associated with a level located below the conduction band edge and it is supported by the PL band centered at 3 eV. Both types of ZnO films were used as the active channel layer in thin film transistors with thermal SiO2 as gate dielectric. Field effect mobility, threshold voltage and current ratio were improved in the devices with ZnO channel deposited with the argon-oxygen mixture (99% Ar/1% O2 vol.). Threshold voltage decreased from 25 V to 15 V, field effect mobility and current ratio increased from 0.8 to 2.4 cm2/Vs and from 102 to 106, in that order.

  8. Role of surface-reaction layer in HBr/fluorocarbon-based plasma with nitrogen addition formed by high-aspect-ratio etching of polycrystalline silicon and SiO2 stacks

    NASA Astrophysics Data System (ADS)

    Iwase, Taku; Matsui, Miyako; Yokogawa, Kenetsu; Arase, Takao; Mori, Masahito

    2016-06-01

    The etching of polycrystalline silicon (poly-Si)/SiO2 stacks by using VHF plasma was studied for three-dimensional NAND fabrication. One critical goal is achieving both a vertical profile and high throughput for multiple-stack etching. While the conventional process consists of multiple steps for each stacked layer, in this study, HBr/fluorocarbon-based gas chemistry was investigated to achieve a single-step etching process to reduce process time. By analyzing the dependence on wafer temperature, we improved both the etching profile and rate at a low temperature. The etching mechanism is examined considering the composition of the surface reaction layer. X-ray photoelectron spectroscopy (XPS) analysis revealed that the adsorption of N–H and Br was enhanced at a low temperature, resulting in a reduced carbon-based-polymer thickness and enhanced Si etching. Finally, a vertical profile was obtained as a result of the formation of a thin and reactive surface-reaction layer at a low wafer temperature.

  9. Determination of tunnelling parameters in ultra-thin oxide layer poly-Si/SiO 2/Si structures

    NASA Astrophysics Data System (ADS)

    Depas, M.; Vermeire, B.; Mertens, P. W.; Van Meirhaeghe, R. L.; Heyns, M. M.

    1995-08-01

    In this work the electron tunnelling in device grade ultra-thin 3-6 nm n +poly-Si/SiO 2/n-Si structures has been analysed. The well known analytic expression for the Fowler-Nordheim tunnelling current was adapted to include the case of direct tunnelling of electrons, which becomes important for oxide layers thinner than 4.5 nm. For these ultra-thin oxide MOS structures it is necessary to take the band bending in the Si substrate and in the poly-Si layer into account to determine the oxide electrical field strength and to derive the tunnelling parameters of the measured current-voltage characteristic. A method is explained to derive the tunnel barrier height φs and the effective mass of the tunnelling electron mox from the experimental tunnel current characteristics. It is shown that both the direct tunnelling and the Fowler-Nordheim tunnelling current can be quantitatively explained by a WKB approximation using mox as the single fitting parameter.

  10. Phase-separated Al-Si thin films

    SciTech Connect

    Fukutani, Kazuhiko; Tanji, Koichi; Saito, Tatsuya; Den, Tohru

    2005-08-01

    Phase-separated Al-Si films composed of Al nanocylinders embedded in an amorphous-Si matrix have been prepared by a sputtering method. By controlling the deposition rate, substrate temperature, and film composition, the average diameter of the Al cylinders can be varied systematically from less than 5 to 13 nm with a cylinder density ranging from 10{sup 15} to in excess of 10{sup 16} cylinders m{sup -2}. A three-dimensional simulation of phase separation in binary thin films was performed using a modified Cahn-Hilliard [J. Chem. Phys. 28, 258 (1958)] equation to understand the growth mechanism. The simulation studies indicate that the surface diffusion length and film composition are important factors which determine film morphology. Experimental and simulation studies are compared and discussed.

  11. Polycrystalline thin film cadmium telluride solar cells fabricated by electrodeposition. Annual technical report, 20 March 1995--19 March 1996

    SciTech Connect

    Trefny, J U; Mao, D

    1997-04-01

    The objective of this project is to develop improved processes for fabricating CdTe/CdS polycrystalline thin-film solar cells. Researchers used electrodeposition to form CdTe; electrodeposition is a non-vacuum, low-cost technique that is attractive for economic, large-scale production. During the past year, research and development efforts focused on several steps that are most critical to the fabricating high-efficiency CdTe solar cells. These include the optimization of the CdTe electrodeposition process, the effect of pretreatment of CdS substrates, the post-deposition annealing of CdTe, and back-contact formation using Cu-doped ZnTe. Systematic investigations of these processing steps have led to a better understanding and improved performance of the CdTe-based cells. Researchers studied the structural properties of chemical-bath-deposited CdS thin films and their growth mechanisms by investigating CdS samples prepared at different deposition times; investigated the effect of CdCl{sub 2} treatment of CdS films on the photovoltaic performance of CdTe solar cells; studied Cu-doped ZnTe as a promising material for forming stable, low-resistance contacts to the p-type CdTe; and investigated the effect of CdTe and CdS thickness on the photovoltaic performance of the resulting cells. As a result of their systematic investigation and optimization of the processing conditions, researchers improved the efficiency of CdTe/CdS cells using ZnTe back-contact and electrodeposited CdTe. The best CdTe/CdS cell exhibited a V{sub oc} of 0.778 V, a J{sub sc} of 22.4 mA/cm{sup 2}, a FF of 74%, and an efficiency of 12.9% (verified at NREL). In terms of individual parameters, researchers obtained a V{sub oc} over 0.8 V and a FF of 76% on other cells.

  12. Auger electron spectroscopy of super-doped Si:Mn thin films

    NASA Astrophysics Data System (ADS)

    Abe, S.; Nakasima, Y.; Okubo, S.; Nakayama, H.; Nishino, T.; Yanagi, H.; Ohta, H.; Iida, S.

    1999-04-01

    Thin films of Si heavily doped with Mn impurities at nonequilibrium doping levels have been successfully prepared by Laser-Ablation MBE. The electronic structure of Mn-doped Si thin films have been investigated by Auger Valence Electron Spectroscopy (AVES). The peak positions of Mn[3p,V,V] (V=3d) Auger spectra of Si:Mn thin films were located at the higher energy region than those of pure Mn and Mn 5Si 3 compound. For the Si:Mn thin film grown on SiO 2/Si(001) substrate, the new Auger peak was observed around 50 eV. The changes of the line shape were observed in Mn[L,M,M] (L=2s,2p; M=3s,3p,3d) Auger spectra of Si:Mn thin films compared with those of pure Mn and Mn 5Si 3 compounds. In the Mn[2s,M,V] (M=3s,3p,V=3d) spectra for Si:Mn thin films, the new peaks were appeared around 700 eV. These new peaks were considered to arise from the new split of the 3d electron states due to the formation of the Mn-Si bonds in Si:Mn thin films.

  13. Effects of postanneal conditions on the dielectric properties of CaCu3Ti4O12 thin films prepared on Pt/Ti/SiO2/Si substrates

    NASA Astrophysics Data System (ADS)

    Fang, Liang; Shen, Mingrong; Cao, Wenwu

    2004-06-01

    High-dielectric-constant CaCu3Ti4O12 (CCTO) thin films were prepared on Pt/Ti/SiO2/Si(100) substrates by pulsed-laser deposition (PLD). The 480 nm thick polycrystalline films have preferred orientation and show obvious crystallization on the surface. The temperature dependence of dielectric constant and loss of the Pt/CCTO/Pt capacitors is comparable with that obtained in the epitaxial CCTO films grown on oxides substrates. We found that the dielectric properties are very sensitive to the postannealing atmosphere and temperature. Postannealing in nitrogen atmosphere produces larger low-frequency dielectric relaxation as the annealing temperature increases, while annealing in oxygen atmosphere at high temperature suppresses the relaxation and decreases the dielectric constant of the thin films. Such results are attributed to the presence of insulating grain-boundary barrier layers.

  14. Electronic transport in highly conducting Si-doped ZnO thin films prepared by pulsed laser deposition

    SciTech Connect

    Kuznetsov, Vladimir L.; Vai, Alex T.; Edwards, Peter P.; Al-Mamouri, Malek; Stuart Abell, J.; Pepper, Michael

    2015-12-07

    Highly conducting (ρ = 3.9 × 10{sup −4} Ωcm) and transparent (83%) polycrystalline Si-doped ZnO (SiZO) thin films have been deposited onto borosilicate glass substrates by pulsed laser deposition from (ZnO){sub 1−x}(SiO{sub 2}){sub x} (0 ≤ x ≤ 0.05) ceramic targets prepared using a sol-gel technique. Along with their structural, chemical, and optical properties, the electronic transport within these SiZO samples has been investigated as a function of silicon doping level and temperature. Measurements made between 80 and 350 K reveal an almost temperature-independent carrier concentration consistent with degenerate metallic conduction in all of these samples. The temperature-dependent Hall mobility has been modeled by considering the varying contribution of grain boundary and electron-phonon scattering in samples with different nominal silicon concentrations.

  15. Structure and mechanical properties of 3dTM ion doped RF sputtered ZnO thin films on Si (100)

    SciTech Connect

    Venkaiah, M. Singh, R.

    2014-04-24

    Mn, Fe and Mn-Fe doped ZnO thin films were deposited on Si (100) substrates by rf- magnetron sputtering using ceramic target in pure oxygen gas environment. The X-ray diffraction shows the polycrystalline wurtzite structure films. The average grain size varies from 32-50 nm, with lower grain size for Fe doped ZnO films. The room temperature loading and unloading curve are continuous without any pop-in. The Young's modulus and hardness are in the range 156-178 GPa and 14-15.5 GPa respectively.

  16. Thickness identification of atomically thin InSe nanoflakes on SiO2/Si substrates by optical contrast analysis

    NASA Astrophysics Data System (ADS)

    Brotons-Gisbert, M.; Sánchez-Royo, J. F.; Martínez-Pastor, J. P.

    2015-11-01

    Single layers of chalcogenide semiconductors have demonstrated to exhibit tunable properties that can be exploited for new field-effect transistors and photonic devices. Among these semiconductors, indium selenide (InSe) is attractive for applications due to its direct bandgap in the near infrared, controllable p- and n-type doping and high chemical stability. For its fundamental study and the development of practical applications, rapid and accurate identification methods of atomically thin nanosheets are essential. Here, we employ a transfer matrix approach to numerically calculate the optical contrast between thin InSe flakes and commonly used SiO2/Si substrates, which nicely reproduces experimental values extracted from optical images on 285 nm SiO2/Si substrates. Standard 90 and ∼300 nm SiO2/Si substrates result to provide an optimized optical contrast to detect few-layer InSe flakes using monochromatic illumination at ∼450 and ∼520 nm, respectively. On the other hand, calculated optical contrast reveals an optimum value of 110 nm for the thickness of the SiO2 film on Si substrates in order to detect InSe nanoflakes as thin as one single layer, under white light illumination. These results demonstrate that the proposed optical contrast method is a very fast and reliable technique to identify atomically thin InSe nanoflakes deposited onto SiO2/Si substrates.

  17. The effects of layering in ferroelectric Si-doped HfO{sub 2} thin films

    SciTech Connect

    Lomenzo, Patrick D.; Nishida, Toshikazu; Takmeel, Qanit; Moghaddam, Saeed; Zhou, Chuanzhen; Liu, Yang; Fancher, Chris M.; Jones, Jacob L.

    2014-08-18

    Atomic layer deposited Si-doped HfO{sub 2} thin films approximately 10 nm thick are deposited with various Si-dopant concentrations and distributions. The ferroelectric behavior of the HfO{sub 2} thin films are shown to be dependent on both the Si mol. % and the distribution of Si-dopants. Metal-ferroelectric-insulator-semiconductor capacitors are shown to exhibit a tunable remanent polarization through the adjustment of the Si-dopant distribution at a constant Si concentration. Inhomogeneous layering of Si-dopants within the thin films effectively lowers the remanent polarization. A pinched hysteresis loop is observed for higher Si-dopant concentrations and found to be dependent on the Si layering distribution.

  18. n +-Microcrystalline-Silicon Tunnel Layer in Tandem Si-Based Thin Film Solar Cells

    NASA Astrophysics Data System (ADS)

    Lee, Ching-Ting; Lee, Hsin-Ying; Chen, Kuan-Hao

    2016-10-01

    In this study, the p-SiC/ i-Si/ n-Si cell and the p-SiC/ i-SiGe/ n-Si cell deposited using plasma-enhanced chemical vapor deposition were cascaded for forming the tandem Si-based thin film solar cells to absorb the wide solar spectrum. To further improve the performances of the tandem Si-based thin film solar cells, a 5-nm-thick n +-microcrystalline-Si ( n +-μc-Si) tunnel layer deposited using the laser-assisted plasma-enhanced chemical vapor deposition was inserted between the p-SiC/ i-Si/ n-Si cell and the p-SiC/ i-SiGe/ n-Si cell. Since both the plasma and the CO2 laser were simultaneously utilized to efficiently decompose the reactant and doping gases, the carrier concentration and the carrier mobility of the n +-μc-Si tunnel layer were significantly improved. The ohmic contact formed between the p-SiC layer and the n +-μc-Si tunnel layer with low resistance was beneficial to the generated current transportation and the carrier recombination rate. Therefore, the conversion efficiency of the tandem solar cells was promoted from 8.57% and 8.82% to 9.91% compared to that without tunnel layer and with 5-nm-thick n +-amorphous-Si tunnel layer.

  19. Effect of yttrium-doping on the microstructures and semiconductor-metal phase transition characteristics of polycrystalline VO2 thin films

    NASA Astrophysics Data System (ADS)

    Gu, Deen; Sun, Zhanhong; Zhou, Xin; Guo, Rui; Wang, Tao; Jiang, Yadong

    2015-12-01

    We investigate the effect of yttrium-doping on the microstructures and semiconductor-metal phase transition characteristics of polycrystalline VO2 thin films prepared by reactively co-sputtering process. XPS analyses indicate the existence of Y3+ in the Y-doped VO2 films, but Y-doping hardly influences the chemical states of V and O elements. X-ray diffraction patterns and Raman spectra reveal that both undoped and Y-doped VO2 thin films have a polycrystalline structure of monoclinic VO2. The introduction of Y greatly reduces the grain size of VO2 thin films as evidenced by scanning electron microscopy analyses. The relationship between the hysteresis width and doping level is not monotonic although the grain size is monotonically reduced with increasing the doping level. Y-doped VO2 films with optimal doping level (1.82 at%) have a notably narrower hysteresis width (4.6 °C) than undoped VO2 films (10.7 °C). This is ascribed to increased heterogeneous nucleation centers due to Y in the VO2 lattice. With the further increase of doping level, the size effect gradually plays a prominent role in SMPT, and the hysteresis width of Y-doped VO2 films increases instead. The SMPT temperature of Y-doped VO2 films obviously decreases compared with undoped VO2 films due to reduced grain size and deformation of local structure around Y atom.

  20. Flexible carbon nanotube/mono-crystalline Si thin-film solar cells

    PubMed Central

    2014-01-01

    Flexible heterojunction solar cells were fabricated from carbon nanotubes (CNTs) and mono-crystalline Si thin films at room temperature. The Si thin films with thickness less than 50 μm are prepared by chemically etching Si wafer in a KOH solution. The initial efficiency of the thin-film solar cell varies from approximately 3% to 5%. After doping with a few drops of 1 M HNO3, the efficiency increases to 6% with a short-circuit current density of 16.8 mA/cm2 and a fill factor of 71.5%. The performance of the solar cells depends on the surface state and thickness of Si thin films, as well as the interface of CNT/Si. The flexible CNT/Si thin-film solar cells exhibit good stability in bending-recovery cycles. PMID:25258617

  1. Flexible carbon nanotube/mono-crystalline Si thin-film solar cells.

    PubMed

    Sun, Huanhuan; Wei, Jinquan; Jia, Yi; Cui, Xian; Wang, Kunlin; Wu, Dehai

    2014-01-01

    Flexible heterojunction solar cells were fabricated from carbon nanotubes (CNTs) and mono-crystalline Si thin films at room temperature. The Si thin films with thickness less than 50 μm are prepared by chemically etching Si wafer in a KOH solution. The initial efficiency of the thin-film solar cell varies from approximately 3% to 5%. After doping with a few drops of 1 M HNO3, the efficiency increases to 6% with a short-circuit current density of 16.8 mA/cm(2) and a fill factor of 71.5%. The performance of the solar cells depends on the surface state and thickness of Si thin films, as well as the interface of CNT/Si. The flexible CNT/Si thin-film solar cells exhibit good stability in bending-recovery cycles. PMID:25258617

  2. A comparative study on in situ grown superconducting YBCO and YBCO-Ag thin films by PLD on polycrystalline SmBa2NbO6 substrate

    NASA Astrophysics Data System (ADS)

    Kurian, J.; John, Asha M.; Wariar, P. R. S.; Sajith, P. K.; Koshy, J.; Pai, S. P.; Pinto, R.

    2000-02-01

    The development and characterization of SmBa2NbO6, which is a new ceramic substrate material for the YBa2Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> superconductor, are reported. SmBa2NbO6 has a complex cubic perovskite structure with lattice constant a = 8.524 Å. The dielectric properties of SmBa2NbO6 are in a range suitable for its use as a substrate for microwave applications. SmBa2NbO6 was found to have a thermal conductivity of 77 W m-1 K-1 and a thermal expansion coefficient of 7.8 × 10-6 °C-1 at room temperature. Superconducting YBa2 Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> and YBa2Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> -Ag thin films have been grown in situ on polycrystalline SmBa2NbO6 by the pulsed laser ablation technique. The films exhibited (00l) orientation of an orthorhombic YBa2 Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> phase and gave a zero resistivity superconducting transition (TC(0)) at 90 K with a transition width of ~1.5 K. The critical current density of YBCO-Ag thin films grown on polycrystalline SmBa2NbO6 substrate was ~3 × 105 A cm-2 at 77 K. A comparative study of YBCO and YBCO-Ag thin films developed on polycrystalline SmBa2NbO6 substrate by PLD based on the crystallinity, orientation and critical current density of the YBCO film is discussed in detail.

  3. Impact of solid-phase crystallization of amorphous silicon on the chemical structure of the buried Si/ZnO thin film solar cell interface

    SciTech Connect

    Bar, M.; Wimmer, M.; Wilks, R. G.; Roczen, M.; Gerlach, D.; Ruske, F.; Lips, K.; Rech, B.; Weinhardt, L.; Blum, M.; Pookpanratana, S.; Krause, S.; Zhang, Y.; Heske, C.; Yang, W.; Denlinger, J. D.

    2010-04-30

    The chemical interface structure between phosphorus-doped hydrogenated amorphous silicon and aluminum-doped zinc oxide thin films is investigated with soft x-ray emission spectroscopy (XES) before and after solid-phase crystallization (SPC) at 600C. In addition to the expected SPC-induced phase transition from amorphous to polycrystalline silicon, our XES data indicates a pronounced chemical interaction at the buried Si/ZnO interface. In particular, we find an SPC-enhanced formation of Si-O bonds and the accumulation of Zn in close proximity to the interface. For an assumed closed and homogeneous SiO2 interlayer, an effective thickness of (5+2)nm after SPC could be estimated.

  4. Local grain orientation and strain in polycrystalline YBa2Cu3O7-δ superconductor thin films measured by Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Amer, Maher S.; Maguire, John; Cai, L.; Biggers, R.; Busbee, J.; LeClair, S. R.

    2001-06-01

    We report direct measurements of local grain orientation and residual strain in polycrystalline, C-axis oriented thin YBa2Cu3O7-δ superconducting films using polarized Raman spectroscopy. Strain dependence of the Ag Raman active mode at 335 cm-1 was calibrated and used to measure local strain in the films. Our data showed that high quality films are associated with the connected path of uniform grain orientation (single crystal-like) across the film and uniform residual strain in the range of -0.3%. Nonuniform grain orientation or high angle grain boundaries and nonuniform local strains were associated with low quality films.

  5. Measured temperature and pressure dependence of Vp and Vs in compacted, polycrystalline sI methane and sII methane-ethane hydrate

    USGS Publications Warehouse

    Helgerud, M.B.; Waite, W.F.; Kirby, S.H.; Nur, A.

    2003-01-01

    We report on compressional- and shear-wave-speed measurements made on compacted polycrystalline sI methane and sII methane-ethane hydrate. The gas hydrate samples are synthesized directly in the measurement apparatus by warming granulated ice to 17??C in the presence of a clathrate-forming gas at high pressure (methane for sI, 90.2% methane, 9.8% ethane for sII). Porosity is eliminated after hydrate synthesis by compacting the sample in the synthesis pressure vessel between a hydraulic ram and a fixed end-plug, both containing shear-wave transducers. Wave-speed measurements are made between -20 and 15??C and 0 to 105 MPa applied piston pressure.

  6. Enhanced conversion efficiency and surface hydrophobicity of nano-roughened Teflon-like film coated poly-crystalline Si solar cells.

    PubMed

    Lin, Gong-Ru; Meng, Fan-Shuen; Pai, Yi-Hao; Lin, Yung-Hsiang

    2012-03-21

    Nano-roughened Teflon-like film coated poly-crystalline Si photovoltaic solar cells (PVSCs) with enhanced surface hydrophobicity and conversion efficiency (η) are characterized and compared with those coated by a Si nanorod array or a standard SiN anti-reflection layer. The Teflon-like film coated PVSC surface reveals a water contact angle increasing from 89.3° to 96.2° as its thickness enlarges from 22 to 640 nm, which is much larger than those of the standard and Si nanorod array coated PVSC surfaces (with angles of 55.6° and 32.8°, respectively). After nano-roughened Teflon-like film passivation, the PVSC shows a comparable η(10.89%) with the standard SiN coated PVSC (η = 11.39%), while the short-circuit current (I(SC)) is slightly reduced by 2% owing to the slightly decreased UV transmittance and unchanged diode performance. In contrast, the Si nanorod array may offer an improved surface anti-reflection with surface reflectance decreasing from 30% to 5% at a cost of optical scattering and randomized deflection, which simultaneously decrease the optical transmittance from 15% to 3% in the visible region without improving hydrophobicity and conversion efficiency. The Si nanorod array covered PVSC with numerous surface dangling bonds induced by 1 min wet-etching, which greatly reduces the open-circuit voltage (V(OC)) by 10-15% and I(SC) by 30% due to the reduced shunt resistance from 3 to 0.24 kΩ. The nano-scale roughened Teflon-like film coated on PVSC has provided better hydrophobicity and conversion efficiency than the Si nanorod array covered PVSC, which exhibits superior water repellant performance and comparable conversion efficiency to be one alternative approach for self-cleaning PVSC applications. PMID:22323107

  7. Enhanced conversion efficiency and surface hydrophobicity of nano-roughened Teflon-like film coated poly-crystalline Si solar cells.

    PubMed

    Lin, Gong-Ru; Meng, Fan-Shuen; Pai, Yi-Hao; Lin, Yung-Hsiang

    2012-03-21

    Nano-roughened Teflon-like film coated poly-crystalline Si photovoltaic solar cells (PVSCs) with enhanced surface hydrophobicity and conversion efficiency (η) are characterized and compared with those coated by a Si nanorod array or a standard SiN anti-reflection layer. The Teflon-like film coated PVSC surface reveals a water contact angle increasing from 89.3° to 96.2° as its thickness enlarges from 22 to 640 nm, which is much larger than those of the standard and Si nanorod array coated PVSC surfaces (with angles of 55.6° and 32.8°, respectively). After nano-roughened Teflon-like film passivation, the PVSC shows a comparable η(10.89%) with the standard SiN coated PVSC (η = 11.39%), while the short-circuit current (I(SC)) is slightly reduced by 2% owing to the slightly decreased UV transmittance and unchanged diode performance. In contrast, the Si nanorod array may offer an improved surface anti-reflection with surface reflectance decreasing from 30% to 5% at a cost of optical scattering and randomized deflection, which simultaneously decrease the optical transmittance from 15% to 3% in the visible region without improving hydrophobicity and conversion efficiency. The Si nanorod array covered PVSC with numerous surface dangling bonds induced by 1 min wet-etching, which greatly reduces the open-circuit voltage (V(OC)) by 10-15% and I(SC) by 30% due to the reduced shunt resistance from 3 to 0.24 kΩ. The nano-scale roughened Teflon-like film coated on PVSC has provided better hydrophobicity and conversion efficiency than the Si nanorod array covered PVSC, which exhibits superior water repellant performance and comparable conversion efficiency to be one alternative approach for self-cleaning PVSC applications.

  8. Atomic-resolution characterization of the effects of CdCl{sub 2} treatment on poly-crystalline CdTe thin films

    SciTech Connect

    Paulauskas, T. Buurma, C.; Colegrove, E.; Guo, Z.; Sivananthan, S.; Klie, R. F.

    2014-08-18

    Poly-crystalline CdTe thin films on glass are used in commercial solar-cell superstrate devices. It is well known that post-deposition annealing of the CdTe thin films in a CdCl{sub 2} environment significantly increases the device performance, but a fundamental understanding of the effects of such annealing has not been achieved. In this Letter, we report a change in the stoichiometry across twin boundaries in CdTe and propose that native point defects alone cannot account for this variation. Upon annealing in CdCl{sub 2}, we find that the stoichiometry is restored. Our experimental measurements using atomic-resolution high-angle annular dark field imaging, electron energy-loss spectroscopy, and energy dispersive X-ray spectroscopy in a scanning transmission electron microscope are supported by first-principles density functional theory calculations.

  9. Large-Scale PV Module Manufacturing Using Ultra-Thin Polycrystalline Silicon Solar Cells: Final Subcontract Report, 1 April 2002--28 February 2006

    SciTech Connect

    Wohlgemuth, J.; Narayanan, M.

    2006-07-01

    The major objectives of this program were to continue advances of BP Solar polycrystalline silicon manufacturing technology. The Program included work in the following areas. (1) Efforts in the casting area to increase ingot size, improve ingot material quality, and improve handling of silicon feedstock as it is loaded into the casting stations. (2) Developing wire saws to slice 100-..mu..m-thick silicon wafers on 290-..mu..m-centers. (3) Developing equipment for demounting and subsequent handling of very thin silicon wafers. (4) Developing cell processes using 100-..mu..m-thick silicon wafers that produce encapsulated cells with efficiencies of at least 15.4% at an overall yield exceeding 95%. (5) Expanding existing in-line manufacturing data reporting systems to provide active process control. (6) Establishing a 50-MW (annual nominal capacity) green-field Mega-plant factory model template based on this new thin polycrystalline silicon technology. (7) Facilitating an increase in the silicon feedstock industry's production capacity for lower-cost solar-grade silicon feedstock..

  10. Thermoelectric properties of Al-doped Mg2Si thin films deposited by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Chen, Zhi-jian; Zhou, Bai-yang; Li, Jian-xin; Wen, Cui-lian

    2016-11-01

    The Al-doped Mg2Si thin films were fabricated by two-target alternative magnetron sputtering technique, and the influences of different Al doping contents on the thermoelectric properties of Al-doped Mg2Si thin films were investigated. The compositions, crystal structures, electronic transport properties and thermoelectric properties of the thin films were examined using energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Hall coefficient measurement and Seebeck coefficient measurement system, respectively. The EDS results show that the thin films doped with Al target sputtering power of 30 W, 60 W and 90 W have the Al content of 0.68 at.%, 1.56 at.% and 2.85 at.%, respectively. XRD results indicate that the diffraction peaks of Mg2Si become stronger with increasing Al dopant. The results of Hall coefficient measurement and Seebeck coefficient measurement system reveal that all the samples are n-type. The conductivities of Al-doped Mg2Si thin films are significantly greater than that of undoped Mg2Si thin film, and increase with increasing Al doping content. With the increase of temperature, the absolute value of the Seebeck coefficients of Mg2Si base thin films increase firstly and then decrease. The maximum power factor obtained is 3.8 mW m-1 k-2 for 1.56 at.% Al-doped Mg2Si thin film at 573 K.

  11. Enhanced electrochemical performance of Si-Cu-Ti thin films by surface covered with Cu3Si nanowires

    NASA Astrophysics Data System (ADS)

    Xu, Kaiqi; He, Yu; Ben, Liubin; Li, Hong; Huang, Xuejie

    2015-05-01

    Si-Cu-Ti thin films with Cu3Si nanowires on the surface and voids in the Cu layer are fabricated for the first time by magnetron sputtering combined with atomic layer deposition (ALD) of alumina. The formation of the surface Cu3Si nanowires is strongly dependent on the thickness of the coated alumina and cooling rate of the thin films during annealing. The maximum coverage of the surface Cu3Si nanowires is obtained with an alumina thickness of 2 nm and a cooling rate of 1 °C min-1. The electrode based on this thin film shows an excellent capacity retention of more than 900 mAh g-1 and a high columbic efficiency of more than 99% after 100 cycles. The improvement of the electrochemical performance of Si-Cu-Ti thin film electrode is attributed to the surface Cu3Si nanowires which reduce the polarization and inhomogeneous lithiation by formation of a surface conductive network, in addition to the alleviation of volume expansion of Si by voids in the Cu layer during cycling.

  12. Co2FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

    NASA Astrophysics Data System (ADS)

    Belmeguenai, M.; Tuzcuoglu, H.; Gabor, M. S.; Petrisor, T.; Tiusan, C.; Zighem, F.; Chérif, S. M.; Moch, P.

    2014-01-01

    10 nm and 50 nm Co2FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (Ta), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing Ta, while the uniaxial anisotropy field is nearly unaffected by Ta within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with Ta. Finally, the FMR linewidth decreases when increasing Ta, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10-3 and 1.3×10-3 for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively).

  13. Polycrystalline CuInSe2 thin films for solar cells by three-source magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Nakada, Tokio; Migita, Kazuo; Kunioka, Akio

    1993-08-01

    Polycrystalline CuInSe2 films were deposited in a wide range of Cu/In ratios by three-source magnetron sputtering technique onto soda-lime glass and Mo-coated glass substrates at elevated substrate temperatures. Good run-to-run reproductibility was achieved in our sputtering system using melt-grown polycrystalline selenium target. In excess films which are desirable for solar cells were obtained in the temperature range of 400 to 500 C. These films showed a preferential (112) orientation of the chalcopyrite structure and possessed an excellent adhesion property to the substrates. Preliminary solar cells with ZnO:Al/CdS/CuInSe2 structure resulted in a conversion efficiency of 6.3% under AM 1.5 illumination.

  14. Growth and properties of YBCO thin films on polycrystalline Ag substrates by inclined substrate pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Li, M.; Ma, B.; Koritala, R. E.; Fisher, B. L.; Dorris, S. E.; Venkataraman, K.; Balachandran, U.

    2002-06-01

    Fully c-axis-oriented YBCO films were directly deposited on polycrystalline silver substrates by inclined substrate pulsed laser ablation. The orientation and microstructure of the YBCO films were characterized by x-ray diffraction 2θ-scans, Ω-scans and pole figure analysis. Surface morphology was examined by scanning electron microscopy. Irregular-mosaic-shaped supergrains were observed in the films. Raman spectroscopy was used to evaluate the quality of the YBCO films. The superconducting transition temperature (Tc) and the critical current density (Jc) of the films were determined by inductive and transport measurements, respectively. Tc = 91 K with sharp transition and Jc = 2.7 × 105 A cm-2 at 77 K in zero field were obtained on a film that was 0.14 μm thick, 5 mm wide and 10 mm long. This work demonstrated a promising approach to obtain high-Jc YBCO films on nontextured polycrystalline silver substrate.

  15. White light emission and optical gains from a Si nanocrystal thin film

    NASA Astrophysics Data System (ADS)

    Wang, Dong-Chen; Hao, Hong-Chen; Chen, Jia-Rong; Zhang, Chi; Zhou, Jing; Sun, Jian; Lu, Ming

    2015-11-01

    We report a Si nanocrystal thin film consisting of free-standing Si nanocrystals, which can emit white light and show positive optical gains for its red, green and blue (RGB) components under ultraviolet excitation. Si nanocrystals with ϕ = 2.31 ± 0.35 nm were prepared by chemical etching of Si powder, followed by filtering. After being mixed with SiO2 sol-gel and thermally annealed, a broadband photoluminescence (PL) from the thin film was observed. The RGB ratio of the PL can be tuned by changing the annealing temperature or atmosphere, which is 1.00/3.26/4.59 for the pure white light emission. The origins of the PL components could be due to differences in oxygen-passivation degree for Si nanocrystals. The results may find applications in white-light Si lasing and Si lighting.

  16. Defect engineering by ultrasound treatment in polycrystalline silicon

    SciTech Connect

    Ostapenko, S.; Jastrzebski, L.

    1995-08-01

    By applying ultrasound treatment (UST) to bulk and thin film polycrystalline Si (poly-Si) we have found a dramatic improvement of recombination and transport properties. The increasing of minority carrier lifetime by as much as one order of magnitude was found in short diffusion length regions, while exhibiting a strong dispersion for entire solar-grade poly-Si wafer. Relevant mechanisms are attributed to ultrasound processing on crystallographic defects, as well as UST stimulated dissociation of Fe-B pairs followed by Fe{sub i} gettering. A spectacular improvement of hydrogenation efficiency in poly-Si thin-films on glass substrate is demonstrated by resistivity study and confirmed using spatially resolved photoluminescence and nanoscale contact potential difference mapping. By applying UST to commercial solar cells we found the increasing of cell efficiency at low light excitation.

  17. Investigation of the vertical electrical transport in a-Si:H/nc-Si:H superlattice thin films.

    PubMed

    Das, Debajyoti; Kar, Debjit

    2015-07-14

    Tuning the size of silicon nano-crystallites (Si-ncs) has been realized simply by controlling the thickness of the nc-Si:H sub-layer (tnc) in the a-Si:H/nc-Si:H superlattice thin films grown by low temperature plasma processing in PE-CVD. The vertical electrical transport phenomena accomplished in superlattice films have been investigated in order to identify their effective utilization in practical device configuration. The reduced size of the Si-ncs at thinner tnc and the associated band gap widening due to quantum confinement effects generates the Coulomb potential barrier at the a-Si/nc-Si interface which in turn obstructs the transport of charge carriers to the allowed energy states in Si-ncs, leading to the Poole-Frenkel tunneling as the prevailing charge transport mechanism in force. The advantages of the conduction process governed by the Poole-Frenkel mechanism are two-fold. The lower barrier height caused by the a-Si:H sub-layer in the superlattice than the silicon oxide sub-layer in conventional structures enhances the conduction current. Moreover, increasing trapped charges in the a-Si:H sub-layer can arbitrarily increase the current conduction. Accordingly, a-Si:H/nc-Si:H superlattice structures could provide superior electrical transport in stacked layer devices e.g., multi-junction all silicon solar cells.

  18. Absorption enhancement in thin film a-Si solar cells with double-sided SiO2 particle layers

    NASA Astrophysics Data System (ADS)

    Chen, Le; Wang, Qing-Kang; Shen, Xiang-Qian; Chen, Wen; Huang, Kun; Liu, Dai-Ming

    2015-10-01

    Light absorption enhancement is very important for improving the power conversion efficiency of a thin film a-Si solar cell. In this paper, a thin-film a-Si solar cell model with double-sided SiO2 particle layers is designed, and then the underlying mechanism of absorption enhancement is investigated by finite difference time domain (FDTD) simulation; finally the feasible experimental scheme for preparing the SiO2 particle layer is discussed. It is found that the top and bottom SiO2 particle layers play an important role in anti-reflection and light trapping, respectively. The light absorption of the cell with double-sided SiO2 layers greatly increases in a wavelength range of 300 nm-800 nm, and the ultimate efficiency increases more than 22% compared with that of the flat device. The cell model with double-sided SiO2 particle layers reported here can be used in varieties of thin film solar cells to further improve their performances. Project supported by the National High-Tech Research and Development Program of China (Grant No. 2011AA050518), the University Research Program of Guangxi Education Department, China (Grant No. LX2014288), and the Natural Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant No. 2013GXNSBA019014).

  19. Sub-kT/q Subthreshold-Slope Using Negative Capacitance in Low-Temperature Polycrystalline-Silicon Thin-Film Transistor

    PubMed Central

    Park, Jae Hyo; Jang, Gil Su; Kim, Hyung Yoon; Seok, Ki Hwan; Chae, Hee Jae; Lee, Sol Kyu; Joo, Seung Ki

    2016-01-01

    Realizing a low-temperature polycrystalline-silicon (LTPS) thin-film transistor (TFT) with sub-kT/q subthreshold slope (SS) is significantly important to the development of next generation active-matrix organic-light emitting diode displays. This is the first time a sub-kT/q SS (31.44 mV/dec) incorporated with a LTPS-TFT with polycrystalline-Pb(Zr,Ti)O3 (PZT)/ZrTiO4 (ZTO) gate dielectrics has been demonstrated. The sub-kT/q SS was observed in the weak inversion region at −0.5 V showing ultra-low operating voltage with the highest mobility (250.5 cm2/Vsec) reported so far. In addition, the reliability of DC negative bias stress, hot carrier stress and self-heating stress in LTPS-TFT with negative capacitance was investigated for the first time. It was found that the self-heating stress showed accelerated SS degradation due to the PZT Curie temperature. PMID:27098115

  20. Sub-kT/q Subthreshold-Slope Using Negative Capacitance in Low-Temperature Polycrystalline-Silicon Thin-Film Transistor

    NASA Astrophysics Data System (ADS)

    Park, Jae Hyo; Jang, Gil Su; Kim, Hyung Yoon; Seok, Ki Hwan; Chae, Hee Jae; Lee, Sol Kyu; Joo, Seung Ki

    2016-04-01

    Realizing a low-temperature polycrystalline-silicon (LTPS) thin-film transistor (TFT) with sub-kT/q subthreshold slope (SS) is significantly important to the development of next generation active-matrix organic-light emitting diode displays. This is the first time a sub-kT/q SS (31.44 mV/dec) incorporated with a LTPS-TFT with polycrystalline-Pb(Zr,Ti)O3 (PZT)/ZrTiO4 (ZTO) gate dielectrics has been demonstrated. The sub-kT/q SS was observed in the weak inversion region at ‑0.5 V showing ultra-low operating voltage with the highest mobility (250.5 cm2/Vsec) reported so far. In addition, the reliability of DC negative bias stress, hot carrier stress and self-heating stress in LTPS-TFT with negative capacitance was investigated for the first time. It was found that the self-heating stress showed accelerated SS degradation due to the PZT Curie temperature.

  1. Sub-kT/q Subthreshold-Slope Using Negative Capacitance in Low-Temperature Polycrystalline-Silicon Thin-Film Transistor.

    PubMed

    Park, Jae Hyo; Jang, Gil Su; Kim, Hyung Yoon; Seok, Ki Hwan; Chae, Hee Jae; Lee, Sol Kyu; Joo, Seung Ki

    2016-04-21

    Realizing a low-temperature polycrystalline-silicon (LTPS) thin-film transistor (TFT) with sub-kT/q subthreshold slope (SS) is significantly important to the development of next generation active-matrix organic-light emitting diode displays. This is the first time a sub-kT/q SS (31.44 mV/dec) incorporated with a LTPS-TFT with polycrystalline-Pb(Zr,Ti)O3 (PZT)/ZrTiO4 (ZTO) gate dielectrics has been demonstrated. The sub-kT/q SS was observed in the weak inversion region at -0.5 V showing ultra-low operating voltage with the highest mobility (250.5 cm(2)/Vsec) reported so far. In addition, the reliability of DC negative bias stress, hot carrier stress and self-heating stress in LTPS-TFT with negative capacitance was investigated for the first time. It was found that the self-heating stress showed accelerated SS degradation due to the PZT Curie temperature.

  2. Low temperature production of large-grain polycrystalline semiconductors

    DOEpatents

    Naseem, Hameed A.; Albarghouti, Marwan

    2007-04-10

    An oxide or nitride layer is provided on an amorphous semiconductor layer prior to performing metal-induced crystallization of the semiconductor layer. The oxide or nitride layer facilitates conversion of the amorphous material into large grain polycrystalline material. Hence, a native silicon dioxide layer provided on hydrogenated amorphous silicon (a-Si:H), followed by deposited Al permits induced crystallization at temperatures far below the solid phase crystallization temperature of a-Si. Solar cells and thin film transistors can be prepared using this method.

  3. Transmission electron microscopy study on ion-beam-synthesized amorphous Fe-Si thin layers

    NASA Astrophysics Data System (ADS)

    Naito, Muneyuki; Ishimaru, Manabu; Hirotsu, Yoshihiko; Valdez, James A.; Sickafus, Kurt E.

    2005-12-01

    Ion-beam-synthesized amorphous Fe-Si thin layers have been characterized using transmission electron microscopy (TEM) in combination with imaging plate techniques. Si single crystals with a (111) orientation were irradiated with 120keV Fe+ ions to a fluence of 4.0×1017cm-2 at cryogenic temperature (120K). Cross-sectional TEM observations indicated the formation of an amorphous bilayer on the topmost layer of the Si substrate. It was found that the upper layer is an amorphous Fe-Si with the composition, in terms of atomic ratio, of Fe /Si ˜1/2, while the lower one is an amorphous Si. Atomic pair-distribution functions extracted from microbeam electron diffraction patterns revealed that the nature of short-range order in amorphous Fe-Si thin layer can be well described by the atomic arrangements of crystalline iron silicides.

  4. Electrical Characteristics of Low-Temperature Polycrystalline Silicon Complementary Metal-Oxide-Semiconductor Thin-Film Transistors with Six-Step Photomask Structure

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Jin; Park, Jae-Hoon; Oh, Kum-Mi; Lee, Seok-Woo; Lee, Kyung-Eon; Shin, Woo-Sup; Jun, Myung-chul; Yang, Yong-Suk; Hwang, Yong-Kee

    2011-06-01

    We propose two types of six-step photomask, complementary metal-oxide-semiconductor (CMOS), thin-film transistor (TFT) PCT device structures in order to simplify their fabrication process compared with that of conventional, low-temperature, polycrystalline silicon (LTPS) CMOS TFT devices. The initial charge transfer characteristics of both types of six-step PCT are equivalent to those of the conventional nine-step PCT. Both types of six-step PCT are comparable to the conventional nine-step mask lightly doped drain (LDD) device in terms of the dc device lifetime of over 10 years at Vds=5 V for line inversion driving, which is the normally recognized duration time for semiconducting devices.

  5. Driving Method Compensating for the Hysteresis of Polycrystalline Silicon Thin-Film Transistors for Active-Matrix Organic Light-Emitting Diode Displays

    NASA Astrophysics Data System (ADS)

    Jung, Myoung-Hoon; Kim, Ohyun; Kim, Byeong-Koo; Chung, Hoon-Ju

    2009-05-01

    A new driving method for active-matrix organic light-emitting diode displays is proposed and evaluated. The pixel structure of the proposed driving method is composed of three thin-film transistors (TFTs) and one capacitor. It inserts black data into display images to reset driving TFTs for the purpose of maintaining constant electrical characteristics of driving TFTs. The proposed driving scheme is less sensitive to the hysteresis of low-temperature polycrystalline silicon (LTPS) TFTs than the conventional pixel structure with two TFTs and one capacitor, and this scheme can virtually eliminate the recoverable residual image that occurs owing to the hysteresis characteristics of LTPS TFTs. In the proposed driving scheme, black data are inserted into displayed images so that the motion image quality is improved.

  6. A low-temperature polycrystalline-silicon thin-film transistor micro-manipulation array with indium tin oxide micro-coils and real-time detection

    NASA Astrophysics Data System (ADS)

    Chen, Chih-Yang; Huang, Chien-Yu; Lin, Chrong-Jung; King, Ya-Chin

    2009-12-01

    This study proposes an array for a bio-handling system consisting of microcoils on top of photodetectors fabricated by low-temperature polycrystalline-silicon thin-film transistor (LTPS-TFT) technology on a glass substrate. Using magnetic beads as the medium, the proposed system can simultaneously monitor and manipulate micrometer-sized bio-samples. In a manipulation system based on magnetic force, photo-detecting is a reliable method, immune to the interference caused by electromagnetic fields. Under 480 lux ambient white light, the sensor can detect a microbead as small as 23 µm in diameter with detectable output difference. It provides a new, easier way for handling samples on a small chip.

  7. Well-aligned polycrystalline lanthanum silicate oxyapatite grown by reactive diffusion between solid La2SiO5 and gases [SiO+1/2O2

    NASA Astrophysics Data System (ADS)

    Fukuda, Koichiro; Hasegawa, Ryo; Kitagawa, Takuya; Nakamori, Hiroshi; Asaka, Toru; Berghout, Abid; Béchade, Emilie; Masson, Olivier; Jouin, Jenny; Thomas, Philippe

    2016-03-01

    The c-axis-oriented polycrystalline lanthanum silicate oxyapatite, La9.48(Si5.89□0.11)O26 (□ denotes a vacancy in the Si site), was successfully prepared by the reactive diffusion between randomly grain-oriented La2SiO5 polycrystal and [SiO+1/2O2] gases at 1873 K in Ar atmosphere. The polycrystal was characterized using optical microscopy, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, micro-Raman spectroscopy, X-ray diffractometry, and impedance spectroscopy. The crystal structure (space group P63/m) showed the deficiency of Si site at ca. 1.9%. The bulk oxide-ion conductivity along the grain-alignment direction steadily increased from 9.2 × 10-3 to 1.17 × 10-2 S/cm with increasing temperature from 923 to 1073 K. The activation energy of conduction was 0.23(2) eV.

  8. An ultra-thin buffer layer for Ge epitaxial layers on Si

    SciTech Connect

    Kawano, M.; Yamada, S.; Tanikawa, K.; Miyao, M.; Hamaya, K.; Sawano, K.

    2013-03-25

    Using an Fe{sub 3}Si insertion layer, we study epitaxial growth of Ge layers on a Si substrate by a low-temperature molecular beam epitaxy technique. When we insert only a 10-nm-thick Fe{sub 3}Si layer in between Si and Ge, epitaxial Ge layers can be obtained on Si. The detailed structural characterizations reveal that a large lattice mismatch of {approx}4% is completely relaxed in the Fe{sub 3}Si layer. This means that the Fe{sub 3}Si layers can become ultra-thin buffer layers for Ge on Si. This method will give a way to realize a universal buffer layer for Ge, GaAs, and related devices on a Si platform.

  9. Near single-crystalline, high-carrier-mobility silicon thin film on a polycrystalline/amorphous substrate

    DOEpatents

    Findikoglu, Alp T.; Jia, Quanxi; Arendt, Paul N.; Matias, Vladimir; Choi, Woong

    2009-10-27

    A template article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material; is provided, together with a semiconductor article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material, and, a top-layer of semiconductor material upon the buffer material layer.

  10. Magnetron-sputter epitaxy of {beta}-FeSi{sub 2}(220)/Si(111) and {beta}-FeSi{sub 2}(431)/Si(001) thin films at elevated temperatures

    SciTech Connect

    Liu Hongfei; Tan Chengcheh; Chi Dongzhi

    2012-07-15

    {beta}-FeSi{sub 2} thin films have been grown on Si(111) and Si(001) substrates by magnetron-sputter epitaxy at 700 Degree-Sign C. On Si(111), the growth is consistent with the commonly observed orientation of [001]{beta}-FeSi{sub 2}(220)//[1-10]Si(111) having three variants, in-plane rotated 120 Degree-Sign with respect to one another. However, on Si(001), under the same growth conditions, the growth is dominated by [-111]{beta}-FeSi{sub 2}(431)//[110]Si(001) with four variants, which is hitherto unknown for growing {beta}-FeSi{sub 2}. Photoelectron spectra reveal negligible differences in the valance-band and Fe2p core-level between {beta}-FeSi{sub 2} grown on Si(111) and Si(001) but an apparent increased Si-oxidization on the surface of {beta}-FeSi{sub 2}/Si(001). This phenomenon is discussed and attributed to the Si-surface termination effect, which also suggests that the Si/Fe ratio on the surface of {beta}-FeSi{sub 2}(431)/Si(001) is larger than that on the surface of {beta}-FeSi{sub 2}(220)/Si(111).

  11. Ultra-Low-Cost Room Temperature SiC Thin Films

    NASA Technical Reports Server (NTRS)

    Faur, Maria

    1997-01-01

    The research group at CSU has conducted theoretical and experimental research on 'Ultra-Low-Cost Room Temperature SiC Thin Films. The effectiveness of a ultra-low-cost room temperature thin film SiC growth technique on Silicon and Germanium substrates and structures with applications to space solar sells, ThermoPhotoVoltaic (TPV) cells and microelectronic and optoelectronic devices was investigated and the main result of this effort are summarized.

  12. Polycrystalline Silicon ISFETs on Glass Substrate

    PubMed Central

    Yan, Feng; Estrela, Pedro; Mo, Yang; Migliorato, Piero; Maeda, Hiroshi

    2005-01-01

    The Ion Sensitive Field Effect Transistor (ISFET) operation based on polycrystalline silicon thin film transistors is reported. These devices can be fabricated on inexpensive disposable substrates such as glass or plastics and are, therefore, promising candidates for low cost single-use intelligent multisensors. In this work we have developed an extended gate structure with PE-CVD Si3N4 deposited on top of a conductor, which also provides the electrical connection to the remote TFT gate. Nearly ideal pH sensitivity (54 mV/pH) and stable operation have been achieved. Temperature effects have also been characterized. A penicillin sensor has been fabricated by functionalizing the sensing area with penicillinase. The shift increases almost linearly upon the increase of penicillin concentration until saturation is reached for ∼ 7 mM. Poly-Si TFT structures with a gold sensing area have been also successfully applied to field-effect detection of DNA.

  13. Ag Nanodots Emitters Embedded in a Nanocrystalline Thin Film Deposited on Crystalline Si Solar Cells.

    PubMed

    Park, Seungil; Ryu, Sel Gi; Ji, HyungYong; Kim, Myeong Jun; Peck, Jong Hyeon; Kim, Keunjoo

    2016-06-01

    We fabricated crystalline Si solar cells with the inclusion of various Ag nanodots into the additional emitters of nanocrystallite Si thin films. The fabricated process was carried out on the emitter surface of p-n junction for the textured p-type wafer. The Ag thin films were deposited on emitter surfaces and annealed at various temperatures. The amorphous Si layers were also deposited on the Ag annealed surfaces by hot-wire chemical vapor deposition and then the deposited layers were doped by the second n-type doping process to form an additional emitter. From the characterization, both the Ag nanodots and the deposited amorphous Si thin films strongly reduce photo-reflectances in a spectral region between 200-400 nm. After embedding Ag nanodots in nanocrystallite Si thin films, a conversion efficiency of the sample with added emitter was achieved to 15.1%, which is higher than the 14.1% of the reference sample and the 14.7% of the de-posited sample with a-Si:H thin film after the Ag annealing process. The additional nanocrystallite emitter on crystalline Si with Ag nanodots enhances cell properties. PMID:27427665

  14. IR spectra of ICPCVD SiNx thin films for MEMS structures

    NASA Astrophysics Data System (ADS)

    Rudakov, G.; Reshetnikov, I.

    2015-11-01

    Optical properties of non-stoichiometric silicon nitride (SiNx) films for thermo sensitive membranes of microelectromechanical systems (MEMS) and microoptomechanical systems (MOMS) has been studied applying infrared (IR) spectroscopy. For the structures SiNx/Si and (thin metal layer)/SiNx/Si transmission and reflection spectra in the region of wave numbers of 500-7000 cm-1 has been investigated. For the investigated structures analysis of optical properties observed in the IR spectra both in the form of selective absorption bands and interference modulation of a baseline was conducted.

  15. Moessbauer study in thin films of FeSi2 and FeSe systems

    NASA Technical Reports Server (NTRS)

    Escue, W. J.; Aggarwal, K.; Mendiratta, R. G.

    1978-01-01

    Thin films of FeSi2 and FeSe were studied using Moessbauer spectroscopy information regarding dangling bond configuration and nature of crystal structure in thin films was derived. A significant influence of crystalline aluminum substrate on film structure was observed.

  16. Time-Domain Thermoreflectance Measurements of Thermal Transport in Amorphous SiC Thin Films

    NASA Astrophysics Data System (ADS)

    Daly, Brian; Hondongwa, Donald; King, Sean

    2010-03-01

    We present ultrafast optical pump-probe measurements of thermal transport in a series of amorphous SiC samples. The samples were grown on Si wafers by plasma enhanced chemical vapor deposition utilizing various combinations of methylsilanes and H2 and He diluent gases. The sample films were well characterized and found to have densities (1.3 -- 2.3 g cm-3) and dielectric constants (4.0 -- 7.2) that spanned a wide range of values. Prior to their measurement, the samples were coated with 40-70 nm of polycrystalline Al. The pump-probe measurements were performed at room temperature using a modelocked Ti:sapphire laser that produced sub-picosecond pulses of a few nJ. The pulses heat the Al coating, causing a transient reflectivity change. As the Al film cools into the SiC film, the reflectivity change can be measured, giving a measure of the thermal effusivity of the SiC film. We then extract values for the thermal conductivity of the SiC films and find that it varies from less than half of the thermal conductivity of amorphous SiO2 for the lower density materials to somewhat larger than amorphous SiO2 for the highest density films.

  17. The electro-optical behavior of liquid crystal molecules on the surface of SiO2 inorganic thin films.

    PubMed

    Sung, Shi-Joon; Yang, Kee-Jeong; Kim, Dae-Hwan; Do, Yun Seon; Kang, Jin-Kyu; Choi, Byeong-Dae

    2009-12-01

    Inorganic thin films are well known for the liquid crystal alignment layers for LCoS application due to the higher thermal and photochemical stability of inorganic materials. The switching time of liquid crystals is the important factor for the projection application and the faster switching time is required for the high quality display. The switching behavior of liquid crystal molecules on inorganic thin films might be closely related with the surface properties of the inorganic thin films. Therefore the understanding of surface properties of the inorganic thin films is required for the enhancement of the switching time of liquid crystals of LCoS devices. In this work, we prepared the SiO2 inorganic thin films and the electro-optical behavior of liquid crystal molecules on SiO2 thin film was investigated. The sputtering condition of SiO2 thin film was closely related with the thickness and the surface morphology of SiO2 thin film. The switching time of liquid crystals with negative dielectric constant on SiO2 inorganic thin films was dominantly affected by the size of protrusion on the surface of SiO2 thin film and the surface roughness of SiO2 thin film was also related with the switching time of liquid crystals. From these results, it is possible to prepare the SiO2 inorganic thin film suitable for the liquid crystal alignment layer for VAN LC mode.

  18. Strain engineering effects on electrical properties of lead-free piezoelectric thin films on Si wafers.

    PubMed

    Ohno, Tomoya; Kamai, Yuto; Oda, Yuutaro; Sakamoto, Naonori; Matsuda, Takeshi; Wakiya, Naoki; Suzuki, Hisao

    2014-01-01

    Using radio frequency - magnetron sputtering, calcium-doped barium zirconate titanate ((Ba(0.85)Ca(0.15))(Zr(0.1)Ti(0.9))O(3), BCZT) thin films were deposited on Si wafers with different bottom electrodes. The obtained BCZT thin film on a lanthanum nickel oxide (LNO) electrode had a highly c-axis preferred orientation, while the BCZT thin film on a Pt bottom electrode had (111) preferred orientation. Furthermore, the out-of-plane lattice constant of the BCZT on LNO/Si was 3.4% larger than that of the reported bulk material because of the compressive thermal stress from LNO with a large thermal expansion coefficient. This compressive thermal stress engenders an increase of the Curie temperature. The local piezoelectric response of the BCZT thin film on a LNO/Si structure was measured by piezoresponse force microscope.

  19. Thin film solar cells with Si nanocrystallites embedded in amorphous intrinsic layers by hot-wire chemical vapor deposition.

    PubMed

    Park, Seungil; Parida, Bhaskar; Kim, Keunjoo

    2013-05-01

    We investigated the thin film growths of hydrogenated silicon by hot-wire chemical vapor deposition with different flow rates of SiH4 and H2 mixture ambient and fabricated thin film solar cells by implementing the intrinsic layers to SiC/Si heterojunction p-i-n structures. The film samples showed the different infrared absorption spectra of 2,000 and 2,100 cm(-1), which are corresponding to the chemical bonds of SiH and SiH2, respectively. The a-Si:H sample with the relatively high silane concentration provides the absorption peak of SiH bond, but the microc-Si:H sample with the relatively low silane concentration provides the absorption peak of SiH2 bond as well as SiH bond. Furthermore, the microc-Si:H sample showed the Raman spectral shift of 520 cm(-1) for crystalline phase Si bonds as well as the 480 cm(-1) for the amorphous phase Si bonds. These bonding structures are very consistent with the further analysis of the long-wavelength photoconduction tail and the formation of nanocrystalline Si structures. The microc-Si:H thin film solar cell has the photovoltaic behavior of open circuit voltage similar to crystalline silicon thin film solar cell, indicating that microc-Si:H thin film with the mixed phase of amorphous and nanocrystalline structures show the carrier transportation through the channel of nanocrystallites.

  20. Effect of film thickness on the magneto-structural properties of ion beam sputtered transition metal–metalloid FeCoNbB/Si (100) alloy thin films

    NASA Astrophysics Data System (ADS)

    Gupta, Pooja; Tripathi, Yagyanidhi; Kumar, Dileep; Rai, S. K.; Gupta, Mukul; Reddy, V. R.; Svec, Peter

    2016-08-01

    The structure and magnetic properties of ion beam sputtered transition metal–metalloid FeCoNbB/Si(100) alloy thin film have been studied as a function of film thickness using complementary techniques of x-ray reflectivity (XRR), grazing incidence x-ray diffraction, and magneto optical Kerr effect. Thicknesses of the films range from ∼200 to 1500 Å. The coercivity of all the films ranges between 4 and 14 Oe, which suggests soft magnetic nature of FeCoNbB/Si thin films. Films with thickness up to 800 Å are amorphous in nature and are found to possess uniaxial magnetic anisotropy in the film plane, although no magnetic field was applied during deposition. The presence of the two fold symmetry in such amorphous thin films may be attributed to quenched-in stresses developed during deposition. Upon increasing the film thickness to ∼1200 Å and above, the structure of FeCoNbB films transforms from amorphous to partially nanocrystalline structure and has bcc-FeCo nanocrystalline phase dispersed in remaining amorphous matrix. The crystalline volume fraction (cvf) of the films is found to be proportional to the film thickness. Azimuthal angle dependence of remanence confirms the presence of in-plane four-fold anisotropy (FFA) in the crystalline film with cvf ∼75%. Synchrotron x-ray diffraction measurement using area detector suggests random orientation of crystallites and thus clearly establishes that FFA is not related to texture/cubic symmetry in such polycrystalline thin films. As supported by asymmetric Bragg diffraction measurements, the origin of FFA in such partially crystalline thin film is ascribed to the additional compressive stresses developed in the film upon crystallization. Results indicate that promising soft magnetic properties in such films can be optimized by controlling the film thickness. The revelation of controllable and tunable anisotropy suggests that FeCoNbB thin films can have potential application in electromagnetic applications.

  1. Structural and optical characterization of pure Si-rich nitride thin films

    PubMed Central

    2013-01-01

    The specific dependence of the Si content on the structural and optical properties of O- and H-free Si-rich nitride (SiNx>1.33) thin films deposited by magnetron sputtering is investigated. A semiempirical relation between the composition and the refractive index was found. In the absence of Si-H, N-H, and Si-O vibration modes in the FTIR spectra, the transverse and longitudinal optical (TO-LO) Si-N stretching pair modes could be unambiguously identified using the Berreman effect. With increasing Si content, the LO and the TO bands shifted to lower wavenumbers, and the LO band intensity dropped suggesting that the films became more disordered. Besides, the LO and the TO bands shifted to higher wavenumbers with increasing annealing temperature which may result from the phase separation between Si nanoparticles (Si-np) and the host medium. Indeed, XRD and Raman measurements showed that crystalline Si-np formed upon 1100°C annealing but only for SiNx<0.8. Besides, quantum confinement effects on the Raman peaks of crystalline Si-np, which were observed by HRTEM, were evidenced for Si-np average sizes between 3 and 6 nm. A contrario, visible photoluminescence (PL) was only observed for SiNx>0.9, demonstrating that this PL is not originating from confined states in crystalline Si-np. As an additional proof, the PL was quenched while crystalline Si-np could be formed by laser annealing. Besides, the PL cannot be explained neither by defect states in the bandgap nor by tail to tail recombination. The PL properties of SiNx>0.9 could be then due to a size effect of Si-np but having an amorphous phase. PMID:23324447

  2. Thermal reliability of thin SiGe epilayers

    NASA Astrophysics Data System (ADS)

    Wu, Ming-Jhang; Wen, Hua-Chiang; Chiang, Tun-Yuan; Tsai, Chien-Huang; Hsu, Wen-Kuang; Chou, Chang-Pin

    2012-04-01

    The SiGe heterostructures can play a role that drastically enhances the carrier mobility of SiGe heterodevices, such as strained Si metal oxide semiconductor field effect transistors. However, it is difficult to access the both issues, that is, the propagation of the dislocation and thermal reliability of annealed SiGe films. In this study, we used ultrahigh-vacuum chemical vapor deposition to grow Si0.8Ge0.2 films (ca. 200 nm thick for heteroepitaxy) epitaxially on bulk Si. The samples were subsequently furnace-crystallized at temperatures of 800, 900, and 1000 °C. We used nanoscratch techniques to determine the frictional characteristics of the SiGe epilayers under various ramping loads and employed atomic force microscopy to examine their morphologies after scratching. From our investigation of the pile-up phenomena, we observed significant cracking dominating on both sides of the scratches on the films. The SiGe epilayers films that had undergone annealing treatment possessed lower coefficients of friction, suggesting higher shear resistances.

  3. Polycrystalline photovoltaic cell

    SciTech Connect

    Jordan, J.F.; Lampkin, C.M.

    1983-10-25

    A photovoltaic cell is disclosed, having an electrically conductive substrate, which may be glass having a film of conductive tin oxide; a first layer containing a suitable semiconductor, which layer has a first component film with an amorphous structure and a second component film with a polycrystalline structure; a second layer forming a heterojunction with the first layer; and suitable electrodes where the heterojunction is formed from a solution containing copper, the amorphous film component is superposed above an electrically conductive substrate to resist permeation of the copper-containing material to shorting electrical contact with the substrate. The penetration resistant amorphous layer permits a variety of processes to be used in forming the heterojunction with even very thin layers (1-6 /SUB u/ thick) of underlying polycrystalline semiconductor materials. In some embodiments, the amorphous-like structure may be formed by the addition of aluminum or zirconium compounds to a solution of cadmium salts sprayed over a heated substrate.

  4. Buckling and Delamination of Ti/Cu/Si Thin Film During Annealing

    NASA Astrophysics Data System (ADS)

    Lin, Qijing; Yang, Shuming; Jing, Weixuan; Li, Changsheng; Wang, Chenying; Jiang, Zhuangde; Jiang, Kely

    2014-09-01

    In this paper, the formation of buckling and delamination of sandwiched stacking of Ti/Cu/Si thin film are investigated. The crystallization structures, the composition of the Cu/Ti thin films, and the surface morphology are measured during annealing. The results show that the solid-phase reaction between Cu and Ti occurs at the interface. Buckling is initiated in the thin film annealed at 600°C. The volume expansion promotes the buckling and further produces microcracks. With increasing volume expansion, there are cavities formed in the middle layer when the annealing temperature is up to 700°C. Finally, thin film is delaminated from the substrate.

  5. Patterned Si thin film electrodes for enhancing structural stability.

    PubMed

    Cho, Gyu-Bong; Noh, Jung-Pil; Sung, Ho-Jin; Lee, Sang-Hun; Im, Yeon-Min; Ahn, Hyo-Jun; Kim, Ki-Won

    2012-01-01

    A patterned film (electrode) with lozenge-shaped Si tiles could be successfully fabricated by masking with an expanded metal foil during film deposition. Its electrochemical properties and structural stability during the charge-discharge process were examined and compared with those of a continuous (conventional) film electrode. The patterned electrode exhibited a remarkably improved cycleability (75% capacity retention after 120 cycles) and an enhanced structural stability compared to the continuous electrode. The good electrochemical performance of the patterned electrode was attributed to the space between Si tiles that acted as a buffer against the volume change of the Si electrode. PMID:22221620

  6. Patterned Si thin film electrodes for enhancing structural stability

    NASA Astrophysics Data System (ADS)

    Cho, Gyu-Bong; Noh, Jung-Pil; Sung, Ho-Jin; Lee, Sang-Hun; Im, Yeon-Min; Ahn, Hyo-Jun; Kim, Ki-Won

    2012-01-01

    A patterned film (electrode) with lozenge-shaped Si tiles could be successfully fabricated by masking with an expanded metal foil during film deposition. Its electrochemical properties and structural stability during the charge-discharge process were examined and compared with those of a continuous (conventional) film electrode. The patterned electrode exhibited a remarkably improved cycleability (75% capacity retention after 120 cycles) and an enhanced structural stability compared to the continuous electrode. The good electrochemical performance of the patterned electrode was attributed to the space between Si tiles that acted as a buffer against the volume change of the Si electrode.

  7. Consistency of ZT-Scanner for Thermoelectric Measurements from 300 K to 700 K: A Comparative Analysis Using Si80Ge20 Polycrystalline Alloys

    NASA Astrophysics Data System (ADS)

    Vasilevskiy, D.; Simard, J.-M.; Caillat, T.; Masut, R. A.; Turenne, S.

    2016-03-01

    A Harman-based instrument for the characterization of thermoelectric (TE) materials in a wide temperature range (the ZT-Scanner) was introduced in an earlier publication, with a focus on a two-sample system calibration (2SSC) procedure used for the precise evaluation of thermal losses during the measurements. This technique offers an option to accurately measure the main TE parameters from 300 K to 700 K. We now report the results of ZT-Scanner measurements of p-type Si80Ge20 polycrystalline samples, including the TE figure of merit ZT, Seebeck coefficient, and thermal and electrical conductivities. These samples proved to be extremely stable up to the maximum temperature of measurement, and could eventually serve as a standard for thermoelectric characterization. The measurements were performed using both PbSn solder and conductive silver paste contacts. In all cases, Ni plating was used as a protective barrier between the TE alloys and the contact material. The experimental data has been compared to the typical data measured by the Jet Propulsion Laboratory on similar samples, providing a quantitative estimation of the accuracy of the measurement system, which has been found to be better than 0.015, or 5%, up to 700 K for ZT. The consistency of the TE measurements is evaluated by means of a statistical analysis of repetitive tests on the same and on different samples of identical nature. We also analyze the influence of thermal and electrical contact resistance on the measured properties.

  8. Computational Study of In-Plane Phonon Transport in Si Thin Films

    PubMed Central

    Wang, Xinjiang; Huang, Baoling

    2014-01-01

    We have systematically investigated the in-plane thermal transport in Si thin films using an approach based on the first-principles calculations and lattice dynamics. The effects of phonon mode depletion induced by the phonon confinement and the corresponding variation in interphonon scattering, which may be important for the thermal conductivities of ultra-thin films but are often neglected in precedent studies, are considered in this study. The in-plane thermal conductivities of Si thin films with different thicknesses have been predicted over a temperature range from 80 K to 800 K and excellent agreements with experimental results are found. The validities of adopting the bulk phonon properties and gray approximation of surface specularity in thin film studies have been clarified. It is found that in ultra-thin films, while the phonon depletion will reduce the thermal conductivity of Si thin films, its effect is largely offset by the reduction in the interphonon scattering rate. The contributions of different phonon modes to the thermal transport and isotope effects in Si films with different thicknesses under various temperatures are also analyzed. PMID:25228061

  9. Device physics of thin-film polycrystalline cells and modules: Phase 1 annual report: February 1998--January 1999

    SciTech Connect

    Sites, J. R.

    1999-12-21

    This report describes work done by Colorado State University (CSU) during Phase 1 of this subcontract. CSU researchers continued to make basic measurements on CI(G)S and CdTe solar cells fabricated at different labs, to quantitatively deduce the loss mechanisms in these cells, and to make appropriate comparisons that illuminate where progress is being made. Cells evaluated included the new record CIGS cell, CIS cells made with and without CdS, and those made by electrodeposition and electroless growth from solution. Work on the role of impurities focused on sodium in CIS. Cells with varying amounts of sodium added during CIS deposition were fabricated at NREL using four types of substrates. The best performance was achieved with 10{sup {minus}2}--10{sup {minus}1} at% sodium, and the relative merits of proposed mechanisms for the sodium effect were compared. Researchers also worked on the construction and testing of a fine-focused laser-beam apparatus to measure local variations in polycrystalline cell performance. A 1{micro}m spot was achieved, spatial reproducibility in one and two dimensions is less than 1 {micro}m, and photocurrent is reliably measured when the 1{micro}m spot is reduced as low as 1-sun in intensity. In elevated-temperature stress tests, typical CdTe cells held at 100 C under illumination and normal resistive loads for extended periods of time were generally very stable; but those held under reverse or large forward bias and those contacted using larger amounts of copper were somewhat less stable. CdTe cell modeling produced reasonable fits to experimental data, including variations in back-contact barriers. A major challenge being addressed is the photovoltaic response of a single simple-geometry crystallite with realistic grain boundaries.

  10. [Spectral Characteristics of Si Quantum Dots Embedded in SiN(x) Thin Films Prepared by Magnetron Co-Sputtering].

    PubMed

    Chen, Xiao-bo; Yang, Wen; Duan, Liang-fei; Zhang, Li-yuan; Yang, Pei-zhi; Song, Zhao-ning

    2015-07-01

    The silicon-rich SiN(x) films were fabricated on Si(100) substrate and quartz substrate at different substrate temperatures varying from room temperature to 400 degrees C by bipolar pulse ane RF magnetron co-sputtering deposition technique. After deposition, the films were annealed in a nitrogen atmosphere by rapid photothermal annealing at 1050 degrees C for 3 minutes. This thermal step allows the formation of the silicon quantum dots. Fourier transform infrared spectroscopy, Raman spectroscopy, grazing incidence X-ray diffraction and photoluminescence spectroscopy were used to analyze the bonding configurations, microstructures and luminescence properties of the films. The experimental results showed that: silicon-rich Si-N bonds were found in Fourier transform infrared spectra, suggesting that the silicon-rich SiN, films were successfully prepared; when the substrate temperature was not lower than 200 degrees C, the Raman spectra of the films showed the transverse optical mode of Si-Si vibration, while the significant diffraction peaks of Si(111) and Si(311) were shown in grazing incidence X-ray diffraction spectra, confirming the formation of silicon quantum dots; our work indicated that there was an optimal substrate temperature (300 degrees C), which could significantly increase the amount and the crystalline volume fraction of silicon quantum dots; three visible photoluminescence bands can be obtained for both 30 degrees C sample and 400 degrees C sample, and in combination with Raman results, the emission peaks were reasonably explained by using the quantum confinement effect and radiative recombination defect state of Si nanocrystals; the average size of the silicon quantum dots is 3.5 and 3.4 nm for the 300 degrees C sample and 400 degrees C sample, respectively. These results are useful for optimizing the fabrication parameters of silicon quantum dots embedded in SiN. thin films and have valuable implications for silicon based photoelectric device

  11. [Spectral Characteristics of Si Quantum Dots Embedded in SiN(x) Thin Films Prepared by Magnetron Co-Sputtering].

    PubMed

    Chen, Xiao-bo; Yang, Wen; Duan, Liang-fei; Zhang, Li-yuan; Yang, Pei-zhi; Song, Zhao-ning

    2015-07-01

    The silicon-rich SiN(x) films were fabricated on Si(100) substrate and quartz substrate at different substrate temperatures varying from room temperature to 400 degrees C by bipolar pulse ane RF magnetron co-sputtering deposition technique. After deposition, the films were annealed in a nitrogen atmosphere by rapid photothermal annealing at 1050 degrees C for 3 minutes. This thermal step allows the formation of the silicon quantum dots. Fourier transform infrared spectroscopy, Raman spectroscopy, grazing incidence X-ray diffraction and photoluminescence spectroscopy were used to analyze the bonding configurations, microstructures and luminescence properties of the films. The experimental results showed that: silicon-rich Si-N bonds were found in Fourier transform infrared spectra, suggesting that the silicon-rich SiN, films were successfully prepared; when the substrate temperature was not lower than 200 degrees C, the Raman spectra of the films showed the transverse optical mode of Si-Si vibration, while the significant diffraction peaks of Si(111) and Si(311) were shown in grazing incidence X-ray diffraction spectra, confirming the formation of silicon quantum dots; our work indicated that there was an optimal substrate temperature (300 degrees C), which could significantly increase the amount and the crystalline volume fraction of silicon quantum dots; three visible photoluminescence bands can be obtained for both 30 degrees C sample and 400 degrees C sample, and in combination with Raman results, the emission peaks were reasonably explained by using the quantum confinement effect and radiative recombination defect state of Si nanocrystals; the average size of the silicon quantum dots is 3.5 and 3.4 nm for the 300 degrees C sample and 400 degrees C sample, respectively. These results are useful for optimizing the fabrication parameters of silicon quantum dots embedded in SiN. thin films and have valuable implications for silicon based photoelectric device

  12. Characterizations of evaporated α-Si thin films for MEMS application

    NASA Astrophysics Data System (ADS)

    Jiao, X. Q.; Zhang, R.; Yang, J.; Zhong, H.; Shi, Y.; Chen, X. Y.; Shi, J.

    2014-08-01

    Amorphous silicon (α-Si) thin films are widely used as electrical, optical and mechanical materials mainly synthesized by chemical vapor deposition (CVD) methods such as plasma-enhanced chemical vapor deposition (PECVD) and low pressure chemical vapor deposition. However, the physical vapor deposition ways which are seldom studied may demonstrate a proper choice for the deposition of α-Si thin films as the structural material for micro-electromechanical systems application. One of the CVD methods of e-beam thermal evaporation was used for the deposition of α-Si thin films in this study. All samples of deposited α-Si thin films had smooth surface with the root mean square surface roughness less than 1.6 nm. The α-Si film with a relatively low stress of about 250 MPa was obtained with a film thickness of 500 nm at a deposition rate of 4.7-6.1 Å/s. The film thickness variation of α-Si deposited on a 4 inch white glass had a 0.78 % uniformity. The 150-nm-thick α-Si film showed a good conformality on the patterned 500-nm-thick Mo film and it had a leak current density of 2.8 × 10-3 A/cm2 under a 5 V bias voltage. The film's Young's modulus and hardness were extracted by a nano-indenter with values of 71.6 and 7.9 GPa, respectively. Characteristics of evaporated α-Si films and PECVD α-Si:H films were also compared.

  13. Fracture-induced amorphization of polycrystalline SiO2 stishovite: a potential platform for toughening in ceramics

    PubMed Central

    Nishiyama, Norimasa; Wakai, Fumihiro; Ohfuji, Hiroaki; Tamenori, Yusuke; Murata, Hidenobu; Taniguchi, Takashi; Matsushita, Masafumi; Takahashi, Manabu; Kulik, Eleonora; Yoshida, Kimiko; Wada, Kouhei; Bednarcik, Jozef; Irifune, Tetsuo

    2014-01-01

    Silicon dioxide has eight stable crystalline phases at conditions of the Earth's rocky parts. Many metastable phases including amorphous phases have been known, which indicates the presence of large kinetic barriers. As a consequence, some crystalline silica phases transform to amorphous phases by bypassing the liquid via two different pathways. Here we show a new pathway, a fracture-induced amorphization of stishovite that is a high-pressure polymorph. The amorphization accompanies a huge volume expansion of ~100% and occurs in a thin layer whose thickness from the fracture surface is several tens of nanometers. Amorphous silica materials that look like strings or worms were observed on the fracture surfaces. The amount of amorphous silica near the fracture surfaces is positively correlated with indentation fracture toughness. This result indicates that the fracture-induced amorphization causes toughening of stishovite polycrystals. The fracture-induced solid-state amorphization may provide a potential platform for toughening in ceramics. PMID:25297473

  14. Corrosion resistance of sintered NdFeB coated with SiC/Al bilayer thin films by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Huang, Yiqin; Li, Heqin; Zuo, Min; Tao, Lei; Wang, Wei; Zhang, Jing; Tang, Qiong; Bai, Peiwen

    2016-07-01

    The poor corrosion resistance of sintered NdFeB imposes a great challenge in industrial applications. In this work, the SiC/Al bilayer thin films with the thickness of 510 nm were deposited on sintered NdFeB by magnetron sputtering to improve the corrosion resistance. A 100 nm Al buffer film was used to reduce the internal stress between SiC and NdFeB and improve the surface roughness of the SiC thin film. The morphologies and structures of SiC/Al bilayer thin films and SiC monolayer film were investigated with FESEM, AFM and X-ray diffraction. The corrosion behaviors of sintered NdFeB coated with SiC monolayer film and SiC/Al bilayer thin films were analyzed by polarization curves. The magnetic properties were measured with an ultra-high coercivity permanent magnet pulse tester. The results show that the surface of SiC/Al bilayer thin films is more compact and uniform than that of SiC monolayer film. The corrosion current densities of SiC/Al bilayer films coated on NdFeB in acid, alkali and salt solutions are much lower than that of SiC monolayer film. The SiC/Al bilayer thin films have little influence to the magnetic properties of NdFeB.

  15. Development of Nanosphere Lithography Technique with Enhanced Lithographical Accuracy on Periodic Si Nanostructure for Thin Si Solar Cell Application

    NASA Astrophysics Data System (ADS)

    Choi, Jeayoung

    In this thesis, a novel silica nanosphere (SNS) lithography technique has been developed to offer a fast, cost-effective, and large area applicable nano-lithography approach. The SNS can be easily deposited with a simple spin-coating process after introducing a N,N-dimethyl-formamide (DMF) solvent which can produce a highly close packed SNS monolayer over large silicon (Si) surface area, since DMF offers greatly improved wetting, capillary and convective forces in addition to slow solvent evaporation rate. Since the period and dimension of the surface pattern can be conveniently changed and controlled by introducing a desired size of SNS, and additional SNS size reduction with dry etching process, using SNS for lithography provides a highly effective nano-lithography approach for periodically arrayed nano-/micro-scale surface patterns with a desired dimension and period. Various Si nanostructures ( i.e., nanopillar, nanotip, inverted pyramid, nanohole) are successfully fabricated with the SNS nano-lithography technique by using different etching technique like anisotropic alkaline solution (i.e., KOH) etching, reactive-ion etching (RIE), and metal-assisted chemical etching (MaCE). In this research, computational optical modeling is also introduced to design the Si nanostructure, specifically nanopillars (NPs) with a desired period and dimension. The optical properties of Si NP are calculated with two different optical modeling techniques, which are the rigorous coupled wave analysis (RCWA) and finite-difference time-domain (FDTD) methods. By using these two different optical modeling techniques, the optical properties of Si NPs with different periods and dimensions have been investigated to design ideal Si NP which can be potentially used for thin c-Si solar cell applications. From the results of the computational and experimental work, it was observed that low aspect ratio Si NPs fabricated in a periodic hexagonal array can provide highly enhanced light absorption

  16. CBED and FE Study of Thin Foil Relaxation in Cross-Section Samples of Si /Si1-xGex and Si /Si1-xGex /Si Heterostructures

    NASA Astrophysics Data System (ADS)

    Alexandre, L.; Jurczak, G.; Alfonso, C.; Saikly, W.; Grosjean, C.; Charai, A.; Thibault, J.

    In order to determine residual stress/strain fields in CMOS devices and validate tools used to quantify the strain field, we first studied residual strains in Si/Si1-xGex and Si/Si1-xGex/Si TEM samples. Because of sample thinning for TEM observations, elastic relaxation occurs and modifies the initial stress present in the bulk sample. Nevertheless, if the main parameters which play a role on the elastic relaxation process can be determined, we show that it is possible to reproduce from FE and diffraction simulations the complex profile of the HOLZ lines observed on experimental CBED patterns which makes possible the determination of the initial stress state.

  17. A Optical and Microstructural Characterization Study and Microstructural Model of Co-Evaporated Polycrystalline Thin Film Copper Indium Diselenide for Photovoltaic Applications

    NASA Astrophysics Data System (ADS)

    Tuttle, John R.

    The electrical, optical, microstructural, and morphological properties of polycrystalline thin film CuInSe _2 are investigated by X-Ray Diffraction, spectrophotometry, and Transmission Electron Microscopy as a function of compositional parameters and processing conditions. The film microstructure is redefined as a compositionally and temperature dependent polycrystalline aggregate mixture of CuInSe_2 and Cu_{rm x}Se/In _{rm y}Se minor phases, with a core crystallite exhibiting order-disorder phase separation and a CuInSe_2-CuIn_2 Se_{3.5} solid solution. The secondary phase phenomena includes Cu _{1.85}Se at grain boundaries and free surfaces, with sufficient amount for percolation in near-stoichiometric and Cu-rich compositions, and Cu _{rm x}Se inclusions for Cu-rich compositions, and for Cu-poor compositions at substrate temperatures of 500^circC. The inclusions are modeled by the Maxwell-Garnett theory as metallic inclusions with a filling fraction as little as eta = 0.01. The observed polymorphisms include phase separation of ordered chalcopyrite and disordered sphalerite regions, where the latter is the majority phase, and a solid solution of chalcopyrite CuInSe_2 and the ordered vacancy compound (OVC) CuIn_2Se _{3.5}, with an associated temperature dependent lattice shrinkage proportional to the deviation in molecularity. The polymorphisms reported here are the first in the CuInSe_2 material system. The stability of excessive Cu-vacancies observed in the OVC has significant ramifications on the electronic structure of CuInSe_2. The optical absorption coefficient, alpha , for thin film CuInSe_2 is reported as a function of composition and exhibits behavior indicative of a two-phase mixture and a solid solution for Cu-rich and Cu-poor compositions, respectively. The magnitude of alpha is significantly lower than previously reported values, and is substantiated by device modeling that accurately reproduces the measured internal quantum efficiency of Cd

  18. Superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} thin films on polycrystalline ferrite for magnetically tunable microwave components

    SciTech Connect

    Jia, Q.X.; Findikoglu, A.T.; Arendt, P.; Foltyn, S.R.; Roper, J.M.; Groves, J.R.; Coulter, J.Y.; Li, Y.Q.; Dionne, G.F.

    1998-04-01

    Superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO) thin films with a surface resistance of 0.86 m{Omega} at 10 GHz and 76 K have been grown on polycrystalline ferrite yttrium iron garnet (YIG) substrates. The chemical and structural mismatches between YBCO and YIG are solved by using a double buffer layer of biaxially oriented yttria-stabilized zirconia (YSZ) and CeO{sub 2}, where YSZ is deposited by an ion-beam-assisted-deposition technique. The YBCO films are {ital c} axis oriented with an in-plane mosaic spread [full width at half maximum of an x-ray {phi}-scan on (103) reflection] of less than 8{degree}. The films have a superconductive transition temperature above 88 K with a transition width less than 0.3 K, giving a critical current density above 10{sup 6}A/cm{sup 2} in self field at 75 K. At 75 K in an external magnetic field of 1 T perpendicular to the film surface, the films maintain a critical current density over 2{times}10{sup 5}A/cm{sup 2}. {copyright} {ital 1998 American Institute of Physics.}

  19. Atomic-resolution study of dislocation structures and interfaces in poly-crystalline thin film CdTe using aberration-corrected STEM

    NASA Astrophysics Data System (ADS)

    Paulauskas, Tadas; Colegrove, Eric; Buurma, Chris; Kim, Moon; Klie, Robert

    2014-03-01

    Commercial success of CdTe-based thin film photovoltaic devices stems from its nearly ideal direct band gap which very effectively couples to Sun's light spectrum as well as ease of manufacturing and low cost of these modules. However, to further improve the conversion efficiency beyond 20 percent, it is important to minimize the harmful effects of grain boundaries and lattice defects in CdTe. Direct atomic-scale characterization is needed in order identify the carrier recombination centers. Likewise, it is necessary to confirm that passivants in CdTe, such as Cl, are able to diffuse and bind to the target defects. In this study, we characterize dislocation structures and grain boundaries in poly-crystalline CdTe using aberration-corrected cold-field emission scanning transmission electron microscopy (STEM). The chemical composition of Shockley partial, Frank and Lomer-Cottrell dislocations is examined via atomic column-resolved X-ray energy dispersive (XEDS) and electron energy-loss spectroscopies (EELS). Segregation of Cl towards dislocation cores and grain boundaries is shown in CdCl2 treated samples. We also investigate interfaces in ultra-high-vacuum bonded CdTe bi-crystals with pre-defined misorientation angles which are intended to mimic grain boundaries. Funded by: DOE EERE Sunshot Award EE0005956.

  20. Study on the optical property of P-C doped a-Si:H thin films

    NASA Astrophysics Data System (ADS)

    Cai, Haihong; Li, Wei; Jiang, Yadong; Gong, Yuguang; Li, Zhi

    2009-11-01

    Hydrogenated amorphous silicon (a-Si:H) thin films doped with Phosphorus (P) and Carbon (C) were deposited by plasma enhanced chemical vapor deposition (PECVD). The influence of carbon on the optical property and the content of hydrogen and carbon in the P-doped a-Si:H films were investigated by means of X-ray photoelectron spectroscopy, spectroscopic ellipsometry and Fourier-transform infrared spectroscopy, respectively. The results show that the C-Si bonds in the P-C doped a-Si:H thin films can be observed clearly, and the content of hydrogen and carbon as well as the optical band gap increases with increasing CH4 gas flow rate, but the refractive index decreases with increasing CH4 gas flow rate in the CVD chamber.

  1. Optical properties of Yb-doped Y 2SiO 5 thin films

    NASA Astrophysics Data System (ADS)

    Denoyer, A.; Jandl, S.; Viana, B.; Guillot-Noël, O.; Goldner, P.; Pelenc, D.; Thibault, F.

    2007-11-01

    Yb-doped Y2SiO5 thin films Raman active phonons and crystal-field (CF) excitations have been studied by Raman spectroscopy and infrared transmission, and compared to the single crystals results. The thin films, grown on Y2SiO5 undoped substrate, have been co-doped with Ge, Gd or La in order to adjust the lattice mismatch. Raman active phonon bandwidths indicate that thin films present less strains and defects than single crystals. Interesting thin films properties, such as Yb3+ site occupancies and Yb3+-Yb3+ pair interaction types, may be adjusted by the co-dopants. Infrared absorption shows notably that La3+ is a good co-doping ion to enhance selectively one of the two Yb sites and pair satellite contributions. Ge and Gd co-dopants may also be used to form independently Yb3+-Yb3+ ion pairs with either ferromagnetic or antiferromagnetic dominant interactions.

  2. Texture and Magnetic Properties of Rolled Fe-6.5 wt.%Si Thin Sheets

    NASA Astrophysics Data System (ADS)

    Yao, Y. C.; Sha, Y. H.; Liu, J. L.; Zhang, F.; Zuo, L.

    2014-01-01

    Thin (0.20 mm) Fe-6.5 wt.%Si sheets have been successfully fabricated by the continuous rolling method. The designed rolling process parameters, including the initial hot-band grain size, grain size after intermediate annealing, cold rolling reduction, and cold rolling temperature, were selected to control the texture development. Dominant recrystallization η fiber [rolling direction (RD)//] was achieved after high-temperature annealing. The produced Fe-6.5 wt.%Si thin sheets are promising alternatives for use in power electronics because of their magnetic properties from 400 Hz to 40 kHz.

  3. Features of the magnetic properties of Co/Si/Co thin-film systems

    NASA Astrophysics Data System (ADS)

    Shalygina, E. E.; Kharlamova, A. M.; Rozhnovskaya, A. A.; Kurlyandskaya, G. V.; Svalov, A. V.

    2013-12-01

    The magnetic properties of Co/Si/Co thin-film structures grown by magnetron sputtering have been studied using magnetooptical techniques. It is established that the saturation field ( H S) of trilayers exhibits oscillations as a function of the thickness of the semiconductor (silicon) interlayer. This behavior is explained by structural features of the Co/Si/Co system and the presence of antiferromagnetic exchange coupling between magnetic layers via the silicon interlayer.

  4. Epitaxial Cu{sub 2}ZnSnS{sub 4} thin film on Si (111) 4° substrate

    SciTech Connect

    Song, Ning; Liu, Fangyang; Huang, Yidan; Hao, Xiaojing E-mail: xj.hao@unsw.edu.au; Green, Martin A.; Young, Matthew; Erslev, Pete; Harvey, Steven P.; Teeter, Glenn E-mail: xj.hao@unsw.edu.au; Wilson, Samual

    2015-06-22

    To explore the possibility of Cu{sub 2}ZnSnS{sub 4} (CZTS)/Si based tandem solar cells, the heteroepitaxy of tetragonal Cu{sub 2}ZnSnS{sub 4} thin films on single crystalline cubic Si (111) wafers with 4° miscut is obtained by molecular beam epitaxy. The X-ray θ-2θ scan and selected area diffraction patterns of the CZTS thin films and Si substrates, and the high resolution transmission electron microscopy image of the CZTS/Si interface region demonstrate that the CZTS thin films are epitaxially grown on the Si substrates. A CZTS/Si P-N junction is formed and shows photovoltaic responses, indicating the promising application of epitaxial CZTS thin films on Si.

  5. Structure and optical properties of aSiAl and aSiAlHx magnetron sputtered thin films

    NASA Astrophysics Data System (ADS)

    Thøgersen, Annett; Stange, Marit; Jensen, Ingvild J. T.; Røyset, Arne; Ulyashin, Alexander; Diplas, Spyros

    2016-03-01

    Thin films of homogeneous mixture of amorphous silicon and aluminum were produced with magnetron sputtering using 2-phase Al-Si targets. The films exhibited variable compositions, with and without the presence of hydrogen, aSi1-xAlx and aSi1-xAlxHy. The structure and optical properties of the films were investigated using transmission electron microscopy, X-ray photoelectron spectroscopy, UV-VisNIR spectrometry, ellipsometry, and atomistic modeling. We studied the effect of alloying aSi with Al (within the range 0-25 at. %) on the optical band gap, refractive index, transmission, and absorption. Alloying aSi with Al resulted in a non-transparent film with a low band gap (<1 eV). Hydrogenation of the films increased the band gap to values >1 eV. Variations of the Al and hydrogen content allowed for tuning of the optoelectronic properties. The films are stable up to a temperature of 300 °C. At this temperature, we observed Al induced crystallization of the amorphous silicon and the presence of large Al particles in a crystalline Si matrix.

  6. Growth of Si thin film on 6H-SiC(0001)

    NASA Astrophysics Data System (ADS)

    Wu, Hsin-Ju; Hoang, M. Tien; Li, Yuntao; First, Phillip N.

    2015-03-01

    Graphene is much studied for its unusual electronic properties. Other carbon group elements such as silicon (Si) and germanium (Ge) also are predicted to have stable 2D phases for which the electronic structure and properties could be still more interesting. Silicon carbide, already an excellent insulating substrate for epitaxial graphene, could potentially play a similar role for silicene. Commonalities in the substrate and processing may lead to the integration of carbon and silicon technologies. Here, we use surface analysis techniques (LEED, AES, STM) to investigate the formation of 2D Si on SiC(0001), under low pressures of silane or silicon. Similar methods allow control of surface graphene growth by compensating Si desorption from SiC. Among several Si-rich reconstructions, we find a single stable hexagonal phase, at a coverage close to twice the Si density predicted for silicene, and with a unit cell consistent with a commensurate layer of silicene or silicane. For a graphitized SiC starting surface, silane is shown to etch graphene, reforming SiC. Work supported in part by NSF (DMR-1106131, DMR-0820382 [MRSEC]).

  7. Si (211) substrate thinning technology for HgCdTe focal plane arrays on Si substrates

    NASA Astrophysics Data System (ADS)

    Zhang, Shan; Wang, Chenfei; Cao, Juying; Hu, Xiaoning

    2010-10-01

    A wet chemical etching method for (211)Si substrates was demonstrated in this paper. The morphologies and cleanness of (211) Si surface etched in different mixture ratio HF-HNO3-HAC solutions have been studied by using optical microscope and the surface profile measuring system (SPMS). The analysis of the surface images indicated that the Si etched by the HF-HNO3-HAC (2:15:5) has the smoother surface, and the wet chemical etching can effectively eliminate the damage introduced by the chemo-mechanical polishing. An auto wet chemical etching agitator which can move in the vertical orientation was used. The wet chemical etching rate of (211) Si was obtained in the room temperature and the transmitted spectra of (211) Si with different thickness were measured by Fourier Transform Infrared Spectroscopy (FTIR) and compared. It is confirmed that the Si with different thickness make no difference to the spectral response in mid-wave. By using this novel technology, the Si substrate of HgCdTe/Si detector was removed completely with the HF-HNO3- HAC (2:15:5) solution. It is obvious that the wet chemical etching method can remove the (211) Si substrates with no damage and detector can work better.

  8. Surface Modification of Polycrystalline Cu(In,Ga)Se2 Thin-Film Solar Cell Absorber Surfaces for PEEM Measurements

    SciTech Connect

    Wilks, R. G.; Contreras, M. A.; Lehmann, S.; Herrero-Albillos, J.; Bismaths, L. T.; Kronast, F.; Noufi, R.; Bar, M.

    2011-01-01

    We present a thorough examination of the {micro}m-scale topography of Cu(In, Ga)Se{sub 2} ('CIGSe') thin-film solar cell absorbers using different microscopy techniques. We specifically focus on the efficacy of preparing smooth sample surfaces - by etching in aqueous bromine solution - for a spatially resolved study of their chemical and electronic structures using photoelectron emission microscopy (PEEM). The etching procedure is shown to reduce the CIGSe surface roughness from ca. 40 to 25 nm after 40s etching, resulting in an increase in the quality of the obtained PEEM images. Furthermore we find that the average observed grain size at the etched surfaces appears larger than at the unetched surfaces. Using a liftoff procedure, it is additionally shown that the backside of the absorber is flat but finely patterned, likely due to being grown on the finely-structured Mo back contact.

  9. The effect of Ta doping in polycrystalline TiO{sub x} and the associated thin film transistor properties

    SciTech Connect

    Ok, Kyung-Chul Park, Yoseb Park, Jin-Seong E-mail: jsparklime@hanyang.ac.kr; Chung, Kwun-Bum E-mail: jsparklime@hanyang.ac.kr

    2013-11-18

    Tantalum (Ta) is suggested to act as an electron donor and crystal phase stabilizer in titanium oxide (TiO{sub x}). A transition occurs from an amorphous state to a crystalline phase at an annealing temperature above 300 °C in a vacuum ambient. As the annealing temperature increases from 300 °C to 450 °C, the mobility increases drastically from 0.07 cm{sup 2}/Vs to 0.61 cm{sup 2}/Vs. The remarkable enhancement of thin film transistor performance is suggested to be due to the splitting of Ti 3d band orbitals as well as the increase in Ta{sup 5+} ions that can act as electron donors.

  10. Symmetry dependent optoelectronic properties of grain boundaries in polycrystalline Cu(In,Ga)Se{sub 2} thin films

    SciTech Connect

    Müller, Mathias; Bertram, Frank; Christen, Jürgen; Abou-Ras, Daniel Rissom, Thorsten

    2014-01-14

    In a correlative study applying electron backscatter diffraction as well as spatially and spectrally resolved cathodoluminescence spectroscopy at low temperatures of about 5 K, the symmetry-dependent optoelectronic properties of grain boundaries in Cu(In,Ga)Se{sub 2} thin films have been investigated. We find that grain boundaries with lower symmetries tend to show a distinct spectral red shift of about 10 meV and a weak influence on the emission intensity. These behaviors are not detected at high-symmetry Σ3 grain boundaries, or at least in a strongly reduced way. The investigations in the present work help to clarify the ambivalent properties reported for grain boundaries in Cu(In,Ga)Se{sub 2}.

  11. Optoelectronic characterization of wide-bandgap (AgCu)(InGa)Se 2 thin-film polycrystalline solar cells including the role of the intrinsic zinc oxide layer

    NASA Astrophysics Data System (ADS)

    Obahiagbon, Uwadiae

    Experiments and simulations were conducted to vary the thickness and the sheet resistance of the high resistance (HR) ZnO layer in polycrystalline thin film (AgCu)(GaIn)Se2 (ACIGS) solar cells. The effect of varying these parameters on the electric field distribution, depletion width and hence capacitance were studied by SCAPS simulation. Devices were then fabricated and characterized by a number of optoelectronic techniques. Thin film CIGS has received a lot of attention, for its use as an absorber layer for thin film solar cells. However, the addition of Silver (Ag) to the CIGS alloy system increases the band gap as indicated from optical transmission measurements and thus higher open circuit voltage (Voc) could be obtained. Furthermore, addition of Ag lowers the melting temperature of the alloy and it is expected that this lowers the defect densities in the absorber and thus leads to higher performance. Transient photocapacitance analysis on ACIGS devices shows sharper band edge indicating lower disorder than CIGS. Presently there is a lack of fundamental knowledge relating film characteristics to device properties and performance. This is due to the fact that some features in the present solar cell structure have been optimized empirically. The goal of this research effort was to develop a fundamental and detailed understanding of the device operation as well as the loss mechanism(s) limiting these devices. Recombination mechanisms in finished ACIGS solar cell devices was studied using advanced admittance techniques (AS, DLCP, CV) to identify electronically active defect state(s) and to study their impact on electronic properties and device performance. Analysis of various optoelectronic measurements of ACIGS solar cells provided useful feedback regarding the impact on device performance of the HR ZnO layer. It was found that thickness between 10-100 nm had negligible impact on performance but reducing the thickness to 0 nm resulted in huge variability in all

  12. Optical properties of CdS{sub x}Te{sub 1{minus}x} polycrystalline thin films

    SciTech Connect

    Wood, D.A.; Lane, D.W.; Rogers, K.D.; Coath, J.A.

    1999-11-12

    Thin films of CdS{sub x}Te{sub 1{minus}x} (0 {le} x {le} 1) have been prepared by vacuum evaporation from solid solutions. Rutherford backscattering spectrometry has been used to determine the thickness of the films, which is in the range 8--50 nm, and x-ray diffraction analysis has been used to determine the phase. The refractive index and extinction coefficient of the films has been calculated from reflectance and transmittance measurements for the wavelength region 250--3,200 nm. Polynomial functions are given for each sample, which describe the variation in refractive index and extinction coefficient over the entire wavelength range. Least squares fitting to the absorption spectra revealed that the films all have a direct band gap, although photon energies required for indirect transitions have also been found. CdS{sub 0.8}Te{sub 0.2} is found to have the lowest absorption coefficient at energies greater than 2.1 eV.

  13. Linear and nonlinear optical investigations of nano-scale Si-doped ZnO thin films: spectroscopic approach

    NASA Astrophysics Data System (ADS)

    Jilani, Asim; Abdel-wahab, M. Sh.; Zahran, H. Y.; Yahia, I. S.; Al-Ghamdi, Attieh A.

    2016-09-01

    Pure and Si-doped ZnO (SZO) thin films at different concentration of Si (1.9 and 2.4 wt%) were deposited on highly cleaned glass substrate by radio frequency (DC/RF) magnetron sputtering. The morphological and structural investigations have been performed by atomic force electron microscope (AFM) and X-ray diffraction (XRD). The X-ray photoelectron spectroscopy was employed to study the composition and the change in the chemical state of Si-doped ZnO thin films. The optical observations like transmittance, energy band gap, extinction coefficient, refractive index, dielectric loss of pure and Si-doped ZnO thin films have been calculated. The linear optical susceptibility, nonlinear refractive index, and nonlinear optical susceptibility were also studied by the spectroscopic approach rather than conventional Z-scan method. The energy gap of Si-doped ZnO thin films was found to increase as compared to pure ZnO thin films. The crystallinity of the ZnO thin films was effected by the Si doping. The O1s spectra in pure and Si-doped ZnO revealed the bound between O-2 and Zn+2 ions and reduction in the surface oxygen with the Si doping. The chemical state analysis of Si 2p showed the conversation of Si to SiOx and SiO2. The increase in the first-order linear optical susceptibility χ (1) and third-order nonlinear optical susceptibility χ (3) was observed with the Si doping. The nonlinear studies gave some details about the applications of metal oxides in nonlinear optical devices. In short, this study showed that Si doping through sputtering has effected on the structural, surface and optical properties of ZnO thin films which could be quite useful for advanced applications such as metal-oxide-based optical devices.

  14. Conformal Thin Film Packaging for SiC Sensor Circuits in Harsh Environments

    NASA Technical Reports Server (NTRS)

    Scardelletti, Maximilian C.; Karnick, David A.; Ponchak, George E.; Zorman, Christian A.

    2011-01-01

    In this investigation sputtered silicon carbide annealed at 300 C for one hour is used as a conformal thin film package. A RF magnetron sputterer was used to deposit 500 nm silicon carbide films on gold metal structures on alumina wafers. To determine the reliability and resistance to immersion in harsh environments, samples were submerged in gold etchant for 24 hours, in BOE for 24 hours, and in an O2 plasma etch for one hour. The adhesion strength of the thin film was measured by a pull test before and after the chemical immersion, which indicated that the film has an adhesion strength better than 10(exp 8) N/m2; this is similar to the adhesion of the gold layer to the alumina wafer. MIM capacitors are used to determine the dielectric constant, which is dependent on the SiC anneal temperature. Finally, to demonstrate that the SiC, conformal, thin film may be used to package RF circuits and sensors, an LC resonator circuit was fabricated and tested with and without the conformal SiC thin film packaging. The results indicate that the SiC coating adds no appreciable degradation to the circuits RF performance. Index Terms Sputter, silicon carbide, MIM capacitors, LC resonators, gold etchants, BOE, O2 plasma

  15. Investigations of ultra-thin single layer a-Si:H films

    SciTech Connect

    Koehler, S.A.

    1997-07-01

    Measurements are presented as direct evidence of tail states in ultra-thin a-Si:H single layer films. Including tail states in computer simulations completely removes the staircase structure in the differential optical spectra, previously associated with the quantum confinement of carriers.

  16. Photovoltaic performance of Gallium-doped ZnO thin film/Si nanowires heterojunction diodes

    NASA Astrophysics Data System (ADS)

    Akgul, Guvenc; Aksoy Akgul, Funda; Emrah Unalan, Husnu; Turan, Rasit

    2016-04-01

    In this work, photovoltaic performance of Ga-doped ZnO thin film/Si NWs heterojunction diodes was investigated. Highly dense and vertically well-aligned Si NW arrays were successfully synthesised on a p-type (1 0 0)-oriented Si wafer through cost-effective metal-assisted chemical etching technique. Ga-doped ZnO thin films were deposited onto Si NWs via radio frequency magnetron sputtering to construct three-dimensional heterostructures. Photovoltaic characteristics of the fabricated diodes were determined with current density (J)-voltage (V) measurements under simulated solar irradiation of AM 1.5 G. The optimal open-circuit voltage, short-circuit current density, fill factor and power conversion efficiency were found to be 0.37 V, 3.30 mA cm-2, 39.00 and 0.62%, respectively. Moreover, photovoltaic diodes exhibited relatively high external quantum efficiency over the broadband wavelengths between 350 and 1100 nm interval of the spectrum. The observed photovoltaic performance in this study clearly indicates that the investigated device structure composed of Ga-doped ZnO thin film/Si NWs heterojunctions could facilitate an alternative pathway for optoelectronic applications in future, and be a promising alternative candidate for high-performance low-cost new-generation photovoltaic diodes.

  17. Charge trapping phenomena of tetraethylorthosilicate thin film containing Si nanocrystals synthesized by solid-state reaction.

    PubMed

    Lau, H W; Tan, O K; Liu, Y; Trigg, D A; Chen, T P

    2006-08-28

    In this work, we report on the fabrication of tetraethylorthosilicate (TEOS) thin dielectric film containing silicon nanocrystals (Si nc), synthesized by solid-state reaction, in a capacitor structure. A metal-insulator-semi-conductor (MIS) capacitor, with 28 nm thick Si nc in a TEOS thin film, has been fabricated. For this MIS, both electron and hole trapping in the Si nc are possible, depending on the polarity of the bias voltage. A V(FB) shift greater than 1 V can be experienced by a bias voltage of 16 V applied to the metal electrode for 1 s. Though there is no top control oxide, the discharge time for 10% of charges can be up to 4480 s when it is biased at 16 V for 1 s. It is further demonstrated that charging and discharging mechanisms are due to the Si nc rather than the TEOS oxide defects. This form of Si nc in a TEOS thin film capacitor provides the possibility of memory applications at low cost.

  18. Si-SiGe hetero-structure thin-film solar cells using integrated electro-optical modeling

    NASA Astrophysics Data System (ADS)

    Khizar, Muhammad; Mei, Dongming

    2012-02-01

    Hetrostructure Si-SiGe thin film solar cells have been designed and optimized using advance electro-optical theoretical modeling and simulation. Some of the key characteristics such as short-circuit current density (Jsc), open circuit voltage (Voc), and fill factor (FF) have been studied for varying concentration of Ge in SiGe buffer layer. The effect of thickness variation of alloyed layer for varying Ge composition ˜0.1---10% has been performed. The improvement in the conversion efficiency of these cells was calculating by tailoring the thickness of p+ doped layer. An approach relying on phenomena of improved absorption of the alloys which leads to a gain in the current was explored. Improved infrared response with higher short circuit current has been obtained for about 25 μm thick structures. With the optimized Ge concentration, and the incorporated structure design parameters, as much as 4-6% enhancement in the overall efficiency of the solar cells has been calculated compared to that of the conventional single crystal Si solar cells. Moreover, the efficiency of these cells can further be improved because Si-SiGe based solar cells have improved absorption characteristics and offer minimum operating temperature sensitivity. It is believed that with better understanding of the band-gap engineering of SiGe when used as buffer and junction layers, the overall conversion efficiency of such devices can further be improved and could play a critical role to develop low cost and high efficiency solar cells technology. This work is supported by DOE grant DE-FG02-10ER46709 and the state of South Dakota.

  19. Polycrystalline semiconductor processing

    DOEpatents

    Glaeser, Andreas M.; Haggerty, John S.; Danforth, Stephen C.

    1983-01-01

    A process for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by imgingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step.

  20. Polycrystalline semiconductor processing

    DOEpatents

    Glaeser, A.M.; Haggerty, J.S.; Danforth, S.C.

    1983-04-05

    A process is described for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by impingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step. 10 figs.

  1. Sulfur evaporation and magnetic induction in thin-gauged 3%Si-Fe sheets

    SciTech Connect

    Heo, N.H.; Kim, M.T.; Chai, K.H.; Na, J.G.; Woo, J.S.

    1999-04-09

    Singly oriented 3%Si-Fe is one of the most popular soft magnetic materials. Used as the core material of pole and power transformers, it is highly oriented to (110)[001] Goss texture and has one direction of easy magnetization in the rolling plane. The formation mechanism of Goss texture in thin-gauged 3%Si-Fe sheets can be explained by considering the influence of impurities (especially, sulfur) on the surface energy of (110) and other planes. It is the purpose of this study to investigate the effect of sulfur evaporation on the magnetic induction in thin-gauged 3%Si-Fe sheets by prolonged holding of silicon-iron melts or by annealing of hot-rolled plates.

  2. Correlation between structural, magnetic and transport properties of Co2FeSi thin films

    NASA Astrophysics Data System (ADS)

    Krishna Hazra, Binoy; Manivel Raja, M.; Srinath, S.

    2016-02-01

    Co2FeSi thin films are grown on a Si (1 0 0) substrate using ultrahigh-vacuum magnetron sputtering at different substrate temperatures from 300 °C to 550 °C. The films are characterized using grazing incidence x-ray diffraction, magnetization, and ferromagnetic resonance and temperature-dependent resistivity measurements. The films deposited at 450 °C (TS450) have better magnetic as well as structural properties with the minimum disorder. The temperature dependence of line-width (Δ H ) suggests two-magnon scattering is responsible for the line broadening. The correlation between the disorder and extrinsic broadening of the line-width is brought out clearly for the first time in Co2FeSi thin films. TS450 film has minimum Δ H (33 Oe) and Gilbert damping parameter (α  =  0.005) at room temperature making it ideal for spintronic applications.

  3. Electrical and optical properties of Ta-Si-N thin films deposited by reactive magnetron sputtering

    SciTech Connect

    Oezer, D.; Sanjines, R.; Ramirez, G.; Rodil, S. E.

    2012-12-01

    The electrical and optical properties of Ta{sub x}Si{sub y}N{sub z} thin films deposited by reactive magnetron sputtering from individual Ta and Si targets were studied in order to investigate the effects of nitrogen and silicon contents on both properties and their correlation to the film microstructure. Three sets of fcc-Ta{sub x}Si{sub y}N{sub z} thin films were prepared: sub-stoichiometric Ta{sub x}Si{sub y}N{sub 0.44}, nearly stoichiometric Ta{sub x}Si{sub y}N{sub 0.5}, and over-stoichiometric Ta{sub x}Si{sub y}N{sub 0.56}. The optical properties were investigated by near-normal-incidence reflectivity and ellipsometric measurements in the optical energy range from 0.375 eV to 6.8 eV, while the d.c. electrical resistivity was measured in the van der Pauw configuration from 20 K to 300 K. The optical and electrical measurements were interpreted using the standard Drude-Lorentz model and the so-called grain boundary scattering model, respectively. The electronic properties were closely correlated with the compositional and structural modifications of the Ta{sub x}Si{sub y}N{sub z} films due to variations in the stoichiometry of the fcc-TaN{sub z} system and the addition of Si atoms. According to the nitrogen and silicon contents, fcc-Ta{sub x}Si{sub y}N{sub z} films can exhibit room temperature resistivity values ranging from 10{sup 2} {mu}{Omega} cm to about 6 Multiplication-Sign 10{sup 4} {mu}{Omega} cm. The interpretation of the experimental temperature-dependent resistivity data within the Grain Boundary Scattering model, combined with the results from optical investigations, showed that the mean electron transmission probability G and the free carriers concentration, N, are the main parameters that control the transport properties of these films. The results indicated that the correlation between electrical and optical measurements with the chemical composition and the nanostructure of the Ta{sub x}Si{sub y}N{sub z} thin films provides a pertinent and

  4. Self-consistent modelling of X-ray photoelectron spectra from air-exposed polycrystalline TiN thin films

    NASA Astrophysics Data System (ADS)

    Greczynski, G.; Hultman, L.

    2016-11-01

    We present first self-consistent modelling of x-ray photoelectron spectroscopy (XPS) Ti 2p, N 1s, O 1s, and C 1s core level spectra with a cross-peak quantitative agreement for a series of TiN thin films grown by dc magnetron sputtering and oxidized to different extent by varying the venting temperature Tv of the vacuum chamber before removing the deposited samples. So-obtained film series constitute a model case for XPS application studies, where certain degree of atmosphere exposure during sample transfer to the XPS instrument is unavoidable. The challenge is to extract information about surface chemistry without invoking destructive pre-cleaning with noble gas ions. All TiN surfaces are thus analyzed in the as-received state by XPS using monochromatic Al Kα radiation (hν = 1486.6 eV). Details of line shapes and relative peak areas obtained from deconvolution of the reference Ti 2p and N 1 s spectra representative of a native TiN surface serve as an input to model complex core level signals from air-exposed surfaces, where contributions from oxides and oxynitrides make the task very challenging considering the influence of the whole deposition process at hand. The essential part of the presented approach is that the deconvolution process is not only guided by the comparison to the reference binding energy values that often show large spread, but in order to increase reliability of the extracted chemical information the requirement for both qualitative and quantitative self-consistency between component peaks belonging to the same chemical species is imposed across all core-level spectra (including often neglected O 1s and C 1s signals). The relative ratios between contributions from different chemical species vary as a function of Tv presenting a self-consistency check for our model. We propose that the cross-peak self-consistency should be a prerequisite for reliable XPS peak modelling as it enhances credibility of obtained chemical information, while relying

  5. Thin SiGe virtual substrates for Ge heterostructures integration on silicon

    SciTech Connect

    Cecchi, S. Chrastina, D.; Frigerio, J.; Isella, G.; Gatti, E.; Guzzi, M.; Müller Gubler, E.; Paul, D. J.

    2014-03-07

    The possibility to reduce the thickness of the SiGe virtual substrate, required for the integration of Ge heterostructures on Si, without heavily affecting the crystal quality is becoming fundamental in several applications. In this work, we present 1 μm thick Si{sub 1−x}Ge{sub x} buffers (with x > 0.7) having different designs which could be suitable for applications requiring a thin virtual substrate. The rationale is to reduce the lattice mismatch at the interface with the Si substrate by introducing composition steps and/or partial grading. The relatively low growth temperature (475 °C) makes this approach appealing for complementary metal-oxide-semiconductor integration. For all the investigated designs, a reduction of the threading dislocation density compared to constant composition Si{sub 1−x}Ge{sub x} layers was observed. The best buffer in terms of defects reduction was used as a virtual substrate for the deposition of a Ge/SiGe multiple quantum well structure. Room temperature optical absorption and photoluminescence analysis performed on nominally identical quantum wells grown on both a thick graded virtual substrate and the selected thin buffer demonstrates a comparable optical quality, confirming the effectiveness of the proposed approach.

  6. Optimal design of light trapping in thin-film solar cells enhanced with graded SiNx and SiOxNy structure.

    PubMed

    Zhao, Yongxiang; Chen, Fei; Shen, Qiang; Zhang, Lianmeng

    2012-05-01

    In this paper, a graded SiNx and SiOxNy structure is proposed as antireflection coatings deposited on top of amorphous silicon (α-Si) thin-film solar cell. The structural parameters are optimized by differential evolution in order to enhance the optical absorption of solar cells to the greatest degree. The optimal design result demonstrates that the nonlinear profile of dielectric constant is superior to the linear profile, and discrete multilayer graded antireflection coatings can outperform near continuously graded antireflection coatings. What's more, the electric field intensity distributions clearly demonstrate the proposed graded SiNx and SiOxNy structure can remarkably increase the magnitude of electric field of a-Si:H layer and hence, enhance the light trapping of a-Si:H thin-film solar cells in the whole visible and near-infrared spectrum. Finally, we have compared the optical absorption enhancements of proposed graded SiNx and SiOxNy structure with nanoparticles structure, and demonstrated that it can result in higher enhancements compared to the dielectric SiC and TiO2 nanoparticles. We have shown that the optimal graded SiNx and SiOxNy structure optimized by differential evolution can reach 33.31% enhancement which has exceeded the ideal limit of 32% of nanoparticles structure including plasmonic Ag nanoparticles, dielectric SiC and TiO2 nanoparticles. PMID:22565735

  7. Optimal design of light trapping in thin-film solar cells enhanced with graded SiNx and SiOxNy structure.

    PubMed

    Zhao, Yongxiang; Chen, Fei; Shen, Qiang; Zhang, Lianmeng

    2012-05-01

    In this paper, a graded SiNx and SiOxNy structure is proposed as antireflection coatings deposited on top of amorphous silicon (α-Si) thin-film solar cell. The structural parameters are optimized by differential evolution in order to enhance the optical absorption of solar cells to the greatest degree. The optimal design result demonstrates that the nonlinear profile of dielectric constant is superior to the linear profile, and discrete multilayer graded antireflection coatings can outperform near continuously graded antireflection coatings. What's more, the electric field intensity distributions clearly demonstrate the proposed graded SiNx and SiOxNy structure can remarkably increase the magnitude of electric field of a-Si:H layer and hence, enhance the light trapping of a-Si:H thin-film solar cells in the whole visible and near-infrared spectrum. Finally, we have compared the optical absorption enhancements of proposed graded SiNx and SiOxNy structure with nanoparticles structure, and demonstrated that it can result in higher enhancements compared to the dielectric SiC and TiO2 nanoparticles. We have shown that the optimal graded SiNx and SiOxNy structure optimized by differential evolution can reach 33.31% enhancement which has exceeded the ideal limit of 32% of nanoparticles structure including plasmonic Ag nanoparticles, dielectric SiC and TiO2 nanoparticles.

  8. Bi4Si3O12 thin films for scintillator applications

    NASA Astrophysics Data System (ADS)

    Rincón-López, J. A.; Fernández-Benavides, D. A.; Giraldo-Betancur, A. L.; Cruz-Muñoz, B.; Riascos, H.; Muñoz-Saldaña, J.

    2016-04-01

    Bismuth silicate Bi4Si3O12 or BSO thin films were synthesized by pulsed laser deposition and a subsequent annealing treatment from a Bi-Fe-O and compared with films obtained with a pure Bi2O3 target. Bi-Fe-O amorphous thin films of different thicknesses were deposited on silicon substrates at room temperature and subsequently heat treated at 800 °C at different times to study the phase transformations, keeping in all steps a constant oxygen atmosphere. After annealing, Bi-Si-O crystalline phases are formed in all cases with different synthesis kinetics. The Bi-Fe-O target clearly increases the synthesis kinetic of a textured BSO phase having a dissociation and precipitation of homogeneously distributed Fe2O3 particles in the BSO matrix. The key aspects to obtain the Bi4Si3O12 stoichiometric phase are both the film thickness and the heat treatment time to allow the reaction between the Bi2O3 from the target and the SiO2 obtained after the oxidation of the substrate. A deposition time of Bi-Fe-O for 120 and 30 min annealing fulfills the conditions to obtain the Bi4Si3O12 stoichiometric composition and thus scintillation performance. The scintillation properties were measured by a fluorescence spectrophotometry. The stoichiometric Bi4Si3O12 samples show that under 260 nm excitation the material exhibits a peak emission at 466.6 nm. These Bi4Si3O12 thin films crystallize in eulytite phase with cubic structure (a = b = c = 10.291 Å). The phase content was obtained by Rietveld analysis of X-ray diffraction patterns.

  9. Adhesion of ZrN and SiC thin films on titanium and nickel alloys

    SciTech Connect

    Gruss, K.A.; James, R.D.; Davis, R.F.

    1996-12-31

    Chemically inert ceramic coatings are currently being investigated to extend the lifetime of metallic components operating in severe environments. Polycrystalline ZrN and amorphous SiC coatings were deposited by cathodic arc evaporation and by PACVD, respectively, on Titanium Grade 12 and Incoloy 825 metal substrates. The structure of the coatings was verified by SEM and XRD. Residual stress analyses were performed on the ZrN coatings via XRD using the sin{sup 2} {phi} method. Compressive stresses of 3.7 GPa and 2.5 GPa were calculated in the ZrN on the Incoloy and Titanium substrates, respectively. Studies of the interfacial chemistry via AES revealed chemically abrupt interfaces. Scratch tests were employed to assess the critical load for interfacial failure and fracture mechanisms for the various coating systems. Critical loads, characterized by a kidney-shaped crack patterns found in the scratch tracks, occurred at 12 N for ZrN on Titanium and 20 N for ZrN on Incoloy. Interfacial failure of SiC on Titanium was dominated by brittle fracture of the SiC coating at 3N loads.

  10. Measurement of Young's modulus and residual stress of thin SiC layers for MEMS high temperature applications

    NASA Astrophysics Data System (ADS)

    Pabst, Oliver; Schiffer, Michael; Obermeier, Ernst; Tekin, Tolga; Lang, Klaus Dieter; Ngo, Ha-Duong

    2011-06-01

    Silicon carbide (SiC) is a promising material for applications in harsh environments. Standard silicon (Si) microelectromechanical systems (MEMS) are limited in operating temperature to temperatures below 130 °C for electronic devices and below 600 °C for mechanical devices. Due to its large bandgap SiC enables MEMS with significantly higher operating temperatures. Furthermore, SiC exhibits high chemical stability and thermal conductivity. Young's modulus and residual stress are important mechanical properties for the design of sophisticated SiC-based MEMS devices. In particular, residual stresses are strongly dependent on the deposition conditions. Literature values for Young's modulus range from 100 to 400 GPa, and residual stresses range from 98 to 486 MPa. In this paper we present our work on investigating Young's modulus and residual stress of SiC films deposited on single crystal bulk silicon using bulge testing. This method is based on measurement of pressure-dependent membrane deflection. Polycrystalline as well as single crystal cubic silicon carbide samples are studied. For the samples tested, average Young's modulus and residual stress measured are 417 GPa and 89 MPa for polycrystalline samples. For single crystal samples, the according values are 388 GPa and 217 MPa. These results compare well with literature values.

  11. Co{sub 2}FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

    SciTech Connect

    Belmeguenai, M. Tuzcuoglu, H.; Zighem, F.; Chérif, S. M.; Moch, P.; Gabor, M. S. Petrisor, T.; Tiusan, C.

    2014-01-28

    10 nm and 50 nm Co{sub 2}FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (T{sub a}), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing T{sub a}, while the uniaxial anisotropy field is nearly unaffected by T{sub a} within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with T{sub a}. Finally, the FMR linewidth decreases when increasing T{sub a}, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10{sup −3} and 1.3×10{sup −3} for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively)

  12. Interface reactions between Pd thin films and SiC by thermal annealing and SHI irradiation

    NASA Astrophysics Data System (ADS)

    Njoroge, E. G.; Theron, C. C.; Skuratov, V. A.; Wamwangi, D.; Hlatshwayo, T. T.; Comrie, C. M.; Malherbe, J. B.

    2016-03-01

    The solid-state reactions between Pd thin films and 6H-SiC substrates induced by thermal annealing, room temperature swift heavy ion (SHI) irradiation and high temperature SHI irradiation have been investigated by in situ and real-time Rutherford backscattering spectrometry (RBS) and Grazing incidence X-ray diffraction (GIXRD). At room temperature, no silicides were detected to have formed in the Pd/SiC samples. Two reaction growth zones were observed in the samples annealed in situ and analysed by real time RBS. The initial reaction growth region led to formation of Pd3Si or (Pd2Si + Pd4Si) as the initial phase(s) to form at a temperature of about 450 °C. Thereafter, the reaction zone did not change until a temperature of 640 °C was attained where Pd2Si was observed to form in the reaction zone. Kinetic analysis of the initial reaction indicates very fast reaction rates of about 1.55 × 1015 at cm-2/s and the Pd silicide formed grew linear with time. SHI irradiation of the Pd/SiC samples was performed by 167 MeV Xe26+ ions at room temperature at high fluences of 1.07 × 1014 and 4 × 1014 ions/cm2 and at 400 °C at lower fluences of 5 × 1013 ions/cm2. The Pd/SiC interface was analysed by RBS and no SHI induced diffusion was observed for room temperature irradiations. The sample irradiated at 400 °C, SHI induced diffusion was observed to occur accompanied with the formation of Pd4Si, Pd9Si2 and Pd5Si phases which were identified by GIXRD analysis.

  13. Tin induced a-Si crystallization in thin films of Si-Sn alloys

    SciTech Connect

    Neimash, V. E-mail: oleks.goushcha@nuportsoft.com; Poroshin, V.; Goushcha, A. O. E-mail: oleks.goushcha@nuportsoft.com; Shepeliavyi, P.; Yukhymchuk, V.; Melnyk, V.; Kuzmich, A.; Makara, V.

    2013-12-07

    Effects of tin doping on crystallization of amorphous silicon were studied using Raman scattering, Auger spectroscopy, scanning electron microscopy, and X-ray fluorescence techniques. Formation of silicon nanocrystals (2–4 nm in size) in the amorphous matrix of Si{sub 1−x}Sn{sub x}, obtained by physical vapor deposition of the components in vacuum, was observed at temperatures around 300 °C. The aggregate volume of nanocrystals in the deposited film of Si{sub 1−x}Sn{sub x} exceeded 60% of the total film volume and correlated well with the tin content. Formation of structures with ∼80% partial volume of the nanocrystalline phase was also demonstrated. Tin-induced crystallization of amorphous silicon occurred only around the clusters of metallic tin, which suggested the crystallization mechanism involving an interfacial molten Si:Sn layer.

  14. Influence of the preparation conditions on the morphology of perylene thin films on Si(111) and Si(100)

    SciTech Connect

    Casu, M. B.; Yu, X.; Schmitt, S.; Heske, C.; Umbach, E.

    2008-12-28

    Thin films of perylene on Si(111) and Si(100) substrates have been investigated using a variety of experimental techniques. We find that the structural and morphological properties as well as the growth modes strongly depend on the preparation parameters. In general, we observe the existence of a relatively weak coupling between perylene and the two single crystal substrates. However, under special preparation conditions, it is possible to obtain a multilayer phase on the Si(111) substrate that is characterized by flat-lying, parallel-oriented molecules, and strong coupling with the substrate in the first layer. This phase has different structural, electronic, and intermolecular bonding properties as compared to the known crystalline phases. On Si(100), by varying the deposition rate between 0.1 and 10 nm/min, it is possible to observe a transition from island growth mode, with large and isolated crystallites, to homogeneous film growth. These findings contribute to the basic knowledge for film engineering. Thus, the film morphology could be designed ranging from the growth of very large single grains suitable for a complete nanodevice to homogenous films for application in large displays.

  15. Electron microscopy study of Ni induced crystallization in amorphous Si thin films

    SciTech Connect

    Radnóczi, G. Z.; Battistig, G.; Pécz, B.; Dodony, E.; Vouroutzis, N.; Stoemenos, J.; Frangis, N.; Kovács, A.

    2015-02-17

    The crystallization of amorphous silicon is studied by transmission electron microscopy. The effect of Ni on the crystallization is studied in a wide temperature range heating thinned samples in-situ inside the microscope. Two cases of limited Ni source and unlimited Ni source are studied and compared. NiSi{sub 2} phase started to form at a temperature as low as 250°C in the limited Ni source case. In-situ observation gives a clear view on the crystallization of silicon through small NiSi{sub 2} grain formation. The same phase is observed at the crystallization front in the unlimited Ni source case, where a second region is also observed with large grains of Ni{sub 3}Si{sub 2}. Low temperature experiments show, that long annealing of amorphous silicon at 410 °C already results in large crystallized Si regions due to the Ni induced crystallization.

  16. Electronic structure and photoluminescence study of silicon doped diamond like carbon (Si:DLC) thin films

    SciTech Connect

    Ray, S.C. . E-mail: raysekhar@rediffmail.com; Okpalugo, T.I.T.; Pao, C.W.; Tsai, H.M.; Chiou, J.W.; Jan, J.C.; Pong, W.F.; Papakonstantinou, P.; McLaughlin, J.A.; Wang, W.J.

    2005-10-06

    We have investigated the electronic and bonding structure using Fourier-transform infra-red (FT-IR) spectra and studied photoluminescence (PL) from micro-Raman spectra analysis of a-C:H:Si (Si:DLC) thin films deposited by plasma enhanced chemical vapour deposition (PECVD) method. Tetramethylsilane [Si(CH{sub 3}){sub 4}, TMS] vapour was used as Silicon precursor and a bias voltage of 400 V was applied during deposition. It is observed from FT-IR spectra that with increasing TMS flow rate, the intensity of Si-H {sub n} and C-H {sub n} modes is increased significantly. PL study indicates that the PL is increased and that the PL peak position is shifted towards lower energy when the TMS flow rate increases gradually during deposition.

  17. Durability Evaluation of a Thin Film Sensor System With Enhanced Lead Wire Attachments on SiC/SiC Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Lei, Jih-Fen; Kiser, J. Douglas; Singh, Mrityunjay; Cuy, Mike; Blaha, Charles A.; Androjna, Drago

    2000-01-01

    An advanced thin film sensor system instrumented on silicon carbide (SiC) fiber reinforced SiC matrix ceramic matrix composites (SiC/SiC CMCs), was evaluated in a Mach 0.3 burner rig in order to determine its durability to monitor material/component surface temperature in harsh environments. The sensor system included thermocouples in a thin film form (5 microns thick), fine lead wires (75 microns diameter), and the bonds between these wires and the thin films. Other critical components of the overall system were the heavy, swaged lead wire cable (500 microns diameter) that contained the fine lead wires and was connected to the temperature readout, and ceramic attachments which were bonded onto the CMCs for the purpose of securing the lead wire cables, The newly developed ceramic attachment features a combination of hoops made of monolithic SiC or SiC/SiC CMC (which are joined to the test article) and high temperature ceramic cement. Two instrumented CMC panels were tested in a burner rig for a total of 40 cycles to 1150 C (2100 F). A cycle consisted of rapid heating to 1150 C (2100 F), a 5 minute hold at 1150 C (2100 F), and then cooling down to room temperature in 2 minutes. The thin film sensor systems provided repeatable temperature measurements for a maximum of 25 thermal cycles. Two of the monolithic SiC hoops debonded during the sensor fabrication process and two of the SiC/SiC CMC hoops failed during testing. The hoops filled with ceramic cement, however, showed no sign of detachment after 40 thermal cycle test. The primary failure mechanism of this sensor system was the loss of the fine lead wire-to-thin film connection, which either due to detachment of the fine lead wires from the thin film thermocouples or breakage of the fine wire.

  18. Incongruent transfer in laser deposition of FeSiGaRu thin films

    NASA Astrophysics Data System (ADS)

    van de Riet, E.; Kools, J. C. S.; Dieleman, J.

    1993-06-01

    The laser ablation and deposition of FeSiGaRu is studied. The deposited thin films are analyzed with Auger electron spectroscopy and Rutherford backscattering spectrometry. It is found that the gallium and ruthenium content of the thin films is strongly dependent on the laser fluence. At high laser fluences (6 J/cm2) the thin films are depleted of gallium due to preferential sputtering of the gallium atoms from the thin film. Near the threshold fluence (1.9 J/cm2) the films contain an excess of gallium due to preferential evaporation of gallium from the target. The latter conclusions are based on time-of-flight studies of ablated atoms and ions and on measurements of the atoms that are sputtered from the substrate by the incoming flux.

  19. Study and Simulation of the Heterojunction Thin Film Solar Cell a-Si( n)/a-Si( i)/c-Si( p)/a-Si( i)/a-Si( p)

    NASA Astrophysics Data System (ADS)

    Toufik, Zarede; Hamza, Lidjici; Mohamed, Fathi; Achour, Mahrane

    2016-08-01

    In this article, we present a study based on numerical simulation of the electrical characteristics of a thin-film heterojunction solar cell (a-Si( n)/a-Si( i)/c-Si( p)/a-Si( i)/a-Si( p)), using the automat for simulation of hetero-structures (AFORS-Het) software. This cell is composed of four main layers of silicon (Si): (i) 5 nm amorphous silicon doped n, (ii) 100 μm crystalline silicon (substrate) doped p, (iii) 5 nm amorphous silicon doped p, and (iv) 3 nm amorphous silicon intrinsic. This cell has a front and rear metal contact of aluminum and zinc oxide (ZnO) front layer transparent conductive oxide of 80 nm thickness. The simulations were performed at conditions of "One Sun" irradiation with air mass 1.5 (AM1.5), and under absolute temperature T = 300 K. The simulation results have shown a high electrical conversion efficiency of about 30.29% and high values of open circuit voltage V oc = 779 mV. This study has also shown that the studied cell has good quality light absorption on a very broad spectrum.

  20. Scanning Tunneling Microscopy and Transport study of Pb Thin Films Grown on Si Substrates

    NASA Astrophysics Data System (ADS)

    Yu, Hongbin

    2002-03-01

    By varying the interface structures and thus changing the interface energy, Pb film morphology can be modified from Stranski-Krastanov growth mode in the case of Si(111)7x7, to Frank van der Merwe growth mode when Pb is deposited onto Si(111)6x6-Au surface at room temperature. Different superstructures are observed on the Pb films formed on Au interfaces which can be interpreted as the moiré patterns due to the lattice mismatch between Pb film and Si substrate. The Pb(111) film tends to align with Si(111)1x1 when the thickness is between 1ML to 4ML, but in registry with Si(111)root 3 by root3 orientation when layers are thicker than 6ML. Furthermore, atomic lattices of the buried Si(111)root 3 by root 3 interface can be imaged by STM through conduction electrons in the Pb films because of the anisotropic effective mass in Pb layers. Quantum well (QW) states have been observed in Pb films and QW peak positions change due to different thicknesses and thus different confinement condition of electrons. Transport measurement of Pb thin films grown on Si substrate will be discussed.

  1. Oxidation behavior of arc evaporated Al-Cr-Si-N thin films

    SciTech Connect

    Tritremmel, Christian; Daniel, Rostislav; Mitterer, Christian; Mayrhofer, Paul H.; Lechthaler, Markus; Polcik, Peter

    2012-11-15

    The impact of Al and Si on the oxidation behavior of Al-Cr-(Si)-N thin films synthesized by arc evaporation of powder metallurgically prepared Al{sub x}Cr{sub 1-x} targets with x = Al/(Al + Cr) of 0.5, 0.6, and 0.7 and (Al{sub 0.5}Cr{sub 0.5}){sub 1-z}Si{sub z} targets with Si contents of z = 0.05, 0.1, and 0.2 in N{sub 2} atmosphere was studied in detail by means of differential scanning calorimetry, thermogravimetric analysis (TGA), x-ray diffraction, and Raman spectroscopy. Dynamical measurements in synthetic air (up to 1440 Degree-Sign C) revealed the highest onset temperature of pronounced oxidation for nitride coatings prepared from the Al{sub 0.4}Cr{sub 0.4}Si{sub 0.2} target. Isothermal TGA at 1100, 1200, 1250, and 1300 Degree-Sign C highlight the pronounced improvement of the oxidation resistance of Al{sub x}Cr{sub 1-x}N coatings by the addition of Si. The results show that Si promotes the formation of a dense coating morphology as well as a dense oxide scale when exposed to air.

  2. Epitaxial growth of Ti{sub 3}SiC{sub 2} thin films with basal planes parallel or orthogonal to the surface on {alpha}-SiC

    SciTech Connect

    Drevin-Bazin, A.; Barbot, J. F.; Alkazaz, M.; Cabioch, T.; Beaufort, M. F.

    2012-07-09

    The growth of Ti{sub 3}SiC{sub 2} thin films were studied onto {alpha}-SiC substrates differently oriented by thermal annealing of TiAl layers deposited by magnetron sputtering. For any substrate's orientation, transmission electron microscopy coupled with x-ray diffraction showed the coherent epitaxial growth of Ti{sub 3}SiC{sub 2} films along basal planes of SiC. Specifically for the (1120) 4H-SiC, Ti{sub 3}SiC{sub 2} basal planes are found to be orthogonal to the surface. The continuous or textured nature of Ti{sub 3}SiC{sub 2} films does not depend of the SiC stacking sequence and is explained by a step-flow mechanism of growth mode. The ohmic character of the contact was confirmed by current-voltage measurements.

  3. Laser-sintered thin films of doped SiGe nanoparticles

    NASA Astrophysics Data System (ADS)

    Stoib, B.; Langmann, T.; Matich, S.; Antesberger, T.; Stein, N.; Angst, S.; Petermann, N.; Schmechel, R.; Schierning, G.; Wolf, D. E.; Wiggers, H.; Stutzmann, M.; Brandt, M. S.

    2012-06-01

    We present a study of the morphology and the thermoelectric properties of short-pulse laser-sintered (LS) nanoparticle (NP) thin films, consisting of SiGe alloy NPs or composites of Si and Ge NPs. Laser-sintering of spin-coated NP films in vacuum results in a macroporous percolating network with a typical thickness of 300 nm. The Seebeck coefficient for LS samples is the same as for bulk samples prepared by current-assisted sintering and is typical for degenerate doping. The electrical conductivity of LS films is influenced by two-dimensional percolation effects and rises with increasing temperature, approximately following a power-law.

  4. Fabrication of high-quality superconductor-insulator-superconductor junctions on thin SiN membranes

    NASA Technical Reports Server (NTRS)

    Garcia, Edouard; Jacobson, Brian R.; Hu, Qing

    1993-01-01

    We have successfully fabricated high-quality and high-current density superconductor-insulator-superconductor (SIS) junctions on freestanding thin silicon nitride (SIN) membranes. These devices can be used in a novel millimeter-wave and THz receiver system which is made using micromachining. The SIS junctions with planar antennas were fabricated first on a silicon wafer covered with a SiN membrane, the Si wafer underneath was then etched away using an anisotropic KOH etchant. The current-voltage characteristics of the SIS junctions remained unchanged after the whole process, and the junctions and the membrane survived thermal cycling.

  5. Erbium oxide thin films on Si(100) obtained by laser ablation and electron beam evaporation

    NASA Astrophysics Data System (ADS)

    Queralt, X.; Ferrater, C.; Sánchez, F.; Aguiar, R.; Palau, J.; Varela, M.

    1995-02-01

    Erbium oxide thin films have been obtained by laser ablation and electron beam evaporation techniques on Si(100) substrates. The samples were grown under different conditions of oxygen atmosphere and substrate temperature without any oxidation process after deposition. The crystal structure has been studied by X-ray diffraction. Films obtained by laser ablation are highly textured in the [ hhh] direction, although this depends on the conditions of oxygen pressure and substrate temperature. In order to study the depth composition profile of the thin films and the interdiffusion of erbium metal and oxygen towards the silicon substrates, X-ray photoelectron spectroscopy analyses have been carried out.

  6. XRR Analysis of the Transition Layer in SiO2 Thin Film Formed on Si Surface

    NASA Astrophysics Data System (ADS)

    Kurokawa, Akira; Odaka, Kenji; Fujimoto, Tosiyuki; Azuma, Yasushi

    To develop nanometric film thickness standard (FTSs), uniformity of silicon dioxide thin film were investigated by X-ray Reflectometry (XRR). The samples we investigated were thermally grown oxides (O2-Oxides) and ozone-formed oxide(Ozone-Oxide). The O2-oxide were grown on Si(100) substrate at 1000°C and at 700°C. The Ozone-Oxide was grown at 750°C with the highly concentrated ozone gas. With XRR method the bulk-layer density of oxide films were analyzed for; the O2-Oxide formed at 700°C (D700), the O2-Oxide formed at 1000°C(D1000), and the Ozone-Oxide formed at 750°C (Dozone750). We also analyzed the transition-layer density of the O2-Oxide formed at 700°C (DTL700). The results showed the relation was D1000SiO2 thin film, and also indicated that the density of Ozone-Oxide corresponded to that of O2-Oxide with much higher substrate temperature.

  7. Evaluation of microindentation properties of epitaxial 3C-SiC/Si thin films

    NASA Astrophysics Data System (ADS)

    Geetha, D.; Sophia, P. Joice; Arivuoli, D.

    2016-06-01

    The microhardness characteristics of 3C-SiC/Si films grown by vapor phase epitaxy were investigated using Vickers and Knoop indenters. The observed hardness behavior at lower load range is being attributed to indentation size effect while the substrate hardness effect is found to be prominent at higher loads. The related mechanical properties such as fracture toughness, brittleness index, and yield stress were also evaluated. In order to study the nature and behavior of the surface topography during the deformation process for the applied load, detailed atomic force microscopy images were obtained around the indented regions of the samples. It revealed that the indents formed at higher loads showed fracture characteristics with a pattern of radial cracks propagating from the indent corners.

  8. Progress of p-channel bottom-gate poly-Si thin-film transistor by nickel silicide seed-induced lateral crystallization

    NASA Astrophysics Data System (ADS)

    Lee, Sol Kyu; Seok, Ki Hwan; Park, Jae Hyo; Kim, Hyung Yoon; Chae, Hee Jae; Jang, Gil Su; Lee, Yong Hee; Han, Ji Su; Joo, Seung Ki

    2016-06-01

    Excimer laser annealing (ELA) is known to be the most common crystallization technology for the fabrication of low-temperature polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) in the mass production industry. This technology, however, cannot be applied to bottom-gate (BG) TFTs, which are well developed for the liquid-crystal display (LCD) back-planes, because strong laser energy of ELA can seriously damage the other layers. Here, we propose a novel high-performance BG poly-Si TFT using Ni silicide seed-induced lateral crystallization (SILC). The SILC technology renders it possible to ensure low damage in the layers, smooth surface, and longitudinal large grains in the channel. It was observed that the electrical properties exhibited a steep subthreshold slope of 110 mV/dec, high field-effect mobility of 304 cm2/Vsec, high I on/ I off ratio of 5.9 × 107, and a low threshold voltage of -3.9 V.

  9. Structured SiCu thin films in LiB as anodes

    SciTech Connect

    Polat, Billur Deniz; Eryilmaz, Osman Levent; Erck, Robert; Keles, O.; Erdemir, A.; Amine, Khalil

    2014-09-16

    Both helical and inclined columnar Si–10 at.% Cu structured thin films were deposited on Cu substrates using glancing angle deposition (GLAD) technique. In order to deposit Cu and Si two evaporation sources were used. Ion assistance was utilized in the first 5 min of the GLAD to enhance the adhesion and the density of the films. These films were characterized by thin film XRD, GDOES, SEM, and EDS. Electrochemical characterizations were made by testing the thin films as anodes in half-cells for 100 cycles. The results showed that the columnar SiCu thin film delivered 2200 mAh g-1, where the helical one exhibited 2600 mAh g-1, and, their initial coulombic efficiencies were found to be 38%–50% respectively. For the columnar and the helical thin film anodes, sustainable 520 and 800 mAh g-1 with 90% and 99% coulombic efficiencies were achieved for 100 cycles. These sustainable capacities showed the importance of the thin film structure having nano-sized crystals and amorphous particles. The higher surface area of the helices increases the capacity of the electrode because the contact area of the thin film anode with Li ions is increased, and the polarization which otherwise forms on the anode surface due to SEI formation is decreased. In addition, because of larger interspaces between the helices the ability of the anode to accommodate the volumetric changes is improved, which results in a higher coulombic efficiency and capacity retention during cycling test.

  10. Thermal phonon transport in Si thin film with dog-leg shaped asymmetric nanostructures

    NASA Astrophysics Data System (ADS)

    Kage, Yuta; Hagino, Harutoshi; Yanagisawa, Ryoto; Maire, Jeremie; Miyazaki, Koji; Nomura, Masahiro

    2016-08-01

    Thermal phonon transport in single-crystalline Si thin films with dog-leg shaped nanostructures was investigated. Thermal conductivities for the forward and backward directions were measured and compared at 5 and 295 K by micro thermoreflectance. The Si thin film with dog-leg shaped nanostructures showed lower thermal conductivities than those of nanowires and two-dimensional phononic crystals with circular holes at the same surface-to-volume ratio. However, asymmetric thermal conductivity was not observed at small temperature gradient condition in spite of the highly asymmetric shape though the size of the pattern is within thermal phonon mean free path range. We conclude that strong temperature dependent thermal conductivity is required to observe the asymmetric thermal phonon conduction in monolithic materials with asymmetric nanostructures.

  11. Effects of Mev Si Ions and Thermal Annealing on Thermoelectric and Optical Properties of SiO2/SiO2+Ge Multi-nanolayer thin Films

    NASA Astrophysics Data System (ADS)

    Budak, S.; Alim, M. A.; Bhattacharjee, S.; Muntele, C.

    Thermoelectric generator devices have been prepared from 200 alternating layers of SiO2/SiO2+Ge superlattice films using DC/RF magnetron sputtering. The 5 MeV Si ionsbombardmenthasbeen performed using the AAMU Pelletron ion beam accelerator to formquantum dots and / or quantum clusters in the multi-layer superlattice thin films to decrease the cross-plane thermal conductivity, increase the cross-plane Seebeck coefficient and increase the cross-plane electrical conductivity to increase the figure of merit, ZT. The fabricated devices have been annealed at the different temperatures to tailor the thermoelectric and optical properties of the superlattice thin film systems. While the temperature increased, the Seebeck coefficient continued to increase and reached the maximum value of -25 μV/K at the fluenceof 5x1013 ions/cm2. The decrease in resistivity has been seen between the fluence of 1x1013 ions/cm2 and 5x1013 ions/cm2. Transport properties like Hall coefficient, density and mobility did not change at all fluences. Impedance spectroscopy has been used to characterize the multi-junction thermoelectric devices. The loci obtained in the C*-plane for these data indicate non-Debye type relaxation displaying the presence of the depression parameter.

  12. Au/SiO{sub x} composite thin film as catalyst for solvent-free hydrocarbon oxidation

    SciTech Connect

    Han, Xiao; Huang, Hui; Zhang, Hengchao; Zhang, Xing; Li, Haitao; Liu, Ruihua; Liu, Yang Kang, Zhenhui

    2013-10-15

    Graphical abstract: Au/SiO{sub x} composite thin film possesses high catalytic activity and stability for selective oxidation of cis-cyclooctene. - Highlights: • Au/SiO{sub x} composite thin film was synthesized by a facile and efficient chemical approach. • The Au/SiO{sub x} composite thin film exhibits high catalytic ability for the selective oxidation. • The Au/SiO{sub x} composite thin film possesses high structural and catalytic stability. - Abstract: We report a facile and efficient chemical approach for the controllable preparation of Au/SiO{sub x} composite thin film using silicon quantum dots as SiO{sub x} sources. Au/SiO{sub x} composite thin film exhibits high catalytic activity (65.04% conversion based on cis-cyclooctene and 78.34% selectivity for 2-hydroxycyclooctanone) and stability for selective oxidation of cis-cyclooctene in the absence of solvent using TBHP as radical initiator and oxygen (in the air) as oxidant at 80 °C.

  13. Photoluminescence and structure of sputter-deposited Zn2SiO4:Mn thin films

    NASA Astrophysics Data System (ADS)

    Lee, Yeon Oh; Kim, Joo Han

    2016-01-01

    Mn-doped Zn2SiO4 thin films were deposited on Si (100) substrates by radio-frequency (RF) magnetron sputtering. The deposited films were then annealed at temperatures ranging from 600 to 1200 °C in an air ambient for 1 hour. The as-deposited Zn2SiO4:Mn films exhibited an amorphous structure having a smooth surface and showed no photoluminescence (PL). Annealing at 600 °C was found to have little effect on the properties of the films. The films still remained amorphous with no PL. After annealing at 800 °C, the films were crystallized in a mixture of orthorhombic β-Zn2SiO4 and rhombohedral α-Zn2SiO4 phases. These films showed a PL emission spectrum that could be resolved into two bands, one centered at 520 nm in the green region and the other at 571 nm in the yellow region. The green PL emission originated from the 4T1 → 6A1 intrashell transition of Mn2+ ions in the α-Zn2SiO4 phase while the yellow emission was attributed to Mn2+ ions in β-Zn2SiO4. The films annealed at and above a temperature of 900 °C exhibited only the α-Zn2SiO4 phase, and the PL spectra of these films showed only the green emission band with a peak maximum at around 523 nm. The PL emission intensity increased with increasing annealing temperature, which was due to the better crystalline quality and the rougher surface morphology of the Zn2SiO4:Mn films annealed at higher temperatures.

  14. Electrical Properties of PVP-SiO2-TMSPM Hybrid Thin Films as OFET Gate Dielectric

    NASA Astrophysics Data System (ADS)

    Bahari, A.; Shahbazi, M.

    2016-02-01

    Organic-inorganic polyvinylpyrrolidone-silicon dioxide-3-(trimethoxysilyl)propyl methacrylate (PVP-SiO2-TMSPM) hybrid solutions have been synthesized using the sol-gel process with different amounts of TMSPM as coupling agent and equivalent amounts of PVP and SiO2. Hybrid solutions were deposited on p-type Si(111) substrates using the spin coating technique, as a gate dielectric material for use in thin-film transistors. The structural properties of the samples were investigated using Fourier-transform infrared spectroscopy and x-ray diffraction analysis. Atomic force microscopy and scanning electron microscopy techniques were applied to study the topography and morphology of the hybrid thin-film samples. Current-voltage ( I- V) curves, capacitance-voltage ( C- V) measurements, and the electrical properties of the organic hybrid thin-film gate dielectrics were also studied in a metal-insulator/polymer-semiconductor structure. According to the results, the J GS curves in terms of V GS showed gate leakage current densities small enough for use as gate dielectric material at interface layers. At V DS = 30 V, in the saturation region, I DS curves in terms of V GS presented higher charge carrier mobility ( μ FET,S = 0.0584 cm2 s-1 V-1) due to lower dielectric constant ( k = 11.43) in the sample with 0.05 weight ratio of TMSPM compared with other samples with different weight ratios of TMSPM.

  15. Hydrogen plasma induced modification of photoluminescence from a-SiNx:H thin films

    NASA Astrophysics Data System (ADS)

    Bommali, R. K.; Ghosh, S.; Vijaya Prakash, G.; Gao, K.; Zhou, S.; Khan, S. A.; Srivastava, P.

    2014-02-01

    Low temperature (250-350 °C) hydrogen plasma annealing (HPA) treatments have been performed on amorphous hydrogenated silicon nitride (a-SiNx:H) thin films having a range of compositions and subsequent modification of photoluminescence (PL) is investigated. The PL spectral shape and peak positions for the as deposited films could be tuned with composition and excitation energies. HPA induced modification of PL of these films is found to depend on the N/Si ratio (x). Upon HPA, the PL spectra show an emergence of a red emission band for x ≤ 1, whereas an overall increase of intensity without change in the spectral shape is observed for x > 1. The emission observed in the Si rich films is attributed to nanoscale a-Si:H inclusions. The enhancement is maximum for off-stoichiometric films (x ˜ 1) and decreases as the compositions of a-Si (x = 0) and a-Si3N4 (x = 1.33) are approached, implying high density of non-radiative defects around x = 1. The diffusion of hydrogen in these films is also analyzed by Elastic Recoil Detection Analysis technique.

  16. Double-metal-gate nanocrystalline Si thin film transistors with flexible threshold voltage controllability

    SciTech Connect

    Chiou, Uio-Pu; Pan, Fu-Ming; Shieh, Jia-Min E-mail: jmshieh@faculty.nctu.edu.tw; Yang, Chih-Chao; Huang, Wen-Hsien; Kao, Yo-Tsung

    2013-11-11

    We fabricated nano-crystalline Si (nc-Si:H) thin-film transistors (TFTs) with a double-metal-gate structure, which showed a high electron-mobility (μ{sub FE}) and adjustable threshold voltages (V{sub th}). The nc-Si:H channel and source/drain (S/D) of the multilayered TFT were deposited at 375 °C by inductively coupled plasma chemical vapor deposition. The low grain-boundary defect density of the channel layer is responsible for the high μ{sub FE} of 370 cm{sup 2}/V-s, a steep subthreshold slope of 90 mV/decade, and a low V{sub th} of −0.64 V. When biased with the double-gate driving mode, the device shows a tunable V{sub th} value extending from −1 V up to 2.7 V.

  17. In vitro biocompatibility response of Ti-Zr-Si thin film metallic glasses

    NASA Astrophysics Data System (ADS)

    Ke, J. L.; Huang, C. H.; Chen, Y. H.; Tsai, W. Y.; Wei, T. Y.; Huang, J. C.

    2014-12-01

    In this study, the bio-electrochemical response of the Ti-Zr-Si thin film metallic glasses (TFMGs) in simulated body fluid with different contents of titanium is measured via potentiostat. According to the results of bio-corrosion potential and current, as well as the polarization resistance, it is concluded that the Ti66Zr25Si9 TFMGs possess the highest bio-electrochemical resistance. With increasing content of titanium, the corrosion resistance becomes progressively higher. The passive current results reveal that amorphous alloys can form a more protective and denser passive film on the metallic glass surface than the crystalline materials. In addition, the mechanical performance of the Ti-Zr-Si TFMGs is better than the crystalline counterparts. As a result, the Ti-based TFMGs are considered to be potential materials for bio-coating applications.

  18. Nanoporous SiO2 thin films made by atomic layer deposition and atomic etching

    NASA Astrophysics Data System (ADS)

    Ghazaryan, Lilit; Kley, E.-Bernhard; Tünnermann, Andreas; Szeghalmi, Adriana

    2016-06-01

    A new route to prepare nanoporous SiO2 films by mixing atomic-layer-deposited alumina and silica in an Å-scale is presented. The selective removal of Al2O3 from the composites using wet chemical etching with phosphoric acid resulted in nanoporous thin SiO2 layers. A diffusion-controlled dissolution mechanism is identified whereby an interesting reorganization of the residual SiO2 is observed. The atomic scale oxide mixing is decisive in attaining and tailoring the film porosity. The porosity and the refractive index of nanoporous silica films were tailored from 9% to 69% and from 1.40 to 1.13, respectively. The nanoporous silica was successfully employed as antireflection coatings and as diffusion membranes to encapsulate nanostructures.

  19. Cobalt-free polycrystalline Ba0.95La0.05FeO3-δ thin films as cathodes for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Chen, Dengjie; Chen, Chi; Dong, Feifei; Shao, Zongping; Ciucci, Francesco

    2014-03-01

    Ba0.95La0.05FeO3-δ (BLF) thin films as electrodes for intermediate-temperature solid oxide fuel cells are prepared on single-crystal yttria-stabilized zirconia (YSZ) substrates by pulsed laser deposition. The phase structure, surface morphology and roughness of the BLF thin films are characterized by X-ray diffraction, scanning electron microscopy and atomic force microscopy. X-ray photoelectron spectroscopy is used to analyze the compositions of the deposited thin film and the chemical state of transition metal. The dense thin film exhibits a polycrystalline perovskite structure with a low surface roughness and a high oxygen vacancy concentration on the surface. Ag (paste or strip) and Au (strip) are applied on both surfaces of the symmetric cells as current collectors to evaluate electrochemical performance of the thin films. The electrode polarization resistances of the symmetric cells are found to be lower than those of most cobalt-free thin-film electrodes, e.g., 0.437 Ω cm2 at 700 °C and 0.21 atm. The oxygen reduction reaction mechanism of the BLF cathode in symmetric cells is studied by electrochemical impedance spectroscopy thanks to the equivalent fitting analysis. Both the oxygen surface exchange reaction and charge transfer are shown to determine the overall oxygen reduction reaction.

  20. Thermal stability of nanostructured TiZrSiN thin films subjected to helium ion irradiation

    NASA Astrophysics Data System (ADS)

    Uglov, V. V.; Abadias, G.; Zlotski, S. V.; Saladukhin, I. A.; Skuratov, V. A.; Leshkevich, S. S.; Petrovich, S.

    2015-07-01

    The phase stability, upon vacuum annealing up to 1000 °C, of nanostructured (Ti,Zr)1-xSixN thin films is investigated by X-ray diffraction analysis as a function of Si content (0.13 ⩽ x ⩽ 0.25) and prior irradiation with He ions (40 kV). The quaternary TiZrSiN thin films were deposited by reactive magnetron sputtering from elemental targets at the substrate temperature of 600 °C. It was found that the increase in Si content, x, results in the transformation of structure from nanocrystalline (x = 0.13, grain size of 11 nm) to nanocomposite state (0.19 < x ⩽ 0.25, grain size of 5 nm). The phase composition of the films changes from single-phase, cubic c-(Ti,Zr)N columns with (1 1 1) preferred orientation to dual-phase system consisting of c-(Ti,Zr)N crystallites and amorphous SiNy. Irradiation with He ions at the doses of 2 × 1016 and 5 × 1016 cm-2 does change the phase composition of the films. It is found that the onset temperature for phase decomposition decreases from 1000 °C to 800 °C with increasing Si content for unirradiated films. The formation of a secondary ZrN phase is observed concomitantly with increased broadening of the (2 0 0) c-(Ti,Zr)N diffraction peak. For irradiated films, the subsequent annealing at 1000 °C leads to decomposition of the c-(Ti,Zr)N solid solution into TiN- and ZrN-rich phases as well as crystallization of hexagonal Si3N4 phase.

  1. Morphological and optical comparison of the Si doped GaN thin film deposited onto the transparent substrates

    NASA Astrophysics Data System (ADS)

    Özen, Soner; Şenay, Volkan; Pat, Suat; Korkmaz, Şadan

    2016-04-01

    The aim of this paper is to expand the body of knowledge about the silicon doped gallium nitride thin films deposited on different substrates. The physical properties of the Si doped GaN thin films deposited on the glass and polyethylene terephthalate substrates by thermionic vacuum arc which is plasma production technique were investigated. Thermionic vacuum arc method is a method of producing pure material plasma. The Si doped GaN thin films were analyzed using the following methods and the devices: atomic force microscopy, x-ray diffraction device, spectroscopic ellipsometer and energy dispersive x-ray spectroscopy detector. The produced Si doped GaN thin films are in the (113) orientation. The thicknesses and refractive index were determined by using Cauchy dispersion model. Surface morphologies of produced thin films are homogenous and low roughness. Our analysis showed that the thermionic vacuum arc method present important advantages for optical and industrial applications.

  2. On the way to enhance the optical absorption of a-Si in NIR by embedding Mg2Si thin film

    NASA Astrophysics Data System (ADS)

    Chernev, I. M.; Shevlyagin, A. V.; Galkin, K. N.; Stuchlik, J.; Remes, Z.; Fajgar, R.; Galkin, N. G.

    2016-07-01

    Mg2Si thin film was embedded in amorphous silicon matrix by solid phase epitaxy. The structure and optical properties were investigated by electron energy loss, X-ray photoelectron, Raman, and photo thermal deflection spectroscopy measurements. It was found that in the photon energy range of 0.8-1.7 eV, the light absorption of the structure with magnesium silicide (Mg2Si) film embedded in a-Si(i) matrix is 1.5 times higher than that for the same structure without Mg2Si.

  3. [Study on the Properties of the Pc-Si Films Prepared by Magnetron Co-Sputtering at Low Temperature].

    PubMed

    Duan, Liang-fei; Yang, Wen; Zhang, Li-yuan; Li, Xue-ming; Chen, Xiao-bo; Yang, Pei-zhi

    2016-03-01

    The polycrystalline silicon thin films play an important role in the field of electronics. In the paper, α-SiAl composite membranes on glass substrates was prepared by magnetron co-sputtering. The contents of Al radicals encapsulated-in the α-Si film can be adjusted by changing the Al to Si sputtering power ratios. The as-prepared α-Si films were converted into polycrystalline films by using a rapid thermal annealing (RTP) at low temperature of 350 degrees C for 10 minutes in N2 atmosphere. An X-ray diffractometer, and Raman scattering and UV-Visible-NIR Spectrometers were used to characterize the properties of the Pc-Si films. The influences of Al content on the properties of the Pc-Si films were studied. The results showed that the polycrystalline silicon films were obtained from α-SiAl composite films which were prepared by magnetron co-sputtering at a low temperature following by a rapid thermal annealing. The grain size and the degree of crystallization of the Pc-Si films increased with the increase of Al content, while the optical band gap was reduced. The nc-Si films were prepared when the Al to Si sputtering power ratio was 0.1. And a higher Crystallization rate (≥ 85%) of polycrystalline silicon films were obtained when the ratio was 0.3. The band gaps of the polycrystalline silicon films can be controlled by changing the aluminum content in the films.

  4. Recombination and thin film properties of silicon nitride and amorphous silicon passivated c-Si following ammonia plasma exposure

    SciTech Connect

    Wan, Yimao; Thomson, Andrew F.; Cuevas, Andres; McIntosh, Keith R.

    2015-01-26

    Recombination at silicon nitride (SiN{sub x}) and amorphous silicon (a-Si) passivated crystalline silicon (c-Si) surfaces is shown to increase significantly following an ammonia (NH{sub 3}) plasma exposure at room temperature. The effect of plasma exposure on chemical structure, refractive index, permittivity, and electronic properties of the thin films is also investigated. It is found that the NH{sub 3} plasma exposure causes (i) an increase in the density of Si≡N{sub 3} groups in both SiN{sub x} and a-Si films, (ii) a reduction in refractive index and permittivity, (iii) an increase in the density of defects at the SiN{sub x}/c-Si interface, and (iv) a reduction in the density of positive charge in SiN{sub x}. The changes in recombination and thin film properties are likely due to an insertion of N–H radicals into the bulk of SiN{sub x} or a-Si. It is therefore important for device performance to minimize NH{sub 3} plasma exposure of SiN{sub x} or a-Si passivating films during subsequent fabrication steps.

  5. UV Laser Photocarrier Radiometry of c-Silicon with Surface Thin Hydrogenated Amorphous Si Film

    NASA Astrophysics Data System (ADS)

    Melnikov, A.; Mandelis, A.; Halliop, B.; Kherani, N. P.

    2015-06-01

    Photocarrier radiometry (PCR) with 355 nm laser excitation was used for the study of c-Si covered with intrinsic thin hydrogenated amorphous Si (i-a-Si:H) on one, or both, sides, with thicknesses ranging from 10 nm to 90 nm. Short wavelength excitation allows one to resolve the contribution of the upper i-a-S layer to the PCR signal due to the very small absorption depth (tens of nm) of the excitation beam. As a result, fundamental transport parameters of the composite structure can be evaluated from the PCR frequency dependence. A theoretical model has been developed to describe the diffuse carrier density wave (CDW) in this two-layer system. The model of the one-dimensional CDW fields for composite electronic solids involves front, interface, and back surface recombination velocities, the diffusion coefficient, recombination lifetimes in the upper and lower layers, and the unoccupied trap density at the interface. Simulations of the transport parameter influence on the PCR signal were performed, and the theoretical model was able to describe the experimental data accurately, therefore, making it possible to evaluate the transport parameters of i-a-Si:H and c-Si as well as to elucidate the role of interface electronic traps in the PCR frequency dependence under short wavelength excitation.

  6. Transport mechanisms and charge trapping in thin dielectric/Si nano-crystals structures

    NASA Astrophysics Data System (ADS)

    De Salvo, B.; Ghibaudo, G.; Luthereau, P.; Baron, T.; Guillaumot, B.; Reimbold, G.

    2001-08-01

    In this work the transport mechanisms and charge trapping of novel dielectric systems based on semiconductor nano-crystals embedded in a dielectric matrix are studied. In particular, stacked films composed of a thin bottom dielectric (2-4 nm thick SiO2 or Si3N4), with an embedded two-dimensional (2-D) array of Si nano-crystals (obtained by low pressure chemical vapor deposition or by annealing of silicon rich oxide) and a thick top dielectric (8 nm-thick SiO2) are investigated. Gate leakage currents, at medium/high electric fields, are examined at temperatures varying between 77 and 473 K. Charge trapping phenomena, occurring at low electric fields, are studied as a function of the stressing gate voltage and the stressing time. Experimental results are explained by means of an elastic tunneling model, which takes into account the main structural characteristics of the Si-dots (size dispersion, density, spatial distribution) as well as the effect of trapped charges in the silicon nano-crystals.

  7. Enlargement of Step-Free SiC Surfaces by Homoepitaxial Web-Growth of Thin SiC Cantilevers

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony; Beheim, Glenn M.; Benavage, Emye L.; Abel, Phillip B.; Trunek, Andrew J.; Spry, David J.; Dudley, Michael; Vetter, William M.

    2002-01-01

    Lateral homoepitaxial growth of thin cantilevers emanating from mesa patterns that were reactive ion etched into on-axis commercial SiC substrates prior to growth is reported. The thin cantilevers form after pure stepflow growth removes almost all atomic steps from the top surface of a mesa, after which additional adatoms collected by the large step-free surface migrate to the mesa sidewall where they rapidly incorporate into the crystal near the top of the mesa sidewall. The lateral propagation of the step-free cantilevered surface is significantly affected by pregrowth mesa shape and orientation, with the highest lateral expansion rates observed at the inside concave comers of V-shaped pregrowth mesas with arms lengthwise oriented along the {1100} direction. Complete spanning of the interiors of V's and other mesa shapes with concave comers by webbed cantilevers was accomplished. Optical microscopy, synchrotron white beam x-ray topography and atomic force microscopy analysis of webbed regions formed over a micropipe and closed-core screw dislocations show that c-axis propagation of these defects is terminated by the webbing. Despite the nonoptimized process employed in this initial study, webbed surfaces as large as 1.4 x 10(exp -3) square centimeters, more than four times the pregrowth mesa area, were grown. However, the largest webbed surfaces were not completely free of bilayer steps, due to unintentional growth of 3C-SiC that occurred in the nonoptimized process. Further process optimization should enable larger step-free webs to be realized.

  8. Deposition of thin Si and Ge films by ballistic hot electron reduction in a solution-dripping mode and its application to the growth of thin SiGe films

    NASA Astrophysics Data System (ADS)

    Suda, Ryutaro; Yagi, Mamiko; Kojima, Akira; Mentek, Romain; Mori, Nobuya; Shirakashi, Jun-ichi; Koshida, Nobuyoshi

    2015-04-01

    To enhance the usefulness of ballistic hot electron injection into solutions for depositing thin group-IV films, a dripping scheme is proposed. A very small amount of SiCl4 or GeCl4 solution was dripped onto the surface of a nanocrystalline Si (nc-Si) electron emitter, and then the emitter is driven without using any counter electrodes. It is shown that thin Si and Ge films are deposited onto the emitting surface. Spectroscopic surface and compositional analyses showed no extrinsic carbon contaminations in deposited thin films, in contrast to the results of a previous study using the dipping scheme. The availability of this technique for depositing thin SiGe films is also demonstrated using a mixture SiCl4+GeCl4 solution. Ballistic hot electrons injected into solutions with appropriate kinetic energies promote preferential reduction of target ions with no by-products leading to nuclei formation for the thin film growth. Specific advantageous features of this clean, room-temperature, and power-effective process is discussed in comparison with the conventional dry and wet processes.

  9. Characterization of Thick and Thin Film SiCN for Pressure Sensing at High Temperatures

    PubMed Central

    Leo, Alfin; Andronenko, Sergey; Stiharu, Ion; Bhat, Rama B.

    2010-01-01

    Pressure measurement in high temperature environments is important in many applications to provide valuable information for performance studies. Information on pressure patterns is highly desirable for improving performance, condition monitoring and accurate prediction of the remaining life of systems that operate in extremely high temperature environments, such as gas turbine engines. A number of technologies have been recently investigated, however these technologies target specific applications and they are limited by the maximum operating temperature. Thick and thin films of SiCN can withstand high temperatures. SiCN is a polymer-derived ceramic with liquid phase polymer as its starting material. This provides the advantage that it can be molded to any shape. CERASET™ also yields itself for photolithography, with the addition of photo initiator 2, 2-Dimethoxy-2-phenyl-acetophenone (DMPA), thereby enabling photolithographical patterning of the pre-ceramic polymer using UV lithography. SiCN fabrication includes thermosetting, crosslinking and pyrolysis. The technology is still under investigation for stability and improved performance. This work presents the preparation of SiCN films to be used as the body of a sensor for pressure measurements in high temperature environments. The sensor employs the phenomenon of drag effect. The pressure sensor consists of a slender sensitive element and a thick blocking element. The dimensions and thickness of the films depend on the intended application of the sensors. Fabrication methods of SiCN ceramics both as thin (about 40–60 μm) and thick (about 2–3 mm) films for high temperature applications are discussed. In addition, the influence of thermosetting and annealing processes on mechanical properties is investigated. PMID:22205871

  10. Novel chemical route for atomic layer deposition of MoS₂ thin film on SiO₂/Si substrate.

    PubMed

    Jin, Zhenyu; Shin, Seokhee; Kwon, Do Hyun; Han, Seung-Joo; Min, Yo-Sep

    2014-11-01

    Recently MoS₂ with a two-dimensional layered structure has attracted great attention as an emerging material for electronics and catalysis applications. Although atomic layer deposition (ALD) is well-known as a special modification of chemical vapor deposition in order to grow a thin film in a manner of layer-by-layer, there is little literature on ALD of MoS₂ due to a lack of suitable chemistry. Here we report MoS₂ growth by ALD using molybdenum hexacarbonyl and dimethyldisulfide as Mo and S precursors, respectively. MoS₂ can be directly grown on a SiO₂/Si substrate at 100 °C via the novel chemical route. Although the as-grown films are shown to be amorphous in X-ray diffraction analysis, they clearly show characteristic Raman modes (E(1)₂g and A₁g) of 2H-MoS₂ with a trigonal prismatic arrangement of S-Mo-S units. After annealing at 900 °C for 5 min under Ar atmosphere, the film is crystallized for MoS₂ layers to be aligned with its basal plane parallel to the substrate.

  11. Improved Si/SiOx interface passivation by ultra-thin tunneling oxide layers prepared by rapid thermal oxidation

    NASA Astrophysics Data System (ADS)

    Gad, Karim M.; Vössing, Daniel; Balamou, Patrice; Hiller, Daniel; Stegemann, Bert; Angermann, Heike; Kasemann, Martin

    2015-10-01

    We analyze the influence of different oxidation methods on the chemical passivation quality of silicon oxide-nanolayers on crystalline silicon wafers with surface photo voltage and quasi-steady-state photo conductance measurements. We present a simple method by means of rapid thermal oxidation (RTO) and subsequent annealing in forming gas, which requires no complex surface pre-treatment or surface pre-conditioning after cleaning. This technique allows a reproducible preparation of high-quality ultra-thin oxide-nanolayers (1.3-1.6 nm) with a nearly intrinsic energetic distribution of interface states and a defect density of states of only 1 × 1012 cm-2 eV-1 at the minimum of the distribution. These results are compared with silicon oxide-nanolayers prepared by wet chemical oxidation and plasma oxidation where only a slight reduction of the interface defect density is achieved by subsequent anneal in forming gas environment. Furthermore, it is shown that applying the RTO oxide-nanolayer as an intermediate layer between Si and an a-SiNx:H layer, leads to a significant improvement of the surface passivation quality.

  12. Polycrystalline Silicon: a Biocompatibility Assay

    SciTech Connect

    Pecheva, E.; Fingarova, D.; Pramatarova, L.; Hikov, T.; Laquerriere, P.; Bouthors, Sylvie; Dimova-Malinovska, D.; Montgomery, P.

    2010-01-21

    Polycrystalline silicon (poly-Si) layers were functionalized through the growth of biomimetic hydroxyapatite (HA) on their surface. HA is the mineral component of bones and teeth and thus possesses excellent bioactivity and biocompatibility. MG-63 osteoblast-like cells were cultured on both HA-coated and un-coated poly-Si surfaces for 1, 3, 5 and 7 days and toxicity, proliferation and cell morphology were investigated. The results revealed that the poly-Si layers were bioactive and compatible with the osteoblast-like cells. Nevertheless, the HA coating improved the cell interactions with the poly-Si surfaces based on the cell affinity to the specific chemical composition of the bone-like HA and/or to the higher HA roughness.

  13. Ferroelectric and ferromagnetic properties in BaTiO{sub 3} thin films on Si (100)

    SciTech Connect

    Singamaneni, Srinivasa Rao Prater, John T.; Punugupati, Sandhyarani; Hunte, Frank; Narayan, Jagdish

    2014-09-07

    In this paper, we report on the epitaxial integration of room temperature lead-free ferroelectric BaTiO{sub 3} thin (∼1050 nm) films on Si (100) substrates by pulsed laser deposition technique through a domain matching epitaxy paradigm. We employed MgO and TiN as buffer layers to create BaTiO{sub 3}/SrRuO{sub 3}/MgO/TiN/Si (100) heterostructures. C-axis oriented and cube-on-cube epitaxial BaTiO{sub 3} is formed on Si (100) as evidenced by the in-plane and out-of-plane x-ray diffraction, and transmission electron microscopy. X-ray photoemission spectroscopic measurements show that Ti is in 4(+) state. Polarization hysteresis measurements together with Raman spectroscopy and temperature-dependent x-ray diffraction confirm the room temperature ferroelectric nature of BaTiO{sub 3}. Furthermore, laser irradiation of BaTiO{sub 3} thin film is found to induce ferromagnetic-like behavior but affects adversely the ferroelectric characteristics. Laser irradiation induced ferromagnetic properties seem to originate from the creation of oxygen vacancies, whereas the pristine BaTiO{sub 3} shows diamagnetic behavior, as expected. This work has opened up the route for the integration of room temperature lead-free ferroelectric functional oxides on a silicon platform.

  14. Interfacial reactions and surface analysis of W thin film on 6H-SiC

    NASA Astrophysics Data System (ADS)

    Thabethe, T. T.; Hlatshwayo, T. T.; Njoroge, E. G.; Nyawo, T. G.; Ntsoane, T. P.; Malherbe, J. B.

    2016-03-01

    Tungsten (W) thin film was deposited on bulk single crystalline 6H-SiC substrate and annealed in vacuum at temperatures ranging from 700 to 1000 °C for 1 h. The resulting solid-state reactions, phase composition and surface morphology were investigated by Rutherford backscattering spectroscopy (RBS), grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). XRD was used to identify the phases present and to confirm the RBS results. The RBS spectra were simulated using the RUMP software in order to obtain the deposited layer thickness, composition of reaction zone and detect phase formation at the interface. RBS results showed that interaction between W and SiC started at 850 °C. The XRD analysis showed that WC and CW3 were the initial phases formed at 700 and 800 °C. The concentration of the phases was however, too low to be detected by RBS analysis. At temperatures of 900 and 1000 °C, W reacted with the SiC substrate and formed a mixed layer containing a silicide phase (WSi2) and a carbide phase (W2C). The SEM images of the as-deposited samples showed that the W thin film had a uniform surface with small grains. The W layer became heterogeneous during annealing at higher temperatures as the W granules agglomerated into island clusters at temperatures of 800 °C and higher.

  15. Fabrication of strained Ge film using a thin SiGe virtual substrate

    NASA Astrophysics Data System (ADS)

    Lei, Guo; Shuo, Zhao; Jing, Wang; Zhihong, Liu; Jun, Xu

    2009-09-01

    This paper describes a method using both reduced pressure chemical vapor deposition (RPCVD) and ultrahigh vacuum chemical vapor deposition (UHVCVD) to grow a thin compressively strained Ge film. As the first step, low temperature RPCVD was used to grow a fully relaxed SiGe virtual substrate layer at 500 °C with a thickness of 135 nm, surface roughness of 0.3 nm, and Ge content of 77%. Then, low temperature UHVCVD was used to grow a high quality strained pure Ge film on the SiGe virtual substrate at 300 °C with a thickness of 9 nm, surface roughness of 0.4 nm, and threading dislocation density of ~ 105 cm-2. Finally, a very thin strained Si layer of 1.5-2 nm thickness was grown on the Ge layer at 550 °C for the purpose of passivation and protection. The whole epitaxial layer thickness is less than 150 nm. Due to the low growth temperature, the two-dimensional layer-by-layer growth mode dominates during the epitaxial process, which is a key factor for the growth of high quality strained Ge films.

  16. Reduced Cu concentration in CuAl-LPE-grown thin Si layers

    SciTech Connect

    Wang, T.H.; Ciszek, T.F.; Asher, S.; Reedy, R.

    1995-08-01

    Cu-Al has been found to be a good solvent system to grow macroscopically smooth Si layers with thicknesses in tens of microns on cast MG-Si substrates by liquid phase epitaxy (LPE) at temperatures near 900{degrees}C. This solvent system utilizes Al to ensure good wetting between the solution and substrate by removing silicon native oxides, and employs Cu to control Al doping into the layers. Isotropic growth is achieved because of a high concentration of solute silicon in the solution and the resulting microscopically rough interface. The incorporation of Cu in the Si layers, however, was a concern since Cu is a major solution component and is generally regarded as a bad impurity for silicon devices due to its fast diffusivity and deep energy levels in the band gap. A study by Davis shows that Cu will nonetheless not degrade solar cell performance until above a level of 10{sup 17} cm{sup -3}. This threshold is expected to be even higher for thin layer silicon solar cells owing to the less stringent requirement on minority carrier diffusion length. But to ensure long term stability of solar cells, lower Cu concentrations in the thin layers are still preferred.

  17. Compositionally graded SiCu thin film anode by magnetron sputtering for lithium ion battery

    SciTech Connect

    Polat, B. D.; Eryilmaz, O. L.; Keles, O; Erdemir, A; Amine, Khalil

    2015-10-22

    Compositionally graded and non-graded composite SiCu thin films were deposited by magnetron sputtering technique on Cu disks for investigation of their potentials in lithium ion battery applications. The compositionally graded thin film electrodes with 30 at.% Cu delivered a 1400 mAh g-1 capacity with 80% Coulombic efficiency in the first cycle and still retained its capacity at around 600 mAh g-1 (with 99.9% Coulombic efficiency) even after 100 cycles. On the other hand, the non-graded thin film electrodes with 30 at.% Cu exhibited 1100 mAh g-1 as the first discharge capacity with 78% Coulombic efficiency but the cycle life of this film degraded very quickly, delivering only 250 mAh g-1 capacity after 100th cycles. Not only the Cu content but also the graded film thickness were believed to be the main contributors to the much superior performance of the compositionally graded SiCu films. We also believe that the Cu-rich region of the graded film helped reduce internal stress build-up and thus prevented film delamination during cycling. In particular, the decrease of Cu content from interface region to the top of the coating reduced the possibility of stress build-up across the film during cycling, thus leading to a high electrochemical performance.

  18. Investigation of the chemo-mechanical coupling in lithiation/delithiation of amorphous Si through simulations of Si thin films and Si nanospheres

    NASA Astrophysics Data System (ADS)

    Wang, Miao; Xiao, Xinran

    2016-09-01

    A strong asymmetric rate behavior between lithiation and delithiation has been observed in amorphous Si (a-Si) anode in the form of thin films, but not in other geometries, such as Si nanospheres. This work investigated the rate behavior of the two geometries through numerical simulations. The results reveal that the rate behavior is affected by the geometry and the constraint of the electrode, the chemo-mechanical coupling, and the prior process. A substrate-constrained film has a relatively low surface/volume ratio and a constant surface area. Its lithiation has a great tendency to be hindered by surface limitation. The chemo-mechanical coupling also plays an important role. The stress profiles differ in the two geometries but both affect the lithiation process more than the delithiation process. The overall delithiation capacity is affected very little by the chemo-mechanical coupling. In cyclic loading, the delithiation capacity is reduced at the same rate as the lithiation capacity because of the low initial state of charge in the electrode. The asymmetric rate behavior was absent under cyclic loading. On the other hand, a slow charging process resulted in a better retained delithiation capacity and an asymmetric rate behavior at higher rates.

  19. Manufacturing and photoelectrical properties of P-doped a-Si:H thin films deposited by PECVD

    NASA Astrophysics Data System (ADS)

    Liao, Naiman; Li, Wei; Jiang, Yadong; Kuang, Yuejun; Qi, Kangcheng; Wu, Zhiming; Li, Shibin

    2007-12-01

    The effect of gas temperature (T g) on surface morphology, surface roughness, photoelectrical performances of a-Si:H thin films deposited by PECVD at 250°C substrate temperature has been investigated by atomic force microscopy, spectrometric ellipsometry and semiconductor characterization system, respectively. It is found that the surface morphology and density (ρ) as well as the photoelectrical properties such as refractive index (n), dark conductivity (σ), temperature coefficient of resistance (TCR) and activation energy (E a) remarkably depend on T g of SiH 4 fed in reaction chamber. The higher the T g, the larger the clusters of a-Si:H thin films deposited. Also, refractive index of a-Si:H thin films increase as T g rises and the relationship between T g enhancement of n and the densification of the films is observed. It is indicated that σ varies by two orders of magnitude but TCR decreases by 1.6 %/°C, and E a gradually decreases linearly from 289.0 to 138.1 meV with T g varying from room temperature to 160°C. The results of present study suggest that T g in PECVD chamber plays an important role in the deposition of a-Si:H thin films and directly affects the surface morphology and photoelectrical properties of films. Control of surface morphology, photoelectrical properties of a-Si:H thin films through changing T g can be usefully applied to the manufacturing of photoelectrical devices.

  20. High-conductivity SiO2-matrix B-doped Si-NC thin films by following ion-beam treatment

    NASA Astrophysics Data System (ADS)

    Huang, Junjun; Wang, Weiyan; Yang, Jie; Tan, Yongzhen; Chen, Wei; Ge, Tianyu; Zhang, Yajun; Gao, Min; Chen, Zhenming

    2016-09-01

    In this work, further ion-beam was performed on SiO2-matrix B-doped Si-NC (SBC) thin films in order to enhance conductivity. The effect of ionbeam type on the electrical properties of SBC thin films was investigated systematically. The results indicated that the conductivities of SBC thin films were significantly improved by both argon and hydrogen ion-beam treatments, and the higher the hydrogen ion ratio, the higher the conductivity of SBC thin films. The conductivity of SBC thin films was increased from 1.82 × 10-6 S/cm to 3.2 × 10-3 S/cm with following hydrogen-ion-beam treatment. The change in conductivity of SBC thin films was most possibly resultant from the ion-beam treatment facilitating the formation of higher superficial order and lower defects. An alternative method was proposed to prepare high-conductivity SBC thin films, which may be applied to other heterogeneous thin films.

  1. Improved gate oxide integrity of strained Si n-channel metal oxide silicon field effect transistors using thin virtual substrates

    NASA Astrophysics Data System (ADS)

    Yan, L.; Olsen, S. H.; Escobedo-Cousin, E.; O'Neill, A. G.

    2008-05-01

    This work presents a detailed study of ultrathin gate oxide integrity in strained Si metal oxide silicon field effect transistors (MOSFETs) fabricated on thin virtual substrates aimed at reducing device self-heating. The gate oxide quality and reliability of the devices are compared to those of simultaneously processed Si control devices and conventional thick virtual substrate devices that have the same Ge content (20%), strained Si channel thickness, and channel strain. The thin virtual substrates offer the same mobility enhancement as the thick virtual substrates (˜100% compared to universal mobility data) and are effective at reducing device self-heating. Up to 90% improvement in gate leakage current is demonstrated for the strained Si n-channel MOSFETs compared to that for the bulk Si controls. The lower leakage arises from the increased electron affinity in tensile strained Si and is significant due to the sizeable strain generated by using wafer-level stressors. The strain-induced leakage reductions also lead to major improvements in stress-induced leakage current (SILC) and oxide reliability. The lower leakage current of the thin and thick virtual substrate devices compares well to theoretical estimates based on the Wentzel-Kramers-Brillouin approximation. Breakdown characteristics also differ considerably between the devices, with the strained Si devices exhibiting a one order of magnitude increase in time to hard breakdown (THBD) compared to the Si control devices following high-field stressing at 17 MV cm-1. The strained Si devices are exempted from soft breakdown. Experimental based analytical leakage modeling has been carried out across the field range for the first time in thin oxides and demonstrates that Poole-Frenkel (PF) emissions followed by Fowler-Nordheim tunneling dominate gate leakage current at low fields in all of the devices. This contrasts to the frequently reported assumption that direct tunneling dominates gate leakage in ultrathin

  2. Fabrication and properties of ZnO/GaN heterostructure nanocolumnar thin film on Si (111) substrate

    PubMed Central

    2013-01-01

    Zinc oxide thin films have been obtained on bare and GaN buffer layer decorated Si (111) substrates by pulsed laser deposition (PLD), respectively. GaN buffer layer was achieved by a two-step method. The structure, surface morphology, composition, and optical properties of these thin films were investigated by X-ray diffraction, field emission scanning electron microscopy, infrared absorption spectra, and photoluminiscence (PL) spectra, respectively. Scanning electron microscopy images indicate that the flower-like grains were presented on the surface of ZnO thin films grown on GaN/Si (111) substrate, while the ZnO thin films grown on Si (111) substrate show the morphology of inclination column. PL spectrum reveals that the ultraviolet emission efficiency of ZnO thin film on GaN buffer layer is high, and the defect emission of ZnO thin film derived from Zni and Vo is low. The results demonstrate that the existence of GaN buffer layer can greatly improve the ZnO thin film on the Si (111) substrate by PLD techniques. PMID:23448090

  3. Suppression of excess oxygen for environmentally stable amorphous In-Si-O thin-film transistors

    SciTech Connect

    Aikawa, Shinya E-mail: TSUKAGOSHI.Kazuhito@nims.go.jp; Mitoma, Nobuhiko; Kizu, Takio; Tsukagoshi, Kazuhito E-mail: TSUKAGOSHI.Kazuhito@nims.go.jp; Nabatame, Toshihide

    2015-05-11

    We discuss the environmental instability of amorphous indium oxide (InO{sub x})-based thin-film transistors (TFTs) in terms of the excess oxygen in the semiconductor films. A comparison between amorphous InO{sub x} doped with low and high concentrations of oxygen binder (SiO{sub 2}) showed that out-diffusion of oxygen molecules causes drastic changes in the film conductivity and TFT turn-on voltages. Incorporation of sufficient SiO{sub 2} could suppress fluctuations in excess oxygen because of the high oxygen bond-dissociation energy and low Gibbs free energy. Consequently, the TFT operation became rather stable. The results would be useful for the design of reliable oxide TFTs with stable electrical properties.

  4. Structural and Electromagnetic Properties of Ni-Mn-Ga Thin Films Deposited on Si Substrates

    NASA Astrophysics Data System (ADS)

    Pereira, M. J.; Lourenço, A. A. C. S.; Amaral, V. S.

    2014-07-01

    Ni2MnGa thin films raise great interest due to their properties, which provide them with strong potential for technological applications. Ni2MnGa thin films were prepared by r.f. sputtering deposition on Si substrates at low temperature (400 ºC). Film thicknesses in the range 10-120 nm were obtained. A study of the structural, magnetic and electrical properties of the films is presented. We find that the deposited films show some degree of crystallinity, with coexisting cubic and tetragonal structural phases, the first one being preponderant over the latter, particularly in the thinner films. The films possess soft magnetic properties and their coercivity is thickness dependent in the range 15-200 Oe at 300K. Electrical resistivity measurements signal the structural transition and suggest the occurrence of avalanche and return-point memory effects, in temperature cycling through the magnetic/structural transition range.

  5. External beam IBA set-up with large-area thin Si3N4 window

    NASA Astrophysics Data System (ADS)

    Palonen, V.; Mizohata, K.; Nissinen, T.; Räisänen, J.

    2016-08-01

    A compact external beam setup has been constructed for Particle Induced X-ray Emission (PIXE) and Nuclear Reaction (NRA) analyses. The key issue in the design has been to obtain a wide beam spot size with maximized beam current utilizing a thin Si3N4 exit window. The employed specific exit window support enables use of foils with thickness of 100 nm for a beam spot size of 4 mm in diameter. The durable thin foil and the large beam spot size will be especially important for the complementary external beam NRA measurements. The path between the exit foil and sample is filled with flowing helium to minimize radiation hazard as well as energy loss and straggling, and to cool the samples. For sample-independent beam current monitoring and irradiation fluence measurement, indirect charge integration, based on secondary electron current measurement from a beam profilometer, is utilized.

  6. Compositional dependence of Young's moduli for amorphous FeCo-SiO{sub 2} thin films

    SciTech Connect

    Zhang, L.; Xie, J. L.; Deng, L. J.; Guo, Q.; Zhu, Z. W.; Bi, L.

    2011-04-01

    Systematic force-deflection measurements with microcantilevers and a combinatorial-deposition method have been used to investigate the Young's moduli of amorphous composite FeCo-SiO{sub 2} thin films as a function of film composition, with high compositional resolution. It is found that the modulus decreases monotonically with increasing FeCo content. Such a trend can be explained in terms of the metalloid atoms having a significant effect on the Young's moduli of metal-metalloid composites, which is associated with the strong chemical interaction between the metalloid and themetallic atoms rather than that between the metallic components themselves. This work provides an efficient and effective method to study the moduli of magnetic thin films over a largecomposition coverage, and to compare the relative magnitudes of moduli for differentcompositions at high compositional resolution.

  7. Design guideline of high efficiency crystalline Si thin film solar cell with nanohole array textured surface

    NASA Astrophysics Data System (ADS)

    Wang, Fei; Yu, Hongyu; Li, Junshuai; Wong, Shemein; Sun, Xiao Wei; Wang, Xincai; Zheng, Hongyu

    2011-04-01

    Silicon thin film with a nanohole (NH) array textured surface is systematically studied via simulation for solar energy harvesting and compared with a nanopillar (NP) array textured one. It is found that for the same thickness and optimized structure parameters, the NH array shows superior light trapping capability and thus, higher power conversion efficiency than its NP counterpart. The requirement for efficient cells at the optically optimized NH and NP geometries are studied in terms of minority carrier diffusion length, emitter doping level, and the emitter junction depth after considering the impact of surface recombination velocity. The results provide a practical guideline to design and fabricate high efficiency and cost effective NH textured Si thin film solar cells.

  8. Nanostructural features of nc-Si:H thin films prepared by PECVD

    NASA Astrophysics Data System (ADS)

    Shim, J.-H.; Im, Seongil; Cho, N.-H.

    2004-07-01

    Nanocrystalline hydrogenated silicon (nc-Si:H) thin films were deposited at room temperature by plasma enhanced chemical vapor deposition (PECVD): a mixture of SiH 4 and H 2 was introduced into the evacuated reaction chamber. When the H 2 flow rate was low, the density of SiH 3 bonds was high in the films. In particular, when the H 2 flow rate was 50 sccm, ˜2 nm-sized nanocrystallites were present in the films; a large number of Si clusters consisting of SiH 3 and SiH 2 bonds were present in the amorphous matrix of the films. When the H 2 flow rate was high, e.g. 100 sccm, a large number of SiH bonds contributed to the passivation of the surface of the large volume of nanocrystallites; a small number of Si clusters consisting of SiH 2 bonds were present in the amorphous matrix. The relative fraction of the SiH 3 and SiH 2 bonds in the amorphous matrix varied sensitively with either the H 2 flow rate or post-deposition annealing temperature. The variation was associated with the change in the intensity as well as the wavelength of the main PL peaks, indicating the change in the total volume as well as the size of the nanocrystallites in the films.

  9. Properties of thin a-C/Si:H coatings applied to TEXTOR

    NASA Astrophysics Data System (ADS)

    von Seggern, J.; Winter, J.; Grobusch, L.; Esser, H. G.; Vietzke, E.; Weschenfelder, F.; Hollenstein, Ch.; Künzli, H.; Ross, G. G.; Rubel, M.

    1995-04-01

    Thin, hydrogenated silicon and carbon containing films have been deposited by the siliconization procedure on targets made from some metal alloys, pure metals, graphite and Si single crystal. The deposits were investigated by electron microprobe and surface analysis techniques combined with ion sputtering, infrared spectroscopy, mass spectrometry, ellipsometry and by nuclear reaction and backscattering techniques. The stoichiometry of the layers were controlled by particle balance. They are amorphous, semitransparent, and homogeneous throughout the layer. They are hard, non abrasive, and adhere firmly to the substrate. Their density is ≈ 1.5 g cm -3 for a-C/Si:H and ≈2.0 g cm -3 for a-Si:H, the refractive index n = 2 ± 0.2, the extinction coefficient k ≪ 0.01. Carbon and silicon form carbidic SiC bonds, hydrogen is attached both to carbon and to silicon. The deposits are chemically inert to molecular oxygen, but they strongly getter O-ions. Chemical erosion rates of a-C/Si:H films by H + are a factor 30 less than those of pure carbon films (a-C:H).

  10. One-dimensional edge state of Bi thin film grown on Si(111)

    SciTech Connect

    Kawakami, Naoya; Lin, Chun-Liang; Kawai, Maki; Takagi, Noriaki; Arafune, Ryuichi

    2015-07-20

    The geometric and electronic structures of the Bi thin film grown on Si(111) were investigated by using scanning tunneling microscopy and spectroscopy. We have found two types of edges, one of which hosts an electronic state localized one-dimensionally. We also revealed the energy dispersion of the localized edge state from the evolution of quasiparticle interference patterns as a function of energy. These spectroscopic findings well reproduce those acquired for the cleaved surface of the bulk Bi crystal [I. K. Drozdov et al., Nat. Phys. 10, 664 (2014)]. The present results indicate that the deposited Bi film provides a tractable stage for further scrutiny of the one-dimensional edge state.

  11. Light-soaking effects on photoconductivity in a-Si:H thin films

    SciTech Connect

    Morgado, E.; Da Silva, M.R.; Henriques, R.T.

    1997-07-01

    Metastable defects have been created by light exposure in thin films of a-Si:H. The samples have been characterized by Photothermal Deflection Spectroscopy, Electron Spin Resonance, dark- and photo-conductivity. The experimental results are consistent with numerical calculations with a recombination model involving band tails and one class of correlated dangling-bond states. The effects of light-soaking on the light intensity and defect density dependences of photoconductivity are reproduced by the calculations. The model allows to explain the experimental trends by changes in the electronic occupation of the gap states produced by light-induced defects.

  12. Equilibrium shapes of polycrystalline silicon nanodots

    SciTech Connect

    Korzec, M. D. Wagner, B.; Roczen, M.; Schade, M.; Rech, B.

    2014-02-21

    This study is concerned with the topography of nanostructures consisting of arrays of polycrystalline nanodots. Guided by transmission electron microscopy (TEM) measurements of crystalline Si (c-Si) nanodots that evolved from a “dewetting” process of an amorphous Si (a-Si) layer from a SiO{sub 2} coated substrate, we investigate appropriate formulations for the surface energy density and transitions of energy density states at grain boundaries. We introduce a new numerical minimization formulation that allows to account for adhesion energy from an underlying substrate. We demonstrate our approach first for the free standing case, where the solutions can be compared to well-known Wulff constructions, before we treat the general case for interfacial energy settings that support “partial wetting” and grain boundaries for the polycrystalline case. We then use our method to predict the morphologies of silicon nanodots.

  13. Temperature-dependent ion mixing and diffusion during sputtering of thin films of CrSi2 on silicon

    NASA Technical Reports Server (NTRS)

    Shreter, U.; Nicolet, M.-A.; Fernandez, R.

    1983-01-01

    Measurements of sputtering yields and composition profiles have been carried out using backscattering spectrometry for samples of CrSi2 on Si irradiated wth 200-keV Xe ions. When the CrSi2 layer is thinner than the ion range, the sputtering yield ratio of Si to Cr increases from 3.5 for room-temperature irradiation to 65 at 290 C. For a thick sample, the corresponding increase is from 2.4 to 4.0 only. These changes are explained in terms of a rise in the Si surface concentration ot 290 C. The driving force for this process seems to be the establishment of stoichiometric CrSi2 compound. Transport of Si to the surface is by ion mixing in the thin sample and thermal diffusion through the thick layer.

  14. Controlled fabrication of Si nanocrystal delta-layers in thin SiO{sub 2} layers by plasma immersion ion implantation for nonvolatile memories

    SciTech Connect

    Bonafos, C.; Ben-Assayag, G.; Groenen, J.; Carrada, M.; Spiegel, Y.; Torregrosa, F.; Normand, P.; Dimitrakis, P.; Kapetanakis, E.; Sahu, B. S.; Slaoui, A.

    2013-12-16

    Plasma Immersion Ion Implantation (PIII) is a promising alternative to beam line implantation to produce a single layer of nanocrystals (NCs) in the gate insulator of metal-oxide semiconductor devices. We report herein the fabrication of two-dimensional Si-NCs arrays in thin SiO{sub 2} films using PIII and rapid thermal annealing. The effect of plasma and implantation conditions on the structural properties of the NC layers is examined by transmission electron microscopy. A fine tuning of the NCs characteristics is possible by optimizing the oxide thickness, implantation energy, and dose. Electrical characterization revealed that the PIII-produced-Si NC structures are appealing for nonvolatile memories.

  15. Robust topological surface states of Bi2Se3 thin films on amorphous SiO2/Si substrate and a large ambipolar gating effect

    NASA Astrophysics Data System (ADS)

    Bansal, Namrata; Koirala, Nikesh; Brahlek, Matthew; Han, Myung-Geun; Zhu, Yimei; Cao, Yue; Waugh, Justin; Dessau, Daniel S.; Oh, Seongshik

    2014-06-01

    The recent emergence of topological insulators (TI) has spurred intensive efforts to grow TI thin films on various substrates. However, little is known about how robust the topological surface states (TSS) are against disorders and other detrimental effects originating from the substrates. Here, we report the observation of a well-defined TSS on Bi2Se3 films grown on amorphous SiO2 (a-SiO2) substrates and a large gating effect on these films using the underneath doped-Si substrate as the back gate. The films on a-SiO2 were composed of c-axis ordered but random in-plane domains. However, despite the in-plane randomness induced by the amorphous substrate, the transport properties of these films were superior to those of similar films grown on single-crystalline Si(111) substrates, which are structurally better matched but chemically reactive with the films. This work sheds light on the importance of chemical compatibility, compared to lattice matching, for the growth of TI thin films, and also demonstrates that the technologically important and gatable a-SiO2/Si substrate is a promising platform for TI films.

  16. Deposition of SiNx Thin Film Using µ-SLAN Surface Wave Plasma Source

    NASA Astrophysics Data System (ADS)

    Xu, Ying-Yu; Ogishima, Takuya; Korzec, Dariusz; Nakanishi, Yoichiro; Hatanaka, Yoshinori

    1999-07-01

    A slot antenna (µ-SLAN) microwave surface wave plasma source was developed for SiNx thin film preparation. A µ-SLAN-produced argon plasma density up to 1011 cm-3 has been achieved at an axial position of about 43 cm from the ring cavity at a microwave power of 500 W and a chamber pressure of 0.5 Torr. High-speed deposition of SiNx thin film was performed using the µ-SLAN-assisted remote plasma enhanced chemical vapor deposition method incorporating tris(dimethylamino)silane (TDMAS) as a monomer source. The film deposition rate increased rapidly up to 270 nm/min when some hydrogen was mixed in the nitrogen gas and increased from 0 to 1%. A further increase of hydrogen content, however, only slightly increased the film deposition rate. A high deposition rate of 280 nm/min was obtained when 15% hydrogen was mixed in the nitrogen gas, with the chamber pressure and microwave power at 1.5 Torr and 500 W, respectively.

  17. Time-resolved analysis of the white photoluminescence from chemically synthesized SiCxOy thin films and nanowires

    NASA Astrophysics Data System (ADS)

    Tabassum, Natasha; Nikas, Vasileios; Ford, Brian; Huang, Mengbing; Kaloyeros, Alain E.; Gallis, Spyros

    2016-07-01

    The study reported herein presents results on the room-temperature photoluminescence (PL) dynamics of chemically synthesized SiCxOy≤1.6 (0.19 < x < 0.6) thin films and corresponding nanowire (NW) arrays. The PL decay transients of the SiCxOy films/NWs are characterized by fast luminescence decay lifetimes that span in the range of 350-950 ps, as determined from their deconvoluted PL decay spectra and their stretched-exponential recombination behavior. Complementary steady-state PL emission peak position studies for SiCxOy thin films with varying C content showed similar characteristics pertaining to the variation of their emission peak position with respect to the excitation photon energy. A nearly monotonic increase in the PL energy emission peak, before reaching an energy plateau, was observed with increasing excitation energy. This behavior suggests that band-tail states, related to C-Si/Si-O-C bonding, play a prominent role in the recombination of photo-generated carriers in SiCxOy. Furthermore, the PL lifetime behavior of the SiCxOy thin films and their NWs was analyzed with respect to their luminescence emission energy. An emission-energy-dependent lifetime was observed, as a result of the modulation of their band-tail states statistics with varying C content and with the reduced dimensionality of the NWs.

  18. Nanocalorimetry: Using Si-micromachined Devices for Thermodynamic Measurements of Thin Films and Tiny Crystals

    NASA Astrophysics Data System (ADS)

    Hellman, Frances

    2006-03-01

    We have used Si micromachining to fabricate membrane-based calorimeters for measuring thermodynamic properties of microgram-quantity samples over a temperature range from 1.7 to 550K in magnetic fields to 8T. Prototype scaled down devices have been made which allow precise measurements of nanogram quantities. Different types of thermometers are used for different purposes and in different temperature ranges. Current development efforts are extending the temperature range to 0.3 - 800K, and we are collaborating with the national high magnetic field lab to extend the field range to 65T in pulsed magnets. These devices are particularly useful for specific heat measurements of thin film samples (100-400 nm thick) deposited directly onto the membrane through a Si micromachined evaporation mask. They have also been used for small bulk samples attached by conducting paint or In, and for powder samples dissolved in a solvent and dropped onto devices. The measurement technique used (relaxation method) is particularly suited to high fields because thermal conductance is measured in zero field and is field independent, while the relaxation time constant does not depend on thermometer calibration. The devices have been used with little modification for thermal conductivity and thermopower measurements, and are well suited to measurements of calorimetric signals such as those occurring at phase transitions or under irreversible thermal behavior. I will discuss device fabrication and thermal analysis which allow us to precisely identify heat flow in the devices and consequent limits on the absolute accuracy, as well as possible future directions for device development. I will also briefly discuss examples of measurements on several materials of current interest: 1) amorphous Si and its alloys, 2) high precision critical temperature studies of La1-xSrxMnO3 and La1-xCaxMnO3, 3) antiferromagnetic CoO nanoparticles and thin layers, 4) Fe/Cr giant magnetoresistance multilayers.

  19. Observations on Si-based micro-clusters embedded in TaN thin film deposited by co-sputtering with oxygen contamination

    SciTech Connect

    Lee, Young Mi; Jung, Min-Sang; Choi, Duck-Kyun E-mail: mcjung@oist.jp; Jung, Min-Cherl E-mail: mcjung@oist.jp

    2015-08-15

    Using scanning electron microscopy (SEM) and high-resolution x-ray photoelectron spectroscopy with the synchrotron radiation we investigated Si-based micro-clusters embedded in TaSiN thin films having oxygen contamination. TaSiN thin films were deposited by co-sputtering on fixed or rotated substrates and with various power conditions of TaN and Si targets. Three types of embedded micro-clusters with the chemical states of pure Si, SiO{sub x}-capped Si, and SiO{sub 2}-capped Si were observed and analyzed using SEM and Si 2p and Ta 4f core-level spectra were derived. Their different resistivities are presumably due to the different chemical states and densities of Si-based micro-clusters.

  20. Nanostructured multilayered thin film barriers for Mg{sub 2}Si thermoelectric materials

    SciTech Connect

    Battiston, S.; Boldrini, S.; Fiameni, S.; Agresti, F.; Famengo, A.; Fabrizio, M.; Barison, S.

    2012-06-26

    The Mg{sub 2}Si-based alloys are promising candidates for thermoelectric energy conversion in the middle-high temperature range in order to replace lead compounds. The main advantages of silicide-based thermoelectrics are the nontoxicity and the abundance of their constituent elements in the earth crust. The drawback of such kind of materials is their oxygen sensitivity at high temperature that entails their use under vacuum or inert atmosphere. In order to limit the corrosion phenomena, nanostructured multilayered molybdenum silicide-based materials were deposited via RF magnetron sputtering onto stainless steel, alumina and silicon (100) to set up the deposition process and then onto Mg{sub 2}Si pellets. XRD, EDS, FE-SEM and electrical measurements at high temperature were carried out in order to obtain, respectively, the structural, compositional, morphological and electrical characterization of the deposited coatings. At the end, the mechanical behavior of the system thin film/Mg{sub 2}Si-substrate as a function of temperature and the barrier properties for oxygen protection after thermal treatment in air at high temperature were qualitatively evaluated by FE-SEM.

  1. Electrical switching in sol-gel derived Ag -SiO2 nanocomposite thin films

    NASA Astrophysics Data System (ADS)

    Sarkar, D. K.; Cloutier, F.; El Khakani, M. A.

    2005-04-01

    The sol-gel technique has been used to produce Ag -SiO2 nanocomposite thin films consisting of silver nanoparticles embedded in a SiO2 matrix. The size of the silver nanoparticles is of about (4±0.2)nm when the firing temperature is in the (500-700°C ) range, as determined from ultraviolet-visible spectroscopy analysis. The increase of the firing temperature beyond 300°C, was found to lead to an outer diffusion of Ag toward the surface. As a consequence the surface atomic concentration of Ag is found to increase from 1.3% to 12% for the as-dried (at 120°C) and for those further fired at 600°C, respectively. On the other hand, it is shown that the electrical behavior of these Ag -SiO2 nanocomposite films can drastically change from highly insulating to conducting depending on the firing temperature used. In the intermediate firing temperature (300-400°C) range, the films were found to exhibit a reversible switching behavior with a resistivity transition of about 7 orders of magnitude between the insulating (OFF) and the conducting (ON) state. Such an electrical switching could be explained by a change in the predominant conduction mechanism of the films.

  2. Nanostructured multilayered thin film barriers for Mg2Si thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Battiston, S.; Boldrini, S.; Fiameni, S.; Agresti, F.; Famengo, A.; Fabrizio, M.; Barison, S.

    2012-06-01

    The Mg2Si-based alloys are promising candidates for thermoelectric energy conversion in the middle-high temperature range in order to replace lead compounds. The main advantages of silicide-based thermoelectrics are the nontoxicity and the abundance of their constituent elements in the earth crust. The drawback of such kind of materials is their oxygen sensitivity at high temperature that entails their use under vacuum or inert atmosphere. In order to limit the corrosion phenomena, nanostructured multilayered molybdenum silicide-based materials were deposited via RF magnetron sputtering onto stainless steel, alumina and silicon (100) to set up the deposition process and then onto Mg2Si pellets. XRD, EDS, FE-SEM and electrical measurements at high temperature were carried out in order to obtain, respectively, the structural, compositional, morphological and electrical characterization of the deposited coatings. At the end, the mechanical behavior of the system thin film/Mg2Si-substrate as a function of temperature and the barrier properties for oxygen protection after thermal treatment in air at high temperature were qualitatively evaluated by FE-SEM.

  3. Electrochemical Evaluation of Thin-Film Li-Si Anodes Prepared by Plasma Spraying

    SciTech Connect

    GUIDOTTI,RONALD A.; REINHARDT,FREDERICK W.; SCHARRER,GREGORY L.

    1999-09-08

    Thin-film electrodes of a plasma-sprayed Li-Si alloy were evaluated for use as anodes in high-temperature thermally activated (thermal) batteries. These anodes were prepared using 44% Li/56% Si (w/w) material as feed material in a special plasma-spray apparatus under helium or hydrogen, to protect this air- and moisture-sensitive material during deposition. Anodes were tested in single cells using conventional pressed-powder separators and lithiated pyrite cathodes at temperatures of 400 to 550 C at several different current densities. A limited number of 5-cell battery tests were also conducted. The data for the plasma-sprayed anodes was compared to that for conventional pressed-powder anodes. The performance of the plasma-sprayed anodes was inferior to that of conventional pressed-powder anodes, in that the cell emfs were lower (due to the lack of formation of the desired alloy phases) and the small porosity of these materials severely limited their rate capability. Consequently, plasma-sprayed Li-Si anodes would not be practical for use in thermal batteries.

  4. Investigations of Ar ion irradiation effects on nanocrystalline SiC thin films

    NASA Astrophysics Data System (ADS)

    Craciun, V.; Craciun, D.; Socol, G.; Behdad, S.; Boesl, B.; Himcinschi, C.; Makino, H.; Socol, M.; Simeone, D.

    2016-06-01

    The effects of 800 keV Ar ion irradiation on thin nanocrystalline SiC films grown on (100) Si substrates using the pulsed laser deposition (PLD) technique were investigated. On such PLD grown films, which were very dense, flat and smooth, X-ray reflectivity, glancing incidence X-ray diffraction and nanoindentation investigations were easily performed to evaluate changes induced by irradiation on the density, surface roughness, crystalline structure, and mechanical properties. Results indicated that the SiC films retained their crystalline nature, the cubic phase partially transforming into the hexagonal phase, which had a slightly higher lattice parameter then the as-deposited films. Simulations of X-ray reflectivity curves indicated a 3% decrease of the films density after irradiation. Nanoindentation results showed a significant decrease of the hardness and Young's modulus values with respect to those measured on as-deposited films. Raman and X-ray photoelectron spectroscopy investigations found an increase of the Csbnd C bonds and a corresponding decrease of the Sisbnd C bonds in the irradiated area, which could explain the degradation of mechanical properties.

  5. Deposition of SiNx Thin Film Using μ-SLAN Surface Wave Plasma Source

    NASA Astrophysics Data System (ADS)

    Ying-Yu, Xu; Takuya, Ogishima; Dariusz, Korzec; Yoichiro, Nakanishi; Yoshinori, Hatanaka

    1998-10-01

    Remote plasma CVD method has been used in fabrication of high quality thin films. It is a useful method in decreasing damage from ion bombardment and in analysis of film formation mechanism. In our research, as the film deposition rate depends on neutral radical density, hence high-density plasma is needed for high-speed deposition. In this research, a μ-SLAN (Slot ANtenna) microwave surface wave plasma source was adapted for thin film deposition. The μ-SLAN is an efficient plasma generator in which microwave power is coupled from a ring cavity with several slots around quartz discharge tube. We measured parameters of argon plasma along the discharge tube by a double Langmuir probe. The electron density was measured as about 10^11 cm-3 at an axial position of 43 cm from ring cavity, a microwave power of 500 W and a pressure of 0.5 torr. Using μ-SLAN, SiNx thin film was deposited and high deposition rate was obtained. The highest deposition rate of 280 nm/min was obtained for plasma gas containing 15% of hydrogen in nitrogen with the pressure and power of 1.5 torr and 500 W respectively.

  6. Ordered arrays of Si and Ge nanocrystals via dewetting of pre-patterned thin films

    NASA Astrophysics Data System (ADS)

    Berbezier, I.; Aouassa, M.; Ronda, A.; Favre, L.; Bollani, M.; Sordan, R.; Delobbe, A.; Sudraud, P.

    2013-02-01

    We develop self-organisation processes for the fabrication of 2D arrays of Si and Ge quantum dots. The processes make use of the dewetting phenomenon which involves the transformation of a 2D thin film into an array of isolated 3D islands through a morphological instability. We show that self-organization of monodisperse ultra-small nanocrystals (NCs) into large scale patterns with ad hoc features can be created via heterogeneous dewetting. The process involves dewetting of thin films nanopatterned by electron beam lithography (EBL) or liquid metal alloy source focused ion beam (LMAIS-FIB). Heterogeneous dewetting is initiated at the edges of the patterns. It provokes the retraction of the thin film following the kinetics of surface diffusion and ends by the formation of faceted monocrystalline NCs regularly positioned. Their geometrical features and lateral arrangements can be tuned by changing the pitch, size, and shape of the patterns. The process developed in this study is adapted to the fabrication of NCs based floating gate memories.

  7. Ferromagnetism and Nonmetallic Transport of Thin-Film α-FeSi2 : A Stabilized Metastable Material

    DOE PAGESBeta

    Cao, Guixin; Singh, D. J.; Zhang, X. -G.; Samolyuk, German; Qiao, Liang; Parish, Chad; Jin, Ke; Zhang, Yanwen; Guo, Hangwen; Tang, Siwei; et al

    2015-04-07

    Tmore » he epitaxially stabilized metallic α-FeSi2 thin films on Si(001) were grown using pulsed laser deposition. While the bulk material of α-FeSi2 is a high temperature metastable phase and nonmagnetic, the thin film is stabilized at room temperature and shows unusual electronic transport and magnetic properties due to strain modification. he transport renders two different conducting states with a strong crossover at 50 K accompanied by an onset of ferromagnetism as well as a substantial magnetocaloric effect and magnetoresistance. hese experimental results are discussed in terms of the unusual electronic structure of α-FeSi2 obtained within density functional calculations and Boltzmann transport calculations with and without strain. Our findings provide an example of a tailored material with interesting physics properties for practical applications.« less

  8. Strain-Induced Electrical Properties of Lead Zirconate Titanate Thin Films on a Si wafer with Controlled Oxide Electrode Structure

    NASA Astrophysics Data System (ADS)

    Ohno, Tomoya; Ishiduka, Masaaki; Arai, Takashi; Yanagida, Hiroaki; Matsuda, Takeshi; Sakamoto, Naonori; Wakiya, Naoki; Suzuki, Hisao

    2012-09-01

    This paper shows the electrical properties of ferroelectric thin films with large compressive residual stress. In this study, the large compressive strain was applied to lead zirconate titanate (PZT) thin films by designing the bottom electrode structure on a Si wafer. The materials selected for the bottom electrode were lanthanum nickel oxide (LNO) and lanthanum strontium cobalt oxide [LSCO; (La0.5Sr0.5)CoO3] from the viewpoint of thermal expansion coefficients. As a result, the PZT thin films with morphotropic phase boundary (MPB) composition received compressive residual stress up to approximately 0.8 GPa from the bottom electrode even on a Si wafer. The compressive residual stress concomitantly increased with increasing LSCO layer thickness. In addition, the remanent polarization of the PZT thin films increased with increasing compressive residual stress.

  9. Thickness of the {SiO2}/{Si} interface and composition of silicon oxide thin films: effect of wafer cleaning procedures

    NASA Astrophysics Data System (ADS)

    Stedile, F. C.; Baumvol, I. J. R.; Oppenheim, I. F.; Trimaille, I.; Ganem, J.-J.; Rigo, S.

    1996-09-01

    We determined the areal density of Si atoms constituting the oxide-silicon interface and the stoichiometry of ultra-thin silicon oxide films, thermally grown on Si(001) in dry 18O 2 atmospheres, using the channeling of α-particles along the <001> axis of the Si substrates associated with grazing angle detection of the scattered particles. The amount of 18O atoms in the films was determined independently using the 18O(p,α) 15N nuclear reaction at 730 keV. The Si wafers were submitted to different cleaning procedures before oxidation in 18O 2, namely: standard RCA cleaning, HF etching followed by a rinse in ethanol and rapid thermal cleaning (RTC) under high vacuum. The stoichiometry of all oxide films having thicknesses between 2 and 13 nm could be fitted assuming a ratio {O}/{Si} = 2 , that is, the films were constituted by silicon dioxide. By comparing the results for samples cleaned in different ways, however, we noticed a pronounced change in the number of atoms in the non-registered Si layers at the {SiO2}/{Si} interface and so in the thickness of these interfaces.

  10. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Growth of High Quality Strained-Si on Ultra-Thin SiGe-on-Insulator Substrate

    NASA Astrophysics Data System (ADS)

    Liu, Xu-Yan; Liu, Wei-Li; Ma, Xiao-Bo; Chen, Chao; Song, Zhi-Tang; Lin, Cheng-Lu

    2009-11-01

    Ultra-thin and near-fully relaxed SiGe substrate is fabricated using a modified Ge condensation technique, and then a 25-nm-thick biaxially tensile strained-Si with a low rms roughness is epitaxially deposited on a SiGeon-Insulator (SGOI) substrate by ultra high vacuum chemical vapor deposition (UHVCVD). High-Resolution cross-sectional transmission electron microscope (HR-XTEM) observations reveal that the strained-Si/SiGe layer is dislocation-free and the atoms at the interface are well aligned. Furthermore, secondary ion mass spectrometry (SIMS) results show a sharp interface between layers and a uniform distribution of Ge in the SiGe layer. One percent in-plane tensile strain in the strained-Si layer is confirmed by ultraviolet (UV) Raman spectra, and the stress maintained even after a 30-s rapid thermal annealing (RTA) process at 1000°C According to those results, devices based on strained-Si are expected to have a better performance than the conventional ones.

  11. Environmental aging in polycrystalline-Si photovoltaic modules: comparison of chamber-based accelerated degradation studies with field-test data

    NASA Astrophysics Data System (ADS)

    Lai, T.; Biggie, R.; Brooks, A.; Potter, B. G.; Simmons-Potter, K.

    2015-09-01

    Lifecycle degradation testing of photovoltaic (PV) modules in accelerated-degradation chambers can enable the prediction both of PV performance lifetimes and of return-on-investment for installations of PV systems. With degradation results strongly dependent on chamber test parameters, the validity of such studies relative to fielded, installed PV systems must be determined. In the present work, accelerated aging of a 250 W polycrystalline silicon module is compared to real-time performance degradation in a similar polycrystalline-silicon, fielded, PV technology that has been operating since October 2013. Investigation of environmental aging effects are performed in a full-scale, industrial-standard environmental chamber equipped with single-sun irradiance capability providing illumination uniformity of 98% over a 2 x 1.6 m area. Time-dependent, photovoltaic performance (J-V) is evaluated over a recurring, compressed night-day cycle providing representative local daily solar insolation for the southwestern United States, followed by dark (night) cycling. This cycle is synchronized with thermal and humidity environmental variations that are designed to mimic, as closely as possible, test-yard conditions specific to a 12 month weather profile for a fielded system in Tucson, AZ. Results confirm the impact of environmental conditions on the module long-term performance. While the effects of temperature de-rating can be clearly seen in the data, removal of these effects enables the clear interpretation of module efficiency degradation with time and environmental exposure. With the temperature-dependent effect removed, the normalized efficiency is computed and compared to performance results from another panel of similar technology that has previously experienced identical climate changes in the test yard. Analysis of relative PV module efficiency degradation for the chamber-tested system shows good comparison to the field-tested system with ~2.5% degradation following

  12. CO Oxidation Prefers the Eley-Rideal or Langmuir-Hinshelwood Pathway: Monolayer vs Thin Film of SiC.

    PubMed

    Sinthika, S; Vala, Surya Teja; Kawazoe, Y; Thapa, Ranjit

    2016-03-01

    Using the first-principles approach, we investigated the electronic and chemical properties of wurtzite silicon carbide (2H-SiC) monolayer and thin film structures and substantiated their catalytic activity toward CO oxidation. 2H-SiC monolayer, being planar, is quite stable and has moderate binding with O2, while CO interacts physically; thus, the Eley-Rideal (ER) mechanism prevails over the Langmuir-Hinshelwood (LH) mechanism with an easily cleared activation barrier. Contrarily, 2H-SiC thin film, which exhibits a nonplanar structure, allows moderate binding of both CO and O2 on its surface, thus favoring the LH mechanism over the ER one. Comprehending these results leads to a better understanding of the reaction mechanisms involving structural contrast. Weak overlapping between the 2p(z)(C) and 3p(z)(Si) orbitals of the SiC monolayer system has been found to be the primary reason to revert the active site toward sp(3) hybridization, during interaction with the molecules. In addition, the influences of graphite and Ag(111) substrates on the CO oxidation mechanism were also studied, and it is observed that the ER mechanism is preserved on SiC/G system, while CO oxidation on the SiC/Ag(111) system follows the LH mechanism. The calculated Sabatier activities of the SiC catalysts show that the catalysts are very efficient in catalyzing CO oxidation.

  13. CO Oxidation Prefers the Eley-Rideal or Langmuir-Hinshelwood Pathway: Monolayer vs Thin Film of SiC.

    PubMed

    Sinthika, S; Vala, Surya Teja; Kawazoe, Y; Thapa, Ranjit

    2016-03-01

    Using the first-principles approach, we investigated the electronic and chemical properties of wurtzite silicon carbide (2H-SiC) monolayer and thin film structures and substantiated their catalytic activity toward CO oxidation. 2H-SiC monolayer, being planar, is quite stable and has moderate binding with O2, while CO interacts physically; thus, the Eley-Rideal (ER) mechanism prevails over the Langmuir-Hinshelwood (LH) mechanism with an easily cleared activation barrier. Contrarily, 2H-SiC thin film, which exhibits a nonplanar structure, allows moderate binding of both CO and O2 on its surface, thus favoring the LH mechanism over the ER one. Comprehending these results leads to a better understanding of the reaction mechanisms involving structural contrast. Weak overlapping between the 2p(z)(C) and 3p(z)(Si) orbitals of the SiC monolayer system has been found to be the primary reason to revert the active site toward sp(3) hybridization, during interaction with the molecules. In addition, the influences of graphite and Ag(111) substrates on the CO oxidation mechanism were also studied, and it is observed that the ER mechanism is preserved on SiC/G system, while CO oxidation on the SiC/Ag(111) system follows the LH mechanism. The calculated Sabatier activities of the SiC catalysts show that the catalysts are very efficient in catalyzing CO oxidation. PMID:26866799

  14. High-quality eutectic-metal-bonded AlGaAs-GaAs thin films on Si substrates

    NASA Astrophysics Data System (ADS)

    Venkatasubramanian, R.; Timmons, M. L.; Humphreys, T. P.; Keyes, B. M.; Ahrenkiel, R. K.

    1992-02-01

    Device quality GaAs-AlGaAs thin films have been obtained on Si substrates, using a novel approach called eutectic-metal-bonding (EMB). This involves the lattice-matched growth of GaAs-AlGaAs thin films on Ge substrates, followed by bonding onto a Si wafer. The Ge substrates are selectively removed by a CF4/O2 plasma etch, leaving high-quality GaAs-AlGaAs thin films on Si substrates. A minority-carrier lifetime of 103 ns has been obtained in a EMB GaAs-AlGaAs double heterostructure on Si, which is nearly forty times higher than the state-of-the-art lifetime for heteroepitaxial GaAs on Si, and represents the largest reported minority-carrier lifetime for a freestanding GaAs thin film. In addition, a negligible residual elastic strain in the EMB GaAs-AlGaAs films has been determined from Raman spectroscopy measurements.

  15. Structural and photoelectronic properties of a-SiGe:H thin films with varied Ge prepared by PECVD

    NASA Astrophysics Data System (ADS)

    Xu, Rui; Li, Wei; He, Jian; Qi, Kang-Cheng; Jiang, Ya-Dong

    2011-12-01

    Hydrogenated amorphous silicon-germanium (a-SiGe:H) alloy thin films were fabricated by conventional radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) with a gas mixture of silane (SiH4) and germane (GeH4). The structural, optical and electrical properties of the films with different gas volume fraction of germane were investigated by Raman and Fourier transform infrared (FTIR) spectroscopy, ultraviolet and visible (UV-vis) spectroscopy and I-V curves, respectively. The amorphous network and structural disorder in the a-SiGe:H thin films were evaluated by Raman spectroscopy. Meanwhile, the Si-H and Ge-H configurations of the films were investigated by FTIR spectroscopy. From UV-vis spectroscopy and I-V curves, the optical and electrical properties of the testing films could be deduced with varied germanium. It can be concluded that the structural and photoelectronic properties of a-SiGe:H thin films can be influenced apparently by varing of GeH4/(SiH4+ GeH4) ratio in PECVD process.

  16. Structural properties of reactively sputtered W-Si-N thin films

    SciTech Connect

    Vomiero, A.; Boscolo Marchi, E.; Quaranta, A.; Della Mea, G.; Brusa, R. S.; Mariotto, G.; Felisari, L.; Frabboni, S.; Tonini, R.; Ottaviani, G.; Mattei, G.; Scandurra, A.; Puglisi, O.

    2007-08-01

    Tungsten-silicon-nitrogen, W-Si-N, ternary thin films have been reactively sputter deposited from W{sub 5}Si{sub 3} and WSi{sub 2} targets using several nitrogen partial pressures. The films have been thermal annealed in the 600-1000 deg. C temperature range and a wide region of the W-Si-N ternary phase diagram has been explored by changing the N{sub 2}/Ar ratio during the deposition. Multitechnique approach was adopted for the analysis of the samples. Composition has been determined via ion beam analysis; chemical states were investigated using x-ray photoelectron spectroscopy (XPS); crystalline structure was studied using transmission electron microscopy (TEM) and x-ray diffraction (XRD) and surface morphology by scanning electron microscope. The films deposited in pure argon atmosphere are tungsten rich and approach the target contents as N{sub 2}/Ar ratio is varied during deposition. Tungsten enrichment in the films is caused by resputtering of silicon which can be inhibited by the formation of silicon nitride, allowing films with Si/W ratio closer to the target compositions. The higher capability to form nitrides with silicon than with tungsten favors enhancement of nitrogen content in samples deposited from the silicon rich target (WSi{sub 2}). The samples with excess nitrogen content have shown losses of this element after thermal treatment. XPS measurements show a break of W-N bonds caused by thermal instability of tungsten nitrides. TEM and XRD revealed the segregation of tungsten in form of metallic or silicide nanoclusters in samples with low nitrogen content (W{sub 58}Si{sub 21}N{sub 21} and W{sub 24}Si{sub 42}N{sub 34}). High amounts of nitrogen were revealed to be highly effective in inhibiting metallic cluster coalescence. Measurements of electrical resistivity of as deposited films were performed using four point probe technique. They were found to lie in the range between 0.4 and 79 m{omega} cm depending on sample composition.

  17. Electrical evaluation of crack generation in SiNx and SiOxNy thin-film encapsulation layers for OLED displays

    NASA Astrophysics Data System (ADS)

    Park, Eun Kil; Kim, Sungmin; Heo, Jaeyeong; Kim, Hyeong Joon

    2016-05-01

    By measuring leakage current density, we detected crack generation in silicon nitride (SiNx) and silicon oxynitride (SiOxNy) thin-film encapsulation layers, and correlated with the films' water vapor permeability characteristics. After repeated bending cycles, both the changes in water vapor transmission rate and leakage current density were directly proportional to the crack density. Thick SiNx films had better water vapor barrier characteristics in their pristine state, but cyclic loading led to fast failure. Varying the atomic concentration of the SiOxNy films affected their bending reliability. We attribute these differences to changes in the shape of the crack tip as the oxygen content varies.

  18. Internal structure of copper(II)-phthalocyanine thin films on SiO{sub 2}/Si substrates investigated by grazing incidence x-ray reflectometry

    SciTech Connect

    Brieva, A. C.; Jenkins, T. E.; Jones, D. G.; Stroessner, F.; Evans, D. A.; Clark, G. F.

    2006-04-01

    The internal structure of copper(II)-phthalocyanine (CuPc) thin films grown on SiO{sub 2}/Si by organic molecular beam deposition has been studied by grazing incidence x-ray reflectometry (GIXR) and atomic force microscopy. The electronic density profile is consistent with a structure formed by successive monolayers of molecules in the {alpha} form with the b axis lying in the substrate surface plane. The authors present an electronic density profile model of CuPc films grown on SiO{sub 2}/Si. The excellent agreement between the model and experimental data allows postdeposition monitoring of the internal structure of the CuPc films with the nondestructive GIXR technique, providing a tool for accurate control of CuPc growth on silicon-based substrates. In addition, since the experiments have been carried out ex situ, they show that these structures can endure ambient conditions.

  19. Anomalous Hall effect in polycrystalline Mn x Si1- x ( x ≈ 0.5) films with the self-organized distribution of crystallites over their shapes and sizes

    NASA Astrophysics Data System (ADS)

    Chernoglazov, K. Yu.; Nikolaev, S. N.; Rylkov, V. V.; Semisalova, A. S.; Zenkevich, A. V.; Tugushev, V. V.; Vasil'ev, A. L.; Chesnokov, Yu. M.; Pashaev, E. M.; Matveev, Yu. A.; Granovskii, A. B.; Novodvorskii, O. A.; Vedeneev, A. S.; Bugaev, A. S.; Drachenko, O.; Zhou, S.

    2016-04-01

    The structural, transport, and magnetic characteristics of polycrystalline Mn x Si1- x ( x ≈ 0.51-0.52) films grown by pulsed laser deposition onto Al2O3(0001) substrates when the low-energy components are deposited owing to collisions with the atoms of the buffer gas have been studied in the "shadow" geometry. The magnetization of these films is determined by two ferromagnetic phases—the high-temperature phase with the Curie temperature T C ≈ 370 K and the low-temperature one with T C ≈ 46 K. The anomalous Hall effect changes sign from positive to negative with a decrease in temperature. The sign change occurs in the temperature range of 30-50 K; the specific value of this temperature depends on the thickness of the Mn x Si1- x film. The results can be interpreted in terms of the structural self-organization related to the formation of two layers in the course of film growth. These layers have nearly the same chemical composition but significantly differ in the shapes and sizes of crystallites. This leads to a drastic difference in the values of T C and in the value and the sign of the anomalous Hall effect for such layers.

  20. Wake-up effects in Si-doped hafnium oxide ferroelectric thin films

    SciTech Connect

    Zhou, Dayu; Xu, Jin; Li, Qing; Guan, Yan; Cao, Fei; Dong, Xianlin; Müller, Johannes; Schenk, Tony; Schröder, Uwe

    2013-11-04

    Hafnium oxide based ferroelectric thin films have shown potential as a promising alternative material for non-volatile memory applications. This work reports the switching stability of a Si-doped HfO{sub 2} film under bipolar pulsed-field operation. High field cycling causes a “wake-up” in virgin “pinched” polarization hysteresis loops, demonstrated by an enhancement in remanent polarization and a shift of negative coercive voltage. The rate of wake-up is accelerated by either reducing the frequency or increasing the amplitude of the cycling field. We suggest de-pinning of domains due to reduction of the defect concentration at bottom electrode interface as origin of the wake-up.

  1. Large enhancement of positive magnetoresistance by Ce doping in Si epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Miyata, Y.; Ueno, K.; Togawa, Y.; Yoshimura, T.; Ashida, A.; Fujimura, N.

    2016-09-01

    We report the investigation into a large enhancement of the magnetoresistance (MR) by Ce doping in Si epitaxial thin films at room temperature. The positive MR is proportional to the square of the magnetic field at low magnetic fields below 5 T, while it increases linearly with regards to the strength of the magnetic field above 5 T. Based on the experimental finding that the change in the donor level corresponds to that of the MR ratio as a function of Ce concentration, the electronic state turns out to be influenced by Ce doping and strongly correlate the magnetotransport characteristics. It is concluded that this MR effect appears via the Lorentz force effect on the carrier motion, which is enhanced by the random scattering potential distribution arising from the Ce doping.

  2. The Urbach focus and optical properties of amorphous hydrogenated SiC thin films

    NASA Astrophysics Data System (ADS)

    Guerra, J. A.; Angulo, J. R.; Gomez, S.; Llamoza, J.; Montañez, L. M.; Tejada, A.; Töfflinger, J. A.; Winnacker, A.; Weingärtner, R.

    2016-05-01

    We report on the optical bandgap engineering of sputtered hydrogenated amorphous silicon carbide (a-SiC:H) thin films under different hydrogen dilution conditions during the deposition process and after post-deposition annealing treatments. The Tauc-gap and Urbach energy are calculated from ultraviolet-visible optical transmittance measurements. Additionally, the effect of the thermal annealing temperature on the hydrogen out-diffusion is assessed through infra-red absorption spectroscopy. A new model for the optical absorption of amorphous semiconductors is presented and employed to determine the bandgap as well as the Urbach energy from a single fit of the absorption coefficient. This model allowed the discrimination of the Urbach tail from the Tauc region without any external bias. Finally, the effect of the hydrogen dilution on the band-edge and the Urbach focus is discussed.

  3. Metal silicide/Si thin-film Schottky-diode bolometers

    NASA Astrophysics Data System (ADS)

    Yuryev, Vladimir A.; Chizh, Kirill V.; Chapnin, Valery V.; Kalinushkin, Victor P.

    2015-06-01

    Recently, we have demonstrated Ni silicide/poly-Si diodes as a budget alternative to SOI-diode temperature sensors in uncooled microbolometer FPAs. This paper introduces a solution still more suitable for industry: We have developed PtSi/poly-Si Schottky diodes for microbolometers. Ease of integration of the PtSi/poly-Si diode formation process into the CMOS technology, in analogy with the internal photoemission PtSi/Si IR FPAs, is the merit of the PtSi/poly-Si sensors. Now we demonstrate PtSi/poly-Si diode microbolometers and propose them as a promising solution for focal plane arrays.

  4. Impact of deposition parameters on the material quality of SPC poly-Si thin films using high-rate PECVD of a-Si:H

    NASA Astrophysics Data System (ADS)

    Kumar, Avishek; Widenborg, Per Ingemar; Dalapati, Goutam Kumar; Sandhya Subramanian, Gomathy; Aberle, Armin Gerhard

    2015-05-01

    The impact of the deposition parameters such as gas flow (sccm) and RF plasma power density (W/cm2) on the deposition rate of a-Si:H films is systematically investigated. A high deposition rate of up to 146 nm/min at 13.56 MHz is achieved for the a-Si:H films deposited with high lateral uniformity on 30 × 40 cm2 large-area glass substrates. A relationship between the SiH4 gas flow and the RF power density is established. The SiH4 gas flow to RF power density ratio of about 2.4 sccm/mW cm-2 is found to give a linear increase in the deposition rate. The influence of the deposition rate on the material quality is studied using UV-VIS-NIR spectrophotometer and Raman characterisation techniques. Poly-Si thin film with crystal quality as high as 90% of single-crystalline Si wafer is obtained from the SPC of high rate deposited a-Si:H films.

  5. Time-resolved, nonequilibrium carrier dynamics in Si-on-glass thin films for photovoltaic cells

    DOE PAGESBeta

    Serafini, John; Akbas, Yunus; Crandall, Lucas; Bellman, Robert; Williams, Carlo Kosik; Sobolewski, Robert

    2016-03-02

    Here, a femtosecond pump–probe spectroscopy method was used to characterize the growth process and transport properties of amorphous silicon-on-glass, thin films, intended as absorbers for photovoltaic cells. We collected normalized transmissivity change (ΔT/T) waveforms and interpreted them using a comprehensive three-rate equation electron trapping and recombination model. Optically excited ~300–500 nm thick Si films exhibited a bi-exponential carrier relaxation with the characteristic times varying from picoseconds to nanoseconds depending on the film growth process. From our comprehensive trapping model, we could determine that for doped and intrinsic films with very low hydrogen dilution the dominant relaxation mode was carrier trapping;more » while for intrinsic films with large hydrogen content and some texture, it was the standard electron–phonon cooling. In both cases, the initial nonequilibrium relaxation was followed by Shockley–Read–Hall recombination. An excellent fit between the model and the ΔT/T experimental transients was obtained and a correlation between the Si film growth process, its hydrogen content, and the associated trap concentration was demonstrated.« less

  6. Time-resolved, nonequilibrium carrier dynamics in Si-on-glass thin films for photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Serafini, John; Akbas, Yunus; Crandall, Lucas; Bellman, Robert; Kosik Williams, Carlo; Sobolewski, Roman

    2016-04-01

    A femtosecond pump-probe spectroscopy method was used to characterize the growth process and transport properties of amorphous silicon-on-glass, thin films, intended as absorbers for photovoltaic cells. We collected normalized transmissivity change (ΔT/T) waveforms and interpreted them using a comprehensive three-rate equation electron trapping and recombination model. Optically excited ˜300-500 nm thick Si films exhibited a bi-exponential carrier relaxation with the characteristic times varying from picoseconds to nanoseconds depending on the film growth process. From our comprehensive trapping model, we could determine that for doped and intrinsic films with very low hydrogen dilution the dominant relaxation mode was carrier trapping; while for intrinsic films with large hydrogen content and some texture, it was the standard electron-phonon cooling. In both cases, the initial nonequilibrium relaxation was followed by Shockley-Read-Hall recombination. An excellent fit between the model and the ΔT/T experimental transients was obtained and a correlation between the Si film growth process, its hydrogen content, and the associated trap concentration was demonstrated.

  7. Magnetic and structural properties of Co2FeAl thin films grown on Si substrate

    NASA Astrophysics Data System (ADS)

    Belmeguenai, Mohamed; Tuzcuoglu, Hanife; Gabor, Mihai; Petrisor, Traian; Tiusan, Coriolan; Berling, Dominique; Zighem, Fatih; Mourad Chérif, Salim

    2015-01-01

    The correlation between magnetic and structural properties of Co2FeAl (CFA) thin films of different thicknesses (10 nmSi/SiO2 substrates and annealed at 600 °C has been studied. x-ray diffraction (XRD) measurements revealed an (011) out-of-plane textured growth of the films. The deduced lattice parameter increases with the film thickness. Moreover, pole figures showed no in-plane preferential growth orientation. The magneto-optical Kerr effect hysteresis loops showed the presence of a weak in-plane uniaxial anisotropy with a random easy axis direction. The coercive field, measured with the applied field along the easy axis direction, and the uniaxial anisotropy field increase linearly with the inverse of the CFA thickness. The microstrip line ferromagnetic resonance measurements for in-plane and perpendicular applied magnetic fields revealed that the effective magnetization and the uniaxial in-plane anisotropy field follow a linear variation versus the inverse CFA thickness. This allows deriving a perpendicular surface anisotropy coefficient of -1.86 erg/cm2.

  8. Atomic-layer-deposited Al2O3 thin films with thin SiO2 layers grown by in situ O3 oxidation

    NASA Astrophysics Data System (ADS)

    Kim, Seong Keun; Hwang, Cheol Seong

    2004-08-01

    The growth, thermal annealing behaviors, and electrical properties of Al2O3 thin films grown by atomic layer deposition (ALD) on bare (100)Si and various oxidized Si wafers, by in situ O3 oxidation at 400°C and ex situ rapid thermal annealing (RTA) under O2 atmosphere at 900°C, were investigated. The ALD process was performed using Al(CH3)3 and high concentration of O3(400gm3). The high oxidation potential of O3 oxidized the Si surface at a very early stage of film growth and eliminated the incubation period even on a bare Si surface. The as-grown Al2O3 films had excess oxygen in the films, which diffused to the film Si interface and increased the interfacial layer by oxidizing the Si substrates during postannealing. The Al2O3 films grown on a bare Si substrate had the highest concentration of excess oxygen which resulted in the largest increase in the interfacial layer thickness during postannealing. As a result, the initial oxidation of the Si wafer did not significantly decrease the capacitance density compared to the films grown on a nonoxidized Si wafer at the as-deposited and postannealed states. Therefore, the Al2O3 layers grown using a high concentration of O3 oxidant on the in situ O3 oxidized Si wafers showed real high-k gate dielectric performance although the dielectric constants of the Al2O3 films were rather small (˜9) compared to other high-k gate dielectric films.

  9. A cost-effective growth of SiO(x) thin films by reactive sputtering: photoluminescence tuning.

    PubMed

    Pappas, S D; Grammatikopoulos, S; Poulopoulos, P; Kapaklis, V; Delimitis, A; Trachylis, D; Politis, C

    2011-04-01

    We present a new cost-effective method to produce substoichiometric SiO2 thin films by means of a simple sputter-coater operated at a base pressure of 1 x 10(-3) mbar. During sputtering air is introduced through a fine valve so that the sputtering gas is a mixture of air/Ar. High-resolution electron microscopy shows the formation of amorphous SiO(x) thin films for the as-deposited samples. The index x approaches 1 when the ratio of the partial pressure of air/Ar tends to 0.1. On the other hand, pure silica is formed when the ratio of the partial pressure of air/Ar approaches 0.5. The films in the as-deposited state show intense green-yellow photoluminescence. This fades away with short annealing under air at 950 degrees C. If on the other hand, prolonged annealing is performed under Argon atmosphere at 1000 degrees C, red-infrared photoluminescence is recorded due to the formation of Si nanocrystals embedded in SiO2. This simple method could be suitable for the production of thin SiO(x) films with embedded nanocrystals for optoelectronic or photovoltaic applications. PMID:21776754

  10. Comparison of Skutterudites and Advanced Thin-Film B4C/B9C and Si/SiGe Materials in Advanced Thermoelectric Energy Recovery Systems

    SciTech Connect

    Hendricks, Terry J.

    2007-03-15

    Various advanced thermoelectric (TE) materials have properties that are inherently advantageous for particular TE energy recovery applications. Skutterudites, 0- and 1-dimensional quantum-well materials, and thin-film superlattice materials are providing enhanced opportunities for advanced TE energy recovery. This work demonstrates that early skutterudites materials in dual-material, segmented couple designs may be best suited for higher temperature applications associated with spacecraft power systems and very high temperature exhaust waste heat recovery in heavy vehicles. Early thin-film BxC/Si-SiGe materials appear to be well suited for mid-temperature ranges in exhaust waste heat recovery in heavy-duty and passenger vehicles. Potential power generation at specific exhaust temperature levels and for various heat exchanger performance levels are presented showing the current design sensitivities using each of these TE material sets. Mathematical relationships inherently linking optimum TE design variables and the thermal systems design (i.e., heat exchangers) are also investigated.

  11. Strain-Field Evaluation of Strain-Relaxed Thin SiGe Layers Fabricated by Ion Implantation Method

    NASA Astrophysics Data System (ADS)

    Sawano, Kentarou; Ozawa, Yusuke; Fukumoto, Atsushi; Usami, Noritaka; Yamanaka, Junji; Suzuki, Kumiko; Arimoto, Keisuke; Nakagawa, Kiyokazu; Shiraki, Yasuhiro

    2005-10-01

    Strain-relaxed thin SiGe layers grown on ion-implanted Si substrates were evaluated by X-ray diffraction reciprocal space mapping and spatially resolved micro-Raman spectroscopy. It was found that implantation-induced defects effectively facilitated the misfit dislocation generation and multiplication during postannealing after growth, leading to large and homogeneous strain relaxation. While in-plane strain-field fluctuation with crosshatch morphology was clearly observed in the SiGe layer without implantation, a very uniform strain distribution without such morphology was realized in the sample with implantation. These results indicate that the ion implantation method is a very promising approach for realization of high-quality and extremely thin buffer layers.

  12. Nanograin-enhanced in-plane thermoelectric figure of merit in n-type SiGe thin films

    NASA Astrophysics Data System (ADS)

    Lu, Jianbiao; Guo, Ruiqiang; Huang, Baoling

    2016-04-01

    SiGe thin films are desirable candidates for many thermoelectric applications because of their low cost, low toxicity, and high compatibility with microelectronics fabrications. Currently, their applications are limited by their very poor thermoelectric performance. In this study, phosphorus-doped SiGe thin films with improved thermoelectric properties were grown using low pressure chemical vapor deposition, and the effects of different annealing treatments, doping concentration, composition, and temperature on their thermoelectric properties were explored. It is found that the segregation of phosphorus dopants plays an important role in grain growth and thermoelectric transport properties. The improved thermoelectric performance is mainly attributed to the significantly reduced in-plane thermal conductivity by the naturally formed nanograins. By adjusting the growth conditions, doping and post treatments, an in-plane ZT ˜ 0.16 at 300 K was obtained for the optimized n-type samples, which is even ˜50% higher than the record of bulk SiGe.

  13. Near zero temperature coefficient of resistance in Ti:Si:O thin films deposited by magnetron co-sputtering

    NASA Astrophysics Data System (ADS)

    Mireles, Marcela; Quevedo Lopez, M. A.

    2016-10-01

    Thin films of titanium/silicon/oxygen (Ti:Si:O) deposited by sputtering were evaluated as thin film resistors and the resulting resistance and temperature coefficient of resistance (TCR) was studied. The films were deposited in an Argon atmosphere at room temperature with 1% oxygen and their electrical properties evaluated before and after forming gas (5% H2: 95% N2) annealing at 325 and 450 °C for 1 h. The physical structure was characterized by x-ray diffraction (XRD), elemental composition and depth profile by Rutherford backscattering (RBS), and film composition by x-ray photoelectron spectroscopy (XPS). Carrier mobility, type and concentration were evaluated by Hall effect measurements. Thin films with a Ti:Si ratio of 1.6 exhibited a near zero TCR (-405 ppm °C-1) and sheet resistance (Rsh) at 25 °C of 1 kOhm sq-1.

  14. Y1Ba2Cu3O(6+delta) growth on thin Y-enhanced SiO2 buffer layers on silicon

    NASA Technical Reports Server (NTRS)

    Robin, T.; Mesarwi, A.; Wu, N. J.; Fan, W. C.; Espoir, L.; Ignatiev, A.; Sega, R.

    1991-01-01

    SiO2 buffer layers as thin as 2 nm have been developed for use in the growth of Y1Ba2Cu3O(6+delta) thin films on silicon substrates. The SiO2 layers are formed through Y enhancement of silicon oxidation, and are highly stoichiometric. Y1Ba2Cu3O(6+delta) film growth on silicon with thin buffer layers has shown c orientation and Tc0 = 78 K.

  15. In vacuo growth studies of Ru thin films on Si, SiN, and SiO2 by high-sensitivity low energy ion scattering

    NASA Astrophysics Data System (ADS)

    Coloma Ribera, R.; van de Kruijs, R. W. E.; Sturm, J. M.; Yakshin, A. E.; Bijkerk, F.

    2016-08-01

    In vacuo high-sensitivity low energy ion scattering (HS-LEIS) has been used to investigate the initial growth stages of DC sputtered Ru on top of Si, SiN, and SiO2. The high surface sensitivity of this technique allowed an accurate determination of surface coverages and thicknesses required for closing the Ru layer on all three substrates. The Ru layer closes (100% Ru surface signal) at about 2.0, 3.2, and 4.7 nm on top of SiO2, SiN, and Si, respectively. In-depth Ru concentration profiles can be reconstructed from the Ru surface coverages when considering an error function like model. The large intermixing (4.7 nm) for the Ru-on-Si system is compared to the reverse system (Si-on-Ru), where only 0.9 nm intermixing occurs. The difference is predominantly explained by the strong Si surface segregation that is observed for Ru-on-Si. This surface segregation effect is also observed for Ru-on-SiN but is absent for Ru-on-SiO2. For this last system, in vacuo HS-LEIS analysis revealed surface oxygen directly after deposition, which suggests an oxygen surface segregation effect for Ru-on-SiO2. In vacuo XPS measurements confirmed this hypothesis based on the reaction of Ru with oxygen from the SiO2, followed by oxygen surface segregation.

  16. Photoluminescence study of wurtzite Si-doped GaN thin films

    NASA Astrophysics Data System (ADS)

    Soltani, Mohammed; Carlone, Cosmo; Charbonneau, N. Sylvain; Khanna, Shyam M.

    1998-10-01

    The photoluminescence (PL) temperature dependence of wurtzite n-type GaN thin films grown on (0001) sapphire substrates by Magnetron sputter epitaxy is reported. Samples were non-intentionally doped, lightly and highly Si-doped. The PL of non-intentionally doped samples consist of the near band edge emission and a broad yellow band (YB) near 2.2 eV. This yellow emission is equally present in spectra of all Si-doped samples. The bound exciton (D0-X) at 3.488 eV and (A0-X) at 3.456 eV are present only in the lightly Si-doped samples. The evolution of the energy position of the (D0-X) is the same as the band gap temperature variation, but the (A0-X) transition is anormally independent of the temperature in the range studied here. In both Si-doped GaN samples a peak at 3.318 eV and transitions between 3.36 and 3.39 eV are observed. The temperature dependence of the latter shows a fine structure composed of four peaks at 3.364 eV, 3.368 eV, 3.375 eV and 3.383 eV. They are tentatively attributed to the superposition of two donor-acceptor and band-acceptor transitions. This interpretation implies the presence of two donors (D1,D2) and two acceptors (A1,A2). From the energy position of the band-acceptor and the energy gap of GaN at 20 K, an acceptor ionization energy of 120 and 135 meV respectively is obtained. Assuming 10 meV for a Coulomb interaction energy of the ionized donor-acceptor pairs, a donor ionization energy of 14 and 18 meV respectively is obtained from the energy difference between the donor-acceptor and the band-acceptor positions. An activation energy of 10.8 meV is deduced from the temperature dependence of the YB. The shallow donor (about 10 meV) contributes to the mechanism of the YB.

  17. Effect of Si additions on thermal stability and the phase transition sequence of sputtered amorphous alumina thin films

    SciTech Connect

    Bolvardi, H.; Baben, M. to; Nahif, F.; Music, D. Schnabel, V.; Shaha, K. P.; Mráz, S.; Schneider, J. M.; Bednarcik, J.; Michalikova, J.

    2015-01-14

    Si-alloyed amorphous alumina coatings having a silicon concentration of 0 to 2.7 at. % were deposited by combinatorial reactive pulsed DC magnetron sputtering of Al and Al-Si (90-10 at. %) split segments in Ar/O{sub 2} atmosphere. The effect of Si alloying on thermal stability of the as-deposited amorphous alumina thin films and the phase formation sequence was evaluated by using differential scanning calorimetry and X-ray diffraction. The thermal stability window of the amorphous phase containing 2.7 at. % of Si was increased by more than 100 °C compared to that of the unalloyed phase. A similar retarding effect of Si alloying was also observed for the α-Al{sub 2}O{sub 3} formation temperature, which increased by more than 120 °C. While for the latter retardation, the evidence for the presence of SiO{sub 2} at the grain boundaries was presented previously, this obviously cannot explain the stability enhancement reported here for the amorphous phase. Based on density functional theory molecular dynamics simulations and synchrotron X-ray diffraction experiments for amorphous Al{sub 2}O{sub 3} with and without Si incorporation, we suggest that the experimentally identified enhanced thermal stability of amorphous alumina with addition of Si is due to the formation of shorter and stronger Si–O bonds as compared to Al–O bonds.

  18. Si-based thin film coating on Y-TZP: Influence of deposition parameters on adhesion of resin cement

    NASA Astrophysics Data System (ADS)

    Queiroz, José Renato Cavalcanti; Nogueira Junior, Lafayette; Massi, Marcos; Silva, Alecssandro de Moura; Bottino, Marco Antonio; Sobrinho, Argemiro Soares da Silva; Özcan, Mutlu

    2013-10-01

    This study evaluated the influence of deposition parameters for Si-based thin films using magnetron sputtering for coating zirconia and subsequent adhesion of resin cement. Zirconia ceramic blocks were randomly divided into 8 groups and specimens were either ground finished and polished or conditioned using air-abrasion with alumina particles coated with silica. In the remaining groups, the polished specimens were coated with Si-based film coating with argon/oxygen magnetron discharge at 8:1 or 20:1 flux. In one group, Si-based film coating was performed on air-abraded surfaces. After application of bonding agent, resin cement was bonded. Profilometry, goniometry, Energy Dispersive X-ray Spectroscopy and Rutherford Backscattering Spectroscopy analysis were performed on the conditioned zirconia surfaces. Adhesion of resin cement to zirconia was tested using shear bond test and debonded surfaces were examined using Scanning Electron Microscopy. Si-based film coating applied on air-abraded rough zirconia surfaces increased the adhesion of the resin cement (22.78 ± 5.2 MPa) compared to those of other methods (0-14.62 MPa) (p = 0.05). Mixed type of failures were more frequent in Si film coated groups on either polished or air-abraded groups. Si-based thin films increased wettability compared to the control group but did not change the roughness, considering the parameters evaluated. Deposition parameters of Si-based thin film and after application of air-abrasion influenced the initial adhesion of resin cement to zirconia.

  19. Thermally evaporated SiO thin films as a versatile interlayer for plasma-based OLED passivation.

    PubMed

    Yun, Won Min; Jang, Jaeyoung; Nam, Sooji; Kim, Lae Ho; Seo, Sang Joon; Park, Chan Eon

    2012-06-27

    Silicon monoxide (SiO) thin films were introduced as an efficient interlayer for achieving plasma-based organic light-emitting diode (OLED) surface passivation. The SiO thin films could be consecutively formed via thermal evaporation, without breaking the vacuum, after deposition of the OLED cathode. The plasma resistivity and UV-blocking characteristics of the SiO interlayer protected the OLED devices against electrical and optical degradation during the plasma-enhanced atomic layer deposition (PEALD) and plasma-enhanced chemical vapor deposition (PECVD) passivation processes. In addition, the nonconformal deposition and hydroxyl group-rich surface characteristics of the SiO thin films yielded enhanced surface pinhole coverage and a higher initial film density in the subsequently deposited PEALD-based Al2O3 barrier film. As a result, the OLEDs with a SiO/Al2O3 bilayer passivation layer displayed a remarkably increased device shelf life compared to devices prepared using Al2O3-only passivation. A MOCON test showed that the water vapor transmission rate (WVTR) of the SiO/Al2O3 bilayer film was 0.0033 g/(m(2) day), 2.3 times lower than the rate of a single Al2O3 barrier film. The results of our study demonstrated the multipurpose role of a SiO interlayer in plasma-based OLED passivation. The layer acted as a damage-free protective layer for the underlying OLED devices and an assistant layer to improve the upper barrier film performance.

  20. Amorphous SnO2-SiO2 thin films with reticular porous morphology for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Chen, L. B.; Li, C. C.; Wang, T. H.

    2008-12-01

    Amorphous SnO2-SiO2 thin films with reticular porous morphology were fabricated by electrostatic spray deposition method for lithium-ion batteries. An initial discharge capacity of the SnO2-SiO2 electrodes with 15% of SiO2 was about 1271 mA h/g, and the reversible capacity stayed in the range of 869-501 mA h/g during the successive 100 cycles, but only 1141 and 694-174 mA h/g for the pure SnO2 electrodes. The high capacity was attributed to the addition of SiO2, which facilitated the formation of the Li-Sn alloy. The improved cycle performance was due to reticular porous structure, which accommodated the volume change during cycling.

  1. Spin Hall magnetoresistance in Co2FeSi/Pt thin films: dependence on Pt thickness and temperature

    NASA Astrophysics Data System (ADS)

    Huang, Xiufeng; Dai, Zhiwen; Huang, Lin; Lu, Guangduo; Liu, Min; Piao, Hongguang; Kim, Dong-Hyun; Yu, Seong-cho; Pan, Liqing

    2016-11-01

    We have investigated the temperature and the Pt layer thickness dependence of the magnetoresistances (MRs) in Co2FeSi/Pt thin films. Based on the field dependent measurements, it can be seen that the spin-current-induced spin Hall magnetoresistance (SMR) plays the dominant role in the MRs in the Co2FeSi/Pt bilayers in the whole temperature range. Meanwhile, a quite small part of anisotropic magnetoresistance (AMR) existed in the MRs. It proved to be originated from magnetic proximity effect (MPE) by measuring the Pt thickness and temperature dependence of the AMR. Moreover, the Co2FeSi layer thickness has much weaker effect on the SMR and AMR compared to the Pt layer thickness. These results indicate that the Co2FeSi/Pt interface is beneficial to be used in the spin-current-induced physical phenomena.

  2. Structural and optical study of Ce segregation in Ce-doped SiO{sub 1.5} thin films

    SciTech Connect

    Beainy, G.; Castro, C.; Pareige, P.; Talbot, E.; Weimmerskirch-Aubatin, J.; Stoffel, M.; Vergnat, M.; Rinnert, H.

    2015-12-21

    Cerium doped SiO{sub 1.5} thin films fabricated by evaporation and containing silicon nanocrystals were investigated by atom probe tomography. The effect of post-growth annealing treatment has been systematically studied to correlate the structural properties obtained by atom probe tomography to the optical properties measured by photoluminescence spectroscopy. The atom probe results demonstrated the formation of Ce-Si rich clusters upon annealing at 900 °C which leads to a drastic decrease of the Ce-related luminescence. At 1100 °C, pure Si nanocrystals and optically active cerium silicate compounds are formed. Consequently, the Ce-related luminescence is found to re-appear at this temperature while no Si-nanocrystal related luminescence is observed for films containing more than 3% Ce.

  3. Ferromagnetism and nonmetallic transport of thin-film α-FeSi(2): a stabilized metastable material.

    PubMed

    Cao, Guixin; Singh, D J; Zhang, X-G; Samolyuk, German; Qiao, Liang; Parish, Chad; Jin, Ke; Zhang, Yanwen; Guo, Hangwen; Tang, Siwei; Wang, Wenbin; Yi, Jieyu; Cantoni, Claudia; Siemons, Wolter; Payzant, E Andrew; Biegalski, Michael; Ward, T Z; Mandrus, David; Stocks, G M; Gai, Zheng

    2015-04-10

    A metastable phase α-FeSi_{2} was epitaxially stabilized on a silicon substrate using pulsed laser deposition. Nonmetallic and ferromagnetic behaviors are tailored on α-FeSi_{2} (111) thin films, while the bulk material of α-FeSi_{2} is metallic and nonmagnetic. The transport property of the films renders two different conducting states with a strong crossover at 50 K, which is accompanied by the onset of a ferromagnetic transition as well as a substantial magnetoresistance. These experimental results are discussed in terms of the unusual electronic structure of α-FeSi_{2} obtained within density functional calculations and Boltzmann transport calculations with and without strain. Our finding sheds light on achieving ferromagnetic semiconductors through both their structure and doping tailoring, and provides an example of a tailored material with rich functionalities for both basic research and practical applications.

  4. Growth and characterization of Pt-protected Gd5Si4 thin films

    SciTech Connect

    Hadimani, R L; Mudryk, Y; Prost, T E; Pecharsky, V K; Gschneidner, K A; Jiles, D C

    2014-05-07

    Successful growth and characterization of thin films of giant magnetocaloric Gd5(SixGe1-x)4 were reported in the literature with limited success. The inherent difficulty in producing this complex material makes it difficult to characterize all the phases present in the thin films of this material. Therefore, thin film of binary compound of Gd5Si4 was deposited by pulsed laser deposition. It was then covered with platinum on the top of the film to protect against any oxidation when the film was exposed to ambient conditions. The average film thickness was measured to be approximately 350 nm using a scanning electron microscopy, and the composition of the film was analyzed using energy dispersive spectroscopy. X-ray diffraction analysis indicates the presence of Gd5Si4 orthorhombic structure along with Gd5Si3 secondary phase. The transition temperature of the film was determined from magnetic moment vs. temperature measurement. The transition temperature was between 320 and 345 K which is close to the transition temperature of the bulk material. Magnetic moment vs. magnetic field measurement confirmed that the film was ferromagnetic below 342 K.

  5. Opto-electronic properties of P-doped nc-Si-QD/a-SiC:H thin films as foundation layer for all-Si solar cells in superstrate configuration

    NASA Astrophysics Data System (ADS)

    Kar, Debjit; Das, Debajyoti

    2016-07-01

    With the advent of nc-Si solar cells having improved stability, the efficient growth of nc-Si i-layer of the top cell of an efficient all-Si solar cell in the superstrate configuration prefers nc-Si n-layer as its substrate. Accordingly, a wide band gap and high conducting nc-Si alloy material is a basic requirement at the n-layer. Present investigation deals with the development of phosphorous doped n-type nanocrystalline silicon quantum dots embedded in hydrogenated amorphous silicon carbide (nc-Si-QD/a-SiC:H) hetero-structure films, wherein the optical band gap can be widened by the presence of Si-C bonds in the amorphous matrix and the embedded high density tiny nc-Si-QDs could provide high electrical conductivity, particularly in P-doped condition. The nc-Si-QDs simultaneously facilitate further widening of the optical band gap by virtue of the associated quantum confinement effect. A complete investigation has been made on the electrical transport phenomena involving charge transfer by tunneling and thermionic emission prevailing in n-type nc-Si-QD/a-SiC:H thin films. Their correlation with different phases of the specific heterostructure has been carried out for detailed understanding of the material, in order to improve its device applicability. The n-type nc-Si-QD/a-SiC:H films exhibit a thermally activated electrical transport above room temperature and multi-phonon hopping (MPH) below room temperature, involving defects in the amorphous phase and the grain-boundary region. The n-type nc-Si-QD/a-SiC:H films grown at ˜300 °C, demonstrating wide optical gap ˜1.86-1.96 eV and corresponding high electrical conductivity ˜4.5 × 10-1-1.4 × 10-2 S cm-1, deserve to be an effective foundation layer for the top nc-Si sub-cell of all-Si solar cells in n-i-p structure with superstrate configuration.

  6. Fabrication and characterization of Al{sub 2}O{sub 3} /Si composite nanodome structures for high efficiency crystalline Si thin film solar cells

    SciTech Connect

    Zhang, Ruiying; Zhu, Jian; Zhang, Zhen; Wang, Yanyan; Qiu, Bocang; Liu, Xuehua; Zhang, Jinping; Zhang, Yi; Fang, Qi; Ren, Zhong; Bai, Yu

    2015-12-15

    We report on our fabrication and characterization of Al{sub 2}O{sub 3}/Si composite nanodome (CND) structures, which is composed of Si nanodome structures with a conformal cladding Al{sub 2}O{sub 3} layer to evaluate its optical and electrical performance when it is applied to thin film solar cells. It has been observed that by application of Al{sub 2}O{sub 3}thin film coating using atomic layer deposition (ALD) to the Si nanodome structures, both optical and electrical performances are greatly improved. The reflectivity of less than 3% over the wavelength range of from 200 nm to 2000 nm at an incident angle from 0° to 45° is achieved when the Al{sub 2}O{sub 3} film is 90 nm thick. The ultimate efficiency of around 27% is obtained on the CND textured 2 μm-thick Si solar cells, which is compared to the efficiency of around 25.75% and 15% for the 2 μm-thick Si nanodome surface-decorated and planar samples respectively. Electrical characterization was made by using CND-decorated MOS devices to measure device’s leakage current and capacitance dispersion. It is found the electrical performance is sensitive to the thickness of the Al{sub 2}O{sub 3} film, and the performance is remarkably improved when the dielectric layer thickness is 90 nm thick. The leakage current, which is less than 4x10{sup −9} A/cm{sup 2} over voltage range of from -3 V to 3 V, is reduced by several orders of magnitude. C-V measurements also shows as small as 0.3% of variation in the capacitance over the frequency range from 10 kHz to 500 kHz, which is a strong indication of surface states being fully passivated. TEM examination of CND-decorated samples also reveals the occurrence of SiO{sub x} layer formed between the interface of Si and the Al{sub 2}O{sub 3} film, which is thin enough that ensures the presence of field-effect passivation, From our theoretical and experimental study, we believe Al{sub 2}O{sub 3} coated CND structures is a truly viable approach to achieving higher device

  7. Single-crystal p-i-n-Si thin-film solar cells grown on Si substrate by sputter epitaxy

    NASA Astrophysics Data System (ADS)

    Yeh, Wenchang; Tatebe, Kyohei

    2015-08-01

    An intrinsic sputter-epitaxial (SE) Si film with a thickness of 1000 nm and a 50-nm-thick n+ SE-Si film were successfully grown as the light-absorbing layer and emitter layer, respectively, on a heavily doped p-Si(100) wafer to form the p-i-n junction of a solar cell (SC). Heavily doped n+ SE-Si with an electron concentration n of 3 × 1020 cm-3 was grown by cosputtering of Sb with Si. The characteristics of SE-Si grown at 310 °C was investigated in relation to annealing temperature. The oxygen concentration in SE-Si was ˜1018 cm-3, which was found to originate from the gas released in the chamber. Oxygen-induced thermal donors then became the source of n in the film, and n was reduced to 1 × 1016 cm-3 after forming-gas annealing at 700 °C because the thermal donors were neutralized by hydrogen. The SC exhibited a maximum internal quantum efficiency of 73.7%.

  8. Tunable photoluminescence from nc-Si/a-SiNx:H quantum dot thin films prepared by ICP-CVD.

    PubMed

    Sain, Basudeb; Das, Debajyoti

    2013-03-21

    Intense visible photoluminescence (PL) tunable within 1.66-2.47 eV, under UV 325 nm excitation, was obtained from nanocrystalline silicon quantum dots (∼5.72-1.67 nm in diameter) embedded in amorphous silicon-nitride matrix (nc-Si/a-SiN(x):H) prepared in RF-ICPCVD (13.56 MHz) at substrate temperatures between 400 to 150 °C. The dominant component of PL, having a narrow band width of ∼0.16-0.45 eV, originates from quasi-direct band-to-band recombination due to quantum confinement effect (QCE) in the nanocrystalline silicon quantum dots (nc-Si QDs) of appropriate size; however, the contribution of defects arose at lower substrate temperatures leading to asymmetric broadening. Intense atomic hydrogen flux in high-density inductively coupled plasmas (ICPs) provides a very high surface coverage, passivates well the nonradiative dangling bonds, and thereby favors the PL intensity. The average size of nc-Si QDs measured by HR-TEM appears consistent with similar estimates from Raman studies. The red shift of the Raman line and corresponding line broadening originates from the confinement of optical phonons within nc-Si QDs. Photoluminescence emerging from nc-Si/a-SiN(x):H quantum dots obtained from the low temperature and single-step plasma processing holds great promise for the fabrication of light-emitting devices and flexible flat panel displays. PMID:23407687

  9. KCl ultra-thin films with polar and non-polar surfaces grown on Si(111)7 × 7

    PubMed Central

    Beinik, Igor; Barth, Clemens; Hanbücken, Margrit; Masson, Laurence

    2015-01-01

    The growth of ultra-thin KCl films on the Si(111)7 × 7 reconstructed surface has been investigated as a function of KCl coverage and substrate temperature. The structure and morphology of the films were characterized by means of scanning tunneling microscopy (STM) under ultra-high vacuum (UHV) conditions. Detailed analysis of the atomically resolved STM images of islands grown at room and high temperatures (400 K–430 K) revealed the presence of KCl(001) and KCl(111) islands with the ratio between both structures depending on the growth temperature. At room temperature, the growth of the first layer, which covers the initial Si(111)7 × 7 surface, contains double/triple atomic layers of KCl(001) with a small fraction of KCl(111) islands. The high temperature growth promotes the appearance of large KCl(111) areas, which are built up by three atomic layers. At room and high temperatures, flat and atomically well-defined ultra-thin KCl films can be grown on the Si(111)7 × 7 substrate. The formation of the above mentioned (111) polar films is interpreted as a result of the thermally activated dissociative adsorption of KCl molecules on Si(111)7 × 7, which produces an excess of potassium on the Si surface. PMID:25650038

  10. Electrical characteristics of Au/n-GaAs structures with thin and thick SiO{sub 2} dielectric layer

    SciTech Connect

    Altuntas, H.; Altindal, S.; Corekci, S.; Ozturk, M. K.; Ozcelik, S.

    2011-10-15

    The aim of this study, to explain effects of the SiO{sub 2} insulator layer thickness on the electrical properties of Au/n-GaAs Shottky barrier diodes (SBDs). Thin (60 A) and thick (250 A) SiO{sub 2} insulator layers were deposited on n-type GaAs substrates using the plasma enganced chemical vapour deposition technique. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics have been carried out at room temperature. The main electrical parameters, such as ideality factor (n), zero-bias barrier height ({phi}{sub Bo}), series resistance (R{sub s}), leakage current, and interface states (N{sub ss}) for Au/SiO{sub 2}/n-GaAs SBDs have been investigated. Surface morphologies of the SiO{sub 2} dielectric layer was analyzed using atomic force microscopy. The results show that SiO{sub 2} insulator layer thickness very affects the main electrical parameters. Au/n-GaAs SBDs with thick SiO{sub 2} insulator layer have low leakage current level, small ideality factor, and low interface states. Thus, Au/n-GaAs SBDs with thick SiO{sub 2} insulator layer shows better diode characteristics than other.

  11. Impact of oxygen bonding on the atomic structure and photoluminescence properties of Si-rich silicon nitride thin films

    SciTech Connect

    Nguyen, P. D.; Sunding, M. F.; Vestland, L. O.; Finstad, T. G.; Olsen, A.; Kepaptsoglou, D. M.; Ramasse, Q. M.

    2012-10-01

    The atomic structure and optical properties of Si-rich silicon nitride thin films have been for decades the subject of intense research, both theoretically and experimentally. It has been established in particular that modifying the chemical composition of this material (e.g., the Si excess concentration) can lead to dramatic differences in its physical, optical, and electrical properties. The present paper reports on how the incorporation of oxygen into silicon nitride networks influences their chemical bonding and photoluminescence properties. Here, by using a combination of analytical scanning transmission electron microscopy and x-ray photoelectron spectroscopy it is demonstrated that the structure of Si-rich silicon nitride with low O content can be described by the co-existence of Si nanocrystals in a Si{sub 3}N{sub 4} matrix, with occasional localized nano-regions of a Si{sub 2}ON{sub 2} phase, depending on the amount of excess Si. Furthermore, it is shown that the structure of silicon nitride with high O content can be adequately described by a so-called random bonding model, according to which the material consists in bonded networks of randomly distributed tetrahedral SiO{sub x}N{sub 4-x} (where x = 0, 1, 2, 3, and 4). Photoluminescence measurements indicate that the effect of O is to introduce a gap state in the band gap of Si{sub 3}N{sub 4} matrix. When a large amount of O is introduced, on the other hand, the photoluminescence measurements are in agreement with a shifted conduction band minimum in the dielectric. For both cases (high and low O content), Si dangling bonds were found to give rise to the deep level in the band gap of the nitride matrix, causing the dominant emission band in the photoluminescence of the films.

  12. Si Passivation and Chemical Vapor Deposition of Silicon Nitride: Final Technical Report, March 18, 2007

    SciTech Connect

    Atwater, H. A.

    2007-11-01

    This report investigated chemical and physical methods for Si surface passivation for application in crystalline Si and thin Si film photovoltaic devices. Overall, our efforts during the project were focused in three areas: i) synthesis of silicon nitride thin films with high hydrogen content by hot-wire chemical vapor deposition; ii) investigation of the role of hydrogen passivation of defects in crystalline Si and Si solar cells by out diffusion from hydrogenated silicon nitride films; iii) investigation of the growth kinetics and passivation of hydrogenated polycrystalline. Silicon nitride films were grown by hot-wire chemical vapor deposition and film properties have been characterized as a function of SiH4/NH3 flow ratio. It was demonstrated that hot-wire chemical vapor deposition leads to growth of SiNx films with controllable stoichiometry and hydrogen.

  13. Effects of rolling conditions on grain orientation and magnetic properties of thin-gauged 3% Si-Fe sheets

    SciTech Connect

    Kim, J.C.; Heo, N.H.; Chai, K.H.; Na, J.G.; Woo, J.S.; Kim, G.M.

    1998-04-03

    3% Si-Fe sheets are widely used as core material of large transformers, large rotating machines and pole transformers due to characteristic soft magnetic properties, where energy losses during magnetization are critically concerned. The magnetic characteristics in silicon iron arises from a preferred grain orientation, i.e. (110) [001] Goss texture which forms after cold rolling followed by secondary recrystallization. In this paper, effects of rolling direction on the grain orientation and magnetic properties of the thin-gauged 3% Si-Fe sheets are investigated.

  14. Characterization Of Fe{sub 1-x}Co{sub x}Si Thin Films Deposited Via Pulsed Laser Deposition

    SciTech Connect

    Manyala, N.; Ngom, Balla; Kana-Kana, J. B.; Bucher, Remy; Maaza, M.; Di Tusa, J. F.

    2008-09-23

    We report on the structural and morphological characterization of B20 cubic structure Fe{sub 1-x}Co{sub x}Si thin films grown by pulsed laser deposition for the concentration range 0{<=}x{<=}0.3 deposited on Si (111) substrate. The x-ray diffraction, Rutherford back scattering (RBS), Scanning Electron microscopy (SEM) and Atomic force microscopy (AFM) of the films show that all the films are single phase B20 cubic structure with concentrations close to expected values, very smooth and dense with surface roughness less than 0.8 nm.

  15. Band gap tuning of epitaxial SrTiO{sub 3-δ}/Si(001) thin films through strain engineering

    SciTech Connect

    Cottier, Ryan J.; Steinle, Nathan A.; Currie, Daniel A.; Theodoropoulou, Nikoleta

    2015-11-30

    We investigate the effect of strain and oxygen vacancies (V{sub O}) on the crystal and optical properties of oxygen deficient, ultra-thin (4–30 nm) films of SrTiO{sub 3-δ} (STO) grown heteroepitaxially on p-Si(001) substrates by molecular beam epitaxy. We demonstrate that STO band gap tuning can be achieved through strain engineering and show that the energy shift of the direct energy gap transition of SrTiO{sub 3-δ}/Si films has a quantifiable dimensional and doping dependence that correlates well with the changes in crystal structure.

  16. Oxidation of atomically thin MoS2 on SiO2

    NASA Astrophysics Data System (ADS)

    Yamamoto, Mahito; Cullen, William; Einstein, Theodore; Fuhrer, Michael

    2013-03-01

    Surface oxidation of MoS2 markedly affects its electronic, optical, and tribological properties. However, oxidative reactivity of atomically thin MoS2 has yet to be addressed. Here, we investigate oxidation of atomic layers of MoS2 using atomic force microscopy and Raman spectroscopy. MoS2 is mechanically exfoliated onto SiO2 and oxidized in Ar/O2 or Ar/O3 (ozone) at 100-450 °C. MoS2 is much more reactive to O2 than an analogous atomic membrane of graphene and monolayer MoS2 is completely etched very rapidly upon O2 treatment above 300 °C. Thicker MoS2 (> 15 nm) transforms into MoO3 after oxidation at 400 °C, which is confirmed by a Raman peak at 820 cm-1. However, few-layer MoS2 oxidized below 400 °C exhibits no MoO3 Raman mode but etch pits are formed, similar to graphene. We find atomic layers of MoS2 shows larger reactivity to O3 than to O2 and monolayer MoS2 transforms chemically upon O3 treatment even below 100 °C. Work supported by the U. of Maryland NSF-MRSEC under Grant No. DMR 05-20741.

  17. Material properties of pulsed-laser crystallized Si thin films grown on yttria-stabilized zirconia crystallization-induction layers by two-step irradiation method

    NASA Astrophysics Data System (ADS)

    Thi Kieu Lien, Mai; Horita, Susumu

    2016-03-01

    Amorphous Si thin films on yttria-stabilized zirconia (YSZ) layers were crystallized widely in solid phase by the two-step method with a pulsed laser, moving the sample stage. The crystalline quality, impurity diffusion, and electrical properties of the crystallized Si films were investigated. It was found that the crystallinity of the Si thin films was improved and their surface was smooth without an incubation layer at the interface, indicating the uniform crystallinity of Si on YSZ. The diffusion of Zr and Y into the Si thin films was as small as or smaller than the order of 1017 atoms/cm3. We evaluated the electrical properties of carrier concentration and Hall mobility of the Si thin films with/without YSZ layers by using the resistivity and AC Hall effect measurements. The temperature and doping concentration dependences were measured for both undoped and P-doped films. It was found that both the undoped and P-doped Si/YSZ/glass films showed higher mobilities and carrier concentrations (and therefore higher conductivities), which indicate a smaller number of defects, than the Si/glass films. This suggested that the Si film crystallized on the YSZ layer is more suitable for application to electronic devices than the Si film on glass.

  18. Growth Behavior of Ga-Doped ZnO Thin Films Deposited on Au/SiN/Si(001) Substrates by Radio Frequency Magnetron Sputtering

    NASA Astrophysics Data System (ADS)

    Seo, Seon Hee; Kang, Hyon Chol

    2013-11-01

    This paper reports the growth behavior of Ga-doped ZnO (ZnO:Ga) thin films deposited on Au/SiN/Si(001) substrates by radio-frequency magnetron sputtering. The microstructures of the overgrown ZnO:Ga thin films were investigated by performing X-ray diffraction, scanning electron microcopy, and transmission electron microscopy analyses. It was confirmed that the growth process proceeds through three stages. In the first stage, nano-scale ZnO:Ga islands were grown on the SiN layer, while a fairly continuous flat structure was formed on the Au nanoparticles (NPs). In the second stage of the growth process, ZnO:Ga domains with different growth orientations, depending strongly on the crystalline planes of the host Au NPs, were nucleated. These domains then grew at different rates, resulting in a change in the morphology from the initial shape reflecting that of the Au NPs to a sunflower-type shape. In the final stage, columnar growth with a preferred (0002) orientation along the surface normal direction became dominant.

  19. Magnetic properties and microstructure of TbxDy1-xFe2 thin films sputtered on Pt/TiO2/SiO2/Si substrate

    NASA Astrophysics Data System (ADS)

    Zhu, Jiang; Cibert, Christophe; Domenges, Bernadette; Bouregba, Rachid; Poullain, Gilles

    2013-05-01

    TbxDy1-xFe2 thin films are grown on Pt/TiO2/SiO2/Si substrate by multi-target sputtering. In order to achieve the best magnetic properties, samples grown while heating the sample holder (in situ films) are compared to those prepared at room temperature followed by thermal annealing. The effect of Tb, Dy and Fe content is also examined. It is found that the magnetic properties are very sensitive to the deposition parameters. Magnetization value as high as 680 emu/cm3 with very low coercivity is achieved in a 140 nm thick film whose composition (Tb0.3Dy0.7)Fe2 corresponds to the TERFENOL-D formulation. Observation of soft ferromagnetism and high magnetization are related to crystallization of nano-grains (size 7-10 nm) as deduced from microstructure investigation by X ray diffraction and transmission electron microscopy. It is shown the possibility of growing TERFENOL-D thin films with properties suitable for observation of extrinsic magneto-electric coupling in future thin film devices combining piezoelectric and magnetostrictive materials on metallized silicon substrate.

  20. Preparation and characterization of transparent hydrophilic photocatalytic TiO2/SiO2 thin films on polycarbonate.

    PubMed

    Fateh, Razan; Dillert, Ralf; Bahnemann, Detlef

    2013-03-19

    Transparent hydrophilic photocatalytic TiO2 coatings have been widely applied to endow the surfaces self-cleaning properties. A mixed metal oxide (TiO2/SiO2) can enhance the photocatalytic performance improving the ability of surface adsorption and increasing the amount of hydroxyl surface groups. The present work introduces a systematic study concerning the effect of the SiO2 addition to TiO2 films on the wettability, the photocatalytic activity, the adhesion strength, and the mechanical stability of the films. Transparent hydrophilic photocatalytic TiO2/SiO2 thin films were used to coat the polycarbonate (PC) substrate which was precoated by an intermediate SiO2 layer. The TiO2/SiO2 thin film was prepared employing a bulk TiO2 powder (Sachtleben Hombikat UV 100) and different molar ratios of tetraethoxysilane in acidic ethanol. A dip-coating process was used to deposit the films onto the polycarbonate substrate. The films were characterized by UV/vis spectrophotometry, FTIR spectroscopy, ellipsometry, BET, AFM, XRD, and water contact angle measurements. The mechanical stability and the UV resistance were examined. The photocatalytic activity of the coated surface was calculated from the kinetic analysis of methylene blue photodegradation measurements and compared with the photocatalytic activity of Pilkington Activ sheet glass. The coated surfaces displayed considerable photocatalytic activity and superhydrophilicity after exposure to UV light. The addition of SiO2 results in an improvement of the photocatalytic activity of the TiO2 film reaching the highest value at molar ratio TiO2/SiO2 equal to 1:0.9. The prepared films exhibit a good stability against UV(A) irradiation.

  1. Pixel-Level Digital-to-Analog Conversion Scheme for Compact Data Drivers of Active Matrix Organic Light-Emitting Diodes with Low-Temperature Polycrystalline Silicon Thin-Film Transistors

    NASA Astrophysics Data System (ADS)

    Kim, Tae-Wook; Choi, Byong-Deok

    2010-03-01

    This paper shows that a part of a digital-to-analog conversion (DAC) function can be included in a pixel circuit to save the circuit area of an integrated data driver fabricated with low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs). Because the pixel-level DAC can be constructed by two TFTs and one small capacitor, the pixel circuit does not become markedly complex. The design of an 8-bit DAC, which combines a 6-bit resistor-string-based DAC and a 2-bit pixel-level DAC for a 4-in. diagonal VGA format active matrix organic light-emitting diode (AMOLED), is shown in detail. In addition, analysis results are presented, revealing that the 8-bit DAC scheme including a 2-bit pixel-level DAC with 1:3 demultiplexing can be applied to very high video formats, such as XGA, for a 3 to 4-in. diagonal AMOLED. Even for a 9- to 12-in. diagonal AMOLED, the proposed scheme can still be applied to the XGA format, even though no demultiplexing is allowed. The total height of the proposed 8-bit DAC is approximately 960 µm, which is almost one-half of that of the previous 6-bit resistor-string-based DAC.

  2. Pixel-Level Digital-to-Analog Conversion Scheme for Compact Data Drivers of Active Matrix Organic Light-Emitting Diodes with Low-Temperature Polycrystalline Silicon Thin-Film Transistors

    NASA Astrophysics Data System (ADS)

    Tae-Wook Kim,; Byong-Deok Choi,

    2010-03-01

    This paper shows that a part of a digital-to-analog conversion (DAC) function can be included in a pixel circuit to save the circuit area of an integrated data driver fabricated with low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs). Because the pixel-level DAC can be constructed by two TFTs and one small capacitor, the pixel circuit does not become markedly complex. The design of an 8-bit DAC, which combines a 6-bit resistor-string-based DAC and a 2-bit pixel-level DAC for a 4-in. diagonal VGA format active matrix organic light-emitting diode (AMOLED), is shown in detail. In addition, analysis results are presented, revealing that the 8-bit DAC scheme including a 2-bit pixel-level DAC with 1:3 demultiplexing can be applied to very high video formats, such as XGA, for a 3 to 4-in. diagonal AMOLED. Even for a 9- to 12-in. diagonal AMOLED, the proposed scheme can still be applied to the XGA format, even though no demultiplexing is allowed. The total height of the proposed 8-bit DAC is approximately 960 μm, which is almost one-half of that of the previous 6-bit resistor-string-based DAC.

  3. Heteroepitaxial growth of nonpolar Cu-doped ZnO thin film on MnS-buffered (100) Si substrate

    NASA Astrophysics Data System (ADS)

    Nakamura, Tatsuru; Nguyen, Nam; Nagata, Takahiro; Takahashi, Kenichiro; Ri, Sung-Gi; Ishibashi, Keiji; Suzuki, Setsu; Chikyow, Toyohiro

    2015-06-01

    The preparation of nonpolar ZnO and Cu-doped ZnO thin films on Si substrates was studied for the application to the fabrication of green-light-emitting diodes. The use of rocksalt MnS and wurtzite AlN as buffer layers is a key technology for achieving the heteroepitaxial growth of nonpolar ZnO thin film on a (100) Si substrate. X-ray diffraction and photoluminescence measurements revealed that deposition under a high oxygen partial pressure (∼1 Torr) can enhance the nonpolar crystallization of undoped ZnO, and can simultaneously suppress the formation of defects such as oxygen vacancies. These techniques can be also applied to the growth of Cu-doped ZnO. A room-temperature photoluminescence study revealed that nonpolar [11\\bar{2}0]-oriented Cu-doped ZnO film exhibits enhanced green emission owing to the doped Cu ions.

  4. Hybrid ZnO nanowire/a-Si:H thin-film radial junction solar cells using nanoparticle front contacts

    SciTech Connect

    Pathirane, M. Iheanacho, B.; Lee, C.-H.; Wong, W. S.; Tamang, A.; Knipp, D.; Lujan, R.

    2015-10-05

    Hydrothermally synthesized disordered ZnO nanowires were conformally coated with a-Si:H thin-films to fabricate three dimensional hybrid nanowire/thin-film structures. The a-Si:H layer formed a radial junction p-i-n diode solar cell around the ZnO nanowire. The cylindrical hybrid solar cells enhanced light scattering throughout the UV-visible-NIR spectrum (300 nm–800 nm) resulting in a 22% increase in short-circuit current density compared to the reference planar p-i-n device. A fill factor of 69% and a total power conversion efficiency of 6.5% were achieved with the hybrid nanowire solar cells using a spin-on indium tin oxide nanoparticle suspension as the top contact.

  5. Time-integrated photoluminescence and pump-probe reflection spectroscopy of Si doped InN thin films

    SciTech Connect

    Mohanta, Antaryami; Jang, Der-Jun Wang, Ming-Sung; Tu, L. W.

    2014-01-28

    Temperature and excitation power dependent time-integrated photoluminescence of Si doped InN thin films are investigated. Photoluminescence (PL) spectra at low temperatures are described by single emission peak ensued due to “free-to-bound” recombination; whereas PL spectra at higher temperatures above 150 K are characterized by both “band-to-band” and “free-to-bound” transition. Carrier dynamics of Si doped InN thin films is studied using pump-probe reflection spectroscopy at room temperature. The hot electron cooling process is well described by electron-electron scattering. The dependence of the hot electron cooling rate on total electron density shows sublinear to linear behavior with increase of background electron density. The variation of the carrier recombination lifetime with total electron density implicates the dominance of the defect-related nonradiative recombination channel over other recombination processes.

  6. Low cost back contact heterojunction solar cells on thin c-Si wafers. Integrating laser and thin film processing for improved manufacturability

    SciTech Connect

    Hegedus, Steven S.

    2015-09-08

    An interdigitated back contact (IBC) Si wafer solar cell with deposited a-Si heterojunction (HJ) emitter and contacts is considered the ultimate single junction Si solar cell design. This was confirmed in 2014 by both Panasonic and Sharp Solar producing IBC-HJ cells breaking the previous record Si solar cell efficiency of 25%. But manufacturability at low cost is a concern for the complex IBC-HJ device structure. In this research program, our goals were to addressed the broad industry need for a high-efficiency c-Si cell that overcomes the dominant module cost barriers by 1) developing thin Si wafers synthesized by innovative, kerfless techniques; 2) integrating laser-based processing into most aspects of solar cell fabrication, ensuring high speed and low thermal budgets ; 3) developing an all back contact cell structure compatible with thin wafers using a simplified, low-temperature fabrication process; and 4) designing the contact patterning to enable simplified module assembly. There were a number of significant achievements from this 3 year program. Regarding the front surface, we developed and applied new method to characterize critical interface recombination parameters including interface defect density Dit and hole and electron capture cross-section for use as input for 2D simulation of the IBC cell to guide design and loss analysis. We optimized the antireflection and passivation properties of the front surface texture and a-Si/a-SiN/a-SiC stack depositions to obtain a very low (< 6 mA/cm2) front surface optical losses (reflection and absorption) while maintaining excellent surface passivation (SRV<5 cm/s). We worked with kerfless wafer manufacturers to apply defect-engineering techniques to improve bulk minority-carrier lifetime of thin kerfless wafers by both reducing initial impurities during growth and developing post-growth gettering techniques. This led insights about the kinetics of nickel, chromium, and dislocations in PV-grade silicon and to

  7. Low cost back contact heterojunction solar cells on thin c-Si wafers. integrating laser and thin film processing for improved manufacturability

    SciTech Connect

    Hegedus, Steven S.

    2015-09-08

    An interdigitated back contact (IBC) Si wafer solar cell with deposited a-Si heterojunction (HJ) emitter and contacts is considered the ultimate single junction Si solar cell design. This was confirmed in 2014 by both Panasonic and Sharp Solar producing IBC-HJ cells breaking the previous record Si solar cell efficiency of 25%. But manufacturability at low cost is a concern for the complex IBC-HJ device structure. In this research program, our goals were to addressed the broad industry need for a high-efficiency c-Si cell that overcomes the dominant module cost barriers by 1) developing thin Si wafers synthesized by innovative, kerfless techniques; 2) integrating laser-based processing into most aspects of solar cell fabrication, ensuring high speed and low thermal budgets ; 3) developing an all back contact cell structure compatible with thin wafers using a simplified, low-temperature fabrication process; and 4) designing the contact patterning to enable simplified module assembly. There were a number of significant achievements from this 3 year program. Regarding the front surface, we developed and applied new method to characterize critical interface recombination parameters including interface defect density Dit and hole and electron capture cross-section for use as input for 2D simulation of the IBC cell to guide design and loss analysis. We optimized the antireflection and passivation properties of the front surface texture and a-Si/a-SiN/a-SiC stack depositions to obtain a very low (< 6 mA/cm2) front surface optical losses (reflection and absorption) while maintaining excellent surface passivation (SRV<5 cm/s). We worked with kerfless wafer manufacturers to apply defect-engineering techniques to improve bulk minority-carrier lifetime of thin kerfless wafers by both reducing initial impurities during growth and developing post-growth gettering techniques. This led insights about the kinetics of nickel, chromium, and dislocations in PV-grade silicon and to

  8. Self heating in Si0.5Ge0.5/Si and GaAs/Si thin film device structures

    NASA Astrophysics Data System (ADS)

    Zheng, H.; Jagannadham, K.

    2014-09-01

    Si0.5Ge0.5 and GaAs films grown on Si substrates were used to measure the interface thermal conductance between the films and the substrate. Transient thermoreflectance technique was used with the one-dimensional heat equation to simulate the experimental results. The results showed that the interface thermal conductance of SiGe/Si interface is 100 MW m-2 K-1 and that of GaAs/Si is 20 MW m-2 K-1. These values of interface thermal conductance combined with the thermal conductivity of the films were used to conclude that SiGe films are less susceptible to self heating than GaAs films of same thickness.

  9. Optical characterization of SiO2 thin films using universal dispersion model over wide spectral range

    NASA Astrophysics Data System (ADS)

    Franta, Daniel; Nečas, David; Ohlídal, Ivan; Giglia, Angelo

    2016-04-01

    Vacuum evaporated SiO2 thin films are very important in a design and manufacturing of optical devices produced in optics industry. In this contribution a reliable and precise optical characterization of such SiO2 thin films is performed using the combined method of spectrophotometry at normal incidence and variable-angle spectroscopic ellipsometry applied over spectral range from far IR to extreme UV (0.01-45 eV). This method uses the Universal Dispersion Model based on parametrization of the joint density of states and structural model comprising film defects such as nanometric boundary roughness, inhomogeneity and area non-uniformity. The optical characterization over the wide spectral range provides not only the spectral dependencies of the optical constants of the films within the wide range but, more significantly, it enables their correct and precise determination within the spectral range of interest, i.e. the range of their transparency. Furthermore, measurements in the ranges of film absorption, i. e. phonon excitations in IR and electron excitations in UV, reveal information about the material structure. The results of the optical characterization of the SiO2 thin films prepared on silicon single crystal substrates under various technological conditions are presented in detail for two selected samples. Beside film thicknesses and values of dispersion parameters and spectral dependencies of the optical constants of the SiO2 films, the characterization also enables quantification of film defects and their parameters are presented as well. The results concerning the optical constants of SiO2 films are compared with silica optical constants determined in our earlier studies.

  10. Radiation-induced charge trapping in thin Al2O3/SiOxNy/Si(100) gate dielectric stacks.

    SciTech Connect

    D'Emic, Chris; Gusev, Evgeni P.; Schrimpf, Ronald D.; Fleetwood, Daniel M.; Schwank, James Ralph; Felix, James Andrew; Shaneyfelt, Marty Ray; Dodd, Paul Emerson; Meisenheimer, Timothy Lee

    2003-07-01

    We examine the total-dose radiation response of capacitors and transistors with stacked Al{sub 2}O{sub 3} on oxynitride gate dielectrics with Al and poly-Si gates after irradiation with 10 keV X-rays. The midgap voltage shift increases monotonically with dose and depends strongly on both Al{sub 2}O{sub 3} and SiO{sub x}N{sub y} thickness. The thinnest dielectrics, of most interest to industry, are extremely hard to ionizing irradiation, exhibiting only {approx}50 mV of shift at a total dose of 10 Mrad(SiO{sub 2}) for the worst case bias condition. Oxygen anneals are found to improve the total dose radiation response by {approx}50% and induce a small amount of capacitance-voltage hysteresis. Al{sub 2}O{sub 3}/SiO{sub x}N{sub y} dielectrics which receive a {approx}1000 C dopant activation anneal trap {approx}12% more of the initial charge than films annealed at 550 C. Charge pumping measurements show that the interface trap density decreases with dose up to 500 krad(SiO{sub 2}). This surprising result is discussed with respect to hydrogen effects in alternative dielectric materials, and may be the result of radiation-induced hydrogen passivation of some of the near-interfacial defects in these gate dielectrics.

  11. "Un-annealed and Annealed Pd Ultra-Thin Film on SiC Characterized by Scanning Probe Microscopy and X-ray Photoelectron Spectroscopy"

    NASA Technical Reports Server (NTRS)

    Lu, W. J.; Shi, D. T.; Elshot, K.; Bryant, E.; Lafate, K.; Chen, H.; Burger, A.; Collins, W. E.

    1998-01-01

    Pd/SiC has been used as a hydrogen and a hydrocarbon gas sensor operated at high temperature. UHV (Ultra High Vacuum)-Scanning Tunneling Microscopy (STM), Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) techniques were applied to study the relationship between the morphology and chemical compositions for Pd ultra-thin films on SiC (less than 30 angstroms) at different annealing temperatures. Pd ultra-thin film on 6H-SiC was prepared by the RF sputtering method. The morphology from UHV-STM and AFM shows that the Pd thin film was well deposited on SiC substrate, and the Pd was partially aggregated to round shaped participates at an annealing temperature of 300 C. At 400 C, the amount of surface participates decreases, and some strap shape participates appear. From XPS, Pd2Si was formed on the surface after annealing at 300 C, and all Pd reacted with SiC to form Pd2Si after annealing at 400 C. The intensity of the XPS Pd peak decreases enormously at 400 C. The Pd film diffused into SiC, and the Schottky barrier height has almost no changes. The work shows the Pd sicilides/SiC have the same electronic properties with Pd/SiC, and explains why the Pd/SiC sensor still responds to hydrogen at high operating temperatures.

  12. Glancing angle deposition of SiO{sub 2} thin film microstructures: Investigations of optical and morphological properties

    SciTech Connect

    Tokas, R. B. E-mail: tokasstar@gmail.com; Jena, S. E-mail: tokasstar@gmail.com; Sarkar, P. E-mail: tokasstar@gmail.com; Thakur, S. E-mail: tokasstar@gmail.com; Sahoo, N. K. E-mail: tokasstar@gmail.com

    2014-04-24

    In present work, the optical and the morphological properties of micro-structured SiO{sub 2} thin films fabricated by using glancing angle deposition (GLAD) technique has been carried out. The results are compared with the normally deposited SiO{sub 2} films for the gained advantages. The influence of the glancing angle on the refractive index of porous SiO{sub 2} film was investigated by the spectral transmission measurement in 400–950 nm wavelength regimes. The refractive index has been found to be 1.14@532 nm for the porous SiO{sub 2} film deposited at a glancing angle of 85°. The density and surface qualities of these samples were primarily investigated by using grazing angle X-ray reflectivity (GIXR) and atomic force microscope (AFM) measurements. Results indicate a substantial decrease in film density and refractive index and increase in surface roughness and grain size for GLAD SiO{sub 2} compared to normally deposited SiO{sub 2} films.

  13. Interaction of Ni90Ti10 alloy thin film with 6H-SiC single crystal

    NASA Astrophysics Data System (ADS)

    Levit, M.; Grimberg, I.; Weiss, B.-Z.

    1996-07-01

    Interfacial reactions, phase formation, microstructure, and composition, as functions of heat treatments (400-800 °C) were investigated in Ni90Ti10 alloy thin film coevaporated on an n-type 6H-SiC (0001) single-crystal substrate. The study was carried out with the aid of Auger electron spectroscopy, x-ray diffraction, and analytical transmission electron microscopy. The interaction was found to begin at 450 °C. Ni and C are the dominant diffusing species. The reaction zone is divided into three layers. In the first layer, adjacent to the SiC substrate, the presence of Ni-rich silicide, Ni2Si, and C precipitates, was observed. The second layer is composed mainly of TiC, while the third consists of Ni2Si. This composite structure, consisting of the silicide as a low resistivity ohmic contact, and of the carbide as a diffusion barrier, promises high-temperature stability crucial to ohmic contact development for SiC technology. Factors controlling phase formation in the Ni-Ti/SiC system are discussed.

  14. Studies on VO{sub x} thin films deposited over Si{sub 3}N{sub 4} coated Si substrates

    SciTech Connect

    Raj, P. Deepak; Sridharan, M.; Gupta, Sudha

    2015-06-24

    Vanadium oxide (VO{sub x}) thin films were deposited on to the silicon nitride (Si{sub 3}N{sub 4}) coated silicon (Si) substrate using reactive direct current magnetron sputtering at different substrate temperatures (T{sub s}). The deposited films were characterized for their structural, morphological, optical and electrical properties. The average grain size of the deposited films was in the range of 95 to 178 nm and the strain varied from 0.071 to 0.054 %. The optical bandgap values of the films were evaluated using UV-Vis spectroscopy and lies in the range of 2.46 to 3.88 eV. The temperature coefficient of resistance (TCR) for the film deposited at 125 °C was -1.23%/°C with the sheet resistivity of 2.7 Ω.cm.

  15. Hydrogen migration in polycrystalline silicon

    SciTech Connect

    Nickel, N.H.; Jackson, W.B.; Walker, J.

    1996-03-01

    Hydrogen migration in solid-state crystallized and low-pressure chemical-vapor-deposited (LPCVD) polycrystalline silicon (poly-Si) was investigated by deuterium diffusion experiments. The concentration profiles of deuterium, introduced into the poly-Si samples either from a remote D plasma or from a deuterated amorphous-silicon layer, were measured as a function of time and temperature. At high deuterium concentrations the diffusion was dispersive depending on exposure time. The dispersion is consistent with multiple trapping within a distribution of hopping barriers. The data can be explained by a two-level model used to explain diffusion in hydrogenated amorphous silicon. The energy difference between the transport level and the deuterium chemical potential was found to be about 1.2{endash}1.3 eV. The shallow levels for hydrogen trapping are about 0.5 eV below the transport level, while the deep levels are about 1.5{endash}1.7 eV below. The hydrogen chemical potential {mu}{sub H} decreases as the temperature increases. At lower concentrations, {mu}{sub H} was found to depend markedly on the method used to prepare the poly-Si, a result due in part to the dependence of crystallite size on the deposition process. Clear evidence for deuterium deep traps was found only in the solid-state crystallized material. The LPCVD-grown poly-Si, with columnar grains extending through the film thickness, displayed little evidence of deep trapping, and exhibited enhanced D diffusion. Many concentration profiles in the columnar LPCVD material indicated complex diffusion behavior, perhaps reflecting spatial variations of trap densities, complex formation, and/or multiple transport paths. Many aspects of the diffusion in poly-Si are consistent with diffusion data obtained in amorphous silicon. {copyright} {ital 1996 The American Physical Society.}

  16. Kinetics of growth of thin-films of Co2Si, Ni2Si, WSi2 and VSi2 during a reactive diffusion process

    NASA Astrophysics Data System (ADS)

    Akintunde, S. O.; Selyshchev, P. A.

    A theoretical approach is developed which describes the growth kinetics of thin films of near noble metal silicide (especially of cobalt silicide (Co2Si) and nickel silicide (Ni2Si)) and refractory metal silicide (particularly of tungsten disilicide (WSi2) and vanadium disilicide (VSi2)) at the interfaces of metal-silicon system. In this approach, metal species are presented as A-atoms, silicon as B-atoms, and silicide as AB-compound. The AB-compound is formed as a result of chemical transformation between A- and B-atoms at the reaction interfaces A/AB and AB/B. The growth of AB-compound at the interfaces occurs in two stages. The first growth stage is reaction controlled stage which takes place at the interface with excess A or B-atoms and the second stage is diffusion limited stage which occurs at both interfaces. The critical thickness of AB-compound and the corresponding time is determined at the transition point between the two growth stages. The result that follows from this approach shows that the growth kinetics of any growing silicides depends on the number of kinds of dominant diffusing species in the silicide layer and also on their number densities at the reaction interface. This result shows a linear-parabolic growth kinetics for WSi2, VSi2, Co2Si, and Ni2Si and it is in good agreement with experiment.

  17. Hydrogen kinetics in a-Si:H and a-SiC:H thin films investigated by real-time ERD

    NASA Astrophysics Data System (ADS)

    Halindintwali, S.; Khoele, J.; Nemroaui, O.; Comrie, C. M.; Theron, C. C.

    2015-04-01

    Hydrogen effusion from hydrogenated amorphous silicon (a-Si:H) and amorphous silicon carbide (a-Si1-xCx:H) thin films during a temperature ramp between RT and 600 °C was studied by in situ real-time elastic recoil detection analysis. Point to point contour maps show the hydrogen depth profile and its evolution with the ramped temperature. This paper proposes a diffusion limited evolution model to study H kinetic properties from total retained H contents recorded in a single ramp. In a compact a-Si:H layer where H predominantly effuses at high temperatures between 500 and 600 °C, an activation energy value of ∼1.50 eV and a diffusion pre-factor of 0.41 × 10-4 cm2/s were obtained. Applied to an non-stoichiometric a-Si1-xCx:H film in the same range of temperature, the model led to reduced values of activation energy and diffusion prefactor of ∼0.33 eV and 0.59 × 10-11 cm2/s, respectively.

  18. Growth and modification of thin SiGeC films at low substrate temperatures through UV laser assisted processing

    NASA Astrophysics Data System (ADS)

    López, E.; Chiussi, S.; Serra, J.; González, P.; Serra, C.; Kosch, U.; León, B.; Fabbri, F.; Fornarini, L.; Martelli, S.

    2004-07-01

    Enhancing the performance of solar cells, near infrared photo-detectors and microelectronic devices through band gap engineering caused an increasing attention in processes for growing thin silicon germanium carbon (SiGeC) films in a wide range of composition and crystalline structures. Moreover, the demand of using cheap substrates and the development of new devices with advanced materials like "high- k dielectrics" and "organic materials" implies the need of new processes avoiding high substrate temperatures that may decompose or alter the substrate materials, crystallise part of the heterostructures or promote segregation effects. Laser induced chemical vapour deposition (LCVD) and excimer laser assisted crystallisation (ELC) are such alternative and relatively cheap "low thermal budget" techniques that, in addition, are compatible with conventional IC silicon technology. The present study will show the possibility of tailoring the composition of amorphous SiGeC coatings through the adjustment of gas flow rates in LCVD processes performed at substrate temperatures between 180 and 400 °C. The modification of an amorphous film through a subsequent ELC process performed at room temperature is analysed through SEM and depth profile XPS in order to study the effects of controlled laser radiation on it, as well as on a very thin underlaying interfacial SiO 2 layer and on the Si(1 0 0) substrate.

  19. Application of Extremely Thin ZrN Film as Diffusion Barrier between Cu and SiOC

    NASA Astrophysics Data System (ADS)

    Sato, Masaru; Takeyama, Mayumi B.; Aoyagi, Eiji; Noya, Atsushi

    2008-01-01

    As an extremely thin diffusion barrier applicable to Cu interconnects for the 45 nm technology nodes, we propose a barrier material without interface layers that can become a cause of barrier consumption owing to solid-phase reaction and/or intermixing. We examine the barrier properties of a reactively sputtered ZrN barrier as thin as 5 nm between Cu and SiOC. The ZrN barrier with a slightly N-rich composition tolerates annealing at 500 °C for 30 min. Transmission electron microscopy indicates the absence of interface layers adjoining the barrier. Using the ZrN barrier, we can demonstrate the effectiveness of the interface-layer-free characteristics for an extremely thin barrier of high performance.

  20. Research on polycrystalline thin-film CuInGaSe{sub 2} solar cells. Annual subcontract report, 3 May 1991--21 May 1993

    SciTech Connect

    Chen, W.S.; Stewart, J.M.; Mickelsen, R.A.; Devaney, W.E.; Stanbery, B.J.

    1993-10-01

    This report describes work to fabricate high-efficiency CdZnS/CuInGaSe{sub 2}, thin-film solar cells and to develop improved transparent conductor window layers such as ZnO. The specific technical milestone for Phase I was to demonstrate an air mass (AM) 1.5 global 13% , 1-cm{sup 2} total-area CuInGaSe{sub 2} (CIGS) thin-film solar cell. For Phase II, the objective was to demonstrate an AM1.5 global 13.5%, 1-cm{sup 2} total-area efficiency. We focused our activities on three areas. First, we modified the CIGS deposition system to double its substrate capacity. Second, we developed new tooling to enable investigation of a modified aqueous CdZnS process in which the goal was to improve the yield of this critical step in the device fabrication process. Third, we upgraded the ZnO sputtering system to improve its reliability and reproducibility. A dual rotatable cathode metallic source was installed, and the sputtering parameters were further optimized to improve ZnO`s properties as a transparent conducting oxide (TCO). Combining the refined CdZnS process with CIGS from the newly fixtured deposition system enable us to fabricate and deliver a ZnO/Cd{sub 0.08}Zn{sub 0.20}S/CuIn{sub 0.74}Ga{sub 0.26}Se{sub 2} cell on alumina with I-V characteristics, as measured by NREL under standard test conditions, of 13.7% efficiency with V{proportional_to} = 0.5458 V, J{sub sc} = 35.48 mA/cm{sup 2}, FF = 0.688, and efficiency = 14.6%.

  1. Recrystallization of polycrystalline silicon

    NASA Technical Reports Server (NTRS)

    Lall, C.; Kulkarni, S. B.; Graham, C. D., Jr.; Pope, D. P.

    1981-01-01

    Optical metallography is used to investigate the recrystallization properties of polycrystalline semiconductor-grade silicon. It is found that polycrystalline silicon recrystallizes at 1380 C in relatively short times, provided that the prior deformation is greater than 30%. For a prior deformation of about 40%, the recrystallization process is essentially complete in about 30 minutes. Silicon recrystallizes at a substantially slower rate than metals at equivalent homologous temperatures. The recrystallized grain size is insensitive to the amount of prestrain for strains in the range of 10-50%.

  2. Large-area SiC membrane produced by plasma enhanced chemical vapor deposition at relatively high temperature

    SciTech Connect

    Liu, Yu; Xie, Changqing

    2015-09-15

    Advances in the growth of silicon carbide (SiC) thin films with outstanding thermal and mechanical properties have received considerable attention. However, the fabrication of large-area free-standing SiC membrane still remains a challenge. Here, the authors report a plasma enhanced chemical vapor deposition process at a relatively high temperature to improve the free-standing SiC membrane area. A systematic study on the microstructural, mechanical, and optical properties of hydrogenated polycrystalline silicon carbide (poly-SiC{sub x}:H) thin films deposited at 600 °C with different annealing temperatures has been performed. In the as-deposited state, SiC{sub x}:H thin films show a polycrystalline structure. The crystallinity degree can be further improved with the increase of the postdeposition annealing temperature. The resulting process produced free-standing 2-μm-thick SiC membranes up to 70 mm in diameter with root mean square roughness of 3.384 nm and optical transparency of about 70% at 632.8 nm wavelength. The large-area SiC membranes made out of poly-SiC{sub x}:H thin films deposited at a relatively high temperature can be beneficial for a wide variety of applications, such as x-ray diffractive optical elements, optical and mechanical filtering, lithography mask, lightweight space telescopes, etc.

  3. Performance of very thin Gd2SiO5 scintillator bars for the LHCf experiment

    NASA Astrophysics Data System (ADS)

    Suzuki, T.; Kasahara, K.; Kawade, K.; Murakami, T.; Masuda, K.; Sako, T.; Torii, S.

    2013-01-01

    To increase the radiation resistivity of the calorimeter, the LHCf group plans to replace its plastic scintillator with Gd2SiO5 (GSO) scintillator. In this report, we present the basic performance of very thin GSO scintillator bars that will replace the scintillating fibers employed as the position sensitive part of the current LHCf detector. The size of a bar is 1 mm × 1 mm × 40 mm. White acrylic paint was painted on one group of GSO bars and a second group was unpainted. After observing a clear peak of cosmic ray muons corresponding to 3 to 4 photoelectrons, a quantitative test was performed by using a 290 MeV/n carbon beam at HIMAC in Japan. The non-painted bars have less position dependence of light collection efficiency (effective attenuation length is about 140 mm) and less piece-to-piece variation. The unpainted bars show about 8% cross talk between adjacent bars which is larger than the painted ones. However, for estimating the center of a cascade shower inside the calorimeter, uniformity of light collection is more important than cross talk, so we have decided to use non-painted bars in the LHCf detector. A simulation of a 100 GeV electron injected in the center of the detector shows that position dependence and cross talk cause only a 0.04 mm shift of the shower centroid without any correction applied. This shows that these effects are relatively small compared to the uncertainty of the beam center position which was 1 mm for the LHCf experiments already performed at √s =7 TeV.

  4. Microstructure and dielectric properties of pulsed-laser-deposited CaCu3Ti4O12 thin films on LaNiO3 buffered Pt/Ti/SiO2/Si substrates

    NASA Astrophysics Data System (ADS)

    Fang, L.; Shen, M.; Yao, D.

    2005-05-01

    CaCu3Ti4O12 (CCTO) thin films have been prepared by a pulsed-laser-deposition method on LaNiO3 buffered Pt/Ti/SiO2/Si substrates, and their microstructure and dielectric properties have been compared with those of the films deposited directly on Pt/Ti/SiO2/Si substrates. The crystalline structure and the surface morphology of the CCTO thin films were markedly affected by the bottom electrodes. Both the films show temperature-independent dielectric properties in a wide temperature range, which is similar to those properties obtained in single-crystal or epitaxial thin films, while the room-temperature dielectric constant of the 350-nm-thick CCTO films on LaNiO3/Pt/Ti/SiO2/Si substrates at 100 kHz was found to be 2300, which was increased significantly compared with that obtained in the films on Pt/Ti/SiO2/Si substrates. Using the impedance spectroscopy technique, it has been suggested that the high dielectric constant response of the CCTO thin films originates from the grain boundary layer mechanism as found in internal barrier layer capacitors.

  5. Growth of SiC thin films on (100) and (111) silicon by pulsed laser deposition combined with a vacuum annealing process

    SciTech Connect

    Huang, J.; Wang, L.; Wen, J.; Wang, Y.; Lin, C.; Zetterling, C.M.; Oestling, M.

    1999-07-01

    Crystalline 3C-SiC thin films were successfully grown on (100) and (111) Si substrates by using ArF pulsed laser ablation from a SiC ceramic target combined with a vacuum annealing process. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were employed to study the effect of annealing on the structure of thin films deposited at 800 C. It was demonstrated that vacuum annealing could transform the amorphous SiC films into crystalline phase and that the crystallinity was strongly dependent on the annealing temperature. For the samples deposited on (100) and (111) Si, the optimum annealing temperatures were 980 and 920 C, respectively. Scanning electron microscope (SEM) micrographs exhibited different characteristic microstructure for the (100) and (111) Si cases, similar to that observed for the carbonization layer initially formed in chemical vapor deposition of SiC films on Si. This also showed the presence of the epitaxial relationship of 3C-SiC[100]//Si[100] and 3C-SiC[111]//Si[111] in the direction of growth.

  6. Substrate effect on excimer laser assisted crystal growth in phosphor Ca 0.997Pr 0.002TiO 3 polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Nakajima, Tomohiko; Tsuchiya, Tetsuo; Kumagai, Toshiya

    2007-12-01

    Ca 0.997Pr 0.002TiO 3 thin films that show strong red luminescence were successfully prepared by means of an excimer laser assisted metal organic deposition process with a KrF laser at a fluence of 100 mJ/cm 2 at 100 °C. The CPTO films grew on the silica, borosilicate, and indium-tin-oxide coated glasses. The crystallinity of the Ca 0.997Pr 0.002TiO 3 films depended on the substrates; the borosilicate and indium-tin-oxide coated glasses with a large optical absorption of a KrF laser ( λ = 248 nm) were effective for the crystallization for the Ca 0.997Pr 0.002TiO 3. In addition, a high thermal conductivity of the indium-tin-oxide coated glass substrate could also improve the crystallinity due to an enhancement of thermal propagation to the film. Oxygen annealing at 500 °C for 6 h successfully eliminated the oxygen vacancy produced by the laser irradiation, and also remarkably improved the PL emission intensity. Thus, we have shown that substrate properties such as an optical absorbance and a thermal conductivity were quite important factors for the crystal growth and the PL emission for the Ca 0.997Pr 0.002TiO 3 in the excimer laser assisted metal organic deposition process.

  7. Research on polycrystalline thin-film submodules based on CuInSe{sub 2} materials. Final subcontract report, 11 November 1990--30 June 1995

    SciTech Connect

    Arya, R; Fogleboch, J; Kessler, J; Russell, L; Skibo, S; Wiedeman, S

    1996-01-01

    This report describes work performed in development of CIS-based photovoltaic (PV) products. The activity began with developing manufacturable deposition methods for all required thin-film layers and developing and understanding processes using those methods. It included demonstrating the potential for high conversion efficiency and followed with developing viable methods for module segment formation and interconnection. These process steps were integrated to fabricate monolithic CIS-based submodules. An important result of this program is the basis of understanding established in developing this material for PV applications, which is necessary to address issues of manufacturability and cost-which were recognized early in the program as being determined by successful solutions to issues of yield, reproducibility, and control as much as by material and energy costs, conversion efficiency, and process speed. Solarex identified at least one absorber formation process that is very robust to shunt formation from pinholes or point defects, tolerant of variation in processing temperature and elemental composition, and is capable of producing high conversion efficiency. This program also allowed development and scale-up of processes for the deposition of all other substrate, heterojunction buffer, and window layers and associated scribing/module formation operations to 1000-CM{sup 2} size. At the completion of this program, Solarex has in place most of the necessary elements to begin the transition to pilot operation of CIS manufacturing activities.

  8. Cubic SiC nano-thin films and nano-wires: high vacuum metal-organic chemical vapor deposition, surface characterization, and application tests.

    PubMed

    Hyun, J S; Nam, S H; Kang, B C; Park, J H; Boo, J H

    2008-10-01

    Single-crystalline and epitaxial cubic silicon carbide (beta-SiC) nano-thin films have been deposited on Si(100) substrates at a sample temperature of approximately 900 degrees C using single source precursors by the thermal metal-organic chemical vapor deposition (MOCVD) method. Diethylmethylsilane and 1,3-disilabutane, which contain Si and C atoms in the same molecule, were used as precursors without any carrier or bubbler gas. Upon increasing the deposition temperature from 900 to 950 degrees C, beta-SiC nano-thin films with relatively small crystals and smoother surfaces were created on Si(100) substrates. Moreover, beta-SiC nano-wires with 40 approximately 100 nm in diameter have also been grown selectively on nickel catalyzed Si(100) substrates with dichloromethylvinylsilane by the MOCVD method. The deposition temperature in this case was as low as 800 degrees C under the pressure of 5.0 x 10(-2) Torr. It is worth noting that the initial growth rates of deposited beta-SiC nano-thin films and nano-wires strongly depend on the deposition temperature rather than the time. In order to test the possibility of applications of these materials for electronic components such as field emitter, MEMS, and high-power transistor, we fabricated the nanoelectronic devices using both beta-SiC nano-wires and nano-thin films. With these preliminary application tests, it is expected that SiC nanowires can be used as field emitter and nanoelectronic high-power transistor, and application of the SiC nano-thin films to MEMS is promising as well.

  9. [Study on the Properties of the Pc-Si Films Prepared by Magnetron Co-Sputtering at Low Temperature].

    PubMed

    Duan, Liang-fei; Yang, Wen; Zhang, Li-yuan; Li, Xue-ming; Chen, Xiao-bo; Yang, Pei-zhi

    2016-03-01

    The polycrystalline silicon thin films play an important role in the field of electronics. In the paper, α-SiAl composite membranes on glass substrates was prepared by magnetron co-sputtering. The contents of Al radicals encapsulated-in the α-Si film can be adjusted by changing the Al to Si sputtering power ratios. The as-prepared α-Si films were converted into polycrystalline films by using a rapid thermal annealing (RTP) at low temperature of 350 degrees C for 10 minutes in N2 atmosphere. An X-ray diffractometer, and Raman scattering and UV-Visible-NIR Spectrometers were used to characterize the properties of the Pc-Si films. The influences of Al content on the properties of the Pc-Si films were studied. The results showed that the polycrystalline silicon films were obtained from α-SiAl composite films which were prepared by magnetron co-sputtering at a low temperature following by a rapid thermal annealing. The grain size and the degree of crystallization of the Pc-Si films increased with the increase of Al content, while the optical band gap was reduced. The nc-Si films were prepared when the Al to Si sputtering power ratio was 0.1. And a higher Crystallization rate (≥ 85%) of polycrystalline silicon films were obtained when the ratio was 0.3. The band gaps of the polycrystalline silicon films can be controlled by changing the aluminum content in the films. PMID:27400496

  10. Impact of reductive N2/H2 plasma on porous low-dielectric constant SiCOH thin films

    NASA Astrophysics Data System (ADS)

    Cui, Hao; Carter, Richard J.; Moore, Darren L.; Peng, Hua-Gen; Gidley, David W.; Burke, Peter A.

    2005-06-01

    Porous low-dielectric constant (low-κ) SiCOH thin films deposited using a plasma-enhanced chemical-vapor deposition have been comprehensively characterized before and after exposure to a reactive-ion-etch-type plasma of N2 and H2 chemistry. The low-κ film studied in this work is a carbon-doped silicon oxide film with a dielectric constant (κ) of 2.5. Studies show that a top dense layer is formed as a result of significant surface film densification after exposure to N2/H2 plasma while the underlying bulk layer remains largely unchanged. The top dense layer is found to seal the porous bulk SiCOH film. SiCOH films experienced significant thickness reduction, κ increase, and leakage current degradation after plasma exposure, accompanied by density increase, pore collapse, carbon depletion, and moisture content increase in the top dense layer. Both film densification and removal processes during N2/H2 plasma treatment were found to play important roles in the thickness reduction and κ increase of this porous low-κ SiCOH film. A model based upon mutually limiting film densification and removal processes is proposed for the continuous thickness reduction during plasma exposure. A combination of surface film densification, thickness ratio increase of top dense layer to bulk layer, and moisture content increase results in the increase in κ value of this SiCOH film.

  11. Polycrystalline thin-film cadmium telluride solar cells fabricated by electrodeposition. Annual subcontract report, 20 March 1992--19 March 1993

    SciTech Connect

    Trefny, J.U.; Furtak, T.E.; Wada, N.; Williamson, D.L.; Kim, D.

    1993-08-01

    This report describes progress during the first year of a 3-year program at Colorado School of Mines, based upon earlier studies performed by Ametek Corporation, to develop specific layers of the Ametek n-i-p structure as well as additional studies of several transparent conducting oxides. Thin films of ZnO and ZnO:Al were deposited under various conditions. For the n-layer of the Ametek structure, a dip-coating method was developed for the deposition of CdS films. The authors also present data on the characterization of these films by X-ray diffraction, Raman spectroscopy, scanning tunneling microscopy, small-angle X-ray scattering, and other techniques. They made progress in the electrodeposition of the CdTe i-layer of the Ametek structure. They developed appropriate electrochemical baths and are beginning to understand the role of the many experimental parameters that must be controlled to obtain high-quality films of this material. They explored the possibility of using an electrochemical process for fabricating the ZnTe p-layer. Some preliminary success was achieved, and this step will be pursued in the next phase. Finally, they fabricated a number of ``dot`` solar cells with the structure glass/SnO{sub 2}/CdS/CdTe/Au. Several cells with efficiencies in the range of 5%-6% were obtained, and they are confident, given recent progress, that cells with efficiencies in excess of 10% will be achieved in the near future.

  12. Pyroelectric and piezoelectric responses of thin AlN films epitaxy-grown on a SiC/Si substrate

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Osipov, A. V.; Sergeeva, O. N.; Kiselev, D. A.; Bogomolov, A. A.; Solnyshkin, A. V.; Kaptelov, E. Yu.; Senkevich, S. V.; Pronin, I. P.

    2016-05-01

    This paper presents the results of pyroelectric and piezoelectric studies of AlN films formed by chloride-hydride epitaxy (CHE) and molecular beam epitaxy (MBE) on epitaxial SiC nanolayers grown on Si by the atom substitution method. The surface topography and piezoelectric and pyroelecrtric responses of AlN films have been analyzed. The results of the study have shown that the vertical component of the piezoresponse in CHE-grown AlN films is more homogeneous over the film area than that in MBE-grown AlN films. However, the signal from the MBE-synthesized AlN films proved to be stronger. The inversion of the polar axis (polarization vector) on passage from MBE-grown AlN films to CHE-grown AlN films has been found experimentally. It has been shown that the polar axis in MBE-grown films is directed from the free surface of the film toward the Si substrate while, in CHE-grown films, the polarization vector is directed toward the free surface.

  13. A Semitransparent and Flexible Single Crystal Si Thin Film: Silicon on Nothing (SON) Revisited.

    PubMed

    Park, Sanghyun; Lee, Yong Hwan; Wi, Jung-Sub; Oh, Jihun

    2016-07-27

    Ultrathin single crystal Si films offer a versatile vehicle for high performance flexible and semitransparent electric devices due to their outstanding optoelectric and mechanical properties. Here, we demonstrate the formation of an ultrathin (100) single crystal Si film based on morphological evolution of nanoporous Si during high temperature annealing. Square arrays of cylindrical Si pores are formed by nanoimprint lithography and deep reactive etching and then subjected to annealing in hydrogen ambient. By controlling the aspect ratio of nanoporous Si, defect-free single crystal Si membranes with controlled thicknesses from 330 to 470 nm are formed on a platelike void after the annealing. In addition, we investigate the role of oxygen impurities in a hydrogen atmosphere on defect formation on a Si surface and eliminate the oxygen-related defects on Si by controlling gas phase diffusion of oxygen impurities during annealing in a conventional tube furnace. Finally, we demonstrate the transfer of a defect-free, flexible, and wafer scale Si membrane with thickness of 470 nm onto a PDMS substrate, utilizing the platelike void under the membrane as a releaser. The ultrathin flexible Si film on PDMS shows optical transmittance of about 30-70% in visible and near-infrared light. PMID:27352938

  14. A Semitransparent and Flexible Single Crystal Si Thin Film: Silicon on Nothing (SON) Revisited.

    PubMed

    Park, Sanghyun; Lee, Yong Hwan; Wi, Jung-Sub; Oh, Jihun

    2016-07-27

    Ultrathin single crystal Si films offer a versatile vehicle for high performance flexible and semitransparent electric devices due to their outstanding optoelectric and mechanical properties. Here, we demonstrate the formation of an ultrathin (100) single crystal Si film based on morphological evolution of nanoporous Si during high temperature annealing. Square arrays of cylindrical Si pores are formed by nanoimprint lithography and deep reactive etching and then subjected to annealing in hydrogen ambient. By controlling the aspect ratio of nanoporous Si, defect-free single crystal Si membranes with controlled thicknesses from 330 to 470 nm are formed on a platelike void after the annealing. In addition, we investigate the role of oxygen impurities in a hydrogen atmosphere on defect formation on a Si surface and eliminate the oxygen-related defects on Si by controlling gas phase diffusion of oxygen impurities during annealing in a conventional tube furnace. Finally, we demonstrate the transfer of a defect-free, flexible, and wafer scale Si membrane with thickness of 470 nm onto a PDMS substrate, utilizing the platelike void under the membrane as a releaser. The ultrathin flexible Si film on PDMS shows optical transmittance of about 30-70% in visible and near-infrared light.

  15. Plasmonic metal nanocubes for broadband light absorption enhancement in thin-film a-Si solar cells

    NASA Astrophysics Data System (ADS)

    Veenkamp, R. J.; Ye, W. N.

    2014-03-01

    The behaviour of plasmonic metal nanoparticles (MNPs) placed in contact with a thin dielectric film on a high refractive index substrate is examined through finite-difference time domain simulations. The optical properties of this configuration are studied in the context of light trapping for thin-film amorphous silicon (a-Si) solar cells. We explore several different MNP configurations including both silver (Ag) and aluminium (Al) nanocubes along with traditional Ag nanospheres for reference. We demonstrate a large increase in the fraction of light coupled into the substrate (Fsubs), and consequently in the absorbed power, by spacing nanocubes away from the substrate. Further study concluded that blue-shifting the plasmonic resonances significantly reduced parasitic absorption in the visible spectrum and increased forward scattering by the MNPs. Transitioning to Al MNPs facilitated a large blue-shift in the plasmonic resonances allowing broadband enhancement in light absorption. For wavelengths less than the band-gap of a-Si, combining the effects of Al nanocubes on a 20 nm SiO2 spacer layer with a 25% surface coverage resulted in a 13.8% increase in solar power absorption over cells with optimally designed Ag nanocube and nanosphere arrays, and a 38.9% enhancement over a MNP free reference cell.

  16. Ordered growth of topological insulator Bi2Se3 thin films on dielectric amorphous SiO2 by MBE.

    PubMed

    Jerng, Sahng-Kyoon; Joo, Kisu; Kim, Youngwook; Yoon, Sang-Moon; Lee, Jae Hong; Kim, Miyoung; Kim, Jun Sung; Yoon, Euijoon; Chun, Seung-Hyun; Kim, Yong Seung

    2013-11-01

    Topological insulators (TIs) are exotic materials which have topologically protected states on the surface due to strong spin-orbit coupling. However, a lack of ordered growth of TI thin films on amorphous dielectrics and/or insulators presents a challenge for applications of TI-junctions. We report the growth of topological insulator Bi2Se3 thin films on amorphous SiO2 by molecular beam epitaxy (MBE). To achieve the ordered growth of Bi2Se3 on an amorphous surface, the formation of other phases at the interface is suppressed by Se passivation. Structural characterizations reveal that Bi2Se3 films are grown along the [001] direction with a good periodicity by the van der Waals epitaxy mechanism. A weak anti-localization effect of Bi2Se3 films grown on amorphous SiO2 shows a modulated electrical property by the gating response. Our approach for ordered growth of Bi2Se3 on an amorphous dielectric surface presents considerable advantages for TI-junctions with amorphous insulator or dielectric thin films.

  17. Characterization of ion-assisted induced absorption in A-Si thin-films used for multivariate optical computing

    NASA Astrophysics Data System (ADS)

    Nayak, Aditya B.; Price, James M.; Dai, Bin; Perkins, David; Chen, Ding Ding; Jones, Christopher M.

    2015-06-01

    Multivariate optical computing (MOC), an optical sensing technique for analog calculation, allows direct and robust measurement of chemical and physical properties of complex fluid samples in high-pressure/high-temperature (HP/HT) downhole environments. The core of this MOC technology is the integrated computational element (ICE), an optical element with a wavelength-dependent transmission spectrum designed to allow the detector to respond sensitively and specifically to the analytes of interest. A key differentiator of this technology is it uses all of the information present in the broadband optical spectrum to determine the proportion of the analyte present in a complex fluid mixture. The detection methodology is photometric in nature; therefore, this technology does not require a spectrometer to measure and record a spectrum or a computer to perform calculations on the recorded optical spectrum. The integrated computational element is a thin-film optical element with a specific optical response function designed for each analyte. The optical response function is achieved by fabricating alternating layers of high-index (a-Si) and low-index (SiO2) thin films onto a transparent substrate (BK7 glass) using traditional thin-film manufacturing processes (e.g., ion-assisted e-beam vacuum deposition). A proprietary software and process are used to control the thickness and material properties, including the optical constants of the materials during deposition to achieve the desired optical response function. The ion-assisted deposition is useful for controlling the densification of the film, stoichiometry, and material optical constants as well as to achieve high deposition growth rates and moisture-stable films. However, the ion-source can induce undesirable absorption in the film; and subsequently, modify the optical constants of the material during the ramp-up and stabilization period of the e-gun and ion-source, respectively. This paper characterizes the unwanted

  18. Thermal expansion coefficient and thermomechanical properties of SiN(x) thin films prepared by plasma-enhanced chemical vapor deposition.

    PubMed

    Tien, Chuen-Lin; Lin, Tsai-Wei

    2012-10-20

    We present a new method based on fast Fourier transform (FFT) for evaluating the thermal expansion coefficient and thermomechanical properties of thin films. The silicon nitride thin films deposited on Corning glass and Si wafers were prepared by plasma-enhanced chemical vapor deposition in this study. The anisotropic residual stress and thermomechanical properties of silicon nitride thin films were studied. Residual stresses in thin films were measured by a modified Michelson interferometer associated with the FFT method under different heating temperatures. We found that the average residual-stress value increases when the temperature increases from room temperature to 100°C. Increased substrate temperature causes the residual stress in SiN(x) film deposited on Si wafers to be more compressive, but the residual stress in SiN(x) film on Corning glass becomes more tensile. The residual-stress versus substrate-temperature relation is a linear correlation after heating. A double substrate technique is used to determine the thermal expansion coefficients of the thin films. The experimental results show that the thermal expansion coefficient of the silicon nitride thin films is 3.27×10(-6)°C(-1). The biaxial modulus is 1125 GPa for SiN(x) film. PMID:23089776

  19. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Tunable Anisotropic Absorption of Ag-Embedded SiO2 Thin Films by Oblique Angle Deposition

    NASA Astrophysics Data System (ADS)

    Xiao, Xiu-Di; Dong, Guo-Ping; Shao, Jian-Da; Fan, Zheng-Xiu; He, Hong-Bo; Qi, Hong-Ji

    2009-08-01

    Ag-embedded SiO2 thin films are prepared by oblique angle deposition. Through field emission scanning electron microscopy (SEM), an orientated slanted columnar structure is observed. Energy-dispersive x-ray (EDX) analysis shows the Ag concentration is about 3% in the anisotropic SiO2 matrix. Anisotropic surface plasma resonance (SPR) absorption is observed in the Ag-embedded SiO2 thin films, which is dependent on polarization state and incidence angle of two orthogonal polarized lights and the deposition angle. This means that optical properties and anisotropic SPR absorption can be tunable in Ag-embedded SiO2 thin films. Broadband polarization splitting is also observed and the transmission ratio Tp/Ts between p- and s-polarized lights is up to 2.7 for thin films deposited at α = 70°, which means that Ag-embedded SiO2 thin films are a promising candidate for thin film polarizers.

  20. MIS and SIS solar cells on polycrystalline silicon

    SciTech Connect

    Cheek, G.; Mertens, R.

    1980-02-01

    MIS and SIS structured solar cells are receiving much attention in the photovoltaic community. Seemingly, these cells could be a viable alternative to thermally diffused p-n junctions for use on thin-film polycrystalline silicon substrates. This review describes MIS/SIS structured solar cells and the possible advantages of these structures for use with thin-film polycrystalline silicon. The results of efficiency calculations are presented. Also addressed are lifetime stability and fabrication techniques amenable to large scale production. Finally, the relative advantages and disadvantages of these cells and the results obtained are presented.

  1. Atmospheric Pressure Chemical Vapor Deposition of High Silica SiO2-TiO2 Antireflective Thin Films for Glass Based Solar Panels

    SciTech Connect

    Klobukowski, Erik R; Tenhaeff, Wyatt E; McCamy, James; Harris, Caroline; Narula, Chaitanya Kumar

    2013-08-30

    The atmospheric pressure chemical vapor deposition (APCVD) of SiO2-TiO2 thin films employing [[(tBuO)3Si]2O-Ti(OiPr)2], which can be prepared from commercially available materials, results in antireflective thin films on float glass under industrially relevant manufacturing conditions. It was found that while the deposition temperature had an effect on the SiO2:TiO2 ratio, the thickness was dependent on the time of deposition. This study shows that it is possible to use APCVD employing a single source precursor containing titanium and silicon to produce thin films on float glass with high SiO2:TiO2 ratios.

  2. Semiconducting ZnSnN2 thin films for Si/ZnSnN2 p-n junctions

    NASA Astrophysics Data System (ADS)

    Qin, Ruifeng; Cao, Hongtao; Liang, Lingyan; Xie, Yufang; Zhuge, Fei; Zhang, Hongliang; Gao, Junhua; Javaid, Kashif; Liu, Caichi; Sun, Weizhong

    2016-04-01

    ZnSnN2 is regarded as a promising photovoltaic absorber candidate due to earth-abundance, non-toxicity, and high absorption coefficient. However, it is still a great challenge to synthesize ZnSnN2 films with a low electron concentration, in order to promote the applications of ZnSnN2 as the core active layer in optoelectronic devices. In this work, polycrystalline and high resistance ZnSnN2 films were fabricated by magnetron sputtering technique, then semiconducting films were achieved after post-annealing, and finally Si/ZnSnN2 p-n junctions were constructed. The electron concentration and Hall mobility were enhanced from 2.77 × 1017 to 6.78 × 1017 cm-3 and from 0.37 to 2.07 cm2 V-1 s-1, corresponding to the annealing temperature from 200 to 350 °C. After annealing at 300 °C, the p-n junction exhibited the optimum rectifying characteristics, with a forward-to-reverse ratio over 103. The achievement of this ZnSnN2-based p-n junction makes an opening step forward to realize the practical application of the ZnSnN2 material. In addition, the nonideal behaviors of the p-n junctions under both positive and negative voltages are discussed, in hope of suggesting some ideas to further improve the rectifying characteristics.

  3. Investigation of Nanomechanical Properties of β-Si3N4 Thin Layers in a Prismatic Plane under Tension: A Molecular Dynamics Study.

    PubMed

    Lu, Xuefeng; La, Peiqing; Guo, Xin; Wei, Yupeng; Nan, Xueli; He, Ling

    2013-06-01

    We report molecular dynamics simulations of the nanomechanical properties and fracture mechanisms of β-Si3N4 thin layers in a prismatic plane under uniaxial tension. It is found that the thin layers in the y loading direction display a linear stress-strain relationship at ε < 0.021, and afterward, the stress increases nonlinearly with the strain until fracture occurs. However, for the z direction, the linear response is located at ε < 0.051. The calculated fracture stresses and strains of the thin layers increase with strain rates both in both directions. The thin layers exhibit the higher Young's modulus of 0.345 TPa in the z direction, higher than that in the y direction. The origins of crack derive from N(2c-1)-Si and N(6h-1)-Si bonds for the y and z loading directions, respectively.

  4. High-efficiency superconducting nanowire single-photon detectors fabricated from MoSi thin-films

    NASA Astrophysics Data System (ADS)

    Verma, V. B.; Korzh, B.; Bussières, F.; Horansky, R. D.; Dyer, S. D.; Lita, A. E.; Vayshenker, I.; Marsili, F.; Shaw, M. D.; Zbinden, H.; Mirin, R. P.; Nam, S. W.

    2015-12-01

    We demonstrate high-efficiency superconducting nanowire single-photon detectors (SNSPDs) fabricated from MoSi thin-films. We measure a maximum system detection efficiency (SDE) of 87 +- 0.5 % at 1542 nm at a temperature of 0.7 K, with a jitter of 76 ps, maximum count rate approaching 10 MHz, and polarization dependence as low as 3.4 +- 0.7 % The SDE curves show saturation of the internal efficiency similar to WSi-based SNSPDs at temperatures as high as 2.3 K. We show that at similar cryogenic temperatures, MoSi SNSPDs achieve efficiencies comparable to WSi-based SNSPDs with nearly a factor of two reduction in jitter.

  5. Enhanced photovoltaic performances of graphene/Si solar cells by insertion of a MoS₂ thin film.

    PubMed

    Tsuboi, Yuka; Wang, Feijiu; Kozawa, Daichi; Funahashi, Kazuma; Mouri, Shinichiro; Miyauchi, Yuhei; Takenobu, Taishi; Matsuda, Kazunari

    2015-09-14

    Transition-metal dichalcogenides exhibit great potential as active materials in optoelectronic devices because of their characteristic band structure. Here, we demonstrated that the photovoltaic performances of graphene/Si Schottky junction solar cells were significantly improved by inserting a chemical vapor deposition (CVD)-grown, large MoS2 thin-film layer. This layer functions as an effective electron-blocking/hole-transporting layer. We also demonstrated that the photovoltaic properties are enhanced with the increasing number of graphene layers and the decreasing thickness of the MoS2 layer. A high photovoltaic conversion efficiency of 11.1% was achieved with the optimized trilayer-graphene/MoS2/n-Si solar cell.

  6. Differentiation of Effects due to Grain and Grain Boundary Traps in Laser Annealed Poly-Si Thin Film Transistors

    NASA Astrophysics Data System (ADS)

    Armstrong, G.; Uppal, S.; Brotherton, S.; Ayres, J.

    1998-04-01

    A new physical model based on two dimensional simulations for high quality laser re-crystallised poly-Si thin film transistors is presented. It has been shown that to adequately explain the improved subthreshold slope and the lack of saturation of the output characteristics in these transistors, it is essential to distribute the density of defect states between traps in the grains alongside traps localised at grain boundaries. A double exponential density of states has been extracted for thin film transistors (TFTs) annealed at different excimer laser energies, using the field effect conductance method. By splitting the density of states between grain traps and grain boundary traps good fits to the output characteristics have been achieved. Lack of saturation is shown to be due to decrease in potential barrier at grain boundaries with increase in drain bias. At high gate voltages, however, evidence of a self-heating effect similar to that observed in silicon-on-insulator (SOI) transistors is apparent.

  7. Si(Li) detectors with thin dead layers for low energy x-ray detection

    SciTech Connect

    Rossington, C.S.; Walton, J.T.; Jaklevic, J.M.

    1990-10-01

    Regions of incomplete charge collection, or dead layers'', are compared for Si(Li) detectors fabricated with Au and Pd entrance window electrodes. The dead layers were measured by characterizing the detector spectral response to x-ray energies above and below the Si K{alpha} absorption edge. It was found that Si(Li) detectors with Pd electrodes exhibit consistently thinner effective Si dead layers than those with Au electrodes. Furthermore, it is demonstrated that the minimum thickness required for low resistivity Pd electrodes is thinner than that required for low resistivity Au electrodes, which further reduces the signal attenuation in Pd/Si(Li) detectors. A model, based on Pd compensation of oxygen vacancies in the SiO{sub 2} at the entrance window Si(Li) surface, is proposed to explain the observed differences in detector dead layer thickness. Electrode structures for optimum Si(Li) detector performance at low x-ray energies are discussed. 18 refs., 8 figs., 1 tab.

  8. Structure, magnetic properties and electrical resistivity of Co2FeSi1-xGax Heusler alloy thin films

    NASA Astrophysics Data System (ADS)

    Ramudu, M.; Raja, M. Manivel; Chelvane, J. Arout; Kamat, S. V.

    2016-11-01

    The influence of Ga on the structural, magnetic and half-metallic properties of Co2FeSi1-xGax (0≤x≤1) thin films grown on Si (100) substrates using ultra high vacuum magnetron sputtering has been systematically investigated. The linear increase in cubic lattice parameter from 5.63 Å to 5.73 Å and the Curie temperature (TC) from 854 K to 941 K with x varying from 0 to 1 indicate the progressive substitution of Ga for Si. The coercivity (Hc) was found to decrease from 26 Oe (x=0) to 3 Oe (x=1) at room temperature and is attributed to the decrease in magnetic anisotropy. The magnetic hysteresis loops measured from 300-873 K revealed that the film where Ga completely replaces Si exhibit better stability in both saturation magnetization (Ms) and Hc with temperature. The increase in coercivity at higher temperatures is attributed to the film to substrate interaction. The measured Ms at 100 K decreases from 5.01 μB/f.u. (x=0) to 4.49 μB/f.u. (x=1) and follows the trend of Slater-Pauling rule. The indirect evidence of half-metallic nature is examined from the temperature dependent electrical resistivity measurements.

  9. Etching of a-Si:H thin films by hydrogen plasma: A view from in situ spectroscopic ellipsometry

    SciTech Connect

    Hadjadj, Aomar Larbi, Fadila; Gilliot, Mickaël; Roca i Cabarrocas, Pere

    2014-08-28

    When atomic hydrogen interacts with hydrogenated amorphous silicon (a-Si:H), the induced modifications are of crucial importance during a-Si:H based devices manufacturing or processing. In the case of hydrogen plasma, the depth of the modified zone depends not only on the plasma processing parameters but also on the material. In this work, we exposed a-Si:H thin films to H{sub 2} plasma just after their deposition. In situ UV-visible spectroscopic ellipsometry measurements were performed to track the H-induced changes in the material. The competition between hydrogen insertion and silicon etching leads to first order kinetics in the time-evolution of the thickness of the H-modified zone. We analyzed the correlation between the steady state structural parameters of the H-modified layer and the main levers that control the plasma-surface interaction. In comparison with a simple doped layer, exposure of a-Si:H based junctions to the same plasma treatment leads to a thinner H-rich subsurface layer, suggesting a possible charged state of hydrogen diffusing.

  10. Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer.

    PubMed

    Heilmann, Martin; Munshi, A Mazid; Sarau, George; Göbelt, Manuela; Tessarek, Christian; Fauske, Vidar T; van Helvoort, Antonius T J; Yang, Jianfeng; Latzel, Michael; Hoffmann, Björn; Conibeer, Gavin; Weman, Helge; Christiansen, Silke

    2016-06-01

    The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts.

  11. Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer.

    PubMed

    Heilmann, Martin; Munshi, A Mazid; Sarau, George; Göbelt, Manuela; Tessarek, Christian; Fauske, Vidar T; van Helvoort, Antonius T J; Yang, Jianfeng; Latzel, Michael; Hoffmann, Björn; Conibeer, Gavin; Weman, Helge; Christiansen, Silke

    2016-06-01

    The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts. PMID:27124605

  12. Optical Gratings Coated with Thin Si3N4 Layer for Efficient Immunosensing by Optical Waveguide Lightmode Spectroscopy

    PubMed Central

    Diéguez, Lorena; Caballero, David; Calderer, Josep; Moreno, Mauricio; Martínez, Elena; Samitier, Josep

    2012-01-01

    New silicon nitride coated optical gratings were tested by means of Optical Waveguide Lightmode Spectroscopy (OWLS). A thin layer of 10 nm of transparent silicon nitride was deposited on commercial optical gratings by means of sputtering. The quality of the layer was tested by x-ray photoelectron spectroscopy and atomic force microscopy. As a proof of concept, the sensors were successfully tested with OWLS by monitoring the concentration dependence on the detection of an antibody-protein pair. The potential of the Si3N4 as functional layer in a real-time biosensor opens new ways for the integration of optical waveguides with microelectronics. PMID:25585707

  13. Morphology, structure, and magnetism of FeCo thin films electrodeposited on hydrogen-terminated Si(111) surfaces.

    PubMed

    Zarpellon, J; Jurca, H F; Mattoso, N; Klein, J J; Schreiner, W H; Ardisson, J D; Macedo, W A A; Mosca, D H

    2007-12-15

    In this work we describe the fabrication of FeCo alloy (less than 10 at% Co) thin films from aqueous ammonium sulfate solutions onto n-type Si(111) substrates using potentiostatic electrodeposition at room temperature. The incorporation of Co into the deposits tends to inhibit Fe silicide formation and to protect deposits against oxidation under air exposure. As the incorporation of Co was progressively increased, the sizes of nuclei consisting of FeCo alloy increased, leading to films with a highly oriented body-centered cubic structure with crystalline texture, where (110) planes remain preferentially oriented parallel to the film surface. PMID:17900605

  14. Epitaxial growth of Bi{sub 2}Se{sub 3} topological insulator thin films on Si (111)

    SciTech Connect

    He Liang; Xiu Faxian; Huang Guan; Kou Xufeng; Lang Murong; Wang, Kang L.; Wang Yong; Fedorov, Alexei V.; Beyermann, Ward P.; Zou Jin

    2011-05-15

    In this paper, we report the epitaxial growth of Bi{sub 2}Se{sub 3} thin films on Si (111) substrate, using molecular beam epitaxy (MBE). We show that the as-grown samples have good crystalline quality, and their surfaces exhibit terracelike quintuple layers. Angel-resolved photoemission experiments demonstrate single-Dirac-conelike surface states. These results combined with the temperature- and thickness-dependent magneto-transport measurements, suggest the presence of a shallow impurity band. Below a critical temperature of {approx}100K, the surface states of a 7 nm thick film contribute up to 50% of the total conduction.

  15. Morphology, structure, and magnetism of FeCo thin films electrodeposited on hydrogen-terminated Si(111) surfaces.

    PubMed

    Zarpellon, J; Jurca, H F; Mattoso, N; Klein, J J; Schreiner, W H; Ardisson, J D; Macedo, W A A; Mosca, D H

    2007-12-15

    In this work we describe the fabrication of FeCo alloy (less than 10 at% Co) thin films from aqueous ammonium sulfate solutions onto n-type Si(111) substrates using potentiostatic electrodeposition at room temperature. The incorporation of Co into the deposits tends to inhibit Fe silicide formation and to protect deposits against oxidation under air exposure. As the incorporation of Co was progressively increased, the sizes of nuclei consisting of FeCo alloy increased, leading to films with a highly oriented body-centered cubic structure with crystalline texture, where (110) planes remain preferentially oriented parallel to the film surface.

  16. Suppression effect of silicon (Si) on Er3+ 1.54μm excitation in ZnO thin films

    NASA Astrophysics Data System (ADS)

    Xu, Bo; Lu, Fei; Ma, Changdong; Fan, Ranran

    2016-08-01

    We have investigated the photoluminescence (PL) characteristics of ZnO:Er thin films on Si (100) single crystal and SiO2-on-silicon (SiO2) substrates, synthesized by radio frequency magnetron sputtering. Rutherford backscattering/channeling spectrometry (RBS), X-ray diffraction (XRD) and atomic force microscope (AFM) were used to analyze the properties of thin films. The diffusion depth profiles of Si were determined by second ion mass spectrometry (SIMS). Infrared spectra were obtained from the spectrometer and related instruments. Compared with the results at room temperature (RT), PL (1.54μm) intensity increased when samples were annealed at 250°C and decreased when at 550°C. A new peak at 1.15μm from silicon (Si) appeared in 550°C samples. The Si dopants in ZnO film, either through the diffusion of Si from the substrate or ambient, directly absorbed the energy of pumping light and resulted in the suppression of Er3+ 1.54μm excitation. Furthermore, the energy transmission efficiency between Si and Er3+ was very low when compared with silicon nanocrystal (Si-NC). Both made the PL (1.54μm) intensity decrease. All the data in experiments proved the negative effects of Si dopants on PL at 1.54μm. And further research is going on.

  17. Novel chemical route for atomic layer deposition of MoS2 thin film on SiO2/Si substrate

    NASA Astrophysics Data System (ADS)

    JinThese Authors Equally Contributed To This Work., Zhenyu; Shin, Seokhee; Kwon, Do Hyun; Han, Seung-Joo; Min, Yo-Sep

    2014-11-01

    Recently MoS2 with a two-dimensional layered structure has attracted great attention as an emerging material for electronics and catalysis applications. Although atomic layer deposition (ALD) is well-known as a special modification of chemical vapor deposition in order to grow a thin film in a manner of layer-by-layer, there is little literature on ALD of MoS2 due to a lack of suitable chemistry. Here we report MoS2 growth by ALD using molybdenum hexacarbonyl and dimethyldisulfide as Mo and S precursors, respectively. MoS2 can be directly grown on a SiO2/Si substrate at 100 °C via the novel chemical route. Although the as-grown films are shown to be amorphous in X-ray diffraction analysis, they clearly show characteristic Raman modes (E12g and A1g) of 2H-MoS2 with a trigonal prismatic arrangement of S-Mo-S units. After annealing at 900 °C for 5 min under Ar atmosphere, the film is crystallized for MoS2 layers to be aligned with its basal plane parallel to the substrate.Recently MoS2 with a two-dimensional layered structure has attracted great attention as an emerging material for electronics and catalysis applications. Although atomic layer deposition (ALD) is well-known as a special modification of chemical vapor deposition in order to grow a thin film in a manner of layer-by-layer, there is little literature on ALD of MoS2 due to a lack of suitable chemistry. Here we report MoS2 growth by ALD using molybdenum hexacarbonyl and dimethyldisulfide as Mo and S precursors, respectively. MoS2 can be directly grown on a SiO2/Si substrate at 100 °C via the novel chemical route. Although the as-grown films are shown to be amorphous in X-ray diffraction analysis, they clearly show characteristic Raman modes (E12g and A1g) of 2H-MoS2 with a trigonal prismatic arrangement of S-Mo-S units. After annealing at 900 °C for 5 min under Ar atmosphere, the film is crystallized for MoS2 layers to be aligned with its basal plane parallel to the substrate. Electronic supplementary

  18. Structural damage in thin SLIM-Cut c-Si foils fabricated for solar cell purposes: atomic assessment by electron spin resonance

    NASA Astrophysics Data System (ADS)

    Kepa, J.; Martini, R.; Stesmans, A.

    2015-11-01

    Within the context of reducing production costs, thin (<90 μm) silicon foils intended for photovoltaic applications have been fabricated from standard (100)Si wafers using a low-temperature (<150 °C) stress-induced lift-off process. A multi-frequency electron spin resonance (ESR) study was performed in order to evaluate, at atomic scale, the quality of the material in terms of defects, including identification and quantification. Generally, a complex ESR spectrum is observed, disentangled as the superposition of three separate signals. This includes, most prominently (˜91% of total density) the D-line (Si3 ≡ Si· dangling bonds in a disordered Si environment), a set (˜6%) of highly anisotropic signals ascribed to dislocations (K1-like), and a triplet, identified as the Si-SL5 N-donor defect. Defect density depth profiling from the lift-off side shows all signals disappear in tandem after etching off a ˜33 μm thick Si layer, indicating a highly correlated-equal in relative terms-distribution of the three types of defects over the affected top part of the Si foil. The defect density is found to be highly non-uniform laterally, with the density peaking near the crack initiation point, from which defect generation spreads. It is thus found that the SLIM-Cut method for fabrication of thin Si foils results in the introduction of defects that would unacceptably impair the functionality of photovoltaic cells built on these substrates. Fortunately, this may be cured by etching off a thin top Si layer, resulting in a most useful thin Si foil of standard high quality.

  19. Ion-beam-induced nanodots formation from Au/Si thin films on quartz surface

    NASA Astrophysics Data System (ADS)

    Datta, D. P.; Siva, V.; Singh, A.; Joshi, S. R.; Kanjilal, D.; Sahoo, P. K.

    2016-07-01

    We report the synthesis of Si nanodots on quartz surface using ion irradiation. When a bi-layer of ultrathin Au and Si on quartz surface is irradiated by 500 keV Xe-ion beam, the bi-layer spontaneously transforms into nanodots at a fluence of 5 × 1014 ions cm-2. The spatial density and diameter of the nanodots are reduced with increase in applied ion fluence. The nanostructures exhibit photoluminescence in the visible range at room temperature where the intensity and wavelength depends upon ion fluence. The observed evolution seems to be correlated to ion beam mixing induced silicide formation at Au-Si interface.

  20. Composition and resistivity changes of reactively sputtered W-Si-N thin films under vacuum annealing

    SciTech Connect

    Vomiero, A.; Boscolo Marchi, E.; Mariotto, G.; Quaranta, A.; Della Mea, G.; Ottaviani, G.; Tonini, R.; Butturi, M.; Martinelli, G.

    2006-01-16

    W-Si-N layers about 200 nm thick with different nitrogen content were reactively sputtered from a W{sub 5}Si{sub 3} target on oxidized silicon substrates. The thermal stability of the films' composition and resistivity was studied with ion beam analysis and four-point probe measurements. Upon vacuum annealing from 600 to 980 deg. C for 1.5 h, a sample with an initial 56 at. % of nitrogen gradually loses nitrogen down to 36%. This composition lies close to the W-Si{sub 3}N{sub 4} tie line. Concurrently, the room temperature resistivity decreases from 4.7 to about 2 m{omega} cm. The composition changes only a little for a sample whose initial composition is near the W-Si{sub 3}N{sub 4} tie line and the resistivity changes significantly less than for the nitrogen-rich film. Interpretations are discussed.