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Sample records for polycrystalline si thin

  1. Polycrystalline GeSn thin films on Si formed by alloy evaporation

    NASA Astrophysics Data System (ADS)

    Kim, Munho; Fan, Wenjuan; Seo, Jung-Hun; Cho, Namki; Liu, Shih-Chia; Geng, Dalong; Liu, Yonghao; Gong, Shaoqin; Wang, Xudong; Zhou, Weidong; Ma, Zhenqiang

    2015-06-01

    Polycrystalline GeSn thin films on Si substrates with a Sn composition up to 4.5% have been fabricated and characterized. The crystalline structure, surface morphology, and infrared (IR) absorption coefficient of the annealed GeSn thin films were carefully investigated. It was found that the GeSn thin films with a Sn composition of 4.5% annealed at 450 °C possessed a desirable polycrystalline structure according to X-ray diffraction (XRD) analyses and Raman spectroscopy analyses. In addition, the absorption coefficient of the polycrystalline GeSn thin films in the IR region was significantly better than that of the single crystalline bulk Ge.

  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. 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.

  4. 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.

  5. Polycrystalline thin film photovoltaics

    NASA Astrophysics Data System (ADS)

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

    Significant progress has recently been made towards improving the efficiencies of polycrystalline thin-film solar cells and modules using CuInSe2 and CdTe. The history of using CuInSe2 and CdTe for solar cells is reviewed. Initial outdoor stability tests of modules are encouraging. Progress in semiconductor deposition techniques has also been substantial. Both CuInSe2 and CdTe are positioned for commercialization during the 1990s. The major participants in developing these materials are described. The US DOE/SERI (Solar Energy Research Institute) program recognizes the rapid progress and important potential of polycrystalline thin films to meet ambitious cost and performance goals. US DOE/SERI is in the process of funding an initiative in this area with the goal of ensuring US leadership in the development of these technologies. The polycrystalline thin-film module development initiative, the modeling and stability of the devices, and health and safety issues are discussed.

  6. Polycrystalline thin-films

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Mitchell, R.

    1986-02-01

    This annual report summarizes the status, accomplishments, and projected future research directions of the Polycrystalline Thin Film Task in the Photovoltaic Program Branch of the Solar Energy Research Institute's Solar Electric Research Division. Major subcontracted work in this area has concentrated on development of CuInSe2 and CdTe technologies. During FY 1985, major progress was achieved by subcontractors in: (1) developing a new, low-cost method of fabricating CuInSe2, and (2) improving the efficiency of CuInSe2 devices by about 10% (relative). The report also lists research planned to meet the Department of Energy's goals in these technologies.

  7. 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.

  8. Polycrystalline thin films

    NASA Astrophysics Data System (ADS)

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

    1987-02-01

    This annual report for fiscal year 1986 summarizes the status, accomplishments, and projected future research directions of the Polycrystalline Thin Film Task in the Photovoltaic Program Branch of the Solar Energy Research Institute's Solar Electric Research Division. Subcontracted work in this area has concentrated on the development of CuInSe2 and CdTe technologies. During FY 1986, major progress was achieved by subcontractors in (1) achieving 10.5% (SERI-verified) efficiency with CdTe, (2) improving the efficiency of selenized CuInSe2 solar cells to nearly 8%, and (3) developing a transparent contact to CdTe cells for potential use in the top cells of tandem structures.

  9. 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.

  10. High quality SiO2/Si interfaces of poly-crystalline silicon thin film transistors by annealing in wet atmosphere

    NASA Astrophysics Data System (ADS)

    Sano, Naoki; Sekiya, Mitsunobu; Hara, Masaki; Kohno, Atsushi; Sameshima, Toshiyuki

    1995-05-01

    A new post-metallization annealing technique was developed to improve the quality of metal-oxide-semiconductor (MOS) devices using SiO2 films formed by a parallel-plate remote plasma chemical vapor deposition as gate insulators. The quality of the interface between SiO2 and crystalline Si was investigated by capacitance-voltage (C-V) measurements. An H2O vapor annealing at 270 C for 30 min efficiently decreased the interface trap density to 2.0 x 10(exp 10) cm(exp -2) eV(exp -1), and the effective oxide charge density from 1 x 10(exp 12) to 5 x 10(exp 9) cm(exp -2). This annealing process was also applied to the fabrication of Al-gate polycrystalline silicon thin film transistors (poly-Si TFT's) at 270 C. In p-channel poly-Si TFT's, the carrier mobility increased from 60-400 cm(exp 2) V(exp -1) s(exp - 1) and the threshold voltage decreased from - 5.5 to - 1.7 V.

  11. 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.

  12. 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%.

  13. 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

  14. Interaction of metal layers with polycrystalline Si

    NASA Technical Reports Server (NTRS)

    Nakamura, K.; Olowolafe, J. O.; Lau, S. S.; Nicolet, M.-A.; Mayer, J. W.; Shima, R.

    1976-01-01

    Solid-phase reactions of metal films deposited on 0.5-micron-thick polycrystalline layers of Si grown by chemical vapor deposition at 640 C were investigated by MeV He-4 backscattering spectrometry, glancing angle X-ray diffraction, and SEM observations. For the metals Al, Ag, and Au, which form simple eutectics, heat treatment at temperatures below the eutectic results in erosion of the poly-Si layer and growth of Si crystallites in the metal film. Crystallite formation is observed at temperatures exceeding 550 C for Ag, at those exceeding 400 C for Al, and at those exceeding 200 C for Au films. For Pd, Ni, and Cr, heat treatment results in silicide formation. The same initial silicides (Pd2Si, Ni2Si, and CrSi2), are formed at similar temperatures on single-crystal substrates.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    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 (CuInSe2), cadmium telluride (CdTe), and thin film polycrystalline silicon (x-Si) deposited on ceramic substrates. The first of these materials, polycrystalline thin film CuInSe2, has made some rapid advances in terms of high efficiency and long term reliability. For CuInSe2 power modules, a world record has been reported on a 0.4 sq m module with an aperture-area efficiency of 10.4 pct. and a power output of 40.4 W. Additionally, outdoor reliability testing of CuInSe2 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 sq cm. 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 pct.; 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.

  1. 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.

  2. US Polycrystalline Thin Film Solar Cells Program

    NASA Astrophysics Data System (ADS)

    Ullal, Harin S.; Zweibel, Kenneth; Mitchell, Richard L.

    1989-11-01

    The Polycrystalline Thin Film Solar Cells Program, part of the United States National Photovoltaic Program, performs R and 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 U.S. Department of Energy's long-term goals by achieving high efficiencies (15 to 20 percent), 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 CuInSe2 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 U.S. Department of Energy has increased its funding through an initiative through the Solar Energy Research Institute in CuInSe2 and CdTe with subcontracts to start in spring 1990.

  3. 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.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin (≈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.

  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 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1990-11-01

    DOE supports research activities in polycrystalline thin films through the Polycrystalline Thin Film Program. This program includes includes R and D in both copper indium diselenide and cadmium telluride thin films for photovoltaic applications. The objective is to support R and D of photovoltaic cells and modules that meet the DOE long term goals of high efficiency (15 to 20 percent), low cost ($50/sq cm), and reliability (30-year life time). Research carried out in this area is receiving increased recognition due to important advances in polycrystalline thin film CuInSe2 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. The recent progress and future directions are studied of the Polycrystalline Thin Film Program and the status of the subcontracted research on these promising photovoltaic materials.

  12. 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.

  13. 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.

  14. Efficient organic light-emitting diodes using polycrystalline silicon thin films as semitransparent anode

    NASA Astrophysics Data System (ADS)

    Zhu, X. L.; Sun, J. X.; Peng, H. J.; Meng, Z. G.; Wong, M.; Kwok, H. S.

    2005-08-01

    Polycrystalline silicon (p-Si) is a good material for the construction of thin-film transistors (TFT). It is used for fabricating active-matrix organic light-emitting diode (AMOLED) displays. In this letter, we propose and demonstrate the application of boron-doped p-Si as a semi-transparent anode in making different color OLEDs. Without removing the ultrathin native oxide on the p-Si surface and employing p-doped hole transport layer to enhance holes injection, these OLEDs show comparable or even better performance to conventional OLEDs which use ITO as anodes. The present technique has the advantage of less masking steps in making AMOLED.

  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. Nucleation and growth of polycrystalline SiC

    NASA Astrophysics Data System (ADS)

    Kaiser, M.; Schimmel, S.; Jokubavicius, V.; Linnarsson, M. K.; Ou, H.; Syväjärvi, M.; Wellmann, P.

    2014-03-01

    The nucleation and bulk growth of polycrystalline SiC in a 2 inch PVT setup using isostatic and pyrolytic graphite as substrates was studied. Textured nucleation occurs under near-thermal equilibrium conditions at the initial growth stage with hexagonal platelet shaped crystallites of 4H, 6H and 15R polytypes. It is found that pyrolytic graphite results in enhanced texturing of the nucleating gas species. Reducing the pressure leads to growth of the crystallites until a closed polycrystalline SiC layer containing voids with a rough surface is developed. Bulk growth was conducted at 35 mbar Ar pressure at 2250°C in diffusion limited mass transport regime generating a convex shaped growth form of the solid-gas interface leading to lateral expansion of virtually [001] oriented crystallites. Growth at 2350°C led to the stabilization of 6H polytypic grains. The micropipe density in the bulk strongly depends on the substrate used.

  1. Polycrystalline organic thin film transistors for advanced chemical sensing

    NASA Astrophysics Data System (ADS)

    Torsi, Luisa; Tanese, Maria C.; Cioffi, Nicola; Sabbatini, Luigia; Zambonin, Pier G.

    2003-11-01

    Organic thin-film transistors have seen a dramatic improvement of their performance in the last decade. They have been also proposed as gas sensors. This paper deals with the interesting new aspects that polycrystalline based conducting polymer transistors present when operated as chemical sensors. Such devices are capable to deliver multi-parameter responses that are also extremely repeatable and fast at room temperature. Interesting are also the perspectives for their use as chemically selective devices in array type sensing systems.

  2. Polycrystalline Superconducting Thin Films: Texture Control and Critical Current Density

    NASA Astrophysics Data System (ADS)

    Yang, Feng

    1995-01-01

    The growth processes of polycrystalline rm YBa_2CU_3O_{7-X} (YBCO) and yttria-stabilized-zirconia (YSZ) thin films have been developed. The effectiveness of YSZ buffer layers on suppression of the reaction between YBCO thin films and metallic substrates was carefully studied. Grown on the chemically inert surfaces of YSZ buffer layers, YBCO thin films possessed good quality of c-axis alignment with the c axis parallel to the substrate normal, but without any preferred in-plane orientations. This leads to the existence of a large percentage of the high-angle grain boundaries in the YBCO films. The critical current densities (rm J_{c}'s) found in these films were much lower than those in single crystal YBCO thin films, which was the consequence of the weak -link effect of the high-angle grain boundaries in these films. It became clear that the in-plane alignment is vital for achieving high rm J_{c }s in polycrystalline YBCO thin films. To induce the in-plane alignment, ion beam-assisted deposition (IBAD) technique was integrated into the conventional pulsed laser deposition process for the growth of the YSZ buffer layers. It was demonstrated that using IBAD the in-plane orientations of the YSZ grains could be controlled within a certain range of a common direction. This ion -bombardment induced in-plane texturing was explained using the anisotropic sputtering yield theory. Our observations and analyses have provided valuable information on the optimization of the IBAD process, and shed light on the texturing mechanism in YSZ. With the in-plane aligned YSZ buffer layers, YBCO thin films grown on metallic substrates showed improved rm J_{c}s. It was found that the in-plane alignment of YSZ and that of YBCO were closely related. A direct correlation was revealed between the rm J_{c} value and the degree of the in-plane alignment for the YBCO thin films. To explain this correlation, a numerical model was applied to multi-grain superconducting paths with different

  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. Thin film polycrystalline silicon solar cells

    SciTech Connect

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

    1980-01-01

    During the present quarter efficiency of heterostructure solar cells has been increased from 13 to 13.7% for single crystal and from 10.3 to 11.2% for polysilicon. For polysilicon the improvements can be attributed to reductions in grid-area coverage and in reflection losses and for single crystal to a combination of reduction in grid-area coverage and increase in fill factor. The heterostructure cells in both cases were IT0/n-Si solar cells. Degradation in Sn0/sub 2//n-Si solar cells can be greatly reduced to negligible proportions by proper encapsulation. The cells used in stability tests have an average initial efficiency of 11% which reduces to a value of about 10.5% after 6 months of exposure to sunlight and ambient conditions. This small degradation occurs within the first month, and the efficiency remains constant subsequently. The reduction in efficiency is due to a decrease in the open-circuit voltage only, while the short-circuit current and fill factor remain constant. The effects of grain-size on the Hall measurements in polysilicon have been analyzed and interpreted, with some modifications, using a model proposed by Bube. This modified model predicts that the measured effective Hall voltage is composed of components originating from the bulk and space-charge region. For materials with large grains, the carrier concentration is independent of the inter-grain boundary barrier, whereas the mobility is dependent on it. However, for small rains, both the carrier density and mobility depend on the barrier. These predictions are consistant with experimental results of mm-size Wacker polysilicon and ..mu..m-size NTD polysilicon.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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. PMID:26763192

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  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. Photovoltaic effect in transition metal modified polycrystalline BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Sreenivas Puli, Venkata; Pradhan, Dhiren Kumar; Katiyar, Rajesh Kumar; Coondoo, Indrani; Panwar, Neeraj; Misra, Pankaj; Chrisey, Douglas B.; Scott, J. F.; Katiyar, Ram S.

    2014-02-01

    We report photovoltaic (PV) effect in multiferroic Bi0.9Sm0.1Fe0.95Co0.05O3 (BSFCO) thin films. Transition metal modified polycrystalline BiFeO3 (BFO) thin films have been deposited on Pt/TiO2/SiO2/Si substrate successfully through pulsed laser deposition (PLD). PV response is observed under illumination both in sandwich and lateral electrode configurations. The open-circuit voltage (Voc) and the short-circuit current density (Jsc) of the films in sandwich electrode configuration under illumination are measured to be 0.9 V and -0.051 µA cm-2. Additionally, we report piezoresponse for BSFCO films, which confirms ferroelectric piezoelectric behaviour.

  17. 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.

  18. 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.

  19. Fracture toughness of low-pressure chemical-vapor-deposited polycrystalline silicon carbide thin films

    NASA Astrophysics Data System (ADS)

    Hatty, V.; Kahn, H.; Trevino, J.; Zorman, C. A.; Mehregany, M.; Ballarini, R.; Heuer, A. H.

    2006-01-01

    The fracture toughness of thin-film polycrystalline silicon carbide (poly-SiC) deposited on silicon (Si) wafers via low-pressure chemical-vapor deposition (LPCVD) has been measured on a scale useful for micromachined devices; the results are compared to previous studies on poly-SiC thin films deposited by atmospheric pressure chemical-vapor deposition (APCVD) [Bellante et al., Appl. Phys. Lett. 86, 071920 (2005)]. Samples in this study included those with and without silicon dioxide (SiO2) sacrificial release layers. The LPCVD processing technique induces residual tensile stresses in the films. Doubly clamped microtensile specimens were fabricated using standard micromachining processes, and microindentation was used to initiate atomically sharp precracks. The residual stresses in the films create stress intensity factors K at the crack tips; upon release, the precracks whose K exceeded a critical value, KIC, propagated to failure. The fracture toughness KIC was the same for both types of devices, 2.9+/-0.2 MPa m1/2 for the SiC on Si samples and 3.0+/-0.2 MPa m1/2 for the SiC on SiO2/Si samples, and similar to that found for APCVD poly-SiC, 2.8<=KIC<=3.4 MPa m1/2 [Bellante et al., Appl. Phys. Lett. 86, 071920 (2005)], indicating that KIC is truly a structure-insensitive material property. The fracture toughness of poly-SiC compares favorably with that for polysilicon, 0.85+/-0.05 MPa m1/2 [Kahn et al., Science 298, 1215 (2002)].

  20. Growth, electrical and thermal properties of doped mono and polycrystalline SiGe-based quantum dot superlattices

    NASA Astrophysics Data System (ADS)

    Savelli, G.; Hauser, D.; Michel, H.; Simon, J.

    2012-06-01

    SiGe materials present several advantages such as their compatibility with microelectronic techniques and non toxicity, but present a low figure-of-merit at room temperature. However it was shown theoretically that the figure of merit ZT could be highly increased by embedding nanoparticles in SiGe offering new potential applications. We report here the growth of different monocrystalline and polycrystalline SiGe-based quantum dot superlattices on Si (001) substrate. The QDSLs were grown using an industrial Reduced Pressure Chemical Vapor Deposition tool. In this work, SiGe spacer width as well as Ge dots sizes and densities have been controlled. The SiGe layers were heavily doped during the growth. Electrical and thermal properties of such structures have been measured and compared to standard SiGe thin films.

  1. Polycrystalline silicon thin-film transistors fabricated by Joule-heating-induced crystallization

    NASA Astrophysics Data System (ADS)

    Hong, Won-Eui; Ro, Jae-Sang

    2015-01-01

    Joule-heating-induced crystallization (JIC) of amorphous silicon (a-Si) films is carried out by applying an electric pulse to a conductive layer located beneath or above the films. Crystallization occurs across the whole substrate surface within few tens of microseconds. Arc instability, however, is observed during crystallization, and is attributed to dielectric breakdown in the conductor/insulator/transformed polycrystalline silicon (poly-Si) sandwich structures at high temperatures during electrical pulsing for crystallization. In this study, we devised a method for the crystallization of a-Si films while preventing arc generation; this method consisted of pre-patterning an a-Si active layer into islands and then depositing a gate oxide and gate electrode. Electric pulsing was then applied to the gate electrode formed using a Mo layer. The Mo layer was used as a Joule-heat source for the crystallization of pre-patterned active islands of a-Si films. JIC-processed poly-Si thin-film transistors (TFTs) were fabricated successfully, and the proposed method was found to be compatible with the standard processing of coplanar top-gate poly-Si TFTs.

  2. Resistive switching in polycrystalline YMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Bogusz, A.; Müller, A. D.; Blaschke, D.; Skorupa, I.; Bürger, D.; Scholz, A.; Schmidt, O. G.; Schmidt, H.

    2014-10-01

    We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown by pulsed laser deposition and sandwiched between Au top and Ti/Pt bottom electrodes. The ratio of the resistance in the OFF and ON state is larger than 103. The observed phenomena can be attributed to the formation and rupture of conductive filaments within the multiferroic YMnO3 film. The generation of conductive paths under applied electric field is discussed in terms of the presence of grain boundaries and charged domain walls inherently formed in hexagonal YMnO3. Our findings suggest that engineering of the ferroelectric domains might be a promising route for designing and fabrication of novel resistive switching devices.

  3. Analysis of loss mechanisms in polycrystalline thin film solar cells

    NASA Astrophysics Data System (ADS)

    Sites, J. R.

    1990-08-01

    Our goal for thin-film polycrystalline solar cell analysis was to increase the useful information extracted from relatively straightforward electrical measurements. The strategy was to (1) systematize measurements and reporting, (2) organize results in terms of quantitative values for individual sources of current and voltage loss, and (3) evaluate possible analytical techniques to enhance precision and avoid pitfalls, and (4) insist on a viable physical explanation of each loss mechanism. Current-voltage, quantum efficiency, and capacitance measurements on CuInSe2 and CdTe solar cells from a variety of sources have been analyzed. In many cases losses were identified that may be lessened relatively easily. However, the operating voltage loss due to excessive forward recombination current throughout the depletion region remains the primary obstacle to efficiencies competitive with single crystal cells.

  4. Improved ferroelectric property and domain structure of highly a-oriented polycrystalline CaBi2Nb2O9 thin film

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Son, Jong Yeog

    2015-12-01

    A Lead-free ferroelectric CaBi2Nb2O9 (CBNO) thin film was deposited on Si substrate by pulsed laser deposition. TiO2 buffer layer was employed and Pt electrode was used for nano-scale capacitor. The x-ray diffraction reveals that the CBNO thin film has highly a-oriented polycrystalline structure. The highly a-oriented polycrystalline CBNO thin film significantly exhibit the enhanced ferroelectric property with a remnant polarization of 10 μC/cm2 compared to other values reported previously. In particular, the highly a-oriented polycrystalline CBNO thin film show faster ferroelectric switching characteristics than the epitaxially c-oriented CBNO thin film.

  5. 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

    2016-07-01

    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.

  6. Magnetic Properties of Polycrystalline Bismuth Ferrite Thin Films Grown by Atomic Layer Deposition.

    PubMed

    Jalkanen, Pasi; Tuboltsev, Vladimir; Marchand, Benoît; Savin, Alexander; Puttaswamy, Manjunath; Vehkamäki, Marko; Mizohata, Kenichiro; Kemell, Marianna; Hatanpää, Timo; Rogozin, Valentin; Räisänen, Jyrki; Ritala, Mikko; Leskelä, Markku

    2014-12-18

    The atomic layer deposition (ALD) method was applied to grow thin polycrystalline BiFeO3 (BFO) films on Pt/SiO2/Si substrates. The 50 nm thick films were found to exhibit high resistivity, good morphological integrity, and homogeneity achieved by the applied ALD technique. Magnetic characterization revealed saturated magnetization of 25 emu/cm(3) with temperature-dependent coercivity varying from 5 to 530 Oe within the temperature range from 300 to 2 K. Magnetism observed in the films was found to change gradually from ferromagnetic spin ordering to pinned magnetic domain interactions mixed with weak spin-glass-like behavior of magnetically frustrated antiferromagnetic/ferromagnetic (AFM-FM) spin ordering depending on the temperature and magnitude of the applied magnetic field. Antiferromagnetic order of spin cycloids was broken in polycrystalline films by crystal sizes smaller than the cycloid length (∼60 nm). Uncompensated spincycloids and magnetic domain walls were found to be the cause of the high magnetization of the BFO films. PMID:26273981

  7. 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. PMID:26266847

  8. Fundamentals of polycrystalline thin film materials and devices

    NASA Astrophysics Data System (ADS)

    Baron, Bill N.; Birkmire, Robert W.; Phillips, James E.; Shafarman, William N.; Hegedus, Steven S.; McCandless, Brian E.

    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 CuInSe2 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 CuInSe2 thin films and demonstrated a CuInSe2 solar cell with 7 percent efficiency. We added Ga, to increase the band gap of CuInSe2 devices to increase the open-circuit voltage to 0.55 V. We fabricated and analyzed CuInGaSe2/CuInSe2 devices to demonstrate the potential for combining the benefits of higher V(sub oc) while retaining the current-generating capacity of CuInSe2. We fabricated an innovative superstrate device design with more than 5 percent efficiency, as well as a bifacial spectral-response technique for determining the electron diffusion length and optical absorption coefficient of CuInSe2 in an operational cell. The diffusion length was found to be greater than 1 micron. We qualitatively modeled the effect of reducing heat treatments in hydrogen and oxidizing treatments in air on the I-V behavior of CuInSe2 devices. We also investigated post-deposition heat treatments and chemical processing and used them to fabricate a 9.6 percent-efficient CdTe/CdS solar cell using physical vapor deposition.

  9. 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.

  10. Leakage Current Suppression on Metal-Induced Laterally Crystallized Polycrystalline Silicon Thin-Film Transistors by Asymmetrically Deposited Nickel

    NASA Astrophysics Data System (ADS)

    Byun, Chang Woo; Son, Se Wan; Lee, Yong Woo; Hyo Park, Jae; Vakilipour Takaloo, Ashkan; Joo, Seung Ki

    2013-10-01

    The electrical performance of low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) fabricated by metal-induced lateral crystallization (MILC) is greatly affected by metal catalyst contaminations, such as Ni and Ni silicide trapped in the channel, since they concentrate in front of laterally grown crystallites. In the present work, the effect of the MILC/MILC boundary (MMB) on MILC polycrystalline silicon (poly-Si) TFTs is investigated by the comparison of MILC poly-Si TFTs with MMB at the center of the channel, and equivalent TFTs with MMB at a position ejected from the channel. The MMB location was controlled by the Ni catalyst position. Both a low off-state leakage current and a free from short channel effect (kink effect) were observed in high electric-field conditions. Furthermore, the field-effect mobility and drain current noise were drastically improved by ejecting the MILC boundary in the source direction.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. Structural and electrical properties of polycrystalline Bi(Fe0.6Mn0.4)O3 thin films

    NASA Astrophysics Data System (ADS)

    Kim, S. W.; Kim, W. J.; Lee, M. H.; Song, T. K.; Do, D.

    2013-12-01

    A 40% Mn-substituted BiFeO3 (BFMO) thin film was deposited on a Pt(111)/Ti/SiO2/Si(100) substrate by using a pulsed laser deposition method. The coexistence of rhombohedral and orthorhombic structures in the BFMO thin film was confirmed by using X-ray diffraction and Raman spectra investigation. The leakage current density of the BFMO thin film was larger than that of a pure polycrystalline BiFeO3 (BFO) thin film. In order to understand the leakage current behaviors, was investigated the leakage current mechanisms. The leakage current mechanism of the BFO thin film was found to be space-charge-limited conduction (SCLC), followed by trap-filled conduction causal by the increasing electric field strength. On the other hand, trap-filled conduction was not observed in the BFMO thin film. A leaky ferroelectric hysteresis loop was observed in the BFMO thin film, but not in the BFO thin film.

  18. Synthesis and characterization of ordered and disordered polycrystalline La2NiMnO6 thin films by sol-gel.

    PubMed

    Zhang, Zhiqing; Jian, Hongbin; Tang, Xianwu; Yang, Jie; Zhu, Xuebin; Sun, Yuping

    2012-10-14

    Polycrystalline La(2)NiMnO(6) thin films are prepared on Pt/Ti/SiO(2)/Si substrates by the sol-gel method. Through controlling the processing parameters, the cation ordering can be tuned. The disordered and ordered thin films exhibit distinct differences for crystal structures as well as properties. The crystal structure at room temperature characterized by X-ray diffraction and Raman spectra is suggested to be monoclinic (P2(1)/n) and orthorhombic (Pbnm) for the ordered and disordered thin films, respectively. The ferromagnetic-paramagnetic transition is 263 K and 60 K for the ordered and disordered samples respectively, whereas the saturation magnetic moment at 5 K is 4.9 μ(B) fu(-1) (fu = formula unit) and 0.9 μ(B) fu(-1). The dielectric constant as well as magnetodielectric effect is higher for the ordered La(2)NiMnO(6) thin films. The magnetodielectric effect for the ordered thin film is dominantly contributed to the intrinsic coupling of electric dipole ordering and fluctuations and magnetic ordering and fluctuations, while it is mainly contributed to Maxwell-Wagner (M-W) effects for the disordered thin film. The successful achievements of ordered and disordered polycrystalline La(2)NiMnO(6) thin films will provide an effective route to fabricate double-perovskite polycrystalline thin films by the sol-gel method. PMID:22910689

  19. Nanophotonic light trapping in polycrystalline silicon thin-film solar cells using periodically nanoimprint-structured glass substrates

    NASA Astrophysics Data System (ADS)

    Becker, Christiane; Xavier, Jolly; Preidel, Veit; Wyss, Philippe; Sontheimer, Tobias; Rech, Bernd; Probst, Jürgen; Hülsen, Christoph; Löchel, Bernd; Erko, Alexei; Burger, Sven; Schmidt, Frank; Back, Franziska; Rudigier-Voigt, Eveline

    2013-09-01

    A smart light trapping scheme is essential to tap the full potential of polycrystalline silicon (poly-Si) thin-film solar cells. Periodic nanophotonic structures are of particular interest as they allow to substantially surpass the Lambertian limit from ray optics in selected spectral ranges. We use nanoimprint-lithography for the periodic patterning of sol-gel coated glass substrates, ensuring a cost-effective, large-area production of thin-film solar cell devices. Periodic crystalline silicon nanoarchitectures are prepared on these textured substrates by high-rate silicon film evaporation, solid phase crystallization and chemical etching. Poly-Si microhole arrays in square lattice geometry with an effective thickness of about 2μm and with comparatively large pitch (2 μm) exhibit a large absorption enhancement (A900nm = 52%) compared to a planar film (A900nm ~ 7%). For the optimization of light trapping in the desired spectral region, the geometry of the nanophotonic structures with varying pitch from 600 nm to 800 nm is tailored and investigated for the cases of poly-Si nanopillar arrays of hexagonal lattice geometry, exhibiting an increase in absorption in comparison to planar film attributed to nanophotonic wave optic effects. These structures inspire the design of prospective applications such as highly-efficient nanostructured poly-Si thin-film solar cells and large-area photonic crystals.

  20. Polycrystalline SrFe12O19 thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Garcia, Tupac; de Posada, E.; Jimenez, Ernesto; Sanchez Ll., J. L.; Diaz Castanon, S.; Bartolo-Perez, Pascual; Cauich, W.; Oliva, I.; Pena, J. L.; Ceh, O.

    1999-07-01

    Polycrystalline SrFe12O19 thin films were deposited on Si (100) substrates by PLD using a Nd-YAG laser ((lambda) equals 1064 nm). During the deposition process substrates were kept at room temperature. As-deposited films were annealed in air at temperatures between 600 degree(s)C and 840 degree(s)C. Samples were characterized by AES, ESCA, SEM, AFM, x-ray diffraction and VSM. It is presented the relevance of the preparation of the target surface on the film quality. Some differences in the chemical composition of as-deposited films, compared with the target and the annealed films, were observed. The x-ray diffraction spectra show a textured as- deposited films. Samples annealed at 600 degree(s)C, and below, showed a very weak magnetic response. In contrast annealing in the temperature range 700 degree(s)C - 840 degree(s)C led to the formation of a nanocrystalline particle system (average particle size 150 - 350 nm) which behave as a single domain in the thermally demagnetized state. The obtained coercivities (5750 - 6850 Oe) are among the highest values reported for films, powders and sintered samples.

  1. 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.

  2. X-ray diffraction study of polycrystalline BiFeO3 thin films under electric field

    NASA Astrophysics Data System (ADS)

    Nakashima, Seiji; Sakata, Osami; Nakamura, Yoshitaka; Kanashima, Takeshi; Funakubo, Hiroshi; Okuyama, Masanori

    2008-07-01

    Diffraction measurements using 12.4keV x-ray of synchrotron radiation have been performed in (001)pc- and (110)pc-oriented polycrystalline 350-nm-thick BiFeO3 thin films on a Pt /TiO2/SiO2/Si substrate under electric field in air at RT. Unipolar rectangular pulse voltages having a 150ns width and a 804.09ns period have been applied to BiFeO3 with a Pt top electrode. A diffraction peak of the (001)pc [(110)pc] plane shifts from 14.602° (20.520°) to 14.588 (20.505°) due to piezoelectric response when a 12V (11V ) pulse is applied. Piezoelectric constants (d33) of (001)pc-oriented and (110)pc-oriented domains estimated from these peak shifts are 27.8 and 26.4pm/V, respectively.

  3. Improvement in pH sensitivity of low-temperature polycrystalline-silicon thin-film transistor sensors using H2 sintering.

    PubMed

    Yen, Li-Chen; Tang, Ming-Tsyr; Chang, Fang-Yu; Pan, Tung-Ming; Chao, Tien-Sheng; Lee, Chiang-Hsuan

    2014-01-01

    In this article, we report an improvement in the pH sensitivity of low-temperature polycrystalline-silicon (poly-Si) thin-film transistor (TFT) sensors using an H2 sintering process. The low-temperature polycrystalline-silicon (LTPS) TFT sensor with H2 sintering exhibited a high sensitivity than that without H2 sintering. This result may be due to the resulting increase in the number of Si-OH2(+) and Si-O(-) bonds due to the incorporation of H in the gate oxide to reduce the dangling silicon bonds and hence create the surface active sites and the resulting increase in the number of chemical reactions at these surface active sites. Moreover, the LTPS TFT sensor device not only offers low cost and a simple fabrication processes, but the technique also can be extended to integrate the sensor into other systems. PMID:24573308

  4. Fabrication of a high-performance poly-Si thin-film transistor using a poly-Si film prepared by silicide-enhanced rapid thermal annealing process

    NASA Astrophysics Data System (ADS)

    Yang, Yong Ho; Ahn, Kyung Min; Kang, Seung Mo; Moon, Sun Hong; Ahn, Byung Tae

    2014-11-01

    A 50-nm thick polycrystalline Si film was fabricated by the crystallization of anamorphous Si film using silicide-enhanced rapid thermal annealing (SERTA). The amorphous Si film was deposited on a 5-nm thick polycrystalline Si seed layer containing nickel silicide precipitates in grain boundary areas. With the help of the silicide precipitates, the RTA temperature decreased from 730 to 680°C and the grain size of the crystallized polycrystalline Si film increased to 1.4 — 2.2 μm. Few defects were found within the grains and the Ni concentration in the polycrystalline film decreased to 1 × 1018 cm-3 due to the very-thin seed layer that contained nickel silicide precipitates. As a result, the field-effect hole mobility in the p-channel poly-Si thin film transistors (TFTs), fabricated employing the polycrystalline Si film, was as high as 169 cm2/V•s at a drain voltage of V D = -0.1 V; the subthreshold swing was as small as 0.24 V/decade. The minimum leakage current at V D= 5V was 1.5 × 10-10 A with very good diode characteristics. [Figure not available: see fulltext.

  5. 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

  6. 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.

  7. Optimized growth and dielectric properties of barium titanate thin films on polycrystalline Ni foils

    NASA Astrophysics Data System (ADS)

    Liang, Wei-Zheng; Ji, Yan-Da; Nan, Tian-Xiang; Huang, Jiang; Zeng, Hui-Zhong; Du, Hui; Chen, Chong-Lin; Lin, Yuan

    2012-06-01

    Barium titanate (BTO) thin films were deposited on polycrystalline Ni foils by using the polymer assisted deposition (PAD) technique. The growth conditions including ambient and annealing temperatures were carefully optimized based on thermal dynamic analysis to control the oxidation processing and interdiffusion. Crystal structures, surface morphologies, and dielectric performance were examined and compared for BTO thin films annealed under different temperatures. Correlations between the fabrication conditions, microstructures, and dielectric properties were discussed. BTO thin films fabricated under the optimized conditions show good crystalline structure and promising dielectric properties with inr ~ 400 and tan δ < 0.025 at 100 kHz. The data demonstrate that BTO films grown on polycrystalline Ni substrates by PAD are promising in device applications.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Structural and Magnetic Properties of Sputter-Deposited Polycrystalline Ni-Mn-Ga Ferromagnetic Shape-Memory Thin Films

    NASA Astrophysics Data System (ADS)

    Vinodh Kumar, S.; Seenithurai, S.; Manivel Raja, M.; Mahendran, M.

    2015-10-01

    Polycrystalline Ni-Mn-Ga ferromagnetic shape-memory thin films have been deposited on Si (100) substrates using a direct-current magnetron sputtering technique. The microstructure and the temperature dependence of magnetic properties of the films have been investigated by x-ray diffraction, scanning electron microscopy, and thermomagnetic measurements. As-deposited Ni50.2Mn30.6Ga19.2 film showed quasi-amorphous structure with paramagnetic nature at room temperature. When annealed at 873 K, the quasi-amorphous film attained crystallinity and possessed L21 cubic ordering with high magnetic transition temperature. Saturation magnetization and coercivity values for the annealed film were found to be 220 emu/cm3 and 70 Oe, respectively, indicating soft ferromagnetic character with low magnetocrystalline anisotropy. The magnetic transitions of the film deposited at 100 W were above room temperature, making this a potential candidate for use in microelectromechanical system devices.

  14. Study of Nitrogen Effect on the Boron Diffusion during Heat Treatment in Polycrystalline Silicon/Nitrogen-Doped Silicon Thin Films

    NASA Astrophysics Data System (ADS)

    Saci, Lynda; Mahamdi, Ramdane; Mansour, Farida; Boucher, Jonathan; Collet, Maéva; Bedel Pereira, Eléna; Temple-Boyer, Pierre

    2011-05-01

    The present paper studies the boron (B) diffusion in nitrogen (N) doped amorphous silicon (a-Si) layer in original bi-layer B-doped polycrystalline silicon (poly-Si)/in-situ N-doped Si layers (NIDOS) thin films deposited by low pressure chemical vapor deposition (LPCVD) technique. The B diffusion in the NIDOS layer was investigated by secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR) analysis. A new extended diffusion model is proposed to fit the SIMS profile of the bi-layer films. This model introduces new terms which take into account the effect of N concentration on the complex diffusion phenomena of B atoms in bi-layer films. SIMS results show that B diffusion does not exceed one third of NIDOS layer thickness after annealing. The reduction of the B diffusion in the NIDOS layer is due to the formation of complex B-N as shown by infrared absorption measurements. Electrical measurements using four-probe and Hall effect techniques show the good conductivity of the B-doped poly-Si layer after annealing treatment.

  15. Polycrystalline Silicon Thin-film Solar cells with Plasmonic-enhanced Light-trapping

    PubMed Central

    Varlamov, Sergey; Rao, Jing; Soderstrom, Thomas

    2012-01-01

    conditions. An optimised nanoparticle array alone results in cell Jsc enhancement of about 28%, similar to the effect of the diffuse reflector. The photocurrent can be further increased by coating the nanoparticles by a low refractive index dielectric, like MgF2, and applying the diffused reflector. The complete plasmonic cell structure comprises the polycrystalline silicon film, a silver nanoparticle array, a layer of MgF2, and a diffuse reflector. The Jsc for such cell is 21-23 mA/cm2, up to 45% higher than Jsc of the original cell without light-trapping or ~25% higher than Jsc for the cell with the diffuse reflector only. Introduction Light-trapping in silicon solar cells is commonly achieved via light scattering at textured interfaces. Scattered light travels through a cell at oblique angles for a longer distance and when such angles exceed the critical angle at the cell interfaces the light is permanently trapped in the cell by total internal reflection (Animation 1: Light-trapping). Although this scheme works well for most solar cells, there are developing technologies where ultra-thin Si layers are produced planar (e.g. layer-transfer technologies and epitaxial c-Si layers) 1 and or when such layers are not compatible with textures substrates (e.g. evaporated silicon) 2. For such originally planar Si layer alternative light trapping approaches, such as diffuse white paint reflector 3, silicon plasma texturing 4 or high refractive index nanoparticle reflector 5 have been suggested. Metal nanoparticles can effectively scatter incident light into a higher refractive index material, like silicon, due to the surface plasmon resonance effect 6. They also can be easily formed on the planar silicon cell surface thus offering a light-trapping approach alternative to texturing. For a nanoparticle located at the air-silicon interface the scattered light fraction coupled into silicon exceeds 95% and a large faction of that light is scattered at angles above critical providing

  16. Room-temperature ferromagnetic and ferroelectric behavior in polycrystalline ZnO-based thin films

    NASA Astrophysics Data System (ADS)

    Lin, Yuan-Hua; Ying, Minghao; Li, Ming; Wang, Xiaohui; Nan, Ce-Wen

    2007-05-01

    Polycrystalline ZnO-based thin films with Li and/or Co doping have been prepared by a sol-gel spin-coating method on silicon substrates. Magnetization measurements reveal that Li-doped ZnO film shows paramagnetic behavior. However, the Co-doped ZnO thin films show obvious room-temperature ferromagnetic properties, and ferromagnetic properties can be enhanced by the Li codoping, which may be ascribed to indirect exchange via Li-related defects. All ZnO-based films exhibit ferroelectric behavior, and ferroelectric properties can be tuned by the dopants.

  17. High-performance poly-Si thin film transistors with highly biaxially oriented poly-Si thin films using double line beam continuous-wave laser lateral crystallization

    NASA Astrophysics Data System (ADS)

    Yamano, Masayuki; Kuroki, Shin-Ichiro; Sato, Tadashi; Kotani, Koji

    2014-01-01

    Highly biaxially oriented poly-Si thin films were formed by double-line beam continuous-wave laser lateral crystallization (DLB-CLC). The crystallinities of the DLB-CLC poly-Si thin films were (110), (111), and (211) for the laser scan, transverse, and surface directions, respectively, and an energetically stable Σ3 grain boundary was observed to be dominant. All silicon grains were elongated in the laser scan direction and one-dimensionally very large silicon grains with lengths of more than 100 µm were fabricated. Using these biaxially oriented polycrystalline silicon (poly-Si) films, low-temperature poly-Si TFTs (LTPS-TFTs) were fabricated at low temperatures (≦550 °C) by a metal gate self-aligned process. As a result, a TFT with a high electron field effect mobility of μFE = 450 cm2 V-1 s-1 in a linear region was realized.

  18. 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

  19. Influence of carbon content on cold rolling and recrystallization texture in polycrystalline 3% Si-Fe

    NASA Astrophysics Data System (ADS)

    Takenaka, M.; Shingaki, Y.; Imamura, T.; Hayakawa, Y.

    2015-04-01

    The influence of carbon content on cold rolling and recrystallization texture in polycrystalline 3%Si-Fe under the relatively high rolling reduction condition has been investigated. The main component of recrystallization texture was {554}<225> orientation in ultra low carbon (ULC) 3%Si-Fe and {411}<148> orientation in low carbon (LC) 3%Si-Fe. The origin of {411}<148> recrystallization texture development in LC 3%Si-Fe is discussed in terms of the rotation of deformation twin from {100}<011> to {411}<148> orientation with the generation of the slip bands inside the neighboring matrix grain {111}<011>. The rotation axis of this crystal rotation was estimated <112> axis. Assuming the single slip system activation in BCC metal, crystal rotation around <112> axis indicates an activation of {110}<111> slip system. In terms of Schmid factor, {112}<111> slip system must be activated in {100}<011> matrix. This is not in agreement with the estimation of {110}<111> slip system activation. Detailed observation on the cold rolled sample revealed that common slip plane passed through the deformation twin and surrounding deformed matrix grains. It is considered that slip plane matching (SPM) with neighboring grains activates the lower Schmid factor slip system in deformation twin. These results suggest that not only Schmid factor but also SPM with neighboring grains should be considered to decide the active slip systems in polycrystalline metals.

  20. Polycrystalline ZnS(x)Se(1 - x) thin films deposited on ITO glass by MBE.

    PubMed

    Shen, Da-Ke; Sou, I K; Han, Gao-Rong; Du, Pi-Yi; Que, Duan-Lin

    2003-01-01

    MBE growth of ZnS(x)Se(1 - x) thin films on ITO coated glass substrates were carried out using ZnS and Se sources with the substrate temperature ranging from 270 degrees C to 330 degrees C . The XRD theta/2theta spectra resulted from these films indicated that the as-grown polycrystalline ZnS(x)Se(1 - x) thin films had a preferred orientation along the (111) planes. The evaluated crystal sizes as deduced from the FWHM of the XRD layer peaks showed strong growth temperature dependence, with the optimized temperature being about 290 degrees C. Both AFM and TEM measurements of these thin films also indicated a similar growth temperature dependence. High quality ZnS(x)Se(1 - x) thin film grown at the optimized temperature had the smoothest surface with lowest RMS value of 1.2 nm and TEM cross-sectional micrograph showing a well defined columnar structure. PMID:12659224

  1. 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.

  2. Structural, Optical, and Electrical Properties of Applied Amorphized and Polycrystalline Sb2S3 Thin Films

    NASA Astrophysics Data System (ADS)

    Janošević, Valentina; Mitrić, Miodrag; Savić, Jasmina; Validžić, Ivana Lj

    2016-03-01

    One of the intermediate steps in the organo-colloidal synthesis of crystalline Sb2S3 is a synthesis of spherical amorphous Sb2S3. In order to prove that the synthesized semiconductor can be considered an absorbing material for a solar device, the electronic and photovoltage properties of the amorphized and polycrystalline Sb2S3 thin films deposited by synthesized amorphous nanoparticles were studied. Optical studies revealed that the direct band gap energy was 1.65 eV and, two direct allowed transition of 1.57 and 1.91 eV for polycrystalline and amorphized thin films, respectively. The PL spectra of Sb2S3 showed an emission peak at 1.65 eV for both films. In order to obtain current-voltage ( I- V) characteristics, two cells based on the Sb2S3 thin films as both an absorbing material and an electrolyte were designed and made. The observed Sb2S3 thin films, with a thickness of around 10 μm, are of p-type. The exponential growth of the I- V curves reveals that the cells can work as a generator of electricity.

  3. () preferential orientation of polycrystalline AlN grown on SiO2/Si wafers by reactive sputter magnetron technique

    NASA Astrophysics Data System (ADS)

    Bürgi, Juan; García Molleja, Javier; Bolmaro, Raúl; Piccoli, Mattia; Bemporad, Edoardo; Craievich, Aldo; Feugeas, Jorge

    2016-04-01

    Aluminum nitride (AlN) is a ceramic compound that could be used as a processing material for semiconductor industry. However, the AlN crystalline structure plays a crucial role in its performance. In this paper, polycrystalline AlN films have been grown onto Si(1 1 1) and Si(1 0 0) (with an oxide native coverage of SiO2) wafers by RSM (reactive sputter magnetron) technique using a small (5 L) reactor. The development of polycrystalline AlN films with a good texture along () planes, i.e., semi-polar structure, was shown. Analyses were done using X-ray diffraction in the Bragg-Brentano mode and in the GIXRD (grazing incidence X-ray diffraction) one, and the texture was determined through pole figures. The structure and composition of these films were also studied by TEM and EDS techniques. Nevertheless, the mapping of the magnetic field between the magnetron and the substrate has shown a lack of symmetry at the region near the substrate. This lack of symmetry can be attributable to the small dimensions of the chamber, and the present paper suggests that this phenomenon is the responsible for the unusual () texture developed.

  4. 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.

  5. 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.

  6. FAST TRACK COMMUNICATION: Magnetic exchange hardening in polycrystalline GdN thin films

    NASA Astrophysics Data System (ADS)

    Senapati, K.; Fix, T.; Vickers, M. E.; Blamire, M. G.; Barber, Z. H.

    2010-08-01

    We report the observation of intrinsic exchange hardening in polycrystalline GdN thin films grown at room temperature by magnetron sputtering. We find, in addition to the ferromagnetic phase, that a fraction of GdN crystallizes in a structural polymorphic form which orders antiferromagnetically. The relative fraction of these two phases was controlled by varying the relative abundance of reactive species in the sputtering plasma by means of the sputtering power and N2 partial pressure. An exchange bias of ~ 30 Oe was observed at 10 K. The exchange coupling between the ferromagnetic and the antiferromagnetic phases resulted in an order of magnitude enhancement in the coercive field in these films.

  7. Specific features of hydrogenation of chromium-doped polycrystalline thin vanadium dioxide films

    NASA Astrophysics Data System (ADS)

    Andreev, V. N.; Klimov, V. A.; Kompan, M. E.; Melekh, B. A.

    2014-09-01

    It has been found that hydrogen penetration into chromium-doped polycrystalline thin vanadium dioxide films occurs with a lower rate than in the case of pure vanadium dioxide films. It has been shown that hydrogenation of films with low chromium concentrations is accompanied by a decrease in the phase transition temperature below T c = 340 K. However, at room temperature in these hydrogenated films, no traces of M1 monoclinic phase have been observed. As the chromium concentration increases, hydrogenation ceases to be accompanied by the decrease in the phase transition temperature.

  8. Improvement in pH Sensitivity of Low-Temperature Polycrystalline-Silicon Thin-Film Transistor Sensors Using H2 Sintering

    PubMed Central

    Yen, Li-Chen; Tang, Ming-Tsyr; Chang, Fang-Yu; Pan, Tung-Ming; Chao, Tien-Sheng; Lee, Chiang-Hsuan

    2014-01-01

    In this article, we report an improvement in the pH sensitivity of low-temperature polycrystalline-silicon (poly-Si) thin-film transistor (TFT) sensors using an H2 sintering process. The low-temperature polycrystalline-silicon (LTPS) TFT sensor with H2 sintering exhibited a high sensitivity than that without H2 sintering. This result may be due to the resulting increase in the number of Si–OH2+ and Si–O− bonds due to the incorporation of H in the gate oxide to reduce the dangling silicon bonds and hence create the surface active sites and the resulting increase in the number of chemical reactions at these surface active sites. Moreover, the LTPS TFT sensor device not only offers low cost and a simple fabrication processes, but the technique also can be extended to integrate the sensor into other systems. PMID:24573308

  9. 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.

  10. Effect of mechanical stress on current-voltage characteristics of thin film polycrystalline diamond Schottky diodes

    SciTech Connect

    Zhao, G.; Charlson, E.M.; Charlson, E.J.; Stacy, T.; Meese, J.M. ); Popovici, G.; Prelas, M. )

    1993-02-15

    Schottky diodes utilized for mechanical stress effect studies were fabricated using aluminum contacts to polycrystalline diamond thin films grown by a hot-filament-assisted chemical vapor deposition process. Compressive stress was found to have a large effect on the forward biased current-voltage characteristics of the diode, whereas the effect on the reverse biased characteristics was relatively small. This stress effect on the forward biased diamond Schottky diode was attributed to piezojunction and piezoresistance effects that dominated the diode current-voltage characteristics in the small and large bias regions, respectively. At a large constant forward bias current, a good linear relationship between output voltage and applied force was observed for force of less than 10 N, as predicted by the piezoresistance effect. The measured force sensitivity of the diode was as high as 0.75 V/N at 1 mA forward bias. Compared to either silicon or germanium junction diodes and tunnel diodes, polycrystalline diamond Schottky diodes not only are very stress sensitive but also have good linearity. This study shows polycrystalline diamond Schottky diodes have potential as mechanical sensors.

  11. Analysis of the Temperature Characteristics in Polycrystalline Si Solar Cells Using Modified Equivalent Circuit Model

    NASA Astrophysics Data System (ADS)

    Nishioka, Kensuke; Sakitani, Nobuhiro; Kurobe, Ken-ichi; Yamamoto, Yukie; Ishikawa, Yasuaki; Uraoka, Yukiharu; Fuyuki, Takashi

    2003-12-01

    We have evaluated the influence of grain boundaries on the temperature dependence of cell performance using a modified 2-diode equivalent circuit model. In this model, microscopic inhomogeneity of resistivity at or near grain boundaries can be taken into consideration. The calculated results by the modified 2-diode model agreed well with the measured current-voltage curves, and the validity of the fitting parameters in this model was discussed. One of the fitting parameters, r is defined as the ratio of the recombination area, in which the recombination of minority carriers is pronounced. At 20°C, r of the polycrystalline Si cell was larger than that of the single-crystalline Si cell. However, the difference in r between them became negligible at temperatures above 80°C. These dependences were explained by considering the behavior of the free carriers in the recombination centers.

  12. Structural characterization and optical properties of Sol-gel-derived polycrystalline Pb(Zr0.35Ti0.65)O3 thin films

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Zhang, Rong Jun; Wang, Zi Yi; Zheng, Yu Xiang; Wang, Song You; Zhao, Hai Bin; Chen, Liang Yao; Liu, Xiao Bin; Jiang, An Quan

    2013-07-01

    Polycrystalline Pb(Zr0.35Ti0.65)O3 thin films prepared on Pt/Ti/SiO2/Si substrate by using solgel technique were characterized by using X-ray diffraction (XRD) and atomic force microscopy (AFM). The optical properties of the films were investigated by using spectroscopic ellipsometry (SE) with a four-phase optical model, air/roughness layer/PZT layer/Pt layer in the spectral range of 300-800 nm. The optical band gap of the films calculated following the Tauc's Law was smaller than that of an amorphous PZT thin film with some microcrystals existing on the surface. The result indicates that the quantum-size effect leads to an increase in band gap when the crystalline dimensions become very small.

  13. Effect of bottom electrodes on nanoscale switching characteristics and piezoelectric response in polycrystalline BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Yan, F.; Zhu, T. J.; Lai, M. O.; Lu, L.

    2011-10-01

    We have investigated the nanoscale switching characteristics and piezoelectric response based on polycrystalline BiFeO3 (BFO) thin films with different orientations deposited on different oxide bottom electrodes. The BFO film deposited on the LaNiO3 (LNO)-coated Si substrate shows a (001) preferred orientation and higher ferroelectric properties, while the BFO film grown on the SrRuO3 (SRO) buffered Si substrate shows a random orientation. The domain structures have been determined via piezoresponse force microscopy (PFM) for both films, predicting that the BFO film with the LNO bottom electrode has a larger piezoelectricity property corresponding to the ferroelastic domain. Through local switching spectroscopy measurements, the evidence of ferroelectric switching and the origin of the enhanced piezoresponse properties have been provided. A greatly improved piezoelectric response has been demonstrated using PFM that is 66.8 pm V-1 for the BFO with a SRO bottom electrode, while we obtain a value of 348.2 pm V-1 for the BFO with a LNO bottom electrode due to the increased density of the polarization vectors along the external electrical field.

  14. Ferroelectric properties of lead-free polycrystalline CaBi2Nb2O9 thin films on glass substrates

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Jang, Joonkyung; Son, Jong Yeog

    2016-03-01

    CaBi2Nb2O9 (CBNO) thin film, a lead-free ferroelectric material, was prepared on a Pt/Ta/glass substrate via pulsed laser deposition. The Ta film was deposited on the glass substrate for a buffer layer. A (115) preferred orientation of the polycrystalline CBNO thin film was verified via X-ray diffraction measurements. The CBNO thin film on a glass substrate exhibited good ferroelectric properties with a remnant polarization of 4.8 μC/cm2 (2Pr ˜9.6 μC/cm2), although it had lower polarization than the epitaxially c-oriented CBNO thin film reported previously. A mosaic-like ferroelectric domain structure was observed via piezoresponse force microscopy. Significantly, the polycrystalline CBNO thin film showed much faster switching behavior within about 100 ns than that of the epitaxially c-oriented CBNO thin film.

  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. Deposition and characterization of polycrystalline silicon films on glass for thin film solar cells

    SciTech Connect

    Bergmann, R.B.; Krinke, J.; Strunk, H.P.; Werner, J.H.

    1997-07-01

    The authors deposit phosphorus-doped, amorphous Si by low pressure chemical vapor deposition and subsequently crystallize the films by furnace annealing at a temperature of 600 C. Optical in-situ monitoring allows one to control the crystallization process. Phosphorus doping leads to faster crystallization and a grain size enhancement with a maximum grain size of 15 {micro}m. Using transmission electron microscopy they find a log-normal grain size distribution in their films. They demonstrate that this distribution not only arises from solid phase crystallization of amorphous Si but also from other crystallization processes based on random nucleation and growth. The log-normal grain size distribution seems to be a general feature of polycrystalline semiconductors.

  18. 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.

  19. Studies of polycrystalline pentacene thin-film transistors at the microscopic level

    NASA Astrophysics Data System (ADS)

    Cheng, Horng-Long; Chou, Wei-Yang; Kuo, Chia-Wei; Mai, Yu-Shen; Tang, Fu-Ching; Lai, Szu-Hao

    2006-08-01

    The electronic transport properties of polycrystalline pentacene-based thin film transistors (TFTs) were investigated at the microscopic level using microRaman spectroscopy. All the pentacene film, which were thermally evaporated as a layer with thickness of 70 nm, featured polycrystalline structure with only "thin film" phase polymorph and grain morphology as verified by x-ray diffraction (XRD) measurements. We have investigated the molecular vibrational modes of pentacene in the active channel during operations the organic TFT devices using in-situ Raman spectroscopy. Extra vibrational modes resulting from vibrational coupling effect in pentacene film were studied. The interlayer and intralayer intermolecular vibrational coupling energy was calculated from the Davydov splitting using a simple coupled-oscillator model. The results suggest that the C-H in-plane bending vibrational coupling energy of pentacene molecules in solid film is affected by operating device. Additionally, the aromatic C-C stretching vibrational modes also were investigated. However, it is rather difficult to obtain the variations of lattice parameters of pentacene film in a very small active channel by using electron diffraction and XRD. At the same time, MicroRaman technique provides the capability to explore the intermolecular coupling and molecular structure modifications.

  20. Magnetization studies of first-order magnetostructural phase transition in polycrystalline FeRh thin films

    NASA Astrophysics Data System (ADS)

    Lu, Wei; Huang, Ping; Chen, Zhe; He, Chenchong; Wang, Yuxin; Yan, Biao

    2012-10-01

    The nucleation and growth of the transformed phase in the matrix of the original phase played an important role in the progress of magnetic transition. In spite of extensive investigations in B2 ordered FeRh alloy systems, until now few studies have been conducted for clarifying the nucleation and growth mechanism of the antiferromagnetic-ferromagnetic phase transition in FeRh alloys. In this work, B2 ordered polycrystalline FeRh thin films were fabricated on glass substrates by a sputtering technique and subsequent heat treatment. The as-deposited film shows a nonmagnetic property because of its face centred cubic structure. After annealing, the polycrystalline FeRh thin films show a clear first-order magnetostructural phase transition. The FeRh thin film shows an overall activation energy of about 228.6 kJ mol-1 for the entire first-order magnetostructural phase transition process. Results suggest that the first-order magnetostructural phase transition in ordered FeRh thin films follows the Johnson-Mehl-Avrami model with characteristic exponent n in the range 1-4, indicating that the phase transition process is a multi-step process characterized by different nucleation and growth mechanisms of the new ferromagnetic phase. The results obtained in this study will shed light on the underlying physics of the first-order magnetostructural phase transition of ordered FeRh alloys. The applicability of the concepts used in this study to the FeRh system shows universality and can be applied to other material systems where there is a first-order magnetostructural phase transition such as in manganites.

  1. 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.

  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. Femtosecond laser heat affected zones profiled in Co/Si multilayer thin films

    SciTech Connect

    Picard, Yoosuf N.; Yalisove, Steven M.

    2008-01-07

    In this letter, we describe an approach for assessing collateral thermal damage resulting from high intensity, femtosecond laser irradiation. Polycrystalline Co thin films deposited on Si (100) substrates and buried under an amorphous Si film were prepared for plan-view transmission electron microscopy (TEM) prior to laser irradiation by femtosecond laser pulses. A heat affected zone (HAZ) resulting from single pulse irradiation at a fluence of 0.9 J/cm{sup 2} was determined by TEM imaging and point-wise selected area diffraction. The spatially Gaussian laser pulse generated a HAZ extending up to 3 {mu}m radially from the femtosecond laser irradiated region.

  5. 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.

  6. 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.

  7. Abnormal Threshold Voltage Shifts in P-Channel Low-Temperature Polycrystalline Silicon Thin Film Transistors Under Negative Bias Temperature Stress.

    PubMed

    Kim, Sang Sub; Choi, Pyung Ho; Baek, Do Hyun; Lee, Jae Hyeong; Choi, Byoung Deog

    2015-10-01

    In this research, we have investigated the instability of P-channel low-temperature polycrystalline silicon (poly-Si) thin-film transistors (LTPS TFTs) with double-layer SiO2/SiNx dielectrics. A negative gate bias temperature instability (NBTI) stress was applied and a turn-around behavior phenomenon was observed in the Threshold Voltage Shift (Vth). A positive threshold voltage shift occurs in the first stage, resulting from the negative charge trapping at the SiNx/SiO2 dielectric interface being dominant over the positive charge trapping at dielectric/Poly-Si interface. Following a stress time of 7000 s, the Vth switches to the negative voltage direction, which is "turn-around" behavior. In the second stage, the Vth moves from -1.63 V to -2 V, overwhelming the NBTI effect that results in the trapping of positive charges at the dielectric/Poly-Si interface states and generating grain-boundary trap states and oxide traps. PMID:26726370

  8. Effect of top electrodes on photovoltaic properties of polycrystalline BiFeO3 based thin film capacitors

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Li, Mi; Liu, Yiwei; Zuo, Zhenghu; Zhuge, Fei; Zhan, Qing-Feng; Li, Run-Wei

    2011-05-01

    We investigated capacitors based on polycrystalline narrow-band-gap BiFeO3 (BFO) thin films with different top electrodes. The photovoltaic response for the capacitor with a Sn-doped In2O3 (ITO) top electrode is about 25 times higher than that with a Au top electrode, which indicates that the electrode plays a key role in determining the photovoltaic response of ferroelectric thin film capacitors, as simulated by Qin et al (2009 Appl. Phys. Lett. 95 22912). The light-to-electricity photovoltaic efficiency for the ITO/polycrystalline BFO/Pt capacitor can reach 0.125%. Furthermore, under incident light of 450 µW cm - 2 and zero bias, the corresponding photocurrent varies from 0.2 to 200 pA, that is, almost a 1000-fold photoconductivity enhancement. Our experiments suggest that polycrystalline BFO films are promising materials for application in photo-sensitive and energy-related devices.

  9. 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.

  10. Energy loss of protons and deuterons at low energies in Pd polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Celedón, C.; Sánchez, E. A.; Moreno, M. S.; Arista, N. R.; Uribe, J. D.; Mery, M.; Valdés, J. E.; Vargas, P.

    2013-07-01

    We have investigated experimentally and by computer simulations the energy-loss distributions of low-energy (E<10 keV) protons and deuterons transmitted through polycrystalline palladium thin films. In contrast to previous experiments on various transition metals we find that the stopping power of Pd is proportional to the ion velocity. Data of protons and deuterons are coincident within the experimental uncertainties, showing the absence of an isotopic effect on the stopping power of Pd in this energy range. The experimental results were analyzed and compared with Monte Carlo computer simulations and previous theoretical models. The difference in the velocity dependence of the energy loss of hydrogen ions in Pd with respect to other transition metals (Cu, Ag, and Au) is explained by a theoretical analysis based on the properties of the d-electron bands of those elements.

  11. 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.

  12. 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.

  13. Very thin poly-SiC films for micro/nano devices.

    PubMed

    Fu, Xiao-An; Noh, Sangsoo; Chen, Li; Mehregany, Mehran

    2008-06-01

    We report characterization of nitrogen-doped, very thin, low-stress polycrystalline silicon carbide (poly-SiC) films suitable for fabricating micro/nano devices. The poly-SiC films are deposited on 100 mm-diameter (100) silicon wafers in a large-scale, hot-wall, horizontal LPCVD furnace using SiH2Cl2 and C2H2 as precursors and NH, as doping gas. The deposition temperature and pressure are fixed at 900 degrees C and 4 Torr, respectively. The deposition rate increases substantially in the first 50 minutes, transitioning to a limiting value thereafter. The deposited films exhibit (111)-orientated polycrystalline 3C-SiC texture. HR-TEM indicates a 1 nm to 4 nm amorphous SiC layer at the SiC/silicon interface. The residual stress and the resistivity of the films are found to be thickness dependent in the range of 100 nm to 1 microm. Films with thickness less than 100 nm suffer from voids or pinholes. Films thicker than 100 nm are shown to be suitable for fabricating micro/nano devices. PMID:18681047

  14. Grain-size effects on electrical properties of n-type polycrystalline chemical vapor deposition Si films

    SciTech Connect

    Yang, J.J.; Simpson, W.I.; Manasevit, H.M.; Ruth, R.P.

    1984-04-15

    The electrical properties of phosphorus-doped n-type polycrystalline Si films deposited by chemical vapor deposition were investigated as a function of both impurity concentration and average grain sizes in the films. Sets of simultaneously grown films with average grains ranging from <1 to >100 ..mu..m have been deposited on polished selected polycrystalline high-purity alumina substrates. The impurity concentrations were in the range 10/sup 15/--10/sup 18/ cm/sup -3/. The transport properties of the n-type polycrystalline films have been determined by Hall-effect measurements as a function of sample temperature in the range 77--420 /sup 0/K using the van der Pauw technique. The experimental results are interpreted in terms of a grain-boundary model.

  15. Chemical speciation at buried interfaces in high-temperature processed polycrystalline silicon thin-film solar cells on ZnO:Al

    NASA Astrophysics Data System (ADS)

    Becker, Christiane; Pagels, Marcel; Zachäus, Carolin; Pollakowski, Beatrix; Beckhoff, Burkhard; Kanngießer, Birgit; Rech, Bernd

    2013-01-01

    The combination of polycrystalline silicon (poly-Si) thin films with aluminum doped zinc oxide layers (ZnO:Al) as transparent conductive oxide enables the design of appealing optoelectronic devices at low costs, namely in the field of photovoltaics. The fabrication of both thin-film materials requires high-temperature treatments, which are highly desired for obtaining a high electrical material quality. Annealing procedures are typically applied during crystallization and defect-healing processes for silicon and can boost the carrier mobility and conductivity of ZnO:Al layers. In a combined poly-Si/ZnO:Al layer system, an in-depth knowledge of the interaction of both layers and the control of interface reactions upon thermal treatments is crucial. Therefore, we analyze the influence of rapid thermal treatments up to 1050 °C on solid phase crystallized poly-Si thin-film solar cells on ZnO:Al-coated glass, focusing on chemical interface reactions and modifications of the poly-Si absorber material quality. The presence of a ZnO:Al layer in the solar cell stack was found to limit the poly-Si solar cell performance with open circuit voltages only below 390 mV (compared to 435 mV without ZnO film), even if a silicon nitride (SiN) diffusion barrier was included. A considerable amount of diffused zinc inside the silicon was observed. By grazing-incidence X-ray fluorescence spectrometry, a depth-resolving analysis of the elemental composition close to the poly-Si/(SiN)/ZnO:Al interface was carried out. Temperatures above 1000 °C were found to promote the formation of new chemical compounds within about 10 nm of interface, such as zinc silicates (Zn2SiO4) and aluminium oxide (AlxOy). These results give valuable insights about the temperature-limitations of Si/ZnO thin-film solar cell fabrication and the formation of high-mobility ZnO-layers by thermal anneal.

  16. 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

  17. Strain evolution of each type of grains in poly-crystalline (Ba,Sr)TiO3 thin films grown by sputtering

    NASA Astrophysics Data System (ADS)

    Park, Woo Young; Park, Min Hyuk; Lee, Jong Ho; Yoon, Jung Ho; Han, Jeong Hwan; Choi, Jung-Hae; Hwang, Cheol Seong

    2012-12-01

    The strain states of [111]-, [110]-, and [002]-oriented grains in poly-crystalline sputtered (Ba,Sr)TiO3 thin films on highly [111]-oriented Pt electrode/Si substrates were carefully examined by X-ray diffraction techniques. Remarkably, [002]-oriented grains respond more while [110]- and [111]-oriented grains do less than the theoretically estimated responses, which is understandable from the arrangement of the TiO6 octahedra with respect to the stress direction. Furthermore, such mechanical responses are completely independent of the degree of crystallization and film thickness. The transition growth temperature between the positive and negative strains was also different depending on the grain orientation. The unstrained lattice parameter for each type of grain was different suggesting that the oxygen vacancy concentration for each type of grain is different, too. The results reveal that polycrystalline (Ba,Sr)TiO3 thin films are not an aggregation of differently oriented grains which simply follow the mechanical behavior of single crystal with different orientations.

  18. 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. PMID:26285640

  19. Carrier and heat transport properties of polycrystalline GeSn films on SiO2

    NASA Astrophysics Data System (ADS)

    Uchida, Noriyuki; Maeda, Tatsuro; Lieten, Ruben R.; Okajima, Shingo; Ohishi, Yuji; Takase, Ryohei; Ishimaru, Manabu; Locquet, Jean-Pierre

    2015-12-01

    We evaluated the potential of polycrystalline (poly-) GeSn as channel material for the fabrication of thin film transistors (TFTs) at a low thermal budget (<600 °C). Poly-GeSn films with a grain size of ˜50 nm showed a carrier mobility of ˜30 cm2 V-1 s-1 after low-temperature annealing at 475-500 °C. Not only carrier mobility but also thermal conductivity of the films is important in assessing the self-heating effect of the poly-GeSn channel TFT. The thermal conductivity of the poly-GeSn films is 5-9 W m-1 K-1, which is significantly lower compared with 30-60 W m-1 K-1 of bulk Ge; this difference results from phonon scattering at grain boundaries and Sn interstitials. The poly-GeSn films have higher carrier mobility and thermal conductivity than poly-Ge films annealed at 600 °C, because of the improved crystal quality and coarsened grain size resulting from Sn-induced crystallization. Therefore, the poly-GeSn film is well-suited as channel material for TFTs, fabricated with a low thermal budget.

  20. 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.

  1. Synthesis and characterization of polycrystalline semiconductor Caesium-Tin tri-Iodide thin-films

    NASA Astrophysics Data System (ADS)

    Chen, Zhuo

    This thesis deals with a virtually unexplored semiconductor material CsSnI3 from material synthesis, structural, optical, and electrical characterization to the fabrication and validation of CsSnI3 thin-film solar cells. We started with synthesizing CsSnI3 thin films based on CsI and SnCl2 (or SnI2) by using an apparatus which consists of e-beam and thermal evaporators. The quality of polycrystalline CsSnI3 thin-films were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Experimental data on XRD and electron diffraction patterns taking from the synthesized thin-films match very well to the theoretically calculated ones based the first principles calculations, confirming that the synthesized CsSnI3 thin-films have an orthorhombic crystal structure. With the well-defined crystal structure, we theoretically studied the electronic band structure of CsSnI3. Extensive optical characterizations of CsSnI3 thin-films were then carried out revealing many extraordinary properties such as 1) direct band gap energy of 1.32 eV at 300 K with its abnormal temperature dependence, 2) extremely high photoluminescence quantum yield, 3) large exciton binding energy, and 4) strong two-phonon assisted excitonic absorption near band edge. These properties are interpreted in terms of the unique electronic and structural properties of CsSnI3. The value of 1.3 eV for the energy band gap of CsSnI3 suggests a unique application of CsSnI3 thin-films on solar cells. This is because this value is right in the small range of the optimal band gaps for the Shockley-Queisser maximum efficiency limit of a single-junction solar cell. A prototype Schottky solar cell was designed, fabricated, and validated. The measured power conversion efficiency (PCE) is 0.9 % which is presently limited by the series and shunt resistance. The improvement strategy on PCE is given at the end of my thesis. In order to make the CsSnI3 thin-film solar cells

  2. 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

  3. 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.

  4. 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.

  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. 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.

  7. 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.

  8. High-performance flexible thin-film transistors fabricated using print-transferrable polycrystalline silicon membranes on a plastic substrate

    NASA Astrophysics Data System (ADS)

    Qin, Guoxuan; Yuan, Hao-Chih; Yang, Hongjun; Zhou, Weidong; Ma, Zhenqiang

    2011-02-01

    Inexpensive polycrystalline Si (poly-Si) with large grain size is highly desirable for flexible electronics applications. However, it is very challenging to directly deposit high-quality poly-Si on plastic substrates due to processing constrictions, such as temperature tolerance and residual stress. In this paper, we present our study on poly-Si membranes that are stress free and most importantly, are transferrable to any substrate including a low-temperature polyethylene terephthalate (PET) substrate. We formed poly-Si-on-insulator by first depositing small-grain size poly-Si on an oxidized Si wafer. We then performed high-temperature annealing for recrystallization to obtain larger grain size. After selective doping on the poly-Si-on-insulator, buried oxide was etched away. By properly patterning the poly-Si layer, residual stress in the released poly-Si membranes was completely relaxed. The flat membrane topology allows the membranes to be print transferred to any substrates. High-performance TFTs were demonstrated on the transferred poly-Si membranes on a PET substrate.

  9. 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

  10. 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.

  11. 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.

  12. Height-resolved quantification of microstructure and texture in polycrystalline thin films using TEM orientation mapping.

    PubMed

    Aebersold, A Brian; Alexander, Duncan T L; Hébert, Cécile

    2015-12-01

    A method is presented for the quantitative investigation of microstructure and texture evolution in polycrystalline thin films based on in-plane automated crystal orientation mapping in transmission electron microscopy, from the substrate up. To demonstrate the method we apply it to the example of low pressure metal-organic chemical vapor deposited ZnO layers. First, orientation mapping is applied to standard cross-section and plan-view transmission electron microscopy samples of films, illustrating how plan-view samples both reduce the occurrence of grain overlap that is detrimental to reliable orientation mapping and also improve sampling statistics compared to cross-sections. Motivated by this, orientation mapping has been combined with a double-wedge method for specimen preparation developed by Spiecker et al. (2007) [1], which creates a large area plan-view sample that traverses the film thickness. By measuring >10,000 grains in the film, the resulting data give access to grain size, orientation and misorientation distributions in function of height above the substrate within the film, which are, in turn, the inputs necessary for quantitative assessment of growth models and simulations. The orientation data are directly related to microstructural images, allowing correlation of orientations with in-plane and out-of-plane grain sizes and shapes. The spatial correlation of the entire data set gives insights into previously unnoticed growth mechanisms such as the presence of renucleation or preferred misorientations. Finally, the data set can be used to guide targeted, local studies by other transmission electron microscopy techniques. This is demonstrated by the site-specific application of nano-beam diffraction to validate the presence of coherent [21̄1̄0]/(011̄3) twin boundaries first suggested by the orientation mapping. PMID:26363209

  13. Thin-film formation of Si clathrates on Si wafers

    NASA Astrophysics Data System (ADS)

    Ohashi, Fumitaka; Iwai, Yoshiki; Noguchi, Akihiro; Sugiyama, Tomoya; Hattori, Masashi; Ogura, Takuya; Himeno, Roto; Kume, Tetsuji; Ban, Takayuki; Nonomura, Shuichi

    2014-04-01

    In this study, we prepared Si clathrate films (Na8Si46 and NaxSi136) using a single-crystalline Si substrate. Highly oriented film growth of Zintl-phase sodium silicide, which is a precursor of Si clathrate, was achieved by exposing Na vapour to Si substrates under an Ar atmosphere. Subsequent heat treatment of the NaSi film at 400 °C (3 h) under vacuum (<10-2 Pa) resulted in a film of Si clathrates having a thickness of several micrometres. Furthermore, this technique enabled the selective growth of Na8Si46 and NaxSi136 using the appropriate crystalline orientation of Si substrates.

  14. Organic solar cells based on liquid crystalline and polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Yoo, Seunghyup

    This dissertation describes the study of organic thin-film solar cells in pursuit of affordable, renewable, and environmentally-friendly energy sources. Particular emphasis is given to the molecular ordering found in liquid crystalline or polycrystalline films as a way to leverage the efficiencies of these types of cells. Maximum efficiencies estimated based on excitonic character of organic solar cells show power conversion efficiencies larger than 10% are possible in principle. However, their performance is often limited due to small exciton diffusion lengths and poor transport properties which may be attributed to the amorphous nature of most organic semiconductors. Discotic liquid crystal (DLC) copper phthalocyanine was investigated as an easily processible building block for solar cells in which ordered molecular arrangements are enabled by a self-organization in its mesophases. An increase in photocurrent and a reduction in series resistance have been observed in a cell which underwent an annealing process. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements suggest that structural and morphological changes induced after the annealing process are related to these improvements. In an alternative approach, p-type pentacene thin films prepared by physical vapor deposition were incorporated into heterojunction solar cells with C60 as n-type layers. Power conversion efficiencies of 2.7% under broadband illumination (350--900 nm) with a peak external quantum efficiency of 58% have been achieved with the broad spectral coverage across the visible spectrum. Analysis using an exciton diffusion model shows this efficient carrier generation is mainly due to the large exciton diffusion length of pentacene films. Joint XRD and AFM studies reveal that the highly crystalline nature of pentacene films can account for the observed large exciton diffusion length. In addition, the electrical characteristics are studied as a function of light intensity using

  15. 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.

  16. 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.

  17. 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.

  18. Mechanisms of dark conductivity and photosensitivity in PbSe polycrystalline films on glass and Si substrates

    SciTech Connect

    Tetyorkin, V.V.; Orletskii, V.B.; Sizov, F.F.; Tashtanbajev, N.O.; Stepanushkin, A.G. )

    1994-05-01

    Temperature dependencies of dark electrical characteristics (Hall effect and conductivity) are investigated in PbSe polycrystalline films with different crystallite sizes deposited on glass and Si substrates. In these films the spectral dependencies of photoelectrical characteristics and the lifetime of photoexcited carriers on the crystallite sizes are studied. It is shown that the experimental data may be explained by the existence of the potential barriers for the majority carriers (holes ) at the grain boundaries. The height of the barriers is found to depend on the crystallite sizes. PbSe photosensitive structures with detectivity D[sup [star

  19. High-performance p-channel polycrystalline-germanium thin-film transistors via excimer laser crystallization and counter doping

    NASA Astrophysics Data System (ADS)

    Liao, Chan-Yu; Huang, Ching-Yu; Huang, Ming-Hui; Chou, Chia-Hsin; Cheng, Huang-Chung

    2016-04-01

    High-quality polycrystalline-germanium (poly-Ge) thin films have been successfully fabricated by excimer laser crystallization (ELC). Grains as large as 1 µm were achieved by ELC at 300 mJ/cm2. Meanwhile, the defect-generated hole concentrations in Ge thin films were significantly reduced. Furthermore, the majority carriers could then be converted to n-type by counter doping (CD) with a suitable dose. Then, high-performance p-channel Ge thin-film transistors (TFTs) with a high on/off current ratio of up to 1.7 × 103 and a high field-effect mobility of up to 208 cm2 V-1 s-1 were demonstrated for a channel width and length both of 0.5 µm. It was revealed that ELC combined with CD is effective for attaining high-performance p-channel poly-Ge TFTs.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Growth of (111) oriented NiFe{sub 2}O{sub 4} polycrystalline thin films on Pt (111) via sol-gel processing

    SciTech Connect

    Seifikar, Safoura; Sachet, Edward; Rawdanowicz, Thomas; Schwartz, Justin; Tabei, Ali; Bassiri-Gharb, Nazanin

    2012-09-15

    Polycrystalline NiFe{sub 2}O{sub 4} (NFO) thin films are grown on (111) platinized Si substrates via chemical solution processing. {theta}-2{theta} x-ray diffraction, x-ray pole figures and electron diffraction indicate that the NFO has a high degree of <111> uniaxial texture normal to the film plane. The texturing is initiated by nucleation of (111) planes at the Pt interface and is enhanced with decreasing film thickness. As the NFO magnetic easy-axis is <111>, the out-of-plane magnetization exhibits improved M{sub r}/M{sub s} and coercivity with respect to randomly oriented films on silicon substrates. The out-of-plane M{sub r}/M{sub s} ratio for (111) textured NFO thin film is improved from 30% in 150 nm-thick films to above 70% in 50 nm-thick films. The improved out-of-plane magnetic anisotropy is comparable to epitaxial NFO films of comparable thickness deposited by pulsed laser deposition and sputtering.

  5. Reliability in Short-Channel p-Type Polycrystalline Silicon Thin-Film Transistor under High Gate and Drain Bias Stress

    NASA Astrophysics Data System (ADS)

    Choi, Sung-Hwan; Kim, Sun-Jae; Mo, Yeon-Gon; Kim, Hye-Dong; Han, Min-Koo

    2010-03-01

    We have investigated the electrical characteristics of short-channel p-type excimer laser annealed (ELA) polycrystalline silicon (poly-Si) thin-film transistors (TFTs) under high gate and drain bias stress. We found that the threshold voltage of short-channel TFTs was significantly shifted in the negative direction owing to high gate and drain bias stress (ΔVTH = -2.08 V), whereas that of long-channel TFTs was rarely shifted in the negative direction (ΔVTH = -0.10 V). This negative shift of threshold voltage in the short-channel TFT may be attributed to interface state generation near the source junction and deep trap state creation near the drain junction between the poly-Si film and the gate insulator layer. It was also found that the gate-to-drain capacitance (CGD) characteristic of the stressed TFT severely stretched for the gate voltage below the flat band voltage VFB. The effects of high gate and drain bias stress are related to hot-hole-induced donor like interface state generation. The transfer characteristics of the forward and reverse modes after the high gate and drain bias stress also indicate that the interface state generation at the gate insulator/channel interface occurred near the source junction region.

  6. Reliability in Short-Channel p-Type Polycrystalline Silicon Thin-Film Transistor under High Gate and Drain Bias Stress

    NASA Astrophysics Data System (ADS)

    Sung-Hwan Choi,; Sun-Jae Kim,; Yeon-Gon Mo,; Hye-Dong Kim,; Min-Koo Han,

    2010-03-01

    We have investigated the electrical characteristics of short-channel p-type excimer laser annealed (ELA) polycrystalline silicon (poly-Si) thin-film transistors (TFTs) under high gate and drain bias stress. We found that the threshold voltage of short-channel TFTs was significantly shifted in the negative direction owing to high gate and drain bias stress (Δ VTH = -2.08 V), whereas that of long-channel TFTs was rarely shifted in the negative direction (Δ VTH = -0.10 V). This negative shift of threshold voltage in the short-channel TFT may be attributed to interface state generation near the source junction and deep trap state creation near the drain junction between the poly-Si film and the gate insulator layer. It was also found that the gate-to-drain capacitance (CGD) characteristic of the stressed TFT severely stretched for the gate voltage below the flat band voltage VFB. The effects of high gate and drain bias stress are related to hot-hole-induced donor like interface state generation. The transfer characteristics of the forward and reverse modes after the high gate and drain bias stress also indicate that the interface state generation at the gate insulator/channel interface occurred near the source junction region.

  7. 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.

  8. Infrared absorption of thin films MoSi2/SiNx micro-bridge

    NASA Astrophysics Data System (ADS)

    Jiang, Bo; Su, Yan; He, Yong; Wang, Kaiying

    2016-02-01

    In this paper, we report the infrared absorption and opto-electrical characteristics of multilayered thin films of MoSi2/SiNx with a micro-bridge structure. The thin films of MoSi2 deposited by radio frequency magnetron sputtering exhibit a relatively smooth surface (RMS roughness <1 nm, ˜0.98 Å/s), on which their square resistance is linearly increased from 340 to 550 Ω/sq. as the thickness decreases from 32 to 16 nm. Fourier transform infrared spectroscopy analysis indicates that the thin film MoSi2 with a thickness of ˜24 nm (450 Ω/sq.) presents the maximum infrared absorption on nearly dielectric thin film SiNx. Optical simulation verifies that the resistivity of the nearly dielectric thin film SiNx has an important influence on the infrared absorption of the thin film MoSi2. This work provides the physical understanding regarding the building of micro-bridges with the high infrared absorption.

  9. Thin-film polycrystalline n-ZnO/p-CuO heterojunction

    SciTech Connect

    Lisitski, O. L.; Kumekov, M. E.; Kumekov, S. E. Terukov, E. I.

    2009-06-15

    Results of X-ray diffraction and spectral-optical studies of n-ZnO and p-CuO films deposited by gas-discharge sputtering with subsequent annealing are presented. It is shown that, despite the difference in the crystal systems, the polycrystallinity of n-ZnO and p-CuO films enables fabrication of a heterojunction from this pair of materials.

  10. Infrared detection of hydrogen-generated free carriers in polycrystalline ZnO thin films

    SciTech Connect

    Wolden, Colin A.; Barnes, Teresa M.; Baxter, Jason B.; Aydil, Eray S.

    2005-02-15

    The changes in the free-carrier concentration in polycrystalline ZnO films during exposure to H{sub 2} and O{sub 2} plasmas were studied using in situ attenuated total reflection Fourier transform infrared spectroscopy. The carrier concentration and mobility were extracted from the free-carrier absorption in the infrared using a model for the dielectric function. The electron density in polycrystalline zinc oxide films may be significantly increased by >10{sup 19} cm{sup -3} by brief exposures to hydrogen plasma at room temperature and decreased by exposure to O{sub 2} plasmas. Room-temperature oxygen plasma removes a fraction of the H at donor sites but both elevated temperatures ({approx}225 deg. C) and O{sub 2} plasma were required to remove the rest. We demonstrate that combinations of O{sub 2} and H{sub 2} plasma treatments can be used to manipulate the carrier density in ZnO films. However, we also show the existence of significant drifts ({approx}15%) in the carrier concentrations over very long time scales (hours). Possible sites for H incorporation in polycrystalline films and reasons for the observed carrier-concentration changes are proposed.

  11. Ferroelectric properties of Bi2VO5.5 thin films on LaAlO3 and SiO2/Si substrates with LaNiO3 base electrode

    NASA Astrophysics Data System (ADS)

    Satyalakshmi, K. M.; Varma, K. B. R.; Hegde, M. S.

    1995-07-01

    Ferroelectric bismuth vanadate Bi2VO5.5 (BVO) thin films have been grown on LaAlO3 (LAO) and SiO2/Si substrates with LaNiO3 (LNO) base electrodes by the pulsed laser deposition technique. The effect of substrate temperature on the ferroelectric properties of BVO thin films, has been studied by depositing the thin films at different temperatures. The BVO thin films grown on LNO/LAO were textured whereas the thin films grown on LNO/SiO2/Si were polycrystalline. The BVO thin films grown at 450 °C exhibited good ferroelectric properties indicating that LNO acts as a good electrode material. The remanent polarization Pr and coercive field Ec obtained for the BVO thin films grown at 450 °C on LNO/LAO and LNO/SiO2/Si were 2.5 μC/cm2, 37 kV/cm and 4.6μC/cm2, 93 kV/cm, respectively.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Polycrystalline InN thin films prepared by ion-beam-assisted filtered cathodic vacuum arc technique

    NASA Astrophysics Data System (ADS)

    Ji, X. H.; Lau, S. P.

    2005-09-01

    We report on the fabrication of indium nitride (InN) thin films on silicon (1 0 0) substrates by radio frequency ion-beam-assisted filtered cathodic vacuum arc technique at low temperature. The effects of nitrogen ion energy on the structural properties of InN films have been investigated by X-ray diffraction and Raman spectroscopy. The InN films exhibit polycrystalline wurtzite structure. At nitrogen ion energy of 100 eV, the film shows preferred (0 0 0 2) orientation. The preferred orientation is changed to ( 1 0 1¯ 1) when the nitrogen ion energy is more than 100 eV. Three Raman-active optical phonons have been clearly identified and assigned to A 1(LO) at ˜588 cm -1, E22 at ˜490 cm -1 and A 1(TO) at ˜449 cm -1 of InN films, which confirmed the hexagonal structure of InN.

  17. Fatigue failure in thin-film polycrystalline silicon is due to subcritical cracking within the oxide layer

    NASA Astrophysics Data System (ADS)

    Alsem, D. H.; Stach, E. A.; Muhlstein, C. L.; Ritchie, R. O.

    2005-01-01

    It has been established that microelectromechanical systems created from polycrystalline silicon thin films are subject to cyclic fatigue. Prior work by the authors has suggested that although bulk silicon is not susceptible to fatigue failure in ambient air, fatigue in micron-scale silicon is a result of a "reaction-layer" process, whereby high stresses induce a thickening of the post-release oxide at stress concentrations such as notches, which subsequently undergoing moisture-assisted cracking. However, there exists some controversy regarding the post-release oxide thickness of the samples used in the prior study. In this letter, we present data from devices from a more recent fabrication run that confirm our prior observations. Additionally, new data from tests in high vacuum show that these devices do not fatigue when oxidation and moisture are suppressed. Each of these observations lends credence to the "reaction-layer" mechanism.

  18. 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.

  19. Stress distribution in Si under patterned thin film structures

    SciTech Connect

    Wong, S.P.; Huang, L.; Guo, W.S.; Cheung, W.Y.; Zhao, S.

    1997-05-01

    The authors have employed the infrared photoelasticity (PE) method to study the stress distribution in Si substrates under patterned thin film structures such as thermal oxide layers partially covered by metal films and oxide layers with long trench openings. It is demonstrated that a lot of information on the two dimensional stress distribution in the substrate under patterned thin film structures can be obtained from PE experiments. The capability, limitation, and further development of the PE method for semiconductor applications are discussed.

  20. 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.

  1. Stress-Induced Off-Current under On- and Off-State Stress Voltages in Low-Temperature n-Channel Polycrystalline Silicon Thin-Film Transistors

    NASA Astrophysics Data System (ADS)

    Seishiro Hirata,; Toshifumi Satoh,; Hiroyuki Tango,

    2010-03-01

    The changes in off-current under on- and off-state stress voltages in n-channel polycrystalline silicon (poly-Si) thin-film transistors (TFTs) are investigated through measurements and simulations. It is found that the off-current increases markedly in the shallow-negative-gate-voltage region and decreases in the deep-gate-voltage region after applying both on- and off-state stresses, resulting in a weaker dependence on negative gate voltage. It can be supposed from the simulations and experiments that the donor-type trap states (positive charges) with a hump-type state profile, located at 0.1-0.2 eV below the midgap, and tail states are generated near the drain junction after applying both stresses. The amount of donor-type states increases in phonon-assisted tunneling with the Pool-Frenkel effect (PAT) and Schockley-Read-Hall generation (SRH) owing to the increase in the deep-trap-state density, and decreases in band-to-band tunneling (BBT) owing to the decrease in electric field, giving rise to a predominant PAT+SRH current in off-current in a wide-negative-gate-voltage region.

  2. 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.

  3. 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.

  4. 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.

  5. Elastic properties of supported polycrystalline thin films and multilayers: An X-ray diffraction study

    SciTech Connect

    Goudeau, P.; Villain, P.; Tamura, N.; Renault, P.-O.; Badawi, K.F.; Padmore, H.A.

    2003-08-13

    Numerous experimental and theoretical studies have shown that thin film elastic behavior may be different from the bulk one due to size effects related to grain boundaries, free surfaces and interfaces. In addition, thin films often present high compressive residual stresses which may be responsible of thin film buckling. These two features will be discussed in this communication through recent x-ray diffraction experiments: in situ tensile testing for elastic constant analysis and scanning x-ray micro diffraction for stress relaxation measurements associated with film buckling.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. Electronic and atomic structure of thin CoSi2 films on Si(111) and Si(100)

    NASA Astrophysics Data System (ADS)

    Chambliss, D. D.; Rhodin, T. N.; Rowe, J. E.

    1992-01-01

    The electronic and atomic structure of very thin epitaxial cobalt silicide films was studied to provide insight into the initial stages of interface formation. Thin CoSi2 films (3-30 Å) on Si(111) and Si(100) were studied experimentally using angle-resolved photoemission spectroscopy, low-energy electron diffraction (LEED), and Auger electron spectroscopy, and computationally using the pseudofunction method of Kasowski for determining the electronic band structure. The experimental and computational results support the models of Hellman and Tung for Co-rich and Si-rich CoSi2(111) surfaces. The surface-state dispersion that we measure for the Co-rich variant agrees with the behavior that we calculate for the Hellman-Tung model. For the Si-rich variant, the essentially bulklike bonding environment of the outermost Co atoms in the Hellman-Tung model agrees with the photoemission results. Preliminary results for thin films of CoSi2 on Si(100) grown by a template technique show clearly a strong dependence of film quality on the annealing temperature and initial Co thickness. A model for surface structure is suggested that accounts for LEED and photoemission results.

  13. Oxidation of thin ErSi 1.7 overlayers on Si(111)

    NASA Astrophysics Data System (ADS)

    Guerfi, N.; Tan, T. A. Nguyen; Veuillen, J. Y.; Lollman, D. B.

    The oxidation of ErSi 1.7 thin films, epitaxially grown on Si(111)(7×7) surfaces by solid phase epitaxy, has been investigated by X-ray and UV photoelectron spectroscopies. Oxidation has been carried out at room temperature under low pressure (≤ 2×10 -5mbar) and 1 atm of oxygen, and at 700°C under 2 × 10 -5 mbar of oxygen. In all cases, both Si and Er react with oxygen. At room temperature the reaction depends on the pressure. Under low pressure the silicide surface is rather inert: a chemisorption phase of oxygen on Si and Er is detected only after exposures < 10 3 langmuir. High oxygen pressure produces a thin layer of mixed SiO 2, Si su☐ides and Er 2O 3. At 700°C, SiO 2 and Er 2O 3 are simultaneously formed, thus implying the decomposition of the silicide. The oxide layer has a SiO 2 termination at the surface. Only about half of the decomposed Si atoms react with oxygen. The preferential oxidation of Er is attributed to the high value of the heat of formation of Er 2O 3. An oxidation mechanism is proposed.

  14. Thin crystalline 3C-SiC layer growth through carbonization of differently oriented Si substrates

    NASA Astrophysics Data System (ADS)

    Severino, A.; D'Arrigo, G.; Bongiorno, C.; Scalese, S.; La Via, F.; Foti, G.

    2007-07-01

    The growth of thin cubic silicon carbide (3C-SiC) buffer layers in an horizontal hot-wall chemical vapor deposition reactor, through the carbonization of differently oriented Si surfaces, is presented. A qualitative and quantitative study has been performed on statistical parameters related to voids due to the buffer layer growth on the different substrate orientations emphasizing shape, size, and density as a function of the substrate orientation. Variation in the void parameters can be attributed to the atomic packing density related to the substrate orientations, which were (100) Si, (111) Si, and (110) Si in this study. Scanning electron microscopy and transmission electron microscopy were performed to analyze the surface and the crystalline quality of the 3C-SiC films grown and, eventually, an empirical model for the carbonization of Si surfaces formulated. Large platens characterize the 3C-SiC films with shapes related to the orientations of the substrate. These platens derive from the two-dimensional growth of different SiC islands which enlarge during the process due to the continuous reaction between Si and C atoms. The interior part of platens was characterized by the presence of a pure crystalline material with the presence of small tilts affecting some grains in the 3C-SiC layer in order to relief the stress generated with the substrate.

  15. 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.

  16. 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.

  17. 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.

  18. Pressure and strain dependence on the strength of sintered polycrystalline Mg[subscript 2]SiO[subscript 4] ringwoodite

    SciTech Connect

    Nishiyama, N.; Wang, Y.; Uchida, T.; Irifune, T.; Rivers, M.L.; Sutton, S.R.

    2010-07-20

    Differential stresses in a cylindrical rock of polycrystalline Mg{sub 2}SiO{sub 4} ringwoodite were measured at room temperature with pressures up to 10 GPa, axial strains in excess of 20%, and strain rates between 5 x 10{sup -5} and 4 x 10{sup -6} s{sup -1}, using the deformation-DIA coupled with monochromatic X-rays. The sample exhibited ductile behavior in axial shortening-lengthening cycles with reproducible hysteresis loops, yielding multiple well-defined stress-strain curves. Significant strain hardening was observed beyond the yield point, which occurs at axial strains around 1.5%. Large discrepancies in strength data on ringwoodite reported in previous studies, where no strain information could be obtained, can be reconciled by the strain hardening behavior. Above 8% axial strain, sample stresses reach saturation and the deformation reaches steady state, during which process the ultimate strength increases with hydrostatic pressure but are insensitive to strain rate, suggesting that the sample deforms in low-temperature plasticity regime.

  19. 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.

  20. Stress relaxation in Si-rich silicon nitride thin films

    SciTech Connect

    Habermehl, S.

    1998-05-01

    Si-rich silicon nitride thin films have been deposited by low pressure chemical vapor deposition, at 850{degree}C from mixtures of dichlorosilane and ammonia. The films{close_quote} elastic properties have been studied as a function of film composition. Fourier transform infrared spectroscopy and ellipsometric data indicate that the local atomic strain is a strong function of the calculated volume fraction of Si contained in the films. A relationship is observed that shows the strain to be inversely proportional to the cube root of the Si volume fraction. A model that accounts for distortion in Si{endash}Si{sub x}N{sub 4{minus}x} tetrahedra (x=0{endash}4), upon substitution of silicon for nitrogen in the film is applied to the data. The model is shown to be consistent with measurements of intrinsic film stress across a compositional range from stoichiometric silicon nitride, Si{sub 3}N{sub 4}, to nitrogen-free amorphous silicon, a-Si. {copyright} {ital 1998 American Institute of Physics.}

  1. Controlled tuning of thin film deposition of IrO2 on Si using pulsed laser ablation technique

    NASA Astrophysics Data System (ADS)

    Koshy, Abraham M.; Bhat, Shwetha G.; Kumar, P. S. Anil

    2016-05-01

    We have successfully grown a stable phase of polycrystalline IrO2 on Si (100) substrate. We have found that the phase of IrO2 can be controllably tuned to obtain either Ir or IrO2 using pulsed laser ablation technique. O2 conditions during the deposition influences the phase directly and drastically whereas annealing conditions do not show any variation in the phase of thin film. X-ray diffraction and X-ray photoemission experiments confirm both Ir and IrO2 can be successively grown on Si using IrO2 target. Also, the morphology is found to be influenced by the O2 conditions.

  2. 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.

  3. 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).

  4. Preferred orientation in polycrystalline Cu(In,Ga)Se{sub 2} and its effect on absorber thin-films and devices

    SciTech Connect

    Contreras, M. A.; Jones, K. M.; Gedvilas, L.; Matson, R.

    2000-05-15

    The purpose of this work is to investigate physical properties of Cu(In,Ga)Se{sub 2} polycrystalline thin-films exhibiting a high degree of preferred orientation. Specifically, by using Na-free Cu(In,Ga)Se{sub 2} thin-films, it is intended to experimentally determine differences (if any) between films with a (110/102)-preferred orientation and films with a (112)-preferred orientation. The approach to the problem is a systematic comparative analysis of film and device properties in which the most significant variable is the preferred orientation of the Cu(In,Ga)Se{sub 2} polycrystalline absorbers. To complement the results of Na-free absorbers and devices, a microstructural analysis is presented on (110)-oriented high efficiency Cu(In,Ga)Se{sub 2} absorbers that are grown on standard Mo-coated soda-lime glass substrates.

  5. Influence of molecular structure and microstructure on device performance of polycrystalline pentacene thin-film transistors

    NASA Astrophysics Data System (ADS)

    Cheng, Horng-Long; Mai, Yu-Shen; Chou, Wei-Yang; Chang, Li-Ren

    2007-04-01

    The authors have fabricated the pentacene thin films on polymethylmethacrylate (PMMA) and on silicon dioxide dielectric surfaces featuring similar surface energy and surface roughness. On both surfaces the pentacene films displayed high crystal quality from x-ray diffraction scans, although the film on PMMA had significantly smaller grain size. The pentacene transistors with PMMA exhibited excellent electrical characteristics, including high mobility of above 1.1cm2/Vs, on/off ratio above 106, and sharp subthreshold slope below 1V/decade. The analysis of molecular microstructure of the pentacene films provided a reasonable explanation for the high performance using resonance micro-Raman spectroscopy.

  6. 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.

  7. 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.

  8. Stable, high-efficiency, CuInSe2-based, polycrystalline, thin-film tandem solar cells

    NASA Astrophysics Data System (ADS)

    Birkmire, R. W.; Phillips, J. E.

    1987-10-01

    The long-term objective of this research was to obtain a stable, thin-film solar cell based on polycrystalline materials with an efficiency of 15 percent. The approach was to make a tandem cell based on CuInSe2/CdS as the bottom cell and CdTe/CdS as the top cell. An essential feature was to develop a CdTe cell with transport contacts. A suitable contacting system was developed using transparent conducting oxides (ITO and SnO2) in conjunction with a thin layer of copper. Cells were made with efficiencies over 8.5 percent. A reproducible fabrication process for CuInSe2/(CdZn)S cells was developed based on CuInSe2 films grown by vacuum evaporation using Knudsen-type effusion sources. These cells were made with efficiencies over 10 percent. The composition of the CuInSe2 films can be varied over a considerable range and still yield high-efficiency cells. Adding Zn to the CdS did not increase the V(sub oc) of the devices; analysis showed that the V(sub oc) is not controlled by interface recombination. The effect of oxidizing and reducing heat treatments on CuInSe2 cells is to change carrier concentration and thus V(sub oc). Analysis suggests that J(sub o) is controlled by band-to-band recombination. Monolithic tandem CuInSe2 CdTe cells have been made with efficiencies of approximately 3 percent, demonstrating the feasibility of this approach.

  9. 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.

  10. 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.

  11. Wear resistance of TiAlSiN thin coatings.

    PubMed

    Silva, F J G; Martinho, R P; Alexandre, R J D; Baptista, A P M

    2012-12-01

    In the last decades TiAIN coatings deposited by PVD techniques have been extensively investigated but, nowadays, their potential development for tribological applications is relatively low. However, new coatings are emerging based on them, trying to improve wear behavior. TiAlSiN thin coatings are now investigated, analyzing if Si introduction increases the wear resistance of PVD films. Attending to the application, several wear test configurations has been recently used by some researchers. In this work, TiAISiN thin coatings were produced by PVD Unbalanced Magnetron Sputtering technique and they were conveniently characterized using Scanning Electron Microscopy (SEM) provided with Energy Dispersive Spectroscopy (EDS), Atomic Force Microscopy (AFM), Electron Probe Micro-Analyzer (EPMA), Micro Hardness (MH) and Scratch Test Analysis. Properties as morphology, thickness, roughness, chemical composition and structure, hardness and film adhesion to the substrate were investigated. Concerning to wear characterization, two very different ways were chosen: micro-abrasion with ball-on-flat configuration and industrial non-standardized tests based on samples inserted in a feed channel of a selected plastic injection mould working with 30% (wt.) glass fiber reinforced polypropylene. TiAISiN coatings with a small amount of about 5% (wt.) Si showed a similar wear behavior when compared with TiAIN reported performances, denoting that Si addition does not improve the wear performance of the TiAIN coatings in these wear test conditions. PMID:23447962

  12. 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.

  13. Research on polycrystalline thin-film CuGaInSe[sub 2] solar cells

    SciTech Connect

    Stanbery, B.J.; Chen, W.S.; Devaney, W.E.; Stewart, J.W. . Defense and Space Systems Group)

    1992-11-01

    This report describes research to fabricate high-efficiency CdZnS/CuInGaSe[sub 2] (CIGS) thin-film solar cells, and to develop improved transparent conductor window layers such as ZnO. A specific technical milestone was the demonstration of an air mass (AM) 1.5 global, 13% efficient, 1-cm[sup 2]-total-area CIGS thin-film solar cell. Our activities focused on three areas. First, a CIGS deposition: system was modified to double its substrate capacity, thus increasing throughput, which is critical to speeding the process development by providing multiple substrates from the same CIGS run. Second, new tooling was developed to enable an investigation of a modified aqueous CdZnS process. The goal was to improve the yield of this critical step in the device fabrication process. Third, our ZnO sputtering system was upgraded to improve its reliability, and the sputtering parameters were further optimized to improve its properties as a transparent conducting oxide. The characterization of the new CIGS deposition system substrate fixturing was completed, and we produced good thermal uniformity and adequately high temperatures for device-quality CIGS deposition. Both the CIGS and ZnO deposition processes were refined to yield a ZnO//Cd[sub 0.82]Zn[sub 0.18]S/CuIn[sub 0.80]Ga[sub 0.20]Se[sub 2] cell that was verified at NREL under standard testing conditions at 13.1% efficiency with V[sub oc] = 0.581 V, J[sub sc] = 34.8 mA/cm[sup 2], FF = 0.728, and a cell area of 0.979 cm[sup 2].

  14. Thin film polycrystalline silicon solar cells. Second technical progress report, July 16, 1980-October 15, 1980

    SciTech Connect

    1980-10-01

    The objectives of this contract are to fabricate large area thin film silicon solar cells with AM1 efficiency of 10% or greater with good reproducibility and good yield and to assess the feasibility of implementing this process for manufacturing solar cells at a cost of $300/kWe. Efforts have been directed to the purification of metallurgical silicon, the preparation and characterization of substrates and epitaxial silicon layers, and the fabrication and characterization of solar cells. The partial purification of metallurgical silicon by extraction with aqua regia has been further investigated in detail, and the resulting silicon was analyzed by the atomic absorption technique. The unidirectional solidification of aqua regia-extracted metallurgical silicon on graphite was used for the preparation of substrates, and the impurity distribution in the substrate was determined and compared with the impurity content in metallurgical silicon. The effects of heat treatment on the impurity distribution in the substrate and in the epitaxial layer have also been investigated. Large area (30 to 60 cm/sup 2/) solar cells have been prepared from aqua regia-extracted metallurgical silicon substrates by depositing a p-n junction structure using the thermal reduction of trichlorosilane containing appropriate dopants. The AM1 efficiencies are about 9% for cells of 30 to 35 cm/sup 2/ area. Larger area, 60 cm/sup 2/, thin film solar cells have been fabricated for the first time, and their AM1 efficiencies are slightly higher than 8%. The spectral response, minority carrier diffusion length, and I/sub sc/-V/sub oc/ relation in a number of solr cells have been measured.

  15. 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.

  16. Development of stable high efficiency polycrystalline thin-film solar cells based on CulnSe/sub 2/. Final report, 16 March 1983-15 March 1984

    SciTech Connect

    Birkmire, R.W.; Hall, R.B.; Phillips, J.E.; Meakin, J.D.

    1985-03-01

    A two-junction, monolithic, optically and electrically coupled solar cell has been designed and a successful prototype produced. Each junction is a thin-film polycrystalline cell, namely, CuInSe/sub 2//(CdZn)S and CdTe/(CdZn)S. All active semi-conductor layers are produced by physical vapor deposition. During this contract year, a procedure for producing thin-film p-type CdTe by physical vapor deposition and a usable transparent interconnect for the tandem cell were developed.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. Thin film polycrystalline silicon solar cells: first technical progress report, April 15, 1980-July 15, 1980

    SciTech Connect

    1980-07-01

    The objectives of this contract are to fabricate large area thin film silicon solar cells with AM1 efficiency of 10% or greater with good reproducibility and good yield and to assess the feasibility of implementing this process for manufacturing solar cells at a cost of $300/kWe. Efforts during the past quarter have been directed to the purification of metallurgical silicon, the preparation of substrates, and the fabrication and characterization of solar cells. The partial purification of metallurgical silicon by extraction with aqua regia has been investigated in detail, and the resulting silicon was analyzed by the atomic absorption technique. The unidirectional solidification of aqua regia-extracted metallurgical silicon on graphite was used for the preparation of substrates, and the impurity distribution in the substrate was also determined. Large area (> 30 cm/sup 2/) solar cells have been prepared from aqua regia-extracted metallurgical silicon substrates by the thermal reduction of trichlorosilane containing appropriate dopants. Chemically deposited tin-dioxide films were used as antireflection coatings. Solar cells with AM1 efficiencies of about 8.5% have been obtained. Their spectral response, minority carrier diffusion length, and I/sub sc/-V/sub oc/ relation have been measured.

  2. Electrochemical characterisation of copper thin-film formation on polycrystalline platinum.

    PubMed

    Berkes, Balázs B; Henry, John B; Huang, Minghua; Bondarenko, Alexander S

    2012-09-17

    Electrochemically formed thin films are vital for a broad range of applications in virtually every field of modern science and technology. Understanding the film formation process could provide a means to aid the characterisation and control of film properties. Herein, we present a fundamental approach that combines two well-established analytical techniques (namely, electrochemical impedance spectroscopy and electrogravimetry) with a theoretical approach to provide physico-chemical information on the electrode/electrolyte interface during film formation. This approach allows the monitoring of local and overall surface kinetic parameters with time to enable an evaluation of the different modes of film formation. This monitoring is independent of surface area and surface concentrations of electroactive species and so may allow current computational methods to calculate these parameters and provide a deeper physical understanding of the electrodeposition of new bulk phases. The ability of this method to characterise 3D phase growth in situ in more detail than that obtained by conventional approaches is demonstrated through the study of a model system, namely, Cu bulk-phase deposition on a Pt electrode covered with a Cu atomic layer (Cu(ad)/Pt). PMID:22730305

  3. Heteroepitaxial growth of β-SiC thin films on Si(100) substrate using bis-trimethylsilylmethane

    NASA Astrophysics Data System (ADS)

    Bahng, Wook; Kim, Hyeong Joon

    1996-12-01

    A non-toxic and non-flammable organosilicon source having alternate Si-C bonding structure, bis-trimethylsilylmethane [C7H20Si2], was first used to deposit epitaxial β-SiC films at low growth temperature by chemical vapor deposition. Epitaxial β-SiC films were successfully grown on carburized Si(100) substrates at temperatures as low as 1100 °C, although the carburized buffer layer was a well-oriented, (100) polycrystalline film. Transmission electron microscopy analysis revealed that the films contain twins, stacking faults, and antiphase boundaries. Without the carburized buffer layer, highly (111) preferred oriented β-SiC films were grown by increasing the growth temperature.

  4. Influence of sputtering power on structural, mechanical and photoluminescence properties of nanocrystalline SiC thin films

    NASA Astrophysics Data System (ADS)

    Singh, Narendra; Kaur, Davinder

    2016-05-01

    In the present study, SiC thin films were deposited on Si (100) substrate by magnetron sputtering using a 4N purity commercial SiC target in argon atmosphere. The effect of sputtering RF power (140-170W) on structural, mechanical and photoluminescence properties were systematically studied by X-ray diffraction, field emission scanning electron microscopy, Nanoindentation and Spectrophotometer respectively. X-ray diffraction shows polycrystalline 4H-SiC phase with (105) preferred orientation and an enhancement in crystallite size with increasing power was also observed. The decrement in hardness and Young's modulus with increment in RF power was ascribed to Hall-Petch relation. The maximum hardness and Young's modulus were found to be 32 GPa and 232 GPa respectively. The photoluminescence spectra show peaks at 384 nm (3.22 eV) which corresponds to bandgap of 4H-SiC (phonon assisted band to band recombination) and 416 nm (2.99 eV) may be attributed to defect states and intensity of both peaks decreases as power increases.

  5. 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.

  6. 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.

  7. 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

    2016-05-01

    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.

  8. Structural Characterization of Polycrystalline 3C-SiC Films Prepared at High Rates by Atmospheric Pressure Plasma Chemical Vapor Deposition Using Monomethylsilane

    NASA Astrophysics Data System (ADS)

    Kakiuchi, Hiroaki; Ohmi, Hiromasa; Nakamura, Ryota; Aketa, Masatoshi; Yasutake, Kiyoshi

    2006-10-01

    Polycrystalline cubic silicon carbide (3C-SiC) films were deposited at a relatively low temperature of 1070 K on Si(001) substrates by atmospheric pressure plasma chemical vapor deposition. Monomethylsilane (CH3SiH3) was used as the single source. CH4 and SiH4 dual sources were also used to compare deposition characteristics. Under the present deposition conditions, very high deposition rates of more than 3 nm/s were obtained. The structure of the SiC films was evaluated by reflection high-energy electron diffraction, Fourier transform infrared absorption spectroscopy and cross-sectional transmission electron microscopy. In addition, optical emission spectroscopy was employed to study the chemical reactions in the CH4/SiH4 and CH3SiH3 plasmas. The results showed that increasing H2 concentration is essential in forming a high quality 3C-SiC film by enhancing the hydrogen elimination reaction at the film-growing surface. From the optical emission spectra, it was found that atomic hydrogen generated by adding H2 in the plasma increase the amount of principal precursors for the film growth. The utilization of CH3SiH3 also led to a higher concentration of principal precursors in the plasma, enhancing the incorporation of Si-C bonds into the film. As a consequence of simultaneously using a high H2 concentration and the CH3SiH3 single source, the columnar growth of 3C-SiC crystallites was achieved.

  9. 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.

  10. 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.

  11. Si-STEEL Thin-Strip Prepared by Twin-Roll Continuous Casting

    NASA Astrophysics Data System (ADS)

    Yi, Yu; Zhou, Zehua; Wang, Zehua; Jiang, Shaoqun; Huang, Weidong

    The fabrication process of Si-steel thin-strip by twin-roll continuous casting was described and the quality of the obtained Si-steel thin-strip was measured. Si-steel strips with 0.5-6.5 wt.% Si content were successfully prepared, and proper parameters including pouring temperature, height of molten pool, casting speed and pouring head mode were optimized, and their mechanisms were discussed. The relationship between quality factors of Si-steel including cracks, strip thickness, impurity and process parameters such as Si content and so on were discussed. The morphologies of the strips with different Si content were studied.

  12. A Monte Carlo simulation study of boron profiles as-implanted into LPCVD NiDoS polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Boukezzata, M.; Ait-Kaki, A.; Temple-Boyer, P.; Scheid, E.

    2003-03-01

    This work presents a Monte Carlo simulation study of boron profiles obtained from as-implanted ions into thin films nitrogen doped silicon (NiDoS) thin films. These films are performed by LPCVD technique from Si2H6 and NH3 gas sources, four values deliberately chosen, of the ratio NH3/Si2H6 to obtain samples, differently in situ nitrogen-doped. Taking into account the effect of the codoping case, and the structure specificity of these films, an accurate Monte Carlo model based on binary collisions in a multi-atomic target was performed. Nitrogen atoms present in the target is shown to affect the boron profiles and confirms clearly a reduction penetration effect which becomes more significant at high nitrogen concentrations. Whereas, the fine-grained polysilicon structure, and thus the presence of grains (G) and grain boundaries (GB), is known to enhance the opposite phenomenon by assuming an effective role played by GB's in the scattering calculation process of the incident ions. This role is represented by the change in direction of the incident ion after interaction with GB without corresponding loss in its energy. The results obtained show an enhancement of the stopping parameter when nitrogen concentration increases, while the GB interaction remains very important. This behavior is due to a great number of GB's interactions with boron atoms which gave low deflection angles. So that, the average positions described by the sequences of trajectories took place farther than what expected with channeling effect in crystal silicon materials.

  13. 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.

  14. Study of the Micro-Structure of PtxSi Ultra-Thin Film

    NASA Astrophysics Data System (ADS)

    Liu, Shuang; Falco, Charles M.; Zhong, Zhiyong

    Ultra-thin platinum (Pt) films were deposited on Si(100) substrates at 160°C by magnetron sputtering and subsequently annealed to form silicides. The thickness of the PtxSi films was found to be approximately 4 nm as determined by transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) analysis shows that these films consist of PtSi and Pt2Si phases, and a multi-layer configuration of SiOx/PtSi/Pt2 Si/Si was detected by angle-resolved XPS. However, the Pt3Si phase was not detected by X-ray diffraction (XRD).

  15. A spatially resolved investigation of the local, micro-magnetic domain structure of single and polycrystalline Co2FeSi

    NASA Astrophysics Data System (ADS)

    Gloskovskii, Andrei; Barth, Joachim; Balke, Benjamin; Fecher, Gerhard H.; Felser, Claudia; Kronast, Florian; Ovsyannikov, Ruslan; Dürr, Hermann; Eberhard, Wolfgang; Schönhense, Gerd

    2007-03-01

    The Heusler compound Co2FeSi is a promising material for magneto-electronic devices. With a Curie temperature of 1100 K and a saturation magnetization of 6 Bohr magnetons and a high spin polarization at the Fermi edge it fulfils the essential requirements for magnetic sensors or spin valve structures. An essential feature for such devices is the micro-magnetic domain structure. X-ray magnetic circular dichroism-photo emission electron microscopy has been used for a direct observation of the domain structure of single- and polycrystalline samples. The polycrystalline material exhibits a micro-magnetic ripple structure, as it is well known for pure Co and other polycrystalline Heusler compounds. The (1 1 0)-oriented surface of the single crystal exhibits a multi-domain pattern characteristic for systems with an easy axis that might point out of the surface. Asymmetric 180° Bloch walls with changing sense of rotation are observed between oppositely magnetized domains. Spin polarized photo emission from a single domain of the single crystal shows a spin polarization of 16% at the Fermi energy and up to 35% in the d-bands, at room temperature.

  16. 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.

  17. CW Laser Annealing of Polycrystalline Silicon on SiO2 and Effects of Successive Furnace Annealing

    NASA Astrophysics Data System (ADS)

    Kugimiya, Koichi; Fuse, Genshu; Inoue, Kaoru

    1982-01-01

    CW Ar laser annealing was carried out to reduce the resistivity of polycrystalline silicon implanted with light doses of 1× 1012-5× 1014B+/cm2. Laser annealing, actually laser melting, and successive furnace annealing effectively reduced the resistivity to almost that of single crystal silicon. TEM, OM and stress observations revealed that the reduction was due primarily to the grain growth of polycrystalline silicon and secondarily to stress relief, from 9× 109 dyne/cm2 to 5× 109 dyne/cm2, caused by annealing. Grain growth of up to about 3× 100 μm and bamboo-joint-like growth were observed.

  18. 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.

  19. The effects of layering in ferroelectric Si-doped HfO2 thin films

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    Atomic layer deposited Si-doped HfO2 thin films approximately 10 nm thick are deposited with various Si-dopant concentrations and distributions. The ferroelectric behavior of the HfO2 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.

  20. 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

    2016-06-01

    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.

  1. 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

  2. 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

  3. Thin wetting films from aqueous electrolyte solutions on SiC/Si wafer.

    PubMed

    Diakova, B; Filiatre, C; Platikanov, D; Foissy, A; Kaisheva, M

    2002-02-25

    The stability and rupture of thin wetting films from aqueous NaCl or Na2SO4 solutions of different concentrations on silicon carbide were investigated. The flat surface of SiC was obtained by plasma-enhanced chemical vapor deposition (PE-CVD) on top of a silicon wafer. The microinterferometric method was used for measuring the film thickness with time. The light reflectance was calculated as a function of film thickness for the four-layer system: air/aqueous solution/SiC/Si wafer. The microinterferometric experiments showed that films from aqueous NaCl and Na2SO4 solutions with concentrations up to 0.01 M were stable independent of the pre-treatment of the substrate. The pre-treatment of the SiC surface was crucial for the wetting film stability at electrolyte concentrations greater than 0.01 M. The films were unstable and ruptured if SiC was washed with 5% hydrofluoric acid and concentrated sulfuric acid, while they were stable if washing was in sulfuric acid only, without immersing SiC in HF. The average equilibrium film thickness was determined as a function of electrolyte concentration. Measurements of the electrokinetic potential zeta were performed by electrophores of SiC powder in 0.001 M NaCl. It was shown that silicon carbide surface was negatively charged. The theory of heterocoagulation was used for the interpretation of the results. Besides the DLVO forces, the structural disjoining pressure (both positive and negative) has been included in the analysis. PMID:11908786

  4. Effects of reductive annealing on insulating polycrystalline thin films of Nb-doped anatase TiO2: recovery of high conductivity

    NASA Astrophysics Data System (ADS)

    Nakao, Shoichiro; Hirose, Yasushi; Hasegawa, Tetsuya

    2016-02-01

    We studied the effects of reductive annealing on insulating polycrystalline thin films of anatase Nb-doped TiO2 (TNO). The insulating TNO films were intentionally fabricated by annealing conductive TNO films in oxygen ambient at 400 °C. Reduced free carrier absorption in the insulating TNO films indicated carrier compensation due to excess oxygen. With H2-annealing, both carrier density and Hall mobility recovered to the level of conducting TNO, demonstrating that the excess oxygen can be efficiently removed by the annealing process without introducing additional scattering centers.

  5. 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.

  6. Epitaxial Cu2ZnSnS4 thin film on Si (111) 4° substrate

    NASA Astrophysics Data System (ADS)

    Song, Ning; Young, Matthew; Liu, Fangyang; Erslev, Pete; Wilson, Samual; Harvey, Steven P.; Teeter, Glenn; Huang, Yidan; Hao, Xiaojing; Green, Martin A.

    2015-06-01

    To explore the possibility of Cu2ZnSnS4 (CZTS)/Si based tandem solar cells, the heteroepitaxy of tetragonal Cu2ZnSnS4 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.

  7. Thin polycrystalline diamond films protecting zirconium alloys surfaces: From technology to layer analysis and application in nuclear facilities

    NASA Astrophysics Data System (ADS)

    Ashcheulov, P.; Škoda, R.; Škarohlíd, J.; Taylor, A.; Fekete, L.; Fendrych, F.; Vega, R.; Shao, L.; Kalvoda, L.; Vratislav, S.; Cháb, V.; Horáková, K.; Kůsová, K.; Klimša, L.; Kopeček, J.; Sajdl, P.; Macák, J.; Johnson, S.; Kratochvílová, I.

    2015-12-01

    Zirconium alloys can be effectively protected against corrosion by polycrystalline diamond (PCD) layers grown in microwave plasma enhanced linear antenna chemical vapor deposition apparatus. Standard and hot steam oxidized PCD layers grown on Zircaloy2 surfaces were examined and the specific impact of polycrystalline Zr substrate surface on PCD layer properties was investigated. It was found that the presence of the PCD coating blocks hydrogen diffusion into the Zircaloy2 surface and protects Zircaloy2 material from degradation. PCD anticorrosion protection of Zircaloy2 can significantly prolong life of Zircaloy2 material in nuclear reactors even at temperatures above Zr phase transition temperatures.

  8. Development of transparent polycrystalline beta-silicon carbide

    NASA Astrophysics Data System (ADS)

    Bayya, Shyam S.; Villalobos, Guillermo R.; Hunt, Michael P.; Sanghera, Jasbinder S.; Sadowski, Bryan M.; Aggarwal, Ishwar D.; Cinibulk, Michael; Carney, Carmen; Keller, Kristin

    2013-09-01

    Transparent beta-SiC is of great interest because its high strength, low coefficient of thermal expansion, very high thermal conductivity, and cubic crystal structure give it a very high thermal shock resistance. A transparent, polycrystalline beta-SiC window will find applications in armor, hypersonic missiles, and thermal control for thin disc lasers. SiC is currently available as either small transparent vapor grown disks or larger opaque shapes. Neither of which are useful in window applications. We are developing sintering technology to enable transparent SiC ceramics. This involves developing procedures to make high purity powders and studying their densification behavior. We have been successful in demonstrating transparency in thin sections using Field Assisted Sintering Technology (FAST). This paper will discuss the reaction mechanisms in the formation of beta-SiC powder and its sintering behavior in producing transparent ceramics.

  9. Improved AMOLED with aligned poly-Si thin-film transistors by laser annealing and chemical solution treatments

    NASA Astrophysics Data System (ADS)

    Wu, G. M.; Chen, C. N.; Feng, W. S.; Lu, H. C.

    2009-12-01

    Low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFT) were prepared for the active-matrix organic light-emitting displays (AMOLED). The excimer laser annealing (ELA) recrystallization technique was employed with a chemical solution treatment process to improve the TFT characteristic uniformity and the AMOLED display image quality. The characteristics of the poly-Si array thin films were influenced by XeCl ELA optic module design, TFT device channel direction, and laser irradiation overlap ratio. The ELA system module provided aligned poly-Si grain size of 0.3 μm by the homogenization lens design. The chemical solution treatment process included a dilute HF solution (DHF), ozone (O 3) water, and buffer oxide etching solution (BOE). The PMOS TFT showed better field effect mobility of 87.6 cm 2/V s, and the threshold voltage was -1.35 V. The off current ( Ioff) was 1.25×10 -11 A, and the on/off current ratio was 6.27×10 6. In addition, the image quality of the AMOLED display was highly improved using the 2T1C structure design without any compensation circuit.

  10. Studies on VOx thin films deposited over Si3N4 coated Si substrates

    NASA Astrophysics Data System (ADS)

    Raj, P. Deepak; Gupta, Sudha; Sridharan, M.

    2015-06-01

    Vanadium oxide (VOx) thin films were deposited on to the silicon nitride (Si3N4) coated silicon (Si) substrate using reactive direct current magnetron sputtering at different substrate temperatures (Ts). 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.

  11. 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.

  12. Atomic-resolution characterization of the effects of CdCl2 treatment on poly-crystalline CdTe thin films

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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 CdCl2 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 CdCl2, 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.

  13. Enhanced mobility of solution-processed polycrystalline zinc tin oxide thin-film transistors via direct incorporation of water into precursor solution

    NASA Astrophysics Data System (ADS)

    Huang, Genmao; Duan, Lian; Zhao, Yunlong; Dong, Guifang; Zhang, Deqiang; Qiu, Yong

    2014-09-01

    Phase transition and the consequent variation in crystalline orientation of metal oxides have profound impact on their transport properties. In this work, we report a simple method to enhance field-effect mobility of solution-processed zinc tin oxide (ZTO) thin-film transistors (TFTs) via direct incorporation of water into precursor solution. It is confirmed H2O molecules could effectively facilitate the conversion and alloying processes during ZTO film formation, characterized by the enhancement of spinel Zn2SnO4 phase and the reduction of cassiterite SnO2 phase. The preferred orientation of metal oxide crystallites varies according to the amount of water added into precursor solutions. Smooth and densely packed polycrystalline ZTO films with only a few organic residuals and moderate oxygen defects are fabricated from water-containing precursor solutions. With the incorporation of 1.67 M H2O, the extracted field-effect mobility of TFT devices could be improved by a factor of 2.3, from 0.92 to 2.11 cm2 V-1 s-1. This work offers a facile and cost-effective route towards high-mobility TFTs based on solution-processed polycrystalline metal oxide thin films.

  14. 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..

  15. [Spectral analyzing effects of atmosphere states on the structure and characteristics of CdTe polycrystalline thin films made by close-spaced sublimation].

    PubMed

    Zheng, Hua-jing; Zheng, Jia-gui; Feng, Liang-huan; Zhang, Jing-quan; Xie, Er-qing

    2005-07-01

    The structure and characteristics of CdTe thin films are dependent on the working atmosphere states in close-spaced sublimation. In the present paper, CdTe polycrystalline thin films were deposited by CSS in mixture atmosphere of argon and oxygen. The physical mechanism of CSS was analyzed, and the temperature distribution in CSS system was measured. The dependence of preliminary nucleus creation on the atmosphere states (involving component and pressure) was studied. Transparencies were measured and optic energy gaps were calculated. The results show that: (1) The CdTe films deposited in different atmospheres are cubic structure. With increasing oxygen concentration, a increases and reaches the maximum at 6% oxygen concentration, then reduces, and increases again after passing the point at 12% oxygen concentration. Among them, the sample depositing at 9% oxygen concentration is the best. The optic energy gaps are 1.50-1.51 eV for all CdTe films. (2) The samples depositing at different pressures at 9% oxygen concentration are all cubical structure of CdTe, and the diffraction peaks of CdS and SnO2:F still appear. With the gas pressure increasing, the crystal size of CdTe minishes, the transparency of the thin film goes down, and the absorption side shifts to the short-wave direction. (3) The polycrystalline thin films with high quality deposit in 4 minutes under the depositing condition that the substrate temperature is 550 degrees C, and source temperature is 620 degrees C at 9% oxygen concentration. PMID:16241058

  16. Effect of Heat Treatment in Air on Thermoelectric Properties of Polycrystalline Type-I Silicon-Based Clathrate: Ba8Al15Si31

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Shirataki, Ritsuko

    2015-06-01

    The effect of heat treatment in air on the thermoelectric properties was investigated for polycrystalline Ba8Al15Si31, where the Al content is almost at the maximum in the Ba8Al x Si46- x system, to evaluate the thermal stability in air at high temperatures, which is indispensable for practical use in thermoelectric applications. Samples were prepared by combining arc melting and spark plasma sintering techniques. Heat treatments were performed in air at 873 K for 10 days and 20 days. The Seebeck coefficient, electrical conductivity, and thermal conductivity were measured before and after the heat treatments. The microstructure and chemical composition were also analyzed before and after the heat treatments, using scanning electron microscopy with energy-dispersive x-ray spectroscopy. Although an oxidation layer was formed on the surface by the heat treatment in air, the chemical composition of the interior of Ba8Al15Si31 was found to be stable in air at 873 K for 10 days and 20 days. The Seebeck coefficient, the electrical conductivity, and the thermal conductivity were found to be almost unchanged after the heat treatment, indicating that Ba8Al15Si31 clathrate is promising as a thermoelectric material with high thermal stability for use in air at 873 K.

  17. 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.

  18. Study of CVD SiC thin film for space mirror

    NASA Astrophysics Data System (ADS)

    Zhang, Jianhan; Zhang, Yumin; Han, Jiecai; He, Xiaodong

    2006-01-01

    The performance of space mirror lied on the properties of the mirror surface material to a great extent. In this paper, the silicon carbide thin film deposited on reaction-bonded silicon carbide (RBSC) space mirror blank was produced by Chemical Vapor Deposition (CVD) process. Some mechanical and physical properties of the SiC thin film were tested because they were important to study ability to work of space mirror. The result of XRD phase analysis indicated that the component of the SiC thin film was β-SiC. The micro hardness of the film was tested. The thickness of SiC thin film was tested using needle touch contour graph. The results showed that the thickness of SiC film was about 20 μm and film was even in the macro scope. The adhesion strength of SiC thin film and RBSC substrate was tested by scratch method and the results showed that was excellent. The residual stress of SiC thin film was tested by X-ray, at the same time; the origin of residual stress and the calculation of thermal stress were discussed. In the room temperature, the residual stress of the SiC film was compressive. After precision grinding, the surface topography and roughness of the SiC thin film was tested by Atomic Force Microscope (AFM). The results showed that the surface of SiC thin film had extremely low surface roughness and high surface form accuracy. The thermal shock resistance of SiC film was fine by tested.

  19. 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).

  20. 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.

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

    PubMed

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

    2015-11-27

    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. PMID:26538479

  2. 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.

  3. Hybrid Systems in Foil (HySiF) exploiting ultra-thin flexible chips

    NASA Astrophysics Data System (ADS)

    Harendt, Christine; Kostelnik, Jan; Kugler, Andreas; Lorenz, Enno; Saller, Stefan; Schreivogel, Alina; Yu, Zili; Burghartz, Joachim N.

    2015-11-01

    Electronics embedded in foil is an enabling technology for flexible electronics and for special form factors of electronic components. In contrast to strictly printed electronics, Hybrid Systems-in-Foil (HySiF), comprising thin flexible, embedded chips and large-area thin-film electronic elements, feature a versatile and reliable technological solution for industrial applications of flexible electronics. This paper provides a comprehensive overview of HySiF technology, including aspects of thin-chip fabrication, reliability and assembly. Also presented is an industrial demonstrator utilizing such a HySiF component.

  4. 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.

  5. 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

  6. 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

    2016-01-01

    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 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. PMID:27098115

  7. 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).

  8. 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.

  9. 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.

  10. Mechanical stress induced voltage shift in polycrystalline Bi3.25La0.75Ti3O12 thin films

    NASA Astrophysics Data System (ADS)

    Wu, Xiumei; Zhai, Ya; Kan, Yi; Lu, Xiaomei; Zhu, Jinsong

    2009-10-01

    Imprint behavior of polycrystalline Bi3.25La0.75Ti3O12 thin films under stress was studied. The voltage shift along the positive voltage axis can be depressed by tensile stress while increased by compressive stress. With the measured voltage increasing, the voltage shift referred above increases and the increase trend gets enhanced under both compressive and tensile stress compared with that at zero stress. The asymmetric distribution of the trapped charged in films, which is caused by the increase of the in-plane polarization component for the domain reorientation induced by stress or for the voltage-assisted domain walls depinning, was considered the contribution to the voltage shift.

  11. Thermoelectric generators from SiO2/SiO2 + Ge nanolayer thin films modified by MeV Si ions

    NASA Astrophysics Data System (ADS)

    Budak, S.; Gulduren, E.; Allen, B.; Cole, J.; Lassiter, J.; Colon, T.; Muntele, C.; Alim, M. A.; Bhattacharjee, S.; Johnson, R. B.

    2015-01-01

    We prepared thermoelectric generator devices from 100 alternating layers of SiO2/SiO2 + Ge superlattice thin films using Magnetron DC/RF Sputtering. Rutherford Backscattering Spectrometry (RBS) and RUMP simulation software package were used to determine the proportions of Si and Ge in the grown multilayer films and the thickness of the grown multi-layer films. 5 MeV Si ion bombardments were performed using the AAMU-Pelletron ion beam accelerator, to form quantum clusters in the multi-layer superlattice thin films, in order to tailor the thermoelectrical and optical properties. We characterized the fabricated thermoelectric devices using cross-plane Seebeck coefficient, van der Pauw resistivity, mobility, density (carrier concentration), Hall Effect coefficient, Raman, Fluorescence, Photoluminescence, Atomic Force Microscopy (AFM) and Impedance analyzing measurements. Some suitable high energy ion fluences and thermal annealings caused some remarkable thermoelectrical and optical changes in the fabricated multilayer thin film systems.

  12. 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.

  13. 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.

  14. Mass Enhancement of Two-Dimensional Electrons in Thin Oxide Si-MOSFETs

    SciTech Connect

    Draper, B.L.; Pan, W.; Tsui, D.C.

    1998-11-02

    We report in this paper a study of the effective mass in thin oxide Si-MOSFETs, using the temperature dependence of the Shubnikov-de Haas (SdH) effect and following the methodology developed by Smith and Stiles.

  15. 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.

  16. Fabrication of multiple Si nanohole thin films from bulk wafer by controlling metal-assisted etching direction

    NASA Astrophysics Data System (ADS)

    Shiu, Shu-Chia; Lin, Tzu-Ching; Pun, Keng-Lam; Syu, Hong-Jhang; Hung, Shih-Che; Lin, Ching-Fuh

    2011-10-01

    Crystalline Si photovoltaic modules still have high production cost due to significant consumption of the Si wafer. Reducing the large amount of Si material consumption is thus a critical issue. Here we develop a two-step metal-assisted etching technique for forming vertically-aligned Si nanohole thin films from bulk Si wafers. The formation of Si nanohole thin films includes a series of solution processes: deposition of Ag nanoparticles in an AgNO3/ HF aqueous solution, formation of Si nanohole arrays at the first-step metal-assisted etching, and side etching of the roots of the nanohole structure at the second-step metal-assisted etching. All the processes can proceed at around room temperature. A Si nanohole thin film with an average hole-size of 100 nm and a thickness of 5ìm-20ìm was hence formed at the top of the wafer. Afterwards, the Si nanohole thin film was transferred onto alien substrates. The Si nanohole thin film has the crystal quality similar to the bulk Si wafer. The above bulk Si substrate can be reused. With similar processes, other Si nanohole thin films can be formed from the above recycled Si wafer. The hole size and thickness are similar. The Si wafers recycled will significantly reduce the material consumption of Si. Thus, such technique is promising for lowering the cost of Si solar cells.m.

  17. The role of lattice mismatch and kinetics in texture development: Co1-xNixSi2 thin films on Si(100)

    NASA Astrophysics Data System (ADS)

    Smeets, D.; Vantomme, A.; De Keyser, K.; Detavernier, C.; Lavoie, C.

    2008-03-01

    Mixed Co1-xNixSi2 films (0≤x≤1) were grown by solid phase reaction of homogeneous Co1-xNix metal films, codeposited on Si(100). The texture of these films was contemplated using complementary experimental techniques: Rutherford backscattering and channeling spectrometry, x-ray pole figure measurements, and orientation imaging with electron backscattering diffraction. Based on the increasing Co1-xNixSi2 lattice parameter with increasing Ni concentration, a gradual, continuous improvement of the epitaxial quality of the film would be expected. The observed trend is significantly different. The epitaxial quality of the disilicide film indeed improves with increasing Ni concentration, but only up to 15% Ni. Moreover, the increasing epitaxial quality is due to a large volume fraction of (110)-oriented grains, instead of the anticipated (100) orientation. The most abundant texture component is not necessarily the one with the best in-plane match with the substrate, i.e., epitaxy, nor the one which assures the continuity of crystallographic planes across the plane of the interface, i.e., axiotaxy. Clearly, geometrical arguments alone cannot account for the observed large size and high volume fraction of (110)-oriented grains. On the other hand, we demonstrate that growth kinetics plays an important role in texture development and epitaxial growth during the solid phase reaction. Above 15% Ni, the epitaxial quality rapidly decreases and a polycrystalline film is formed for 40% Ni. This decrease is explained by a gradual shift of the disilicide nucleation site from the interface with the substrate to the surface of the thin film. For high Ni concentrations, i.e., ≥50% Ni, the (100) orientation dominates the thin-film texture, due to the growth of a NiSi2-rich film at the substrate interface. The changing nucleation site, due to this phase separation, and the differing growth kinetics can significantly alter the texture of ternary films. These two factors should be

  18. 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).

  19. 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.

  20. The reduction of the change of secondary ions yield in the thin SiON/Si system

    NASA Astrophysics Data System (ADS)

    Sameshima, J.; Yamamoto, H.; Hasegawa, T.; Nishina, T.; Nishitani, T.; Yoshikawa, K.; Karen, A.

    2006-07-01

    For the analyses of gate insulating materials of thin silicon oxy-nitride (SiON) and dielectric films, SIMS is one of the available tool along with TEM and ESCA, etc. Especially, to investigate the distribution of dopant in the thin films, SIMS is appreciably effective in these techniques because of its depth profiling capability and high sensitivity. One of the problem occurring in this SIMS measurement is the change of secondary ion yield at the interface as well as in the layers with different chemical composition. To solve this problem, some groups have researched the phenomenon for SiO 2/Si interface [W. Vandervorst, T. Janssens, R. Loo, M. Caymax, I. Peytier, R. Lindsay, J. Fruhauf, A. Bergmaier, G. Dollinger, Appl. Surf. Sci. 203-204 (2003) 371-376; S. Hayashi, K.Yanagihara, Appl. Surf. Sci. 203-204 (2003) 339-342; M. Barozzi, D. Giubertoni, M.Anderle, M. Bersani, Appl. Surf. Sci. 231-232 (2004) 632-635; T.H. Buyuklimanli, J.W. Marino, S.W. Novak, Appl. Surf. Sci. 231-232 (2004) 636-639]. In the present study, profiles of boron and matrix elements in the Si/SiON layers on Si substrate have been investigated. The sensitivity change of Si and B profiles in SiON layer become smaller by using oxygen flood than those without oxygen flood for both O 2+ and Cs + beam. At the range of 0-25 at.% of N composition, 11B dosimetry in SiON layer implanted through amorphous Si depends on N composition. This trend could be caused by the sensitivity change of 11B, or it indicates real 11B concentration change in SiON lyaer. N areal density determined by Cs + SIMS with oxygen flooding also shows linear relationship with N composition estimated by XPS.

  1. 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

  2. Laser-induced amorphization of silicon during pulsed-laser irradiation of TiN/Ti/polycrystalline silicon/SiO2/silicon

    NASA Astrophysics Data System (ADS)

    Chong, Y. F.; Pey, K. L.; Wee, A. T. S.; Thompson, M. O.; Tung, C. H.; See, A.

    2002-11-01

    In this letter, we report on the complex solidification structures formed during laser irradiation of a titanium nitride/titanium/polycrystalline silicon/silicon dioxide/silicon film stack. Due to enhanced optical coupling, the titanium nitride/titanium capping layer increases the melt depth of polycrystalline silicon by more than a factor of 2. It is found that the titanium atoms diffuse through the entire polycrystalline silicon layer during irradiation. Contrary to the expected polycrystalline silicon growth, distinct regions of polycrystalline and amorphous silicon are formed instead. Possible mechanisms for the formation of these microstructures are proposed.

  3. Photovoltaic mechanisms in polycrystalline thin film silicon solar cells. Final report, 30 June 1979-29 June 1980

    SciTech Connect

    Sopori, B.L.

    1980-11-01

    The objectives of this program were: (1) to develop appropriate measurement techniques to facilitate a quantitative study of the electrical activity of structural defects and at a grain boundary (G.B.) in terms of generation-recombination, barrier height, and G.B. conductivity; (2) to characterize G.B.s in terms of physical properties such as angle of misfit and local stress, and to correlate them with the electrical activity; (3) to determine the influence of solar cell processing on the electrical behavior of structural defects and G.B.s; and (4) to evaluate polycrystalline solar cell performance based on the above study, and to compare it with the experimentally measured performance. Progress is reported in detail. (WHK)

  4. Calculating Optical Absorption Spectra of Thin Polycrystalline Organic Films: Structural Disorder and Site-Dependent van der Waals Interaction

    PubMed Central

    2015-01-01

    We propose a new approach for calculating the change of the absorption spectrum of a molecule when moved from the gas phase to a crystalline morphology. The so-called gas-to-crystal shift Δm is mainly caused by dispersion effects and depends sensitively on the molecule’s specific position in the nanoscopic setting. Using an extended dipole approximation, we are able to divide Δm= −QWm in two factors, where Q depends only on the molecular species and accounts for all nonresonant electronic transitions contributing to the dispersion while Wm is a geometry factor expressing the site dependence of the shift in a given molecular structure. The ability of our approach to predict absorption spectra is demonstrated using the example of polycrystalline films of 3,4,9,10-perylenetetracarboxylic diimide (PTCDI). PMID:25834658

  5. Investigation of photovoltaic mechanisms in polycrystalline thin-film solar cells. Interim technical report, November 1, 1980-July 31, 1981

    SciTech Connect

    Temofonte, T. A.; Szedon, J. R.; O'Keeffe, T. W.

    1982-03-05

    Effort is reported on measurement technique development to assess the utility of Deep-Level Transient Spectroscopy (DLTS) methods in characterizing polycrystalline silicon that was deliberately doped with Ti during growth. Difficulties encountered with lateral DLTS measurements are discussed. In this approach, modulation of the grain boundary, double-depletion region produces the entire DLTS signal. Major effort has been applied in grain boundary characterization and control. The most significant accomplishments to date have involved laser scanning of slices of Wacker SILSO polysilicon having nearly identical grain structure. By using various kinds of treatments and by comparing treated and untreated substrates having nearly identical grain structure, control of grain boundary photocurrent suppression (..delta..I/sub ph/) over the range 1% less than or equal to ..delta..I/sub ph/ less than or equal to 40% was demonstrated.

  6. 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.

  7. 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.

  8. Optical Properties Of {beta}-FeSi2 Thin Films Grown By Magnetron Sputtering

    SciTech Connect

    Tatar, B.; Kutlu, K.

    2007-04-23

    {beta}-FeSi2 semiconductor thin films have been grown on Si(100) and Si(111) substrate at room temperature by unbalanced magnetron sputtering. The thicknesses of {beta}-FeSi2 thin films have been prepared to have value between 0.3-1{mu}m. Optical characteristic of the {beta}-FeSi2 films have been deduced using Fourier Transform Infrared Spectroscopy (FT-IR) in the wavelength range 1000-2000nm. The {beta}-FeSi2 films have been determinated to have optical direct band gap from the plot of ({alpha}h{upsilon})2 vs. h{upsilon} The direct band gap values of the films have been observed to vary between 0.82-0.89 eV depending on the type of substrates.

  9. Characterization of the visible photoluminescence from porous a-Si:H and porous a-Si:C:H thin films

    SciTech Connect

    Estes, M.J.; Hirsch, L.R.; Wichart, S.; Moddel, G.

    1996-12-31

    The authors report on the influence of doping, temperature, porosity, and bandgap on the visible photoluminescence properties of anodically-etched porous a-Si:H and a-Si:C:H thin films. Only boron-doped, p-type a-Si:H or a-Si:C:H samples exhibited any visible photoluminescence. The authors see evidence of discrete defect or impurity levels in temperature-dependent luminescence measurements. Unlike in porous crystalline silicon, they see no correlation of luminescence energy with porosity. The authors do, though, observe a correlation of luminescence energy with bandgap of the starting a-Si:C:H films. They discuss the implication of these observations on the nature of the luminescence mechanism.

  10. Control of the growth orientation and electrical properties of polycrystalline Cu2O thin films by group-IV elements doping

    NASA Astrophysics Data System (ADS)

    Ishizuka, Shogo; Akimoto, Katsuhiro

    2004-11-01

    The effects of group-IV element dopants on the structural and electrical properties of Cu2O thin films were studied. Similar dopant-induced behavior was found in the observed variations of the growth orientation and electrical properties of Si- and Ge-doped Cu2O thin films. Ge doping was found to induce electrically active acceptors with an activation energy of 0.18 eV, comparable to the 0.19 eV value of Si-doped Cu2O. These results suggest that locally formed silicate and germanate have the same effect on the structural and electrical properties of Cu2O. On the other hand, Sn and Pb likely act as donors when incorporated substitutionally onto Cu-lattice sites, although further study may be required to suppress self-compensation effects in Cu2O to achieve n-type conductivity.

  11. Laser processing for thin-film photovoltaics

    NASA Astrophysics Data System (ADS)

    Compaan, Alvin D.

    1995-04-01

    Over the past decade major advances have occurred in the field of thin- film photovoltaics (PV) with many of them a direct consequence of the application of laser processing. Improved cell efficiencies have been achieved in crystalline and polycrystalline Si, in hydrogenated amorphous silicon, and in two polycrystalline thin-film materials. The use of lasers in photovoltaics includes laser hole drilling for emitter wrap-through, laser trenching for buried bus lines, and laser texturing of crystalline and polycrystalline Si cells. In thin-film devices, laser scribing is gaining increased importance for module interconnects. Pulsed laser recrystallization of boron-doped hydrogenated amorphous silicon is used to form highly conductive p-layers in p-i-n amorphous silicon cells and in thin-film transistors. Optical beam melting appears to be an attractive method for forming metal semiconductor alloys for contact formation. Finally, pulsed lasers are used for deposition of the entire semiconductor absorber layer in two types of polycrystalline thin-film cells-those based on copper indium diselenide and those based on cadmium telluride. In our lab we have prepared and studied heavily doped polycrystalline silicon thin films and also have used laser physical vapor deposition (LPVD) to prepare 'all-LPVD' CdS/CdTe solar cells on glass with efficiencies tested at NREL at 10.5%. LPVD is highly flexible and ideally suited for prototyping PV cells using ternary or quaternary alloys and for exploring new dopant combinations.

  12. 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.

  13. Polycrystalline BiFeO3 thin film synthesized via sol-gel assisted spin coating technique for photosensitive application

    NASA Astrophysics Data System (ADS)

    Bogle, K. A.; Narwade, R. D.; Phatangare, A. B.; Dahiwale, S. S.; Mahabole, M. P.; Khairnar, R. S.

    2016-05-01

    We are reporting photosensitivity property of BiFeO3 thin film under optical illumination. The thin film used for photosensitivity work was fabricated via sol-gel assisted spin coating technique. I-V measurements on the Cu/BiFeO3/Al structure under dark condition show a good rectifying property and show dramatic blue shit in threshold voltage under optical illumination. The microstructure, morphology and elemental analysis of the films were characterized by using XRD, UV-Vis, FTIR, SEM and EDS.

  14. 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.

  15. Dielectric dynamics of the polycrystalline Ba0.5Sr0.5TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Pečnik, Tanja; Eršte, Andreja; Matavž, Aleksander; Bobnar, Vid; Ivanov, Maksim; Banys, Juras; Xiang, Feng; Wang, Hong; Malič, Barbara; Glinšek, Sebastjan

    2016-05-01

    Polycrystalline Ba0.5Sr0.5TiO3 films, with thicknesses between 90 and 600 nm, were prepared on alumina substrates at 900 °C by chemical solution deposition (CSD) and a dielectric spectroscopy investigation of the in-plane properties was performed. The 5-kHz permittivity ε‧ shows a non-monotonic thickness dependence, reaching 1230 at room temperature for the 310-nm-thick film, whose grain size is ∼75 nm. Its 15-GHz-value and losses are 1105 and 0.05, respectively. The temperature of the permittivity maximum T max at 5 kHz decreases with increasing thickness from 277 to 250 K for the 170- and 600-nm-thick films, respectively, which has been linked to the residual biaxial stress. A hysteresis is observed in the permittivity ε‧-electric field E DC characteristics in all the films up to ∼50 K above T max . Frequency dispersion in which permittivity decreases with increasing frequency is present below T max in films thicker than 90 nm. The high permittivity values of the thinnest films, which are among the highest reported in the (Ba,Sr)TiO3 films with grain sizes below 75 nm, are a direct proof of the optimized CSD processing conditions.

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

    PubMed

    Debieu, Olivier; Nalini, Ramesh Pratibha; Cardin, Julien; Portier, Xavier; Perrière, Jacques; Gourbilleau, Fabrice

    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

  17. 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

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

    NASA Astrophysics Data System (ADS)

    Debieu, Olivier; Nalini, Ramesh Pratibha; Cardin, Julien; Portier, Xavier; Perrière, Jacques; Gourbilleau, Fabrice

    2013-01-01

    The specific dependence of the Si content on the structural and optical properties of O- and H-free Si-rich nitride (SiN x>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 SiN x<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 SiN x>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 SiN x>0.9 could be then due to a size effect of Si-np but having an amorphous phase.

  19. 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.

  20. Losses in polycrystalline silicon waveguides

    NASA Astrophysics Data System (ADS)

    Foresi, J. S.; Black, M. R.; Agarwal, A. M.; Kimerling, L. C.

    1996-04-01

    The losses of polycrystalline silicon (polySi) waveguides clad by SiO2 are measured by the cutback technique. We report losses of 34 dB/cm at a wavelength of 1.55 μm in waveguides fabricated from chemical mechanical polished polySi deposited at 625 °C. These losses are two orders of magnitude lower than reported absorption measurements for polySi. Waveguides fabricated from unpolished polySi deposited at 625 °C exhibit losses of 77 dB/cm. We find good agreement between calculated and measured losses due to surface scattering.

  1. 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.

  2. 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.

  3. 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.

  4. Elasticity and sound velocities of polycrystalline grossular garnet (Ca3Al2Si3O12) at simultaneous high pressures and high temperatures

    NASA Astrophysics Data System (ADS)

    Gwanmesia, Gabriel D.; Wang, Liping; Heady, Adaire; Liebermann, Robert C.

    2014-03-01

    The elastic wave velocities of a dense polycrystalline specimen (99.7% of theoretical density) of synthetic grossular garnet (Ca3Al2Si3O12) were measured to pressures of ∼10 GPa and temperatures of 1000 K by transfer-function ultrasonic interferometry in conjunction with energy-dispersive synchrotron X-radiation in a deformation DIA-type cubic-anvil apparatus. The calculated elastic bulk (Ks) and shear (G) moduli data were fitted to functions of Eulerian strain to 3rd order, yielding the zero-pressure values [Ks = 171.2 (8) GPa; G = 107.4 (2) GPa] and their pressure derivatives [(∂Ks/∂P)T = 4.47 (2); (∂G/∂P)T = 1.29 (5)]. The temperature dependences of the elastic moduli obtained from linear regression of entire P-T-Ks and P-T-G data are: (∂Ks/∂T)P = -1.38 (3) × 10-2 GPa/K and (∂G/∂T)P = -1.28 (2) × 10-2 GPa/K. These results together with those from previous studies for garnets with varying compositions suggest that most of the thermo-elastic properties of garnet are insensitive to grossular content, with the exception of the shear modulus, which significantly depends on the calcium content.

  5. Origins of electrostatic potential wells at dislocations in polycrystalline Cu(In,Ga)Se{sub 2} thin films

    SciTech Connect

    Dietrich, J.; Abou-Ras, D. Schmidt, S. S.; Rissom, T.; Unold, T.; Cojocaru-Mirédin, O.; Niermann, T.; Lehmann, M.; Koch, C. T.; Boit, C.

    2014-03-14

    Thin-film solar cells based on Cu(In,Ga)Se{sub 2} (CIGSe) reach high power-conversion efficiencies in spite of large dislocation densities of up to 10{sup 10}–10{sup 11} cm{sup −2}. The present work gives insight into the structural and compositional properties of dislocations in CIGSe thin films, which are embedded in a complete solar cell stack. These properties are related to the average electrical potential distributions obtained by means of inline electron holography. At a part of the dislocations studied, the average electrostatic potential shows local minima, all with depths of about −1.4 V. The measured average electrostatic potential distributions were modeled in order to reveal possible influences from strain fields, excess charge, and also compositional changes at the dislocation core. Cu depletion around the dislocation core, as evidenced by atom-probe tomography, explains best the measured potential wells. Their influences of the strain field around the dislocation core and of excess charge at the dislocation core are small. A structural model of dislocations in CIGSe thin films is provided which includes a Cu-depleted region around the dislocation core and gives a possible explanation for why decent photovoltaic performances are possible in the presence of rather large dislocation densities.

  6. [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

  7. 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

  8. Full potential of radial junction Si thin film solar cells with advanced junction materials and design

    NASA Astrophysics Data System (ADS)

    Qian, Shengyi; Misra, Soumyadeep; Lu, Jiawen; Yu, Zhongwei; Yu, Linwei; Xu, Jun; Wang, Junzhuan; Xu, Ling; Shi, Yi; Chen, Kunji; Roca i Cabarrocas, Pere

    2015-07-01

    Combining advanced materials and junction design in nanowire-based thin film solar cells requires a different thinking of the optimization strategy, which is critical to fulfill the potential of nano-structured photovoltaics. Based on a comprehensive knowledge of the junction materials involved in the multilayer stack, we demonstrate here, in both experimental and theoretical manners, the potential of hydrogenated amorphous Si (a-Si:H) thin film solar cells in a radial junction (RJ) configuration. Resting upon a solid experimental basis, we also assess a more advanced tandem RJ structure with radially stacking a-Si:H/nanocrystalline Si (nc-Si:H) PIN junctions, and show that a balanced photo-current generation with a short circuit current density of Jsc = 14.2 mA/cm2 can be achieved in a tandem RJ cell, while reducing the expensive nc-Si:H absorber thickness from 1-3 μ m (in planar tandem cells) to only 120 nm. These results provide a clearly charted route towards a high performance Si thin film photovoltaics.

  9. 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.

  10. 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.

  11. 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

  12. X-Ray Diffraction Analysis of Residual Stress in Thin Polycrystalline Anatase Films and Elastic Anisotropy of Anatase

    NASA Astrophysics Data System (ADS)

    Matěj, Z.; Kužel, R.; Nichtová, L.

    2011-11-01

    The importance of residual stress in anatase thin films for their photo-induced hydrophilicity was proved recently. Detailed X-ray diffraction (XRD) studies of residual stresses in titanium dioxide films are presented here. Measurements including multiple hkl reflections on several series of these films revealed the presence of tensile stresses in the films that were obtained by crystallization from amorphous state. Significant anisotropy of the strain was also found and compared with that of anatase, resulting from its theoretically calculated single-crystal elastic constants. The XRD data support the experimental evidence of the hypothesis that the [00 l] axis is the elastically soft anatase direction, whereas the directions in the [ h00] × [ hk0] plane are elastically stiff. This is in agreement with the anisotropy predicted by single-crystal elastic constants that are obtained from ab-initio calculations. Residual stress analysis for materials with tetragonal symmetry is described and the theory is used to analyze the data. The anisotropy is very different from that for the rutile phase, and the experimental results agree well with the values calculated for anatase. A simplified method of XRD residual stress analysis in thin anatase films by total pattern fitting (TPF) is also presented. Tensile stresses are formed during the crystallization process and increase rapidly with reduced film thickness. They inhibit crystallization, which is then very slow in the thinnest films.

  13. Thin film polycrystalline silicon solar cells. Quarterly technical progress report No. 3, 1 April 1980-30 June 1980

    SciTech Connect

    Sarma, K. R.; Rice, M. J.; Legge, R.; Ellis, R. J.

    1980-06-01

    During this third quarter of the program, the high pressure plasma (hpp) deposition process has been thoroughly evaluated using SiHCl/sub 3/ and SiCl/sub 4/ silicon source gases, by the gas chromatographic analysis of the effluent gases from the reactor. Both the deposition efficiency and reactor throughput rate were found to be consistently higher for hpp mode of operation compared to conventional CVD mode. The figure of merit for various chlorosilanes as a silicon source gas for hpp deposition is discussed. A new continuous silicon film deposition scheme is developed, and system design is initiated. This new system employs gas interlocks and eliminates the need for gas curtains which have been found to be problematic. Solar cells (2 cm x 2 cm area) with AM1 efficiencies of up to 12% were fabricated on RTR grain enhanced hpp deposited films. The parameters of a 12% cell under simulated AM1 illumination were: V/sub OC/ = 0.582 volts, J/sub SC/ = 28.3 mA/cm/sup 2/ and F.F. = 73.0%.

  14. Ferroelectric properties of (117)- and (001)-oriented Bi3.25La0.75Ti3O12 polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Sun, Yu-Ming; Chen, Yi-Chan; Gan, Jon-Yiew; Hwang, Jenn-Chang

    2002-10-01

    Highly (117)- and (001)-oriented Bi3.25La0.75Ti3O12 (BLT) thin films were fabricated on Pt/TiO2/SiO2)/Si(100 substrates by chemical solution deposition under the appropriate baking and crystallization conditions. The (117)-oriented BLT films exhibited higher remanent polarization (2Pr=24 muC/cm2), than did (001)-oriented BLT films, which exhibited only a slight amount of polarization (2Pr=6.6 muC/cm2). The results of fatigue and retention tests revealed that neither film was fatigued up to 1 x1010 switching cycles, and the retained charge was unchanged for 1 x104 s.

  15. Tailoring of a metastable material: alfa-FeSi2 thin film

    DOE PAGESBeta

    Cao, Guixin; Singh, David J; Zhang, Xiaoguang; Samolyuk, German D; Qiao, Liang; Parish, Chad M; Ke, Jin; Zhang, Yanwen; Guo, Hangwen; Wang, Wenbin; et al

    2015-01-01

    The epitaxially stabilized metallic -FeSi2 thin films on Si(001) were grown using pulsed laser deposition. While the bulk material of -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. The 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. These experimental results are discussed in terms of the unusual electronic structure of -FeSi2 obtained within density functional calculations and Boltzmann transportmore » calculations with and without strain. Our findings provide an example of a tailored material with interesting physics properties for practical applications.« less

  16. Spalling of a Thin Si Layer by Electrodeposit-Assisted Stripping

    NASA Astrophysics Data System (ADS)

    Kwon, Youngim; Yang, Changyol; Yoon, Sang-Hwa; Um, Han-Don; Lee, Jung-Ho; Yoo, Bongyoung

    2013-11-01

    A major goal in solar cell research is to reduce the cost of the final module. Reducing the thickness of the crystalline silicon substrate to several tens of micrometers can reduce material costs. In this work, we describe the electrodeposition of a Ni-P alloy, which induces high stress in the silicon substrate at room temperature. The induced stress enables lift-off of the thin-film silicon substrate. After lift-off of the thin Si film, the mother substrate can be reused, reducing material costs. Moreover, the low-temperature process expected to be improved Si substrate quality.

  17. High efficiency thin-film crystalline Si/Ge tandem solar cell.

    PubMed

    Sun, G; Chang, F; Soref, R A

    2010-02-15

    We propose and simulate a photovoltaic solar cell comprised of Si and Ge pn junctions in tandem. With an anti-reflection film at the front surface, we have shown that optimal solar cells favor a thin Si layer and a thick Ge layer with a thin tunnel hetero-diode placed in between. We predict efficiency ranging from 19% to 28% for AM1.5G solar irradiance concentrated from 1 approximately 1000 Suns for a cell with a total thickness approximately 100 microm. PMID:20389384

  18. 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.

  19. 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.

  20. Confined phase separation in SiOX nanometric thin layers

    NASA Astrophysics Data System (ADS)

    Roussel, M.; Talbot, E.; Pareige, C.; Pratibha Nalini, R.; Gourbilleau, F.; Pareige, P.

    2013-11-01

    Phase separation in silicon-rich silica/silica multilayers was investigated using Atom Probe Tomography and Atomistic Kinetic Monte Carlo simulation. It is shown that the thickness of silicon-rich silicon oxide sublayers plays an important role during phase transformation. It determines the morphology of Si-rich phase formed after subsequent annealing, which is of prime interest for microelectronic and optoelectronic applications. Monte Carlo simulation reveals that the formation of isolated Si clusters can be achieved even in the case of spinodal decomposition and is directly related to the ratio between the spinodal wavelength and the sublayer thickness.

  1. 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}.

  2. Hysteresis in single and polycrystalline iron thin films: Major and minor loops, first order reversal curves, and Preisach modeling

    NASA Astrophysics Data System (ADS)

    Cao, Yue; Xu, Ke; Jiang, Weilin; Droubay, Timothy; Ramuhalli, Pradeep; Edwards, Danny; Johnson, Bradley R.; McCloy, John

    2015-12-01

    Hysteretic behavior was studied in a series of Fe thin films, grown by molecular beam epitaxy, having different grain sizes and grown on different substrates. Major and minor loops and first order reversal curves (FORCs) were collected to investigate magnetization mechanisms and domain behavior under different magnetic histories. The minor loop coefficient and major loop coercivity increase with decreasing grain size due to higher defect concentration resisting domain wall movement. First order reversal curves allowed estimation of the contribution of irreversible and reversible susceptibilities and switching field distribution. The differences in shape of the major loops and first order reversal curves are described using a classical Preisach model with distributions of hysterons of different switching fields, providing a powerful visualization tool to help understand the magnetization switching behavior of Fe films as manifested in various experimental magnetization measurements.

  3. 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.

  4. 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.

  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. 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

  8. Ion-assisted laser deposition of intermediate layers for YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin film growth on polycrystalline and amorphous substrates

    SciTech Connect

    Reade, R.P.

    1993-11-01

    The growth of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) high-temperature superconductor thin films has largely been limited to deposition on single-crystal substrates to date. In order to expand the range of potential applications, growth on polycrystalline and amorphous substrates is desirable. In particular, the deposition of YBCO thin films with high critical current densities on polycrystalline metal alloys would allow the manufacture of superconducting tapes. However, it is shown that it is not possible to grow YBCO thin films directly on this type of substrate due to chemical and structural incompatibility. This work investigates the use of a yttria-stabilized zirconia (YSZ) intermediate layer to address this problem. An ion-assisted pulsed-laser deposition process is developed to provide control of orientation during the growth of the YSZ layers. The important properties of YBCO and YSZ are summarized and the status of research on thin film growth of these materials is reviewed. An overview of the pulsed-laser deposition (PLD) technique is presented. The use of ion-assisted deposition techniques to control thin film properties is discussed.

  9. Persistent photoconductivity studies in a-Si:H/nc-Si:H thin film superlattices

    NASA Astrophysics Data System (ADS)

    Yadav, Asha; Agarwal, Pratima

    2015-09-01

    The electronic properties of undoped a-Si:H/nc-Si:H superlattice structures have been investigated by photoconductivity measurements. Multilayer structures having alternate layers of a-Si:H and nc-Si:H were deposited on corning 1737 glass substrate by Hot wire chemical vapor deposition technique, keeping the total thickness of films constant at 700 nm. Dark and photo conductivity along with persistent photoconductivity (PPC) are measured in coplanar geometry using Ag paste as electrodes. Quite interestingly room temperature PPC has been observed in these undoped a-Si:H/nc-Si:H superlattice structures. PPC decay time constant, its dependence on exposure time, electric field, number of periods and annealing temperature have been studied in detail. The origin of PPC is understood in terms of competition between carriers transport in the lateral direction due to external field and along the depth due to band bending at a-Si:H/nc-Si:H interfaces. Carriers trapped in the interfaces states or the separation of carriers due to band bending are likely to be responsible for observed PPC.

  10. Photoinduced current transient spectroscopy technique applied to the study of point defects in polycrystalline CdS thin films

    SciTech Connect

    El Akkad, Fikry; Ashour, Habib

    2009-05-01

    CdS thin films of variable thickness (between 160 and 1200 nm) were prepared using rf magnetron sputtering. X-ray diffraction measurements showed that the films have hexagonal structure and that the crystallites are preferentially oriented with the <002> axis perpendicular to the substrate surface. The results of electrical conductivity measurements as a function of film thickness and of temperature provide evidence that the conductivity is controlled by a thermally activated mobility in the presence of an intergrain barrier. The room temperature barrier height phi decreases with the increase in film thickness. Values of phi between 0 and 0.25 eV were determined. Photoinduced current transient spectroscopy performed on five samples having different thicknesses showed the presence of 11 traps with activation energies in the range 0.08-1.06 eV; deeper traps being observed on thinner films. By comparison with literature results, seven traps are attributed to native defects and foreign impurities (mainly Cu, Au, and Ag). Four other traps, not previously observed, are attributed to residual defects. The observation that deeper traps are detected in samples with larger barrier heights has been discussed and interpreted in terms of the energy band profile near the grain boundary.

  11. Growth of 3C-SiC( 1 0 0 ) thin films on Si( 1 0 0 ) by the molecular ion beam deposition

    NASA Astrophysics Data System (ADS)

    Matsumoto, Takashi; Kiuchi, Masato; Sugimoto, Satoshi; Goto, Seiichi

    2001-11-01

    Silicon carbide (SiC) thin films were produced on Si(1 0 0) at low growth temperatures of 750-1000°C, using the molecular ion beam deposition (IBD) technique with a precursor of organosilicon ions. The ions extracted at 25 keV were mass selected, and decelerated to 100 eV. The precursor of methylsilicenium ions (SiCH 3+), which has a Si-C bond in the molecular structure, was generated from dimethylsilane (SiH 2(CH 3) 2). The energy distribution of SiCH 3+ ions was measured by a PPM421 plasma process monitor. It was confirmed that the energy distributions were 100±1 eV. The chemical bondings and surface structures of SiC thin films were analyzed by Raman spectroscopy and reflection high-energy electron diffraction (RHEED). In the Raman spectrum, a peak at 796 cm -1 was assigned to transverse optic phonon scattering in 3C-SiC. As a result of the analysis of RHEED patterns, 3C-SiC(1 0 0) were formed on Si(1 0 0) substrates. Using the molecular IBD technique with the precursor of methylsilicenium ions, the formation of SiC thin films is available on Si(1 0 0) at low temperature (750°C).

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. Nanostructures based in boro nitride thin films deposited by PLD onto Si/Si3N4/DLC substrate

    NASA Astrophysics Data System (ADS)

    Román, W. S.; Riascos, H.; Caicedo, J. C.; Ospina, R.; Tirado-Mejía, L.

    2009-05-01

    Diamond-like carbon and boron nitride were deposited like nanostructered bilayer on Si/Si3N4 substrate, both with (100) crystallographic orientation, these films were deposited through pulsed laser technique (Nd: YAG: 8 Jcm-2, 9ns). Graphite (99.99%) and boron nitride (99.99%) targets used to growth the films in argon atmosphere. The thicknesses of bilayer were determined with a perfilometer, active vibration modes were analyzed using infrared spectroscopy (FTIR), finding bands associated around 1400 cm-1 for B - N bonding and bands around 1700 cm-1 associated with C=C stretching vibrations of non-conjugated alkenes and azometinic groups, respectively. The crystallites of thin films were analyzed using X-ray diffraction (XRD) and determinated the h-BN (0002), α-Si3N4 (101) phases. The aim of this study is to relate the dependence on physical and chemical characteristics of the system Si/Si3N4/DLC/BN with gas pressure adjusted at the 1.33, 2.67 and 5.33 Pa values.

  17. 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.

  18. 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.

  19. 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.

  20. Heteroepitaxial reflector for the fabrication of Si thin film photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Asante, Kofi; Cross, Michael; Varhue, Walter

    2013-10-01

    Thin film crystalline Si diodes are a viable solution to the goal of fabricating economical photovoltaic (PV) cells. A functional, light trapping, thin film PV was fabricated with a heteroepitaxial (YSZ) reflecting layer which also served as a complaint layer for the growth of crystalline Si or SiGe active layers. X-ray analysis confirmed that the deposited semiconductor layers were crystalline. It was observed that the light trapping PV cell formed with the YSZ reflector layer increased the short circuit current under illumination by 22% over that fabricated without the YSZ reflector layer. It was further observed that the surface texture in the YSZ layer contributed to both the ability to grow crystalline semiconductor layers and to act as an effective light trapping structure.

  1. Photovoltaic characteristics in polycrystalline and epitaxial (Pb0.97La0.03)(Zr0.52Ti0.48)O3 ferroelectric thin films sandwiched between different top and bottom electrodes

    NASA Astrophysics Data System (ADS)

    Qin, Meng; Yao, Kui; Liang, Yung C.

    2009-03-01

    Photovoltaic responses, including photovoltage, photocurrent, illuminated J-V curve, and light-to-electricity power conversion efficiency, were investigated in chemical-solution-derived polycrystalline and epitaxial (Pb0.97La0.03)(Zr0.52Ti0.48)O3 (PLZT) thin films sandwiched between different metal and oxide electrodes. The epitaxial PLZT films with Au/PLZT/Nb-doped SrTiO3 structure exhibited about one order of magnitude larger photocurrent and efficiency over the randomly oriented polycrystalline PLZT films with Au/PLZT/Pt structure due to the high crystalline quality with the reduced defects and enhanced depolarization field. The illuminated J-V curve was approximately linear for both polycrystalline and epitaxial PLZT thin films. The nonzero photovoltaic outputs in the unpoled films were induced by asymmetric interfacial Schottky barriers. The illuminated J-V curve shifted toward the positive voltage direction after positive poling and toward the negative voltage direction after negative poling, and the enhancement of efficiency only occurred when the polarization direction accorded with the direction of Schottky barrier difference at the two electrode interfaces. Thickness dependences of photovoltage, photocurrent, and light-to-electricity conversion efficiency were also examined. It was observed that photovoltage linearly increased with film thickness while both photocurrent and efficiency exponentially increased with the decrease in thickness. Furthermore, at a fixed small film thickness, efficiency was also found to increase reciprocally with the decrease of incident UV intensity.

  2. 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

  3. 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.

  4. Low temperature Ti-Si-C thin film deposition by ion beam assisted methods

    NASA Astrophysics Data System (ADS)

    Twardowska, Agnieszka; Rajchel, Boguslaw; Jaworska, Lucyna

    2010-11-01

    Thin, multiphase Ti-Si-C coatings were formed by IBSD or by IBAD methods on AISI 316L steel substrates in room temperature, using single Ti3SiC2 target. In those methods the TiXSiCY coatings were formed from the flux of energetic atoms and ions obtained by ion sputtering of the Ti3SiC2 compound sample. As sputtering beam the beam of Ar+ ions at energy of 15keV was applied. In the IBAD method the dynamically formed coatings were additionally bombarded by beam of Ar+ ions at energy of 15keV. The ion beams parameters were obtained by using Monte Carlo computer simulations. The morphology (SEM, TEM), chemical (EDS/EDX) and phase composition (XRD) examinations of formed coatings were provided as well as confocal Raman microspectroscopy. Analyzed coatings were relatively thin (150nm-1μm), flat and dense. XRD analysis indicated in amorphous TiSi, the traces of Ti5Si3 and other phases from Ti-Si-C system (TiSi, TiSi2,Ti3SiC2). For chemical bonds investigation, the laser beam with length of 532nm was used. Those analyses were performed in the low (LR) or in high (HR) resolution modes in room temperature and in 4000C. In the HR mode the spectral resolution was close to 2 cm-1. In Raman spectra peaks at: 152cm-1, 216cm-1, 278cm-1, 311 cm-1, 608cm-1, 691cm-1 were recorded. Nanoindentation tests were done on coated and uncoated substrates with diamond, Berkovich-type indenter. Vickers hardness HIT and reduced elastic modulus EIT were calculated using Olivier& Pharr method. HIT for coated substrates was in the range 2.7 to 5.3 GPa, EIT was 160 GPa.

  5. 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.

  6. Bondability of Al-Si thin film in thermosonic gold wire bonding. [integrated circuits

    NASA Technical Reports Server (NTRS)

    Nakagawa, K.; Miyata, K.; Banjo, T.; Shimada, W.

    1985-01-01

    The bondability of two kinds of Al-Si thin films in thermosonic Au wire bonding was examined by means of microshear tests. One type of film was formed by sputtering an Al-2% Si alloy, and the other was formed by depositing an 0.05 micrometer-thick polysilicon layer on SiO2 by chemical vapor deposition (CVD) and then depositing a 1.2 micrometer-thick Al layer on them by evaporation. After heat-treatment at 450 deg for 30 min., Si in the Al-Si film crystallized. The grain size of the crystallized Si affects the thermosonic wire bondability, i.e., for Al-2% Si sputtered films, good bondability was obtained under relatively small (1.0 micrometer) grain size conditions. In the successive layer process, on the other hand, the grain size of crystallized Si varies with the polysilicon CVD temperature. The optimum CVD temp. was determined from the standpoint of bondability with respect to grain size.

  7. The effects of spatial location of defect states on the switching characteristics of amorphous and polycrystalline silicon thin film transistors: A numerical simulation using AMPS 2-D

    SciTech Connect

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

    1994-06-01

    We demonstrate a two-dimensional device simulator for MOSFET structures that incorporates models for defect distributions and show predicted effects on device switching performance for various spatial distributions of defects in amorphous and polycrystalline silicon.

  8. 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)

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Spectroscopic and microscopic studies of self-assembled nc-Si/a-SiC thin films grown by low pressure high density spontaneous plasma processing.

    PubMed

    Das, Debajyoti; Kar, Debjit

    2014-12-14

    In view of suitable applications in the window layer of nc-Si p-i-n solar cells in superstrate configuration, the growth of nc-Si/a-SiC composite films was studied, considering the trade-off relation between individual characteristics of its a-SiC component to provide a wide optical-gap and electrically conducting nc-Si component to simultaneously retain enough crystalline linkages to facilitate proper crystallization to the i-nc-Si absorber-layer during its subsequent growth. Self-assembled nc-Si/a-SiC thin films were spontaneously grown by low-pressure planar inductively coupled plasma CVD, operating in electromagnetic mode, providing high atomic-H density. Spectroscopic simulations of ellipsometry and Raman data, and systematic chemical and structural analysis by XPS, TEM, SEM and AFM were performed. Corresponding to optimized inclusion of C essentially incorporated as Si-C bonds in the network, the optical-gap of the a-SiC component widened, void fraction including the incubation layer thickness reduced. While the bulk crystallinity decreased only marginally, Si-ncs diminished in size with narrower distribution and increased number density. With enhanced C-incorporation, formation of C-C bonds in abundance deteriorates the Si continuous bonding network and persuades growth of an amorphous dominated silicon-carbon heterostructure containing high-density tiny Si-ncs. Stimulated nanocrystallization identified in the Si-network, induced by a limited amount of carbon incorporation, makes the material most suitable for applications in nc-Si solar cells. The novelty of the present work is to enable spontaneous growth of self-assembled superior quality nc-Si/a-SiC thin films and simultaneous spectroscopic simulation-based optimization of properties for utilization in devices. PMID:25342429

  14. 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.

  15. Miniaturized fracture tests for thin-walled tubular SiC specimens

    SciTech Connect

    Byun, Thak Sang; Lara-Curzio, Edgar; Lowden, Richard Andrew; Snead, Lance Lewis; Katoh, Yutai

    2007-01-01

    Two testing methods have been developed for miniaturized tubular specimens to evaluate the fracture stress of chemically vapor deposited (CVD) SiC coatings in nuclear fuel particles. In the first method hoop stress is applied to a thin-walled tubular specimen by internal pressurization using a polyurethane insert. The second method is a crushing technique, in which tubular specimen is fractured by diametrical compressive loading. Tubular SiC specimens with a wall thickness of about 100 {micro}m and inner diameters of about 0.9 mm (SiC-A) and 1 mm (SiC-B) were extracted from surrogate nuclear fuels and tested using the two test methods. Mean fracture stresses of 239, 263, and 283 MPa were measured for SiC-A and SiC-B by internal pressurization, and SiC-A by diametrical loading, respectively. In addition, size effects in the fracture stress were investigated using tubular alumina specimens with various sizes. A significant size effect was found in the experimental data and was also predicted by the effective area-based scaling method.

  16. Crossover between silicene and ultra-thin Si atomic layers on Ag(111) surfaces

    NASA Astrophysics Data System (ADS)

    Guo, Zhi-Xin; Oshiyama, Atsushi

    2015-04-01

    We report on total-energy electronic structure calculations in the density-functional theory performed for the ultra-thin atomic layers of Si on Ag(111) surfaces. We find several distinct stable silicene structures: \\sqrt{3}× \\sqrt{3}, 3 × 3, \\sqrt{7}× \\sqrt{7} with the thickness of Si increasing from monolayer to quad-layer. The structural bistability and tristability of the multilayer silicene structures on Ag surfaces are obtained, where the calculated transition barriers infer the occurrence of the flip-flop motion at low temperature. The calculated scanning tunneling microscope (STM) images agree well with the experimental observations. We also find the stable existence of 2 × 1 π-bonded chain and 7 × 7 dimer-adatom-stacking fault Si(111)-surface structures on Ag(111), which clearly shows the crossover of silicene-silicon structures for the multilayer Si on Ag surfaces. We further find the absence of the Dirac states for multilayer silicene on Ag(111) due to the covalent interactions of the silicene-Ag interface and Si-Si interlayer. Instead, we find a new state near the Fermi level composed of π orbitals located on the surface layer of \\sqrt{3}× \\sqrt{3} multilayer silicene, which satisfies the hexagonal symmetry and exhibits the linear energy dispersion. By examining the electronic properties of 2 × 1 π-bonded chain structures, we find that the surface-related π states of multilayer Si structures are robust on Ag surfaces.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Recent advances in the transparent conducting ZnO for thin-film Si solar cells

    NASA Astrophysics Data System (ADS)

    Moon, Taeho; Shin, Gwang Su; Park, Byungwoo

    2015-11-01

    The key challenge for solar-cell development lies in the improvement of power-conversion efficiency and the reduction of fabrication cost. For thin-film Si solar cells, researches have been especially focused on the light trapping for the breakthrough in the saturated efficiencies. The ZnO-based transparent conducting oxides (TCOs) have therefore received strong attention because of their excellent light-scattering capability by the texture-etched surface and cost effectiveness through in-house fabrication. Here, we have highlighted our recent studies on the transparent conducting ZnO for thin-film Si solar cells. From the electrical properties and their degradation mechanisms, bilayer deposition and organic-acid texturing approaches for enhancing the light trapping, and finally the relation between textured ZnO and electrical cell performances are sequentially introduced in this review article. [Figure not available: see fulltext.

  3. 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.

  4. Optical properties of thin GaSe/n-Si(111) films

    SciTech Connect

    Kisselyuk, M. P.; Vlasenko, O. I.; Gentsar, P. O. Vuychik, M. V.; Zayats, M. S.; Kruglenko, I. V.; Litvin, O. S.; Kryskov, Ts. A.

    2010-08-15

    Morphological and optical studies (ellipsometry and reflectance spectroscopy in the ranges 400-750 nm and 1.4-25 {mu}m) of thin GaSe films fabricated by thermal evaporation on the n-Si (111) single-crystal substrates are reported. The film thickness was 15-60 nm. It is established that, in the initial stage of growth, the growth of GaSe on the n-Si (111) substrates occurs via formation of islands (three-dimensional growth). It is shown that, as the thickness increases, the physical parameters of the film change and the films approach single crystals in crystalline and energy band structure. For films with a thickness of 60 nm, the reflectance band peak is attributed to indirect optical transitions enhanced by reflection from the film-substrate interface. From the results of optical studies, quantum effects in the surface region of the thin films are conjectured.

  5. 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.

  6. 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.

  7. Ultra-thin low loss Si3N4 optical waveguides at 1310 nm

    NASA Astrophysics Data System (ADS)

    Lim, Soon Thor; Gandhi, Alagappan; Png, Ching Eng; Lu, Ding; Ang, Norman Soo Seng; Teo, Ee Jin; Teng, Jinghua

    2014-03-01

    Recent advances in optical waveguides have brought long-awaited technologies closer to practical realization. Although the concept of a single-mode (SM) waveguide has been around for a while, SM condition usually posed very stringent conditions in fabrication for small waveguides. Researchers have developed low loss silicon nitride (Si3N4) at 1550nm wavelength, the developments in specific application have down converted to 1310nm (O-band) so they do not have to compete with internet data for bandwidth and could share the existing optical fiber infrastructure. However, wavelengthdemultiplexer technology at this band is not readily commercial available. Custom-made O-band optical devices for wavelength-demultiplexing have typical losses. Such high losses deplete more than 75% of the already-scarce photons. We studied Si3N4 channel waveguide with ultra-thin slab for (SM) condition at 1310nm wavelength using finite element method (FEM) and 3-D imaginary beam propagation method (IDBPM). We have shown that SM condition is possible for ultra-thin slab with wide waveguide width; such condition can ease the constraint of photolithography, allowing deposition of thin Si3N4 layer to be accomplished in minutes. Studies show that for ultra-thin layer, for example, at 60nm, we can achieve a wide range of widths that fulfilled the SM condition, ranging from 2μm to 5μm. SM condition becomes more stringent when the Si3N4 layer increases. Substrate losses are estimated at 0.001 dB/cm, 0.003 dB/cm, and 0.1 dB/cm for slab height at 100nm, 80nm, and 60nm respectively.

  8. 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.

  9. Decoupled front/back dielectric textures for flat ultra-thin c-Si solar cells.

    PubMed

    Isabella, Olindo; Vismara, Robin; Ingenito, Andrea; Rezaei, Nasim; Zeman, M

    2016-03-21

    The optical analysis of optically-textured and electrically-flat ultra-thin crystalline silicon (c-Si) slabs is presented. These slabs were endowed with decoupled front titanium-dioxide (TiO2) / back silicon-dioxide (SiO2) dielectric textures and were studied as function of two types of back reflectors: standard silver (Ag) and dielectric modulated distributed Bragg reflector (MDBR). The optical performance of such systems was compared to that of state-of-the-art flat c-Si slabs endowed with so-called front Mie resonators and to those of similar optical systems still endowed with the same back reflectors and decoupled front/back texturing but based on textured c-Si and dielectric coatings (front TiO2 and back SiO2). Our optimized front dielectric textured design on 2-µm thick flat c-Si slab with MDBR resulted in more photo-generated current density in c-Si with respect to the same optical system but featuring state-of-the-art Mie resonators ( + 6.4%), mainly due to an improved light in-coupling between 400 and 700 nm and light scattering between 700 and 1050 nm. On the other hand, the adoption of textured dielectric layers resulted in less photo-generated current density in c-Si up to -20.6% with respect to textured c-Si, depending on the type of back reflector taken into account. PMID:27136888

  10. The hybrid photocatalyst of TiO2-SiO2 thin film prepared from rice husk silica

    NASA Astrophysics Data System (ADS)

    Klankaw, P.; Chawengkijwanich, C.; Grisdanurak, N.; Chiarakorn, Siriluk

    2012-03-01

    The TiO2-SiO2 thin film was prepared by self-assembly method by mixing SiO2 precursor with titanium precursor solution and aged to obtain a co-precipitation of silica and titanium crystals. Dip coating method was applied for thin film preparation on glass slide. The X-ray diffraction (XRD) of the self-assembly thin film had no characteristic property of SiO2 and even anatase TiO2 but indicated new crystal structure which was determined from the Fourier Transform Infrared Spectrophotometer (FTIR) as a hybridized Ti-O-Si bonding. The surface area and surface volume of the self-assembly sample were increased when SiO2 was incorporated into the film. The self-assembly TiO2-SiO2 thin film exhibited the enhanced photocatalytic decolorization of methylene blue (MB) dye. The advantages of SiO2 are; (1) to increase the adsorbability of the film and (2) to provide the hydroxyl radical to promote the photocatalytic reaction. The self-assembly thin film with the optimum molar ratio (SiO2:TiO2) as 20:80 gave the best performance for photocatalytic decolorization of MB dye with the overall efficiency of 81%.

  11. 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.

  12. Investigation of the kinetics of surface-limited thin film growth of SiGe alloys

    SciTech Connect

    Sharp, J.W. . Dept. of Physics and Astronomy); Eres, G. )

    1992-11-01

    The kinetics of surface-limited thin film growth of SiGe alloys was investigated by time-resolved surface differential reflectometry. The source gas, mixtures of disilane and digermane in ratios from 1:1 to 6:1 in helium carrier gas, was delivered to a heated substrate by a fast-acting pulsed molecular jet valve. The adsorption and desorption kinetics were determined from the surface differential reflectance signal obtained using a polarized, high-stability HeNe probe laser. Thin film growth was studied in the temperature range of 400--600[degrees]C on Si(001) substrates. Preferential incorporation of digermane into the film produces an alloy composition that depends upon but does not mirror the gas composition. For all gas mixtures, there is a strong temperature dependence of the rate at which the adsorption layer decomposes into film plus by-product. The kinetic data and the alloy compositions provide a basis for deducing some of the characteristics of the reaction sequence that leads to SiGe alloy thin film growth.

  13. Investigation of the kinetics of surface-limited thin film growth of SiGe alloys

    SciTech Connect

    Sharp, J.W.; Eres, G.

    1992-11-01

    The kinetics of surface-limited thin film growth of SiGe alloys was investigated by time-resolved surface differential reflectometry. The source gas, mixtures of disilane and digermane in ratios from 1:1 to 6:1 in helium carrier gas, was delivered to a heated substrate by a fast-acting pulsed molecular jet valve. The adsorption and desorption kinetics were determined from the surface differential reflectance signal obtained using a polarized, high-stability HeNe probe laser. Thin film growth was studied in the temperature range of 400--600{degrees}C on Si(001) substrates. Preferential incorporation of digermane into the film produces an alloy composition that depends upon but does not mirror the gas composition. For all gas mixtures, there is a strong temperature dependence of the rate at which the adsorption layer decomposes into film plus by-product. The kinetic data and the alloy compositions provide a basis for deducing some of the characteristics of the reaction sequence that leads to SiGe alloy thin film growth.

  14. A blazed grating for light trapping in a-Si thin-film solar cells

    NASA Astrophysics Data System (ADS)

    Ji, L.; Varadan, V. V.

    2012-09-01

    A blazed grating has been studied to improve light absorption in thin-film solar cells (TFSCs). The grating is a periodic arrangement of wedges made of aluminum zinc oxide (AZO) that also serves as the back spacer. The absorber layer of the photovoltaic (PV) device can be made of inorganic or organic semiconductor material. Here we study hydrogenated amorphous silicon (a-Si:H) and nano-crystalline Si (nc-Si). Full wave, finite element simulations were performed to optimize the design for the highest short circuit current (Jsc). The Jsc of the optimized 1D grating design was 16.05 mA cm-2 for TE polarization and 15.18 mA cm-2 for TM polarization, with an effective a-Si:H layer thickness of only 277 nm. As compared to a planar cell with the same volume of a-Si:H, the enhancement of Jsc by the 1D grating design was 27.6% for TE polarization and 20.7% for TM polarization. We extended this design to a 2D grating structure that was less sensitive to polarization as compared to the 1D grating design. With an equivalent a-Si:H layer thickness of 322 nm, the optimized design yielded a Jsc of 17.16 mA cm-2. The blazed grating surface can be fabricated using the glancing angle deposition method.

  15. 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.

  16. Growth of polycrystalline Heusler alloys for spintronic devices

    NASA Astrophysics Data System (ADS)

    Sagar, J.; Yu, C. N. T.; Lari, L.; Hirohata, A.

    2014-07-01

    We have prepared polycrystalline Co2FeSi thin films on a number of seed layers to optimize their structural and magnetic properties. Using a Cr/Ag combined seed layer, films have been produced with extremely low interfacial roughness (<1 nm) and controllable coercivities in the range 12-27 Oe. Such a structure would be suitable for the free layer in a spintronic device. Using a NiCr seed layer and IrMn as an antiferromagnetic layer a small exchange bias of ˜30 Oe has been achieved. However the use of a 0.5 nm Mn layer at the IrMn/Co2FeSi interface increases the exchange bias (Hex) to 375 Oe after annealing. This structure would be suitable for the pinned layer in a spintronic device.

  17. Thermochromic properties of VO2 thin film on SiNx buffered glass substrate

    NASA Astrophysics Data System (ADS)

    Koo, Hyun; You, HyunWoo; Ko, Kyeong-Eun; Kwon, O.-Jong; Chang, Se-Hong; Park, Chan

    2013-07-01

    VO2 thin films were deposited on soda lime glass substrates with silicon nitride sodium-diffusion barrier layer as diffusion barrier, in order to investigate the effect of sodium ion diffusion on the formation of VO2. SiNx layers with thicknesses over 30 nm were found to successfully prevent sodium ion diffusion in VO2 thin film and also contribute to the formation of VO2 thin film, which was confirmed by XRD spectra and XPS measurements. The change of infrared transmittance at 2500 nm wavelength with temperature change from room temperature to 80 °C was increased significantly, and the optical hysteresis width of the sample decreased by almost 6 K as well. The results suggest that applying diffusion barrier can improve the thermochromic properties of the VO2 films for energy-saving smart coatings, and silicon nitride can be one of the effective materials to prevent sodium ion diffusion.

  18. Nanoporous SiO2 thin films made by atomic layer deposition and atomic etching.

    PubMed

    Ghazaryan, Lilit; Kley, E-Bernhard; Tünnermann, Andreas; Szeghalmi, Adriana

    2016-06-24

    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. PMID:27176497

  19. Thermally activated electron capture by mobile protons in SiO{sub 2} thin films

    SciTech Connect

    Vanheusden, K.; Karna, S.P.; Pugh, R.D.; Warren, W.L.; Fleetwood, D.M.; Devine, R.A.

    1998-01-01

    The annihilation of mobile protons in thin SiO{sub 2} films by capture of ultraviolet-excited electrons has been analyzed for temperatures between 77 and 500 K. We observe a strong increase in proton annihilation with increasing temperature, and derive an activation energy for electron capture of about 0.2 eV. Based on quantum chemical [(OH){sub 3}Si]{sub 2}{endash}O{endash}H{sup +} cluster calculations, we suggest photoexcitation of electrons from excited vibrational states of the ground electronic (valence band) state to a nearby excited electronic (SiO{sub 2} gap) state. It is argued that the latter excitation can result in H{sup 0} formation at elevated temperatures. {copyright} {ital 1998 American Institute of Physics.}

  20. Oxidation induced internal exoemission in thin film Mg/Si Schottky diodes

    NASA Astrophysics Data System (ADS)

    Nienhaus, Hermann

    2005-03-01

    When thin film Mg/p-Si(111) diodes are exposed to oxygen molecules an internal reverse current is observed. Such chemicurrents are due to electron-hole pairs created by the chemical reaction at the metal surface and indicate the non-adiabatic character of chemical energy dissipation. The transient of the current represents the kinetics of the Mg oxidation process and may be explained by a nucleation-and-growth model. Two types of Mg/Si diodes with different homogeneous Schottky barrier heights of 0.7 and 0.8 eV, respectively, could be fabricated by modifying the Mg/Si interface. A dependence between the homogeneous barrier height and the sensitivity of the diode to detect the chemically induced hot charge carriers can be demonstrated. The energy distribution of the internally excited charge carriers deduced from the data may be described by a Boltzmann exponential function with an effective electron temperature of approximately 1600 K.

  1. 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.

  2. 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.

  3. Growth temperature effect on a-Si:H thin films studied by constant photocurrent method

    NASA Astrophysics Data System (ADS)

    Wadibhasme, N. A.; Dusane, R. O.

    2013-02-01

    Hydrogenated amorphous silicon (a-Si:H) thin films are synthesized by tuning different process parameters among which substrate temperature of film growth plays an important role in monitoring the device quality of the film. In this paper we have used the constant photocurrent method (CPM) to study the effect of growth temperature on the electronic and optical parameters of a-Si:H films at different photon energies. This technique primarily measures the absorption coefficient which is a result of different electronic transitions that contribute to the photocurrent. The nature of absorption coefficient changes with growth temperature that explicitly provides the information about the density of defect states present in the mid gap of a-Si:H.

  4. ToF-MEIS stopping measurements in thin SiC films

    NASA Astrophysics Data System (ADS)

    Linnarsson, M. K.; Khartsev, S.; Primetzhofer, D.; Possnert, G.; Hallén, A.

    2014-08-01

    Electronic stopping in thin, amorphous, SiC films has been studied by time-of-flight medium energy ion scattering and conventional Rutherford backscattering spectrometry. Amorphous SiC films (8, 21 and 36 nm) were prepared by laser ablation using a single crystalline silicon carbide target. Two kinds of substrate films, one with a lower atomic mass (carbon) and one with higher atomic mass (iridium) compared to silicon has been used. Monte Carlo simulations have been used to evaluate electronic stopping from the shift in energy for the signal scattered from Ir with and without SiC. The two kinds of samples are used to illustrate the strength and challenges for ToF-MEIS compared to conventional RBS.

  5. Structural properties and preparation of Si-rich Si1-xCx thin films by radio-frequency magnetron sputtering

    NASA Astrophysics Data System (ADS)

    He, Yisong; Ye, Chao; Wang, Xiangying; Gao, Mingwei; Guo, Jiaming; Yang, Peifang

    2016-02-01

    Si-rich silicon carbide (Si1-xCx) thin films were prepared by radio-frequency (2 MHz, 13.56 MHz and 27.12 MHz) magnetron sputtering. Their structural properties were investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM). The effect of ions energy on films deposition was also analyzed by retarding field energy analyzer. The results show that the films compositions are related to the energy of ions impacting the SiC target. At the lower sputtering power, Si-rich Si1-xCx (1-x = 0.57-0.90) thin films can be well deposited.

  6. 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.

  7. 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.

  8. Local retention behaviors of epitaxial and polycrystalline PbMg1/3Nb2/3O3-PbTiO3 thin films by scanning force microscopy

    NASA Astrophysics Data System (ADS)

    Lee, J. H.; Choi, M. R.; Oh, Y. J.; Jo, W.

    2007-08-01

    The authors report the results of retention in epitaxial and polycrystalline PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT) thin films on SrRuO3 (SRO) and Pt. The SRO electrodes were deposited by pulsed laser deposition and the PMN-PT thin films were coated by a sol-gel method. Local poling behaviors of the PMN-PT domains were investigated as a function of time in both single-poled and reverse-poled regions by scanning force microscopy. An extended exponential decay is observed in the PMN-PT/SRO heterostructures while a fluctuated relaxation is shown in the PMN-PT/Pt films, suggesting that crystal orientation and grain growth is critical to understand retention of relaxor ferroelectrics.

  9. Status of polycrystalline solar cell technologies

    NASA Astrophysics Data System (ADS)

    Kapur, Vijay K.; Basol, Bulent M.

    Thin-film cadmium telluride (CdTe) and thin-film copper indium diselenide (CIS) solar cells are discussed. The issues these technologies face before commercialization are addressed. High-efficiency (15-18 percent) polycrystalline silicon modules could dominate the market in the near future, and impressive results for thin-film CdTe and CIS solar cells and their outdoor stability can attract increased interest in these solar cells, which will accelerate their development.

  10. 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.

  11. 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.

  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. 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

  14. Characterization of thick and thin film SiCN for pressure sensing at high temperatures.

    PubMed

    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

  15. Dissociation of Si{sup +} ion implanted and as-grown thin SiO{sub 2} layers during annealing in ultra-pure neutral ambient by emanation of SiO

    SciTech Connect

    Beyer, V.; Borany, J. von; Heinig, K.-H.

    2007-03-01

    We have observed a very inhomogeneous dissociation of stoichiometric and non-stoichiometric thin SiO{sub 2} layers (thermally grown on Si substrates) during high temperature annealing at a low partial pressure of oxygen. During this process some silicon of the (100)Si substrate and, in case of Si ion implantation, and additionally, excess Si is consumed. The SiO{sub 2} dissociation has been studied by electron microscopy and Rutherford backscattering spectrometry. Large holes (>1 {mu}m) in non-implanted oxide layers have been observed which evolve probably from defects located at the Si/SiO{sub 2} interface. For Si implanted SiO{sub 2} additionally the formation of voids within the oxide during annealing has been observed preferably at the position of the implanted Si excess. Oxygen vacancies are possibly emitted from Si/SiO{sub 2} interfaces into the oxide and migrate through SiO{sub 2} with long-range distortions of the oxide network. In that way the hole and void formation in the oxide can be explained by oxygen-vacancy formation, migration and silicon-monoxide (SiO) emanation. As a driving force for growth of the large holes we identified oxygen diffusion from the Si/SiO{sub 2} interface to the bare Si surface. This surface is a sink of oxygen diffusion due to the emanation of volatile SiO, whereas the Si/SiO{sub 2} interface serves as an oxygen source. The predicted mechanism is consistent with the geometry of the holes in the SiO{sub 2} layer.

  16. 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.

  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. 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.

  19. 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.

  20. 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.

  1. High frequency magnetic properties of FeCoSiB thin films

    NASA Astrophysics Data System (ADS)

    Hadimani, Ravi; Han, Mangui; Jiles, David; Magnetics Research Group Team; Han Team, Prof.

    2014-03-01

    Currently, high frequency properties of magnetic materials are critical for the performances of many mobile electronic devices. Larger permeability can be obtained in ferromagnetic thin films that are suitable for high frequency applications. We report the high frequency properties of FeCoSiB thin films with different treatments and with different structures (single layer or FeCoBSi/SiO2 multilayer). For instance, we have studied the annealing effects on the microwave permeability values. It is found that the as-prepared films and films annealed at 300 °C for 1 hour are found in amorphous states and to be anisotropic in static magnetic properties. Nanocrystalline grains have been found in the films annealed at 400 °C for 1 hour, which are isotropic in magnetic properties. With increasing the annealing temperature, the coercivity and saturation magnetic fields are found decreasing. The resonance frequency shows the same varying trend as the saturation magnetic fields. Very large microwave magnetic losses have been found in all the films, which indicate that FeCoSiB films have potential applications in microwave noise attenuation. This work was supported by the Research Fund for International Young Scientists of NSFC (No. 61250110544), National Natural Science Foundation of China (No. 61271039), and the Program for New Century Excellent Talents in Universities (NCET-11-0060).

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. Passively mode-locked Yb3+:Sc2SiO5 thin-disk laser.

    PubMed

    Wentsch, Katrin Sarah; Zheng, Lihe; Xu, Jun; Ahmed, Marwan Abdou; Graf, Thomas

    2012-11-15

    Experimental investigations on a passively mode-locked Yb(3+):Sc(2)SiO(5) (Yb:SSO) thin-disk laser are presented. The mode-locking was performed with a commercially available semiconductor saturable absorber mirror. The laser was operated at a repetition rate of 27 MHz and generated a maximum average output power of 27.8 W with a pulse duration of 298 fs. The spectrum was centered at 1036 nm. The beam was measured to be close to diffraction limited (M(2)<1.1). The promising results confirm the suitability of Yb:SSO for mode-locked thin-disk laser oscillators and indicate that this comparably new material deserves further attention by optimizing the crystal quality (growth and polishing) and doping levels for further power scaling. PMID:23164901

  8. 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.

  9. Effect of annealing on the superconducting properties of a-NbxSi1-x thin films

    NASA Astrophysics Data System (ADS)

    Crauste, O.; Gentils, A.; Couëdo, F.; Dolgorouky, Y.; Bergé, L.; Collin, S.; Marrache-Kikuchi, C. A.; Dumoulin, L.

    2013-04-01

    a-NbxSi1-x thin films with thicknesses down to 25 Å have been structurally characterized by transmission electron microscopy measurements. As-deposited or annealed films are shown to be continuous and homogeneous in composition and thickness, up to an annealing temperature of 500 ∘C. We have carried out low-temperature transport measurements on these films close to the superconductor-to-insulator transition (SIT) and shown a qualitative difference between the effect of annealing or composition and a reduction of the film thickness on the superconducting properties of a-NbSi. These results question the pertinence of the sheet resistance R□ as the relevant parameter to describe the SIT.

  10. Transparent conducting CeO{sub 2}-SiO{sub 2} thin films

    SciTech Connect

    Zhu, B.; Luo, Z.; Xia, C.

    1999-08-01

    A new type of transparent thin films, based on two-phase materials of CeO{sub 2}-SiO{sub 2}, was developed. The films were prepared on indium time oxide (ITO)-coated glass via a sol-gel process. A study of cyclic voltammetry was conducted on the films, using an electrolyte of 1 M LiClO{sub 4} in propylene carbonate. Li{sup +} insertion/disinsertion took place in the film. For a 24 nm thick GeO{sub 2}-SiO{sub 2} film with 50% silica, the capacity of the charge exchange reached 6--7 nC/CM{sup 2}. After 380 cycles, the charge density dropped by {approximately}30%. In both Li{sup +}-intercalated and free states, the films were highly transparent for visible light. Such films have potential application in counter-electrodes for electrochromic smart windows and other electrochemical devices.

  11. 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.

  12. Study of the optical properties of SiOxNy thin films by effective medium theories

    NASA Astrophysics Data System (ADS)

    Tan, X.; Wojcik, J.; Mascher, P.

    2004-07-01

    Silicon oxynitride (SiOxNy) films were deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) and covered the entire composition range from silicon dioxide to silicon nitride. The composition of the films was determined by Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA), and elastic recoil detection (ERD). These techniques provide the absolute areal concentrations of all elements, including silicon, oxygen, nitrogen, and hydrogen. Additionally, Fourier transform infrared (FTIR) spectroscopy and ellipsometry measurements were performed for the optical characterization of the thin films. Effective medium theories (EMT) were used to model the optical and compositional properties of the SiOxNy films. The refractive index measured by ellipsometry was compared with theoretical calculations using Maxwell-Garnett and Bruggeman equations. The experimental results agree quite well with model data. It is also shown that the concentration of hydrogen in the films has a major influence on the quality of the agreement. .

  13. 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.

  14. 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.

  15. Local Atomic Structure and Magnetism in Amorphous FexSi1-x Thin Films

    NASA Astrophysics Data System (ADS)

    Hellman, Frances; Zhang, Yanning; Bordel, Catherine; Stone, Kevin; Jenkins, Catherine; Smith, David; Hu, J.; Wu, Ruqian; Heald, Steve; Kortright, Jeff; Karel, Julie

    2014-03-01

    Amorphous FexSi1-x thin films exhibit a large enhancement in M compared to crystalline films with the same composition (0.45< x<0.75). XMCD shows enhancement in both spin and orbital moments. Density functional theory (DFT) calculations reproduce this enhanced magnetization. DFT and EXAFS show the amorphous materials have decreased number of nearest neighbors and reduced number density relative to crystalline samples of same x, which leads to the enhanced moment. Thanks to DOE BES LBNL magnetism program for support.

  16. Characterization of UV laser ablation for microprocessing of a-Si:H thin films

    NASA Astrophysics Data System (ADS)

    Molpeceres, C.; Lauzurica, S.; Ocaña, J. L.; Gandía, J. J.; Urbina, L.; Cárabe, J.; Villar, F.; Escarré, J.; Bertomeu, J.; Andreu, J.

    2006-04-01

    Hydrogenated amorphous silicon has been widely studied last years, both from the basic research and industrial points of view, due to the important set of potential applications that this material offers, ranging from Thin Films Transistors (TFTs) to solar cells technologies. In different fabrication steps of a-Si:H based devices, laser sources have been used as appropriate tools for cutting, crystallising, contacting, patterning, etc., and more recent research lines are undertaking the problem of a-Si:H selective laser ablation for different applications. The controlled ablation of photovoltaic materials with minimum debris and small heat affected zone with low processing costs, is one of the main difficulties for the successful implementation of laser micromachining as competitive technology in this field. This work presents a detailed study of a-Si:H laser ablation in the ns regime. Ablation curves are measured and fluence thresholds are determined. Additionally, and due to the improved performance in optolectronic properties associated to the nanocrystalline silicon (nc-Si:H), some samples of this material have been also studied.

  17. Evolution of grain size and morphology of Si thin films fabricated on lunar regolith glass

    NASA Astrophysics Data System (ADS)

    Gramajo, C.; Williams, L.; Feltrin, A.; Alemu, A.; Freundlich, A.

    2006-10-01

    A critical requirement for space colonization and in particular for its lunar exploration component is the availability of large amounts of electric energy. Novel architectures which involve the in situ manufacture of solar cells on the Moon using indigenous lunar materials have been proposed to meet this need [1]. In support of this effort, this study delves on several aspects of interest starting from the fabrication of a glass substrate from lunar regolith, to the deposition of Si films and the effects of thermal processing induced changes on the properties of these films. The experiments were implemented using several types of commercially available glasses as well as in-house fabricated regolith glass. In particular, the study provides valuable information on the effect of temperature on the interactions between Si and the substrates, and also the interaction between metallic contact layers and Si, which could affect regions beyond their common interface. This insight sheds a light on the evolution of grain size and morphology of Si thin films grown on lunar regolith.

  18. Transparent conducting Si-codoped Al-doped ZnO thin films prepared by magnetron sputtering using Al-doped ZnO powder targets containing SiC

    SciTech Connect

    Nomoto, Jun-ichi; Miyata, Toshihiro; Minami, Tadatsugu

    2009-07-15

    Transparent conducting Al-doped ZnO (AZO) thin films codoped with Si, or Si-codoped AZO (AZO:Si), were prepared by radio-frequency magnetron sputtering using a powder mixture of ZnO, Al{sub 2}O{sub 3}, and SiC as the target; the Si content (Si/[Si+Zn] atomic ratio) was varied from 0 to 1 at. %, but the Al content (Al/[Al+Zn] atomic ratio) was held constant. To investigate the effect of carbon on the electrical properties of AZO:Si thin films prepared using the powder targets containing SiC, the authors also prepared thin films using a mixture of ZnO, Al{sub 2}O{sub 3}, and SiO{sub 2} or SiO powders as the target. They found that when AZO:Si thin films were deposited on glass substrates at about 200 degree sign C, both Al and Si doped into ZnO acted as effective donors and the atomic carbon originating from the sputtered target acted as a reducing agent. As a result, sufficient improvement was obtained in the spatial distribution of resistivity on the substrate surface in AZO:Si thin films prepared with a Si content (Si/[Si+Zn] atomic ratio) of 0.75 at. % using powder targets containing SiC. The improvement in resistivity distribution was mainly attributed to increases in both carrier concentration and Hall mobility at locations on the substrate corresponding to the target erosion region. In addition, the resistivity stability of AZO: Si thin films exposed to air for 30 min at a high temperature was found to improve with increasing Si content.

  19. Epitaxial growth and orientation of AlN thin films on Si(001) substrates deposited by reactive magnetron sputtering

    SciTech Connect

    Valcheva, E.; Birch, J.; Persson, P. O. A ring .; Tungasmita, S.; Hultman, L.

    2006-12-15

    Epitaxial domain formation and textured growth in AlN thin films deposited on Si(001) substrates by reactive magnetron sputtering was studied by transmission electron microscopy and x-ray diffraction. The films have a wurtzite type structure with a crystallographic orientation relationship to the silicon substrate of AlN(0001)(parallel sign)Si(001). The AlN film is observed to nucleate randomly on the Si surface and grows three dimensionally, forming columnar domains. The in-plane orientation reveals four domains with their a axes rotated by 15 deg. with respect to each other: AlN<1120>(parallel sign)Si[110], AlN<0110>(parallel sign)Si[110], AlN<1120>(parallel sign)Si[100], and AlN<0110>(parallel sign)Si[100] An explanation of the growth mode based on the large lattice mismatch and the topology of the substrate surface is proposed.

  20. Formation of epitaxial Co{sub 1-x}Ni{sub x}Si{sub 2} nanowires on thin-oxide-capped (001)Si

    SciTech Connect

    Li, Wun-Shan; Lee, Chung-Yang; Liu, Chun-Yi; Chu, Yen-Chang; Chen, Sheng-Yu; Chen, Lih-Juann

    2013-02-28

    Epitaxial Co{sub 1-x}Ni{sub x}Si{sub 2} alloy nanowires have been grown on (001)Si substrates by a combination of reactive deposition epitaxy and oxide-mediated epitaxy. The thin native oxide layer can serve as a diffusion barrier to diminish the flux of metal atoms from the top of oxide layer to Si surface and promote the growth of nanowires. The elemental distributions of Ni and Co in nanowires were determined by energy dispersive spectroscopy in a transmission electron microscope. The factors that cause the distributions of Ni and Co in nanowires were discussed.

  1. 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.

  2. 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.

  3. Epitaxial growth of yttrium-stabilized HfO2 high-k gate dielectric thin films on Si

    NASA Astrophysics Data System (ADS)

    Dai, J. Y.; Lee, P. F.; Wong, K. H.; Chan, H. L. W.; Choy, C. L.

    2003-07-01

    Epitaxial yttrium-stabilized HfO2 thin films were deposited on p-type (100) Si substrates by pulsed laser deposition at a relatively lower substrate temperature of 550 °C. Transmission electron microscopy observation revealed a fixed orientation relationship between the epitaxial film and Si; that is, (100)Si//(100)HfO2 and [001]Si//[001]HfO2. The film/Si interface is not atomically flat, suggesting possible interfacial reaction and diffusion. X-ray photoelectron spectrum analysis also revealed the interfacial reaction and diffusion evidenced by Hf silicate and Hf-Si bond formation at the interface. The epitaxial growth of the yttrium stabilized HfO2 thin film on bare Si is via a direct growth mechanism without involving the reaction between Hf atoms and SiO2 layer. High-frequency capacitance-voltage measurement on an as-grown 40-Å yttrium-stabilized HfO2 epitaxial film yielded an effective dielectric constant of about 14 and equivalent oxide thickness to SiO2 of 12 Å. The leakage current density is 7.0×10-2 A/cm2 at 1 V gate bias voltage.

  4. Epitaxial growth of lead zirconium titanate thin films on Ag buffered Si substrates using rf sputtering

    SciTech Connect

    Wang Chun; Laughlin, David E.; Kryder, Mark H.

    2007-04-23

    Epitaxial lead zirconium titanate (PZT) (001) thin films with a Pt bottom electrode were deposited by rf sputtering onto Si(001) single crystal substrates with a Ag buffer layer. Both PZT(20/80) and PZT(53/47) samples were shown to consist of a single perovskite phase and to have the (001) orientation. The orientation relationship was determined to be PZT(001)[110](parallel sign)Pt(001)[110](parallel sign)Ag(001)[110](parallel sign)Si(001)[110]. The microstructure of the multilayer was studied using transmission electron microscopy (TEM). The electron diffraction pattern confirmed the epitaxial relationship between each layer. The measured remanent polarization P{sub r} and coercive field E{sub c} of the PZT(20/80) thin film were 26 {mu}C/cm{sup 2} and 110 kV/cm, respectively. For PZT(53/47), P{sub r} was 10 {mu}C/cm{sup 2} and E{sub c} was 80 kV/cm.

  5. High acoustic strains in Si through ultrafast laser excitation of Ti thin-film transducers.

    PubMed

    Tzianaki, Eirini; Bakarezos, Makis; Tsibidis, George D; Orphanos, Yannis; Loukakos, Panagiotis A; Kosmidis, Constantine; Patsalas, Panos; Tatarakis, Michael; Papadogiannis, Nektarios A

    2015-06-29

    The role of thin-film metal transducers in ultrafast laser-generated longitudinal acoustic phonons in Si (100) monocrystal substrates is investigated. For this purpose degenerate femtosecond pump-probe transient reflectivity measurements are performed probing the Brillouin scattering of laser photons from phonons. The influence of the metallic electron-phonon coupling factor, acoustical impedance and film thickness is examined. An optical transfer matrix method for thin films is applied to extract the net acoustic strain relative strength for the various transducer cases, taking into account the experimental probing efficiency. In addition, a theoretical thermo-mechanical approach based on the combination of a revised two-temperature model and elasticity theory is applied and supports the experimental findings. The results show highly efficient generation of acoustic phonons in Si when Ti transducers are used. This demonstrates the crucial role of the transducer's high electron-phonon coupling constant and high compressive yield strength, as well as strong acoustical impedance matching with the semiconductor substrate. PMID:26191728

  6. Structural evolution and characterization of heteroepitaxial GaSb thin films on Si(111) substrates

    NASA Astrophysics Data System (ADS)

    Nguyen, Thang; Varhue, Walter; Cross, Michael; Pino, Robinson; Adams, Edward; Lavoie, Mark; Lee, Jaichan

    2007-04-01

    This paper describes the structural evolution and characterization of heteroepitaxial GaSb thin films on Si(111) substrates. The growth process used a combination of atomic sources which included the rf sputtering of Sb and the thermal effusion of Ga. The formation of crystalline GaSb thin films required that initially a monolayer thick Sb buffer layer be applied directly to a clean H-passivated Si(111) substrate surface. The resulting film was characterized by high resolution x-ray diffraction, Rutherford backscattering spectrometry, transmission electron microscopy, secondary ion mass spectroscopy, and atomic force microscopy (AFM). The AFM images were taken from the material after several periods of growth to determine the evolution of crystal structure with thickness. Atomic force microscopy images of the film surface showed that the heteroepitaxial layers were formed via the Stranski-Krastanov growth mechanism. This result is consistent with the heteroepitaxial growth of systems representing large differences in lattice constant. The hole mobility and carrier concentration in the deposited material were determined by the Hall measurement, performed at room temperature and on a 140nm thick sample, to be 66cm2/Vsec and 3×1019 cm-3, respectively. The carrier mobility was relatively low as expected for measurements taken at room temperature.

  7. Low-temperature epitaxial growth of Ge-C and Ge-Si-C alloy thin films

    NASA Astrophysics Data System (ADS)

    Yang, Bi-Ke

    The fabrication of heterostructures based on Si has become important in electronic device technology. Ge is chemically compatible with Si and has a smaller bandgap. However, the lattice mismatch between Si and Ge is rather large (˜4.2%), making it difficult to grow defect-free layers of Ge-Si alloys on Si. The addition of an appropriate amount of substitutional C may compensate some of the lattice mismatch between Ge and Si. However, a major obstacle to the fabrication of these alloys is that carbon is insoluble in bulk Ge or Si. It has been suggested that enhanced C incorporation can be obtained in epitaxially grown thin films. This dissertation describes the epitaxial growth of Ge-C and Ge-Si-C thin film (˜30-70 nm) alloys on Si and Ge by low-temperature molecular bean epitaxy (MBE). The films were characterized by in-situ reflection high energy electron diffraction (RHEED), ex-situ x-ray diffraction (XRD), plan view and cross-section transmission electron microscopy (TEM), Raman scattering, and ellipsometry. It is found that with increasing nominal carbon concentration the lattice parameter of Ge-C and Ge-Si-C films decreases, marginally indicating substitutional carbon incorporation. It is estimated that a maximum of about lat.% C and 2-3at.% C goes into substitutional sites alloying with Ge and with Ge-Si, respectively. The effect of C on the microstructural development including the formation of 3 dimensional islands and planar defects and (311) faceting are presented and discussed. The presence of Ge-C bonding mode was observed and is direct evidence for the presence of substitutional carbon. Si interdiffusion into Ge and Ge-C films at higher temperatures was studied. The presence of carbon significantly suppresses the Si interdiffusion into Ge films.

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

    NASA Astrophysics Data System (ADS)

    Oezer, D.; Ramírez, G.; Rodil, S. E.; Sanjinés, R.

    2012-12-01

    The electrical and optical properties of TaxSiyNz 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-TaxSiyNz thin films were prepared: sub-stoichiometric TaxSiyN0.44, nearly stoichiometric TaxSiyN0.5, and over-stoichiometric TaxSiyN0.56. 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 TaxSiyNz films due to variations in the stoichiometry of the fcc-TaNz system and the addition of Si atoms. According to the nitrogen and silicon contents, fcc-TaxSiyNz films can exhibit room temperature resistivity values ranging from 102 μΩ cm to about 6 × 104 μΩ 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 TaxSiyNz thin films provides a pertinent and consistent description of the evolution of the Ta-Si-N system from a solid solution to a nanocomposite material due to the addition of Si atoms.

  9. (Na, Bi)TiO3 based lead-free ferroelectric thin films on Si substrate for pyroelectric infrared sensors

    NASA Astrophysics Data System (ADS)

    Akai, D.; Yoshita, R.; Ishida, M.

    2013-04-01

    In this study, we report ferroelectric and pyroelectric properties of (Na0.5Bi0.5)TiO3-BaTiO3 (NBT-BT) thin films on Si substrates using chemical solution deposition for the first time. The NBT-BT thin films deposited on Pt/Ti/SiO2/Si substrates have exhibited a typical hysteresis loop with remnant polarization of 5 μC/cm2 and coercive field of 80 kV/cm. Furthermore NBT-BT films showed pyroelectricity with pyroelectric coefficient of 0.6×10-8 C/cm2K. Monolithic-integration of Si electronics and lead-free ferroelectric NBT thin films has been archived using SiN passivation layer. It was previously believed that LSI processes could not incorporate any sodium-containing material which would cause characteristic degradation, such as threshold voltage shift. In this work, no threshold voltage shift in MOS characteristics was observed using this SiN layer. The SiN layer not only blocked diffusion from NBT chemistry, but also from crystallized NBT films during NBT formation process.

  10. 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.

  11. Scribing of a-Si thin-film solar cells with picosecond laser

    NASA Astrophysics Data System (ADS)

    Gečys, P.; Račiukaitis, G.

    2010-09-01

    The thin-film technology is the most promising technology to achieve a significant cost reduction in solar electricity. Laser scribing is an important step to preserve high efficiency of photovoltaic devices on large areas. The high-repetition-rate laser with the pulse duration of 10 ps was applied in selective ablation of multilayer thin-film a-Si solar cells deposited on flexible and rigid substrates. Two types of solar cells with flexible and rigid substrates have been investigated. The first type of solar cells was made of 400 nm a-Si layer coated on both sides with 2 μ m transparent ZnO:Al contact layers deposited by CVD technique on the glass plate. The second type of solar cells was made of a flexible polyimide substrate coated with the Al back-contact, a-Si light absorbing layer and the ITO top-contact. Selection of the right laser wavelength is important to keep the energy coupling in a well defined volume at the interlayer interface. Well-defined shapes of scribes were produced by laser ablation through layers of the solar cell on the glass substrate. Localization of the coupled energy at the inner interface led to the “lift-off” type process rather than evaporation of the top ITO layer when the 355 nm radiation was applied. All laser scribes did not indicate any material melting or other thermal damage caused by laser irradiation. Ultra-short picosecond pulses ensured the high energy input rate into absorbing material therefore peeling of the layers had no influence on the remaining material.

  12. Observations on Si-based micro-clusters embedded in TaN thin film deposited by co-sputtering with oxygen contamination

    NASA Astrophysics Data System (ADS)

    Lee, Young Mi; Jung, Min-Sang; Choi, Duck-Kyun; Jung, Min-Cherl

    2015-08-01

    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, SiOx-capped Si, and SiO2-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.

  13. 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.

  14. Contrasting growth modes of Ru thin film nano-structures on Si and Pd

    NASA Astrophysics Data System (ADS)

    Yin, Xiangshi; Teng, Ao; Özer, Mustafa; Weitering, Hanno; Snijders, Paul

    2011-03-01

    We have studied Ruthenium thin film growth on both Si (111) and Pd (111) surfaces. The films were deposited at low (LN2) temperature and at room temperature, and subsequently annealed at elevated temperatures, up to 600C. The surface structure, morphology, and chemical composition were investigated by LEED, STM, AES and XPS. Upon deposition at low temperature, nanoclusters are formed on both Si and Pd. Remarkably, the nanoclusters are approximately 3 nm in diameter and exhibit narrow size distributions on both substrates. In the case of Ru on Si, XPS spectra indicate silicide formation at the interface above 300C, but the nanocluster surface morphology survives up to 600C. On the other hand, nanoclusters on Pd smoothen into atomically flat films above 200C. The striking difference in adatom mobilities on these substrates is surprising in light of the very high melting temperature of Ru (2400C). Research (PCS) sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.

  15. 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.

  16. Diode laser crystallization processes of Si thin-film solar cells on glass

    NASA Astrophysics Data System (ADS)

    Yun, Jae Sung; Ahn, Cha Ho; Jung, Miga; Huang, Jialiang; Kim, Kyung Hun; Varlamov, Sergey; Green, Martin A.

    2014-07-01

    The crystallization of Si thin-film on glass using continuous-wave diode laser is performed. The effect of various processing parameters including laser power density and scanning speed is investigated in respect to microstructure and crystallographic orientation. Optimal laser power as per scanning speed is required in order to completely melt the entire Si film. When scan speed of 15-100 cm/min is used, large linear grains are formed along the laser scan direction. Laser scan speed over 100 cm/min forms relatively smaller grains that are titled away from the scan direction. Two diode model fitting of Suns-Voc results have shown that solar cells crystallized with scan speed over 100 cm/min are limited by grain boundary recombination (n = 2). EBSD micrograph shows that the most dominant misorientation angle is 60°. Also, there were regions containing high density of twin boundaries up to ~1.2 × 10-8/cm2. SiOx capping layer is found to be effective for reducing the required laser power density, as well as changing preferred orientation of the film from ⟨ 110 ⟩ to ⟨ 100 ⟩ in surface normal direction. Cracks are always formed during the crystallization process and found to be reducing solar cell performance significantly.

  17. 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.

  18. Superconductivity in ion-beam-mixed layered Au-Si thin films

    SciTech Connect

    Jisrawi, N.M.; McLean, W.L. ); Stoffel, N.G.; Hegde, M.S.; Chang, C.C.; Hart, D.L.; Hwang, D.M.; Ravi, T.S.; Wilkens, B.J. ); Sun, J.Z.; Geballe, T.H. )

    1991-04-01

    The superconducting properties of thin films made by mixing alternating layers of Au and Si using ion-beam bombardment correlate with the formation of metastable metallic phases in what is otherwise a simple eutectic system. Transmission-electron-microscopy measurements reveal the superconducting phases to be amorphous. Compound formation and the nature of Au-Si bonding in these metastable phases are demonstrated from x-ray photoelectron spectroscopy and from a previous study of x-ray-absorption spectroscopy. After mixing with a beam of Xe ions, multilayered films with an average nominal composition Au{sub {ital x}}Si{sub 1{minus}{ital x}}, where {ital x}=0.2, 0.4, 0.5, 0.72, and 0.8, exhibited superconducting transition temperatures in the range 0.2--1.2 K. A double transition feature in the magnetic field dependence of the resistivity is attributed to the formation of more than one metastable metallic phase in the same sample as the ion dose increases.

  19. Stress analysis of transferred thin-GaN LED by Au-Si wafer bonding

    NASA Astrophysics Data System (ADS)

    Hsu, S. C.; Liu, C. Y.

    2005-09-01

    Nowadays, the high power GaN-based LED has attracted serious attention for the lighting application. One of key issues for high power GaN-base LED to achieve sufficient lighting efficiency over the traditional light sources, such as, white incandescent and halogen light bulb is the efficiency of heat dissipation. Typically, GaN epi-layer is grown on sapphire substrates. The poor thermal conductivity of sapphire substrate has been identified to be the main limitation for the application of high power GaN LED. To improve the heat dissipation and lighting efficiency, we report a thin GaN structure by using Au-Si wafer bonding and Laser lift-off (LLO) technique. The GaN wafer was first deposited with a Au bonding layer and bonded onto a good thermal conduction substrate, i.e., heavy-doped Si. Then, 248nm KrF excimer Laser was used to strip the original sapphire substrate. To assure a successful GaN epi-layer transferring, Raman spectrum on the transferred GaN layer was performed and the result shows no quality change in the transferred GaN layer. In this work, we also fabricated the vertical LED devices on the transferred GaN epi-layer. Therefore, L-I-V result was obtained which will be presented in this talk. Moreover, we will discuss the effects and advantages of Au-Si bonding on the efficiency of lighting.

  20. Uniaxially oriented polycrystalline thin films and air-stable n-type transistors based on donor-acceptor semiconductor (diC8BTBT)(FnTCNQ) [n = 0, 2, 4

    NASA Astrophysics Data System (ADS)

    Shibata, Yosei; Tsutsumi, Jun'ya; Matsuoka, Satoshi; Matsubara, Koji; Yoshida, Yuji; Chikamatsu, Masayuki; Hasegawa, Tatsuo

    2015-04-01

    We report the fabrication of high quality thin films for semiconducting organic donor-acceptor charge-transfer (CT) compounds, (diC8BTBT)(FnTCNQ) (diC8BTBT = 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene and FnTCNQ [n = 0,2,4] = fluorinated derivatives of 7,7,8,8,-tetracyanoquinodimethane), which have a high degree of layered crystallinity. Single-phase and uniaxially oriented polycrystalline thin films of the compounds were obtained by co-evaporation of the component donor and acceptor molecules. Organic thin-film transistors (OTFTs) fabricated with the compound films exhibited n-type field-effect characteristics, showing a mobility of 6.9 × 10-2 cm2/V s, an on/off ratio of 106, a sub-threshold swing of 0.8 V/dec, and an excellent stability in air. We discuss the suitability of strong intermolecular donor-acceptor interaction and the narrow CT gap nature in compounds for stable n-type OTFT operation.

  1. Phosphorus diffusion in polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Losee, D. L.; Lavine, J. P.; Trabka, E. A.; Lee, S.-T.; Jarman, C. M.

    1984-02-01

    The diffusion of phosphorus in crystallized amorphous Si layers was studied with secondary-ion mass spectroscopy. A two-dimensional diffusion model is used to find effective grain (Dg) and grain-boundary (Dgb) diffusion coefficients. This simplified model leads to Dgb ≤ 10Dg, which is significantly lower than what has been deduced from conventional, larger grained polysilicon. Our result is consistent with specific-gravity measurements, which found a significantly lower ``mass defect'' for layers deposited amorphous and subsequently crystallized as compared to initially polycrystalline layers.

  2. 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

  3. 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

  4. 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.

  5. Paramagnetic point defects in amorphous thin films of SiO{sub 2} and Si{sub 3}N{sub 4}: An update

    SciTech Connect

    Poindexter, E.H.; Warren, W.L.

    1994-06-01

    Recent research on point defects in thin films of SiO{sub 2} and Si{sub 3}SN{sub 4} on Si is presented and reviewed. In SiO{sub 2} it is now clear that no one type of E{prime} center is the sole source of radiation-induced positive charge; hydrogenous moieties or other types of E{prime} are proposed. Molecular orbital theory and easy passivation of E{prime} by H{sub 2} suggest that released H might depassivate P{sub b} sites. A charged E{prime}{sub {delta}} center has been seen in Cl-free SIMOX and thermal oxide film, and it is reassigned to an electron delocalized over four O{sub 3}{equivalent_to}Si units around a fifth Si. In Si{sub 3}N{sub 4} a new model for the amphoteric charging of Si{equivalent_to}N{sub 3} moieties is based on local shifts in defect energy with respect to the Fermi level, arising from nonuniform composition; it does not assume negative-U electron correlation. A new defect NN{sub 2}{sup 0} has been identified, with dangling orbital on a 2-coordinated N atom bonded to another N.

  6. 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

  7. 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.

  8. Room temperature synthesis of porous SiO2 thin films by plasma enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Barranco, A.; Cotrino, J.; Yubero, F.; Espinós, J. P.; González-Elipe, A. R.

    2004-07-01

    Silicon dioxide thin films with variable and controlled porosity have been prepared at room temperature by plasma enhanced chemical vapor deposition in an electron cyclotron resonance microwave reactor with a downstream configuration. The procedure consists of the deposition of successive cycles consisting of a sacrificial organic-polymeric layer and, afterward, a silicon dioxide layer. Toluene and oxygen are used as precursors of the organic layers and Si(CH3)3Cl and oxygen for the SiO2. During deposition of the latter, the organic layer is simultaneously burned off. In these conditions, the release of gases produced by oxidation of the organic-polymeric layer take place while the oxide layer is being deposited. Thus, modification of the nucleation and growing mechanism of the silicon oxide thin film take place. The porosity of the final porous SiO2 thin films increases with the thickness of the sacrificial organic layer. The porous SiO2 films prepared with the aforementioned method are free of carbon and chlorine contamination as confirmed by Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy. Depending on their porosity, the SiO2 thin films are either transparent or scattered visible light. The former have refractive index lower than that of thermal silicon dioxide and the latter show membranelike behavior in gas diffusion experiments. All the samples have good adhesion to the substrates used for the deposition, either polished Si wafer, glass plates, or standard porous supports. They have columnar microstructure, as determined by scanning electron microscopy. A preliminary ultraviolet-visible characterization of the optically transparent thin films reveals that transmission of light through glass increases by 7%-8% when the porous silica is deposited on this substrate. These films prove to be very efficient as antireflective coatings and are of interest for photovoltaic and similar applications

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Improvement of in-plane anisotropy field in FeCoB/NiFe/Si thin films by Kr sputtering

    NASA Astrophysics Data System (ADS)

    Hashimoto, A.; Ito, S.; Nakagawa, S.

    2007-03-01

    Deterioration of magnetic anisotropy field in the FeCoB/NiFe/Si trilayers deposited on glass substrates was investigated. It was found that the choice of Kr as sputtering gas instead of Ar was quite effective to improve the soft magnetic characteristics of FeCoB/NiFe/Si thin films deposited on glass substrates. Kr sputtering is effective to reduce compressive residual stress in the film. The rotatable magnetic anisotropy observed in the FeCoB/NiFe/Si films deposited by Ar sputtering disappeared in the film deposited by Kr sputtering, even though they are prepared on glass disk substrates.

  14. Defects of a-Si Thin-Film Solar Cells Detected by Transmission Photothermal Radiometric Imaging

    NASA Astrophysics Data System (ADS)

    Yan, Laijun; Gao, Chunming; Zhao, Binxing; Sun, Qiming; Liu, Lixian; Huan, Huiting

    2015-06-01

    The photothermal radiometry (PTR) technique is an effective non-destructive testing technique for detecting defects in materials. In this paper, a piece of commercial amorphous silicon (a-Si) thin-film solar cells with some artificial mechanical defects has been investigated by the transmission PTR imaging system. Firstly, a simplified analytical expression of a normalized transmission PTR signal was employed to characterize defects. Secondly, the corresponding experimental system has been set-up for obtaining several thermal images of the sample. Thirdly, different kinds of defects have been analyzed and identified by the thermal images. The results show that not only the artificial mechanical defects on the sample can be detected, but also some defects occurring in the manufacturing process can be detected by the transmission PTR imaging system.

  15. 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.

  16. Calculations of thermoelectric properties: Mg2Si under uniaxial [110] strains versus (110)-oriented thin film

    NASA Astrophysics Data System (ADS)

    Balout, Hilal; Boulet, Pascal; Record, Marie-Christine

    2015-08-01

    Investigations of the electronic properties and transport properties of Mg2Si under uniaxial [110] strain have been performed by using first-principle density-functional and Boltzmann's transport theories. The effect of compressive and tensile uniaxial strains has been studied by changing the γ angle of the conventional cell from ± 1° to ± 4°. We show that, the Seebeck property of the constrained bulk lattice at high temperature, when plotted with respect to the charge carrier concentrations, is similar to that of the (110) thin film at low temperature. This behaviour is evidenced when superimposing the Seebeck coefficient curves of both materials by shifting down the S curve of the constrained structure by about 150 K with respect to the temperature.

  17. 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.

  18. Optical properties of Ag nanoclusters formed by irradiation and annealing of SiO2/SiO2:Ag thin films

    NASA Astrophysics Data System (ADS)

    Güner, S.; Budak, S.; Gibson, B.; Ila, D.

    2014-08-01

    We have deposited five periodic SiO2/SiO2 + Ag multi-nano-layered films on fused silica substrates using physical vapor deposition technique. The co-deposited SiO2:Ag layers were 2.7-5 nm and SiO2 buffer layers were 1-15 nm thick. Total thickness was between 30 and 105 nm. Different concentrations of Ag, ranging from 1.5 to 50 molecular% with respect to SiO2 were deposited to determine relevant rates of nanocluster formation and occurrence of interaction between nanoclusters. Using interferometry as well as in situ thickness monitoring, we measured the thickness of the layers. The concentration of Ag in SiO2 was measured with Rutherford Backscattering Spectrometry (RBS). To nucleate Ag nanoclusters, 5 MeV cross plane Si ion bombardments were performed with fluence varying between 5 × 1014 and 1 × 1016 ions/cm2 values. Optical absorption spectra were recorded in the range of 200-900 nm in order to monitor the Ag nanocluster formation in the thin films. Thermal annealing treatment at different temperatures was applied as second method to form varying size of nanoclusters. The physical properties of formed super lattice were criticized for thermoelectric applications.

  19. Epitaxial growth of β-FeSi2 thin films on Si(111) substrates by radio frequency magnetron sputtering and their application to near-infrared photodetection

    NASA Astrophysics Data System (ADS)

    Promros, Nathaporn; Baba, Ryuji; Takahara, Motoki; Mostafa, Tarek M.; Sittimart, Phongsaphak; Shaban, Mahmoud; Yoshitake, Tsuyoshi

    2016-06-01

    β-FeSi2 thin films were epitaxially grown on p-type Si(111) substrates at a substrate temperature of 560 °C and Ar pressure of 2.66 × 10‑1 Pa by radio-frequency magnetron sputtering (RFMS) using a sintered FeSi2 target, without postannealing. The resultant n-type β-FeSi2/p-type Si heterojunctions were evaluated as near-infrared photodiodes. Three epitaxial variants of β-FeSi2 were confirmed by X-ray diffraction analysis. The heterojunctions exhibited typical rectifying action at room temperature. At 300 K, the heterojunctions showed a substantial leakage current and minimal response for irradiation of near-infrared light. At 50 K, the leakage current was markedly reduced and the ratio of the photocurrent to dark current was considerably enhanced. The detectivity at 50 K was estimated to be 3.0 × 1011 cm Hz1/2/W at a zero bias voltage. Their photodetection was inferior to those of similar heterojunctions prepared using facing-target direct-current sputtering (FTDCS) in our previous study. This inferiority is likely because β-FeSi2 films prepared using RFMS are located in plasma and are damaged by it.

  20. 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.

  1. Spectroscopic Ellipsometry of 3C-SiC Thin Films Grown on Si Substrates Using Organosilane Sources

    NASA Astrophysics Data System (ADS)

    Kubo, Naoki; Moritani, Akihiro; Kitahara, Kuninori; Asahina, Shuichi; Kanayama, Nobuyuki; Tsutsumi, Koichi; Suzuki, Michio; Nishino, Shigehiro

    2005-06-01

    Dielectric function spectra of 3C-SiC films on Si substrates in the energy region of 0.73-6.43 eV were measured by spectroscopic ellipsometry. Hexamethyldisilane (Si2(CH3)6) and tetraethylsilane (Si(C2H5)4) were used as safe organosilane sources for the growth of SiC films. The measured spectra were compared with those of 3C-SiC on a Si(001) substrate grown with disilane (Si2H6). First, the pseudodielectric function spectra gave a shoulder structure corresponding to the direct X5-X1 interband transition in the Brillouin zone. Secondly, the dielectric function of 3C-SiC was determined by applying a four-layer model in which we took into account the surface roughness and mixed crystals of a carbonized interface layer. Finally, the third-derivative lineshape of the imaginary part \\varepsilon2 of the complex-dielectric function provided the values of the interband transition energy Eg and the broadening parameter Γ for the X5-X1 interband transition. The measured values of Γ indicated that the crystalline quality of SiC films grown using organosilane sources is comparable to that of SiC films grown using Si2H6.

  2. Quantum corrections to temperature dependent electrical conductivity of ZnO thin films degenerately doped with Si

    SciTech Connect

    Das, Amit K. Ajimsha, R. S.; Kukreja, L. M.

    2014-01-27

    ZnO thin films degenerately doped with Si (Si{sub x}Zn{sub 1−x}O) in the concentrations range of ∼0.5% to 5.8% were grown by sequential pulsed laser deposition on sapphire substrates at 400 °C. The temperature dependent resistivity measurements in the range from 300 to 4.2 K revealed negative temperature coefficient of resistivity (TCR) for the 0.5%, 3.8%, and 5.8% doped Si{sub x}Zn{sub 1−x}O films in the entire temperature range. On the contrary, the Si{sub x}Zn{sub 1−x}O films with Si concentrations of 1.0%, 1.7%, and 2.0% showed a transition from negative to positive TCR with increasing temperature. These observations were explained using weak localization based quantum corrections to conductivity.

  3. High responsivity, low dark current, heterogeneously integrated thin film Si photodetectors on rigid and flexible substrates

    PubMed Central

    Dhar, Sulochana; Miller, David M.; Jokerst, Nan M.

    2014-01-01

    We report thin film single crystal silicon photodetectors (PDs), composed of 13- 25 μm thick silicon, heterogeneously bonded to transparent Pyrex® and flexible Kapton® substrates. The measured responsivity and dark current density of the PDs on pyrex is 0.19 A/W – 0.34 A/W (λ = 470 nm – 600 nm) and 0.63 nA/cm2, respectively, at ~0V bias. The measured responsivity and dark current density of the flexible PDs is 0.16 A/W – 0.26 A/W (λ = 470 nm – 600 nm) and 0.42 nA/cm2, respectively, at a ~0V bias. The resulting responsivity-to-dark current density ratios for the reported rigid and flexible PDs are 0.3-0.54 cm2/nW and 0.38-0.62 cm2/nW, respectively. These are the highest reported responsivity-to-dark current density ratios for heterogeneously bonded thin film single crystal Si PDs, to the best of our knowledge. These PDs are customized for applications in biomedical imaging and integrated biochemical sensing. PMID:24663844

  4. 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.

  5. 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.

  6. 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

  7. Morphology and kinetics of crystallization of amorphous V75Si25 thin-alloy films

    NASA Astrophysics Data System (ADS)

    Nava, F.; Weiss, B. Z.; Tu, K. N.; Smith, D. A.; Psaras, P. A.

    1986-10-01

    Electrical and microstructural changes of coevaporated V75Si25 alloy thin films have been studied as a function of temperature from room temperature to 830 °C. In situ resistivity measurements, hot-stage transmission electron microscopy, Rutherford backscattering spectroscopy and the Seeman-Bohlin glancing angle incidence x-ray diffraction technique were applied. Upon heat treatment at a heating rate of 8 °C/min, a sharp decrease in resistivity occurs at ˜670 °C which results from an amorphous to crystalline phase transformation. The crystallized phase was identified as V3Si. The mechanism of transformation is random nucleation at a rapidly decreasing rate and a fast quasi-isotropic growth. The kinetics of crystallization have been studied by utilizing electrical resistivity measurements during isothermal heat treatment. Six different temperatures between 570 °C and 630 °C were adopted. The apparent activation energy (˜3.6 eV) obtained from isothermal measurements was found to be in agreement with that obtained from nonisothermal treatments at varying rates of heating. The distinct change of the Avrami mode parameter from 4 to 2 at a constant value of t/τ during the process of crystallization is not immediately understood.

  8. Film Thickness Influences on the Thermoelectric Properties of NiCr/NiSi Thin Film Thermocouples

    NASA Astrophysics Data System (ADS)

    Chen, Y. Z.; Jiang, H. C.; Zhang, W. L.; Liu, X. Z.; Jiang, S. W.

    2013-06-01

    NiCr/NiSi thin film thermocouples (TFTCs) with a multi-layer structure were fabricated on Ni-based superalloy substrates (95 mm × 35 mm × 2 mm) by magnetron sputtering and electron beam evaporation. The five-layer structure is composed of NiCrAlY buffer layer (2 μm), thermally grown Al2O3 bond layer (200 nm), Al2O3 insulating layer (10 μm), NiCr/NiSi TFTCs (1 μm), and Al2O3 protective layer (500 nm). Influences of thermocouple layer thickness on thermoelectric properties were investigated. Seebeck coefficient of the samples with the increase in thermocouple layer thickness from 0.5 μm to 1 μm increased from 27.8 μV/°C to 33.8 μV/°C, but exhibited almost no change with further increase in thermocouple layer thickness from 1 μm to 2 μm. Dependence on temperature of the thermal electromotive force of the samples almost followed standard thermocouple characteristic curves when the thickness of the thermocouple layer was 1 μm and 2 μm. Sensitive coefficient K of the samples increased greatly with the increase in thickness of the thermocouple layer from 0.5 μm to 1 μm, but decreased insignificantly with the increase in thermocouple layer thickness from 1 μm to 2 μm, and continuously decreased with the increase in temperature. The sensitive coefficient and the stability of NiCr/NiSi TFTCs were both improved after annealing at 600°C.

  9. Facile synthesis of multilayer-like Si thin film as high-performance anode materials for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Wang, Mingxu; Geng, Zhongrong

    2016-05-01

    For the silicon anodes in lithium-ion batteries, it is well known that the enormous volumetric expansion/contraction is also the mainly reason for the capacity fading. In this manuscript, a new kind of Si thin films was prepared with a radio frequency magnetron sputtering method. By using a periodic modulation negative bias on the substrate, a density-modulated multilayer-like silicon thin films with different layer densities were used as anode materials of lithium-ion batteries, and which displayed a high capacity and stable cycling performances. The reason for the charming electrochemical performances may be owned to the particular density modulated microstructure of the Si thin films. It is conjectured that the lower density can as compliant layers and which provided the volume for the higher-density layer expansion in the process of the lithiation/delithiation. In contrast to the conventional silicon anodes, the density modulated microstructure in this work could exploit a new approach to silicon thin-film anode materials with outstanding electrochemical properties and mechanical stability. And these reports may be provide a new way to prepare the Si thin films for the high-energy, safe, and low-cost batteries.

  10. 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

  11. 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.

  12. 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.

  13. Diffusion in polycrystalline microstructures

    SciTech Connect

    Swiler, T.P.; Holm, E.A.

    1995-07-01

    Mass transport properties are important in polycrystalline materials used as protective films. Traditionally, such properties have been studied by examining model polycrystalline structures, such as a regular array of straight grain boundaries. However, these models do not account for a number of features of real grain ensembles, including the grain size distribution and the topological aspects of grain boundaries. In this study, a finite difference scheme is developed to study transient and steady-state mass transport through realistic two-dimensional polycrystalline microstructures. Effects of microstructural parameters such as average grain size and grain boundary topology are examined, as are effects due to limits of the model.

  14. Evaluation of crack-healing behavior in SiNx/SiC nanolaminated thin film by microbending test

    NASA Astrophysics Data System (ADS)

    Nakatani, M.; Tonoya, Y.; Harada, Y.

    2015-03-01

    The purpose of this study is to evaluate the crack-healing behavior of SiNx/SiC nanolaminated films quantitatively. SiNx/SiC nanolaminated films were fabricated by alternating ion-beam assisted deposition of SiNx and SiC. The fabricated nanolaminated films consisted of four layers with the top layer being SiNx. Smooth and notched microbeam specimens were fabricated using a focused ion beam (FIB) system. The nanosized notch was introduced in form of an imitational crack on the film surface by FIB. Some notched samples were heated at 1000 ºC for 24 to 96 h in air. The fracture strength was evaluated by bending tests using a nanoindentation system. After heating, the notch was filled with reaction products. Energy dispersive X-ray (EDX) analysis revealed that the reaction products contained oxide compounds, most likely SiO2. The fracture load of the notched specimens recovered with increasing heating time. The filling of the notch with oxidation products caused the recovery of the fracture load. However, the recovery was not complete compared with the strength of a smooth sample. It is concluded that the filling of a notch with oxidation products recovers the mechanical strength of SiNx/SiC nanolaminated films only to a certain extent.

  15. Paramagnetic point defects in amorphous thin films of SiO{sub 2} and Si{sub 3}N{sub 4}: Updates and additions

    SciTech Connect

    Poindexter, E.H.; Warren, W.L.

    1995-07-01

    Recent research on point defects in thin films of silicon dioxide, silicon nitride, and silicon oxynitride on Si is presented and reviewed. In SiO{sub 2}, it now clear that no one type of E{prime} are proposed. Molecular orbital theory and easy passivation of E{prime} by H{sub 2} suggest that released H might depassivate interface P{sub b} sites. A charged E{prime}{sub {delta}} center has been seen in Cl-free SIMOX (separation by implantation of oxygen) and thermal oxide films, and it is reassigned to an electron delocalized over four O{sub 3}{triple_bond}Si units around a fifth Si. In Si{sub 3}N{sub 4}, a new model for the amphoteric charging of {sm_bullet}Si{triple_bond}N{sub 3} moieties is based on local shifts in defect energy with respect to the Fermi level, arising from nonuniform composition; it does not assume negative U electron correlation. A new defect NN{sub 2}{sup 0} has been identified, with dangling orbital on a two-coordinated N atom bonded to another N. Silicon oxynitride defects are briefly presented.

  16. Structural, electrical and optical properties of a Li-doped ZnO thin film fabricated on a Pt(111)/Ti/SiO2/Si(100) substrate

    NASA Astrophysics Data System (ADS)

    Raghavan, C. M.; Kim, J. W.; Jang, K. W.; Kim, S. S.

    2015-04-01

    A Li-doped ZnO (Zn1- x Li x O1- δ , x = 0.12) thin film was fabricated on a Pt(111)/Ti/SiO2/Si(100) substrate by using a chemical solution deposition method. The formation of a wurtzite hexagonal structure was confirmed by an X-ray diffraction and a Raman spectroscopic analysis. Typical hexagonal microcrystalline grains were observed from the surface morphological studies. Room-temperature ferroelectricity with a remnant polarization (2 P r ) of 0.05 μC/cm2 and a coercive field (2 E c ) of 170 kV/cm at an applied electric field of 200 kV/cm was observed in the Li-doped ZnO thin film. The measured leakage current density for the thin film was 1.09 × 10 -4 A/cm2 at an applied electric field of 100 kV/cm. A sharp near-band-edge emission was observed in the photoluminescence spectrum at a wavelength of 375 nm for the thin film.

  17. Optical switching properties of VOx thin films deposited on Si3N4 substrates using ion beam sputtering

    NASA Astrophysics Data System (ADS)

    Lu, Jianing; Hu, Ming; Liang, Jiran; Chen, Tao; Tan, Lei

    2009-07-01

    Vanadium dioxide (VO2) thin films, for their property of metal-insulator transition (MIT), have drawn many researchers' attention on optical devices study. Nowadays it is complicated to fabricate single-phase VO2) thin films. Ion beam sputtering is adopted to deposit VOx thin films (main component is VO2) ) on Si3N4, while sputtering power, substrate temperature and partial oxygen pressure of VOx are adjusted. Then annealing technology is utilized to improve the parameter property of VOx thin films. The thin films are tested by AFM, XPS, XRD, Fourier transform infrared spectrometry, tunable semiconductor laser and optical power meter. Both temperature-driven phasetransition and photoexcitation phasetransition of VOx thin films are applied. The samples are heated from 20°C to 80°C, discovering that the phasetransition temperature is about 59°C and the value of resistance before the phasetransition is two orders of magnitude over the value of resistance after the phasetransition. At the wavelength of 1550 nm, the transmission is from 32% to 1%. Besides, the extinction ratio of the thin films sample is obtained. The optical properties show that the VOx thin films have an apparent switching effect in the optical communication fields.

  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. 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.

  20. 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.

  1. 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.

  2. Origin of instability by positive bias stress in amorphous Si-In-Zn-O thin film transistor

    SciTech Connect

    Hyung Kim, Do; Youn Yoo, Dong; Kwang Jung, Hyun; Hwan Kim, Dae; Yeol Lee, Sang

    2011-10-24

    The origin of instability under positive bias stress (PBS) in amorphous Si-In-Zn-O (SIZO) thin film transistor (TFT) with different Si concentration has been investigated by x-ray photoelectron spectroscopy (XPS) and density of states (DOSs) analysis. It is found that stability of SIZO-TFT with 3 wt. % Si under PBS became more deteriorated than that of 1 wt. % Si incorporated SIZO-TFT due to the increased oxygen related trap distributed in energy range from conduction band to {approx}0.3 eV below the conduction band. The origin of instability under PBS was discussed in terms of oxygen related trap derived from DOSs and XPS analysis.

  3. 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.

  4. 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.

  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. Exploratory development of thin-film polycrystalline silicon photovoltaic devices. Report No. 3. Electron beam ribbon-to-ribbon (EB RTR) recrystallization of microcrystalline silicon ribbons

    SciTech Connect

    Gurtler, R.W.

    1981-09-01

    The electron beam has been applied as the energy source for ribbon-to-ribbon (RTR) recrystallization of thin-film silicon with very small (approx. 1 ..mu..m) grains into sheets with very large grains (> 1 cm). The system described uses two e-guns, one for producing a thin molten region across the microcrystalline ribbon (except for the edges), the other for establishing desirable thermal profiles in the cool-down (and heat-up) regions. In this way, no furnace, heat shield, or cooling structures are present, in contrast to all the other ribbon growing techniques. This simple arrangement is gained at the (reasonable) expense of having to work in a vacuum. A CCTV camera observes the temperature distribution and melt shape during growth; its output is coupled to a real-time image analyzer system and a computer. When there is a need to alter the temperature or melt shape in a region, the deflection/modulation circuitry is appropriately instructed, and (closing the loop) the change is made. The vacuum chamber with cassette feed for ribbons, electron guns, and camera, was completed and placed in operation. The overall system was run with a fined temperature profile for small RTR samples; resulting thin-film silicon ribbon quality was comparable to that obtained with laser beam RTR. The entire electronic system was not finished, however, so potential utility of the system for improving silicon ribbon quality and economics could not be ascertained.

  7. The mechanism of electromigration failure of narrow Al-2Cu-1Si thin-film interconnects

    NASA Astrophysics Data System (ADS)

    Kim, Choongun; Morris, J. W., Jr.

    1993-05-01

    This work is principally concerned with the microstructure of electromigration failure in narrow Al-2Cu-1Si conducting lines on Si. Samples were patterned from 0.5-μm-thick vapor-deposited films with mean grain size of 2.4 μm, and had linewidths of 1.3 μm (W/G≊0.5), 2 μm (W/G≊0.8), and 6 μm (W/G≊2.5). The lines were tested to failure at T=226 °C and j=2.5×106 A/cm2. Other samples were tested over a range of substrate temperatures and current densities to test the effect of these variables, and 1.3 μm lines were tested after preaging at 226 °C for various times to change the Cu-precipitate distribution prior to testing. Three failure modes were observed: The 6 μm specimens failed by separation along grain boundaries with an apparent activation energy of 0.65 eV; the 1.3 μm specimens that were preaged for 24 h failed after very long times by gradual thinning to rupture; all other narrow lines failed by the transgranular-slit mechanism with an activation energy near 0.93 eV. Microstructural studies suggest that the transgranular-slit failure mechanism is due to the accumulation of a supersaturation of vacancies in the bamboo grains that terminate polygranular segments in the line. Failure occurs after Cu has been swept from the grain that fails. Failure happens first at the end of the longest polygranular segment of the line, at a time that decreases exponentially with the polygranular segment length. Preaging the line to create a more stable distribution of Cu lengthens the time required to sweep Cu from the longest polygranular segment, and significantly increases the time to failure. In the optimal case the transgranular-slit failure mechanism is suppressed, and the bamboo grain fails by diffuse thinning to rupture. Preaging is particularly effective in increasing the lifetimes of lines that contain very long polygranular segments, and has the consequence that the time to first failure in an array of lines is much longer than predicted by a log

  8. 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

  9. Fabrication and characterization of Al2O3 /Si composite nanodome structures for high efficiency crystalline Si thin film solar cells

    NASA Astrophysics Data System (ADS)

    Zhang, Ruiying; Zhu, Jian; Zhang, Zhen; Wang, Yanyan; Qiu, Bocang; Liu, Xuehua; Zhang, Jinping; Zhang, Yi; Fang, Qi; Ren, Zhong; Bai, Yu

    2015-12-01

    We report on our fabrication and characterization of Al2O3/Si composite nanodome (CND) structures, which is composed of Si nanodome structures with a conformal cladding Al2O3 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 Al2O3thin 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 Al2O3 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 Al2O3 film, and the performance is remarkably improved when the dielectric layer thickness is 90 nm thick. The leakage current, which is less than 4x10-9 A/cm2 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 SiOx layer formed between the interface of Si and the Al2O3 film, which is thin enough that ensures the presence of field-effect passivation, From our theoretical and experimental study, we believe Al2O3 coated CND structures is a truly viable approach to achieving higher device efficiency.

  10. SYNCHROTRON RADIATION, FREE ELECTRON LASER, APPLICATION OF NUCLEAR TECHNOLOGY, ETC.: Identification of pore size in porous SiO2 thin film by positron annihilation

    NASA Astrophysics Data System (ADS)

    Zhang, Zhe; Qin, Xiu-Bo; Wang, Dan-Ni; Yu, Run-Sheng; Wang, Qiao-Zhan; Ma, Yan-Yun; Wang, Bao-Yi

    2009-02-01

    Positron annihilation lifetime and Doppler broadening of annihilation line techniques have been used to obtain information about the small pore structure and size of porous SiO2 thin film produced by sputtered Al-Si thin film and etched Al-Si thin film. The film is prepared by an Al/Si 75:25 at.-% (Al75Si25) target with the radiofrequency (RF) power of 66 W at room temperature. A 5 wt.-% phosphoric acid solution is used to etch the Al cylinders. All the Al cylinders dissolved in the solution after 15 h at room temperature, and the sample is subsequently rinsed in pure water. In this way, the porous SiO2 on the Si substrate is produced. From our results, the values of all lifetime components in the spectra of Al-Si thin film are less than 1 ns, but the value of one of the lifetime components in the spectra of porous SiO2 thin film is τ = 7.80 ns. With these values of lifetime, RTE (Rectangular Pore Extension) model has been used to analyze the pore size.

  11. Morphological and compositional evolution of Pt-Si intermetallic thin films prepared by the activated adsorption of SiH{sub 4} on Pt(111)

    SciTech Connect

    Bondos, J.C.; Gewirth, A.A.; Nuzzo, R.G.

    1999-04-22

    The authors have investigated using scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES) the growth and structural evolution of Pt-Si intermetallic phases formed via a chemical vapor deposition (CVD) mediated process. The Pt silicide thin films were prepared though the exposure of a Pt(111) crystal to silane (SiH{sub 4}) followed by various annealing treatments. The deposition of Si via the decomposition of silane at room temperature preferentially forms clusters at step edges that avoid the centers of Pt terraces. The sizes and coverages of the clusters increases with silane exposure. The clusters are of intermetallic character (composed of both Si and Pt) and coarsen to give cluster heights much larger than a Pt(111) step height. These observations implicitly establish that Si interdiffusion in the near-surface region is weakly activated. Studies performed as a function of the silane exposure and annealing temperature reveal a complicated phase behavior that incorporates seven separate atomically ordered phases in addition to large-scale surface features such as three-dimensional islands. Growth and degradation mechanisms have been constructed, and the phenomena observed are contrasted with standard kinetic models based on sequential phase growth.

  12. 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

  13. 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

  14. 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.

  15. Growth and characterization of epitaxial Ti3GeC2 thin films on 4H-SiC(0001)

    NASA Astrophysics Data System (ADS)

    Buchholt, K.; Eklund, P.; Jensen, J.; Lu, J.; Ghandi, R.; Domeij, M.; Zetterling, C. M.; Behan, G.; Zhang, H.; Lloyd Spetz, A.; Hultman, L.

    2012-03-01

    Epitaxial Ti3GeC2 thin films were deposited on 4° off-cut 4H-SiC(0001) using magnetron sputtering from high purity Ti, C, and Ge targets. Scanning electron microscopy and helium ion microscopy show that the Ti3GeC2 films grow by lateral step-flow with {112¯0} faceting on the SiC surface. Using elastic recoil detection analysis, atomic force microscopy, and X-Ray diffraction the films were found to be substoichiometric in Ge with the presence of small Ge particles at the surface of the film.

  16. 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.

  17. 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.

  18. 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.

  19. Influence of a thin interfacial oxide layer on the ion beam assisted epitaxial crystallization of deposited Si

    NASA Astrophysics Data System (ADS)

    Priolo, F.; La Ferla, A.; Spinella, C.; Rimini, E.; Ferla, G.; Baroetto, F.; Licciardello, A.

    1988-12-01

    The epitaxial crystallization of chemical vapor deposited Si layers on <100> Si substrates with a thin interfacial oxide layer was induced by a 600 keV Kr beam in the temperature range 350-500 °C. During irradiation the single crystal-amorphous interface velocity was measured in situ by monitoring the reflectivity of He-Ne laser light. We show that a critical irradiation dose is needed before the interfacial oxide breaks down and epitaxial regrowth can take place. This critical dose depends exponentially on the reciprocal temperature with an activation energy of 0.44 eV.

  20. Kinetics of hydrogen desorption in surface-limited thin-film growth of SiGe alloys

    SciTech Connect

    Sharp, J.W. ); Eres, G. )

    1993-05-31

    The kinetics of hydrogen desorption in surface-limited thin-film growth of SiGe alloys from binary mixtures of disilane and digermane was investigated by surface differential reflectance. The hydrogen desorption process from the alloy surface was found to consist of two components. Both components are thermally activated, but the activation energies appear to equal neither the hydrogen desorption energy from pure silicon nor that from pure germanium surfaces. We suggest that the two components represent Ge- and Si-mediated hydrogen desorption, with the former being more rapid than the latter.