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Sample records for ge intermediate layer

  1. GaAs/Si epitaxial integration utilizing a two-step, selectively grown Ge intermediate layer

    NASA Astrophysics Data System (ADS)

    Cederberg, Jeffrey G.; Leonhardt, Darin; Sheng, Josephine J.; Li, Qiming; Carroll, Malcolm S.; Han, Sang M.

    2010-04-01

    We describe efforts to epitaxially integrate GaAs with Si, using thin, relaxed Ge layers. The Ge films are deposited by molecular beam epitaxy using a self-assembled, selective-area growth technique, where atomic Ge etches an SiO 2 mask layer and then grows from pores extending to the Si substrate. The resulting Ge film coalesces over the SiO 2 mask and is planarized, using H 2O 2-based chemical-mechanical polishing. We subsequently deposit a GaAs/AlAs heterostructure on the polished Ge on Si substrate by metal-organic vapor phase epitaxy. While the initial Ge films were completely relaxed and dislocation-free, they contain a high density of stacking faults that propagate through the GaAs/AlAs heterostructure. These stacking faults create phase domains that appear as non-radiative recombination centers in cathodoluminescence images. Further development of two-step Ge epitaxy with an anneal near the Ge melting point eliminates stacking faults in the Ge, but decomposes the SiO 2 mask allowing threading dislocations to form and propagate through the GaAs/AlAs heterostructure. We discuss our strategy to prevent the loss of the SiO 2 mask and thus reduce threading dislocations.

  2. Ge/graded-SiGe multiplication layers for low-voltage and low-noise Ge avalanche photodiodes on Si

    NASA Astrophysics Data System (ADS)

    Miyasaka, Yuji; Hiraki, Tatsurou; Okazaki, Kota; Takeda, Kotaro; Tsuchizawa, Tai; Yamada, Koji; Wada, Kazumi; Ishikawa, Yasuhiko

    2016-04-01

    A new structure is examined for low-voltage and low-noise Ge-based avalanche photodiodes (APDs) on Si, where a Ge/graded-SiGe heterostructure is used as the multiplication layer of a separate-absorption-carrier-multiplication structure. The Ge/SiGe heterojunction multiplication layer is theoretically shown to be useful for preferentially enhancing impact ionization for photogenerated holes injected from the Ge optical-absorption layer via the graded SiGe, reflecting the valence band discontinuity at the Ge/SiGe interface. This property is effective not only for the reduction of operation voltage/electric field strength in Ge-based APDs but also for the reduction of excess noise resulting from the ratio of the ionization coefficients between electrons and holes being far from unity. Such Ge/graded-SiGe heterostructures are successfully fabricated by ultrahigh-vacuum chemical vapor deposition. Preliminary pin diodes having a Ge/graded-SiGe multiplication layer act reasonably as photodetectors, showing a multiplication gain larger than those for diodes without the Ge/SiGe heterojunction.

  3. Comparison of EL emitted by LEDs on Si substrates containing Ge and Ge/GeSn MQW as active layers

    NASA Astrophysics Data System (ADS)

    Schwartz, B.; Arguirov, T.; Kittler, M.; Oehme, M.; Kostecki, K.; Kasper, E.; Schulze, J.

    2015-02-01

    We analyzed Ge- and GeSn/Ge multiple quantum well (MQW) light emitting diodes (LEDs). The structures were grown by molecular beam epitaxy (MBE) on Si. In the Ge LEDs the active layer was 300 nm thick. Sb doping was ranging from 1×1018 to 1×1020 cm-3. An unintentionally doped Ge-layer served as reference. The LEDs with the MQWs consist of ten alternating GeSn/Ge-layers. The Ge-layers were 10 nm thick and the GeSn-layers were grown with 6 % Sn and thicknesses between 6 and 12 nm. The top contact of all LEDs was identical. Accordingly, the light extraction is comparable. The electroluminescence (EL) analysis was performed under forward bias at different currents. Sample temperatures between <300 K and 80 K were studied. For the reference LED the direct transition at 0.8 eV dominates. With increasing current the peak is slightly redshifted due to Joule heating. Sb doping of the active Ge-layer affects the intensity and at 3×1019 cm-3 the strongest emission appears. It is ~4 times higher as compared to the reference. Moreover a redshift of the peak position is caused by bandgap narrowing. The LEDs with undoped GeSn/Ge-MQWs as active layer show a very broad luminescence band with a peak around 0.65 eV, pointing to a dominance of the GeSn-layers. The light emission intensity is at least 17 times stronger as compared to the reference Ge-LED. Due to incorporation of Sn in the MQWs the active layer should approach to a direct semiconductor. In indirect Si and Ge we observed an increase of intensity with increasing temperature, whereas the intensity of GeSn/Ge-MQWs was much less affected. But a deconvolution of the spectra revealed that the energy of indirect transition in the wells is still below the one of the direct transition.

  4. Characterization of High Ge Content SiGe Heterostructures and Graded Alloy Layers Using Spectroscopic Ellipsometry

    NASA Technical Reports Server (NTRS)

    Heyd, A. R.; Alterovitz, S. A.; Croke, E. T.

    1995-01-01

    Si(x)Ge(1-x)heterostructures on Si substrates have been widely studied due to the maturity of Si technology. However, work on Si(x)Ge)1-x) heterostructures on Ge substrates has not received much attention. A Si(x)Ge(1-x) layer on a Si substrate is under compressive strain while Si(x)Ge(1-x) on Ge is under tensile strain; thus the critical points will behave differently. In order to accurately characterize high Ge content Si(x)Ge(1-x) layers the energy shift algorithm used to calculate alloy compositions, has been modified. These results have been used along with variable angle spectroscopic ellipsometry (VASE) measurements to characterize Si(x)Ge(1-x)/Ge superlattices grown on Ge substrates. The results agree closely with high resolution x-ray diffraction measurements made on the same samples. The modified energy shift algorithm also allows the VASE analysis to be upgraded in order to characterize linearly graded layers. In this work VASE has been used to characterize graded Si(x)Ge(1-x) layers in terms of the total thickness, and the start and end alloy composition. Results are presented for a 1 micrometer Si(x)Ge(1-x) layer linearly graded in the range 0.5 less than or equal to x less than or equal to 1.0.

  5. Formation process of high-purity Ge-on-insulator layers by Ge-condensation technique

    NASA Astrophysics Data System (ADS)

    Nakaharai, S.; Tezuka, T.; Hirashita, N.; Toyoda, E.; Moriyama, Y.; Sugiyama, N.; Takagi, S.

    2009-01-01

    Formation process of Ge-on-insulator (GOI) layers by Ge condensation with very high purity of Ge is clarified in terms of diffusion behaviors of Si and Ge in a SiGe layer. It is shown that the diffusion behavior affects the Ge condensation process, and the purity of GOI layer can be determined by the relation between oxidation and diffusion of Si. Experimental results support a model of GOI formation that the selective oxidation of Si in SiGe continues until the formation of a GOI layer with the residual Si fraction of less than 0.01%. Based on this model, we quantitatively clarify the reason why GOI layers can reach very low residual Si fraction without oxidizing Ge by calculating the diffusion behavior of Si during the Ge condensation process. As a result, we have found that the thermal diffusion of Si is sufficiently fast so that the selective oxidation of Si can continue during the GOI formation process until the averaged residual Si fraction in the SGOI layer becomes lower than 0.03%, which is essentially consistent with the experimental results. In addition, we have found that, even if the GOI layer is thick, the Ge purity of GOI layer can approach 100% infinitely in principle by enhancing the Si diffusion in SGOI compared to the oxidation rate of SGOI.

  6. Fabrication of GeO2 layers using a divalent Ge precursor

    NASA Astrophysics Data System (ADS)

    Perego, M.; Scarel, G.; Fanciulli, M.; Fedushkin, I. L.; Skatova, A. A.

    2007-04-01

    Good quality and perfectly stoichiometric GeO2 layers are promising interlayers to be implemented in alternative devices based on high dielectric constant oxide/Ge(100). In this work, the authors report on the growth by atomic layer deposition of GeO2 films using a divalent Ge precursor combined with O3. The films are composed of smooth and perfectly stoichiometric GeO2. The contamination level is extremely low. The deposited GeO2 films have a band gap of 5.81±0.04eV. The conduction and valence band offsets at the GeO2/Ge heterojunction are found to be 0.6±0.1 and 4.5±0.1eV, respectively.

  7. Energy band alignment of atomic layer deposited HfO{sub 2} oxide film on epitaxial (100)Ge, (110)Ge, and (111)Ge layers

    SciTech Connect

    Hudait, Mantu K.; Zhu Yan

    2013-03-21

    Crystallographically oriented epitaxial Ge layers were grown on (100), (110), and (111)A GaAs substrates by in situ growth process using two separate molecular beam epitaxy chambers. The band alignment properties of atomic layer hafnium oxide (HfO{sub 2}) film deposited on crystallographically oriented epitaxial Ge were investigated using x-ray photoelectron spectroscopy (XPS). Valence band offset, {Delta}E{sub v} values of HfO{sub 2} relative to (100)Ge, (110)Ge, and (111)Ge orientations were 2.8 eV, 2.28 eV, and 2.5 eV, respectively. Using XPS data, variation in valence band offset, {Delta}E{sub V}(100)Ge>{Delta}E{sub V}(111)Ge>{Delta}E{sub V}(110)Ge, was obtained related to Ge orientation. Also, the conduction band offset, {Delta}E{sub c} relation, {Delta}E{sub c}(110)Ge>{Delta}E{sub c}(111)Ge>{Delta}E{sub c}(100)Ge related to Ge orientations was obtained using the measured bandgap of HfO{sub 2} on each orientation and with the Ge bandgap of 0.67 eV. These band offset parameters for carrier confinement would offer an important guidance to design Ge-based p- and n-channel metal-oxide field-effect transistor for low-power application.

  8. Excess carrier lifetimes in Ge layers on Si

    SciTech Connect

    Geiger, R. E-mail: hans.sigg@psi.ch; Sigg, H. E-mail: hans.sigg@psi.ch; Frigerio, J.; Chrastina, D.; Isella, G.; Süess, M. J.; Spolenak, R.; Faist, J.

    2014-02-10

    The excess charge carrier lifetimes in Ge layers grown on Si or germanium-on-insulator are measured by synchrotron based pump-probe transmission spectroscopy. We observe that the lifetimes do not strongly depend on growth parameters and annealing procedure, but on the doping profile. The defect layer at the Ge/Si interface is found to be the main non-radiative recombination channel. Therefore, the longest lifetimes in Ge/Si (2.6 ns) are achieved in sufficiently thick Ge layers with a built-in field, which repels electrons from the Ge/Si interface. Longer lifetimes (5.3 ns) are obtained in overgrown germanium-on-insulator due to the absence of the defective interface.

  9. 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.

  10. Ion beam synthesis of SiGe alloy layers

    NASA Astrophysics Data System (ADS)

    Im, Seongil

    1994-05-01

    Procedures required for minimizing structural defects generated during ion beam synthesis of SiGe alloy layers were studied. Synthesis of 200 mm SiGe alloy layers by implantation of 120-keV Ge ions into (100) oriented Si wafers yielded various Ge peak concentrations after the following doses, 2x10(exp 16)cm(exp -2), 3x10(exp 16)cm(exp -2), and 5x10(exp 16)cm(exp -2). Following implantation, solid phase epitaxial (SPE) annealing in ambient N2 at 800 C for 1 hr. resulted in only slight redistribution of the Ge. Two kinds of extended defects were observed in alloy layers over 3x10(exp 16)cm(exp -2) dose at room temperature (RT): end-of-range (EOR) dislocation loops and strain-induced stacking faults. Density of EOR dislocation loops was much lower in alloys produced by 77K implantation than by RT implantation. Decreasing the dose to obtain 5 at percent peak Ge concentration prevents strain relaxation, while those SPE layers with more than 7 at percent Ge peak show high densities of misfit-induced stacking faults. Sequential implantation of C following high dose Ge implantation (12 at percent Ge peak concentration in layer) brought about a remarkable decrease in density of misfit-induced stacking faults. For peak implanted C greater than 0.55 at percent, stacking fault generation in the epitaxial layer was suppressed, owing to strain compensation by C atoms in the SiGe lattice. A SiGe alloy layer with 0.9 at percent C peak concentration under a 12 at percent Ge peak exhibited the best microstructure. Results indicate that optimum Ge/C ratio for strain compensation is between 11 and 22. The interface between amorphous and regrown phases (a/c interface) had a dramatic morphology change during its migration to the surface. Initial (100) planar interface decomposes into a (111) faceted interface, changing the growth kinetics; this is associated with strain relaxation by stacking fault formation on (111) planes in the a/c interface.

  11. Ion beam synthesis of SiGe alloy layers

    SciTech Connect

    Im, Seongil

    1994-05-01

    Procedures required for minimizing structural defects generated during ion beam synthesis of SiGe alloy layers were studied. Synthesis of 200 mm SiGe alloy layers by implantation of 120-keV Ge ions into <100> oriented Si wafers yielded various Ge peak concentrations after the following doses, 2{times}10{sup 16}cm{sup {minus}2}, 3{times}10{sup 16}cm{sup {minus}2} (mid), and 5{times}10{sup 16}cm{sup {minus}2} (high). Following implantation, solid phase epitaxial (SPE) annealing in ambient N2 at 800C for 1 hr. resulted in only slight redistribution of the Ge. Two kinds of extended defects were observed in alloy layers over 3{times}l0{sup 16}cm{sup {minus}2}cm dose at room temperature (RT): end-of-range (EOR) dislocation loops and strain-induced stacking faults. Density of EOR dislocation loops was much lower in alloys produced by 77K implantation than by RT implantation. Decreasing the dose to obtain 5 at% peak Ge concentration prevents strain relaxation, while those SPE layers with more than 7 at% Ge peak show high densities of misfit- induced stacking faults. Sequential implantation of C following high dose Ge implantation (12 at% Ge peak concentration in layer) brought about a remarkable decrease in density of misfit-induced stacking faults. For peak implanted C > 0.55 at%, stacking fault generation in the epitaxial layer was suppressed, owing to strain compensation by C atoms in the SiGe lattice. A SiGe alloy layer with 0.9 at% C peak concentration under a 12 at% Ge peak exhibited the best microstructure. Results indicate that optimum Ge/C ratio for strain compensation is between 11 and 22. The interface between amorphous and regrown phases (a/c interface) had a dramatic morphology change during its migration to the surface. Initial <100> planar interface decomposes into a <111> faceted interface, changing the growth kinetics; this is associated with strain relaxation by stacking fault formation on (111) planes in the a/c interface.

  12. Characterization of SiGe/Ge heterostructures and graded layers using variable angle spectroscopic ellipsometry

    NASA Technical Reports Server (NTRS)

    Croke, E. T.; Wang, K. L.; Heyd, A. R.; Alterovitz, S. A.; Lee, C. H.

    1996-01-01

    Variable angle spectroscopic ellipsometry (VASE) has been used to characterize Si(x)Ge(1-x)/Ge superlattices (SLs) grown on Ge substrates and thick Si(x)Ge(1-x)/Ge heterostructures grown on Si substrates. Our VASE analysis yielded the thicknesses and alloy compositions of all layers within the optical penetration depth of the surface. In addition, strain effects were observed in the VASE results for layers under both compressive and tensile strain. Results for the SL structures were found to be in close agreement with high resolution x-ray diffraction measurements made on the same samples. The VASE analysis has been upgraded to characterize linearly graded Si(x)Ge(1-x) buffer layers. The algorithm has been used to determine the total thickness of the buffer layer along with the start and end alloy composition by breaking the total thickness into many (typically more than 20) equal layers. Our ellipsometric results for 1 (mu)m buffer layers graded in the ranges 0.7 less than or = x less than or = 1.0, and 0.5 less than or = x less than or = 1.0 are presented, and compare favorably with the nominal values.

  13. Atomic Layer Epitaxy of Si and Ge on Si(100)-(2x1)

    NASA Astrophysics Data System (ADS)

    Veyan, Jean-Francois; Choi, Heesung; Ballard, Joshua; McDonnell, Stephen; Kirk, Willey P.; Wallace, Robert M.; Randall, John; Cho, Kyeongjae; Chabal, Yves J.

    2011-03-01

    Atomic Layer Epitaxy of Si and Ge on Si(100) surface using disilane (Si 2 H6) and digermane (Ge 2 H6) as precursors is a critical step for constructing 3-D nano-structures, and is indispensable for Atomically Precise Manufacturing of new devices such as quantum dots. Using IRAS and STM together with DFT calculations, we show that Si 2 H6 chemisorbs on clean Si(100)-(2x1) via beta-hydride elimination pathway, involving the intermediate states Si-H and Si- Si H2 - Si H3 . Thermal decomposition of the chemisorbed Si 2 H5 leads to the formation of Si 2 H2 as an added dimer rotated 90 degrees with respect to the initial dimer row. A similar chemisorption pathway is observed for Ge 2 H6 on Si(100)x(2x1). The thermal decomposition of Ge 2 H5 involves the migration of H from Ge to Si, and Ge ad-dimer formation. Evidence for Ge epitaxial growth on Si(100)x(2x1) using Ge 2 H6 will be presented.

  14. Selective Passivation of GeO2/Ge Interface Defects in Atomic Layer Deposited High-k MOS Structures.

    PubMed

    Zhang, Liangliang; Li, Huanglong; Guo, Yuzheng; Tang, Kechao; Woicik, Joseph; Robertson, John; McIntyre, Paul C

    2015-09-23

    Effective passivation of interface defects in high-k metal oxide/Ge gate stacks is a longstanding goal of research on germanium metal-oxide-semiconductor devices. In this paper, we use photoelectron spectroscopy to probe the formation of a GeO2 interface layer between an atomic layer deposited Al2O3 gate dielectric and a Ge(100) substrate during forming gas anneal (FGA). Capacitance- and conductance-voltage data were used to extract the interface trap density energy distribution. These results show selective passivation of interface traps with energies in the top half of the Ge band gap under annealing conditions that produce GeO2 interface layer growth. First-principles modeling of Ge/GeO2 and Ge/GeO/GeO2 structures and calculations of the resulting partial density of states (PDOS) are in good agreement with the experiment results. PMID:26334784

  15. Si/NiFe seed layers for Ru intermediate layer in perpendicular magnetic recording tape media

    NASA Astrophysics Data System (ADS)

    Saemma, Gaku; Takahashi, Shota; Matsunuma, Satoshi; Inoue, Tetsutaro; Nakagawa, Shigeki

    2012-04-01

    Si/NiFe seed layers prepared at room temperature is effective to attain better c-axis orientation of Ru intermediate layer in the FeCoB/Ru/CoPtCr-SiO2 granular type recording tape media. The crystallinity and c-axis orientation of Ru layer with Si/NiFe seed layers were improved than that without Si/NiFe seed layer deposited on the laminated FeCoB SULs. When the Ru is thicker than 8 nm, Δθ50 of the CoPtCr-SiO2 recording layer shows small value of about 6.5°. Furthermore, even though the Ru thickness was only 3 nm, the Δθ50 retained comparatively small value of 8.0°. Si/NiFe layer is effective as a seed layer for the Ru intermediate layer.

  16. Strain and stability of ultrathin Ge layers in Si/Ge/Si axial heterojunction nanowires

    SciTech Connect

    Ross, Frances M.; Stach, Eric A.; Wen, Cheng -Yen; Reuter, Mark C.; Su, Dong

    2015-02-05

    The abrupt heterointerfaces in the Si/Ge materials system presents useful possibilities for electronic device engineering because the band structure can be affected by strain induced by the lattice mismatch. In planar layers, heterointerfaces with abrupt composition changes are difficult to realize without introducing misfit dislocations. However, in catalytically grown nanowires, abrupt heterointerfaces can be fabricated by appropriate choice of the catalyst. Here we grow nanowires containing Si/Ge and Si/Ge/Si structures respectively with sub-1nm thick Ge "quantum wells" and we measure the interfacial strain fields using geometric phase analysis. Narrow Ge layers show radial strains of several percent, with a corresponding dilation in the axial direction. Si/Ge interfaces show lattice rotation and curvature of the lattice planes. We conclude that high strains can be achieved, compared to what is possible in planar layers. In addition, we study the stability of these heterostructures under heating and electron beam irradiation. The strain and composition gradients are supposed to the cause of the instability for interdiffusion.

  17. Strain and stability of ultrathin Ge layers in Si/Ge/Si axial heterojunction nanowires

    DOE PAGESBeta

    Ross, Frances M.; Stach, Eric A.; Wen, Cheng -Yen; Reuter, Mark C.; Su, Dong

    2015-02-05

    The abrupt heterointerfaces in the Si/Ge materials system presents useful possibilities for electronic device engineering because the band structure can be affected by strain induced by the lattice mismatch. In planar layers, heterointerfaces with abrupt composition changes are difficult to realize without introducing misfit dislocations. However, in catalytically grown nanowires, abrupt heterointerfaces can be fabricated by appropriate choice of the catalyst. Here we grow nanowires containing Si/Ge and Si/Ge/Si structures respectively with sub-1nm thick Ge "quantum wells" and we measure the interfacial strain fields using geometric phase analysis. Narrow Ge layers show radial strains of several percent, with a correspondingmore » dilation in the axial direction. Si/Ge interfaces show lattice rotation and curvature of the lattice planes. We conclude that high strains can be achieved, compared to what is possible in planar layers. In addition, we study the stability of these heterostructures under heating and electron beam irradiation. The strain and composition gradients are supposed to the cause of the instability for interdiffusion.« less

  18. Review of an intermediate-layer lithography approach

    NASA Astrophysics Data System (ADS)

    Luo, Cheng

    2007-04-01

    Conducting polymers, because of their promising potential to replace silicon and metals in building devices, have attracted great attention since the discovery of high conductivity in doped polyacetylene in 1977. Lithographic techniques present significant technical challenges when working with conducting polymers. Sensitivity of conducting polymers to environmental conditions (e.g., air, oxygen, moisture, high temperature and chemical solutions) makes current photolithographic methods unsuitable for patterning the conducting polymers due to the involvement of wet and/or dry etching processes in those methods. Existing non-photolithographic approaches have limitations in throughput, resolution or electrical insulation. Therefore, an intermediate-layer lithography (ILL) approach has been recently developed by my group to produce conducting polymer micro/nanostructures. In the ILL method, an intermediate layer of an electrically insulating polymer is coated between the substrate and a layer of the conducting polymer to be printed. Subsequently, the conducting polymer is printed through mold insertion using a hot-embossing process. The current hot-embossing based methods face the obstacles of residual layer and depth of field (i.e., the height variation in the mold structures). In contrast, the ILL approach does not leave a residual layer in the material of interest, making conducting polymer patterns isolated from one another and avoiding the shorting problem in the electrical applications of these patterns. Furthermore, in the ILL, the height variation potentially existing among the mold structures has been transferred to the intermediate layer, ensuring that all patterns in the mold have been properly transferred to the conducting polymer layer. In addition to conducting polymers, the ILL can also be applied to pattern metals as well as other types of polymers. This paper gives a review of this ILL method and reports the results that we have achieved to date.

  19. Silicon solar cell using optimized intermediate reflector layer

    NASA Astrophysics Data System (ADS)

    Khalifa, Ahmed E.; Swillam, Mohamed A.

    2016-03-01

    Thin film silicon based photovoltaic cells have the advantages of using low cost nontoxic abundant constituents and low thermal manufacturing budget. However, better long-term efficiencies need to be achieved overcoming its inherent bad electrical properties of amorphous and/or microcrystalline Silicon. For the goal of achieving best results, multijunction cells of amorphous and microcrystalline silicon thin layers are industrially and lab utilized in addition to using one or more light management techniques such as textured layers, periodic and plasmonic back reflectors, flattened reflective substrates and intermediate reflector layer (IRL) between multijunction cells. The latter, IRL, which is the focus of this paper, serves as spectrally selective layer between different cells of the multijunction silicon thin film solar cell. IRL, reflects to the top cell short wavelength while permitting and scattering longer ones to achieve the best possible short circuit current. In this study, a new optimized periodic design of Intermediate reflector layer in micromorph (two multijunction cells of Microcrystalline and Amorphous Silicon) thin film solar cells is proposed. The optically simulated short circuit current reaches record values for same thickness designs when using all-ZnO design and even better results is anticipated if Lacquer material is used in combination with ZnO. The design methodology used in the paper can be easily applied to different types of IRL materials and also extended to triple and the relatively newly proposed quadruple thin films solar cells.

  20. Tandem photovoltaic cells with a composite intermediate layer

    SciTech Connect

    Travkin, V. V. Pakhomov, G. L.; Luk’anov, A. Yu.; Stuzhin, P. A.

    2015-11-15

    We have fabricated and tested tandem photovoltaic cells containing series-connected subcells of the “oxide–organic semiconductor–metal” type. The organic semiconductors were two phthalocyanine dyes (SubPc and PcVO); Al or Ag:Mg were used as capping metallic electrodes. A semitransparent composite metal–oxide layer formed by molybdenum oxide MoO{sub x} deposited over an ultrathin Al layer is used to join the subcells. Additionally, a MoO{sub x} layer deposited onto glass/ITO substrates serves as an anode buffer in the front subcell, and LiF deposited onto the dye layers serves as a cathode buffer in the front or rear subcells. Upon optimization of the thickness and composition of the intermediate layer, the open circuit voltage U{sub oc} amounts to 1.6 V reflecting total summation of the contributions from the each of the subcells at a wide spectral coating from 300–1000 nm. The fill factor in the tandem cell is not worse than in individually made single cells with the same scheme or in disconnected subcells.

  1. Atomically flat Ge buffer layers and alternating shutter growth of CaGe2 for large area germanane

    NASA Astrophysics Data System (ADS)

    Xu, Jinsong; Katoch, Jyoti; Ahmed, Adam; Pinchuk, Igor; Williams, Robert; McComb, David; Kawakami, Roland

    Germanane (GeH), which is converted from CaGe2 by soaking in HCl acid, has recently attracted interest because of its novel properties, such as large band gap (1.56eV), spin orbit coupling and predictions of high mobility (18000 cm2/Vs). Previously CaGe2 was successfully grown on Ge(111) substrates by molecular beam epitaxy (MBE) growth. But there were cracks between µm-sized islands, which is not desirable for scientific study and application, and limits the material quality. By growing atomically flat Ge buffer layers and using alternating shutter MBE growth, we are able to grow crack-free, large area films of CaGe2 films. Reflection high energy electron diffraction (RHEED) patterns of Ge buffer layer and CaGe2 indicates high quality two dimensional surfaces, which is further confirmed by atomic force microscopy (AFM), showing atomically flat and uniform Ge buffer layer and CaGe2. The appearance of Laue oscillation in X-ray diffraction (XRD) and Kiessig fringes in X-ray reflectivity (XRR) proves the uniformity of CaGe2 film and the smoothness of the interface. The high quality of CaGe2 film makes it promising to explore novel properties of GeH. Funded by NSF MRSEC DMR-1420451.

  2. Intermediate coating layer for high temperature rubbing seals for rotary regenerators

    DOEpatents

    Schienle, James L.; Strangman, Thomas E.

    1995-01-01

    A metallic regenerator seal is provided having multi-layer coating comprising a NiCrAlY bond layer, a yttria stabilized zirconia (YSZ) intermediate layer, and a ceramic high temperature solid lubricant surface layer comprising zinc oxide, calcium fluoride, and tin oxide. Because of the YSZ intermediate layer, the coating is thermodynamically stable and resists swelling at high temperatures.

  3. On atomic structure of Ge huts growing on the Ge/Si(001) wetting layer

    NASA Astrophysics Data System (ADS)

    Arapkina, Larisa V.; Yuryev, Vladimir A.

    2013-09-01

    Structural models of growing Ge hut clusters—pyramids and wedges—are proposed on the basis of data of recent STM investigations of nucleation and growth of Ge huts on the Si(001) surface in the process of molecular beam epitaxy. It is shown that extension of a hut base along ⟨110⟩ directions goes non-uniformly during the cluster growth regardless of its shape. Growing pyramids, starting from the second monolayer, pass through cyclic formation of slightly asymmetrical and symmetrical clusters, with symmetrical ones appearing after addition of every fourth monolayer. We suppose that pyramids of symmetrical configurations composed by 2, 6, 10, etc., monolayers over the wetting layer are more stable than asymmetrical ones. This might explain less stability of pyramids in comparison with wedges in dense arrays forming at low temperatures of Ge deposition. Possible nucleation processes of pyramids and wedges on wetting layer patches from identical embryos composed by 8 dimers through formation of 1 monolayer high 16-dimer nuclei different only in their symmetry is discussed. Schematics of these processes are presented. It is concluded from precise STM measurements that top layers of wetting layer patches are relaxed when huts nucleate on them.

  4. Atomic layer-by-layer oxidation of Ge (100) and (111) surfaces by plasma post oxidation of Al{sub 2}O{sub 3}/Ge structures

    SciTech Connect

    Zhang, Rui; School of Electronic Science and Engineering, Nanjing University, 22 Hankou Road, Nanjing 210093 ; Huang, Po-Chin; Lin, Ju-Chin; Takenaka, Mitsuru; Takagi, Shinichi

    2013-02-25

    The ultrathin GeO{sub x}/Ge interfaces formed on Ge (100) and (111) surfaces by applying plasma post oxidation to thin Al{sub 2}O{sub 3}/Ge structures are characterized in detail using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy. It is found that the XPS signals assigned to Ge 1+ and the 2+ states in the GeO{sub x} layers by post plasma oxidation have oscillating behaviors on Ge (100) surfaces in a period of {approx}0.3 nm with an increase in the GeO{sub x} thickness. Additionally, the oscillations of the signals assigned to Ge 1+ and 2+ states show opposite phase to each other. The similar oscillation behaviors are also confirmed on Ge (111) surfaces for Ge 1+ and 3+ states in a period of {approx}0.5 nm. These phenomena can be strongly regarded as an evidence of the atomic layer-by-layer oxidation of GeO{sub x}/Ge interfaces on Ge (100) and (111) surfaces.

  5. The generation of crystal defects in Ge-on-insulator (GOI) layers in the Ge-condensation process

    NASA Astrophysics Data System (ADS)

    Nakaharai, S.; Tezuka, T.; Hirashita, N.; Toyoda, E.; Moriyama, Y.; Sugiyama, N.; Takagi, S.

    2007-01-01

    The formation process of crystal defects in a Ge-on-insulator (GOI) layer fabricated by oxidizing a SiGe-on-insulator (SGOI) layer, known as the Ge-condensation technique, is studied systematically. It is found that the crystal defects in the GOI layer are threading dislocations and microtwins that are formed mainly in the Ge fraction range larger than ~0.5. Also, when the Ge fraction reaches ~1 and the GOI layer is formed, the density of microtwins significantly decreases and their width considerably increases. The relaxation of compressive strain, observed in SGOI and GOI layers, is not attributable to the formation of the microtwins, but to the perfect dislocations that cannot be detected as defects in the lattice image.

  6. Photoconductivity of ultra-thin Ge(GeSn) layers grown in Si by low-temperature molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Talochkin, A. B.; Chistokhin, I. B.; Mashanov, V. I.

    2016-04-01

    Photoconductivity (PC) spectra of Si/Ge(GeSn)/Si structures with the ultra-thin (1.0-2.3 nm) Ge and GeSn alloy layers grown by the low-temperature (T = 100 °C) molecular beam epitaxy are studied. Photoresponse in the range of 1.2-0.4 eV related to light absorption in the buried Ge(GeSn) layer is observed. It is shown that in case of lateral PC, a simple diffusion model can be used to determine the absorption coefficient of this layer α ˜ 105 cm-1. This value is 100 times larger than that of a single Ge quantum dot layer and is reached significantly above the band gap of most bulk semiconductors. The observed absorption is caused by optical transitions between electron and hole states localized at the interfaces. The anomalous high value of α can be explained by the unusual state of Ge(GeSn) layer with high concentration of dangling bonds, the optical properties of which have been predicted theoretically by Knief and von Niessen (Phys. Rev. B 59, 12940 (1999)).

  7. Interface Engineering for Atomic Layer Deposited Alumina Gate Dielectric on SiGe Substrates.

    PubMed

    Zhang, Liangliang; Guo, Yuzheng; Hassan, Vinayak Vishwanath; Tang, Kechao; Foad, Majeed A; Woicik, Joseph C; Pianetta, Piero; Robertson, John; McIntyre, Paul C

    2016-07-27

    Optimization of the interface between high-k dielectrics and SiGe substrates is a challenging topic due to the complexity arising from the coexistence of Si and Ge interfacial oxides. Defective high-k/SiGe interfaces limit future applications of SiGe as a channel material for electronic devices. In this paper, we identify the surface layer structure of as-received SiGe and Al2O3/SiGe structures based on soft and hard X-ray photoelectron spectroscopy. As-received SiGe substrates have native SiOx/GeOx surface layers, where the GeOx-rich layer is beneath a SiOx-rich surface. Silicon oxide regrows on the SiGe surface during Al2O3 atomic layer deposition, and both SiOx and GeOx regrow during forming gas anneal in the presence of a Pt gate metal. The resulting mixed SiOx-GeOx interface layer causes large interface trap densities (Dit) due to distorted Ge-O bonds across the interface. In contrast, we observe that oxygen-scavenging Al top gates decompose the underlying SiOx/GeOx, in a selective fashion, leaving an ultrathin SiOx interfacial layer that exhibits dramatically reduced Dit. PMID:27345195

  8. Barrier enhancement of Ge MSM IR photodetector with Ge layer optimization

    NASA Astrophysics Data System (ADS)

    Asar, Tarık; Özçelik, Süleyman

    2015-12-01

    Germanium thin films were deposited on n-type Silicon substrates with three different sputter power by using DC magnetron sputtering system at room temperature. The structural and morphological properties of the samples have been obtained by means of X-ray diffraction and atomic force microscopy measurements. Then, Germanium metal-semiconductor-metal infrared photodetectors were fabricated on these structures. The carrier recombination lifetime and the diffusion length of the devices were also calculated by using the carrier density and mobility data was obtained from the room temperature Hall Effect measurements. The dark current-voltage measurements of devices were achieved at room temperature. The electrical parameters such as ideality factor, Schottky barrier height, saturation current and series resistance were extracted from dark current-voltage characteristics. Finally, it has been shown that the barrier enhancement of Ge MSM IR photodetector can be achieved by Ge layer optimization.

  9. Investigation of Diffusion Barrier Layers for Bi-Doped Mg2(Si,Ge) Thermoelectric Legs

    NASA Astrophysics Data System (ADS)

    Prahoveanu, Codrin; Laversenne, Laetitia; de Vaulx, Cédric; Bès, Alexandre; Azzouz, Kamel; Lacoste, Ana

    2016-08-01

    The performance of thermoelectric (TE) modules is governed not only by the thermoelectric materials whose properties are capitalized, but also on the quality of the electrical contacts which are ubiquitous in the design of the device. To ensure the necessary stability of the interfaces between the TE materials and the electrodes, diffusion barriers are generally used. In this study, attempts are presented in finding diffusion barriers that would be suitable for Mg2(Si,Ge) TE materials. These involved the deposition by microwave plasma-assisted co-sputtering of intermediate gradient layers starting from Mg and Si, ending up with a Ni layer, or the deposition of metallic layers (Ti, Cr, W and Ta). The effectiveness of the deposited layers as diffusion barriers is assessed after the legs were subjected to a brazing process, with the results favoring the use of gradient layers with a thick Ni layer and metallic layers based on Ta and Cr, despite some adherence issues for the latter.

  10. Investigations of segregation phenomena in highly strained Mn-doped Ge wetting layers and Ge quantum dots embedded in silicon

    SciTech Connect

    Prestat, E. Porret, C.; Favre-Nicolin, V.; Tainoff, D.; Boukhari, M.; Bayle-Guillemaud, P.; Jamet, M.; Barski, A.

    2014-03-10

    In this Letter, we investigate manganese diffusion and the formation of Mn precipitates in highly strained, few monolayer thick, Mn-doped Ge wetting layers and nanometric size Ge quantum dot heterostructures embedded in silicon. We show that in this Ge(Mn)/Si system manganese always precipitates and that the size and the position of Mn clusters (precipitates) depend on the growth temperature. At high growth temperature, manganese strongly diffuses from germanium to silicon, whereas decreasing the growth temperature reduces the manganese diffusion. In the germanium quantum dots layers, Mn precipitates are detected, not only in partially relaxed quantum dots but also in fully strained germanium wetting layers between the dots.

  11. Growth and characterization of epitaxial layers of Ge on Si substrates

    SciTech Connect

    Fathy, D.; White, C.W.; Holland, O.W.

    1987-03-01

    Thin single crystalline layers of Ge with atomically sharp boundaries have been formed epitaxially on (100) Si substrates. This was done by /sup 74/Ge ion implantation into Si followed by steam oxidation. Using both Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM), we have found that a Ge layer forms as a result of Ge segregated at the moving SiO/sub 2/ interface during steam oxidation. For a SiO/sub 2/ layer that has swept through the implanted region, essentially all of the Ge is snow-ploughed and no Ge is lost to the oxide layer. The Ge layers and its two bounding interfaces, i.e., Ge/SiO/sub 2/ and Ge/Si, have been characterized as a function of the implantation dose and energy. The thickness of the Ge layer formed is dependent on the implantation dose. Thicknesses from a fraction of a monolayer to greater than 50 monolayers of Ge can be formed on Si by this mechanism. Initially the Ge layer forms a coherent interface with the underlying Si with no misfit dislocations, and misfit dislocations only appear as the thickness of the film is increased.

  12. Formation of alternating interfacial layers in Au-12Ge/Ni joints

    PubMed Central

    Lin, Shih-kang; Tsai, Ming-yueh; Tsai, Ping-chun; Hsu, Bo-hsun

    2014-01-01

    Au-Ge alloys are promising materials for high-power and high-frequency packaging, and Ni is frequently used as diffusion barriers. This study investigates interfacial reactions in Au-12Ge/Ni joints at 300°C and 400°C. For the reactions at 300°C, typical interfacial morphology was observed and the diffusion path was (Au) + (Ge)/NiGe/Ni5Ge3/Ni. However, an interesting phenomenon – the formation of (Au,Ni,Ge)/NiGe alternating layers – was observed for the reactions at 400°C. The diffusion path across the interface was liquid/(Au,Ni,Ge)/NiGe/···/(Au,Ni,Ge)/NiGe/Ni2Ge/Ni. The periodic thermodynamic instability at the NiGe/Ni2Ge interface caused the subsequent nucleation of new (Au,Ni,Ge)/NiGe pairs. The thermodynamic foundation and mechanism of formation of the alternating layers are elaborated in this paper. PMID:24690992

  13. Control of Sn Precipitation and Strain Relaxation in Compositionally Step-Graded Ge1-xSnx Buffer Layers for Tensile-Strained Ge Layers

    NASA Astrophysics Data System (ADS)

    Shimura, Yosuke; Tsutsui, Norimasa; Nakatsuka, Osamu; Sakai, Akira; Zaima, Shigeaki

    2009-04-01

    We investigated the relationship between Sn precipitation and strain relaxation in Ge1-xSnx buffer layers grown by the compositionally step-graded (CSG) method on a virtual Ge substrate. We found that the strain in the upper Ge1-xSnx layers is reduced by Sn precipitation rather than the lateral propagation of misfit dislocations at the interfaces of upper Ge1-xSnx layers in the CSG method. The critical misfit strain was increased to 5.8 ×10-3 compared with that in our previous work by lowering the temperature of the postdeposition annealing, and a Sn content of 6.3% in the Ge1-xSnx buffer layer was achieved with a large degree of strain relaxation using only two stacked layers of the CSG structure. An in-plane tensile strain of 0.62% in a 30-nm-thick Ge layer fabricated on these Ge1-xSnx buffer layers was achieved.

  14. Impact of hydrogen surfactant on crystallinity of Ge1-xSnx epitaxial layers

    NASA Astrophysics Data System (ADS)

    Asano, Takanori; Taoka, Noriyuki; Hozaki, Koya; Takeuchi, Wakana; Sakashita, Mitsuo; Nakatsuka, Osamu; Zaima, Shigeaki

    2015-04-01

    The effect of a hydrogen surfactant on the crystallinity of a Ge1-xSnx epitaxial layer was investigated. The improvement of crystallinity on the in-plane uniformity of Ge1-xSnx epitaxial layer was observed by X-ray diffuse scattering and transmission electron microscopy. We also observed the decrease in the surface roughness of the Ge1-xSnx epitaxial layer. This indicates the suppression of the three-dimensional growth mode of Ge1-xSnx epitaxial layer due to a compressive strain. In addition, we observed the reduction in acceptor-like defect density in an undoped-Ge1-xSnx epitaxial layer from the capacitance-voltage characteristics of a metal-oxide-semiconductor capacitor. Consequently, introducing hydrogen during the growth leads to the improvement of the crystalline quality of the Ge1-xSnx epitaxial layer.

  15. Surface-segregated Si and Ge ultrathin films formed by Ag-induced layer exchange process

    NASA Astrophysics Data System (ADS)

    Kurosawa, Masashi; Ohta, Akio; Araidai, Masaaki; Zaima, Shigeaki

    2016-08-01

    We have developed a new method of growing Si or Ge ultrathin films on a Ag(111) surface by using a Ag-induced layer exchange (ALEX) process toward the creation of 2D honeycomb sheets of Si and Ge, known as silicene and germanene, respectively. In the present paper, we clarify ALEX features, specifically the surface segregation of Si (or Ge) atoms from the underlying substrate, focusing on the annealing temperature and time. Hard X-ray photoelectron spectroscopy analyses demonstrate that surface-segregated Si (or Ge) exists on the Ag surfaces after the epitaxial growth of the Ag layer on Si(111) [or Ge(111)] substrates; the amount of segregated Si (or Ge) can be controlled by a subsequent annealing. Also, we find that the segregation of an ultrathin Si or Ge layer proceeds at an interface between Ag and the AlO x capping layer.

  16. Epitaxial growth and anisotropic strain relaxation of Ge1-xSnx layers on Ge(1 1 0) substrates

    NASA Astrophysics Data System (ADS)

    Asano, Takanori; Shimura, Yosuke; Taoka, Noriyuki; Nakatsuka, Osamu; Zaima, Shigeaki

    2013-05-01

    We have investigated the strain relaxation behavior and dislocation structures of Ge1-xSnx epitaxial layers on Ge(1 1 0) substrates. We found that the anisotropic strain relaxation of a Ge0.966Sn0.034 layer along the [0 0 1] direction preferentially occurs during postdeposition annealing over 500 °C. Transmission electron microscopy observation revealed that the anisotropic strain relaxation is attributed to the propagation of misfit dislocations along the two directions of [1¯ 1 0] and <1 1 2> at the Ge1-xSnx/Ge(1 1 0) interface. We found that the propagation of 60° dislocations preferentially occurs, which contributes to the strain relaxation only for the [0 0 1] direction.

  17. Optimization of ISBD embedded SiGe layers to prevent delamination process for MOSFET applications

    NASA Astrophysics Data System (ADS)

    Wasyluk, Joanna; Ge, Yang; Wurster, Kai; Lenski, Markus; Reichel, Carsten

    2015-08-01

    An interaction between in situ boron doped SiGe layers deposited by low pressure chemical vapor deposition and NH3 plasma treatments was studied in this work. It is shown that NH3 plasma strips introduce H atoms into SiGe layer which further leads to unwanted blistering and exfoliation of the SiGe layer. The SiGe layers with varied boron profiles were examined in this work in order to understand influence of B doping on H accumulation. It is shown that B peak at SiGe/Si interface can be modulated by the temperature and pressure changes between the layers' deposition. It was found that less H atoms diffuse into ISBD SiGe layer with higher B peak at Si cap/main SiGe layer. The SiGe layer with removed B peak at buffer/main SiGe layer interface and increased B peak at Si cap was proven to be delamination free and robust for HN3 plasma strips.

  18. GeSn p-i-n photodetectors with GeSn layer grown by magnetron sputtering epitaxy

    NASA Astrophysics Data System (ADS)

    Zheng, Jun; Wang, Suyuan; Liu, Zhi; Cong, Hui; Xue, Chunlai; Li, Chuanbo; Zuo, Yuhua; Cheng, Buwen; Wang, Qiming

    2016-01-01

    We report an investigation of normal-incidence GeSn-based p-i-n photodetectors (PDs) with a Ge0.94Sn0.06 active layer grown using sputter epitaxy on a Ge(100) substrate. A low dark current density of 0.24 A/cm2 was obtained at a reverse bias of 1 V. A high optical responsivity of the Ge0.94Sn0.06/Ge p-i-n PDs at zero bias was achieved, with an optical response wavelength extending to 1985 nm. The temperature-dependent optical-response measurement was performed, and a clear redshift absorption edge was observed. This work presents an approach for developing efficient and cost-effective GeSn-based infrared devices.

  19. Self-Diffusion of 31Si and 71Ge in Relaxed Si0.20Ge0.80 Layers

    NASA Astrophysics Data System (ADS)

    Laitinen, P.; Strohm, A.; Huikari, J.; Nieminen, A.; Voss, T.; Grodon, C.; Riihimäki, I.; Kummer, M.; Äystö, J.; Dendooven, P.; Räisänen, J.; Frank, W.

    2002-08-01

    Self-diffusion of implanted 31Si and 71Ge in relaxed Si0.20Ge0.80 layers has been studied in the tempera­ture range 730-950 °C by means of a modified radiotracer technique. The temperature dependences of the diffusion coefficients were found to be Arrhenius-type with activation enthalpies of 3.6eV and 3.5eV and preexponential factors of 7.5×10-3 m2 s-1 and 8.1×10-3 m2 s-1 for 31Si and 71Ge, respectively. These results suggest that, as in Ge, in Si0.20Ge0.80 both 31Si and 71Ge diffuse via a vacancy mechanism. Since in Si0.20Ge0.80 71Ge diffuses only slightly faster than 31Si, in self-diffusion studies on Si-Ge 71Ge radioisotopes may be used as substitutes for the ``uncomfortably'' short-lived 31Si radiotracer atoms.

  20. Characterization of 7-nm-thick strained Ge-on-insulator layer fabricated by Ge-condensation technique

    NASA Astrophysics Data System (ADS)

    Nakaharai, Shu; Tezuka, Tsutomu; Sugiyama, Naoharu; Moriyama, Yoshihiko; Takagi, Shin-ichi

    2003-10-01

    A strained Ge-on-insulator (GOI) structure with a 7-nm-thick Ge layer was fabricated for applications to high-speed transistors. The GOI layer was formed by thermal oxidation of a strained SiGe layer grown epitaxially on a silicon-on-insulator (SOI) wafer. In transmission electron microscopy measurements, the obtained GOI layer exhibited a single-crystal structure with the identical orientation to an original SOI substrate and a smooth Ge/SiO2 interface. The rms of the surface roughness of the GOI layer was evaluated to be 0.4 nm by atomic force microscopy. The residual Si fraction in the GOI layer was estimated to be lower than the detection limit of Raman spectroscopy of 0.5% and also than the electron energy loss spectroscope measurements of 3%. It was found that the obtained GOI layer was compressively strained with a strain of 1.1%, which was estimated by the Raman spectroscopy. Judging from the observed crystal quality and the strain value, this technique is promising for fabrication of high-mobility strained Ge channel of high-performance GOI metal-insulator-semiconductor (MIS) transistors.

  1. Voltage sharing effect and interface state calculation of a wafer-bonding Ge/Si avalanche photodiode with an interfacial GeO2 insulator layer.

    PubMed

    Ke, Shaoying; Lin, Shaoming; Li, Xin; Li, Jun; Xu, Jianfang; Li, Cheng; Chen, Songyan

    2016-02-01

    The tunneling effect and interface state in the p-Ge/GeO2p-Si structure of a wafer-bonding Ge/Si avalanche photodiode (APD) are investigated. It is found that the thin interfacial GeO2 layer (1-2 nm) formed by the hydrophilic reaction at the wafer-bonding interface significantly affects the performance of the Ge/Si APD. With the increase of the GeO2 thickness, the dark current of the Ge/Si APD decreases enormously due to the blocking effect of this GeO2 layer. Owing to the carrier accumulation in Ge layer under illumination condition, the voltage sharing effect of the GeO2 layer (thicker) becomes serious, leading to the absence of the electric field in Ge layer. The photon-generated electrons at Ge/GeO2 interface can be captured and released by the interface states at certain reverse bias. This can adjust the avalanche current of the Ge/Si APD. The stronger interface recombination induced by the larger interface state density (ISD) results in the decrease of the electric field in Ge layer. This increases the transit time of carriers, which in turn decreases the 3dB-bandwidth. Due to the drastic increase of the dark current (larger ISD), the gain of the Ge/Si APD decreases. PMID:26906771

  2. Long-Wavelength Stacked SiGe/Si Heterojunction Internal Photoemission Infrared Detectors Using Multiple SiGe/Si Layers

    NASA Technical Reports Server (NTRS)

    Park, J. S.; Lin, T. L.; Jones, E. W.; Castillo, H. M. Del; Gunapala, S. D.

    1994-01-01

    Utilizing low temperature silicon molecular beam epitaxy (MBE) growth, long-wavelength stacked SiGe/Si heterojunction internal photoemission (HIP) infrared detectors with multiple SiGe/Si layers have been fabricated and demonstrated. Using an elemental boron source, high doping concentrations (approximately equal to 4 x 10(sup 20) cm(sup -3)) has been achieved and high crystalline quality multiple Si(sub 0.7)Ge(sub 0.3)/Si layers have been obtained. The detector structure consists of several periods of degenerately boron doped (approximately equal to 4 x 10(sup 20) cm(sup -3)) thin (less than or equal to 50 u Si(sub 0.7)Ge(sub 0.3) layers and undoped thick (approximately equal to 300u Si layers. The multiple p(sup +) - Si(sub 0.7)Ge(sub 0.3)/undoped-Si layers show strong infrared absorption in the long-wavelength regime mainly through free carrier absorption. The stacked Si(sub 0.7)Ge(sub 0.3)/Si HIP detectors with p = 4 x 10(sup 20) cm(sup -3) exhibit strong photoresponse at wavelengths ranging from 2 to 20 (micro)m with quantum efficiencies of about 4% and 1.5% at 10 and 15 (micro)m wavelengths, respectively. The detectors show near ideal thermionic-emission limited dark current characteristics.

  3. Impact of intermediate localized states on nonlinear optical absorption of Ga-Ge-Se nanocolloidal solutions

    NASA Astrophysics Data System (ADS)

    Sebastian, Indu; Divya, S.; Nampoori, V. P. N.; Radhakrishnan, P.; Thomas, Sheenu

    2013-01-01

    We present the linear and nonlinear optical studies on nanocolloidal solutions of Ga9Ge27Se64 glass with varying concentrations. Optical bandgap of the material is found to vary with respect to the concentration of the solute in the solution. An intermediate peak in the band tail of the absorption spectra is observed due to the presence of energy band in the forbidden gap. The existence of fluorescence emission confirms the above argument. Nonlinear absorption is studied using open aperture Z-scan technique. The mechanism behind nonlinear absorption is predicted as two photon as well as two step photon absorption. Nonlinearity increases with decrease in optical bandgap which in turn depends on the concentration of the nanocolloidal solutions.

  4. Surface Morphology Transformation Under High-Temperature Annealing of Ge Layers Deposited on Si(100).

    PubMed

    Shklyaev, A A; Latyshev, A V

    2016-12-01

    We study the surface morphology and chemical composition of SiGe layers after their formation under high-temperature annealing at 800-1100 °C of 30-150 nm Ge layers deposited on Si(100) at 400-500 °C. It is found that the annealing leads to the appearance of the SiGe layers of two types, i.e., porous and continuous. The continuous layers have a smoothened surface morphology and a high concentration of threading dislocations. The porous and continuous layers can coexist. Their formation conditions and the ratio between their areas on the surface depend on the thickness of deposited Ge layers, as well as on the temperature and the annealing time. The data obtained suggest that the porous SiGe layers are formed due to melting of the strained Ge layers and their solidification in the conditions of SiGe dewetting on Si. The porous and dislocation-rich SiGe layers may have properties interesting for applications. PMID:27541814

  5. Integration of GaAs epitaxial layer to Si-based substrate using Ge condensation and low-temperature migration enhanced epitaxy techniques

    SciTech Connect

    Oh, Hoon Jung; Choi, Kyu Jin; Loh, Wei Yip; Htoo, Thwin; Chua, Soo Jin; Cho, Byung Jin

    2007-09-01

    A GaAs defect-free epitaxial layer has been grown on Si via a Ge concentration graded SiGe on insulator (SGOI) for application in high channel-mobility metal-oxide-semiconductor field effect transistor. The SGOI layer, 42 nm thick, serves as the compliant and intermediate buffer to reduce the lattice and thermal expansion mismatches between Si and GaAs. A modified two-step Ge condensation technique achieves the surface Ge concentration in SGOI as high as 71%. It is also found that low-temperature migration enhanced epitaxy during the initial GaAs nucleation on the SGOI surface is critical to obtain a device quality GaAs layer by epitaxial growth.

  6. Infrared Detectors Containing Stacked Si(1-x)Ge(x)/Si Layers

    NASA Technical Reports Server (NTRS)

    Park, Jin S.; Lin, True-Lon; Jones, Eric; Del Castillo, Hector; Gunapala, Sarath

    1996-01-01

    Long-wavelength-infrared detectors containing multiple layers of high-quality crystalline p(+) Si(1-x)Ge(x) alternating with layers of Si undergoing development. Each detector comprises stack of Si(1-x)Ge(x)/Si heterojunction internal photoemission (HIP) photodetectors. In comparison with older HIP detectors containing single Si(1-x)Ge(x)/Si heterojunctions, developmental detectors feature greater quantum efficiencies and stronger photoresponses.

  7. Growth of Ge1-xSnx/Ge strained-layer superlattices on Si(1 0 0) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Su, Shaojian; Zhang, Dongliang; Zhang, Guangze; Xue, Chunlai; Cheng, Buwen

    2013-12-01

    Low-temperature molecular beam epitaxy was employed to grow Ge1-xSnx/Ge strained-layer superlattices (SLSs) on Si(1 0 0) substrates with a Ge buffer layer. The Ge1-xSnx and Ge layers in the SLSs were deposited at the same temperature as low as 180 °C. Surface roughening during the growth was investigated by in situ reflection high-energy electron diffraction (RHEED). The periods, compositions, and quality of the SLSs were characterized by high resolution X-ray diffraction (HR-XRD), random and aligned Rutherford backscattering spectra (RBS), transmission electron microscopy (TEM), and scanning TEM. Besides, a Ge1-xSnx/Ge SLS sample was grown directly on Si(1 0 0) for comparison. It’s found that the quality of the Ge1-xSnx/Ge SLSs grown on a Ge buffer was significantly better than that grown directly on Si(1 0 0) substrate.

  8. Segregation of Sb in Ge epitaxial layers and its usage for the selective doping of Ge-based structures

    SciTech Connect

    Antonov, A. V.; Drozdov, M. N.; Novikov, A. V. Yurasov, D. V.

    2015-11-15

    The segregation of Sb in Ge epitaxial layers grown by the method of molecular beam epitaxy on Ge (001) substrates is investigated. For a growth temperature range of 180–325°C, the temperature dependence is determined for the segregation ratio of Sb in Ge, which shows a sharp increase (by more than three orders of magnitude) with increasing temperature. The strong dependence of the segregation properties of Sb on the growth temperature makes it possible to adapt a method based on the controlled use of segregation developed previously for the doping of Si structures for the selective doping of Ge structures with a donor impurity. Using this method selectively doped Ge:Sb structures, in which the bulk impurity concentration varies by an order of magnitude at distances of 3–5 nm, are obtained.

  9. The nature of intermediate-range order in Ge-As-S glasses : results from reverse Monte Carlo modeling.

    SciTech Connect

    Soyer-Uzun, S.; Benmore, C. J.; Siewenie, J. E.; Sen, S.; X-Ray Science Division; Univ.of California at Davis; LANL

    2010-01-01

    The experimental neutron and x-ray diffraction data for stoichiometric and S-deficient Ge{sub x}As{sub x}S{sub 100-2x} glasses with x = 18.2, 25.0, and 33.3 at.% have been modeled simultaneously using the reverse Monte Carlo (RMC) technique. Nearest-neighbor coordination environments, as obtained in previous x-ray absorption spectroscopy and diffraction experiments, have been employed as short-range order constraints in these simulations. The large scale three-dimensional structural models thus obtained from RMC simulation are used to investigate the nature and compositional evolution of intermediate-range structural order in these ternary glasses. The intermediate-range structural order is controlled by (1) a corner-shared three-dimensional network of AsS{sub 3} pyramids and GeS{sub 4} tetrahedra in the stoichiometric Ge{sub 18.2}As{sub 18.2}S{sub 63.6} glass, (2) a heterogeneous structure that consists of homopolar bonded As-rich regions coexisting with a GeS{sub 2} network in the S-deficient Ge{sub 25}As{sub 25}S{sub 50} glass, and (3) a homogeneous structure resulting from the disruption of the topological continuity of the GeS{sub 2} network and As-rich clusters regions due to the formation of Ge-As bonds in the most S-deficient Ge{sub 33.3}As{sub 33.3}S{sub 33.3} glass. This scenario of the compositional evolution of intermediate-range structural order is consistent with and provides an atomistic explanation of the corresponding evolution in the position, width and intensity of the first sharp diffraction peak and the magnitude of small angle scattering in these glasses.

  10. Improved interfacial and electrical properties of Ge MOS devices with ZrON/GeON dual passivation layer

    NASA Astrophysics Data System (ADS)

    Wenyu, Yuan; Jingping, Xu; Lu, Liu; Yong, Huang; Zhixiang, Cheng

    2016-05-01

    The interfacial and electrical characteristics of Ge metal–oxide–semiconductor (MOS) devices with a dual passivation layer of ZrON/GeON formed by NH3- or N2-plasma treatment are investigated. The experimental results show that the NH3-plasma treated sample exhibits significantly improved interfacial and electrical properties as compared to the samples with N2-plasma treatment and no treatment: a lower interface-state density at the midgap (1.64 × 1011 cm‑2 · eV‑1) and gate leakage current (9.32 × 10‑5 A/cm2 at Vfb + 1 V), a small capacitance equivalent thickness (1.11 nm) and a high k value (32). X-ray photoelectron spectroscopy is used to analyze the involved mechanisms. It is indicated that more GeON and less GeOx (x < 2) are formed on the Ge surface during NH3-plasma treatment than the N2-plasma treatment, resulting in a high-quality high-k/Ge interface, because H atoms and NH radicals in NH3-plasma can enhance volatilization of the unstable low-k GeOx, creating high-quality GeON passivation layer. Moreover, more nitrogen incorporation in ZrON/GeON induced by NH3-plasma treatment can build a stronger N barrier and thus more effectively inhibit in-diffusion of O and Ti from high-k gate dielectric and out-diffusion of Ge. Project supported by the National Natural Science Foundation of China (Nos. 6127411261176100, 61404055).

  11. Reduction of threading dislocation density in Ge/Si using a heavily As-doped Ge seed layer

    NASA Astrophysics Data System (ADS)

    Lee, Kwang Hong; Bao, Shuyu; Wang, Bing; Wang, Cong; Yoon, Soon Fatt; Michel, Jurgen; Fitzgerald, Eugene A.; Tan, Chuan Seng

    2016-02-01

    High quality germanium (Ge) epitaxial film is grown directly on silicon (001) substrate with 6° off-cut using a heavily arsenic (As) doped Ge seed layer. The growth steps consists of (i) growth of a heavily As-doped Ge seed layer at low temperature (LT, at 400 °C), (ii) Ge growth with As gradually reduced to zero at high temperature (HT, at 650 °C), (iii) pure Ge growth at HT. This is followed by thermal cyclic annealing in hydrogen at temperature ranging from 600 to 850 °C. Analytical characterization have shown that the Ge epitaxial film with a thickness of ˜1.5 µm experiences thermally induced tensile strain of 0.20% with a treading dislocation density (TDD) of mid 106/cm2 which is one order of magnitude lower than the control group without As doping and surface roughness of 0.37 nm. The reduction in TDD is due to the enhancement in velocity of dislocations in an As-doped Ge film.

  12. Effect of GeO2 deposition temperature in atomic layer deposition on electrical properties of Ge gate stack

    NASA Astrophysics Data System (ADS)

    Kanematsu, Masayuki; Shibayama, Shigehisa; Sakashita, Mitsuo; Takeuchi, Wakana; Nakatsuka, Osamu; Zaima, Shigeaki

    2016-08-01

    We investigated the effect of GeO2 deposition temperature (T depo) on electronic properties of Al/Al2O3/GeO2/Ge MOS capacitors. Capacitance–voltage characteristics show frequency dispersions under depletion and strong inversion conditions, which can be attributed from the interface states at the atomic layer deposition (ALD)-GeO2/Ge interface and from the defect states in the quasi-neutral region in the Ge substrate, respectively. We found that the interface state density (D it) shows similar values and energy distributions as T depo decreases to 200 from 300 °C, while a higher D it is observed at a T depo of 150 °C. Also, from the temperature dependence of conductance, the frequency dispersion under the strong inversion condition can be related to the minority carrier diffusion to the quasi-neutral region of the Ge substrate. The frequency dependence of conductance reveals that the undesirable increment of the bulk defect density can be suppressed by decreasing T depo. In this study, the bulk defect density in a MOS capacitor prepared at a T depo of 200 °C decreases one tenth compared with that at a T depo of 300 °C. The ALD of GeO2 at a low temperature of around 200 °C is effective for both obtaining a low D it and preventing the undesirable introduction of bulk defect density.

  13. Antiferromagnetic iridium manganese based intermediate layers for perpendicular magnetic recording media

    NASA Astrophysics Data System (ADS)

    Srinivasan, Kumar; Piramanayagam, S. N.; Sbiaa, Rachid

    2008-08-01

    Current generation CoCrPt oxide based perpendicular magnetic recording media use two Ru-based intermediate layers in order to grow crystallographically textured, and magnetically isolated granular media. In this work, the advantage of replacing the Ru grain isolation layer with antiferromagnetic IrMn is demonstrated. Media samples using 7.5nm thick IrMn intermediate layers show perpendicular texture with dispersion below 4°, coercivity of over 4000Oe alongside magnetic exchange decoupling, average grain sizes of 6nm with distributions under 14%, and thermal stability factor of 88. The IrMn layer may also help to stabilize the recording layer grains against thermal instability effects.

  14. Growth of ultrahigh-Sn-content Ge1- x Sn x epitaxial layer and its impact on controlling Schottky barrier height of metal/Ge contact

    NASA Astrophysics Data System (ADS)

    Suzuki, Akihiro; Nakatsuka, Osamu; Shibayama, Shigehisa; Sakashita, Mitsuo; Takeuchi, Wakana; Kurosawa, Masashi; Zaima, Shigeaki

    2016-04-01

    We examined the epitaxial growth of an ultrahigh-Sn-content Ge1- x Sn x layer on a Ge substrate and investigated the impact of a Ge1- x Sn x interlayer on the Schottky barrier height (SBH) of the metal/Ge contact. In this study, we considered guidelines of the strain energy and growth temperature to realize a high-Sn-content Ge1- x Sn x layer while keeping the epitaxial growth and suppressing the Sn precipitation. By reducing the film thickness and keeping a low growth temperature, we formed an atomically flat and uniform Ge1- x Sn x epitaxial layer with a Sn content up to 46% on a Ge(001) substrate. We also performed the current density-voltage measurement for Al/Ge1- x Sn x /n-Ge Schottky diodes to estimate the SBH. We found that the SBH of Al/Ge1- x Sn x /n-Ge contact decreases with increasing Sn content in the Ge1- x Sn x interlayer. The shift of the pinning position towards the conduction band edge of Ge is one of the reasons for the SBH reduction of Al/Ge1- x Sn x /n-Ge contact because the valence band edge of Ge1- x Sn x would rise as the Sn content increases.

  15. GeOx interfacial layer scavenging remotely induced by metal electrode in metal/HfO2/GeOx/Ge capacitors

    NASA Astrophysics Data System (ADS)

    Lee, Taehoon; Jung, Yong Chan; Seong, Sejong; Lee, Sung Bo; Park, In-Sung; Ahn, Jinho

    2016-07-01

    The metal gate electrodes of Ni, W, and Pt have been investigated for their scavenging effect: a reduction of the GeOx interfacial layer (IL) between HfO2 dielectric and Ge substrate in metal/HfO2/GeOx/Ge capacitors. All the capacitors were fabricated using the same process except for the material used in the metal electrodes. Capacitance-voltage measurements, scanning transmission electron microscopy, and electron energy loss spectroscopy were conducted to confirm the scavenging of GeOx IL. Interestingly, these metals are observed to remotely scavenge the interfacial layer, reducing its thickness in the order of Ni, W, and then Pt. The capacitance equivalent thickness of these capacitors with Ni, W, and Pt electrodes are evaluated to be 2.7 nm, 3.0 nm, and 3.5 nm, and each final remnant physical thickness of GeOx IL layer is 1.1 nm 1.4 nm, and 1.9 nm, respectively. It is suggested that the scavenging effect induced by the metal electrodes is related to the concentration of oxygen vacancies generated by oxidation reaction at the metal/HfO2 interface.

  16. Emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional structure

    NASA Astrophysics Data System (ADS)

    Huang, Zhong-Mei; Huang, Wei-Qi; Liu, Shi-Rong; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke; Qin, Cao-Jian

    2016-04-01

    In our experiment, it was observed that the emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional (1D) structure. The results of experiment and calculation demonstrate that the uniaxial tensile strain in the (111) and (110) direction can efficiently transform Ge to a direct bandgap material with the bandgap energy useful for technological application. It is interested that under the tensile strain from Ge-GeSn layers on 1D structure in which the uniaxial strain could be obtained by curved layer (CL) effect, the two bandgaps EΓg and ELg in the (111) direction become nearly equal at 0.83 eV related to the emission of direct-gap band near 1500 nm in the experiments. It is discovered that the red-shift of the peaks from 1500 nm to 1600 nm occurs with change of the uniaxial tensile strain, which proves that the peaks come from the emission of direct-gap band.

  17. Emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional structure.

    PubMed

    Huang, Zhong-Mei; Huang, Wei-Qi; Liu, Shi-Rong; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke; Qin, Cao-Jian

    2016-01-01

    In our experiment, it was observed that the emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional (1D) structure. The results of experiment and calculation demonstrate that the uniaxial tensile strain in the (111) and (110) direction can efficiently transform Ge to a direct bandgap material with the bandgap energy useful for technological application. It is interested that under the tensile strain from Ge-GeSn layers on 1D structure in which the uniaxial strain could be obtained by curved layer (CL) effect, the two bandgaps EΓg and ELg in the (111) direction become nearly equal at 0.83 eV related to the emission of direct-gap band near 1500 nm in the experiments. It is discovered that the red-shift of the peaks from 1500 nm to 1600 nm occurs with change of the uniaxial tensile strain, which proves that the peaks come from the emission of direct-gap band. PMID:27097990

  18. Emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional structure

    PubMed Central

    Huang, Zhong-Mei; Huang, Wei-Qi; Liu, Shi-Rong; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke; Qin, Cao-Jian

    2016-01-01

    In our experiment, it was observed that the emission of direct-gap band in germanium with Ge-GeSn layers on one-dimensional (1D) structure. The results of experiment and calculation demonstrate that the uniaxial tensile strain in the (111) and (110) direction can efficiently transform Ge to a direct bandgap material with the bandgap energy useful for technological application. It is interested that under the tensile strain from Ge-GeSn layers on 1D structure in which the uniaxial strain could be obtained by curved layer (CL) effect, the two bandgaps EΓg and ELg in the (111) direction become nearly equal at 0.83 eV related to the emission of direct-gap band near 1500 nm in the experiments. It is discovered that the red-shift of the peaks from 1500 nm to 1600 nm occurs with change of the uniaxial tensile strain, which proves that the peaks come from the emission of direct-gap band. PMID:27097990

  19. THIN-LAYER SEPARATION OF CITRIC ACID CYCLE INTERMEDIATES, LACTIC ACID, AND THE AMINO ACID TAURINE

    EPA Science Inventory

    This paper describes a two-dimensional mixed-layer method for separating citric acid cycle intermediates, lactic acid and the amino acid taurine. The method cleanly separates all citric acid cycle intermediates tested, excepting citric acid and isocitric acid. The solvents are in...

  20. Atomic-layer etching of Ge using an ultraclean ECR plasma

    NASA Astrophysics Data System (ADS)

    Sugiyama, Takayuki; Matsuura, Takashi; Murota, Junichi

    1997-03-01

    Self-limited atomic-layer etching of Ge(100) has been investigated by alternated chlorine adsorption and Ar + ion irradiation using an ultraclean ECR plasma. With short Ar + ion irradiation, about a quarter of atomic-layer thickness was etched in each cycle under the saturated adsorption condition, which corresponds with the case of Si(100). With increasing irradiation amount of Ar + ions, the etch rate per cycle increases and tends to saturate to the atomic-layer thickness of Ge(100). Taking Ar + ion induced reaction into consideration, a simple exponentially-saturating equation well describes the atomic-layer etch rate of Ge. From measured Ar + ion flux density distribution, it is estimated that the energy of Ar + ions predominantly contributing to the atomic-layer etching of Ge is higher than the order of ˜13 eV.

  1. Mobility Behavior of Ge1-xSnx Layers Grown on Silicon-on-Insulator Substrates

    NASA Astrophysics Data System (ADS)

    Nakatsuka, Osamu; Tsutsui, Norimasa; Shimura, Yosuke; Takeuchi, Shotaro; Sakai, Akira; Zaima, Shigeaki

    2010-04-01

    We have investigated the behaviors of the carrier mobility and concentration of the undoped Ge1-xSnx layers epitaxially grown on silicon-on-insulator (SOI) substrates. Hall measurement revealed the conduction of holes excited from acceptor levels related to vacancy defects whose concentration was as high as 1018 cm-3 in Ge1-xSnx layers. The temperature dependences of the carrier mobility and concentration in the valence band was estimated by reducing the parallel conduction component in the impurity band. The incorporation of Sn at a content lower than 4.0% hardly degraded the hole mobility of heteroepitaxial Ge1-xSnx layers. In contrast, the mobility of the Ge1-xSnx layers was improved by reducing the carrier concentration of the Ge1-xSnx layers by Sn incorporation compared with that of the Ge layer formed under the same growth and annealing conditions. This result suggests that the incorporation of Sn into Ge leads to reducing the hole concentration of the electrically active vacancy defects due to the formation of Sn-vacancy pairs.

  2. Impact of pattern dependency of SiGe layers grown selectively in source/drain on the performance of 22 nm node pMOSFETs

    NASA Astrophysics Data System (ADS)

    Wang, Guilei; Moeen, M.; Abedin, A.; Xu, Yefeng; Luo, Jun; Guo, Yiluan; Qin, Changliang; Tang, Zhaoyun; Yin, Haizhou; Li, Junfeng; Yan, Jiang; Zhu, Huilong; Zhao, Chao; Chen, Dapeng; Ye, Tianchun; Kolahdouz, M.; Radamson, Henry H.

    2015-12-01

    Pattern dependency of selective epitaxy of Si1-xGex (0.20 ⩽ x ⩽ 0.45) grown in recessed source/drain regions of 22 nm pMOSFETs has been studied. A complete substrate mapping over 200 mm wafers was performed and the transistors' characteristics were measured. The designed SiGe profile included a layer with Ge content of 40% at the bottom of recess (40 nm) and capped with 20% Ge as a sacrificial layer (20 nm) for silicide formation. The induced strain in the channel was simulated before and after silicidation. The variation of strain was localized and its effect on the transistors' performance was determined. The chips had a variety of SiGe profile depending on their distance (closest, intermediate and central) from the edge of the 200 mm wafer. SiGe layers with poor epi-quality were observed when the coverage of exposed Si of the chip was below 1%. This causes high Ge contents with layer thicknesses above the critical thickness.

  3. Diffractive intermediate layer enables broadband light trapping for high efficiency ultrathin c-Si tandem cells

    NASA Astrophysics Data System (ADS)

    Li, Guijun; Ho, Jacob Y. L.; Li, He; Kwok, Hoi-Sing

    2014-06-01

    Light management through the intermediate reflector in the tandem cell configuration is of great practical importance for achieving high stable efficiency and also low cost production. So far, however, the intermediate reflectors employed currently are mainly focused on the light absorption enhancement of the top cell. Here, we present a diffractive intermediate layer that allows for light trapping over a broadband wavelength for the ultrathin c-Si tandem solar cell. Compared with the standard intermediate reflector, this nanoscale architectural intermediate layer results in a 35% and 21% remarkable enhancement of the light absorption in the top (400-800 nm) and bottom (800-1100 nm) cells simultaneously, and ultrathin c-Si tandem cells with impressive conversion efficiency of 13.3% are made on the glass substrate.

  4. Dilute Group III-V nitride intermediate band solar cells with contact blocking layers

    DOEpatents

    Walukiewicz, Wladyslaw; Yu, Kin Man

    2012-07-31

    An intermediate band solar cell (IBSC) is provided including a p-n junction based on dilute III-V nitride materials and a pair of contact blocking layers positioned on opposite surfaces of the p-n junction for electrically isolating the intermediate band of the p-n junction by blocking the charge transport in the intermediate band without affecting the electron and hole collection efficiency of the p-n junction, thereby increasing open circuit voltage (V.sub.OC) of the IBSC and increasing the photocurrent by utilizing the intermediate band to absorb photons with energy below the band gap of the absorber layers of the IBSC. Hence, the overall power conversion efficiency of a IBSC will be much higher than an conventional single junction solar cell. The p-n junction absorber layers of the IBSC may further have compositionally graded nitrogen concentrations to provide an electric field for more efficient charge collection.

  5. Dilute group III-V nitride intermediate band solar cells with contact blocking layers

    DOEpatents

    Walukiewicz, Wladyslaw; Yu, Kin Man

    2015-02-24

    An intermediate band solar cell (IBSC) is provided including a p-n junction based on dilute III-V nitride materials and a pair of contact blocking layers positioned on opposite surfaces of the p-n junction for electrically isolating the intermediate band of the p-n junction by blocking the charge transport in the intermediate band without affecting the electron and hole collection efficiency of the p-n junction, thereby increasing open circuit voltage (V.sub.OC) of the IBSC and increasing the photocurrent by utilizing the intermediate band to absorb photons with energy below the band gap of the absorber layers of the IBSC. Hence, the overall power conversion efficiency of a IBSC will be much higher than an conventional single junction solar cell. The p-n junction absorber layers of the IBSC may further have compositionally graded nitrogen concentrations to provide an electric field for more efficient charge collection.

  6. Plastic relaxation in GeSi layers on Si (001) and Si (115) substrates

    SciTech Connect

    Drozdov, Yu. N. Drozdov, M. N.; Yunin, P. A.; Yurasov, D. V.; Shaleev, M. A.; Novikov, A. V.

    2015-01-15

    It is demonstrated using X-ray diffraction and atomic force microscopy that elastic stresses in GeSi layers on Si (115) substrates relax more effectively than in the same layers on Si (001) substrates. This fact is attributed to the predominant contribution of one of the (111) slip planes on the (115) cut. The atomicforce-microscopy image of the GeSi/Si(115) surface reveals unidirectional slip planes, while the GeSi/Si(001) image contains a grid of orthogonal lines and defects at the points of their intersection. As a result, thick GeSi layers on Si (115) have a reduced surface roughness. A technique for calculating the parameters of relaxation of the layer on the Si (115) substrate using X-ray diffraction data is discussed.

  7. Magneto-optical properties of Co /Ge(100) with ultrathin Ag buffer layers

    NASA Astrophysics Data System (ADS)

    Su, C. W.; Tsay, J. S.; Hwang, C. H.; Yao, Y. D.

    2005-05-01

    Magnetic properties of Co films (<2nm) with Ag buffer layers (<0.7nm) grown on Ge(100) at room temperature and 200K were studied by surface magneto-optical Kerr effect. Without the buffer, the films reveal in-plane magnetic anisotropy even Co and Ge forms nonmagnetic interfacial alloys. The hysteresis due to intercalation of Ag can be detected at thinner Co thicknesses. The buffer can effectively cutoff the intermixing of Co and Ge. As the thickness of Ag is reduced, out-of-plane magnetic anisotropy due to the interface interactions between Co /Ag and Co /Ge was discovered and was only at 200K.

  8. Anomalously elastic intermediate phase in randomly layered superfluids, superconductors, and planar magnets.

    PubMed

    Mohan, Priyanka; Goldbart, Paul M; Narayanan, Rajesh; Toner, John; Vojta, Thomas

    2010-08-20

    We show that layered quenched randomness in planar magnets leads to an unusual intermediate phase between the conventional ferromagnetic low-temperature and paramagnetic high-temperature phases. In this intermediate phase, which is part of the Griffiths region, the spin-wave stiffness perpendicular to the random layers displays anomalous scaling behavior, with a continuously variable anomalous exponent, while the magnetization and the stiffness parallel to the layers both remain finite. Analogous results hold for superfluids and superconductors. We study the two phase transitions into the anomalous elastic phase, and we discuss the universality of these results, and implications of finite sample size as well as possible experiments. PMID:20868107

  9. GSMBE growth and structural characterisation of SiGeC layers for HBT

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Neave, J. H.; Li, X. B.; Fewster, P. F.; El Mubarek, H. A. W.; Ashburn, P.; Mitrovic, I. Z.; Buiu, O.; Hall, S.

    2005-05-01

    Gas source molecular beam epitaxy is used for the growth of SiGeC layers from disilane, germane and methylsilane precursors at low substrate temperatures. A systematic method of carbon concentration determination based on a combination of X-ray diffraction and X-ray reflectivity is examined. The grown layers were annealed using rapid thermal annealing and analysed with X-ray diffraction, X-ray reflectivity and secondary ion mass spectrometry. The recovery of compressive strain in the SiGeC layer is correlated to the loss of carbon through diffusion and indicates that the carbon atoms are incorporated substitutionally in the as-grown layers.

  10. Thermoelectric energy conversion in layered structures with strained Ge quantum dots grown on Si surfaces

    NASA Astrophysics Data System (ADS)

    Korotchenkov, Oleg; Nadtochiy, Andriy; Kuryliuk, Vasyl; Wang, Chin-Chi; Li, Pei-Wen; Cantarero, Andres

    2014-03-01

    The efficiency of the energy conversion devices depends in many ways on the materials used and various emerging cost-effective nanomaterials have promised huge potentials in highly efficient energy conversion. Here we show that thermoelectric voltage can be enhanced by a factor of 3 using layer-cake growth of Ge quantum dots through thermal oxidation of SiGe layers stacked in SiO2/Si3N4 multilayer structure. The key to achieving this behavior has been to strain the Ge/Si interface by Ge dots migrating to Si substrate. Calculations taking into account the carrier trapping in the dot with a quantum transmission into the neighboring dot show satisfactory agreement with experiments above ≈200 K. The results may be of interest for improving the functionality of thermoelectric devices based on Ge/Si.

  11. Versatile buffer layer architectures based on Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Roucka, R.; Tolle, J.; Cook, C.; Chizmeshya, A. V. G.; Kouvetakis, J.; D'Costa, V.; Menendez, J.; Chen, Zhihao D.; Zollner, S.

    2005-05-01

    We describe methodologies for integration of compound semiconductors with Si via buffer layers and templates based on the GeSn system. These layers exhibit atomically flat surface morphologies, low defect densities, tunable thermal expansion coefficients, and unique ductile properties, which enable them to readily absorb differential stresses produced by mismatched overlayers. They also provide a continuous selection of lattice parameters higher than that of Ge, which allows lattice matching with technologically useful III-V compounds. Using this approach we have demonstrated growth of GaAs, GeSiSn, and pure Ge layers at low temperatures on Si(100). These materials display extremely high-quality structural, morphological, and optical properties opening the possibility of versatile integration schemes directly on silicon.

  12. Relaxation of strain during solid phase epitaxial growth of Ge + ion implanted layers in silicon

    NASA Astrophysics Data System (ADS)

    Holmén, G.; Songsiriritthigul, Prayoon

    1998-09-01

    Formation of Si 1- xGe x-alloy layers by solid phase epitaxial growth (SPEG) of Ge + ion implanted silicon has been studied. The ion implantations were performed with 40, 100, 150, 200 and 300 keV 74Ge + ions and various ion doses. The SPEG of the ion implanted layers was carried out in a conventional furnace at 850°C for 20 min under a flow of nitrogen gas. The Si 1- xGe x-alloy layers were characterised by Rutherford backscattering spectrometry and transmission electron microscopy (TEM). For a given ion energy, a Si 1- xGe x-alloy layer with no observable extended defects can be manufactured if the ion dose is below a critical value and strain-induced defects are formed in the alloy layer when the ion dose is equal to or above this value. The critical Ge + ion dose increases with ion energy, while the critical maximum Ge concentration decreases. For ion energies ⩽150 keV, the defects observed in the alloy layers are mostly stacking faults parallel to the {1 1 1} planes. For higher ion energies, 200 keV and above, the majority of defects in the alloy layer are hairpin dislocations. In the whole ion energy range, the critical ion dose and the depth position of the nucleation site for the stacking faults obtained from the measurements are in good agreement with theoretical predictions. Extended defects are formed in the alloy layer during the SPEG when the regrowth of the crystalline/amorphous interface has reached the depth position in the crystal where the accumulated strain energy density is equal to the critical value of 235 mJ/m 2.

  13. The role of Ag buffer layer in Fe islands growth on Ge (111) surfaces

    SciTech Connect

    Fu, Tsu-Yi Wu, Jia-Yuan; Jhou, Ming-Kuan; Hsu, Hung-Chan

    2015-05-07

    Sub-monolayer iron atoms were deposited at room temperature on Ge (111)-c(2 × 8) substrates with and without Ag buffer layers. The behavior of Fe islands growth was investigated by using scanning tunneling microscope (STM) after different annealing temperatures. STM images show that iron atoms will cause defects and holes on substrates at room temperature. As the annealing temperature rises, iron atoms pull out germanium to form various kinds of alloyed islands. However, the silver layer can protect the Ag/Ge(111)-(√3×√3) reconstruction from forming defects. The phase diagram shows that ring, dot, and triangular defects were only found on Ge (111)-c(2 × 8) substrates. The kinds of islands found in Fe/Ge system are similar to Fe/Ag/Ge system. It indicates that Ge atoms were pulled out to form islands at high annealing temperatures whether there was a Ag layer or not. But a few differences in big pyramidal or strip islands show that the silver layer affects the development of islands by changing the surface symmetry and diffusion coefficient. The structure characters of various islands are also discussed.

  14. Effects of boron dopants of Si (001) substrates on formation of Ge layers by sputter epitaxy method

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Takahiro; Hirose, Nobumitsu; Kasamatsu, Akifumi; Mimura, Takashi; Matsui, Toshiaki; Suda, Yoshiyuki

    2013-10-01

    The formation of Ge layers on boron-doped Si (001) substrates by our sputter epitaxy method has been investigated. The surface morphology of Ge layers grown on Si substrates depends on the substrate resistance, and flat Ge layers are obtained on Si substrates with 0.015 Ω cm resistivity. Highly boron-doped Si substrates cause a transition in the dislocation structure from complex dislocations with 60° dislocation glide planes to 90° pure-edge dislocations, resulting in the formation of flat Ge layers. Furthermore, we have found that the surface morphology of the Ge layers improves with increasing Ge layer thickness. Ge atoms migrating on the deposited Ge layers tend to position themselves at the reactive sites, where the reactivity is related to the number of bonding contacts between the Ge atom and the surface. This modifies the surface morphology, resulting in a flatter surface. Boron dopants together with the sputter epitaxy method effectively suppress the growth of Ge islands and result in the formation of flat Ge layers.

  15. Effects of boron dopants of Si (001) substrates on formation of Ge layers by sputter epitaxy method

    SciTech Connect

    Tsukamoto, Takahiro; Suda, Yoshiyuki; Hirose, Nobumitsu; Kasamatsu, Akifumi; Mimura, Takashi; Matsui, Toshiaki

    2013-10-21

    The formation of Ge layers on boron-doped Si (001) substrates by our sputter epitaxy method has been investigated. The surface morphology of Ge layers grown on Si substrates depends on the substrate resistance, and flat Ge layers are obtained on Si substrates with 0.015 Ω cm resistivity. Highly boron-doped Si substrates cause a transition in the dislocation structure from complex dislocations with 60° dislocation glide planes to 90° pure-edge dislocations, resulting in the formation of flat Ge layers. Furthermore, we have found that the surface morphology of the Ge layers improves with increasing Ge layer thickness. Ge atoms migrating on the deposited Ge layers tend to position themselves at the reactive sites, where the reactivity is related to the number of bonding contacts between the Ge atom and the surface. This modifies the surface morphology, resulting in a flatter surface. Boron dopants together with the sputter epitaxy method effectively suppress the growth of Ge islands and result in the formation of flat Ge layers.

  16. Greatly improved interfacial passivation of in-situ high κ dielectric deposition on freshly grown molecule beam epitaxy Ge epitaxial layer on Ge(100)

    SciTech Connect

    Chu, R. L.; Liu, Y. C.; Lee, W. C.; Huang, M. L.; Kwo, J. E-mail: mhong@phys.ntu.edu.tw; Lin, T. D.; Hong, M. E-mail: mhong@phys.ntu.edu.tw; Pi, T. W.

    2014-05-19

    A high-quality high-κ/Ge interface has been achieved by combining molecule beam epitaxy grown Ge epitaxial layer and in-situ deposited high κ dielectric. The employment of Ge epitaxial layer has sucessfully buried and/or removed the residue of unfavorable carbon and native oxides on the chemically cleaned and ultra-high vacuum annealed Ge(100) wafer surface, as studied using angle-resolved x-ray photoelectron spectroscopy. Moreover, the scanning tunneling microscopy analyses showed the significant improvements in Ge surface roughness from 3.5 Å to 1 Å with the epi-layer growth. Thus, chemically cleaner, atomically more ordered, and morphologically smoother Ge surfaces were obtained for the subsquent deposition of high κ dielectrics, comparing with those substrates without Ge epi-layer. The capacitance-voltage (C-V) characteristics and low extracted interfacial trap density (D{sub it}) reveal the improved high-κ/Ge interface using the Ge epi-layer approach.

  17. Ge 1- xC x double-layer antireflection and protection coatings

    NASA Astrophysics Data System (ADS)

    Hu, C. Q.; Zheng, W. T.; Li, J. J.; Jiang, Q.; Tian, H. W.; Lu, X. Y.; Liu, J. W.; Xu, L.; Wang, J. B.

    2006-09-01

    The antireflection Germanium carbide (Ge 1- xC x) coating, deposited using RF reactive sputtering, on both sides of ZnS substrate wafer has been developed. The infrared (IR) transmittance spectra show that the IR transmittance in the wavelength region between 8 and 12 μm for the designed system Ge 1- xC x/ZnS/Ge 1- xC x is greatly enhanced compared to that for ZnS substrate. In addition, the double-layer coated ZnS substrate is approximately four times as hard as uncoated ZnS substrate. This investigation indicates that a double-layer Ge 1- xC x coating can be used as an effective antireflection and protection coating on ZnS infrared window.

  18. Electrochemistry of layered GaSe and GeS: applications to ORR, OER and HER.

    PubMed

    Tan, Shu Min; Chua, Chun Kiang; Sedmidubský, David; Sofer, Zdene Combining Breve K; Pumera, Martin

    2016-01-21

    Though many studies examined the properties of the class of IIIA-VIA and IVA-VIA layered materials, few have delved into the electrochemical aspect of such materials. In light of the burgeoning interest in layered structures towards various electrocatalytic applications, we endeavored to study the inherent electrochemical properties of representative layered materials of this class, GaSe and GeS, and their impact towards electrochemical sensing of redox probes as well as catalysis of oxygen reduction, oxygen evolution and hydrogen evolution reactions. In contrast to the typical sandwich structure of MoS2 layered materials, GeS is isoelectronic to black phosphorus with the same structure; GaSe is a layered material consisting of GaSe sheets bonded in the sequence Se-Ga-Ga-Se. We characterized GaSe and GeS by employing scanning electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy complemented by electronic structure calculations. It was found that the encompassing surface oxide layers on GaSe and GeS greatly influenced their electrochemical properties, especially their electrocatalytic capabilities towards hydrogen evolution reaction. These findings provide fresh insight into the electrochemical properties of these IIIA-VIA and IVA-VIA layered structures which enables development for future applications. PMID:26675834

  19. Bidimensional intercalation of Ge between SiC(0001) and a heteroepitaxial graphite top layer

    SciTech Connect

    Kubler, L.; Dentel, D.; Bischoff, J.-L.; Derivaz, M.; Aiet-Mansour, K.; Diani, M.

    2005-09-15

    High temperature annealing of 4H- or 6H-SiC(0001) crystals is well known to desorb Si from the surface and to generate a C-rich (6{radical}3x6{radical}3)R30 deg. (6{radical}3) reconstruction explained as a graphite monolayer in heteroepitaxial registry with the substrate. Ge deposition at room temperature and in the monolayer range on this graphitized reconstruction results in Ge islands. Using a number of surface techniques, we follow subsequent Ge morphology evolutions as a function of isochronal post-annealing treatments at increasing temperatures. In a particular temperature window Ge reacts with the substrate by diffusion under the graphite planes and wets the Si-terminated SiC surface. In spite of this bidimensional insertion of a Ge layer, the epitaxial relationship between the SiC substrate and the graphite is maintained as shown by very clear graphite-(1x1) LEED or RHEED patterns. They denote extended and well-ordered graphite planes at the surface of a graphite/Ge/SiC heterostructure. XPS analyses reveal a complete passivation of the intercalated Ge layer against oxidation by the overlying graphite sheets. Moreover, drastic spectroscopic changes on the bulk-SiC Si 2p and C 1s core levels are observed, depending on whether graphite(6{radical}3)/SiC or graphite(1x1)/Ge/SiC terminations are analyzed. In the latter case, the observed core level splitting of the bulk components is interpreted by a significant upward band bending ({approx}1.2 eV) of the n-doped SiC, making this second interface to act as a Schottky barrier. Above 1300 deg. C, a delayed Ge desorption takes place that allows the graphite sheets to re-form in their initial 6{radical}3 form, i.e., without Ge and with flatter bands.

  20. Effect of Diffusion Control Layer on Reverse Al-Induced Layer Exchange Process for High-Quality Ge/Al/Glass Structure

    NASA Astrophysics Data System (ADS)

    Nakazawa, K.; Toko, K.; Suemasu, T.

    2015-05-01

    Fabricating large-grained polycrystalline Ge (poly-Ge) thin films on conducting-layer coated glass is a promising approach to lower the manufacturing cost of high-efficiency III-V tandem solar cells. We investigated the self-organizing formation of poly-Ge/Al/glass structures by using Al-induced layer exchange. The layer exchange between amorphous Ge and Al layers was completed at a low temperature of 350°C. Forming the interlayer between Ge and Al, i.e., limiting the diffusion of Ge to Al lowered the Ge nucleation rate and then enlarged the grain size of the resulting poly-Ge layer. The natively oxidized Al interlayer, formed by exposing a thin Al membrane (2-nm thickness) to air for 180 min, led to the poly-Ge with grains 46 μm in size. Moreover, the Ge layer was highly (111)-oriented. This Ge/Al/glass structure appears promising for use in the bottom cell of the III-V semiconductor based tandem solar cells, as well as in the epitaxial templates for aligned nanowires and other advanced materials.

  1. Porous Ge based Electric Double Layer Capacitors with High Compatibility for Low Threshold Voltage Diode Rectifiers

    NASA Astrophysics Data System (ADS)

    Sekiguchi, A.; Hara, M.; Oguchi, H.; Kuwano, H.

    2014-11-01

    The final goal of this study is to develop all-Ge-based energy harvesting modules consisting of mechanical generators, rectifiers, capacitors and power managing digital circuits. To make basis for the development of modules, we focused on development of the Ge electrodes for electric double layer capacitors (EDLC). Firstly, to establish a method to make high surface area Ge electrodes, we studied surface etching of the Ge(100) substrates in the acid solution. We found that the substrates with higher dopant concentration forms smaller size micro-pores with higher area density that leads to higher surface area. Secondly we studied stability of Ge in the ionic liquid (IL) electrolyte by ac impedance measurements. The impedance plots verified that Ge is reactive in IL electrolyte, thus not appropriate for electrodes without surface modification. Finally we oxidized Ge surface and tested the stability again. The impedance plot of the surface- oxidized Ge showed little reaction, proving that we succeeded to improve the surface stability.

  2. Growth of high quality GaN layer on carbon nanotube-graphene network structure as intermediate layer

    NASA Astrophysics Data System (ADS)

    Seo, Taeo Hoon; Park, Ah Hyun; Park, Sungchan; Kim, Myung Jong; Suh, Eun-Kyung

    2015-03-01

    In general, high-quality GaN layers are synthesized on low-temperature (LT) GaN buffer layer on a single crystal sapphire substrate. However, large differences in fundamental properties such as lattice constants and thermal expansion coefficients between GaN layer and sapphire substrate generate high density of threading dislocation (TD) that leads to deterioration of optical and structural properties. Graphene has been attracting much attention due to its excellent physical properties However, direct epitaxial growth of GaN film onto graphene layer on substrates is not easily accessible due to the lack of chemical reactivity on graphene which consisted of C-C bond of sp2 hexagonally arranged carbon atoms with no dangling bonds. In this work, an intermediate layer for the GaN growth on sapphire substrate was constructed by inserting carbon nanotubes and graphene hybrid structure (CGH) Optical and structural properties of GaN layer grown on CGH were compared with those of GaN layer directly grown on sapphire CNTs act as nucleation sites and play a crucial role in the growth of single crystal high-quality GaN on graphene layer. Also, graphene film acts as a mask for epitaxial lateral overgrowth of GaN layer, which can effectively reduce TD density. A grant from the Korea Institute of Science and Technology (KIST) institutional program.

  3. Characteristic length scale of the intermediate structure in zero-pressure-gradient boundary layer flow

    PubMed Central

    Barenblatt, G. I.; Chorin, A. J.; Prostokishin, V. M.

    2000-01-01

    In a turbulent boundary layer over a smooth flat plate with zero pressure gradient, the intermediate structure between the viscous sublayer and the free stream consists of two layers: one adjacent to the viscous sublayer and one adjacent to the free stream. When the level of turbulence in the free stream is low, the boundary between the two layers is sharp, and both have a self-similar structure described by Reynolds-number-dependent scaling (power) laws. This structure introduces two length scales: one—the wall-region thickness—determined by the sharp boundary between the two intermediate layers and the second determined by the condition that the velocity distribution in the first intermediate layer be the one common to all wall-bounded flows and in particular coincide with the scaling law previously determined for pipe flows. Using recent experimental data, we determine both these length scales and show that they are close. Our results disagree with the classical model of the “wake region.” PMID:10760253

  4. Spin polarized surface resonance bands in single layer Bi on Ge(1 1 1)

    NASA Astrophysics Data System (ADS)

    Bottegoni, F.; Calloni, A.; Bussetti, G.; Camera, A.; Zucchetti, C.; Finazzi, M.; Duò, L.; Ciccacci, F.

    2016-05-01

    The spin features of surface resonance bands in single layer Bi on Ge(1 1 1) are studied by means of spin- and angle-resolved photoemission spectroscopy and inverse photoemission spectroscopy. We characterize the occupied and empty surface states of Ge(1 1 1) and show that the deposition of one monolayer of Bi on Ge(1 1 1) leads to the appearance of spin-polarized surface resonance bands. In particular, the C 3v symmetry, which Bi adatoms adopt on Ge(1 1 1), allows for the presence of Rashba-like occupied and unoccupied electronic states around the \\overline{\\text{M}} point of the Bi surface Brillouin zone with a giant spin–orbit constant |{α\\text{R}}| =≤ft(1.4+/- 0.1\\right) eV · Å.

  5. Spin polarized surface resonance bands in single layer Bi on Ge(1 1 1).

    PubMed

    Bottegoni, F; Calloni, A; Bussetti, G; Camera, A; Zucchetti, C; Finazzi, M; Duò, L; Ciccacci, F

    2016-05-18

    The spin features of surface resonance bands in single layer Bi on Ge(1 1 1) are studied by means of spin- and angle-resolved photoemission spectroscopy and inverse photoemission spectroscopy. We characterize the occupied and empty surface states of Ge(1 1 1) and show that the deposition of one monolayer of Bi on Ge(1 1 1) leads to the appearance of spin-polarized surface resonance bands. In particular, the C 3v symmetry, which Bi adatoms adopt on Ge(1 1 1), allows for the presence of Rashba-like occupied and unoccupied electronic states around the [Formula: see text] point of the Bi surface Brillouin zone with a giant spin-orbit constant [Formula: see text] eV · Å. PMID:27073190

  6. Layered YSZ/SCSZ/YSZ Electrolytes for Intermediate Temperature SOFC Part I: Design and Manufacturing

    SciTech Connect

    Orlovskaya, Nina; Klimov, Mikhail; Huang, Xinyu; Cullen, David A; Graule, Thomas; Kuebler, Jakob

    2012-01-01

    (Sc2O3)0.1(CeO2)0.01(ZrO2)0.89 (SCSZ) ceramic electrolyte has superior ionic conductivity in the intermediate temperature range (700 800 C), but it does not exhibit good phase and chemical stability in comparison with 8 mol% Y2O3 ZrO2 (YSZ). To maintain high ionic conductivity and improve the stability in the whole electrolyte, layered structures with YSZ outer layers and SCSZ inner layers were designed. Because of a mismatch of coefficients of thermal expansion and Young's moduli of SCSZ and YSZ phases, upon cooling of the electrolytes after sintering, thermal residual stresses will arise, leading to a possible strengthening of the layered composite and, therefore, an increase in the reliability of the electrolyte. Laminated electrolytes with three, four, and six layers design were manufactured using tape-casting, lamination, and sintering techniques. After sintering, while the thickness of YSZ outer layers remained constant at 30 m, the thickness of the SCSZ inner layer varied from 30 m for a Y SC Y three-layered electrolyte, 60 m for a Y 2SC Y four-layered electrolyte, and 120 m for a Y 4SC Y six-layered electrolyte. The microstructure, crystal structure, impurities present, and the density of the sintered electrolytes were characterized by scanning and transmission electron microscopy, X-ray and neutron diffraction, secondary ion mass spectroscopy, and water immersion techniques.

  7. Ge wetting layer increases ohmic plasmon losses in Ag film due to segregation.

    PubMed

    Wróbel, Piotr; Stefaniuk, Tomasz; Trzcinski, Marek; Wronkowska, Aleksandra A; Wronkowski, Andrzej; Szoplik, Tomasz

    2015-05-01

    We have investigated the influence of the Ge wetting layer on both ohmic and scattering losses of a surface plasmon-polariton (SPP) wave in Ag film deposited on SiO2 substrate with an e-beam evaporator. Samples were examined by means of atomic force microscopy (AFM), spectroscopic ellipsometry (SE), two-dimensional X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and microscopic four-point probe (M4PP) sheet resistance measurements. Ag films of 100 nm thickness were deposited at 180 and 295 K directly onto the substrates with or without a Ge interlayer. In AFM scans, we confirm the fact that the commonly used Ge adhesion layer smooths the surface of Ag film and therefore reduces scattering losses of the SPP wave on surface roughness. However, our ellipsometric measurements indicate for the first time that segregation of Ge leads to a considerable increase in ohmic losses connected with a boost of the imaginary part of Ag permittivity in the 500-800 nm spectral range. Moreover, the trend develops over time, as confirmed in a series of measurements performed over an interval of three months. XPS analysis confirms the Ge segregation to the Ag free surface and most probably to grain boundaries. M4PP measurements show that the specific resistivity in Ag films evaporated on a Ge interlayer at 295 K is nearly twice as high as in layers deposited directly on a SiO2 substrate. The use of an amorphous Al2O3 overlayer prevents Ge segregation to free surface. PMID:25871505

  8. Ellipsometric study of Si(0.5)Ge(0.5)/Si strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.

    1993-01-01

    An ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer super lattices grown by MBE at low temperature (500 C) is presented, and results are compared with x ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. It is shown that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. It was also noted that we do not observe any strain effect on the E(sub 1) critical point.

  9. Ellipsometric study of Si(0.5)Ge(0.5)/Si strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.

    1993-01-01

    We present an ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer superlattices grown by MBE at low temperature (500 C), and compare our results with X-ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. We show that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. We also note that we do not observe any strain effect on the E1 critical point.

  10. Intermediate range chemical ordering in amorphous and liquid water, Si, and Ge

    SciTech Connect

    Benmore, C.J.; Hart, R.T.; Mei, Q.; Price, D.L.; Yarger, J.; Tulk, C.A.; Klug, D.D.

    2005-10-01

    Neutron and x-ray diffraction data for low, high, and very high density amorphous ice and liquid water, silicon, and germanium have been compared in terms of the first sharp diffraction peak in the structure factor and at the radial distribution function level. The low and high density forms of H{sub 2}O, Si, and Ge are shown to have very similar structures if the contributions from the hydrogen correlations in water are neglected. The very high density amorphous ice form is shown to be structurally analogous to recently reported high pressure liquid forms of Si and Ge, although there are slight differences in the way interstitial atoms or molecules are pushed into the first coordination shell.

  11. GeSn-based p-i-n photodiodes with strained active layer on a Si wafer

    NASA Astrophysics Data System (ADS)

    Tseng, H. H.; Li, H.; Mashanov, V.; Yang, Y. J.; Cheng, H. H.; Chang, G. E.; Soref, R. A.; Sun, G.

    2013-12-01

    We report an investigation of GeSn-based p-i-n photodiodes with an active GeSn layer that is almost fully strained. The results show that (a) the response of the Ge/GeSn/Ge heterojunction photodiodes is stronger than that of the reference Ge-based photodiodes at photon energies above the 0.8 eV direct bandgap of bulk Ge (<1.55 μm), and (b) the optical response extends to lower energy regions (1.55-1.80 μm wavelengths) as characterized by the strained GeSn bandgap. A cusp-like spectral characteristic is observed for samples with high Sn contents, which is attributed to the significant strain-induced energy splitting of heavy and light hole bands. This work represents a step forward in developing GeSn-based infrared photodetectors.

  12. Manifestation of intermediate phase in mechanical properties: Nano-indentation studies on Ge-Te-Si bulk chalcogenide glasses

    NASA Astrophysics Data System (ADS)

    Das, Chandasree; Kiran, M. S. R. N.; Ramamurty, U.; Asokan, S.

    2012-12-01

    Nano-indentation studies have been undertaken on bulk Ge15Te85-xSix glasses (0≤x≤9), to estimate hardness, H and elastic modulus, E. It is found that E and H increase initially with the increase in the atomic percent of Si. Further, a plateau is seen in the composition dependence of E and H in the composition range 2≤x≤6. It is also seen that the addition of up to 2 at% Si increases the density ρ of the glass considerably; however, further additions of Si lead to a near linear reduction in ρ, in the range 2≤x≤6. Beyond x=6, ρ increases again with Si content. The variation of molar volume Vm brings out a more fascinating picture. A plateau is seen in the intermediate phase suggesting that the molecular structure of the glasses is adapting to keep the count of constraints fixed in this particular phase. The observed variations in mechanical properties are associated with the Boolchand's intermediate phase in the present glassy system, in the composition range 2≤x≤6, suggested earlier from calorimetric and electrical switching studies. The present results reveal rather directly the existence of the intermediate phase in elastic and plastic properties of chalcogenide glasses.

  13. Electrical properties of magnesium oxide layers with different surface pretreatment on high mobility Ge1-xSnx and Ge MOS capacitors

    NASA Astrophysics Data System (ADS)

    Su, Chen-Yi; Lieten, Ruben; Bakalov, Petar; Tseng, Wei-Jhih; Dillemans, Leander; Menghini, Mariela; Smets, Tomas; Seo, Jin Won; Locquet, Jean-Pierre

    2014-02-01

    Germanium based channels are interesting for high performance CMOS devices because of their high carrier mobility. In this study, the electrical properties of MgO on both GeSn and Ge MOS capacitors have been investigated. The low equivalent oxide thickness (EOT) of 2.1 nm for MgO on GeSn with a Ge cap layer indicates the high potential for MOSFET applications. A surface treatment prior to oxide deposition is found essential to reduce the gate leakage. It is shown that HCl and H2O2 dipping followed by ozone treatment improves the leakage and leads to good capacitance-voltage (C-V) behavior.

  14. A Metal Bump Bonding Method Using Ag Nanoparticles as Intermediate Layer

    NASA Astrophysics Data System (ADS)

    Fu, Weixin; Nimura, Masatsugu; Kasahara, Takashi; Mimatsu, Hayata; Okada, Akiko; Shoji, Shuichi; Ishizuka, Shugo; Mizuno, Jun

    2015-11-01

    The future development of low-temperature and low-pressure bonding technology is necessary for fine-pitch bump application. We propose a bump structure using Ag nanoparticles as an intermediate layer coated on a fine-pitch Cu pillar bump. The intermediate layer is prepared using an efficient and cost-saving squeegee-coating method followed by a 100°C baking process. This bump structure can be easily flattened before the bonding process, and the low-temperature sinterability of the nanoparticles is retained. The bonding experiment was successfully performed at 250°C and 39.8 MPa and the bonding strength was comparable to that achieved via other bonding technology utilizing metal particles or porous material as bump materials.

  15. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures

    PubMed Central

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-01-01

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous–crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature. PMID:27220411

  16. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures.

    PubMed

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-01-01

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous-crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature. PMID:27220411

  17. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures

    NASA Astrophysics Data System (ADS)

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-05-01

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous–crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature.

  18. A study on intermediate buffer layer of coated Fiber Bragg Grating cryogenic temperature sensors

    NASA Astrophysics Data System (ADS)

    Freitas, R.; Araujo, F.; Araujo, J.; Neumann, H.; Ramalingam, R.

    2015-12-01

    The sensor characteristics of a coated Fiber Bragg grating (FBG) thermal sensor for cryogenic temperatures depends mainly on the coating materials. The sensitivity of the coated FBG can be improved by enhancing the effective thermal strain transfer between the different layers and the bare FBG. The dual coated FBG's has a primary layer and the secondary layer. The primary coating acts as an intermediate buffer between the secondary coating and the bare FBG. The outer secondary coating is normally made of metals with high thermal expansion coefficient. In this work, a detailed study is carried out on chromium and titanium intermediate buffer layers with various coating thicknesses and combinations. To improve the sensitivity, the secondary coating layer was tested with Indium, Lead and Tin. The sensors were then calibrated in a cryogenic temperature calibration facility at Institute of Technical Physics (ITEP), Karlsruhe Institute of Technology. The sensors were subjected to several thermal cycles between 4.2 and 80 K to study the sensor performance and its thermal characteristics. The sensor exhibits a Bragg wavelength shift of 13pm at 20K. The commercially available detection equipment with a resolution of 1pm can result in a temperature resolution of 0.076 K at 20K.

  19. Strain analysis in ultrathin SiGe-on-insulator layers formed from strained Si-on-insulator substrates by Ge-condensation process

    NASA Astrophysics Data System (ADS)

    Tezuka, Tsutomu; Hirashita, Norio; Moriyama, Yoshihiko; Nakaharai, Shu; Sugiyama, Naoharu; Takagi, Shin-ichi

    2007-04-01

    Ultrathin strained SiGe-on-insulator (sSGOI) layers were fabricated by Ge condensation, in which Si1-xGex layers on strained Si-on-insulator (sSOI) substrates were oxidized, and their strain and defects were investigated. With increasing the Ge fraction x, the compressive strain in the SGOI layers was found to linearly increase up to ˜2%. The linear strain dependence on x was offset by the preexisting tensile strain in the sSOI substrate compared to that of conventional SGOI layers formed on unstrained SOI substrates. As a result, pseudomorphic sSGOI layers were obtained on the sSOI substrate up to higher x (˜0.75) than on a SOI substrate.

  20. Local epitaxial growth of ZrO2 on Ge (100) substrates by atomic layer epitaxy

    NASA Astrophysics Data System (ADS)

    Kim, Hyoungsub; Chui, Chi On; Saraswat, Krishna C.; McIntyre, Paul C.

    2003-09-01

    High-k dielectric deposition processes for gate dielectric preparation on Si surfaces usually result in the unavoidable and uncontrolled formation of a thin interfacial oxide layer. Atomic layer deposition of ˜55-Å ZrO2 film on a Ge (100) substrate using ZrCl4 and H2O at 300 °C was found to produce local epitaxial growth [(001) Ge//(001) ZrO2 and [100] Ge//[100] ZrO2] without a distinct interfacial layer, unlike the situation observed when ZrO2 is deposited using the same method on Si. Relatively large lattice mismatch (˜10%) between ZrO2 and Ge produced a high areal density of interfacial misfit dislocations. Large hysteresis (>200 mV) and high frequency dispersion were observed in capacitance-voltage measurements due to the high density of interface states. However, a low leakage current density, comparable to values obtained on Si substrates, was observed with the same capacitance density regardless of the high defect density.

  1. Unconventional Superconductivity in the Layered Iron Germanide YFe_{2}Ge_{2}.

    PubMed

    Chen, Jiasheng; Semeniuk, Konstantin; Feng, Zhuo; Reiss, Pascal; Brown, Philip; Zou, Yang; Logg, Peter W; Lampronti, Giulio I; Grosche, F Malte

    2016-03-25

    The iron-based intermetallic YFe_{2}Ge_{2} stands out among transition metal compounds for its high Sommerfeld coefficient of the order of 100  mJ/(mol K^{2}), which signals strong electronic correlations. A new generation of high quality samples of YFe_{2}Ge_{2} show superconducting transition anomalies below 1.8 K in thermodynamic, magnetic, and transport measurements, establishing that superconductivity is intrinsic in this layered iron compound outside the known superconducting iron pnictide or chalcogenide families. The Fermi surface geometry of YFe_{2}Ge_{2} resembles that of KFe_{2}As_{2} in the high pressure collapsed tetragonal phase, in which superconductivity at temperatures as high as 10 K has recently been reported, suggesting an underlying connection between the two systems. PMID:27058094

  2. Uniaxial strain relaxation in He{sup +} ion implanted (110) oriented SiGe layers

    SciTech Connect

    Minamisawa, R. A.; Buca, D.; Trinkaus, H.; Hollaender, B.; Mantl, S.; Destefanis, V.; Hartmann, J. M.

    2009-07-20

    Uniaxially strained (011)Si is attractive for high performance p-channel metal oxide semiconductor field effect transistor devices due to the predicted high hole mobilities. Here, we demonstrate the realization of purely uniaxially relaxed (011) SiGe virtual substrates by He{sup +} ion implantation and thermal annealing. Perfect uniaxial relaxation is evidenced by precise ion channeling angular yield scan measurements and plan view transmission electron microscopy as predicted theoretically on the basis of the layer symmetry dependent dislocation dynamics. Strikingly, misfit dislocations propagate exclusively along the [011] direction in the (011) oriented crystal and, in contrast to (100)Si, no crosshatch is formed. We describe dislocation formation and propagation inducing strain relaxation of (011)SiGe and enlighten the differences to (100) oriented SiGe on Si.

  3. Improved conductivity of indium-tin-oxide film through the introduction of intermediate layer

    NASA Astrophysics Data System (ADS)

    Ng, S. W.; Yam, F. K.; Beh, K. P.; Tneh, S. S.; Hassan, Z.

    2016-09-01

    A thin intermediate layer (Ag, AuSn, In, Ni, Sn, SiO2) was individually deposited on glass substrates prior to the deposition of indium-tin-oxide (ITO) thin film by radio-frequency (RF) magnetron sputtering employing ITO target (composition ratio of In2O3:SnO2 = 9:1). The structural, optical and electrical properties were investigated to compare the ITO thin film with and without an intermediate layer. The preferential orientation of all ITO films was along (222) plane. Although all thin films were polycrystalline, the presence of intermediate layer promoted the overall crystallinity. The sheet resistance and resistivity of the ITO film were reduced from ∼68 Ω/□ to ∼29-45 Ω/□, and 16.2 × 10-4 Ω cm up to 7.58 × 10-4 Ω cm, respectively, by inserting a thin metal layer underneath the ITO film, and it is dependent on the degree of crystallization. The optical transmittance in the visible region varies from 40 to 88% for different samples. Based on the evaluation from Tauc plot, the optical band gap falls in the range of 4.02-4.12 eV. Physical film thickness was compared with that evaluated by optical measurement in the visible range and the physical thickness was found to be smaller. Similarly, the carrier concentration/scattering time from Hall effect measurement were also compared with that from optical measurement in the infrared region. Haacke's figure of merit (FOM) was employed to assess the quality of the ITO films, and the highest FOM is credited to ITO/In up to ∼8 × 10-3 Ω-1 in the visible light region.

  4. Engineered Coalescence by Annealing 3D Ge Microstructures into High-Quality Suspended Layers on Si.

    PubMed

    Salvalaglio, Marco; Bergamaschini, Roberto; Isa, Fabio; Scaccabarozzi, Andrea; Isella, Giovanni; Backofen, Rainer; Voigt, Axel; Montalenti, Francesco; Capellini, Giovanni; Schroeder, Thomas; von Känel, Hans; Miglio, Leo

    2015-09-01

    The move from dimensional to functional scaling in microelectronics has led to renewed interest toward integration of Ge on Si. In this work, simulation-driven experiments leading to high-quality suspended Ge films on Si pillars are reported. Starting from an array of micrometric Ge crystals, the film is obtained by exploiting their temperature-driven coalescence across nanometric gaps. The merging process is simulated by means of a suitable surface-diffusion model within a phase-field approach. The successful comparison between experimental and simulated data demonstrates that the morphological evolution is driven purely by the lowering of surface-curvature gradients. This allows for fine control over the final morphology to be attained. At fixed annealing time and temperature, perfectly merged films are obtained from Ge crystals grown at low temperature (450 °C), whereas some void regions still persist for crystals grown at higher temperature (500 °C) due to their different initial morphology. The latter condition, however, looks very promising for possible applications. Indeed, scanning tunneling electron microscopy and high-resolution transmission electron microscopy analyses show that, at least during the first stages of merging, the developing film is free from threading dislocations. The present findings, thus, introduce a promising path to integrate Ge layers on Si with a low dislocation density. PMID:26252761

  5. FePtC magnetic recording media with (200) textured MoC intermediate layer

    SciTech Connect

    Tsai, Jai-Lin Tseng, Yun-Ting; Li, Chia-Ru; Fu, Sheng-Chun

    2015-05-07

    The FePt films with thickness of 4–10 nm were deposited on MoC/CrRu/glass at 425 °C by using magnetron sputtering. The Mo{sub 40}C{sub 60} target was used to form the MoC and C two phases after deposition. The MoC intermediate layer was epitaxially grown on the (200) textured CrRu seed layer at 425 °C and the MoC (200) diffraction peak was not clearly indexed below 10 nm but observed at 25 nm. Finally, the FePt film was prepared on (200) textured MoC at 425 °C and shown the strong (001) texture. Perpendicular anisotropy of 1.7 × 10{sup 7} erg/cm{sup 3} and out-of-plane coercivity of 7.5 kOe has been demonstrated in 10 nm thick FePt film. From microstructure, the FePt grains were distributed in- or between-islands like structure and further separated by excess carbon from MoC intermediate layer. Thinner FePt film was more separated by excess carbon and shown higher coercivity.

  6. Characterization of mismatched SiGe grown on low temperature Si buffer layers by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Linder, K. K.; Zhang, F. C.; Rieh, J.-S.; Bhattacharya, P.

    1997-05-01

    Several types of buffer layer structures, including superlattice and step-graded layers, have been employed to reduce the threading dislocation in SiGe epitaxial layers. A new technique, using a 0.1 μm thick Si buffer grown at 450°C by molecular beam epitaxy, provides the best results. For a 0.5 μm thick Si 0.85Ge 0.15 layer, the dislocation density is ⩽ 10 5cm -2. Hall measurements indicate an improvement in the hole mobility of a 1 μm thick Boron doped Si 0.7Ge 0.3 layer. A {SiGe}/{Si} heterojunction bipolar transistor has been fabricated exploiting the low temperature Si buffer. Transmission electron microscopy of the structure does not indicate any evidence of threading dislocations.

  7. Spectroscopic ellipsometric characterization of Si/Si(1-x)Ge(x) strained-layer superlattices

    NASA Technical Reports Server (NTRS)

    Yao, H.; Woollam, J. A.; Wang, P. J.; Tejwani, M. J.; Alterovitz, S. A.

    1993-01-01

    Spectroscopic ellipsometry (SE) was employed to characterize Si/Si(1-x)Ge(x) strained-layer superlattices. An algorithm was developed, using the available optical constants measured at a number of fixed x values of Ge composition, to compute the dielectric function spectrum of Si(1-x)Ge(x) at an arbitrary x value in the spectral range 17 to 5.6 eV. The ellipsometrically determined superlattice thicknesses and alloy compositional fractions were in excellent agreement with results from high-resolution x ray diffraction studies. The silicon surfaces of the superlattices were subjected to a 9:1 HF cleaning prior to the SE measurements. The HF solution removed silicon oxides on the semiconductor surface, and terminated the Si surface with hydrogen-silicon bonds, which were monitored over a period of several weeks, after the HF cleaning, by SE measurements. An equivalent dielectric layer model was established to describe the hydrogen-terminated Si surface layer. The passivated Si surface remained unchanged for greater than 2 h, and very little surface oxidation took place even over 3 to 4 days.

  8. High-pressure melt growth and transport properties of SiP, SiAs, GeP, and GeAs 2D layered semiconductors

    NASA Astrophysics Data System (ADS)

    Barreteau, C.; Michon, B.; Besnard, C.; Giannini, E.

    2016-06-01

    Silicon and Germanium monopnictides SiP, SiAs, GeP and GeAs form a family of 2D layered semiconductors. We have succeeded in growing bulk single crystals of these compounds by melt-growth under high pressure (0.5-1 GPa) in a cubic anvil hot press. Large (mm-size), shiny, micaceous crystals of GeP, GeAs and SiAs were obtained, and could be exfoliated into 2D flakes. Small and brittle crystals of SiP were yielded by this method. High-pressure sintered polycrystalline SiP and GeAs have also been successfully used as a precursor in the Chemical Vapor Transport growth of these crystals in the presence of I2 as a transport agent. All compounds are found to crystallize in the expected layered structure and do not undergo any structural transition at low temperature, as shown by Raman spectroscopy down to T=5 K. All materials exhibit a semiconducting behavior. The electrical resistivity of GeP, GeAs and SiAs is found to depend on temperature following a 2D-Variable Range Hopping conduction mechanism. The availability of bulk crystals of these compounds opens new perspectives in the field of 2D semiconducting materials for device applications.

  9. Production of three-dimensional quantum dot lattice of Ge/Si core-shell quantum dots and Si/Ge layers in an alumina glass matrix.

    PubMed

    Buljan, M; Radić, N; Sancho-Paramon, J; Janicki, V; Grenzer, J; Bogdanović-Radović, I; Siketić, Z; Ivanda, M; Utrobičić, A; Hübner, R; Weidauer, R; Valeš, V; Endres, J; Car, T; Jerčinović, M; Roško, J; Bernstorff, S; Holy, V

    2015-02-13

    We report on the formation of Ge/Si quantum dots with core/shell structure that are arranged in a three-dimensional body centered tetragonal quantum dot lattice in an amorphous alumina matrix. The material is prepared by magnetron sputtering deposition of Al2O3/Ge/Si multilayer. The inversion of Ge and Si in the deposition sequence results in the formation of thin Si/Ge layers instead of the dots. Both materials show an atomically sharp interface between the Ge and Si parts of the dots and layers. They have an amorphous internal structure that can be crystallized by an annealing treatment. The light absorption properties of these complex materials are significantly different compared to films that form quantum dot lattices of the pure Ge, Si or a solid solution of GeSi. They show a strong narrow absorption peak that characterizes a type II confinement in accordance with theoretical predictions. The prepared materials are promising for application in quantum dot solar cells. PMID:25605224

  10. Strain relaxation in Si - xGe x layers on Si(001)

    NASA Astrophysics Data System (ADS)

    Capano, M. A.; Hart, L.; Bowen, D. K.; Gordon-Smith, D.; Thomas, C. R.; Gibbings, C. J.; Halliwell, M. A. G.; Hobbs, L. W.

    1992-02-01

    The lattice relaxation of strained Si 1- xGe x layers on Si (001) substrates has been examined. Three specimens consisting of a single Si 1- xGe x layer were grown by molecular beam epitaxy. All layers were grown with a nominal composition of x = 0.14 to thicknesses of 0.5, 1.0 or 1.5 μm. Double-crystal and white-radiation topographic methods were used to reveal the misfit dislocation structure and distribution. The misfit dislocations were shown to extend from heterogeneous nucleation sites along the <110> directions in the plane of the interface. A symmetric distribution of dislocations between the orthogonal <110> directions was observed. The Burgers vectors of the misfit dislocation array were evenly distributed amongst the available 60°-type candidates. Double-crystal X-ray diffractometry showed the 0.5 and 1.0 μm layers to be fully strained to within the experimental uncertainty. Secondary branching of misfit dislocations was observed in the 1.0μm layer which indicated cross-slip of the threading dislocation segments.

  11. In-situ observations of intermediate layers in the night time ionosphere

    NASA Astrophysics Data System (ADS)

    Gregory, J.; Swenson, C. M.; Humphries, S.; Fish, C.; Carlson, C.; Barjatya, A.

    2005-12-01

    Night time ionospheric electron density profiles have been obtained using impedance and Langmuir probe techniques showing the presence of intermediate layers. Four sounding rockets were launched in July of 2003 at Wallops Island, VA and two more were launched in August of 2004 from Kwajalein atoll, Marshall Islands. Although these rocket campaigns were conducted at different latitudes they both indicated a patchy spatial structure. All six flights used essentially the same plasma impedance probe but the later campaign included a sweeping Langmuir probe. More emphasis is given to the data from the later campaign, "Scattering Layer in the Bottomside Equatorial F-region Ionosphere" investigation, which was a part of the NASA EQUIS II campaign. Electron density from this data set is analyzed using Balmain's theory for a short antenna in a cold magnetoplasma and compared with data from the sweeping Langmuir probe.

  12. Stress reduction in epitaxial GaN films on Si using cubic SiC as intermediate layers

    NASA Astrophysics Data System (ADS)

    Komiyama, Jun; Abe, Yoshihisa; Suzuki, Shunichi; Nakanishi, Hideo

    2006-08-01

    Stress in the epitaxial films of GaN on Si is reduced by using SiC as intermediate layers. The crystalline films of cubic SiC (0-1μm), thin AlN (50nm), and GaN (1-3μm) were prepared on 3in. (1 1 1) Si substrates—stacked in the order of GaN /AlN/SiC/Si—by metalorganic vapor-phase epitaxy. It is revealed by Raman spectroscopy that the tensile stress in GaN is reduced to half (reduction of about 300MPa) for GaN on Si with SiC intermediate layers compared with GaN on Si without SiC intermediate layers. Because of stress reduction, crack-free GaN on Si with a thickness of 2μm was obtained by using SiC intermediate layers. Cracking was minimized even on thicker GaN on Si (3μm thick) with SiC intermediate layers. The SiC intermediate layers are promising for the realization of nitride based electronic devices on Si.

  13. Discharger Using Cascaded Switched Capacitor Converters and Selectable Intermediate Taps for Electric Double-Layer Capacitors

    NASA Astrophysics Data System (ADS)

    Uno, Masatoshi; Tanaka, Koji

    Electric double-layer capacitors (EDLCs) offer several advantages over traditional batteries, such as long cycle life, high power capability, good low-temperature performance, etc. However, their major drawbacks, such as low specific energy and large voltage variation due to charge/discharge cycling, necessitate the use of high-efficiency power conversion electronics that can be used to efficiently discharge EDLCs and thus completely utilize the precious stored energy. In this study, we propose a novel discharger for EDLCs; this discharger uses cascaded switched capacitor converters (SCCs) and selectable intermediate taps. Although the voltage conversion ratio of SCCs is fixed, the load voltage can be maintained within a desired voltage range by the selectable intermediate taps. The circuit configuration, operating principle, and procedure for designing SCCs and selectable intermediate taps are presented. Experimental tests were performed using an EDLC module and a 200W prototype of the discharger. The obtained results showed that the 60V EDLC could be discharged to 30V with an average efficiency of 96% when the load voltage was maintained within the range 30-40V.

  14. Atomic-layer surface reaction of chlorine on Si and Ge assisted by an ultraclean ECR plasma

    NASA Astrophysics Data System (ADS)

    Matsuura, T.; Sugiyama, T.; Murota, J.

    1998-05-01

    Atomic-layer surface adsorption and reaction of chlorine on Si(100) and Ge(100) as well as Si 0.5Ge 0.5(100) assisted by low-energy Ar + ion irradiation were investigated using an ultraclean ECR plasma system with surface analysis by XPS and FTIR/RAS. Hydrogen termination on Si and Ge prepared by HF-treatment or annealing in H 2 was removed by Ar + ion irradiation, and that on Ge was removed, while not on Si, only by the chlorine molecular supply. By repeating alternate chlorine molecular supply (≳0.02 Pa·s) and Ar + ion irradiation (˜4×10 15 cm -2), atomic-layer etching of Si, Ge, and Si 0.5Ge 0.5 was observed with a saturated etch rate per cycle of 1/4 atomic-layer thickness. When Ar + ion irradiation was increased further under a condition of saturated chlorine molecular adsorption, the etch rate per cycle tended to increase with Ar + ion irradiation up to a saturation value of the single atomic-layer thickness. The Ge atoms indicated a higher reactivity than the Si atoms in the atomic-layer etching.

  15. Low-frequency conductance fluctuations in Si:P and Ge:P δ-layers

    NASA Astrophysics Data System (ADS)

    Shamim, Saquib; Mahapatra, Suddhasatta; Scappucci, Giordano; Klesse, W. M.; Simmons, Michelle Y.; Ghosh, Arindam

    Delta doped Si:P and Ge:P devices offer a formidable platform for application towards quantum computation. The fabrication of single donor devices by STM-lithography takes us forward to address the solid state quantum bits. The atomic scale control however makes the devices extremely sensitive to fluctuations and disorder which affect their long term stability. Hence, a study of low frequency 1/f noise for these devices is desirable. We measure 1/f noise in Si:P and Ge:P δ-layers of varying doping density. Fluctuations in conductivity arise due to fluctuations in mobility and the Hooge parameter scales inversely with mobility as 1 /μ3 for all devices. For highly doped Ge:P δ-layer, the noise magnitude in a perpendicular magnetic field (B⊥) reduces by factors of two at the phase breaking breaking field and the Zeeman field indicating universal conductance fluctuations (UCF). The phase breaking length lϕUCF extracted by fitting the B⊥ dependence of noise to the crossover function matches well with lϕWL extracted from weak localization (WL) fits to magnetoconductivity indicating that both UCF and WL are governed by same scattering rates. Present Address: QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands.

  16. Buffer effects of Ag layers on magneto-optical Co/Ge(1 0 0) ultrathin films

    NASA Astrophysics Data System (ADS)

    Su, C. W.; Tsay, J. S.; Yao, Y. D.

    2006-09-01

    Magnetic properties of the Co/Ag/Ge(1 0 0) films grown at room temperature and 200 K were studied by the surface magneto-optical Kerr effect (SMOKE). More than 1.5 monolayer Ag buffer layers not only effectively block the interdiffusion between the capped Co layers and the Ge(1 0 0) substrate but also stabilize the magnetic phase. The temperature and thickness dependence on coercivity measurements show that interactions upon the interfaces are strongly correlated to the microstructures.

  17. LETTER TO THE EDITOR: Breakdown of intermediate-range order in liquid GeSe2 at high temperatures

    NASA Astrophysics Data System (ADS)

    Massobrio, C.; van Roon, F. H. M.; Pasquarello, Alfredo; DeLeeuw, S. W.

    2000-11-01

    The structure of liquid GeSe2 at T = 1373 K has been investigated by first-principles molecular dynamics. The calculated total neutron structure factor is in good agreement with recent experimental data. We found that the disappearance with increasing temperature of the first sharp diffraction peak (FSDP) in the total neutron structure factor is due to an increase of short-range chemical disorder. At T = 1373 K various bonding configurations coexist in close amounts, such as the Ge-GeSe3, Ge-GeSe2 and Se-SeGe2 motifs. This contrasts with the behaviour of liquid GeSe2 at T = 1050 K, for which more than half of the Ge atoms are four-fold coordinated to Se atoms in regular GeSe4 tetrahedra. Our result correlates the appearance of the FSPD in disordered AX2 network-forming materials to the predominant presence of AX4 subunits.

  18. Low-temperature studies of magnetic phases of the interfacial layers for Co/Ge(100) and Co/Ge(111) films

    NASA Astrophysics Data System (ADS)

    Tsay, J. S.; Su, C. W.; Hwang, C. H.; Yao, Y. D.

    2005-07-01

    Magnetic phases of the interfacial layers were comparatively investigated for Co/Ge(100) and Co/Ge(111) films thinner than 13 ML using surface magneto-optic Kerr effect technique. Co/Ge(100) films are nonferromagnetic up to 12 ML as deposited and measured at 300 K. A transition from nonferromagnetism to ferromagnetism occurs upon cryogenic treatments. Systematic investigations of the magnetic properties for Co/Ge(100) reveal a magnetic phase diagram. The boundary between nonferromagnetic and ferromagnetic phases was experimentally determined to be from below 150 K to above 300 K as the cobalt thickness increases from 9 to 13 ML. This behavior is consistent with the thickness-dependent scaling law of the Curie temperature for a thin film system. Because of the difference of the densities of surface atoms, the different thickness of the formed interfacial compounds could explain the shift of the phase boundary to higher Co thickness side as compared to the Co/Ge(111) system. In addition, the critical exponent β in the power law relationship of magnetization for Co/Ge(100) films lies close to the value expected by the three-dimensional Heisenberg model, while the critical exponent of Co/Ge(111) is close to the value of the two-dimensional XY model. The different behaviors of the magnetic transition are attributed to the different interfacial structures.

  19. Hydrogen gettering and strain-induced platelet nucleation in tensilely strained Si0.4Ge0.6/Ge for layer exfoliation applications

    NASA Astrophysics Data System (ADS)

    Pitera, Arthur J.; Fitzgerald, E. A.

    2005-05-01

    We show that tensilely strained epitaxial layers getter interstitially dissolved hydrogen and accelerate the nucleation of platelets. Both of these result in subsurface crack propagation leading to surface blistering and eventual exfoliation of a H+-implanted semiconductor surface. In this work, a strained Si0.4Ge0.6 layer was used to enhance the exfoliation kinetics of relaxed Ge/Si1-xGex/Si virtual substrates by gettering hydrogen and providing a preferential nucleation site for platelets. Using platelet morphology and strain relaxation data, a nucleation and growth model was formulated accounting for both chemical and strain energy contributions to the free energy of platelet formation, revealing two kinetically limited growth regimes for platelets in tensilely strained Si0.4Ge0.6 films. Low-temperature (<200°C) annealing nucleates 1011-cm-2 platelets which grow in the strain-limited regime with minimal loss of hydrogen to surface effusion. At 250 °C, platelet growth is diffusion limited, requiring transport of H2 molecules to the strained layer. Subsequent annealing of strained Si0.4Ge0.6/Ge gettering structures at a temperature exceeding 300 °C results in significantly improved surface blistering kinetics over samples which do not contain a gettering layer. Incorporation of tensilely strained layers has the potential of reducing the implantation dose and annealing temperature necessary for layer transfer. Combined with virtual substrate bonding, they provide a promising solution for economical integration of high-performance semiconductors with silicon.

  20. Impact of the H 2 anneal on the structural and optical properties of thin and thick Ge layers on Si; Low temperature surface passivation of Ge by Si

    NASA Astrophysics Data System (ADS)

    Hartmann, J. M.; Abbadie, A.; Barnes, J. P.; Fédéli, J. M.; Billon, T.; Vivien, L.

    2010-02-01

    Using a low temperature/high temperature strategy, we have grown thin (0.27 μm) and thick (2.45 μm) Ge layers on Si(0 0 1) substrates that we have submitted to various constant temperature (750 °C) or cyclic (750 °C/890 °C) H 2 anneals, the objective being to identify those yielding the smoothest surfaces, the lowest threading dislocations densities (TDDs) and the highest near infra-red optical absorptions. The best trade-off for thin layers was 750 °C, 60 min H 2 anneals. Using longer duration 750 °C anneals and especially 750 °C/890 °C cyclic anneals indeed yielded rougher surfaces and vastly degraded optical absorption (deleterious formation of GeSi alloys). By contrast, short 750 °C/890 °C thermal cyclings yielded the best metrics in thick Ge layers (while being at the same time the best in terms of throughput): root mean square surface roughness around 0.8 nm, TDD around 10 7 cm -2, slightly tensily-strained layers (which a plus for optical absorption as the absorption edge is shifted to higher wavelengths), a limited penetration of Si into Ge (and thus absorption coefficients at 1.3 and 1.55 μm almost equal to those of as-grown layers), etc. We have also described the low temperature (450 °C/525 °C) process that we have developed to passivate Ge surfaces thanks to SiH 4 prior to gate stack deposition. Si layer thickness should be below 20 Å in order to have conformal deposition. A transition of the growth front to 3 dimensions has indeed been evidenced for 20 Å and higher.

  1. Elemental boron-doped p(+)-SiGe layers grown by molecular beam epitaxy for infrared detector applications

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; George, T.; Jones, E. W.; Ksendzov, A.; Huberman, M. L.

    1992-01-01

    SiGe/Si heterojunction internal photoemission (HIP) detectors have been fabricated utilizing molecular beam epitaxy of p(+)-SiGe layers on p(-)-Si substrates. Elemental boron from a high-temperature effusion cell was used as the dopant source during MBE growth, and high doping concentrations have been achieved. Strong infrared absorption, mainly by free-carrier absorption, was observed for the degenerately doped SiGe layers. The use of elemental boron as the dopant source allows a low MBE growth temperature, resulting in improved crystalline quality and smooth surface morphology of the Si(0.7)Ge(0.3) layers. Nearly ideal thermionic emission dark current characteristics have been obtained. Photoresponse of the HIP detectors in the long-wavelength infrared regime has been demonstrated.

  2. Inversion layer on the Ge(001) surface from the four-probe conductance measurements

    SciTech Connect

    Wojtaszek, Mateusz; Lis, Jakub Zuzak, Rafal; Such, Bartosz; Szymonski, Marek

    2014-07-28

    We report four-probe conductance measurements with sub-micron resolution on atomically clean Ge(001) surfaces. A qualitative difference between n-type and p-type crystals is observed. The scaling behavior of the resistance on n-type samples indicates two-dimensional current flow, while for the p-type crystal a three-dimensional description is appropriate. We interpret this in terms of the formation of an inversion layer at the surface. This result points to the surface states, i.e., dangling bonds, as the driving force behind band bending in germanium. It also explains the intrinsic character of band bending in germanium.

  3. Adjustment of residual stress and intermediate layer to BDD/porous Ti composite membrane

    NASA Astrophysics Data System (ADS)

    Tian, Cheng-lu; Li, Xiao-wei; Chang, Ming

    2013-05-01

    Diamond films are deposited on porous Ti substrates by hot filament chemical vapor deposition (HFCVD) method. For adjusting the residual stress of substrate and the titanium carbide (TiC) intermediate layer, the substrates are under annealing process firstly, then are put into alkaline solution with electricity oxidation, and finally composite membranes are obtained by HFCVD, which are characterized by X-ray diffraction (XRD), metalloscope and scanning electron microscope (SEM). Results show that the composite membranes deposited on unannealed substrates are cracked obviously in both sides and broken off easily. After annealing process, the membranes are no longer cracked easily, because the tensile stress distributed in substrates is significantly relieved. After passivation process, TiC generated between diamond film and substrate is less than that without passivation process.

  4. Two-layer stratified flows over pronounced obstacles at low-to-intermediate Froude numbers

    NASA Astrophysics Data System (ADS)

    Cabeza, Cecilia; Varela, Juan; Bove, Italo; Freire, Daniel; Martí, Arturo C.; Sarasúa, L. G.; Usera, Gabriel; Montagne, Raul; Araujo, Moacyr

    2009-04-01

    Two-layer stratified flows over abrupt topographic obstacles, simulating relevant situations in oceanographic problems, are investigated numerically and experimentally in a simplified two-dimensional situation. Experimental results and numerical simulations are presented at low-to-intermediate Froude numbers for two different obstacles: one semicylindrical and the other prismatic. In both cases, four different flow regimes downstream of the obstacles are found: (I) subcritical flow, (II) internal hydraulic jump, (III) Kelvin-Helmholtz instability at the interface, and (IV) shedding of billows. The critical values of the Froude number for the transition between different regimes depend strongly on the shape of the obstacle. In regime (III), we show that the characteristics of the lee wave that appears past the obstacle can be explained with a theoretical stability analysis. Almost independence of the vortex shedding frequency with upstream velocity is observed and explained.

  5. Enhanced Sensitivity of Anti-Symmetrically Structured Surface Plasmon Resonance Sensors with Zinc Oxide Intermediate Layers

    PubMed Central

    Tu, Yi-Chen; Huang, Teng-Yi; Chiu, Nan-Fu

    2014-01-01

    We report a novel design wherein high-refractive-index zinc oxide (ZnO) intermediary layers are used in anti-symmetrically structured surface plasmon resonance (SPR) devices to enhance signal quality and improve the full width at half maximum (FWHM) of the SPR reflectivity curve. The surface plasmon (SP) modes of the ZnO intermediary layer were excited by irradiating both sides of the Au film, thus inducing a high electric field at the Au/ZnO interface. We demonstrated that an improvement in the ZnO (002) crystal orientation led to a decrease in the FWHM of the SPR reflectivity curves. We optimized the design of ZnO thin films using different parameters and performed analytical comparisons of the ZnO with conventional chromium (Cr) and indium tin oxide (ITO) intermediary layers. The present study is based on application of the Fresnel equation, which provides an explanation and verification for the observed narrow SPR reflectivity curve and optical transmittance spectra exhibited by (ZnO/Au), (Cr/Au), and (ITO/Au) devices. On exposure to ethanol, the anti-symmetrically structured showed a huge electric field at the Au/ZnO interface and a 2-fold decrease in the FWHM value and a 1.3-fold larger shift in angle interrogation and a 4.5-fold high-sensitivity shift in intensity interrogation. The anti-symmetrically structured of ZnO intermediate layers exhibited a wider linearity range and much higher sensitivity. It also exhibited a good linear relationship between the incident angle and ethanol concentration in the tested range. Thus, we demonstrated a novel and simple method for fabricating high-sensitivity, high-resolution SPR biosensors that provide high accuracy and precision over relevant ranges of analyte measurement. PMID:24361929

  6. Enhanced sensitivity of anti-symmetrically structured surface plasmon resonance sensors with zinc oxide intermediate layers.

    PubMed

    Chiu, Nan-Fu; Tu, Yi-Chen; Huang, Teng-Yi

    2013-01-01

    We report a novel design wherein high-refractive-index zinc oxide (ZnO) intermediary layers are used in anti-symmetrically structured surface plasmon resonance (SPR) devices to enhance signal quality and improve the full width at half maximum (FWHM) of the SPR reflectivity curve. The surface plasmon (SP) modes of the ZnO intermediary layer were excited by irradiating both sides of the Au film, thus inducing a high electric field at the Au/ZnO interface. We demonstrated that an improvement in the ZnO (002) crystal orientation led to a decrease in the FWHM of the SPR reflectivity curves. We optimized the design of ZnO thin films using different parameters and performed analytical comparisons of the ZnO with conventional chromium (Cr) and indium tin oxide (ITO) intermediary layers. The present study is based on application of the Fresnel equation, which provides an explanation and verification for the observed narrow SPR reflectivity curve and optical transmittance spectra exhibited by (ZnO/Au), (Cr/Au), and (ITO/Au) devices. On exposure to ethanol, the anti-symmetrically structured showed a huge electric field at the Au/ZnO interface and a 2-fold decrease in the FWHM value and a 1.3-fold larger shift in angle interrogation and a 4.5-fold high-sensitivity shift in intensity interrogation. The anti-symmetrically structured of ZnO intermediate layers exhibited a wider linearity range and much higher sensitivity. It also exhibited a good linear relationship between the incident angle and ethanol concentration in the tested range. Thus, we demonstrated a novel and simple method for fabricating high-sensitivity, high-resolution SPR biosensors that provide high accuracy and precision over relevant ranges of analyte measurement. PMID:24361929

  7. Polydopamine as an intermediate layer for silver and hydroxyapatite immobilisation on metallic biomaterials surface.

    PubMed

    Saidin, Syafiqah; Chevallier, Pascale; Abdul Kadir, Mohammed Rafiq; Hermawan, Hendra; Mantovani, Diego

    2013-12-01

    Hydroxyapatite (HA) coated implant is more susceptible to bacterial infection as the micro-structure surface which is beneficial for osseointegration, could also become a reservoir for bacterial colonisation. The aim of this study was to introduce the antibacterial effect of silver (Ag) to the biomineralised HA by utilising a polydopamine film as an intermediate layer for Ag and HA immobilisation. Sufficient catechol groups in polydopamine were required to bind chemically stainless steel 316 L, Ag and HA elements. Different amounts of Ag nanoparticles were metallised on the polydopamine grafted stainless steel by varying the immersion time in silver nitrate solution from 12 to 24 h. Another polydopamine layer was then formed on the metallised film, followed by surface biomineralisation in 1.5 Simulated Body Fluid (SBF) solution for 3 days. Several characterisation techniques including X-Ray Photoelectron Spectroscopy, Atomic Force Microscopy, Scanning Electron Microscopy and Contact Angle showed that Ag nanoparticles and HA agglomerations were successfully immobilised on the polydopamine film through an element reduction process. The Ag metallisation at 24 h has killed the viable bacteria with 97.88% of bactericidal ratio. The Ag was ionised up to 7 days which is crucial to prevent bacterial infection during the first stage of implant restoration. The aged functionalised films were considered stable due to less alteration of its chemical composition, surface roughness and wettability properties. The ability of the functionalised film to coat complex and micro scale metal make it suitable for dental and orthopaedic implants application. PMID:24094179

  8. Liquid-Sn-driven lateral growth of poly-GeSn on insulator assisted by surface oxide layer

    NASA Astrophysics Data System (ADS)

    Kurosawa, Masashi; Taoka, Noriyuki; Sakashita, Mitsuo; Nakatsuka, Osamu; Miyao, Masanobu; Zaima, Shigeaki

    2013-09-01

    Effects of surface oxide layers on liquid-Sn-driven GeSn crystallization on insulators at various temperatures (<475 °C) are investigated. An amorphous Ge in neighborhood of patterned-Sn (<3.5 μm) becomes to polycrystalline Ge1-xSnx (x ≈ 0.025 - 0.14) after annealing at 150-475 °C, which is independent of the surface oxide thickness. Interestingly, a 50-μm-length lateral growth of polycrystalline Ge0.99Sn0.01 layers achieved by combination of thickening of the surface-oxide treated by NH4OH and annealing above melting temperature of Sn (231.9 °C). The growth length is 15 times longer than without the treatment. The advanced process promises to achieve group-IV-based optic and electronic devices on flexible substrates and Si platforms.

  9. Reduction of dislocation density in mismatched SiGe/Si using a low-temperature Si buffer layer

    NASA Astrophysics Data System (ADS)

    Linder, K. K.; Zhang, F. C.; Rieh, J.-S.; Bhattacharya, P.; Houghton, D.

    1997-06-01

    The reduction of the dislocation density in relaxed SiGe/Si heterostructures using a low-temperature Si(LT-Si) buffer has been investigated. We have shown that a 0.1 μm LT-Si buffer reduces the threading dislocation density in mismatched Si0.85Ge0.15/Si epitaxial layers as low as ˜104cm-2. Samples were grown by both gas-source molecular beam epitaxy and ultrahigh vacuum chemical vapor deposition.

  10. Two-layered dissolving microneedles formulated with intermediate-acting insulin.

    PubMed

    Ito, Yukako; Hirono, Muneyuki; Fukushima, Keizo; Sugioka, Nobuyuki; Takada, Kanji

    2012-10-15

    Two-layered dissolving microneedles (DMs) containing intermediate-acting insulin, protamine sulfate insulin (PSI), were prepared. Then a pharmacodynamic study was performed to evaluate the prolonged hypoglycemic effects in rats. The DMs were approximately 497±5 μm long, with 303±3 μm diameter at their base. The length of the insulin loaded space was 182±4 μm. PSI contents in DMs were 0.51±0.02 IU. A three-month stability study showed that 99.9±1.4% of PSI was recovered at 4 °C. As the temperature increased to 40 °C, recovery decreased to 97.5±2.0%. PSI was released within 5 min from DMs. Hypoglycemic effects of PSI DMs were evaluated in rats where subcutaneous injection preparations were used as references. Total area above the plasma glucose level (% of the pre-dose level) vs. time curve as an index of hypoglycemic effect was 144.0±16.0% h and 243.3±8.5% h for PSI DMs at 1.46 and 3.28 IU/kg. The relative pharmacologic availability of PSI from DMs were 100.2±9.8% and 91.4±4.1%. No significant difference of hypoglycemic curves was found between DMs and injection solutions, which suggests the usefulness of two-layered DMs of PSI for the displacement therapy of sc injection preparation. PMID:22750407

  11. Growth of monolithic full-color GaN-based LED with intermediate carrier blocking layers

    NASA Astrophysics Data System (ADS)

    El-Ghoroury, Hussein S.; Yeh, Milton; Chen, J. C.; Li, X.; Chuang, Chih-Li

    2016-07-01

    Specially designed intermediate carrier blocking layers (ICBLs) in multi-active regions of III-nitride LEDs were shown to be effective in controlling the carrier injection distribution across the active regions. In principle, the majority of carriers, both holes and electrons, can be guided into targeted quantum wells and recombine to generate light of specific wavelengths at controlled current-densities. Accordingly we proposed and demonstrated a novel monolithic InGaN-based LED to achieve three primary colors of light from one device at selected current densities. This LED structure, which has three different sets of quantum wells separated with ICBLs for three primary red-green-blue (RGB) colors, was grown by metal-organic chemical vapor deposition (MOCVD). Results show that this LED can emit light ranging from 460 to 650 nm to cover the entire visible spectrum. The emission wavelength starts at 650 nm and then decreases to 460 nm or lower as the injection current increases. In addition to three primary colors, many other colors can be obtained by color mixing techniques. To the best of our knowledge, this is the first demonstration of monolithic full-color LED grown by a simple growth technique without using re-growth process.

  12. Interface induce growth of intermediate layer for bandgap engineering insights into photoelectrochemical water splitting

    PubMed Central

    Zhang, Jian; Zhang, Qiaoxia; Wang, Lianhui; Li, Xing’ao; Huang, Wei

    2016-01-01

    A model of interface induction for interlayer growing is proposed for bandgap engineering insights into photocatalysis. In the interface of CdS/ZnS core/shell nanorods, a lamellar solid solution intermediate with uniform thickness and high crystallinity was formed under interface induction process. Merged the novel charge carrier transfer layer, the photocurrent of the core/shell/shell nanorod (css-NR) array was significantly improved to 14.0 mA cm−2 at 0.0 V vs. SCE, nearly 8 times higher than that of the perfect CdS counterpart and incident photon to electron conversion efficiency (IPCE) values above 50% under AM 1.5G irradiation. In addition, this array photoelectrode showed excellent photocatalytic stability over 6000 s. These results suggest that the CdS/Zn1−xCdxS/ZnS css-NR array photoelectrode provides a scalable charge carrier transfer channel, as well as durability, and therefore is promising to be a large-area nanostructured CdS-based photoanodes in photoelectrochemical (PEC) water splitting system. PMID:27250648

  13. Interface induce growth of intermediate layer for bandgap engineering insights into photoelectrochemical water splitting.

    PubMed

    Zhang, Jian; Zhang, Qiaoxia; Wang, Lianhui; Li, Xing'ao; Huang, Wei

    2016-01-01

    A model of interface induction for interlayer growing is proposed for bandgap engineering insights into photocatalysis. In the interface of CdS/ZnS core/shell nanorods, a lamellar solid solution intermediate with uniform thickness and high crystallinity was formed under interface induction process. Merged the novel charge carrier transfer layer, the photocurrent of the core/shell/shell nanorod (css-NR) array was significantly improved to 14.0 mA cm(-2) at 0.0 V vs. SCE, nearly 8 times higher than that of the perfect CdS counterpart and incident photon to electron conversion efficiency (IPCE) values above 50% under AM 1.5G irradiation. In addition, this array photoelectrode showed excellent photocatalytic stability over 6000 s. These results suggest that the CdS/Zn1-xCdxS/ZnS css-NR array photoelectrode provides a scalable charge carrier transfer channel, as well as durability, and therefore is promising to be a large-area nanostructured CdS-based photoanodes in photoelectrochemical (PEC) water splitting system. PMID:27250648

  14. Interface induce growth of intermediate layer for bandgap engineering insights into photoelectrochemical water splitting

    NASA Astrophysics Data System (ADS)

    Zhang, Jian; Zhang, Qiaoxia; Wang, Lianhui; Li, Xing’Ao; Huang, Wei

    2016-06-01

    A model of interface induction for interlayer growing is proposed for bandgap engineering insights into photocatalysis. In the interface of CdS/ZnS core/shell nanorods, a lamellar solid solution intermediate with uniform thickness and high crystallinity was formed under interface induction process. Merged the novel charge carrier transfer layer, the photocurrent of the core/shell/shell nanorod (css-NR) array was significantly improved to 14.0 mA cm‑2 at 0.0 V vs. SCE, nearly 8 times higher than that of the perfect CdS counterpart and incident photon to electron conversion efficiency (IPCE) values above 50% under AM 1.5G irradiation. In addition, this array photoelectrode showed excellent photocatalytic stability over 6000 s. These results suggest that the CdS/Zn1‑xCdxS/ZnS css-NR array photoelectrode provides a scalable charge carrier transfer channel, as well as durability, and therefore is promising to be a large-area nanostructured CdS-based photoanodes in photoelectrochemical (PEC) water splitting system.

  15. Critical stresses for Si/sub x/Ge/sub 1-//sub x/ strained-layer plasticity

    SciTech Connect

    Tsao, J.Y.; Dodson, B.W.; Picraux, S.T.; Cornelison, D.M.

    1987-11-23

    We have measured the temperature-dependent onset of strain relief in metastable Si/sub x/Ge/sub 1-//sub x/ strained layers grown on Ge substrates. On the basis of these measurements, and physical arguments, we propose that strained-layer breakdown is most directly determined not by thickness and lattice mismatch, but rather by (1) an ''excess'' stress (the difference between that due to misfit strain and that due to dislocation line tension) and (2) temperature. With use of these parameters, observed regimes of stability and metastability are shown to be described within a simple, unified framework.

  16. Growth and structure evaluation of strain-relaxed Ge1-xSnx buffer layers grown on various types of substrates

    NASA Astrophysics Data System (ADS)

    Takeuchi, Shotaro; Sakai, Akira; Yamamoto, Koji; Nakatsuka, Osamu; Ogawa, Masaki; Zaima, Shigeaki

    2007-01-01

    We have performed growth and structure evaluation of strain-relaxed Ge1-xSnx buffer layers grown on Si(0 0 1), virtual Ge(0 0 1) and bulk Ge(0 0 1) substrates. In the case of Si(0 0 1), amorphous Ge1-xSnx phases are partially formed as well as many threading dislocations in Ge0.98Sn0.02 layers. Employing virtual Ge substrates to reduce the lattice mismatch at the interface leads to epitaxial Ge0.978Sn0.022 layers with a flat surface. Most of threading dislocations in the Ge0.978Sn0.022 layer comes from pre-existing ones in the virtual Ge substrate and propagates laterally, leaving misfit segments at the Ge0.978Sn0.022/virtual Ge interface, after post-deposition annealing (PDA). This simultaneously results in the reduction of threading dislocation density and the promotion of strain relaxation. In the case of bulk Ge(0 0 1), although low threading dislocation density can be achieved, less than 106 cm-2, the film exhibits surface undulation and a lesser degree of strain relaxation even after PDA.

  17. Intermediate valence to heavy fermion through a quantum phase transition in Yb3(Rh1-xTx)4Ge13 (T = Co, Ir) single crystals

    NASA Astrophysics Data System (ADS)

    Rai, Binod; Morosan, Emilia

    Single crystals of Yb3(Rh1-x Tx)4Ge13 (T = Co, Ir) have been grown using the self-flux method. Powder X-ray diffraction data on these compounds are consistent with the cubic structure with space group Pm 3 n . Intermediate valence behavior is observed in Yb3(Rh1-x Tx)4Ge13 upon T = Co doping, while T = Ir doping drives the system into a heavy fermion state. Antiferromagnetic order is observed in the Ir-doped samples Yb3(Rh1-x Tx)4Ge13 for 0.5 < x <= 1 with TN = 0.96 K for Yb3Ir4Ge13. With decreasing x, the magnetic order is suppressed towards a quantum critical point around xc = 0.5, accompanied by non-Fermi liquid behavior evidenced by logarithmic divergence of the specific heat and linear temperature dependence of the resistivity. The Fermi liquid behavior is recovered with the application of large magnetic fields. Gordon and Betty Moore Foundation EPiQS initiative through Grant GBMF4417 and Welch Foundation.

  18. Three dimensional finite element modeling and characterization of intermediate states in single active layer phase change memory devices

    NASA Astrophysics Data System (ADS)

    Cinar, I.; Aslan, O. B.; Gokce, A.; Dincer, O.; Karakas, V.; Stipe, B.; Katine, J. A.; Aktas, G.; Ozatay, O.

    2015-06-01

    The high contrast in the electrical resistivity between amorphous and crystalline states of a phase change material can potentially enable multiple memory levels for efficient use of a data storage medium. We report on our investigation of the role of the current injection site geometry (circular and square) in stabilizing such intermediate states within a nanoscale single-phase change material system (Ge2Sb2Te5). We have developed a three dimensional multiphysics model, which includes phase change kinetics, electrical, thermal, thermoelectric, and percolation effects, all as a function of temperature, using an iterative approach with coupled differential equations. Our model suggests that the physical origin of the formation of stable intermediate states in square top contact devices is mainly due to anisotropic heating during the application of a programming current pulse. Furthermore, the threshold current requirement and the width of the programming window are determined by crystallite nucleation and growth rates such that a higher crystallization rate leads to a narrower range of current pulses for switching to intermediate resistance level(s). The experimentally determined resistance maps, those that are indicative of the crystallinity, show good agreement with the simulated phase change behavior confirming the existence of stable intermediate states. Our model successfully predicts the required programming conditions for such mixed-phase levels, which can be used to optimize memory cells for future ultra-high density data storage applications.

  19. Differential Gene Expression of the Intermediate and Outer Interzone Layers of Developing Articular Cartilage in Murine Embryos

    PubMed Central

    IJpma, Arne; Cleary, Mairead; Heijsman, Daphne; Narcisi, Roberto; van der Spek, Peter J.; Kremer, Andreas; van Weeren, René; Brama, Pieter; van Osch, Gerjo J.V.M.

    2014-01-01

    Nascent embryonic joints, interzones, contain a distinct cohort of progenitor cells responsible for the formation of the majority of articular tissues. However, to date the interzone has largely been studied using in situ analysis for candidate genes in the context of the embryo rather than using an unbiased genome-wide expression analysis on isolated interzone cells, leaving significant controversy regarding the exact role of the intermediate and outer interzone layers in joint formation. Therefore, in this study, using laser capture microdissection (three biological replicates), we selectively harvested the intermediate and outer interzones of mouse embryos at gestational age 15.5 days, just prior to cavitation, when the differences between the layers should be most profound. Microarray analysis (Agilent Whole Mouse Genome Oligo Microarrays) was performed and the differential gene expression between the intermediate interzone cells and outer interzone cells was examined by performing a two-sided paired Student's t-test and pathway analysis. One hundred ninety-seven genes were differentially expressed (≥2-fold) between the intermediate interzone and the outer interzone with a P-value≤0.01. Of these, 91 genes showed higher expression levels in the intermediate interzone and 106 were expressed higher in the outer interzone. Pathway analysis of differentially expressed genes suggests an important role for inflammatory processes in the interzone layers, especially in the intermediate interzone, and hence in joint and articular cartilage development. The high representation of genes relevant to chondrocyte hypertrophy and endochondral ossification in the outer interzone suggests that it undergoes endochondral ossification. PMID:24738827

  20. Differential gene expression of the intermediate and outer interzone layers of developing articular cartilage in murine embryos.

    PubMed

    Jenner, Florien; IJpma, Arne; Cleary, Mairead; Heijsman, Daphne; Narcisi, Roberto; van der Spek, Peter J; Kremer, Andreas; van Weeren, René; Brama, Pieter; van Osch, Gerjo J V M

    2014-08-15

    Nascent embryonic joints, interzones, contain a distinct cohort of progenitor cells responsible for the formation of the majority of articular tissues. However, to date the interzone has largely been studied using in situ analysis for candidate genes in the context of the embryo rather than using an unbiased genome-wide expression analysis on isolated interzone cells, leaving significant controversy regarding the exact role of the intermediate and outer interzone layers in joint formation. Therefore, in this study, using laser capture microdissection (three biological replicates), we selectively harvested the intermediate and outer interzones of mouse embryos at gestational age 15.5 days, just prior to cavitation, when the differences between the layers should be most profound. Microarray analysis (Agilent Whole Mouse Genome Oligo Microarrays) was performed and the differential gene expression between the intermediate interzone cells and outer interzone cells was examined by performing a two-sided paired Student's t-test and pathway analysis. One hundred ninety-seven genes were differentially expressed (≥ 2-fold) between the intermediate interzone and the outer interzone with a P-value ≤ 0.01. Of these, 91 genes showed higher expression levels in the intermediate interzone and 106 were expressed higher in the outer interzone. Pathway analysis of differentially expressed genes suggests an important role for inflammatory processes in the interzone layers, especially in the intermediate interzone, and hence in joint and articular cartilage development. The high representation of genes relevant to chondrocyte hypertrophy and endochondral ossification in the outer interzone suggests that it undergoes endochondral ossification. PMID:24738827

  1. Behavior and mixing of a cold intermediate layer near a sloping boundary

    NASA Astrophysics Data System (ADS)

    Cyr, Frédéric; Bourgault, Daniel; Galbraith, Peter S.

    2015-03-01

    As in many other subarctic basins, a cold intermediate layer (CIL) is found during ice-free months in the Lower St. Lawrence Estuary (LSLE), Canada. This study examines the behavior of the CIL above the sloping bottom using a high-resolution mooring deployed on the northern side of the estuary. Observations show successive swashes/backwashes of the CIL on the slope at a semi-diurnal frequency. It is shown that these upslope and downslope motions are likely caused by internal tides generated at the nearby channel head sill. Quantification of mixing from 322 turbulence casts reveals that in the bottom 10 m of the water column, the time-average dissipation rate of turbulent kinetic energy is 𝜖 10 m = 1.6×10-7Wkg-1, an order of magnitude greater than found in the interior of the basin, far from boundaries. Near-bottom dissipation during the flood phase of the M2 tide cycle (upslope flow) is about four times greater than during the ebb phase (downslope flow). Bottom shear stress, shear instabilities, and internal wave scattering are considered as potential boundary mixing mechanisms near the seabed. In the interior of the water column, far from the bottom, increasing dissipation rates are observed with both increasing stratification and shear, which suggests some control of the dissipation by the internal wave field. However, poor fits with a parametrization for large-scale wave-wave interactions suggests that the mixing is partly driven by more complex non-linear and/or smaller scale waves.

  2. The structure and photoconductivity of SiGe/Si epitaxial layers modified by single-pulse laser radiation

    NASA Astrophysics Data System (ADS)

    Ivlev, G. D.; Kazuchits, N. M.; Prakopyeu, S. L.; Rusetsky, M. S.; Gaiduk, P. I.

    2014-12-01

    The effect of nanosecond pulses of ruby laser radiation on the structural state and morphology of the epitaxial layers of a SiO0.5Ge0.5 solid solution on silicon with the initiation of a crystal-melt phase transition has been studied by electron microscopy. Data on the photoelectric parameters of the laser-modified layers having a cellular structure owing to the segregation of germanium during the solidification of the binary melt have been derived.

  3. Intermediate Progenitor Cohorts Differentially Generate Cortical Layers and Require Tbr2 for Timely Acquisition of Neuronal Subtype Identity.

    PubMed

    Mihalas, Anca B; Elsen, Gina E; Bedogni, Francesco; Daza, Ray A M; Ramos-Laguna, Kevyn A; Arnold, Sebastian J; Hevner, Robert F

    2016-06-28

    Intermediate progenitors (IPs) amplify the production of pyramidal neurons, but their role in selective genesis of cortical layers or neuronal subtypes remains unclear. Using genetic lineage tracing in mice, we find that IPs destined to produce upper cortical layers first appear early in corticogenesis, by embryonic day 11.5. During later corticogenesis, IP laminar fates are progressively limited to upper layers. We examined the role of Tbr2, an IP-specific transcription factor, in laminar fate regulation using Tbr2 conditional mutant mice. Upon Tbr2 inactivation, fewer neurons were produced by immediate differentiation and laminar fates were shifted upward. Genesis of subventricular mitoses was, however, not reduced in the context of a Tbr2-null cortex. Instead, neuronal and laminar differentiation were disrupted and delayed. Our findings indicate that upper-layer genesis depends on IPs from many stages of corticogenesis and that Tbr2 regulates the tempo of laminar fate implementation for all cortical layers. PMID:27320921

  4. Tin surface segregation, desorption, and island formation during post-growth annealing of strained epitaxial Ge1-xSnx layer on Ge(0 0 1) substrate

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Li, Lingzi; Zhou, Qian; Pan, Jisheng; Zhang, Zheng; Tok, Eng Soon; Yeo, Yee-Chia

    2014-12-01

    Annealing of strained Ge1-xSnx epitaxial layers grown on Ge(0 0 1) substrate results in two distinctive regimes marked by changes in composition and morphology. Annealing at low temperatures (200-300 °C or Regime-I) leads to surface enrichment of Sn due to Sn segregation, as indicated by X-ray photoelectron spectroscopy (XPS) results, while the bulk Sn composition (from X-ray diffraction (XRD)) and the surface morphology (from atomic force microscopy (AFM)) do not show discernible changes as compared to the as-grown sample. Annealing at temperatures ranging from 300 °C to 500 °C (Regime-II) leads to a decrease in the surface Sn composition. While the Ge1-xSnx layer remains fully strained, a reduction in the bulk Sn composition is observed when the annealing temperature reaches 500 °C. At this stage, surface roughening also occurs with formation of 3D islands. The island size increases as the annealing temperature is raised to 600 °C. The decrease in the Sn composition at the surface and in the bulk in Regime-II is attributed to additional thermally activated kinetic processes associated with Sn desorption and formation of Sn-rich 3D islands on the surface.

  5. Impact of using high-density polyethylene geomembrane layer as landfill intermediate cover on landfill gas extraction.

    PubMed

    Chen, Zezhi; Gong, Huijuan; Zhang, Mengqun; Wu, Weili; Liu, Yu; Feng, Jin

    2011-05-01

    Clay is widely used as a traditional cover material for landfills. As clay becomes increasingly costly and scarce, and it also reduces the storage capacity of landfills, alternative materials with low hydraulic conductivity are employed. In developing countries such as China, landfill gas (LFG) is usually extracted for utilization during filling stage, therefore, the intermediate covering system is an important part in a landfill. In this study, a field test of LFG extraction was implemented under the condition of using high-density polyethylene (HDPE) geomembrane layer as the only intermediate cover on the landfill. Results showed that after welding the HDPE geomembranes together to form a whole airtight layer upon a larger area of landfill, the gas flow in the general pipe increased 25% comparing with the design that the HDPE geomembranes were not welded together, which means that the gas extraction ability improved. However as the heat isolation capacity of the HDPE geomembrane layer is low, the gas generation ability of a shallow landfill is likely to be weakened in cold weather. Although using HDPE geomembrane layer as intermediate cover is acceptable in practice, the management and maintenance of it needs to be investigated in order to guarantee its effective operation for a long term. PMID:21232931

  6. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Formation of the intermediate semiconductor layer for the Ohmic contact to silicon carbide using Germanium implantation

    NASA Astrophysics Data System (ADS)

    Guo, Hui; Wang, Yue-Hu; Zhang, Yu-Ming; Qiao, Da-Yong; Zhang, Yi-Men

    2009-10-01

    By formation of an intermediate semiconductor layer (ISL) with a narrow band gap at the metallic contact/SiC interface, this paper realises a new method to fabricate the low-resistance Ohmic contacts for SiC. An array of transfer length method (TLM) test patterns is formed on N-wells created by P+ ion implantation into Si-faced p-type 4H-SiC epilayer. The ISL of nickel-metal Ohmic contacts to n-type 4H-SiC could be formed by using Germanium ion implantation into SiC. The specific contact resistance ρc as low as 4.23 × 10-5 Ωcm2 is achieved after annealing in N2 at 800 °C for 3 min, which is much lower than that (> 900 °C) in the typical SiC metallisation process. The sheet resistance Rsh of the implanted layers is 1.5 kΩ/□. The technique for converting photoresist into nanocrystalline graphite is used to protect the SiC surface in the annealing after Ge+ ion implantations.

  7. Metal-HfO{sub 2}-Ge capacitor: Its enhanced charge trapping properties with S-treated substrate and atomic-layer-deposited HfO{sub 2} layer

    SciTech Connect

    Park, In-Sung; Jung, Yong Chan; Seong, Sejong; Ahn, Jinho; Lee, Sung Bo

    2015-01-15

    The charge trapping properties of metal-HfO{sub 2}-Ge capacitor as a nonvolatile memory have been investigated with (NH{sub 4}){sub 2}S-treated Ge substrate and atomic-layer-deposited HfO{sub 2} layer. The interfacial layer generated by (NH{sub 4}){sub 2}S-treated Ge substrate reveals a trace of -S- bonding, very sharp interface edges, and smooth surface morphology. The Ru-HfO{sub 2}-Ge capacitor with (NH{sub 4}){sub 2}S-treated Ge substrate shows an enhanced interface state with little frequency dispersion, a lower leakage current, and very reliable properties with the enhanced endurance and retention than Ru-HfO{sub 2}-Ge capacitor with cyclic-cleaned Ge substrate.

  8. Three-dimensional nanostructures on Ge/Si(100) wetting layers: Hillocks and pre-quantum dots

    NASA Astrophysics Data System (ADS)

    Ramalingam, Gopalakrishnan; Floro, Jerrold A.; Reinke, Petra

    2016-05-01

    The annealing of sub-critical Ge wetting layers (WL < 3.5 ML) initiates the formation of 3D nanostructures, whose shape and orientation is determined by the WL thickness and thus directly related to the strain energy. The emergence of these nanostructures, hillocks and pre-quantum dots, is studied by scanning tunneling microscopy. A wetting layer deposited at 350 °C is initially rough on the nanometer length-scale and undergoes a progressive transformation and smoothening during annealing at T < 460 °C when vacancy lines and the 2xn reconstruction are observed. The metastable Ge WL then collapses to form 3D nanostructures whose morphology is controlled by the WL thickness: first, the hillocks, with a wedding cake-type structure where the step edges run parallel to the ⟨110⟩ direction, are formed from thin wetting layers, while {105}-faceted structures, called pre-quantum dots (p-QDs), are formed from thicker layers. The wetting layer thickness and thus the misfit strain energy controls the type of structure. The crossover thickness between the hillock and p-QDs regime is between 1.6 and 2.1 ML. The hillocks have larger lateral dimensions and volumes than p-QDs, and the p-QDs are exceptionally small quantum dots with a lower limit of 10 nm in width. Our work opens a new pathway to the control of nanostructure morphology and size in the elastically strained Ge/Si system.

  9. Effect of high-pressure H{sub 2}O treatment on elimination of interfacial GeO{sub X} layer between ZrO{sub 2} and Ge stack

    SciTech Connect

    Huang, Chen-Shuo; Liu, Po-Tsun

    2011-08-22

    This investigation demonstrates the effect of high-pressure H{sub 2}O treatment on the elimination of the interfacial germanium suboxide (GeO{sub X}) layer between ZrO{sub 2} and Ge. The formation of GeO{sub X} interlayer increases the gate-leakage current and worsen the controllability of the gate during deposition or thermal cycles. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy reveal that high-pressure H{sub 2}O treatment eliminates the interfacial GeO{sub X} layer. The physical mechanism involves the oxidation of non-oxidized Zr with H{sub 2}O and the reduction of GeO{sub X} by H{sub 2}. Treatment with H{sub 2}O reduces the gate-leakage current of a ZrO{sub 2}/Ge capacitor by a factor of 1000.

  10. Bonding mechanism of a yttrium iron garnet film on Si without the use of an intermediate layer

    SciTech Connect

    Pantzas, Konstantinos; Patriarche, Gilles; Talneau, Anne; Youssef, Jamal Ben

    2014-10-06

    Direct bonding of yttrium iron garnet (YIG) on silicon without the use of an intermediate bonding layer is demonstrated and characterized using scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy. During the bonding experiment, the garnet is reduced in the presence of oxide-free silicon. As a result, a 5 nm thick SiO{sub 2}/amorphous-YIG bilayer is formed and welds the garnet to silicon.

  11. Study of the intermediate layer at the n{sup +}-CdS/p-CdTe interface

    SciTech Connect

    Muzafarova, S. A. Aitbaev, B. U.; Mirsagatov, Sh. A.; Durshimbetov, K.; Zhanabergenov, Zh.

    2008-12-15

    The effect of production conditions and subsequent stimulation by ultrasonic irradiation on the formation of a solid solution at the n-CdS/p-CdTe interface in solar cells has been investigated. The phase composition of the solid-solution transient layer was investigated by a nondestructive photoelectric method (measurement of the spectral distribution of photosensitivity in the gate and photodiode modes). It is shown that the phase composition and thickness of the intermediate CdTe{sub 1-x}S{sub x} layer depend strongly on the heterostructure formation conditions.

  12. Threading dislocation reduction in a GaN film with a buffer layer grown at an intermediate temperature

    NASA Astrophysics Data System (ADS)

    Cho, Youngji; Chang, Jiho; Ha, Joonseok; Lee, Hyun-jae; Fujii, Katsushi; Yao, Takafumi; Lee, Woong; Sekiguchi, Takashi; Yang, Jun-Mo; Yoo, Jungho

    2015-01-01

    Remarkable reduction of the threading dislocation (TD) density has been achieved by inserting a GaN layer grown at an intermediate temperature (900 °C) (IT-GaN layer), just prior to the growth of GaN at 1040 °C by using a hydride vapor phase epitaxy. The variation in the dislocation density variation along the growth direction was observed by using cathodoluminescence (CL) and transmission electron microscopy (TEM). A cross-sectional CL image revealed that the reduction of the TD density happened during the growth of IT-GaN layer. The TEM measurement provided the proof that the TD reduction could be ascribed to the masking of the TD by stacking faults in the IT-GaN layer.

  13. Initial stage growth of GexSi1−x layers and Ge quantum dot formation on GexSi1−x surface by MBE

    PubMed Central

    2012-01-01

    Critical thicknesses of two-dimensional to three-dimensional growth in GexSi1−x layers were measured as a function of composition for different growth temperatures. In addition to the (2 × 1) superstructure for a Ge film grown on Si(100), the GexSi1−x layers are characterized by the formation of (2 × n) reconstruction. We measured n for all layers of Ge/GexSi1−x/Ge heterosystem using our software with respect to the video recording of reflection high-energy electron diffraction (RHEED) pattern during growth. The n reaches a minimum value of about 8 for clear Ge layer, whereas for GexSi1−x films, n is increased from 8 to 14. The presence of a thin strained film of the GexSi1−x caused not only the changes in critical thicknesses of the transitions, but also affected the properties of the germanium nanocluster array for the top Ge layer. Based on the RHEED data, the hut-like island form, which has not been previously observed by us between the hut and dome islands, has been detected. Data on the growth of Ge/GexSi1−x/Ge heterostructures with the uniform array of islands in the second layer of the Ge film have been received. PMID:23043796

  14. Influence of intermediate layers on the surface condition of laser crystallized silicon thin films and solar cell performance

    NASA Astrophysics Data System (ADS)

    Höger, Ingmar; Himmerlich, Marcel; Gawlik, Annett; Brückner, Uwe; Krischok, Stefan; Andrä, Gudrun

    2016-01-01

    The intermediate layer (IL) between glass substrate and silicon plays a significant role in the optimization of multicrystalline liquid phase crystallized silicon thin film solar cells on glass. This study deals with the influence of the IL on the surface condition and the required chemical surface treatment of the crystallized silicon (mc-Si), which is of particular interest for a-Si:H heterojunction thin film solar cells. Two types of IL were investigated: sputtered silicon nitride (SiN) and a layer stack consisting of silicon nitride and silicon oxide (SiN/SiO). X-ray photoelectron spectroscopy measurements revealed the formation of silicon oxynitride (SiOxNy) or silicon oxide (SiO2) layers at the surface of the mc-Si after liquid phase crystallization on SiN or SiN/SiO, respectively. We propose that SiOxNy formation is governed by dissolving nitrogen from the SiN layer in the silicon melt, which segregates at the crystallization front during crystallization. This process is successfully hindered, when additional SiO layers are introduced into the IL. In order to achieve solar cell open circuit voltages above 500 mV, a removal of the formed SiOxNy top layer is required using sophisticated cleaning of the crystallized silicon prior to a-Si:H deposition. However, solar cells crystallized on SiN/SiO yield high open circuit voltage even when a simple wet chemical surface treatment is applied. The implementation of SiN/SiO intermediate layers facilitates the production of mesa type solar cells with open circuit voltages above 600 mV and a power conversion efficiency of 10%.

  15. Tuneable Magnetic Phase Transitions in Layered CeMn2Ge(2-x)Six Compounds.

    PubMed

    Md Din, M F; Wang, J L; Cheng, Z X; Dou, S X; Kennedy, S J; Avdeev, M; Campbell, S J

    2015-01-01

    The structural and magnetic properties of seven CeMn2Ge(2-x)Six compounds with x = 0.0-2.0 have been investigated in detail. Substitution of Ge with Si leads to a monotonic decrease of both a and c along with concomitant contraction of the unit cell volume and significant modifications of the magnetic states - a crossover from ferromagnetism at room temperature for Ge-rich compounds to antiferromagnetism for Si-rich compounds. The magnetic phase diagram has been constructed over the full range of CeMn2Ge(2-x)Six compositions and co-existence of ferromagnetism and antiferromagnetism has been observed in CeMn2Ge1.2Si0.8, CeMn2Ge1.0Si1.0 and CeMn2Ge0.8Si1.2 with novel insight provided by high resolution neutron and X-ray synchrotron radiation studies. CeMn2Ge(2-x)Six compounds (x = 0, 0.4 and 0.8) exhibit moderate isothermal magnetic entropy accompanied with a second-order phase transition around room temperature. Analysis of critical behaviour in the vicinity of TC(inter) for CeMn2Ge2 compound indicates behaviour consistent with three-dimensional Heisenberg model predictions. PMID:26090940

  16. Crystal chemistry of layered carbide, Ti3(Si0.43Ge0.57)C2

    NASA Astrophysics Data System (ADS)

    Yang, Hexiong; Manoun, B.; Downs, R. T.; Ganguly, A.; Barsoum, M. W.

    2006-12-01

    The crystal structure of a layered ternary carbide, Ti3(Si0.43Ge0.57)C2, was studied with single-crystal X-ray diffraction. The compound has a hexagonal symmetry with space group P63/mmc and unit-cell parameters a=3.0823(1) Å, c=17.7702(6) Å, and V=146.21(1) Å3. The Si and Ge atoms in the structure occupy the same crystallographic site surrounded by six Ti atoms at an average distance of 2.7219 Å, and the C atoms are octahedrally coordinated by two types of symmetrically distinct Ti atoms, with an average C Ti distance of 2.1429 Å. The atomic displacement parameters for C and Ti are relatively isotropic, whereas those for A (=0.43Si+0.57Ge) are appreciably anisotropic, with U11 (=U22) being about three times greater than U33. Compared to Ti3SiC2, the substitution of Ge for Si results in an increase in both A Ti and C Ti bond distances. An electron density analysis based on the refined structure shows that each A atom is bonded to 6Ti atoms as well as to its 6 nearest neighbor A site atoms, whether the site is occupied by Si or Ge, suggesting that these bond paths may be significantly involved with electron transport properties.

  17. Phase-change properties of GeSbTe thin films deposited by plasma-enchanced atomic layer depositon

    NASA Astrophysics Data System (ADS)

    Song, Sannian; Yao, Dongning; Song, Zhitang; Gao, Lina; Zhang, Zhonghua; Li, Le; Shen, Lanlan; Wu, Liangcai; Liu, Bo; Cheng, Yan; Feng, Songlin

    2015-02-01

    Phase-change access memory (PCM) appears to be the strongest candidate for next-generation high-density nonvolatile memory. The fabrication of ultrahigh-density PCM depends heavily on the thin-film growth technique for the phase-changing chalcogenide material. In this study, Ge2Sb2Te5 (GST) and GeSb8Te thin films were deposited by plasma-enhanced atomic layer deposition (ALD) method using Ge [(CH3)2 N]4, Sb [(CH3)2 N]3, Te(C4H9)2 as precursors and plasma-activated H2 gas as reducing agent of the metallorganic precursors. Compared with GST-based device, GeSb8Te-based device exhibits a faster switching speed and reduced reset voltage, which is attributed to the growth-dominated crystallization mechanism of the Sb-rich GeSb8Te films. These results show that ALD is an attractive method for preparation of phase-change materials.

  18. Phase-change properties of GeSbTe thin films deposited by plasma-enchanced atomic layer depositon.

    PubMed

    Song, Sannian; Yao, Dongning; Song, Zhitang; Gao, Lina; Zhang, Zhonghua; Li, Le; Shen, Lanlan; Wu, Liangcai; Liu, Bo; Cheng, Yan; Feng, Songlin

    2015-01-01

    Phase-change access memory (PCM) appears to be the strongest candidate for next-generation high-density nonvolatile memory. The fabrication of ultrahigh-density PCM depends heavily on the thin-film growth technique for the phase-changing chalcogenide material. In this study, Ge2Sb2Te5 (GST) and GeSb8Te thin films were deposited by plasma-enhanced atomic layer deposition (ALD) method using Ge [(CH3)2 N]4, Sb [(CH3)2 N]3, Te(C4H9)2 as precursors and plasma-activated H2 gas as reducing agent of the metallorganic precursors. Compared with GST-based device, GeSb8Te-based device exhibits a faster switching speed and reduced reset voltage, which is attributed to the growth-dominated crystallization mechanism of the Sb-rich GeSb8Te films. These results show that ALD is an attractive method for preparation of phase-change materials. PMID:25852385

  19. Characterization of Y-Ba-Cu-O thin films and yttria-stabilized zirconia intermediate layers on metal alloys grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Reade, R. P.; Mao, X. L.; Russo, R. E.

    1991-08-01

    The use of an intermediate layer is necessary for the growth of YBaCuO thin films on polycrystalline metallic alloys for tape conductor applications. A pulsed laser deposition process to grow controlled-orientation yttria-stabilized zirconia (YSZ) films as intermediate layers on Haynes Alloy No. 230 was developed and characterized. YBaCuO films deposited on these YSZ-coated substrates are primarily c-axis oriented and superconducting as deposited. The best YBaCuO films grow on (001)-oriented YSZ intermediate layers and have Tc (R = 0) = 86.0 K and Jc about 3000 A/sq cm at 77 K.

  20. Preferentially oriented BaTiO3 thin films deposited on silicon with thin intermediate buffer layers

    PubMed Central

    2013-01-01

    Barium titanate (BaTiO3) thin films are prepared by conventional 2-methoxy ethanol-based chemical solution deposition. We report highly c-axis-oriented BaTiO3 thin films grown on silicon substrates, coated with a lanthanum oxynitrate buffer layer of 8.9 nm. The influence of the intermediate buffer layer on the crystallization of BaTiO3 film is investigated. The annealing temperature and buffer layer sintering conditions are optimized to obtain good crystal growth. X-ray diffraction measurements show the growth of highly oriented BaTiO3 thin films having a single perovskite phase with tetragonal geometry. The scanning electron microscopy and atomic force microscopy studies indicate the presence of smooth, crack-free, uniform layers, with densely packed crystal grains on the silicon surface. A BaTiO3 film of 150-nm thickness, deposited on a buffer layer of 7.2 nm, shows a dielectric constant of 270, remnant polarization (2Pr) of 5 μC/cm2, and coercive field (Ec) of 60 kV/cm. PMID:23391429

  1. Impact of growth and annealing conditions on the parameters of Ge/Si(001) relaxed layers grown by molecular beam epitaxy

    SciTech Connect

    Yurasov, D. V.; Bobrov, A. I.; Daniltsev, V. M.; Novikov, A. V.; Pavlov, D. A.; Skorokhodov, E. V.; Shaleev, M. V.; Yunin, P. A.

    2015-11-15

    Influence of the Ge layer thickness and annealing conditions on the parameters of relaxed Ge/Si(001) layers grown by molecular beam epitaxy via two-stage growth is investigated. The dependences of the threading dislocation density and surface roughness on the Ge layer thickness, annealing temperature and time, and the presence of a hydrogen atmosphere are obtained. As a result of optimization of the growth and annealing conditions, relaxed Ge/Si(001) layers which are thinner than 1 μm with a low threading dislocation density on the order of 10{sup 7} cm{sup –2} and a root mean square roughness of less than 1 nm are obtained.

  2. GeP and (Ge{sub 1−x}Sn{sub x})(P{sub 1−y}Ge{sub y}) (x≈0.12, y≈0.05): Synthesis, structure, and properties of two-dimensional layered tetrel phosphides

    SciTech Connect

    Lee, Kathleen; Synnestvedt, Sarah; Bellard, Maverick; Kovnir, Kirill

    2015-04-15

    GeP and Sn-doped GeP were synthesized from elements in bismuth and tin flux, respectively. The layered crystal structures of these compounds were characterized by single crystal X-ray diffraction. Both phosphides crystallize in a GaTe structure type in the monoclinic space group C2/m (No. 12) with GeP: a=15.1948(7) Å, b=3.6337(2) Å, c=9.1941(4) Å, β=101.239(2)°; Ge{sub 0.93(3)}P{sub 0.95(1)}Sn{sub 0.12(3)}: a=15.284(9) Å, b=3.622(2) Å, c=9.207(5) Å, β=101.79(1)°. The crystal structure of GeP consists of 2-dimensional GeP layers held together by weak electron lone pair interactions between the phosphorus atoms that confine the layer. Each layer is built of Ge–Ge dumbbells surrounded by a distorted antiprism of phosphorus atoms. Sn-doped GeP has a similar structural motif, but with a significant degree of disorder emphasized by the splitting of all atomic positions. Resistivity measurements together with quantum-chemical calculations reveal semiconducting behavior for the investigated phosphides. - Graphical abstract: Layered phosphides GeP and Sn-doped GeP were synthesized from elements in bismuth and tin flux, respectively. The crystal structure of GeP consists of 2-dimensional GeP layers held together by weak electron lone pair interactions between the phosphorus atoms that confine the layer. Sn-doped GeP has a similar structural motif with a significant degree of disorder emphasized by the splitting of all atomic positions. Resistivity measurements together with quantum-chemical calculations reveal semiconducting behavior for the investigated phosphides. - Highlights: • GeP crystallizes in a layered crystal structure. • Doping of Sn into GeP causes large structural distortions. • GeP is narrow bandgap semiconductor. • Sn-doped GeP exhibits an order of magnitude higher resistivity due to disorder.

  3. Thermal properties of a pyroelectric-ceramic infrared detector with metallic intermediate layer

    NASA Astrophysics Data System (ADS)

    Lee, Moon H.; Bae, Seong H.; Bhalla, Amar S.

    1998-06-01

    Infrared thermal detectors were prepared with pyroelectric PSN-PT-PZ (1/47/52) ceramics, where a signal electrode had a structure Au/metallic buffer/Pb(Zr,Ti)O3 ceramic. The effect of a metallic buffer layer on the voltage responsivity was investigated with a response to a step signal, made by a dynamic pyroelectric measurement. A pyroelectric ceramic wafer was prepared by a mixed-oxide technique. The Au layer (thickness 50 nm) and the metallic buffers (thickness 0 to 20 nm) of Cr, NiCr (80:20), and Ti were prepared by dc magnetron sputtering. In order to improve the light absorptivity, Au black was coated on the Au signal electrode by thermal evaporation. A detector without a buffer layer showed a noisy and fluctuating output signal. Among the three kinds of buffer materials, NiCr (80:20) and Ti adhered well with ceramics and showed good electrical and thermal contact, whereas Cr resulted in bad contacts. Considering the output voltage and thermal properties, the optimum thickness of the buffer layer was about 15 to 20 nm, and sensors with a Ti buffer 15 to 20 nm in thickness showed good detectivity. Thus, the stability and reliability of the infrared thermal sensors could be improved by using an appropriate buffer layer.

  4. Ferromagnetic Order, Strong Magnetocrystalline Anisotropy, and Magnetocaloric Effect in the Layered Telluride Fe(3-δ)GeTe2.

    PubMed

    Verchenko, Valeriy Yu; Tsirlin, Alexander A; Sobolev, Alexei V; Presniakov, Igor A; Shevelkov, Andrei V

    2015-09-01

    The ternary transition-metal compound Fe(3-δ)GeTe2 is formed for 0 < δ < 0.3. X-ray diffraction and Mössbauer spectroscopy reveal its layered crystal structure with occasional Fe vacancies in the Fe2 site, whereas no Fe atoms occupy the interlayer space, so that only van der Waals interactions exist between adjacent layers. We explore magnetic behavior and ensuing functional properties of Fe(2.9)GeTe2 via neutron diffraction, thermodynamic and transport measurements, Mössbauer spectroscopy, and electronic structure calculations. Below T(C) = 225 K, Fe(2.9)GeTe2 is ferromagnetically ordered with the magnetic moments of 1.95(5) and 1.56(4) μ(B) at T = 1.5 K, both directed along c, which is the magnetic easy axis. Electronic structure calculations confirm this magnetic structure and reveal a remarkably high easy-axis anisotropy of 4.2 meV/f.u. Mössbauer spectra reveal the magnetic ordering too, although a drastic influence of Fe vacancies on quadrupolar splittings and local magnetic fields has been observed. A moderate magnetocaloric effect with the magnetic entropy change upon the ferromagnetic ordering transition, -ΔS ∼ 1.1 J·kg(-1)·K(-1) at 5 T, is found. PMID:26267350

  5. Sn migration control at high temperature due to high deposition speed for forming high-quality GeSn layer

    NASA Astrophysics Data System (ADS)

    Taoka, Noriyuki; Capellini, Giovanni; von den Driesch, Nils; Buca, Dan; Zaumseil, Peter; Schubert, Markus Andreas; Klesse, Wolfgang Matthias; Montanari, Michele; Schroeder, Thomas

    2016-03-01

    A key factor for controlling Sn migration during GeSn deposition at a high temperature of 400 °C was investigated. Calculated results with a simple model for the Sn migration and experimental results clarified that low-deposition-speed (vd) deposition with vd’s of 0.68 and 2.8 nm/min induces significant Sn precipitation, whereas high-deposition-speed (vd = 13 nm/min) deposition leads to high crystallinity and good photoluminescence spectrum of the GeSn layer. These results indicate that vd is a key parameter, and that control of Sn migration at a high temperature is possible. These results are of great relevance for the application of high-quality Sn-based alloys in future optoelectronics devices.

  6. Development of Thermal Barrier Coating System with Superior Thermal Cyclic Properties with an Intermediate Layer Containing MoSi2

    NASA Astrophysics Data System (ADS)

    Sonoya, Keiji; Tobe, Shogo

    The authors have developed a method of improving the thermal cyclic resistance of the thermal barrier coating system that is deposited on gas turbine components. A conventional thermal barrier coating consists of a duplex system: a top coating and a bond coating. The developed system has a protective intermediate layer of MoSi2 which prevents oxidation of the bond coating. The conventional duplex plasma -sprayed coating was delaminated after 20 thermal cycles. On the other hand, the developed triple-layered coating system was not delaminated after 60 cycles. The reason for the enhanced resistance to thermal cycles of the developed triple-layered coating system is that the MoSi2 layer between the top coating and the bond coating has a self-repairing property. MoSi2 oxidizes to form SiO2, which seals the cracks and pores formed between the top coating and the bond coating. Thus, the formation of a thermally grown oxide(TGO), which causes the delamination of the coating, is prevented and the thermal cyclic resistance is improved.

  7. Effect of in situ Sb doping on crystalline and electrical characteristics of n-type Ge1- x Sn x epitaxial layer

    NASA Astrophysics Data System (ADS)

    Jeon, Jihee; Asano, Takanori; Shimura, Yosuke; Takeuchi, Wakana; Kurosawa, Masashi; Sakashita, Mitsuo; Nakatsuka, Osamu; Zaima, Shigeaki

    2016-04-01

    We examined the molecular beam epitaxy of Ge1- x Sn x with in situ Sb doping on Ge substrates. The effects of Sb doping on the crystalline and electrical characteristics of Ge1- x Sn x epitaxial layer were investigated in detail. We found that Sb doping with a concentration of 1020 cm-3 remarkably improves the crystallinity, and surface uniformity of the Ge1- x Sn x epitaxial layer by changing the growth mode by the surfactant effect of Sb atoms. Low-temperature Ge1- x Sn x growth with in situ Sb doping realizes a very high electron concentration of 1020 cm-3, which is above the thermal equilibrium solid solubility, as a result of suppressing Sb segregation and precipitation.

  8. Interface magnetism of Co{sub 2}FeGe Heusler alloy layers and magnetoresistance of Co{sub 2}FeGe/MgO/Fe magnetic tunnel junctions

    SciTech Connect

    Tanaka, M. A. Maezaki, D.; Ishii, T.; Okubo, A.; Mibu, K.; Hiramatsu, R.; Ono, T.

    2014-10-28

    The interface magnetism between Co{sub 2}FeGe Heusler alloy layers and MgO layers was investigated using {sup 57}Fe Mössbauer spectroscopy. Interface-sensitive samples, where the {sup 57}Fe isotope was used only for the interfacial atomic layer of the Co{sub 2}FeGe layer on the MgO layer, were prepared using atomically controlled alternate deposition. The {sup 57}Fe Mössbauer spectra of the interface-sensitive samples at room temperature were found similar to those of the bulk-sensitive Co{sub 2}FeGe films in which the {sup 57}Fe isotope was distributed throughout the films. On the other hand, the tunnel magnetoresistance effect of magnetic tunnel junctions with Co{sub 2}FeGe layers as the ferromagnetic electrodes showed strong reduction at room temperature. These results indicate that the strong temperature dependence of the tunneling magnetoresistance of magnetic tunnel junctions using Heusler alloy electrodes cannot be attributed simply to the reduction of the magnetization at the interfaces between the Heusler alloy and insulator layers.

  9. New class of Si-based superlattices - Alternating layers of crystalline Si and porous amorphous Si(1-x)Ge(x) alloys

    NASA Technical Reports Server (NTRS)

    Fathauer, R. W.; George, T.; Jones, E. W.; Pike, W. T.; Ksendzov, A.; Vasquez, R. P.

    1992-01-01

    Superlattices consisting of alternating layers of crystalline Si and porous amorphous Si(1-x)Ge(x) have been fabricated. This is accomplished by first growing a Si/Si(0.7)Ge(0.3) superlattice by molecular beam epitaxy, followed by Ar-ion milling to form mesa structures, and finally by immersion in HF:HNO3:H2O. This solution creates a porous structure similar to that created by anodic etching, and a high selectivity is observed for the conversion of the alloy layers relative to the Si layers. The degree of selectivity is found to depend on alloy-layer thickness and strain. Superlattices have been fabricated from 1-micron wide mesas with Si(0.7)Ge(0.3) layers fully converted to 5-nm thick porous amorphous material.

  10. Intermediate valence in single crystals of (Lu{sub 1−x}Y b{sub x}){sub 3}Rh{sub 4}Ge{sub 13} (0 ≤ x ≤ 1)

    SciTech Connect

    Rai, Binod K.; Morosan, E.

    2015-04-01

    Single crystals of (Lu{sub 1−x}Y b{sub x}){sub 3}Rh{sub 4}Ge{sub 13} were characterized by magnetization, specific heat, and electrical resistivity measurements. Doping Yb into the non-magnetic Lu{sub 3}Rh{sub 4}Ge{sub 13} compound tunes this cubic system’s properties from a superconductor with disordered metal normal state (x < 0.05) to a Kondo for 0.05 ≤ x ≤0.2 and intermediate valence at the highest Yb concentrations. The evidence for intermediate Yb valence comes from a broad maximum in the magnetic susceptibility and X-ray photoelectron spectroscopy. Furthermore, the resistivity displays a local maximum at finite temperatures at intermediate compositions x, followed by apparent metallic behavior closest to the Yb end compound in the series.

  11. Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode

    NASA Astrophysics Data System (ADS)

    Mortemard de Boisse, Benoit; Liu, Guandong; Ma, Jiangtao; Nishimura, Shin-Ichi; Chung, Sai-Cheong; Kiuchi, Hisao; Harada, Yoshihisa; Kikkawa, Jun; Kobayashi, Yoshio; Okubo, Masashi; Yamada, Atsuo

    2016-04-01

    Sodium-ion batteries are attractive energy storage media owing to the abundance of sodium, but the low capacities of available cathode materials make them impractical. Sodium-excess metal oxides Na2MO3 (M: transition metal) are appealing cathode materials that may realize large capacities through additional oxygen redox reaction. However, the general strategies for enhancing the capacity of Na2MO3 are poorly established. Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3. Ordered Na2RuO3 with honeycomb-ordered [Na1/3Ru2/3]O2 slabs delivers a capacity of 180 mAh g-1 (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g-1 (1.0-electron reaction). We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes.

  12. Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode

    PubMed Central

    Mortemard de Boisse, Benoit; Liu, Guandong; Ma, Jiangtao; Nishimura, Shin-ichi; Chung, Sai-Cheong; Kiuchi, Hisao; Harada, Yoshihisa; Kikkawa, Jun; Kobayashi, Yoshio; Okubo, Masashi; Yamada, Atsuo

    2016-01-01

    Sodium-ion batteries are attractive energy storage media owing to the abundance of sodium, but the low capacities of available cathode materials make them impractical. Sodium-excess metal oxides Na2MO3 (M: transition metal) are appealing cathode materials that may realize large capacities through additional oxygen redox reaction. However, the general strategies for enhancing the capacity of Na2MO3 are poorly established. Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3. Ordered Na2RuO3 with honeycomb-ordered [Na1/3Ru2/3]O2 slabs delivers a capacity of 180 mAh g−1 (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g−1 (1.0-electron reaction). We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes. PMID:27088834

  13. Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode.

    PubMed

    Mortemard de Boisse, Benoit; Liu, Guandong; Ma, Jiangtao; Nishimura, Shin-Ichi; Chung, Sai-Cheong; Kiuchi, Hisao; Harada, Yoshihisa; Kikkawa, Jun; Kobayashi, Yoshio; Okubo, Masashi; Yamada, Atsuo

    2016-01-01

    Sodium-ion batteries are attractive energy storage media owing to the abundance of sodium, but the low capacities of available cathode materials make them impractical. Sodium-excess metal oxides Na2MO3 (M: transition metal) are appealing cathode materials that may realize large capacities through additional oxygen redox reaction. However, the general strategies for enhancing the capacity of Na2MO3 are poorly established. Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3. Ordered Na2RuO3 with honeycomb-ordered [Na1/3Ru2/3]O2 slabs delivers a capacity of 180 mAh g(-1) (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g(-1) (1.0-electron reaction). We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes. PMID:27088834

  14. Ge-related faceting and segregation during the growth of metastable (GaAs){sub 1{minus}x}(Ge{sub 2}){sub x} alloy layers by metal{endash}organic vapor-phase epitaxy

    SciTech Connect

    Norman, A.G.; Olson, J.M.; Geisz, J.F.; Moutinho, H.R.; Mason, A.; Al-Jassim, M.M.; Vernon, S.M.

    1999-03-01

    (GaAs){sub 1{minus}x}(Ge{sub 2}){sub x} alloy layers, 0{lt}x{lt}0.22, have been grown by metal{endash}organic vapor-phase epitaxy on vicinal (001) GaAs substrates. Transmission electron microscopy revealed pronounced phase separation in these layers, resulting in regions of GaAs-rich zinc-blende and Ge-rich diamond cubic material that appears to lead to substantial band-gap narrowing. For x=0.1 layers, the phase-separated microstructure consisted of intersecting sheets of Ge-rich material on {l_brace}115{r_brace}B planes surrounding cells of GaAs-rich material, with little evidence of antiphase boundaries. Atomic force microscopy revealed {l_brace}115{r_brace}B surface faceting associated with the phase separation. {copyright} {ital 1999 American Institute of Physics.}

  15. Antiferromagnetic Kondo lattice in the layered compounds Re2NiGa9Ge2 (Re =Ce, Pr, Sm)

    NASA Astrophysics Data System (ADS)

    Zhu, Yanglin; Liu, Jinyu; Hu, Jin; Adams, Daniel; Spinu, Leonard; Mao, Zhiqiang

    Intermetallic compounds containing rare-earth/actinide elements with 4f/5f electrons have formed a special family of strongly correlated materials, i.e. heavy fermion systems. We have recently found a new layered rare earth intermetallic system showing moderate heavy fermion behavior: Re2NiGa9Ge2 (Re =Ce, Sm, Pr). The Re =Ce and Sm members were previously synthesized, while their electronic properties have not been reported. We have recently grown single crystals of Re2NiGa9Ge2 (Re =Ce, Sm, Pr) and characterized their electronic and magnetic properties. We find all these materials are antiferromagnetic, with TN = 2.5 K, 5 K, 3.4 K respectively for Re =Ce, Pr and Sm. Moreover, they also exhibit large values of electronic specific coefficient: γ ~ 101 mJ mol-Ce-1 K-2 for Re =Ce, 368 mJ mol-Pr-1 K-2 for Re =Pr, and 196.4 mJ mol-Sm-1 K-2 for Re =Sm, indicating enhanced Kondo effect and the presence of AFM Kondo lattice. Our findings suggest that Re2NiGa9Ge2 (Re =Ce, Pr, Sm) could be interesting candidate materials for exploring novel exotic properties of correlated electrons through external parameter tuning such as chemical substitution and pressure.

  16. Biaxially oriented CdTe films on glass substrate through nanostructured Ge/CaF2 buffer layers

    NASA Astrophysics Data System (ADS)

    Lord, R. J.; Su, P.-Y.; Bhat, I.; Zhang, S. B.; Lu, T.-M.; Wang, G.-C.

    2015-09-01

    Heteroepitaxial CdTe films were grown by metal organic chemical vapor deposition on glass substrates through nanostructured Ge/CaF2 buffer layers which were biaxially oriented. It allows us to explore the structural properties of multilayer biaxial semiconductor films which possess small angle grain boundaries and to test the principle of a solar cell made of such low-cost, low-growth-temperature semiconductor films. Through the x-ray diffraction and x-ray pole figure analysis, the heteroepitaxial relationships of the mutilayered films are determined as [111] in the out-of-plane direction and <1\\bar{1}0>CdTe//<1\\bar{1}0>Ge//{< \\bar{1}10> }{{{CaF}}2} in the in-plane direction. The I-V curves measured from an ITO/CdS/CdTe/Ge/CaF2/glass solar cell test structure shows a power conversion efficiency of ˜η = 1.26%, illustrating the initial success of such an approach. The observed non-ideal efficiency is believed to be due to a low shunt resistance and high series resistance as well as some residual large-angle grain boundary effects, leaving room for significant further improvement.

  17. Structural and electrical studies of ultrathin layers with Si{sub 0.7}Ge{sub 0.3} nanocrystals confined in a SiGe/SiO{sub 2} superlattice

    SciTech Connect

    Vieira, E. M. F.; Martin-Sanchez, J.; Rolo, A. G.; Levichev, S.; Gomes, M. J. M.; Parisini, A.; Buljan, M.; Capan, I.; Alves, E.; Barradas, N. P.; Conde, O.; Bernstorff, S.; Chahboun, A.

    2012-05-15

    In this work, SiGe/SiO{sub 2} multi-layer (ML) films with layer thickness in the range of a few nanometers were successfully fabricated by conventional RF-magnetron sputtering at 350 deg. C. The influence of the annealing treatment on SiGe nanocrystals (NCs) formation and crystalline properties were investigated by Raman spectroscopy and grazing incidence x-ray diffraction. At the annealing temperature of 800 deg. C, where well defined SiGe NCs were observed, a thorough structural investigation of the whole ML structure has been undertaken by Rutherford backscattering spectroscopy, grazing incidence small angle x-ray scattering, high resolution transmission electron microscopy, and annular dark field scanning transmission electron microscopy. Our results show that the onset of local modifications to the ML composition takes place at this temperature for annealing times of the order of a few tens of minutes with the formation of defective regions in the upper portion of the ML structure. Only the very first layers over the Si substrate appear immune to this problem. This finding has been exploited for the fabrication of a defect free metal-oxide-semiconductor structure with a well-defined single layer of SiGe NCs. A memory effect attributed to the presence of the SiGe NCs has been demonstrated by high frequency capacitance-voltage measurements.

  18. Reflection high-energy electron diffraction evaluation of thermal deoxidation of chemically cleaned Si, SiGe, and Ge layers for solid-source molecular beam epitaxy

    SciTech Connect

    Ali, Dyan; Richardson, Christopher J. K.

    2012-11-15

    The authors present a study on the thermal evolution of the reflection high-energy electron diffraction pattern of chemically cleaned (001)-oriented Si, Ge, and SiGe surfaces, associating observed changes in the reconstructions with the desorption of known residual contaminants for Si and Ge surfaces. The implications of residual oxides prior to epitaxy on stacking fault densities in the grown films are presented. Further evidence for the two-phase nature of oxides on SiGe surfaces is provided, demonstrating that it is necessary to heat a SiGe surface up to the thermal deoxidation temperature of a Si surface to obtain stacking fault-free growth.

  19. Three-Dimensional Multiscale Modeling of Stable Intermediate State Formation Mechanism in a Single Active Layer- Phase Change Memory Cell

    NASA Astrophysics Data System (ADS)

    Dincer, Onur; Cinar, Ibrahim; Karakas, Vedat; Aslan, Ozgur Burak; Gokce, Aisha; Stipe, Barry; Katine, Jordan A.; Aktas, Gulen; Ozatay, Ozhan

    2014-03-01

    Phase change memory (PCM) appears as a potential memory technology with its superior scalability which could be enhanced by a boost in storage density via multiple-bit per cell functionality. Given the large contrast between set and reset states of a PCM cell it is yet unclear whether it is possible to create intermediate logic states reproducibly and controllably in a device with a single active phase change layer. Here we report the results of a 3D finite element model that pinpoints the direct effect of current distribution and the indirect effect of device top contact fabrication induced defects through modification of phase change kinetics (crystallite nucleation and growth rates) on stabilization of intermediate states. A comprehensive picture of the electrical, thermal and phase change dynamics is obtained using a multiphysics approach. Our study shows that homogeneous and heterogeneous phase transition can be induced in the active region such that nonuniform temperature distribution and modification of switching dynamics with various contact shapes and sizes play a major role in the stabilization of a mixed phase state. This work has been supported by the European Commission FP7 Marie Curie IRG grant: PCM-256281 and TUBITAK grant: 113F385.

  20. Experimental Study of Acoustic Properties of (0-3) Composite Materials for Intermediate Layer or Backing of Ultrasonic Transducers

    NASA Astrophysics Data System (ADS)

    Sugawara, Keisuke; Nishihira, Morimasa; Imano, Kazuhiko

    2005-06-01

    The acoustic properties of composite materials used for an intermediate layer or backing of an ultrasonic transducer are studied experimentally. (0-3) composite materials are formed from a mixture of epoxy resin and tungsten powder for various weight ratios and their acoustic properties are measured. The experimental results are compared with the results predicted by different models, which are based on the elastic-wave scattering theory, to verify if the measured acoustic properties agree with theoretical estimations. For the ultrasonic velocities, the estimations of the Devaney model were closest to the experimental results. The weight fractions of tungsten powder for the composite materials, which have objective acoustic properties, can easily be estimated by theoretical calculations using the Devaney model.

  1. Controlled drive-in and precipitation of hydrogen during plasma hydrogenation of silicon using a thin compressively strained SiGe layer

    SciTech Connect

    Okba, F.; Cherkashin, N.; Claverie, A.; Rossi, F.; Merabet, A.

    2010-07-19

    We have quantitatively studied by transmission electron microscopy the growth kinetics of platelets formed during the continuous hydrogenation of a Si substrate/SiGe/Si heterostructure. We have evidenced and explained the massive transfer of hydrogen from a population of platelets initially generated in the upper Si layer by plasma hydrogenation towards a population of larger platelets located in the SiGe layer. We demonstrate that this type of process can be used not only to precisely localize the micro-cracks, then the fracture line at a given depth but also to 'clean' the top layer from pre-existing defects.

  2. Atomic layer deposition of Al2O3 on germanium-tin (GeSn) and impact of wet chemical surface pre-treatment

    NASA Astrophysics Data System (ADS)

    Gupta, Suyog; Chen, Robert; Harris, James S.; Saraswat, Krishna C.

    2013-12-01

    GeSn is quickly emerging as a potential candidate for high performance Si-compatible transistor technology. Fabrication of high-ĸ gate stacks on GeSn with good interface properties is essential for realizing high performance field effect transistors based on this material system. We demonstrate an effective surface passivation scheme for n-Ge0.97Sn0.03 alloy using atomic layer deposition (ALD) of Al2O3. The effect of pre-ALD wet chemical surface treatment is analyzed and shown to be critical in obtaining a good quality interface between GeSn and Al2O3. Using proper surface pre-treatment, mid-gap trap density for the Al2O3/GeSn interface of the order of 1012 cm-2 has been achieved.

  3. Electromodulation spectroscopy of direct optical transitions in Ge1-xSnx layers under hydrostatic pressure and built-in strain

    NASA Astrophysics Data System (ADS)

    Dybała, F.; Żelazna, K.; Maczko, H.; Gladysiewicz, M.; Misiewicz, J.; Kudrawiec, R.; Lin, H.; Chen, R.; Shang, C.; Huo, Y.; Kamins, T. I.; Harris, J. S.

    2016-06-01

    Unstrained Ge1-xSnx layers of various Sn concentration (1.5%, 3%, 6% Sn) and Ge0.97Sn0.03 layers with built-in compressive (ɛ = -0.5%) and tensile (ɛ = 0.3%) strain are grown by molecular beam epitaxy and studied by electromodulation spectroscopy (i.e., contactless electroreflectance and photoreflectance (PR)). In order to obtain unstrained GeSn layers and layers with different built-in in-plane strains, virtual InGaAs substrates of different compositions are grown prior to the deposition of GeSn layers. For unstrained Ge1-xSnx layers, the pressure coefficient for the direct band gap transition is determined from PR measurements at various hydrostatic pressures to be 12.2 ± 0.2 meV/kbar, which is very close to the pressure coefficient for the direct band gap transition in Ge (12.9 meV/kbar). This suggests that the hydrostatic deformation potentials typical of Ge can be applied to describe the pressure-induced changes in the electronic band structure of Ge1-xSnx alloys with low Sn concentrations. The same conclusion is derived for the uniaxial deformation potential, which describes the splitting between heavy-hole (HH) and light-hole (LH) bands as well as the strain-related shift of the spin-orbit (SO) split-off band. It is observed that the HH, LH, and SO related transitions shift due to compressive and tensile strain according to the Bir-Pikus theory. The dispersions of HH, LH, and SO bands are calculated for compressive and tensile strained Ge0.97Sn0.03 with the 8-band kp Hamiltonian including strain effects, and the mixing of HH and LH bands is discussed. In addition, the dispersion of the electronic band structure is calculated for unstrained Ge1-xSnx layers (3% and 6% Sn) at high hydrostatic pressure with the 8-band kp Hamiltonian, and the pressure-induced changes in the electronic band structure are discussed.

  4. Effect of RuCoCr-oxide intermediate layers on the growth, microstructure, and recording performance of CoCrPt-SiO2 perpendicular recording media

    NASA Astrophysics Data System (ADS)

    Srinivasan, Kumar; Piramanayagam, S. N.; Kay, Yew Seng

    2010-02-01

    The crystallographic growth, magnetic properties, microstructure, and recording performance of CoCrPt-SiO2 perpendicular magnetic recording media on RuCoCr type of intermediate layers were systematically investigated. Excellent Co (00•2) crystallographic texture with dispersion Δθ50 as low as 3.2° could be obtained on the RuCoCr as the grain isolation layer, whereas the Δθ50 on the pure Ru grain isolation layer was 3.9°. Upon injecting oxygen into the RuCoCr layer via reactive sputtering and at high sputter pressures, grain center-to-center distance as small as 5.9 nm with a distribution of about 13% was achieved. The Δθ50 deteriorated on the RuCoCr-oxide type of intermediate layers, however, it remained comparable to that on the pure Ru layers. Signal-to-noise ratio also increased on the RuCoCr-oxide grain isolation layers due to the decreased grain sizes. The effectiveness of the RuCoCr-oxide type of intermediate layers toward grain size reduction and in improving the performance of perpendicular magnetic recording media is discussed.

  5. Characterization of Y-Ba-Cu-O thin films and yttria-stabilized zirconia intermediate layers on metal alloys grown by pulsed laser deposition

    SciTech Connect

    Reade, R.P.; Mao, X.L.; Russo, R.E. )

    1991-08-05

    The use of an intermediate layer is necessary for the growth of YBaCuO thin films on polycrystalline metallic alloys for tape conductor applications. A pulsed laser deposition process to grow controlled-orientation yttria-stabilized zirconia (YSZ) films as intermediate layers on Haynes Alloy No. 230 was developed and characterized. YBaCuO films deposited on these YSZ-coated substrates are primarily {ital c}-axis oriented and superconducting as deposited. The best YBaCuO films grow on (001) oriented YSZ intermediate layers and have {ital T}{sub {ital c}} ({ital R}=0) = 86.0 K and {ital J}{sub {ital c}} {similar to} 3{times}10{sup 3} A/cm{sup 2} at 77 K.

  6. Enhancement of recombination process using silver and graphene quantum dot embedded intermediate layer for efficient organic tandem cells.

    PubMed

    Ho, Nhu Thuy; Tien, Huynh Ngoc; Jang, Se-Joeng; Senthilkumar, Velusamy; Park, Yun Chang; Cho, Shinuk; Kim, Yong Soo

    2016-01-01

    High performance of organic tandem solar cell is largely dependent on transparent and conductive intermediate layer (IML). The current work reports the design and fabrication of an IML using a simple solution process. The efficiency of a homo-tandem device with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester as an active layer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly(ethylenimine) as an IML was initially found to be 3.40%. Further enhancement of the cell efficiency was achieved using silver nanoparticles (Ag-NPs) of different sizes and graphene quantum dot embedded IML. A maximum efficiency of 4.03% was achieved using 7 nm Ag-NPs that contribute to a better recombination process. Also, the performance of the tandem cell was solely based on the electrical improvements indicated by the current - voltage measurements, external quantum efficiency and impedance analysis. The use of Ag-NPs in the IML has been shown to lengthen the life time of electron-hole pairs in the device. This study thus paves way to develop such efficient IMLs for more efficient tandem solar cells. PMID:27453530

  7. Enhancement of recombination process using silver and graphene quantum dot embedded intermediate layer for efficient organic tandem cells

    PubMed Central

    Ho, Nhu Thuy; Tien, Huynh Ngoc; Jang, Se-Joeng; Senthilkumar, Velusamy; Park, Yun Chang; Cho, Shinuk; Kim, Yong Soo

    2016-01-01

    High performance of organic tandem solar cell is largely dependent on transparent and conductive intermediate layer (IML). The current work reports the design and fabrication of an IML using a simple solution process. The efficiency of a homo-tandem device with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester as an active layer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly(ethylenimine) as an IML was initially found to be 3.40%. Further enhancement of the cell efficiency was achieved using silver nanoparticles (Ag-NPs) of different sizes and graphene quantum dot embedded IML. A maximum efficiency of 4.03% was achieved using 7 nm Ag-NPs that contribute to a better recombination process. Also, the performance of the tandem cell was solely based on the electrical improvements indicated by the current - voltage measurements, external quantum efficiency and impedance analysis. The use of Ag-NPs in the IML has been shown to lengthen the life time of electron-hole pairs in the device. This study thus paves way to develop such efficient IMLs for more efficient tandem solar cells. PMID:27453530

  8. Enhancement of recombination process using silver and graphene quantum dot embedded intermediate layer for efficient organic tandem cells

    NASA Astrophysics Data System (ADS)

    Ho, Nhu Thuy; Tien, Huynh Ngoc; Jang, Se-Joeng; Senthilkumar, Velusamy; Park, Yun Chang; Cho, Shinuk; Kim, Yong Soo

    2016-07-01

    High performance of organic tandem solar cell is largely dependent on transparent and conductive intermediate layer (IML). The current work reports the design and fabrication of an IML using a simple solution process. The efficiency of a homo-tandem device with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester as an active layer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly(ethylenimine) as an IML was initially found to be 3.40%. Further enhancement of the cell efficiency was achieved using silver nanoparticles (Ag-NPs) of different sizes and graphene quantum dot embedded IML. A maximum efficiency of 4.03% was achieved using 7 nm Ag-NPs that contribute to a better recombination process. Also, the performance of the tandem cell was solely based on the electrical improvements indicated by the current - voltage measurements, external quantum efficiency and impedance analysis. The use of Ag-NPs in the IML has been shown to lengthen the life time of electron-hole pairs in the device. This study thus paves way to develop such efficient IMLs for more efficient tandem solar cells.

  9. Coarse, Intermediate and High Resolution Numerical Simulations of the Transition of a Tropical Wave Critical Layer to a Tropical Storm

    NASA Technical Reports Server (NTRS)

    Montgomery, M. T.; Dunkerton, T. J.; Wang, Z.

    2010-01-01

    Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from within the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the Kurihara and Tuleya problem examining the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km), intermediate (9 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of rotationally dominant region with minimal strain/shear deformation near the center of the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together.

  10. Atomic structure and composition of the 2×N reconstruction of the Ge wetting layer on Si(001) investigated by surface x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Zhou, T.; Renaud, G.; Revenant, C.; Issartel, J.; Schülli, T. U.; Felici, R.; Malachias, A.

    2011-05-01

    The 2 × N reconstruction of the Ge/Si(001) wetting layer has been investigated by surface x-ray diffraction. At a substrate temperature of 670ˆC, the average N periodicity decreases from N = 11.5 to 8 with an increasing Ge coverage from one to three monolayers (ML). The top layer consists of asymmetric dimers with a bond length in the range of 2.50-2.60 Å and a buckling angle in the range of 9.4°-15.6°, depending on the Ge coverage. The obtained dimer bond lengths are similar to those calculated for alternating asymmetric mixed dimers. Intermixing of Ge with Si is found down to the sixth (eighth) layer for 2 (from 3 to 5) ML coverage. For 2 ML coverage, a quantitative surface x-ray diffraction data set has been measured. It is analyzed using a model describing the atomic structure and Ge occupation probability with a limited set of parameters to bypass the intrinsic lack of appreciable reflections of the 2 × N (N = 9) reconstruction. The Ge occupation probability varies periodically along the N direction, having its minimum value below the dimer vacancy lines. In addition, a more direct calculation of the Lorentz and detector acceptance corrections is given for rocking and radial scans.

  11. Enhanced heteroepitaxial growth of CoCrPt -SiO2 perpendicular magnetic recording media on optimized Ru intermediate layers

    NASA Astrophysics Data System (ADS)

    Srinivasan, Kumar; Piramanayagam, S. N.

    2008-01-01

    The crystallographic growth, interfacial roughness, and magnetic properties of CoCrPt -SiO2 perpendicular magnetic recording media prepared on various types of Ru intermediate growth layers were systematically investigated based on high angle and omega offset x-ray diffraction scans, rocking curve scans, synchrotron radiation based grazing incidence reflectivity scans, and magneto-optical Kerr hysteresis loops. For samples that make use of one Ru growth layer, voltage bias applied on the Ru layer was seen to have two observable effects: (1) the dispersion in the Ru(00ṡ2) perpendicular texture increased, but that of the Co(00ṡ2) remained unchanged, leading to identical layered growth and (2) the in-plane a-lattice parameter of the Ru decreased leading to enhanced heteroepitaxy with the Co. There was no significant change in the Ru-Co interfacial roughness with changing the bias on the Ru layer. The bias effect can be used to optimize the design of the Ru intermediate layers. A scheme that makes use of two Ru growth layers consisting of a bottom Ru layer prepared under zero bias, which is inserted below a second Ru layer prepared under biased conditions, is shown to lead to significant benefits such as improved texture without affecting the magnetic properties. This is due to the different functional roles ascribed to each of the Ru growth layers.

  12. Enhanced heteroepitaxial growth of CoCrPt-SiO{sub 2} perpendicular magnetic recording media on optimized Ru intermediate layers

    SciTech Connect

    Srinivasan, Kumar; Piramanayagam, S. N.

    2008-01-15

    The crystallographic growth, interfacial roughness, and magnetic properties of CoCrPt-SiO{sub 2} perpendicular magnetic recording media prepared on various types of Ru intermediate growth layers were systematically investigated based on high angle and omega offset x-ray diffraction scans, rocking curve scans, synchrotron radiation based grazing incidence reflectivity scans, and magneto-optical Kerr hysteresis loops. For samples that make use of one Ru growth layer, voltage bias applied on the Ru layer was seen to have two observable effects: (1) the dispersion in the Ru(00{center_dot}2) perpendicular texture increased, but that of the Co(00{center_dot}2) remained unchanged, leading to identical layered growth and (2) the in-plane a-lattice parameter of the Ru decreased leading to enhanced heteroepitaxy with the Co. There was no significant change in the Ru-Co interfacial roughness with changing the bias on the Ru layer. The bias effect can be used to optimize the design of the Ru intermediate layers. A scheme that makes use of two Ru growth layers consisting of a bottom Ru layer prepared under zero bias, which is inserted below a second Ru layer prepared under biased conditions, is shown to lead to significant benefits such as improved texture without affecting the magnetic properties. This is due to the different functional roles ascribed to each of the Ru growth layers.

  13. Study of formation process of cold intermediate layer based on reanalysis of Black Sea hydrophysical fields for 1971-1993

    NASA Astrophysics Data System (ADS)

    Korotaev, G. K.; Knysh, V. V.; Kubryakov, A. I.

    2014-01-01

    A reanalysis of hydrophysical fields for 1971-1993 is used to study the formation mechanisms of the cold intermediate layer (CIL): the advective mechanism (associated with the advection of cold waters formed in the northwestern shelf (NWS)) and the convective mechanism (caused by wintertime convection inside cyclonic gyres in the central part of the sea). We consider the periods of alternating atmospheric conditions: the mild winter of 1980-1981, normal winter of 1987-1988, and cold winter of 1992-1993. Interannual features of replenishment and renewal of "old" CIL waters caused by these mechanisms are identified. In particular, cooled shelf waters sink along the continental slope and merge with "old" CIL waters during the mild winter of 1980-1981 more than 1 month later than during the cold winter 1992-1993 and more than 3 weeks later than during the normal winter of 1987-1988. The Sevastopol anticyclonic gyre and the northwest branch of the Black Sea Rim Current markedly influence the transformation of entrained cold NWS waters transported to the southwest and the central part of the water area. The local formation process of cold intermediate waters is found to be caused by the wintertime penetrating convection over domelike isosurfaces of temperature and salinity arising due to rising constant halocline (pycnocline) at the centers of cyclonic gyres because of the intensification of the wintertime circulation. Anomalously cold surface water, characterized by increased density, gradually sinks. An analysis of TS indices indicates that the transformed cold water spreads out over isopycnic surfaces with time, being entrained in cyclonic circulation and spreading throughout the sea, thus renewing "old" CIL waters.

  14. Strain relaxation of strained-Si layers on SiGe-on-insulator (SGOI) structures after mesa isolation

    NASA Astrophysics Data System (ADS)

    Usuda, Koji; Mizuno, Tomohisa; Tezuka, Tsutomu; Sugiyama, Naoharu; Moriyama, Yoshihiko; Nakaharai, Shu; Takagi, Shin-ichi

    2004-03-01

    Strained-Si-on-insulator (strained-SOI) MOSFETs are one of the most promising device structures for high-speed and/or low-power CMOS. In realizing strained-Si MOS LSI, fabrication of strained-Si MOSFETs with small active area is indispensable, and thus the strain relaxation of strained-SOI mesa islands was investigated in this study. Thin strained-Si films were grown on thin relaxed SiGe-on-insulator (SGOI) structures. The isolation process was carried out by using chemical-dry-etching (CDE) to fabricate samples with small active areas. Using Raman spectroscopy, strained-Si islands on SGOI substrates were investigated. As a result, it was confirmed that the strained-Si layers grown on relaxed SiGe ( x=0.28) before and after mesa isolation, down to 5 μm in size, had almost no relaxation after rapid-thermal-annealing (RTA) at 1000 °C. Furthermore, it was confirmed that the nano-beam electron diffraction (NBD) measurement showed a similar tendency regarding the strain relaxation.

  15. Electrical characterization of low temperature deposited TiO 2 films on strained-SiGe layers

    NASA Astrophysics Data System (ADS)

    Dalapati, G. K.; Chatterjee, S.; Samanta, S. K.; Maiti, C. K.

    2003-04-01

    Thin films of titanium dioxide have been deposited on strained Si 0.82Ge 0.18 epitaxial layers using titanium tetrakis-isopropoxide [TTIP, Ti(O-i-C 3H 7) 4] and oxygen by microwave plasma enhanced chemical vapor deposition (PECVD). The films have been characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Dielectric constant, equivalent oxide thickness (EOT), interface state density ( Dit), fixed oxide charge density ( Qf/ q) and flat-band voltage ( VFB) of as-deposited films were found to be 13.2, 40.6 Å, 6×10 11 eV -1 cm -2, 3.1×10 11 cm -2 and -1.4 V, respectively. The capacitance-voltage ( C- V), current-voltage ( I- V) characteristics and charge trapping behavior of the films under constant current stressing exhibit an excellent interface quality and high dielectric reliability making the films suitable for microelectronic applications.

  16. Bipolar resistive switching behavior of an amorphous Ge2Sb2Te5 thin films with a Te layer

    NASA Astrophysics Data System (ADS)

    Yoo, Sijung; Eom, Taeyong; Gwon, Taehong; Hwang, Cheol Seong

    2015-03-01

    The mechanism of bipolar resistive switching (BRS) of amorphous Ge2Sb2Te5 (GST) thin films sandwiched between inert electrodes (Ti and Pt) was examined. Typical bipolar resistive switching behavior with a high resistance ratio (~103) and reliable switching characteristics was achieved. High-resolution transmission electron microscopy revealed the presence of a conductive Te-filament bridging between the top and bottom electrodes through an amorphous GST matrix. The conduction mechanism analysis showed that the low-resistance state was semiconducting and dominated by band transport, whereas Poole-Frenkel conduction governed the carrier transport in the high-resistance state. Thus, the BRS behavior can be attributed to the formation and rupture of the semiconducting conductive Te bridge through the migration of the Te ions in the amorphous GST matrix under a high electric field. The Te ions are provided by the thin (~5 nm) Te-rich layer formed at the bottom electrode interface.

  17. Effect of nonstoichiometry on the electrophysical properties of the layered compounds Ge{sub 3}Bi{sub 2}Te{sub 6} and GeBi{sub 2}Te{sub 4}

    SciTech Connect

    Shelimova, L.E.; Karpinskii, O.G.; Avilov, E.S.; Kretova, M.A.; Lubman, C.U.

    1994-12-01

    The objective of this work was to investigate the effect of deviation from stoichiometry on the electrophysical properties (electrical and thermal conductivity, thermoelectric power, and carrier concentration) of the ternary layered semiconducting compounds Ge{sub 3{plus_minus}{delta}1}Bi{sub 2+{delta}2}Te{sub 6+{delta}3} and Ge{sub 1{plus_minus}{delta}3}, which are promising for use in thermoelectric converters.The electrophysical properties were measured at 300 K. The Ge{sub 1-{delta}1}Bi{sub 2+{delta}3} alloys were studied by powder X-ray diffraction analysis on a DRON UM-1 diffractometer (CoK{sub {alpha}} radiation). It was found that Ge{sub 3{plus_minus}{delta}1} Bi{sub 2+{delta}2}Te{sub 6{plus_minus}{delta}3} is a nonstoichiometric phase with p-type conductivity throughout the {delta}{sub 1}, {delta}{sub 2}, and {delta}{sub 3} ranges examined. Our results suggest that cation vacancies are likely to be the dominant nonstoichiometric defects responsible for the high concentration of holes. The conductivity of Ge{sub 1{plus_minus}{delta}1}Bi{sub 2}Te{sub 4} changes from the p-type in the Ge-deficient alloys to the n-type in the Gerich alloys.

  18. Generation of conducting polymer-based heterojunctions, diodes, and capacitors using an intermediate-layer lithography method

    NASA Astrophysics Data System (ADS)

    Liu, Xinchuan; Chakraborty, Anirban; Parthasarathi, Ganga; Luo, Cheng

    2007-04-01

    In this work, conducting polymer-based heterojunctions, diodes and capacitors have been generated using an intermediate-layer lithography (ILL) approach which has been recently developed in our group. Polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), Poly(methyl methacrylate) (PMMA) and aluminum were used as component materials in these devices. Compared with Si-based devices, conducting polymerbased devices have distinctive advantages of low weight and good flexibility, and may potentially replace the corresponding Si-based devices. A challenge is how to fabricate the conducting polymer-based microsystems. Most conducting polymers are sensitive to the environment, and their electrical properties tend to deteriorate over time due to overoxidation (air), moisture, high temperature and chemical alteration. The current fabrication techniques (e.g. lift-off, dry and wet etching processes) used in lithographic approaches involve ultra-violet, electron-beam, x-ray, gases (e.g., oxygen and nitrogen), DI water, and/or chemical solution (e.g. photoresist and acetone), making them improper to pattern conducting polymers. Since the ILL method does not involve aggressive chemistry in generation of patterns, it has been employed in this work to fabricate conducting polymer-based microdevices, particularly diodes and capacitors. In fabrication of the devices, multiple layers of polymers (e.g., PPy and PEDOT) and metals (e.g., Al) are coated on a PMMA sheet followed by the patterning with the insertion of Si molds. The detailed fabrication procedure and testing results are given in this paper.

  19. Evidence of oxygen vacancy and possible intermediate gap state in layered α-MoO3 single-crystal nanobelts

    NASA Astrophysics Data System (ADS)

    Chen, C. Z.; Li, Y.; Tang, X. D.

    2016-01-01

    Multilayered meso-structured MoO3 nanobelts have been synthesized by thermally oxidizing a molybdenum chip in a reduced oxygen atmosphere, with a view to disclosing the existence of oxygen vacancy and understanding the mechanism behind the influence of oxygen vacancy on the electronic structure of molybdenum oxides. Based on the measurements from X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM), it is found that the as-grown sample is single-crystal α-MoO3 with a (001) preferred orientation, which shows an irregular belt-like morphology being composed of some ~20 nm single-crystal thin layers. The present sample includes a lot of oxygen vacancies in the lattice, as evidenced by the considerably reduced coordination number of the central Mo atoms from X-ray absorption spectra (XAS) as well as the red shift of the main Raman peaks. The existence of the oxygen vacancies are further tested by the photoluminescence (PL) results as the main emission peak shows an obvious red shift with the corresponding optical band gap reduced to 2.3 eV. Very importantly, an extra emission positioned at 738 nm (1.68 eV) is believed to originate from the recombination of the electrons from the intermediate band (IB) to the valence band (VB), and the formation of the IB in the gap is also caused by oxygen-ion vacancies.

  20. Magnesium substituted hydroxyapatite coating on titanium with nanotublar TiO2 intermediate layer via electrochemical deposition

    NASA Astrophysics Data System (ADS)

    Yajing, Yan; Qiongqiong, Ding; Yong, Huang; Han, Shuguang; Pang, Xiaofeng

    2014-06-01

    Hydroxyapatite (HAp) coatings doped with magnesium ion is an attractive method to improve the biocompatibility and biodegradability of HAp coatings. In this paper, we used electrochemical deposition to study the production of magnesium-doped HAp (MgHAp) coatings onto pure titanium with anodized titanium oxide (TiO2) nanotubes as intermediate layer. The morphology and composition of coatings were studied by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. Results indicated that Mg was uniformly distributed in the coatings, and each coating was found to be 21 μm thick. With Mg2+ incorporation, Ca2+ was substituted by Mg2+ in the MgHAp coating, thereby reducing apatite crystallinity and weekly increasing bond strength. The bioactivity and corrosion resistance of the coatings were improved in simulated body fluid and polarization tests, respectively. Cell culture tests indicated that the magnesium-substituted coatings had good biocompatibility and no adverse effect.

  1. Low resistivity contact on n-type Ge using low work-function Yb with a thin TiO2 interfacial layer

    NASA Astrophysics Data System (ADS)

    Dev, Sachin; Remesh, Nayana; Rawal, Yaksh; Manik, Prashanth Paramahans; Wood, Bingxi; Lodha, Saurabh

    2016-03-01

    This work demonstrates the benefit of a lower contact barrier height, and hence reduced contact resistivity (ρc), using a low work-function metal (Yb) in unpinned metal-interfacial layer-semiconductor (MIS) contacts on n-type Ge. Fermi-level unpinning in MIS contacts on n-Ge is first established by introducing a 2 nm TiO2-x interfacial layer between various contact metals (Yb, Ti, Ni, Pt) and n-Ge. Further, Yb/TiO2-x/n-Ge MIS contact diodes exhibit higher current densities (up to 100×) and lower effective contact barrier height (up to 30%) versus Ti/TiO2-x control devices over a wide range of TiO2-x thickness (1-5 nm). Finally, low work-function Yb combined with doped TiO2-x having a low conduction band offset with Ge and high substrate doping (n+-Ge: 2.5 ×1019 cm-3) is shown to result in an ultra-low ρc value of 1.4 × 10-8 Ω cm2, 10 × lower than Ti/TiO2-x control devices.

  2. A high-sensitivity fiber-optic evanescent wave sensor with a three-layer structure composed of Canada balsam doped with GeO2.

    PubMed

    Zhong, Nianbing; Zhao, Mingfu; Zhong, Lianchao; Liao, Qiang; Zhu, Xun; Luo, Binbin; Li, Yishan

    2016-11-15

    In this paper, we present a high-sensitivity polymer fiber-optic evanescent wave (FOEW) sensor with a three-layer structure that includes bottom, inter-, and surface layers in the sensing region. The bottom layer and inter-layer are POFs composed of standard cladding and the core of the plastic optical fiber, and the surface layer is made of dilute Canada balsam in xylene doped with GeO2. We examine the morphology of the doped GeO2, the refractive index and composition of the surface layer and the surface luminous properties of the sensing region. We investigate the effects of the content and morphology of the GeO2 particles on the sensitivity of the FOEW sensors by using glucose solutions. In addition, we examine the response of sensors incubated with staphylococcal protein A plus mouse IgG isotype to goat anti-mouse IgG solutions. Results indicate very good sensitivity of the three-layer FOEW sensor, which showed a 3.91-fold improvement in the detection of the target antibody relative to a conventional sensor with a core-cladding structure, and the novel sensor showed a lower limit of detection of 0.2ng/l and a response time around 320s. The application of this high-sensitivity FOEW sensor can be extended to biodefense, disease diagnosis, biomedical and biochemical analysis. PMID:27311112

  3. Fabrication of quantum dots in undoped Si/Si0.8Ge0.2 heterostructures using a single metal-gate layer

    DOE PAGESBeta

    Lu, T. M.; Gamble, J. K.; Muller, R. P.; Nielsen, E.; Bethke, D.; Ten Eyck, G. A.; Pluym, T.; Wendt, J. R.; Dominguez, J.; Lilly, M. P.; et al

    2016-08-29

    Enhancement-mode Si/SiGe electron quantum dots have been pursued extensively by many groups for their potential in quantum computing. Most of the reported dot designs utilize multiple metal-gate layers and use Si/SiGe heterostructures with Ge concentration close to 30%. Here, we report the fabrication and low-temperature characterization of quantum dots in the Si/Si0.8Ge0.2 heterostructures using only one metal-gate layer. We find that the threshold voltage of a channel narrower than 1 μm increases as the width decreases. The higher threshold can be attributed to the combination of quantum confinement and disorder. We also find that the lower Ge ratio used heremore » leads to a narrower operational gate bias range. The higher threshold combined with the limited gate bias range constrains the device design of lithographic quantum dots. We incorporate such considerations in our device design and demonstrate a quantum dot that can be tuned from a single dot to a double dot. Furthermore, the device uses only a single metal-gate layer, greatly simplifying device design and fabrication.« less

  4. Coarse, intermediate and high resolution numerical simulations of the transition of a tropical wave critical layer to a tropical storm

    NASA Astrophysics Data System (ADS)

    Montgomery, M. T.; Wang, Z.; Dunkerton, T. J.

    2010-11-01

    Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from within the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the Kurihara and Tuleya problem examining the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km), intermediate (9 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of a rotationally dominant region with minimal strain/shear deformation near the center of the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together

  5. Investigating the origin of intense photoluminescence in Si capping layer on Ge1-xSnx nanodots by transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Kikkawa, Jun; Nakamura, Yoshiaki; Fujinoki, Norihito; Ichikawa, Masakazu

    2013-02-01

    The authors investigated the annealing effects on atomic structures and elemental compositions in a stacking structure, Si capping layer on Ge1-xSnx nanodots on Si substrate covered with ultrathin SiO2 film, to clarify the origin of intense photoluminescence at ˜0.8 eV from the structure, using transmission electron microscopy. After the annealing, it was found that decay of Ge1-xSnx nanodots, formation of SiOx precipitates embedded in Si-rich Si1-xGex layer at the Si cap/Si substrate interface, formation of SnO2 nanoparticles on the oxidized surface of the Si capping layer, and morphological change of dislocations in the Si capping layer occur. Reaction products that appear as a result of the movement of dislocations can be related to the origin of intense photoluminescence.

  6. Si Waveguide-Integrated Metal-Semiconductor-Metal and p-i-n-Type Ge Photodiodes Using Si-Capping Layer

    NASA Astrophysics Data System (ADS)

    Fujikata, Junichi; Miura, Makoto; Noguchi, Masataka; Okamoto, Daisuke; Horikawa, Tsuyoshi; Arakawa, Yasuhiko

    2013-04-01

    We studied Si waveguide-integrated metal-semiconductor-metal (MSM) and p-i-n-type Ge photodiodes (Ge-PDs), using a Si-capping layer. As for an MSM Ge-PD, the Schottky barrier height was increased up to 0.44 V by applying a 8-20 nm Si-capping layer, and a very low dark current density of approximately 0.4 nA/µm2 was achieved with a high responsivity of 0.8 A/W. In addition, a small electrode spacing of 1 µm realized high-speed photodetection of 20 Gbps. As for a p-i-n-type Ge-PD, by applying a 10-20 nm Si capping layer, the contact resistance between a metal electrode of Ti/TiN/Al and n+-Si capping layer was successfully reduced to 1×10-5 Ω.cm2. A 45 GHz bandwidth was obtained with a low dark current density of 0.8 nA/µm2. Moreover, a more than 20 GHz bandwidth was achieved with zero-bias voltage. In the case of zero-bias voltage operation, a 3 dB bandwidth was a little affected by input power, which would originate from the photocarrier screening effect on the built-in electric field.

  7. Changes in switching fields of CoCrPt-SiO2 perpendicular recording media due to Ru intermediate layer under low and high gas pressures

    NASA Astrophysics Data System (ADS)

    Xia, Weixing; Murakami, Yasukazu; Shindo, Daisuke; Takahashi, Migaku

    2009-01-01

    It is well known that the deposition of an intermediate Ru layer under high Ar pressure during the fabrication of CoCrPt-SiO2 perpendicular recording media is effective in improving the magnetic properties of the upper CoCrPt-SiO2 layer. The change in the switching fields of the CoCrPt-SiO2 recording layer resulting from the presence of the high-pressure Ru layer is investigated through experiments and computer simulation. The monotonous increase in the magnetic anisotropy Ku and the decrease in the intergranular exchange coupling of the CoCrPt grains due to the presence of the high-pressure Ru layer result in a slight increase in the nucleation field, a significant increase in the coercivity and the saturation field, and a decrease in the slope of the hysteresis loop.

  8. Layered Seed-Growth of AgGe Football-like Microspheres via Precursor-Free Picosecond Laser Synthesis in Water

    NASA Astrophysics Data System (ADS)

    Zhang, Dongshi; Gökce, Bilal; Notthoff, Christian; Barcikowski, Stephan

    2015-09-01

    Hybrid particles are of great significance in terms of their adjustable optical, electronic, magnetic, thermal and mechanical properties. As a novel technique, laser ablation in liquids (LAL) is famous for its precursor-free, “clean” synthesis of hybrid particles with various materials. Till now, almost all the LAL-generated particles originate from the nucleation-growth mechanism. Seed-growth of particles similar to chemical methods seems difficult to be achieved by LAL. Here, we not only present novel patch-joint football-like AgGe microspheres with a diameter in the range of 1 ~ 7 μm achievable by laser ablation in distilled water but also find direct evidences of their layered seed growth mechanism. Many critical factors contribute to the formation of AgGe microspheres: fast laser-generated plasma process provide an excellent condition for generating large amount of Ge and Ag ions/atoms, their initial nucleation and galvanic replacement reaction, while cavitation bubble confinement plays an important role for the increase of AgGe nuclei and subsequent layered growth in water after bubble collapse. Driven by work function difference, Ge acts as nucleation agent for silver during alloy formation. This new seed-growth mechanism for LAL technique opens new opportunities to develop a large variety of novel hybrid materials with controllable properties.

  9. Layered Seed-Growth of AgGe Football-like Microspheres via Precursor-Free Picosecond Laser Synthesis in Water

    PubMed Central

    Zhang, Dongshi; Gökce, Bilal; Notthoff, Christian; Barcikowski, Stephan

    2015-01-01

    Hybrid particles are of great significance in terms of their adjustable optical, electronic, magnetic, thermal and mechanical properties. As a novel technique, laser ablation in liquids (LAL) is famous for its precursor-free, “clean” synthesis of hybrid particles with various materials. Till now, almost all the LAL-generated particles originate from the nucleation-growth mechanism. Seed-growth of particles similar to chemical methods seems difficult to be achieved by LAL. Here, we not only present novel patch-joint football-like AgGe microspheres with a diameter in the range of 1 ~ 7 μm achievable by laser ablation in distilled water but also find direct evidences of their layered seed growth mechanism. Many critical factors contribute to the formation of AgGe microspheres: fast laser-generated plasma process provide an excellent condition for generating large amount of Ge and Ag ions/atoms, their initial nucleation and galvanic replacement reaction, while cavitation bubble confinement plays an important role for the increase of AgGe nuclei and subsequent layered growth in water after bubble collapse. Driven by work function difference, Ge acts as nucleation agent for silver during alloy formation. This new seed-growth mechanism for LAL technique opens new opportunities to develop a large variety of novel hybrid materials with controllable properties. PMID:26334136

  10. Growth and characterization of highly tensile strained Ge1-xSnx formed on relaxed InyGa1-yP buffer layers

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Loke, Wan Khai; Yin, Tingting; Zhang, Zheng; D'Costa, Vijay Richard; Dong, Yuan; Liang, Gengchiau; Pan, Jisheng; Shen, Zexiang; Yoon, Soon Fatt; Tok, Eng Soon; Yeo, Yee-Chia

    2016-03-01

    Ge0.94Sn0.06 films with high tensile strain were grown on strain-relaxed InyGa1-yP virtual substrates using solid-source molecular beam epitaxy. The in-plane tensile strain in the Ge0.94Sn0.06 film was varied by changing the In mole fraction in InxGa1-xP buffer layer. The tensile strained Ge0.94Sn0.06 films were investigated by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. An in-plane tensile strain of up to 1% in the Ge0.94Sn0.06 was measured, which is much higher than that achieved using other buffer systems. Controlled thermal anneal experiment demonstrated that the strain was not relaxed for temperatures up to 500 °C. The band alignment of the tensile strained Ge0.94Sn0.06 on In0.77Ga0.23P was obtained by high resolution x-ray photoelectron spectroscopy. The Ge0.94Sn0.06/In0.77Ga0.23P interface was found to be of the type I band alignment, with a valence band offset of 0.31 ± 0.12 eV and a conduction band offset of 0.74 ± 0.12 eV.

  11. Growth of light-emitting SiGe heterostructures on strained silicon-on-insulator substrates with a thin oxide layer

    SciTech Connect

    Baidakova, N. A.; Bobrov, A. I.; Drozdov, M. N.; Novikov, A. V.; Pavlov, D. A.; Shaleev, M. V.; Yunin, P. A.; Yurasov, D. V.; Krasilnik, Z. F.

    2015-08-15

    The possibility of using substrates based on “strained silicon on insulator” structures with a thin (25 nm) buried oxide layer for the growth of light-emitting SiGe structures is studied. It is shown that, in contrast to “strained silicon on insulator” substrates with a thick (hundreds of nanometers) oxide layer, the temperature stability of substrates with a thin oxide is much lower. Methods for the chemical and thermal cleaning of the surface of such substrates, which make it possible to both retain the elastic stresses in the thin Si layer on the oxide and provide cleaning of the surface from contaminating impurities, are perfecte. It is demonstrated that it is possible to use the method of molecular-beam epitaxy to grow light-emitting SiGe structures of high crystalline quality on such substrates.

  12. Magnetic anisotropy induced by crystal distortion in Ge{sub 1−x}Mn{sub x}Te/PbTe//KCl (001) ferromagnetic semiconductor layers

    SciTech Connect

    Knoff, W. Łusakowski, A.; Domagała, J. Z.; Minikayev, R.; Taliashvili, B.; Łusakowska, E.; Pieniążek, A.; Szczerbakow, A.; Story, T.

    2015-09-21

    Ferromagnetic resonance (FMR) study of magnetic anisotropy is presented for thin layers of IV-VI diluted magnetic semiconductor Ge{sub 1−x}Mn{sub x}Te with x = 0.14 grown by molecular beam epitaxy on KCl (001) substrate with a thin PbTe buffer. Analysis of the angular dependence of the FMR resonant field reveals that an easy magnetization axis is located near to the normal to the layer plane and is controlled by two crystal distortions present in these rhombohedral Ge{sub 1−x}Mn{sub x}Te layers: the ferroelectric distortion with the relative shift of cation and anion sub-lattices along the [111] crystal direction and the biaxial in-plane, compressive strain due to thermal mismatch.

  13. High-resolution x-ray diffraction investigation of relaxation and dislocations in SiGe layers grown on (001), (011), and (111) Si substrates

    SciTech Connect

    Zhylik, A.; Benediktovich, A.; Ulyanenkov, A.; Guerault, H.; Myronov, M.; Dobbie, A.; Leadley, D. R.; Ulyanenkova, T.

    2011-06-15

    This work presents a detailed characterization, using high-resolution x-ray diffraction, of multilayered Si{sub 1-x}Ge{sub x} heterostructures grown on (001), (011), and (111) Si substrates by reduced pressure chemical vapor deposition. Reciprocal space mapping has been used to determine both the strain and Ge concentration depth profiles within each layer of the heterostructures after initially determining the crystallographic tilt of all the layers. Both symmetric and asymmetric reciprocal space maps were measured on each sample, and the evaluation was performed simultaneously for the whole data set. The ratio of misfit to threading dislocation densities has been estimated for each individual layer based on an analysis of diffuse x-ray scattering from the defects.

  14. Very low temperature (450 °C) selective epitaxial growth of heavily in situ boron-doped SiGe layers

    NASA Astrophysics Data System (ADS)

    Aubin, J.; Hartmann, J. M.; Veillerot, M.; Essa, Z.; Sermage, B.

    2015-11-01

    We have investigated the feasibility of selectively growing SiGe:B layers at 450 °C, 20 Torr in a 300 mm industrial reduced pressure chemical vapor deposition tool. A reduced H2 carrier gas mass-flow has been used in order to have acceptable growth rates at such a temperature, which is very low indeed. We have first of all studied on blanket Si wafers the in situ boron doping of SiGe with Si2H6, GeH4 and B2H6. A growth rate increase by a factor close to 7 together with a Ge concentration decrease from 53% down to 32% occurred as the diborane mass-flow increased. Very high B+ ion concentrations were obtained in layers that were single crystalline and smooth. Their concentration increased almost linearly with the B2H6 mass-flow, from 1.8 up to 8.3 × 1020 cm-3. The associated resistivity dropped from 0.43 down to 0.26 mΩ cm. We have then tested whether or not selectivity versus SiO2 could be achieved by adding various amounts of HCl to Si2H6 + GeH4 +B2H6. Single crystalline growth rates of intrinsic SiGe(:B) on Si were very similar to poly-crystalline growth rates on SiO2-covered substrates irrespective of the HCl flow. Straightforward selectivity was thus not feasible with a co-flow approach. As a consequence, a 450 °C deposition/etch (DE) process was evaluated. Growth occurred at 20 Torr with the above-mentioned chemistry, while the selective etch of poly-SiGe:B versus c-SiGe:B was conducted at 740 Torr with a medium HCl mass-flow (F(HCl)/F(H2) = 0.2) and a high H2 flow. A 2.2 etch selectivity was achieved while retaining single crystalline if slightly rough SiGe:B layers.

  15. Atomic layer deposition of perovskite oxides and their epitaxial integration with Si, Ge, and other semiconductors

    SciTech Connect

    McDaniel, Martin D.; Ngo, Thong Q.; Hu, Shen; Ekerdt, John G.; Posadas, Agham; Demkov, Alexander A.

    2015-12-15

    Atomic layer deposition (ALD) is a proven technique for the conformal deposition of oxide thin films with nanoscale thickness control. Most successful industrial applications have been with binary oxides, such as Al{sub 2}O{sub 3} and HfO{sub 2}. However, there has been much effort to deposit ternary oxides, such as perovskites (ABO{sub 3}), with desirable properties for advanced thin film applications. Distinct challenges are presented by the deposition of multi-component oxides using ALD. This review is intended to highlight the research of the many groups that have deposited perovskite oxides by ALD methods. Several commonalities between the studies are discussed. Special emphasis is put on precursor selection, deposition temperatures, and specific property performance (high-k, ferroelectric, ferromagnetic, etc.). Finally, the monolithic integration of perovskite oxides with semiconductors by ALD is reviewed. High-quality epitaxial growth of oxide thin films has traditionally been limited to physical vapor deposition techniques (e.g., molecular beam epitaxy). However, recent studies have demonstrated that epitaxial oxide thin films may be deposited on semiconductor substrates using ALD. This presents an exciting opportunity to integrate functional perovskite oxides for advanced semiconductor applications in a process that is economical and scalable.

  16. Ternary arsenides ATt3As3 (A=K, Rb; Tt=Ge, Sn) with layered structures

    NASA Astrophysics Data System (ADS)

    Khatun, Mansura; Stoyko, Stanislav S.; Mar, Arthur

    2016-06-01

    The four ternary arsenides ATt3As3 (A=K, Rb; Tt=Ge, Sn) were obtained by reaction of the elements at 600-650 °C. They adopt an orthorhombic structure (space group Pnma, Z=4, with cell parameters ranging from a=9.9931(11) Å, b=3.7664(4) Å, c=18.607(2) Å for KGe3As3 to a=10.3211(11) Å, b=4.0917(4) Å, c=19.570(2) Å for RbSn3As3) containing corrugated [Tt3As3] layers built from Tt-centred trigonal pyramids and tetrahedra forming five-membered rings decorated with As handles. They can be considered to be Zintl phases with Tt atoms in +4, +3, and +1 oxidation states. Band structure calculations predict that these compounds are semiconductors with narrow band gaps (0.71 eV in KGe3As3, 0.50 eV in KSn3As3).

  17. High-performance ultraviolet detection and visible-blind photodetector based on Cu{sub 2}O/ZnO nanorods with poly-(N-vinylcarbazole) intermediate layer

    SciTech Connect

    Perng, Dung-Ching

    2015-12-14

    This study reports a high-performance hybrid ultraviolet (UV) photodetector with visible-blind sensitivity fabricated by inserting a poly-(N-vinylcarbazole) (PVK) intermediate layer between low-cost processed Cu{sub 2}O film and ZnO nanorods (NRs). The PVK layer acts as an electron-blocking/hole-transporting layer between the n-ZnO and p-Cu{sub 2}O films. The Cu{sub 2}O/PVK/ZnO NR photodetector exhibited a responsivity of 13.28 A/W at 360 nm, a high detectivity of 1.03 × 10{sup 13} Jones at a low bias of −0.1 V under a low UV light intensity of 24.9 μW/cm{sup 2}. The photo-to-dark current ratios of the photodetector with and without the PVK intermediate layer at a bias of −0.5 V are 1.34 × 10{sup 2} and 3.99, respectively. The UV-to-visible rejection ratios (R{sub 360 nm}/R{sub 450 nm}) are 350 and 1.735, respectively. Several features are demonstrated: (a) UV photo-generated holes at the ZnO NRs can effectively be transported through the PVK layer to the p-Cu{sub 2}O layer; (b) the insertion of a PVK buffer layer significantly minimizes the reverse-bias leakage current, which leads to a larger amplification of the photocurrent; and (c) the PVK buffer layer greatly improves the UV-to-visible responsivity ratio, allowing the device to achieve high UV detection sensitivity at a low bias voltage using a very low light intensity.

  18. Surface passivation and interface properties of bulk GaAs and epitaxial-GaAs/Ge using atomic layer deposited TiAlO alloy dielectric.

    PubMed

    Dalapati, G K; Chia, C K; Tan, C C; Tan, H R; Chiam, S Y; Dong, J R; Das, A; Chattopadhyay, S; Mahata, C; Maiti, C K; Chi, D Z

    2013-02-01

    High quality surface passivation on bulk-GaAs substrates and epitaxial-GaAs/Ge (epi-GaAs) layers were achieved by using atomic layer deposited (ALD) titanium aluminum oxide (TiAlO) alloy dielectric. The TiAlO alloy dielectric suppresses the formation of defective native oxide on GaAs layers. X-ray photoelectron spectroscopy (XPS) analysis shows interfacial arsenic oxide (As(x)O(y)) and elemental arsenic (As) were completely removed from the GaAs surface. Energy dispersive X-ray diffraction (EDX) analysis and secondary ion mass spectroscopy (SIMS) analysis showed that TiAlO dielectric is an effective barrier layer for reducing the out-diffusion of elemental atoms, enhancing the electrical properties of bulk-GaAs based metal-oxide-semiconductor (MOS) devices. Moreover, ALD TiAlO alloy dielectric on epi-GaAs with AlGaAs buffer layer realized smooth interface between epi-GaAs layers and TiAlO dielectric, yielding a high quality surface passivation on epi-GaAs layers, much sought-after for high-speed transistor applications on a silicon platform. Presence of a thin AlGaAs buffer layer between epi-GaAs and Ge substrates improved interface quality and gate dielectric quality through the reduction of interfacial layer formation (Ga(x)O(y)) and suppression of elemental out-diffusion (Ga and As). The AlGaAs buffer layer and TiAlO dielectric play a key role to suppress the roughening, interfacial layer formation, and impurity diffusion into the dielectric, which in turn largely enhances the electrical property of the epi-GaAs MOS devices. PMID:23331503

  19. Dependence of the surface topology and raman scattering spectra of Ge{sub x}Si{sub 1-x}/Si films on the composition variation over the layer thickness

    SciTech Connect

    Lunin, L. S.; Sysoev, I. A.; Bavizhev, M. D.; Lapin, V. A.; Kuleshov, D. S.; Malyavin, F. F.

    2013-05-15

    The surface topology and Raman scattering spectra of Ge{sub x}Si{sub 1-x}/Si(100) films are investigated in dependence of the composition variation over the film thickness. It is shown that the character of the Ge content variation in the Ge{sub x}Si{sub 1-x} alloy at the constant cumulative Ge fraction in the film (x{sub int} = 0.5) affects the surface morphology of the grown Ge{sub x}Si{sub 1-x}/Si layer. The heterostructures were grown by molecular-beam epitaxy.

  20. Effect of As Passivation on Vapor-Phase Epitaxial Growth of Ge on (211)Si as a Buffer Layer for CdTe Epitaxy

    NASA Astrophysics Data System (ADS)

    Shintri, Shashidhar; Rao, Sunil; Sarney, Wendy; Garg, Saurabh; Palosz, Witold; Trivedi, Sudhir; Wijewarnasuriya, Priyalal; Bhat, Ishwara

    2011-08-01

    We report an investigation of epitaxial germanium grown by chemical vapor deposition (CVD) on arsenic-terminated (211)Si, which is the preferred substrate in the USA for fabrication of night-vision devices based on mercury cadmium telluride (MCT) grown by molecular-beam epitaxy (MBE). The films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), cross-sectional transmission electron microscopy (XTEM), and x-ray diffraction (XRD). Arsenic passivation was found to be effective in preventing cross-contamination of unwanted residual species present inside the reactor chamber and also in prolonging the evolution of layer-by-layer growth of Ge for significantly more monolayers than on nonpassivated Si. The two-dimensional (2D) to three-dimensional (3D) transition resulted in Ge islands, the density and morphology of which showed a clear distinction between passivated and nonpassivated (211)Si. Finally, thick Ge layers (˜250 nm) were grown at 525°C and 675°C with and without As passivation, where the layers grown with As passivation resulted in higher crystal quality and smooth surface morphology.

  1. Atomic layer deposition of crystalline SrHfO{sub 3} directly on Ge (001) for high-k dielectric applications

    SciTech Connect

    McDaniel, Martin D.; Ngo, Thong Q.; Ekerdt, John G.; Hu, Chengqing; Jiang, Aiting; Yu, Edward T.; Lu, Sirong; Smith, David J.; Posadas, Agham; Demkov, Alexander A.

    2015-02-07

    The current work explores the crystalline perovskite oxide, strontium hafnate, as a potential high-k gate dielectric for Ge-based transistors. SrHfO{sub 3} (SHO) is grown directly on Ge by atomic layer deposition and becomes crystalline with epitaxial registry after post-deposition vacuum annealing at ∼700 °C for 5 min. The 2 × 1 reconstructed, clean Ge (001) surface is a necessary template to achieve crystalline films upon annealing. The SHO films exhibit excellent crystallinity, as shown by x-ray diffraction and transmission electron microscopy. The SHO films have favorable electronic properties for consideration as a high-k gate dielectric on Ge, with satisfactory band offsets (>2 eV), low leakage current (<10{sup −5} A/cm{sup 2} at an applied field of 1 MV/cm) at an equivalent oxide thickness of 1 nm, and a reasonable dielectric constant (k ∼ 18). The interface trap density (D{sub it}) is estimated to be as low as ∼2 × 10{sup 12 }cm{sup −2 }eV{sup −1} under the current growth and anneal conditions. Some interfacial reaction is observed between SHO and Ge at temperatures above ∼650 °C, which may contribute to increased D{sub it} value. This study confirms the potential for crystalline oxides grown directly on Ge by atomic layer deposition for advanced electronic applications.

  2. The properties of SiO 2 films using direct photo-chemical vapor deposition on strained SiGe layers

    NASA Astrophysics Data System (ADS)

    Lin, C. T.; Chang, S. J.; Nayak, D. K.; Shiraki, Y.

    1996-02-01

    Low temperature silicon-dioxide (SiO 2) layers were deposited on strained SiGe by using direct photo-chemical vapor deposition (DPCVD) with a deuterium lamp as the excitation source. It was found that the deposition rate increases linearly with the chamber pressure. The Auger electron spectroscopy profile shows that neither was Ge rejected nor was a Ge-rich layer formed after devices were fabricated. The capacitance-voltage ( C- V) measurements show that the flat-band voltage is about -1.1 V with an effective oxide charge of about 7 × 10 10 cm -2 and interface trap density of 3 × 10 11 cm -2 eV -1. At room temperature, the leakage current is about 3 × 10 -9 A/cm 2 under a 2 × 10 6 V/cm electric field. The breakdown field can reach over 16 MV/cm at 1 μA/cm 2 for these SiGe metal-oxide semiconductor (MOS) diodes.

  3. Design and fabrication of multi-layers infrared antireflection coating consisting of ZnS and Ge on ZnS substrate

    NASA Astrophysics Data System (ADS)

    Zarei Moghadam, R.; Ahmadvand, H.; Jannesari, M.

    2016-03-01

    We have designed, fabricated and characterized a multi-layers antireflection coating on multispectral ZnS substrate, suitable for the infrared range of 8-12 μm. The 4-layers coating (Ge/ZnS/Ge/ZnS) with optimized thicknesses was fabricated by PVD technique and studied by FTIR, nanoindentation and AFM. From FTIR spectroscopy it was found that, in the wavelength range of 8-12 μm, the average transmittance of the double-side coated sample increases by about 26% and its maximum reaches about 98%. To improve the mechanical hardness, a bilayer of Y2O3/carbon was deposited on the coating. Nanoindentation test shows that the coating enhances the mechanical properties. The final coating have successfully passed durability and environmental tests.

  4. Pseudomorphic GeSn/Ge (001) heterostructures

    SciTech Connect

    Tonkikh, A. A.; Talalaev, V. G.; Werner, P.

    2013-11-15

    The synthesis of pseudomorphic GeSn heterostructures on a Ge (001) substrate by molecular-beam epitaxy is described. Investigations by transmission electron microscopy show that the GeSn layers are defect free and possess cubic diamondlike structure. Photoluminescence spectroscopy reveals interband radiative recombination in the GeSn quantum wells, which is identified as indirect transitions between the subbands of heavy electrons and heavy holes. On the basis of experimental data and modeling of the band structure of pseudomorphic GeSn compounds, the lower boundary of the bowing parameter for the indirect band gap is estimated as b{sub L} {>=} 1.47 eV.

  5. Lanthanide Germanate Cluster Organic Frameworks Based on {Ln8Ge12} Clusters: From One-Dimensional Chains to Two-Dimensional Layers and Three-Dimensional Frameworks.

    PubMed

    Li, Lei-Lei; Cao, Gao-Juan; Zhao, Jun-Wei; He, Huan; Yang, Bai-Feng; Yang, Guo-Yu

    2016-06-01

    Under hydrothermal conditions, six series of novel lanthanide (Ln) organogermanates (LnGs) [Ln8Ge12(μ3-O)24E12(H2O)16]·14H2O (Ln(3+) = Pr(3+), 1; Nd(3+), 2; Sm(3+), 3; Eu(3+), 4; Gd(3+), 5; one-dimensional (1-D) LnG cluster organic chain (LnGCOC)), {[Nd8Ge12(μ3-O)24E12(H2O)10](μ2-H2O)2[Nd8Ge12(μ3-O)24E12(H2O)16]}·18H2O (6, two-dimensional (2-D) planar LnG cluster organic layer (LnGCOL)), {[Ln2GeE(HO)2O(H2O)(CH3COO)2(CO3)]2[Ln8Ge12E12(μ3-O)24(H2O)10]}·6H2O (Ln(3+) = Pr(3+), 7; Nd(3+), 8; 2-D wave-shaped LnGCOL), [TbGeE(HO)2O(H2O)(pca)]2[Tb8Ge12E12(μ3-O)24(H2O)8]·10H2O (9, three-dimensional (3-D) LnG cluster organic framework (LnGCOF)), {([Nd(pza)2(H2O)2]2[Nd8Ge12E12(μ3-O)24(H2O)12])([Nd(pza)2]2[Nd8Ge12E12(Hpza)2(μ3-O)24(H2O)10])}·4OH·14H2O (10, 3-D LnGCOF), {[Nd8Ge12E12(μ3-O)24(H2O)10][Nd(pca)(pda)(H2O)]2}·12H2O (11, 3-D LnGCOF) and {[Nd8Ge12E12(μ3-O)24(H2O)10][Nd(pza)(pda)(H2O)]2}·12H2O (12, 3-D LnGCOF) (Hpca = 2-picolinic acid, H2pda = 2,6-pyridinedicarboxylic acid, Hpza = 2-pyrazinecarboxylic acid) were prepared by introducing the second auxiliary ligands into the organogermanate-lanthanide-oxide reaction system. The obtainment of these LnGs realized the utilization of the second auxiliary ligands inducing the assembly from 1-D LnGCOCs to 2-D LnGCOLs and 3-D LnGCOFs based on LnG cluster (LnGC) {Ln8Ge12E12(μ3-O)24(H2O)16}({Ln8Ge12}) units and Ln-organic complexes or organic ligand connectors. It should be noted that the well-organized structural constructions of 1-12 can be visualized as the gradual replacement of active water sites located at equatorial and polar positions on the hypothetical [Ln8Ge12(μ3-O)24E12(H2O)18] LnGC core with oxygen or nitrogen atoms from organic ligands. The solid-state luminescent properties of 2, 3, 4, 6, and 8-12 have been investigated at room temperature. PMID:27216949

  6. Theory of hole mobility in strained Ge and III-V p-channel inversion layers with high-κ insulators

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Fischetti, M. V.; Sorée, B.; O'Regan, T.

    2010-12-01

    We present a comprehensive investigation of the low-field hole mobility in strained Ge and III-V (GaAs, GaSb, InSb, and In1-xGaxAs) p-channel inversion layers with both SiO2 and high-κ insulators. The valence (sub)band structure of Ge and III-V channels, relaxed and under biaxial strain (tensile and compressive) is calculated using an efficient self-consistent method based on the six-band k ṡp perturbation theory. The hole mobility is then computed using the Kubo-Greenwood formalism accounting for nonpolar hole-phonon scattering (acoustic and optical), surface roughness scattering, polar phonon scattering (III-Vs only), alloy scattering (alloys only) and remote phonon scattering, accounting for multisubband dielectric screening. As expected, we find that Ge and III-V semiconductors exhibit a mobility significantly larger than the "universal" Si mobility. This is true for MOS systems with either SiO2 or high-κ insulators, although the latter ones are found to degrade the hole mobility compared to SiO2 due to scattering with interfacial optical phonons. In addition, III-Vs are more sensitive to the interfacial optical phonons than Ge due to the existence of the substrate polar phonons. Strain—especially biaxial tensile stress for Ge and biaxial compressive stress for III-Vs (except for GaAs)—is found to have a significant beneficial effect with both SiO2 and HfO2. Among strained p-channels, InSb exhibits the largest mobility enhancement. In0.7Ga0.3As also exhibits an increased hole mobility compared to Si, although the enhancement is not as large. Finally, our theoretical results are favorably compared with available experimental data for a relaxed Ge p-channel with a HfO2 insulator.

  7. Identification of the Chemical Bonding Prompting Adhesion of a-C:H Thin Films on Ferrous Alloy Intermediated by a SiCx:H Buffer Layer.

    PubMed

    Cemin, F; Bim, L T; Leidens, L M; Morales, M; Baumvol, I J R; Alvarez, F; Figueroa, C A

    2015-07-29

    Amorphous carbon (a-C) and several related materials (DLCs) may have ultralow friction coefficients that can be used for saving-energy applications. However, poor chemical bonding of a-C/DLC films on metallic alloys is expected, due to the stability of carbon-carbon bonds. Silicon-based intermediate layers are employed to enhance the adherence of a-C:H films on ferrous alloys, although the role of such buffer layers is not yet fully understood in chemical terms. The chemical bonding of a-C:H thin films on ferrous alloy intermediated by a nanometric SiCx:H buffer layer was analyzed by X-ray photoelectron spectroscopy (XPS). The chemical profile was inspected by glow discharge optical emission spectroscopy (GDOES), and the chemical structure was evaluated by Raman and Fourier transform infrared spectroscopy techniques. The nature of adhesion is discussed by analyzing the chemical bonding at the interfaces of the a-C:H/SiCx:H/ferrous alloy sandwich structure. The adhesion phenomenon is ascribed to specifically chemical bonding character at the buffer layer. Whereas carbon-carbon (C-C) and carbon-silicon (C-Si) bonds are formed at the outermost interface, the innermost interface is constituted mainly by silicon-iron (Si-Fe) bonds. The oxygen presence degrades the adhesion up to totally delaminate the a-C:H thin films. The SiCx:H deposition temperature determines the type of chemical bonding and the amount of oxygen contained in the buffer layer. PMID:26135943

  8. Ab initio geometry optimization and ground state properties of layered ternary carbides Ti3MC2 (M = Al, Si and Ge)

    NASA Astrophysics Data System (ADS)

    Zhou, Yanchun; Sun, Zhimei; Wang, Xiaohui; Chen, Shengqi

    2001-11-01

    The crystal structures of all layered ternary carbides called '312' phases including Ti3AlC2, Ti3SiC2 and Ti3GeC2 have been fully optimized by means of ab initio total-energy calculations. The equilibrium lattice parameters, the atomic positions in the unit cell and interatomic distances have been determined. The differences between the calculated and the measured lattice constants are generally less than 1%. It is also shown that c/a of the hexagonal lattices decreases from Ti3AlC2 to Ti3GeC2. The calculated bulk moduli are 190 GPa for Ti3AlC2, 202 GPa for Ti3SiC2 and 198 GPa for Ti3GeC2, respectively, which are comparable to that of TiC. The electronic structures reveal that the Ti(1, 2) and C atoms form a strong Ti(2)-C-Ti(1)-C-Ti(2) covalent bond chain, while the bonding between Ti(2) and M (M = Al, Si, Ge) is relatively weak. The strong Ti(2)-C-Ti(1)-C-Ti(2) covalent bond chain corresponds to the high strength and modulus, while the metallic bond corresponds to the metallic conductivity of these ternaries.

  9. Atomic imaging and modeling of H{sub 2}O{sub 2}(g) surface passivation, functionalization, and atomic layer deposition nucleation on the Ge(100) surface

    SciTech Connect

    Kaufman-Osborn, Tobin; Chagarov, Evgueni A.; Kummel, Andrew C.

    2014-05-28

    Passivation, functionalization, and atomic layer deposition nucleation via H{sub 2}O{sub 2}(g) and trimethylaluminum (TMA) dosing was studied on the clean Ge(100) surface at the atomic level using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Chemical analysis of the surface was performed using x-ray photoelectron spectroscopy, while the bonding of the precursors to the substrate was modeled with density functional theory (DFT). At room temperature, a saturation dose of H{sub 2}O{sub 2}(g) produces a monolayer of a mixture of –OH or –O species bonded to the surface. STS confirms that H{sub 2}O{sub 2}(g) dosing eliminates half-filled dangling bonds on the clean Ge(100) surface. Saturation of the H{sub 2}O{sub 2}(g) dosed Ge(100) surface with TMA followed by a 200 °C anneal produces an ordered monolayer of thermally stable Ge–O–Al bonds. DFT models and STM simulations provide a consistent model of the bonding configuration of the H{sub 2}O{sub 2}(g) and TMA dosed surfaces. STS verifies the TMA/H{sub 2}O{sub 2}/Ge surface has an unpinned Fermi level with no states in the bandgap demonstrating the ability of a Ge–O–Al monolayer to serve as an ideal template for further high-k deposition.

  10. High current density and high PVCR Si/Si 1-xGe x DQW RTD formed with quadruple-layer buffer

    NASA Astrophysics Data System (ADS)

    Maekawa, Hirotaka; Sano, Yoshihiro; Ueno, Chihiro; Suda, Yoshiyuki

    2007-04-01

    As a strain-relief relaxed Si 1-xGe x buffer that is used for type II band offset formation, we have proposed a quadruple-Si 1-xGe x-layer (QL) buffer where misfit dislocations are evenly distributed in the lower two interfaces and a buffer surface with good crystallinity was obtained. The crystallinity of the buffer surface does not degrade by high P doping with a P concentration of ˜10 19 cm -3 during the buffer growth. A vertical-type electron-tunneling Si/Si 1-xGe x resonant tunneling diode (RTD) formed with the highly P-doped QL buffer exhibits a high current density and a high peak-to-valley current ratio (PVCR) value. A planer-type electron-tunneling Si/ Si 1-xGe x RTD formed with the same buffer using tetramethyl ammonium hydroxide (TMAH) etching and polyimide insulator, which is better suited for device integration, also exhibits a high current density and a high PVCR value and good initial static performance reproducibility.

  11. Single Junction InGaP/GaAs Solar Cells Grown on Si Substrates using SiGe Buffer Layers

    NASA Technical Reports Server (NTRS)

    Ringel, S. A.; Carlin, J. A.; Andre, C. L.; Hudait, M. K.; Gonzalez, M.; Wilt, D. M.; Clark, E. B.; Jenkins, P.; Scheiman, D.; Allerman, A.

    2002-01-01

    Single junction InGaP/GaAs solar cells displaying high efficiency and record high open circuit voltage values have been grown by metalorganic chemical vapor deposition on Ge/graded SiGe/Si substrates. Open circuit voltages as high as 980 mV under AM0 conditions have been verified to result from a single GaAs junction, with no evidence of Ge-related sub-cell photoresponse. Current AM0 efficiencies of close to 16% have been measured for a large number of small area cells, whose performance is limited by non-fundamental current losses due to significant surface reflection resulting from greater than 10% front surface metal coverage and wafer handling during the growth sequence for these prototype cells. It is shown that at the material quality currently achieved for GaAs grown on Ge/SiGe/Si substrates, namely a 10 nanosecond minority carrier lifetime that results from complete elimination of anti-phase domains and maintaining a threading dislocation density of approximately 8 x 10(exp 5) per square centimeter, 19-20% AM0 single junction GaAs cells are imminent. Experiments show that the high performance is not degraded for larger area cells, with identical open circuit voltages and higher short circuit current (due to reduced front metal coverage) values being demonstrated, indicating that large area scaling is possible in the near term. Comparison to a simple model indicates that the voltage output of these GaAs on Si cells follows ideal behavior expected for lattice mismatched devices, demonstrating that unaccounted for defects and issues that have plagued other methods to epitaxially integrate III-V cells with Si are resolved using SiGe buffers and proper GaAs nucleation methods. These early results already show the enormous and realistic potential of the virtual SiGe substrate approach for generating high efficiency, lightweight and strong III-V solar cells.

  12. Structural properties of relaxed thin film germanium layers grown by low temperature RF-PECVD epitaxy on Si and Ge (100) substrates

    SciTech Connect

    Cariou, R.; Ruggeri, R.; Tan, X.; Nassar, J.; Roca i Cabarrocas, P.; Mannino, Giovanni

    2014-07-15

    We report on unusual low temperature (175 °C) heteroepitaxial growth of germanium thin films using a standard radio-frequency plasma process. Spectroscopic ellipsometry and transmission electron microscopy (TEM) reveal a perfect crystalline quality of epitaxial germanium layers on (100) c-Ge wafers. In addition direct germanium crystal growth is achieved on (100) c-Si, despite 4.2% lattice mismatch. Defects rising from Ge/Si interface are mostly located within the first tens of nanometers, and threading dislocation density (TDD) values as low as 10{sup 6} cm{sup −2} are obtained. Misfit stress is released fast: residual strain of −0.4% is calculated from Moiré pattern analysis. Moreover we demonstrate a striking feature of low temperature plasma epitaxy, namely the fact that crystalline quality improves with thickness without epitaxy breakdown, as shown by TEM and depth profiling of surface TDD.

  13. A Resultant Stress Effect of Contact Etching Stop Layer and Geometrical Designs of Poly Gate on Nanoscaled nMOSFETs with a Si1-xGe(x) Channel.

    PubMed

    Lee, Chang-Chun; Liu, Chuan-Hsi; Chen, Zih-Han; Tzeng, Tzai-Liang

    2015-03-01

    In this research, an n-type metal-oxide-semiconductor field effect transistor (nMOSFET) device with a SiGe channel exerted by the combination of a contact etching stop layer (CESL) and silicon germanium (Si1-xGe(x)) channel stressors is proposed. To explore the foregoing mechanical effect on the stress distribution of nMOSFETs within the channel region, a process-oriented simulated technique is adopted for the concerned nMOSFET device. The loading sources are a 1.1 GPa tensile CESL (t-CESL) and a SiGe channel structure constructed with 0%, 22.5%, and 25%, germanium (Ge) mole fractions. The results of the simulation show that the stress components of the Si1-xGe(x) channel evidently increase when the Ge mole fraction within a Si1-xGe(x) layer is increased. A pulling force exerted on the protruding gate structure by the CESL layer that causes dominant bending deformation and channel stress variation behaviors is a major reason for this phenomenon. Therefore, the degree of bending effect caused by the protruding gate structure is concluded as being the key to determining the trends and stress magnitudes of the Si1-xGe(x) device channel. PMID:26413636

  14. Key role of the wetting layer in revealing the hidden path of Ge/Si(001) Stranski-Krastanow growth onset

    SciTech Connect

    Brehm, Moritz; Grydlik, Martyna; Lichtenberger, Herbert; Hrauda, Nina; Fromherz, Thomas; Schaeffler, Friedrich; Bauer, Guenther; Montalenti, Francesco; Vastola, Guglielmo; Miglio, Leo; Beck, Matthew J.

    2009-11-15

    The commonly accepted Stranski-Krastanow model, according to which island formation occurs on top of a wetting layer (WL) of a certain thickness, predicts for the morphological evolution an increasing island aspect ratio with volume. We report on an apparent violation of this thermodynamic understanding of island growth with deposition. In order to investigate the actual onset of three-dimensional islanding and the critical WL thickness in the Ge/Si(001) system, a key issue is controlling the Ge deposition with extremely high resolution [0.025 monolayer (ML)]. Atomic force microscopy and photoluminescence measurements on samples covering the deposition range 1.75-6.1 ML, taken along a Ge deposition gradient on 4 in. Si substrates and at different growth temperatures (T{sub g}), surprisingly reveal that for T{sub g}>675 deg. C steeper multifaceted domes apparently nucleate prior to shallow (105)-faceted pyramids, in a narrow commonly overlooked deposition range. The puzzling experimental findings are explained by a quantitative modeling of the total energy with deposition. We accurately matched ab initio calculations of layer and surface energies to finite-element method simulations of the elastic energy in islands, in order to compare the thermodynamic stability of different island shapes with respect to an increasing WL thickness. Close agreement between modeling and experiments is found, pointing out that the sizeable progressive lowering of the surface energy in the first few MLs of the WL reverts the common understanding of the SK growth onset. Strong similarities between islanding in SiGe and III/V systems are highlighted.

  15. Atomic imaging and modeling of passivation, functionalization, and atomic layer deposition nucleation of the SiGe(001) surface via H2O2(g) and trimethylaluminum dosing

    NASA Astrophysics Data System (ADS)

    Kaufman-Osborn, Tobin; Chagarov, Evgueni A.; Park, Sang Wook; Sahu, Bhagawan; Siddiqui, Shariq; Kummel, Andrew C.

    2014-12-01

    Passivation, functionalization, and atomic layer deposition (ALD) via H2O2(g) and trimethylaluminum (TMA) dosing were studied on the clean Si0.6Ge0.4(001) surface at the atomic level using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Chemical analysis of the surface was performed with in-situ X-ray photoelectron spectroscopy (XPS) while density functional theory (DFT) was employed to model the bonding of H2O2(g) chemisorbates to the substrate. A room temperature saturation dose of H2O2(g) covers the surface with a monolayer of sbnd OH and sbnd O chemisorbates. XPS and DFT demonstrate that the room temperature H2O2/SiGe surface is composed of only Gesbnd OH and Gesbnd O bonds while annealing induces an atomic layer exchange bringing Si to the surface to bond with sbnd OH or sbnd O while pushing Ge subsurface. The resulting Sisbnd OH and Sisbnd O surface is optimal because it can be used to nucleate high-k ALD and Si dangling bonds are readily passivated by forming gas. After H2O2(g) functionalization, TMA dosing, and a subsequent 230 °C anneal, ordering along the dimer row direction is observed on the surface. STS verifies that the TMA/H2O2/SiGe surface has an unpinned Fermi level with no states in the band gap demonstrating the ability to serve as an ideal template for further high-k deposition.

  16. High efficiency Cu(In,Ga)Se{sub 2} thin film solar cells without intermediate buffer layers

    SciTech Connect

    Ramanathan, K.; Wiesner, H.; Asher, S.; Niles, D.; Bhattacharya, R.N.; Keane, J.; Contreras, M.A.; Noufi, R.

    1998-09-01

    The nature of the interface between CuInGaSe{sub 2} (CIGS) and the chemical bath deposited CdS layer has been investigated. The authors show that heat-treating the absorbers in Cd- or Zn-containing solutions in the presence of ammonium hydroxide sets up an interfacial reaction with the possibility of an ion exchange occurring between Cd and Cu. The characteristics of devices made in this manner suggest that the reaction generates a thin, n-doped region in the absorber. The authors suggest that this aspect might be more important than the CdS layer in the formation of the junction. It is quite possible that the CdS/CuInSe{sub 2} device is a buried, shallow junction with a CdS window layer, rather than a heterojunction between CdS and CIGS. The authors use these ideas to develop methods for fabricating diodes without CdS or Cd.

  17. HfO2 gate dielectric on Ge (1 1 1) with ultrathin nitride interfacial layer formed by rapid thermal NH3 treatment

    NASA Astrophysics Data System (ADS)

    Agrawal, Khushabu S.; Patil, Vilas S.; Khairnar, Anil G.; Mahajan, Ashok M.

    2016-02-01

    Interfacial properties of the ALD deposited HfO2 over the surface nitrided germanium substrate have been studied. The formation of GeON (∼1.7 nm) was confirmed by X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron spectroscopy (HRTEM) over the germanium surface. The effect of post deposition annealing temperature was investigated to study the interfacial and electrical properties of hafnium oxide/germanium oxynitride gate stacks. The high-k MOS devices with ultrathin GeON layer shows the good electrical characteristics including higher k value ∼18, smaller equivalent oxide thickness (EOT) around 1.5 nm and smaller hysteresis value less than 170 mV. The Qeff and Dit values are somewhat greater due to the (1 1 1) orientation of the germanium and may be due to the presence of nitrogen at the interface. The Fowler-Northeim (FN) tunneling of Ge MOS devices has been studied. The barrier height ΦB extracted from the plot is ∼1 eV.

  18. Syntheses, structural variants and characterization of AInM‧S4 (A=alkali metals, Tl; M‧ = Ge, Sn) compounds; facile ion-exchange reactions of layered NaInSnS4 and KInSnS4 compounds

    NASA Astrophysics Data System (ADS)

    Yohannan, Jinu P.; Vidyasagar, Kanamaluru

    2016-06-01

    Ten AInM‧S4 (A=alkali metals, Tl; M‧= Ge, Sn) compounds with diverse structure types have been synthesized and characterized by single crystal and powder X-ray diffraction and a variety of spectroscopic methods. They are wide band gap semiconductors. KInGeS4(1-β), RbInGeS4(2), CsInGeS4(3-β), TlInGeS4(4-β), RbInSnS4(8-β) and CsInSnS4(9) compounds with three-dimensional BaGa2S4 structure and CsInGeS4(3-α) and TlInGeS4(4-α) compounds with a layered TlInSiS4 structure have tetrahedral [InM‧S4]- frameworks. On the other hand, LiInSnS4(5) with spinel structure and NaInSnS4(6), KInSnS4(7), RbInSnS4(8-α) and TlInSnS4(10) compounds with layered structure have octahedral [InM‧S4]- frameworks. NaInSnS4(6) and KInSnS4(7) compounds undergo facile topotactic ion-exchange, at room temperature, with various mono-, di- and tri-valent cations in aqueous medium to give rise to metastable layered phases.

  19. Performance of (La,Sr)(Co,Fe)O 3- x double-layer cathode films for intermediate temperature solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Marinha, D.; Hayd, J.; Dessemond, L.; Ivers-Tiffée, E.; Djurado, E.

    In this study the performance evaluation of (La,Sr)(Co,Fe)O 3- x (LSCF) double-layer films characterized by impedance spectroscopy between 403 and 603 °C to be used for intermediate temperature solid oxide fuel cells (IT-SOFCs) is presented. Two LSCF layers with different microstructures were sequentially deposited onto Ce 0.9Gd 0.1O 1.95 (CGO) substrates in a symmetrical fashion. A first layer of La 0.6Sr 0.4Co 0.2Fe 0.8O 3- x with a thickness of 7 μm and a nano-scaled particle size was deposited by electrostatic spray deposition (ESD) technique. Different deposition conditions were used in preparing the ESD films to evaluate the influence of film morphology on the electrochemical performance. After annealing, a current collector layer of La 0.58Sr 0.4Co 0.2Fe 0.8O 3- x with ∼45 μm in thickness and a larger particle size was deposited by screen printing. Area specific resistances (ASRs) were determined from impedance spectroscopy measurements performed in air between 403 and 603 °C, at 25 °C steps. A dependence of electrochemical performance on the morphology of the LSCF layer deposited by ESD was observed. The lowest ASR, measured during 130 h of isothermal dwelling at 603 °C, averaged 0.13 Ω cm 2 with negligible variation and is the lowest reported value for this composition, to the best of our knowledge. Reported results assure an excellent suitability of this type of assembly for IT-SOFCs.

  20. Cobalt based layered perovskites as cathode material for intermediate temperature Solid Oxide Fuel Cells: A brief review

    NASA Astrophysics Data System (ADS)

    Pelosato, Renato; Cordaro, Giulio; Stucchi, Davide; Cristiani, Cinzia; Dotelli, Giovanni

    2015-12-01

    Nowadays, the cathode is the most studied component in Intermediate Temperature-Solid Oxide Fuel Cells (IT-SOFCs). Decreasing SOFCs operating temperature implies slow oxygen reduction kinetics and large polarization losses. Double perovskites with general formula REBaCo2O5+δ are promising mixed ionic-electronic conductors, offering a remarkable enhancement of the oxygen diffusivity and surface exchange respect to disordered perovskites. In this review, more than 250 compositions investigated in the literature were analyzed. The evaluation was performed in terms of electrical conductivity, Area Specific Resistance (ASR), chemical compatibility with electrolytes and Thermal Expansion Coefficient (TEC). The most promising materials have been identified as those bearing the mid-sized rare earths (Pr, Nd, Sm, Gd). Doping strategies have been analyzed: Sr doping on A site promotes higher electrical conductivity, but worsen ASR and TECs; B-site doping (Fe, Ni, Mn) helps lowering TECs, but is detrimental for the electrochemical properties. A promising boost of the electrochemical activity is obtained by simply introducing a slight Ba under-stoichiometry. Still, the high sensitivity of the electrochemical properties against slight changes in the stoichiometry hamper a conclusive comparison of all the investigated compounds. Opportunities for an improvement of double perovskite cathodes performance is tentatively foreseen in combining together the diverse effective doping strategies.

  1. Performance enhancement of a plasmonic structure comprising of indium oxide-zirconium dioxide-silver-zinc oxide intermediate layers working in visible and infrared wavelength region

    NASA Astrophysics Data System (ADS)

    Brahmachari, Kaushik; Ray, Mina

    2016-07-01

    Modeling of a fused silica (SiO2) glass prism-based plasmonic structure comprising of indium oxide (In2O3)-zirconium dioxide (ZrO2)-silver (Ag)-zinc oxide (ZnO) intermediate layers showing enhancement in sensitivity and figure-of-merit (FOM) in visible and infrared regime has been reported in this paper. Performance of the proposed plasmonic structure has been demonstrated in terms of sensitivity, half width (HW), detection accuracy (DA), and FOM parameters in visible (632.8 nm) and infrared (1200 nm) wavelength of light. High sensitivity of fused silica glass material, In2O3, ZnO films along with high DA and high FOM of Ag and inclusion of ZrO2 as an oxidation protective layer in between In2O3 and Ag have been the most exciting and advantageous features of our proposed structure. Simulated sensitivity values of our proposed structure were found to be 73.8 deg/RIU at 632.8 nm wavelength and it was found enhanced to 109.6 deg/RIU at 1200 nm wavelength and simulated FOM values were also found enhanced from 23.3544 RIU-1 at 632.8 nm to 62.6285 RIU-1 at 1200 nm wavelength for change in sensing layer refractive indices from 1.30 RIU to 1.35 RIU.

  2. Vertical distribution and diel migration of macrozooplankton in the St. Lawrence marine system (Canada) in relation with the cold intermediate layer thermal properties

    NASA Astrophysics Data System (ADS)

    Harvey, Michel; Galbraith, Peter S.; Descroix, Aurélie

    2009-01-01

    Vertical distribution of various species and stages of macrozooplankton (euphausiacea, chaetognatha, cnidaria, mysidacea, amphipoda) were determined for different times of the day and related to the physical environment. Stratified sampling with the BIONESS was carried out during seven cruises in spring and fall 1998, 2000, and 2001, and fall 1999, in two different habitats in the St. Lawrence marine system: the lower St. Lawrence Estuary and the NW Gulf of St. Lawrence. Our results indicate that the various macrozooplankton species were distributed throughout the whole water column including the surface layer, the cold intermediate layer (CIL), and the deep layer at different times of day and night in both areas during all periods. Moreover, three types of migrational patterns were observed within this zooplanktonic community: (1) nocturnal ascent by the whole population, (2) segregation into two groups; one which performed nocturnal accent and another which remained in the deep, and (3) no detectable migration. We also observed that the diel vertical migration (DVM) amplitude in most of the macrozooplankton species varied as a function of physical factors, in particular the spatio-temporal variations of the CIL thermal properties, including the upper and the lower limits of the CIL and the depth of the CIL core temperature. Finally, the different DVM patterns coupled with estuarine circulation patterns and bottom topography could place animals in different flow regimes by night and by day and contribute to their retention (aggregation) and/or dispersion in different areas, time of the day, and seasons.

  3. Effect of intermediate fiber layer on the fracture load and failure mode of maxillary incisors restored with laminate veneers.

    PubMed

    Turkaslan, Suha; Tezvergil-Mutluay, Arzu; Bagis, Bora; Shinya, Akikazu; Vallittu, Pekka K; Lassila, Lippo V

    2008-01-01

    This study evaluated the fracture load and failure mode of various veneer materials cemented with or without the addition of a fiber-reinforced composite (FRC) layer at the adhesive interface. Sixty intact incisors were randomly divided into three groups. Group 1 was fabricated with the heat-press technique (IPS Empress 2); Group 2 with the copy milling technique (ZirkonZahn); and Group 3 with the direct or indirect composite technique (Z250)--and specimens were cemented either with or without FRC at the adhesive interface. The specimens were thermocycled and tested with a universal testing machine. No significant differences in fracture load (p>0.05) were found among the various veneer materials. The addition of FRC at the adhesive layer did not lead to significant differences in the fracture load (p>0.05) but resulted in differences in the failure mode. Laminate veneers made of composite, zirconia, and Empress 2 showed comparable mean fracture loads. However, the use of FRC at the interface changed their failure modes. PMID:18309613

  4. Intermediate and high resolution numerical simulations of the transition of a tropical wave critical layer to a tropical storm

    NASA Astrophysics Data System (ADS)

    Montgomery, M. T.; Wang, Z.; Dunkerton, T. J.

    2009-12-01

    Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis that typifies the trade wind belt. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the problem of the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of a vorticity dominant region with minimal strain/shear deformation within the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together. Implications of these findings are

  5. Azimuthal Anisotropy at Intermediate Rapidity in √SNN = 200 GeV Au-Au Collisions in PHENIX at RHIC-BNL

    NASA Astrophysics Data System (ADS)

    Norman, Benjamin

    2005-04-01

    In mid-central heavy ion collisions, the nuclear overlap region is almond shaped. This spatial anisotropy leads to a momentum space anisotropy, which has symmetry about the plane defined by the beam axis and the impact parameter. This reaction plane (or event plane) can be determined in experiment using the final particle azimuthal distribution. The reaction plane resolution depends on particle multiplicity, azimuthal angle resolution, azimuthal hermeticity, and the amount of actual asymmetry that exists in the collision. We will present the effect of these factors on the resolution of the reaction plane for Au-Au collisions in general and more specifically for the pad planes of the PHENIX Multiplicity Vertex Detector (MVD). These pad planes are in the pseudorapidity range 1.8 < |eta| < 2.6 on either side of the vertex region for which PHOBOS data (nucl-ex/0403025) suggest a v2 of about 4 percent for mid-central Au-Au collisions at √SNN of 200 GeV.

  6. Pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} on amorphous dielectric layers towards monolithic 3D photonic integration

    SciTech Connect

    Li, Haofeng; Brouillet, Jeremy; Wang, Xiaoxin; Liu, Jifeng

    2014-11-17

    We demonstrate pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} crystallized on amorphous layers at <450 °C towards 3D Si photonic integration. We developed two approaches to seed the lateral single crystal growth: (1) utilize the Gibbs-Thomson eutectic temperature depression at the tip of an amorphous GeSn nanotaper for selective nucleation; (2) laser-induced nucleation at one end of a GeSn strip. Either way, the crystallized Ge{sub 0.89}Sn{sub 0.11} is dominated by a single grain >18 μm long that forms optoelectronically benign twin boundaries with others grains. These pseudo single crystal, direct-band-gap Ge{sub 0.89}Sn{sub 0.11} patterns are suitable for monolithic 3D integration of active photonic devices on Si.

  7. Laser-induced nondestructive patterning of a thin ferroelectric polymer film with controlled crystals using Ge8Sb2Te11 alloy layer for nonvolatile memory.

    PubMed

    Bae, Insung; Kim, Richard Hahnkee; Hwang, Sun Kak; Kang, Seok Ju; Park, Cheolmin

    2014-09-10

    We present a simple but robust nondestructive process for fabricating micropatterns of thin ferroelectric polymer films with controlled crystals. Our method is based on utilization of localized heat arising from thin Ge(8)Sb(2)Te(11) (GST) alloy layer upon exposure of 650 nm laser. The heat was generated on GST layer within a few hundred of nanosecond exposure and subsequently transferred to a thin poly(vinylidene fluoride-co-trifluoroethylene) film deposited on GST layer. By controlling exposure time and power of the scanned laser, ferroelectric patterns of one or two microns in size are fabricated with various shape. In the micropatterned regions, ferroelectric polymer crystals were efficiently controlled in both degree of the crystallinity and the molecular orientations. Nonvolatile memory devices with laser scanned ferroelectric polymer layers exhibited excellent device performance of large remnant polarization, ON/OFF current ratio and data retention. The results are comparable with devices containing ferroelectric films thermally annealed at least for 2 h, making our process extremely efficient for saving time. Furthermore, our approach can be conveniently combined with a number of other functional organic materials for the future electronic applications. PMID:25127181

  8. Variability of GeV gamma-ray emission in QSO B0218+357 due to microlensing on intermediate size structures

    NASA Astrophysics Data System (ADS)

    Sitarek, J.; Bednarek, W.

    2016-06-01

    Strong gravitational lensing leads to an occurrence of multiple images, with different magnifications, of a lensed source. Those magnifications can in turn be modified by microlensing on smaller mass scales within the lens. Recently, measurements of the changes in the magnification ratio of the individual images have been proposed as a powerful tool for estimation of the size and velocity of the emission region in the lensed source. The changes of the magnification ratios in blazars PKS1830-211 and QSO B0218+357, if interpreted as caused by a microlensing on individual stars, put strong constraints on those two variables. These constraints are difficult to accommodate with the current models of gamma-ray emission in blazars. In this paper we study if similar changes in the magnification ratio can be caused by microlensing on intermediate size structures in the lensing galaxy. We investigate in details three classes of possible lenses: globular clusters (GCs), open clusters (OCs) and giant molecular clouds (GMCs). We apply this scenario to the case of QSO B0218+357. Our numerical simulations show that changes in magnifications with similar time-scales can be obtained for relativistically moving emission regions with sizes up to 0.01 pc in the case of microlensing on the cores of GCs or clumps in GMCs. From the density of such structures in spiral galaxies we estimate however that lensing in GMCs would be more common.

  9. An unusual phenomenon of surface reaction observed during Ge overgrowth on Mn5Ge3/Ge(111) heterostructures

    NASA Astrophysics Data System (ADS)

    Dau, Minh-Tuan; Le Thanh, Vinh; Michez, Lisa A.; Petit, Matthieu; Le, Thi-Giang; Abbes, Omar; Spiesser, Aurélie; Ranguis, Alain

    2012-10-01

    The Mn5Ge3 compound, thanks to its room-temperature ferromagnetism, metallic character and ability to epitaxially grow on germanium, acts as a potential candidate for spin injection into group-IV semiconductors. Understanding and controlling Ge overgrowth behaviour on Mn5Ge3/Ge heterostructures represents a crucial step to realize Ge/Mn5Ge3/Ge multilayers for numerous spintronic applications. Here, we have combined structural and morphological characterizations with magnetic analyses to study the mechanisms of Ge overgrowth on epitaxial Mn5Ge3 layers in the temperature range of 450-550 °C. It is found that deposited Ge instantly reacts with Mn to form a Mn5Ge3 surface layer, which, acting as a surfactant, continuously floats upwards from the growing surface to a distance larger than 70 nm. New Ge layers are successively formed underneath, allowing such a floating Mn5Ge3 surface layer to be stabilized by epitaxy. These observations can be considered as a typical example in which the stabilization of metastable thin films by epitaxy can overcome thermodynamic equilibrium. We have also investigated the effect of carbon adsorption on the top of the Mn5Ge3 layer prior to Ge deposition to control the Mn:Ge reaction. It is shown that adsorbed carbon effectively reduces the out-diffusion of Mn from Mn5Ge3, allowing Ge layers to stack up on top of Mn5Ge3. However, at temperatures of 450-550 °C, carbon may react with Mn to form manganese carbides and the resulting Ge overlayers are found to change their orientation from the (111) plane to the (001) plane, which has a higher surface energy. Finally, a strategy to realize Ge/Mn5Ge3/Ge multilayers will be addressed.

  10. Bacterial processes in the intermediate and deep layers of the Ionian Sea in winter 1999: Vertical profiles and their relationship to the different water masses

    NASA Astrophysics Data System (ADS)

    Zaccone, R.; Monticelli, L. S.; Seritti, A.; Santinelli, C.; Azzaro, M.; Boldrin, A.; La Ferla, R.; Ribera D'Alcalã, M.

    2003-09-01

    Dissolved and particulate organic carbon, bacterial biomass, microbial enzymatic activities (EEA: leucine aminopeptidase, β-glucosidase, and alkaline phosphatase), bacterial production, respiration rates, and bacterial growth efficiency were determined in 10 stations of the Ionian Sea (winter 1998-1999) with the aim of characterizing the recycling of biogenic carbon and phosphorus in the different water masses, previously identified on the basis of their hydrographical properties. All microbial activities decreased markedly with depth, with a sharp increase in the benthic boundary layer, where potential remineralization rates of phosphorus up to 1.03 μg P·dm-3d-1 and bacterial carbon production of 0.078 μg C·dm-3 d-1 were recorded. Those rates were close to the surface ones; the bacterial growth efficiency was also around 20%, similar to the surface value, sustaining the microbial food chain at the bottom. The daily hydrolysis of the organic carbon pool estimated by EEA varied from 0.67% (Ionian Surface Water) to 0.02% (Deep Water). Alkaline phosphatase activity was generally low in the intermediate and deep layers, in relation to the higher inorganic P content. The last facts support the hypothesis that deep waters of Ionian Sea, and in general of the entire Mediterranean basin, because of their young age, carry a larger amount of labile dissolved organic carbon, which reduces the need for a high recycling activity by bacterial community. As a matter of fact, a relatively higher activity per cell in carbon production rates was found in the deep layer where a large volume of the very recently formed Cretan Sea Outflow Water was present.

  11. Towards III-V solar cells on Si: Improvement in the crystalline quality of Ge-on-Si virtual substrates through low porosity porous silicon buffer layer and annealing

    SciTech Connect

    Calabrese, Gabriele; Baricordi, Stefano; Bernardoni, Paolo; Fin, Samuele; Guidi, Vincenzo; Vincenzi, Donato

    2014-09-26

    A comparison between the crystalline quality of Ge grown on bulk Si and on a low porosity porous Si (pSi) buffer layer using low energy plasma enhanced chemical vapor deposition is reported. Omega/2Theta coupled scans around the Ge and Si (004) diffraction peaks show a reduction of the Ge full-width at half maximum (FWHM) of 22.4% in presence of the pSi buffer layer, indicating it is effective in improving the epilayer crystalline quality. At the same time atomic force microscopy analysis shows an increase in root means square roughness for Ge grown on pSi from 38.5 nm to 48.0 nm, as a consequence of the larger surface roughness of pSi compared to bulk Si. The effect of 20 minutes vacuum annealing at 580°C is also investigated. The annealing leads to a FWHM reduction of 23% for Ge grown on Si and of 36.5% for Ge on pSi, resulting in a FWHM of 101 arcsec in the latter case. At the same time, the RMS roughness is reduced of 8.8% and of 46.5% for Ge grown on bulk Si and on pSi, respectively. The biggest improvement in the crystalline quality of Ge grown on pSi with respect to Ge grown on bulk Si observed after annealing is a consequence of the simultaneous reorganization of the Ge epilayer and the buffer layer driven by energy minimization. A low porosity buffer layer can thus be used for the growth of low defect density Ge on Si virtual substrates for the successive integration of III-V multijunction solar cells on Si. The suggested approach is simple and fast –thus allowing for high throughput-, moreover is cost effective and fully compatible with subsequent wafer processing. Finally it does not introduce new chemicals in the solar cell fabrication process and can be scaled to large area silicon wafers.

  12. The addition of strain in uniaxially strained transistors by both SiN contact etch stop layers and recessed SiGe sources and drains

    NASA Astrophysics Data System (ADS)

    Denneulin, Thibaud; Cooper, David; Hartmann, Jean-Michel; Rouviere, Jean-Luc

    2012-11-01

    SiN contact etch stop layers (CESL) and recessed SiGe sources/drains are two uniaxial strain techniques used to boost the charge carriers mobility in p-type metal oxide semiconductor field effect transistors (pMOSFETs). It has already been shown that the electrical performances of the devices can be increased by combining both of these techniques on the same transistor. However, there are few experimental investigations of their additivity from the strain point of view. Here, spatially resolved strain mapping was performed using dark-field electron holography (DFEH) on pMOSFETs transistors strained by SiN CESL and embedded SiGe sources/drains. The influence of both processes on the strain distribution has been investigated independently before the combination was tested. This study was first performed with non-silicided devices. The results indicated that in the channel region, the strain induced by the combination of both processes is equal to the sum of the individual components. Then, the same investigation was performed after Ni-silicidation of the devices. It was found that in spite of a slight reduction of the strain due to the silicidation, the strain additivity is approximately preserved. Finally, it was also shown that DFEH can be a useful technique to characterize the strain field around dislocations.

  13. In Situ Synchrotron Based X-ray Fluorescence and Scattering Measurements During Atomic Layer Deposition: Initial Growth of HfO2 on Si and Ge Substrates

    SciTech Connect

    K Devloo-Casier; J Dendooven; K Ludwig; G Lekens; J DHaen; C Detavernier

    2011-12-31

    The initial growth of HfO{sub 2} was studied by means of synchrotron based in situ x-ray fluorescence (XRF) and grazing incidence small angle x-ray scattering (GISAXS). HfO{sub 2} was deposited by atomic layer deposition (ALD) using tetrakis(ethylmethylamino)hafnium and H{sub 2}O on both oxidized and H-terminated Si and Ge surfaces. XRF quantifies the amount of deposited material during each ALD cycle and shows an inhibition period on H-terminated substrates. No inhibition period is observed on oxidized substrates. The evolution of film roughness was monitored using GISAXS. A correlation is found between the inhibition period and the onset of surface roughness.

  14. Pulse-height defect due to electron interaction in dead layers of Ge/Li/ gamma-ray detectors

    NASA Technical Reports Server (NTRS)

    Larsen, R. N.; Strauss, M. G.

    1969-01-01

    Study shows the pulse-height degradation of gamma ray spectra in germanium/lithium detectors to be due to electron interaction in the dead layers that exist in all semiconductor detectors. A pulse shape discrimination technique identifies and eliminates these defective pulses.

  15. Application of x-ray nano-particulate markers for the visualization of intermediate layers and interfaces using scanning electron microscopy

    NASA Astrophysics Data System (ADS)

    Bessudnova, Nadezda O.; Bilenko, David I.; Zakharevich, Andrey M.

    2012-03-01

    In this study the methodology of biological sample preparation for dental research using SEM/EDX has been elaborated. (1)The original cutting equipment supplied with 3D user-controlled sample fixation and an adjustable cooling system has been designed and evaluated. (2) A new approach to the root dentine drying procedure has been developed to preserve structure peculiarities of root dentine. (3) A novel adhesive system with embedded X-Ray nanoparticulate markers has been designed. (4)The technique allowing for visualization of bonding resins, interfaces and intermediate layers between tooth hard tissues and restorative materials of endodontically treated teeth using the X-ray nano-particulate markers has been developed and approved. These methods and approaches were used to compare the objective depth of penetration of adhesive systems of different generations in root dentine. It has been shown that the depth of penetration in dentine is less for adhesive systems of generation VI in comparison with bonding resins of generation V, which is in agreement with theoretical evidence. The depth of penetration depends on the correlation between the direction of dentinal tubules, bonding resin delivery and gravity.

  16. Application of x-ray nano-particulate markers for the visualization of intermediate layers and interfaces using scanning electron microscopy

    NASA Astrophysics Data System (ADS)

    Bessudnova, Nadezda O.; Bilenko, David I.; Zakharevich, Andrey M.

    2011-10-01

    In this study the methodology of biological sample preparation for dental research using SEM/EDX has been elaborated. (1)The original cutting equipment supplied with 3D user-controlled sample fixation and an adjustable cooling system has been designed and evaluated. (2) A new approach to the root dentine drying procedure has been developed to preserve structure peculiarities of root dentine. (3) A novel adhesive system with embedded X-Ray nanoparticulate markers has been designed. (4)The technique allowing for visualization of bonding resins, interfaces and intermediate layers between tooth hard tissues and restorative materials of endodontically treated teeth using the X-ray nano-particulate markers has been developed and approved. These methods and approaches were used to compare the objective depth of penetration of adhesive systems of different generations in root dentine. It has been shown that the depth of penetration in dentine is less for adhesive systems of generation VI in comparison with bonding resins of generation V, which is in agreement with theoretical evidence. The depth of penetration depends on the correlation between the direction of dentinal tubules, bonding resin delivery and gravity.

  17. Ge2Sb2Te5 layer used as solid electrolyte in conductive-bridge memory devices fabricated on flexible substrate

    NASA Astrophysics Data System (ADS)

    Deleruyelle, D.; Putero, M.; Ouled-Khachroum, T.; Bocquet, M.; Coulet, M.-V.; Boddaert, X.; Calmes, C.; Muller, C.

    2013-01-01

    This paper shows that the well-know chalcogenide Ge2Sb2Te5 (GST) in its amorphous state may be advantageously used as solid electrolyte material to fabricate Conductive-Bridge Random Access Memory (CBRAM) devices. GST layer was sputtered on preliminary inkjet-printed silver lines acting as active electrode on either silicon or plastic substrates. Whatever the substrate, the resistance switching is unambiguously attested at a nanoscale by means of conductive-atomic force microscopy (C-AFM) using a Pt-Ir coated tip on the GST surface acting as a passive electrode. The resistance change is correlated to the appearance or disappearance of concomitant hillocks and current spots at the surface of the GST layer. This feature is attributed to the formation/dissolution of a silver-rich protrusion beneath the AFM tip during set/reset operation. Beside, this paper constitutes a step toward the elaboration of crossbar memory arrays on flexible substrates since CBRAM operations were demonstrated on W/GST/Ag crossbar memory cells obtained from an heterogeneous fabrication process combining physical deposition and inkjet-printing.

  18. Mn5Ge3C0.6 /Ge(1 1 1) Schottky contacts tuned by an n-type ultra-shallow doping layer

    NASA Astrophysics Data System (ADS)

    Petit, Matthieu; Hayakawa, Ryoma; Wakayama, Yutaka; Le Thanh, Vinh; Michez, Lisa

    2016-09-01

    Mn5Ge3C x compound is of great interest for spintronics applications. The various parameters of Au/Mn5Ge3C0.6/Ge(1 1 1) and Au/Mn5Ge3C0.6/δ-doped Ge(1 1 1) Schottky diodes were measured in the temperature range of 30–300 K by using current–voltage and capacitance–voltage techniques. The Schottky barrier heights and ideality factors were found to be temperature dependent. These anomalous behaviours were explained by Schottky barrier inhomogeneities and interpreted by means of a Gaussian distribution model of the Schottky barrier heights. Following this approach we show that the Mn5Ge3C0.6/Ge contact is described with a single Gaussian distribution and a conduction mechanism mainly based on the thermoionic emission. On the other hand the Mn5Ge3C0.6/δ-doped Ge contact is depicted with two Gaussian distributions according to the temperature and a thermionic-field emission process. The differences between the two types of contacts are discussed according to the distinctive features of the growth of heavily doped germanium thin films.

  19. The performance of La0.6Sr1.4MnO4 layered perovskite electrode material for intermediate temperature symmetrical solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Chen, Gang; Wu, Kai; Cheng, Yonghong

    2014-12-01

    A layered perovskite electrode material, La0.6Sr1.4MnO4+δ (LSMO4), has been studied for intermediate temperature symmetrical solid oxide fuel cells (IT-SSOFCs) on La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte. The chemical compatibility tests indicate that no reaction occurred between LSMO4 oxide and LSGM electrolyte at temperature up to 1000 °C both in air and 5% H2. The lower conductivity in 5% H2 and higher conduction activation energy than those in air would be caused by poorer overlap of both σ and π bonds. DFT + U calculations also show that oxygen vacancies which formed in reducing atmosphere may block the 3D hopping path for electrons or holes through Mn-O-Mn chains. For LSMO4 electrode, SEM results indicate that the electrode formed good contact with the electrolyte after being sintered at 900 °C for 2 h. At 800 °C, the polarization resistance of the LSMO4 cathode is about 0.87 Ω cm2 in air, while the polarization resistance of the LSMO4 anode is about 2.07 Ω cm2 in 5% H2. LSMO4 exhibits better electrochemical activity for oxygen reduction than that for hydrogen oxidation. A cell with LSGM electrolyte, LSMO4-LSGM mixture as anode and cathode simultaneously displays a maximum power density of 59 mW cm-2 at 800 °C.

  20. Reduced GeO2 Nanoparticles: Electronic Structure of a Nominal GeOx Complex and Its Stability under H2 Annealing

    NASA Astrophysics Data System (ADS)

    Zhao, Jia; Yang, Linju; McLeod, John A.; Liu, Lijia

    2015-12-01

    A nominal GeOx (x ≤ 2) compound contains mixtures of Ge, Ge suboxides, and GeO2, but the detailed composition and crystallinity could vary from material to material. In this study, we synthesize GeOx nanoparticles by chemical reduction of GeO2, and comparatively investigate the freshly prepared sample and the sample exposed to ambient conditions. Although both compounds are nominally GeOx, they exhibit different X-ray diffraction patterns. X-ray absorption fine structure (XAFS) is utilized to analyse the detailed structure of GeOx. We find that the two initial GeOx compounds have entirely different compositions: the fresh GeOx contains large amorphous Ge clusters connected by GeOx, while after air exposure; the Ge clusters are replaced by a GeO2-GeOx composite. In addition, the two GeOx products undergo different structural rearrangement under H2 annealing, producing different intermediate phases before ultimately turning into metallic Ge. In the fresh GeOx, the amorphous Ge remains stable, with the GeOx being gradually reduced to Ge, leading to a final structure of crystalline Ge grains connected by GeOx. The air-exposed GeOx on the other hand, undergoes a GeO2→GeOx→Ge transition, in which H2 induces the creation of oxygen vacancies at intermediate stage. A complete removal of oxides occurs at high temperature.

  1. Reduced GeO2 Nanoparticles: Electronic Structure of a Nominal GeOx Complex and Its Stability under H2 Annealing

    PubMed Central

    Zhao, Jia; Yang, Linju; McLeod, John A.; Liu, Lijia

    2015-01-01

    A nominal GeOx (x ≤ 2) compound contains mixtures of Ge, Ge suboxides, and GeO2, but the detailed composition and crystallinity could vary from material to material. In this study, we synthesize GeOx nanoparticles by chemical reduction of GeO2, and comparatively investigate the freshly prepared sample and the sample exposed to ambient conditions. Although both compounds are nominally GeOx, they exhibit different X-ray diffraction patterns. X-ray absorption fine structure (XAFS) is utilized to analyse the detailed structure of GeOx. We find that the two initial GeOx compounds have entirely different compositions: the fresh GeOx contains large amorphous Ge clusters connected by GeOx, while after air exposure; the Ge clusters are replaced by a GeO2-GeOx composite. In addition, the two GeOx products undergo different structural rearrangement under H2 annealing, producing different intermediate phases before ultimately turning into metallic Ge. In the fresh GeOx, the amorphous Ge remains stable, with the GeOx being gradually reduced to Ge, leading to a final structure of crystalline Ge grains connected by GeOx. The air-exposed GeOx on the other hand, undergoes a GeO2→GeOx→Ge transition, in which H2 induces the creation of oxygen vacancies at intermediate stage. A complete removal of oxides occurs at high temperature. PMID:26634908

  2. siRNA delivery from triblock copolymer micelles with spatially-ordered compartments of PEG shell, siRNA-loaded intermediate layer, and hydrophobic core.

    PubMed

    Kim, Hyun Jin; Miyata, Kanjiro; Nomoto, Takahiro; Zheng, Meng; Kim, Ahram; Liu, Xueying; Cabral, Horacio; Christie, R James; Nishiyama, Nobuhiro; Kataoka, Kazunori

    2014-05-01

    Hydrophobized block copolymers have widely been developed for construction of polymeric micelles for stable delivery of nucleic acids as well as anticancer drugs. Herein, we elaborated an A-B-C type of triblock copolymer featuring shell-forming A-segment, nucleic acid-loading B-segment, and stable core-forming C-segment, directed toward construction of a three-layered polymeric micelle as a small interfering RNA (siRNA) vehicle. The triblock copolymer was prepared with nonionic and hydrophilic poly(ethylene glycol) (PEG), cationic poly(l-lysine) (PLys), and poly{N-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} [PAsp(DET)] bearing a hydrophobic dimethoxy nitrobenzyl ester (DN) moiety in the side chain [PEG-PLys-PAsp(DET-DN)]. The resulting triblock copolymers spontaneously formed sub-100 nm-sized polymeric micelles with a hydrophobic PAsp(DET-DN) core as well as PEG shell in an aqueous solution. This micelle was able to incorporate siRNA into the intermediate PLys layer, associated with slightly reduced size and a narrow size distribution. The triblock copolymer micelles (TCMs) stably encapsulated siRNA in serum-containing medium, whereas randomly hydrophobized triblock copolymer [PEG-PLys(DN)-PAsp(DET-DN)] control micelles (RCMs) gradually released siRNA with time and non-PEGylated diblock copolymer [PLys-PAsp(DET-DN)] control micelles (DCMs) immediately formed large aggregates. The TCMs thus induced appreciably stronger sequence-specific gene silencing in cultured cancer cells, compared to those control micelles. The siRNA delivery with TCMs was further examined in terms of cellular uptake and intracellular trafficking. The flow cytometric analysis revealed that the cellular uptake of TCMs was more efficient than that of RCMs, but less efficient than that of DCMs. The intracellular trafficking study using confocal laser scanning microscopy combined with fluorescence resonance energy transfer (FRET) revealed that the TCMs could readily release the siRNA payload

  3. Influence of lattice parameters on the dielectric constant of tetragonal ZrO2 and La-doped ZrO2 crystals in thin films deposited by atomic layer deposition on Ge(001)

    NASA Astrophysics Data System (ADS)

    Wiemer, C.; Debernardi, A.; Lamperti, A.; Molle, A.; Salicio, O.; Lamagna, L.; Fanciulli, M.

    2011-12-01

    In ZrO2 crystals, the highest dielectric constant (k) is ascribed to the tetragonal phase. By the use of density functional theory and synchrotron radiation x-ray diffraction, we show how the a and c lattice parameters of the tetragonal phase influence the resulting k. Highest k values are obtained at increasing both a and c, while k is reduced for compressive strained cells. The determination of a and c on La-doped ZrO2 and ZrO2 thin films deposited by atomic layer deposition on Ge (001) allowed us to elucidate the influence of La doping and Ge diffusion on the k value.

  4. P/N InP solar cells on Ge wafers

    NASA Technical Reports Server (NTRS)

    Wojtczuk, Steven; Vernon, Stanley; Burke, Edward A.

    1994-01-01

    Indium phosphide (InP) P-on-N one-sun solar cells were epitaxially grown using a metalorganic chemical vapor deposition process on germanium (Ge) wafers. The motivation for this work is to replace expensive InP wafers, which are fragile and must be thick and therefore heavy, with less expensive Ge wafers, which are stronger, allowing use of thinner, lighter weight wafers. An intermediate InxGs1-xP grading layer starting as In(0.49)Ga(0.51) at the GaAs-coated Ge wafer surface and ending as InP at the top of the grading layer (backside of the InP cell) was used to attempt to bend some of the threading dislocations generated by lattice-mismatch between the Ge wafer and InP cell so they would be harmlessly confined in this grading layer. The best InP/Ge cell was independently measured by NASA-Lewis with a one-sun 25 C AMO efficiently measured by NASA-Lewis with a one-circuit photocurrent 22.6 mA/sq cm. We believe this is the first published report of an InP cell grown on a Ge wafer. Why get excited over a 9 percent InP/Ge cell? If we look at the cell weight and efficiency, a 9 percent InP cell on an 8 mil Ge wafer has about the same cell power density, 118 W/kg (BOL), as the best InP cell ever made, a 19 percent InP cell on an 18 mil InP wafer, because of the lighter Ge wafer weight. As cell panel materials become lighter, the cell weight becomes more important, and the advantage of lightweight cells to the panel power density becomes more important. In addition, although InP/Ge cells have a low beginning-of-life (BOL) efficiency due to dislocation defects, the InP/Ge cells are very radiation hard (end-of-life power similar to beginning-of-life). We have irradiated an InP/Ge cell with alpha particles to an equivalent fluence of 1.6 x 10(exp 16) 1 MeV electrons/sq cm and the efficiency is still 83 percent of its BOL value. At this fluence level, the power output of these InP/Ge cells matches the GaAs/Ge cell data tabulated in the JPL handbook. Data are presented

  5. Practical aspects of strain measurement in thin SiGe layers by (004) dark-field electron holography in Lorentz mode.

    PubMed

    Denneulin, T; Cooper, D; Rouviere, J L

    2014-07-01

    Dark-field electron holography (DFEH) is a powerful transmission electron microscopy technique for mapping strain with nanometer resolution and high precision. However the technique can be difficult to set up if some practical steps are not respected. In this article, several measurements were performed on thin Si(1-x)Gex layers using (004) DFEH in Lorentz mode. Different practical aspects are discussed such as sample preparation, reconstruction of the holograms and interpretation of the strain maps in terms of sensitivity and accuracy. It was shown that the measurements are not significantly dependent on the preparation tool. Good results can be obtained using both FIB and mechanical polishing. Usually the most important aspect is a precise control of the thickness of the sample. A problem when reconstructing (004) dark-field holograms is the relatively high phase gradient that characterises the strained regions. It can be difficult to perform reconstructions with high sensitivity in both strained and unstrained regions. Here we introduce simple methods to minimise the noise in the different regions using a specific mask shape in Fourier space or by combining several reconstructions. As a test, DFEH was applied to the characterization of eight Si(1-x)Gex samples with different Ge concentrations. The sensitivity of the strain measured in the layers varies between 0.08% and 0.03% for spatial resolutions of 3.5-7 nm. The results were also compared to finite element mechanical simulations. A good accuracy of ±0.1% between experiment and simulation was obtained for strains up to 1.5% and ±0.25% for strains up to 2.5%. PMID:24811992

  6. Development of wider bandgap n-type a-SiOx:H and μc-SiOx:H as both doped and intermediate reflecting layer for a-Si:H/ a-Si1-xGex:H tandem solar cells

    NASA Astrophysics Data System (ADS)

    Chen, Po-Wei; Chen, Pei-Ling; Tsai, Chuang-Chuang

    2016-07-01

    In this work, we developed a-SiOx:H(n) and μc-SiOx:H(n) films as n-type layer, intermediate reflecting layer (IRL), and back-reflecting layer (BRL) to improve the light management in silicon thin-film solar cells. In the development of SiOx:H films, by properly adjusting the oxygen content of the films, the optical bandgap of μc-SiOx:H(n) can be increased while maintaining sufficient conductivity. Similar effect was found for a-SiOx:H(n). In a-Si:H single-junction cells, employing a-SiOx:H(n) as the replacement for a-Si:H(n) resulted in a relative efficiency enhancement of 11.4% due to the reduced parasitic absorption loss. We have also found that μc-SiOx:H(n) can replace back ITO layer as BRL, leading to a relative efficiency gain of 7.6%. For a-Si:H/ a-Si1- x Ge x:H tandem cell, employing μc-SiOx:H(n) as IRL increased the current density of top cell. In addition, employing a-SiOx:H(n) as a replacement of a-Si:H(n) in the top cell increased the current density of bottom cell due to the reduction of absorption loss. Combining all the improvements, the a-Si:H/ a-Si1-xGex:H tandem cell with efficiency of 9.2%, V OC = 1.58 V, J SC = 8.43 mA/cm2, and FF = 68.4% was obtained. [Figure not available: see fulltext.

  7. Kinetics of stabilised Criegee intermediates derived from alkene ozonolysis: reactions with SO2, H2O and decomposition under boundary layer conditions.

    PubMed

    Newland, Mike J; Rickard, Andrew R; Alam, Mohammed S; Vereecken, Luc; Muñoz, Amalia; Ródenas, Milagros; Bloss, William J

    2015-02-14

    The removal of SO2 in the presence of alkene-ozone systems has been studied for ethene, cis-but-2-ene, trans-but-2-ene and 2,3-dimethyl-but-2-ene, as a function of humidity, under atmospheric boundary layer conditions. The SO2 removal displays a clear dependence on relative humidity for all four alkene-ozone systems confirming a significant reaction for stabilised Criegee intermediates (SCI) with H2O. The observed SO2 removal kinetics are consistent with relative rate constants, k(SCI + H2O)/k(SCI + SO2), of 3.3 (±1.1) × 10(-5) for CH2OO, 26 (±10) × 10(-5) for CH3CHOO derived from cis-but-2-ene, 33 (±10) × 10(-5) for CH3CHOO derived from trans-but-2-ene, and 8.7 (±2.5) × 10(-5) for (CH3)2COO derived from 2,3-dimethyl-but-2-ene. The relative rate constants for k(SCI decomposition)/k(SCI + SO2) are -2.3 (±3.5) × 10(11) cm(-3) for CH2OO, 13 (±43) × 10(11) cm(-3) for CH3CHOO derived from cis-but-2-ene, -14 (±31) × 10(11) cm(-3) for CH3CHOO derived from trans-but-2-ene and 63 (±14) × 10(11) cm(-3) for (CH3)2COO. Uncertainties are ±2σ and represent combined systematic and precision components. These values are derived following the approximation that a single SCI is present for each system; a more comprehensive interpretation, explicitly considering the differing reactivity for syn- and anti-SCI conformers, is also presented. This yields values of 3.5 (±3.1) × 10(-4) for k(SCI + H2O)/k(SCI + SO2) of anti-CH3CHOO and 1.2 (±1.1) × 10(13) for k(SCI decomposition)/k(SCI + SO2) of syn-CH3CHOO. The reaction of the water dimer with CH2OO is also considered, with a derived value for k(CH2OO + (H2O)2)/k(CH2OO + SO2) of 1.4 (±1.8) × 10(-2). The observed SO2 removal rate constants, which technically represent upper limits, are consistent with decomposition being a significant, structure dependent, sink in the atmosphere for syn-SCI. PMID:25562069

  8. Strain-conserving doping of a pseudomorphic metastable Ge{sub 0.06}Si{sub 0.94} layer on Si(100) by low-dose BF{sub 2}{sup +} implantation

    SciTech Connect

    Im, S.; Eisen, F.; Nicolet, M.; Tanner, M.O.; Wang, K.L.; Theodore, N.D.

    1997-02-01

    A thick (260 nm) pseudomorphic metastable {ital n}-type Ge{sub 0.06}Si{sub 0.94} layer grown by molecular beam epitaxy on an {ital n}-type Si(100) substrate was implanted at room temperature with 70 keV BF{sub 2}{sup +} ions to a dose of 3{times}10{sup 13} cm{sup {minus}2}, so that a p{minus}n junction was formed in the GeSi layers. The samples were subsequently annealed for 10{endash}40 s in a lamp furnace with a nitrogen ambient, or for 30 min in a vacuum-tube furnace. The samples were characterized by 2 MeV {sup 4}He backscattering/channeling spectrometry, double-crystal x-ray diffractometry, transmission electron microscopy, and by Hall effect measurements using the van der Pauw sample geometry. Samples annealed for either 40 s or 30 min at 800{degree}C exhibit full electrical activation of the boron in the GeSi epilayer without losing their strain. The Hall mobility of the holes is lower than that of {ital p}-type Si doped under the same experimental conditions. These results can be attributed to the Hall factor of heavily doped {ital p}-type GeSi films which is less than unity while the Hall factor of a heavily doped {ital p}-type Si or {ital n}-type GeSi film is close to unity. When annealed at 900{degree}C, the strain in both implanted and unimplanted layers is partly relaxed after 30 min, whereas it is not visibly relaxed after 40 s. {copyright} {ital 1997 American Institute of Physics.}

  9. Novel Solution Process for Fabricating Ultra-Thin-Film Absorber Layers in Fe2SiS4 and Fe2GeS4 Photovoltaics

    SciTech Connect

    Orefuwa, Samuel A.; Lai, Cheng-Yu; Dobson, Kevin D.; Ni, Chaoying; Radu, Daniela R.

    2014-05-12

    Fe2SiS4 and Fe2GeS4 crystalline materials posses direct bandgaps of ~1.55 and ~1.4 eV respectively and an absorption coefficient larger than 10^5 cm–1; their theoretical potential as solar photovoltaic absorbers has been demonstrated. However, no solar devices that employ either Fe2SiS4 or Fe2GeS4 have been reported to date. In the presented work, nanoprecursors to Fe2SiS4 and Fe2GeS4 have been fabricated and employed to build ultra-thin-film layers via spray coating and rod coating methods. Temperature-dependent X-Ray diffraction analyses of nanoprecursors coatings show an unprecedented low temperature for forming crystalline Fe2SiS4 and Fe2GeS4. Fabricating of ultra-thin-film photovoltaic devices utilizing Fe2SiS4 and Fe2GeS4 as solar absorber material is presented.

  10. Efficiency enhancement using a Zn1‑ x Ge x -O thin film as an n-type window layer in Cu2O-based heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Minami, Tadatsugu; Nishi, Yuki; Miyata, Toshihiro

    2016-05-01

    Efficiency enhancement was achieved in Cu2O-based heterojunction solar cells fabricated with a zinc–germanium-oxide (Zn1‑ x Ge x -O) thin film as the n-type window layer and a p-type Na-doped Cu2O (Cu2O:Na) sheet prepared by thermally oxidizing Cu sheets. The Ge content (x) dependence of the obtained photovoltaic properties of the heterojunction solar cells is mainly explained by the conduction band discontinuity that results from the electron affinity difference between Zn1‑ x Ge x -O and Cu2O:Na. The optimal value of x in Zn1‑ x Ge x -O thin films prepared by pulsed laser deposition was observed to be 0.62. An efficiency of 8.1% was obtained in a MgF2/Al-doped ZnO/Zn0.38Ge0.62-O/Cu2O:Na heterojunction solar cell.

  11. Characteristics of ZrO2 gate dielectrics on O2- and N2O-plasma treated partially strain-compensated Si0.69Ge0.3C0.01 layers

    NASA Astrophysics Data System (ADS)

    Mahapatra, R.; Maikap, S.; Lee, Je-Hun; Ray, S. K.

    2006-08-01

    The characteristics of ZrO2 gate dielectric along with the interfacial layer on O2- and N2O-plasma treated partially strain-compensated Si0.69Ge0.3C0.01/Si heterostructures have been investigated using spectroscopic and electrical measurements. Time-of-flight secondary ion mass spectroscopy and x-ray photoelectron spectroscopy analyses show the formation of an oxygen or nitrogen rich Zr-germanosilicate interfacial layer between the deposited ZrO2 and SiGeC films. The electrical and charge trapping properties under a constant current stressing have been studied using a metal-oxide-semiconductor structure. The N2O-plasma treated SiGeC film has a higher effective dielectric constant (k ˜14) than that of the O2-plasma treated (k˜12) films. The equivalent areal densities of charge defects, Neq (cm-2), are found to be ˜1.8×1012 and ˜6×1011cm-2 for O2- and N2O-plasma treated films, respectively. Considerably less trapped charges in the N2O-treated gate dielectric stack under constant current stressing make it highly attractive for SiGeC based scaled metal-oxide-semiconductor device applications.

  12. Thermal Stability of Ge/GeSn Nanostructures Grown by MBE on (001) Si/Ge Virtual Wafers

    NASA Astrophysics Data System (ADS)

    Sadofyev, Yu. G.; Martovitsky, V. P.; Klekovkin, A. V.; Saraikin, V. V.; Vasil'evskii, I. S.

    A stack of five metastable 200-nm-thick elastically strained GeSn epitaxial layers separated by 20-nm-thick Ge spacers was grown on (001) Si/Ge virtual substrate by MBE. The molar fraction of Sn in different layers varied from 0.005 to 0.10, increasing with the layer distance from the Ge buffer. The phase separation of the GeSn alloy during postgrowth annealing takes place along with plastic relaxation. The phase separation begins well before the completion of the plastic relaxation process. The degree of phase separation at a given annealing temperature depends strongly on the Sn content in the GeSn alloy. The Sn released from the decomposed GeSn alloy predominantly accumulates as an amorphous layer on the surface of the sample.

  13. Understanding of interface structures and reaction mechanisms induced by Ge or GeO diffusion in Al{sub 2}O{sub 3}/Ge structure

    SciTech Connect

    Shibayama, Shigehisa; JSPS, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo 102-0083 ; Kato, Kimihiko; Sakashita, Mitsuo; Takeuchi, Wakana; Taoka, Noriyuki; Nakatsuka, Osamu; Zaima, Shigeaki

    2013-08-19

    The reaction mechanisms at Al{sub 2}O{sub 3}/Ge interfaces with thermal oxidation through the Al{sub 2}O{sub 3} layer have been investigated. X-ray photoelectron spectroscopy reveals that an Al{sub 6}Ge{sub 2}O{sub 13} layer is formed near the interface, and a GeO{sub 2} layer is formed on the Al{sub 2}O{sub 3} surface, suggesting Ge or GeO diffusion from the Ge surface. It is also clarified that the Al{sub 6}Ge{sub 2}O{sub 13} layer is formed by the different mechanism with a small activation energy of 0.2 eV, compared with the GeO{sub 2} formation limited by oxygen diffusion. Formation of Al-O-Ge bonds due to the AlGeO formation could lead appropriate interface structures with high interface qualities.

  14. Si/Ge intermixing during Ge Stranski–Krastanov growth

    PubMed Central

    Hoummada, Khalid; Ronda, Antoine; Mangelinck, Dominique; Berbezier, Isabelle

    2014-01-01

    Summary The Stranski–Krastanov growth of Ge islands on Si(001) has been widely studied. The morphology changes of Ge islands during growth, from nucleation to hut/island formation and growth, followed by hut-to-dome island transformation and dislocation nucleation of domes, have been well described, even at the atomic scale, using techniques such as scanning tunneling microscopy and transmission electron microscopy. Although it is known that these islands do not consist of pure Ge (due to Si/Ge intermixing), the composition of the Ge islands is not precisely known. In the present work, atom probe tomography was used to study the composition of buried dome islands at the atomic scale, in the three-dimensional space. The core of the island was shown to contain about 55 atom % Ge, while the Ge composition surrounding this core decreases rapidly in all directions in the islands to reach a Ge concentration of about 15 atom %. The Ge distribution in the islands follows a cylindrical symmetry and Ge segregation is observed only in the {113} facets of the islands. The Ge composition of the wetting layer is not homogeneous, varying from 5 to 30 atom %. PMID:25551065

  15. Optical properties of Ge nanostructures embedded into porous alumina matrices

    NASA Astrophysics Data System (ADS)

    Beltiukov, A.; Valeev, R.; Zakirova, R.

    2016-04-01

    The effect of structural properties and the morphology of Ge@PAA nanocomposites synthesized by thermal deposition of Ge on porous anodic alumina matrices with different porosity on the band gap value and PL properties is investigated. PL in the range of 330–520 nm may be due to F and F2 luminescent centers in the surface of nanopores of PAA matrices. The density of electronic states in this interface depends on the temperature of matrices during deposition and on the surface morphology. The role of radiative recombination centers is played by the broken bonds in a thin intermediate Ge x –Al y –O z layer in the Ge/oxide matrix interface. No obvious effect of the crystalline structure of germanium nanoparticles on the PL maximum position is observed, but the spatial localization of electron–hole pairs of small-sized Ge crystallites of which nanoparticles consist leads to an increase in the optical band gap.

  16. PrBa0.5Sr0.5Co2O5+δ layered perovskite cathode for intermediate temperature solid oxide fuel cells

    SciTech Connect

    Ding, Hanping; Xue, Xingjian

    2010-02-06

    Layered perovskite oxides have ordered A-cations localizing oxygen vacancies, and may potentially improve oxygen ion diffusivity and surface exchange coefficient. The A-site-ordered layered perovskite PrBa0.5Sr0.5Co2O5+δ (PBSC) was evaluated as new cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). The material was characterized using electrochemical impedance spectroscopy in a symmetrical cell system (PBSC/Ce0.9Sm0.1O1.9 (SDC)/PBSC), exhibiting excellent performance in the intermediate temperature range of 500–700 °C. An area-specific-resistance (ASR) of 0.23 Ω cm2 was achieved at 650 °C for cathode polarization. The low activation energy (Ea) 124 kJ mol-1 is comparable to that of La0.8Sr0.2CoO3-δ. A laboratory-scaled SDC-based tri-layer cell of Ni-SDC/SDC/PBSC was tested in intermediate temperature conditions of 550 to 700 °C. A maximum power density of 1045 mW cm-2 was achieved at 700 °C. The interfacial polarization resistance is as low as 0.285, 0.145, 0.09 and 0.05 Ω cm2 at 550, 600, 650 and 700 °C, respectively. Layered perovskite PBSC shows promising performance as cathode material for IT-SOFCs.

  17. Ge/GeSn heterostructures grown on Si (100) by molecular-beam epitaxy

    SciTech Connect

    Sadofyev, Yu. G. Martovitsky, V. P.; Bazalevsky, M. A.; Klekovkin, A. V.; Averyanov, D. V.; Vasil’evskii, I. S.

    2015-01-15

    The growth of GeSn layers by molecular-beam epitaxy on Si (100) wafers coated with a germanium buffer layer is investigated. The properties of the fabricated structures are controlled by reflection high-energy electron diffraction, atomic-force microscopy, X-ray diffractometry, Rutherford backscattering, and Raman scattering. It is shown that GeSn layers with thicknesses up to 0.5 μm and Sn molar fractions up to 0.073 manifest no sign of plastic relaxation upon epitaxy. The lattice constant of the GeSn layers within the growth plane is precisely the same as that of Ge. The effect of rapid thermal annealing on the conversion of metastable elastically strained GeSn layers into a plastically relaxed state is examined. Ge/GeSn quantum wells with Sn molar fraction up to 0.11 are obtained.

  18. Characteristics of Sn segregation in Ge/GeSn heterostructures

    NASA Astrophysics Data System (ADS)

    Li, H.; Chang, C.; Chen, T. P.; Cheng, H. H.; Shi, Z. W.; Chen, H.

    2014-10-01

    We report an investigation of Sn segregation in Ge/GeSn heterostructures occurred during the growth by molecular beam epitaxy. The measured Sn profile in the Ge layer shows that: (a) the Sn concentration decreases rapidly near the Ge/GeSn interface, and (b) when moving away from the interface, the Sn concentration reduced with a much slower rate. The 1/e decay lengths of the present system are much longer than those of the conventional group IV system of Ge segregation in the Si overlayer because of the smaller kinetic potential as modeled by a self-limited two-state exchange scheme. The demonstration of the Sn segregation shows the material characteristics of the heterostructure, which are needed for the investigation of its optical properties.

  19. Amorphous Ge bipolar blocking contacts on Ge detectors

    SciTech Connect

    Luke, P.N.; Cork, C.P.; Madden, N.W.; Rossington, C.S.; Wesela, M.F.

    1991-10-01

    Semiconductor nuclear radiation detectors are usually operated in a full depletion mode and blocking contacts are required to maintain low leakage currents and high electric fields for charge collection. Blocking contacts on Ge detectors typically consist of n-type contacts formed by lithium diffusion and p-type contacts formed by boron ion implantation. Electrical contacts formed using sputtered amorphous Ge (a-Ge) films on high-purity Ge crystals were found to exhibit good blocking behavior in both polarities with low leakage currents. The a-Ge contacts have thin dead layers associated with them and can be used in place of lithium-diffused, ion-implanted or Schottky barrier contacts on Ge radiation detectors. Multi-electrode detectors can be fabricated with very simple processing steps using these contacts. 12 refs.

  20. Direct gap Ge1-ySny alloys: Fabrication and design of mid-IR photodiodes

    NASA Astrophysics Data System (ADS)

    Senaratne, C. L.; Wallace, P. M.; Gallagher, J. D.; Sims, P. E.; Kouvetakis, J.; Menéndez, J.

    2016-07-01

    Chemical vapor deposition methods were developed, using stoichiometric reactions of specialty Ge3H8 and SnD4 hydrides, to fabricate Ge1-ySny photodiodes with very high Sn concentrations in the 12%-16% range. A unique aspect of this approach is the compatible reactivity of the compounds at ultra-low temperatures, allowing efficient control and systematic tuning of the alloy composition beyond the direct gap threshold. This crucial property allows the formation of thick supersaturated layers with device-quality material properties. Diodes with composition up to 14% Sn were initially produced on Ge-buffered Si(100) featuring previously optimized n-Ge/i-Ge1-ySny/p-Ge1-zSnz type structures with a single defected interface. The devices exhibited sizable electroluminescence and good rectifying behavior as evidenced by the low dark currents in the I-V measurements. The formation of working diodes with higher Sn content up to 16% Sn was implemented by using more advanced n-Ge1-xSnx/i-Ge1-ySny/p-Ge1-zSnz architectures incorporating Ge1-xSnx intermediate layers (x ˜ 12% Sn) that served to mitigate the lattice mismatch with the Ge platform. This yielded fully coherent diode interfaces devoid of strain relaxation defects. The electrical measurements in this case revealed a sharp increase in reverse-bias dark currents by almost two orders of magnitude, in spite of the comparable crystallinity of the active layers. This observation is attributed to the enhancement of band-to-band tunneling when all the diode layers consist of direct gap materials and thus has implications for the design of light emitting diodes and lasers operating at desirable mid-IR wavelengths. Possible ways to engineer these diode characteristics and improve carrier confinement involve the incorporation of new barrier materials, in particular, ternary Ge1-x-ySixSny alloys. The possibility of achieving type-I structures using binary and ternary alloy combinations is discussed in detail, taking into account

  1. Robustness of Sn precipitation during thermal oxidation of Ge1-xSnx on Ge(001)

    NASA Astrophysics Data System (ADS)

    Kato, Kimihiko; Asano, Takanori; Taoka, Noriyuki; Sakashita, Mitsuo; Takeuchi, Wakana; Nakatsuka, Osamu; Zaima, Shigeaki

    2014-08-01

    The thermal robustness of Sn segregation and precipitation in epitaxial Ge1-xSnx layers on Ge(001) substrates with a Sn content greater than the equilibrium solubility limit has been investigated for applications of Ge1-xSnx in high-performance metal-oxide-semiconductor field-effect transistors (MOSFETs). Sn segregation and precipitation occur on the Ge1-xSnx surface after epitaxial growth of the Ge1-xSnx layer at 150 °C. After the thermal oxidation of the Ge1-xSnx layer below 500 °C, there are no significant decreases in the average Sn content in the Ge1-xSnx layer and no additional Sn segregation on the Ge1-xSnx surface. However, Sn precipitation occurs at the Ge1-xSnx surface during the thermal oxidation of the Ge1-xSnx layer with an average Sn content as high as 8.7% at 600 °C, causing a decrease in the Sn content in the Ge1-xSnx layer. The Sn content in the Ge1-xSnx oxide is 1.5 times greater than that observed near the Ge1-xSnx surface for the sample with a Sn content of 8.7% after the thermal oxidation at 400 to 500 °C. The capacitance-voltage characteristics of the Al/Al2O3/Ge1-xSnx/Ge MOS capacitors treated with thermal oxidation at 400 °C indicate that the slow state density increases with the Sn content. Meanwhile, the small interface state density could be achieved via thermal oxidation of the Ge1-xSnx layer, even with a high Sn content.

  2. Screening of remote charge scattering sites from the oxide/silicon interface of strained Si two-dimensional electron gases by an intermediate tunable shielding electron layer

    SciTech Connect

    Huang, Chiao-Ti Li, Jiun-Yun; Chou, Kevin S.; Sturm, James C.

    2014-06-16

    We report the strong screening of the remote charge scattering sites from the oxide/semiconductor interface of buried enhancement-mode undoped Si two-dimensional electron gases (2DEGs), by introducing a tunable shielding electron layer between the 2DEG and the scattering sites. When a high density of electrons in the buried silicon quantum well exists, the tunneling of electrons from the buried layer to the surface quantum well can lead to the formation of a nearly immobile surface electron layer. The screening of the remote charges at the interface by this newly formed surface electron layer results in an increase in the mobility of the buried 2DEG. Furthermore, a significant decrease in the minimum mobile electron density of the 2DEG occurs as well. Together, these effects can reduce the increased detrimental effect of interface charges as the setback distance for the 2DEG to the surface is reduced for improved lateral confinement by top gates.

  3. Highly effective strain-induced band-engineering of (111) oriented, direct-gap GeSn crystallized on amorphous SiO2 layers

    NASA Astrophysics Data System (ADS)

    Li, Haofeng; Wang, Xiaoxin; Liu, Jifeng

    2016-03-01

    We demonstrate highly effective strain-induced band-engineering of (111) oriented direct-gap Ge1-xSnx thin films (0.074 < x < 0.085) crystallized on amorphous SiO2 towards 3D photonic integration. Due to a much smaller Poisson's ratio for (111) vs. (100) orientation, 0.44% thermally induced biaxial tensile strain reduces the direct-gap by 0.125 eV towards enhanced direct-gap semiconductor properties, twice as effective as the tensile strain in Ge(100) films. Correspondingly, the optical response is extended to λ = 2.8 μm. A dilatational deformation potential of a = -12.8 ± 0.8 eV is derived. These GeSn films also demonstrate high thermal stability, offering both excellent direct-gap optoelectronic properties and fabrication/operation robustness for integrated photonics.

  4. Segmented SiGe-PbTe couples

    NASA Technical Reports Server (NTRS)

    Eggers, P. E.; Mueller, J. J.

    1969-01-01

    New design of segmented couples incorporates an intermediate junction contacted by pressure, and eliminates transition members that bond materials differing in thermal expansion. Development of a reproducible and reliable intermediate junction between PbTe and SiGe will be applicable to direct conversion of energy.

  5. Enhancement of magnetoresistance by inserting thin NiAl layers at the interfaces in Co2FeGa0.5Ge0.5/Ag/Co2FeGa0.5Ge0.5 current-perpendicular-to-plane pseudo spin valves

    NASA Astrophysics Data System (ADS)

    Jung, J. W.; Sakuraba, Y.; Sasaki, T. T.; Miura, Y.; Hono, K.

    2016-03-01

    We have investigated the effects of insertion of a thin NiAl layer (≤0.63 nm) into a Co2FeGa0.5Ge0.5 (CFGG)/Ag interface on the magnetoresistive properties in CFGG/Ag/CFGG current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo spin valves (PSVs). First-principles calculations of ballistic transmittance clarified that the interfacial band matching at the (001)-oriented NiAl/CFGG interface is better than that at the (001)-Ag/CFGG interface. The insertion of 0.21-nm-thick NiAl layers at the Co2FeGa0.5Ge0.5/Ag interfaces effectively improved the magnetoresistance (MR) output; the observed average and the highest MR ratio (ΔRA) are 62% (25 mΩ μm2) and 77% (31 mΩ μm2) at room temperature, respectively, which are much higher than those without NiAl insertion. Microstructural analysis using scanning transmission electron microscopy confirmed the existence of thin NiAl layers at the Ag interfaces with only modest interdiffusion even after annealing at 550 °C. The improvement of the interfacial spin-dependent scattering by very thin NiAl insertion can be a predominant reason for the enhancement of the MR output.

  6. Data requirements for intermediate energy nuclear applications

    SciTech Connect

    Pearlstein, S.

    1990-01-01

    Several applications that include spallation neutron sources, space radiation effects, biomedical isotope production, accelerator shielding and radiation therapy make use of intermediate energy nuclear data extending to several GeV. The overlapping data needs of these applications are discussed in terms of what projectiles, targets and reactions are of interest. Included is a discussion of what is generally known about these data and what is needed to facilitate their use in intermediate energy applications. 40 refs., 2 figs., 2 tabs.

  7. Selective epitaxial growth of Ge(1 1 0) in trenches using the aspect ratio trapping technique

    NASA Astrophysics Data System (ADS)

    Destefanis, V.; Hartmann, J. M.; Baud, L.; Delaye, V.; Billon, T.

    2010-03-01

    The aim of this study was to assess the efficiency of aspect ratio trapping in improving the crystalline quality of relaxed Ge(1 1 0) layers selectively grown in trenches surrounded by SiO 2. The 400 °C growth of a few hundreds of nanometers thick Ge layers has first been studied on blanket Si(1 1 0) surfaces then in recessed areas of Si(1 1 0) patterned wafers. The influence of 1 min H 2 anneals (in-between 600 and 850 °C) on the surface morphology, crystalline quality and strain state of blanket Ge(1 1 0) layers has notably been quantified. Intermediate annealing temperatures (750 °C) have improved the crystalline quality and increased the macroscopic strain relaxation of those layers, without too high a surface roughening. (1 1 0) Si windows (surrounded by shallow trench isolation) of patterned wafers have then been recessed by ≈300 nm using gaseous HCl, with a definite faceting and a slight roughening of the resulting cavities. Epitaxial lateral overgrowth of Ge has then been implemented in those trenches, followed by 1' H 2 bakes at 750 °C. Chemical mechanical polishing has been used afterwards to get rid of the several hundreds of nm thick Ge layer overflowing on the SiO 2 areas (very reduced dishing and flat Ge(1 1 0) surfaces obtained in the end). The efficiency of aspect ratio trapping in reducing the defect density in those Ge(1 1 0) layers is not obvious. Indeed, some trapping of inclined defects in the SiO 2 sidewalls of narrow Ge(1 1 0) patterns (˜80 nm long) has been evidenced. However, the theoretically unexpected appearance of defects at 90° to the surface (i.e. normal to (1 1 0)) that were consequently not trapped was detrimental to defect density reduction. Those 90° defects may have arisen from interactions of inclined defects with one another. The reduction of the high defect density in relaxed (1 1 0) layers is thus still challenging and requires further investigations.

  8. Room-temperature electroluminescence from Ge/Ge1-xSnx/Ge diodes on Si substrates

    NASA Astrophysics Data System (ADS)

    Du, Wei; Zhou, Yiyin; Ghetmiri, Seyed A.; Mosleh, Aboozar; Conley, Benjamin R.; Nazzal, Amjad; Soref, Richard A.; Sun, Greg; Tolle, John; Margetis, Joe; Naseem, Hameed A.; Yu, Shui-Qing

    2014-06-01

    Double heterostructure Ge/Ge1-xSnx/Ge light-emitting diodes (LEDs) with 6% and 8% Sn were grown on Si substrates using chemical vapor deposition. The electroluminescence emission spectra from the fabricated LEDs were investigated at room-temperature under different injection levels. The observed emission peaks at 0.645 eV and 0.601 eV are attributed to the direct bandgap transition of the Ge0.94Sn0.06 and Ge0.92Sn0.08 layers, respectively. Moreover, the integrated emission intensity increases as the Sn composition increases under the same injection condition.

  9. Enhancement of thermal stability and water resistance in yttrium-doped GeO{sub 2}/Ge gate stack

    SciTech Connect

    Lu, Cimang Hyun Lee, Choong; Zhang, Wenfeng; Nishimura, Tomonori; Nagashio, Kosuke; Toriumi, Akira

    2014-03-03

    We have systematically investigated the material and electrical properties of yttrium-doped GeO{sub 2} (Y-GeO{sub 2}) on Germanium (Ge). A significant improvement of both thermal stability and water resistance were demonstrated by Y-GeO{sub 2}/Ge stack, compared to that of pure GeO{sub 2}/Ge stack. The excellent electrical properties of Y-GeO{sub 2}/Ge stacks with low D{sub it} were presented as well as enhancement of dielectric constant in Y-GeO{sub 2} layer, which is beneficial for further equivalent oxide thickness scaling of Ge gate stack. The improvement of thermal stability and water resistance are discussed both in terms of the Gibbs free energy lowering and network modification of Y-GeO{sub 2}.

  10. Mn segregation in Ge/Mn5Ge3 heterostructures: The role of surface carbon adsorption

    NASA Astrophysics Data System (ADS)

    Dau, Minh-Tuan; Thanh, Vinh Le; Le, Thi-Giang; Spiesser, Aurélie; Petit, Mathieu; Michez, Lisa A.; Daineche, Rachid

    2011-10-01

    Mn5Ge3 compound, with its room-temperature ferromagnetism and possibility to epitaxially grow on Ge, acts as a potential spin injector into group-IV semiconductors. However, the realization of Ge/Mn5Ge3 multilayers is highly hampered by Mn segregation toward the Ge growing surface. Here, we show that adsorption of some monolayers of carbon on top of the Mn5Ge3 surface prior to Ge deposition allows to greatly reduce Mn segregation. In addition, a fraction of deposited carbon can diffuse down to the underneath Mn5Ge3 layers, resulting in an enhancement of the Curie temperature up to ˜360 K. The obtained results will be discussed in terms of the formation of a diffusion barrier by filling interstitial sites of Mn5Ge3 by carbon.

  11. Intermediate-Scale Experimental and Numerical Study of Multiphase CO2 Attenuation in Layered Shallow Aquifers During Leakage from Geologic Sequestration Site

    NASA Astrophysics Data System (ADS)

    Plampin, M. R.; Pawar, R.; Porter, M. L.; Illangasekare, T. H.

    2015-12-01

    In order to effectively predict and mitigate the potential risks from leakage of stored CO2, we must first understand the physicochemical processes that CO2 undergoes during migration through shallow aquifers, including dissolved phase advection and dispersion as well as gas phase exsolution, multiphase flow, and dissolution. Since field sites are inherently large-scale, heterogeneous, 3-D systems, large-scale experimental data is important to validate numerical models and to make confident predictions regarding CO2 migration. A large, highly instrumented, two-dimensional tank was built and packed with porous media to represent a portion of a layered shallow aquifer. Flow of water across the tank was established by applying a small difference in head between the two ends. A separate stream of water was then saturated with dissolved CO2 and injected into the bottom of the tank near the upstream end. Various saturation sensors measured the spatiotemporal pattern of gas phase evolution in the tank, while an external sensor and an Ion Chromatograph were used to monitor the dissolved CO2 concentrations at various locations in the system. The top of the tank was baffled into four sealed compartments, each of which was connected to a gas flow meter to monitor the spatiotemporal pattern of gas phase CO2 release to the atmosphere. Numerical simulations were also performed to better understand the fundamental physics that drove the observed CO2 evolution processes, and to help validate a widely used code using the experimental data. The simulations were performed with the Finite Element Heat and Mass Transfer (FEHM) software that was developed at Los Alamos National Laboratory. The model domain, porous media properties, and initial conditions were set up to match those of the experiment, and the boundary conditions were adjusted to investigate the mass transfer between the dissolved and gaseous phases of CO2 that developed within the system. Results from both the experiments

  12. Centrality and pseudorapidity dependence of charged hadron production at intermediate p{sub t} in Au+Au collisions at {radical}s{sub NN} = 130 GeV

    SciTech Connect

    Adams, J.; Aggarwal, M.M.; Ahammed, Z.; Amonett, J.; Anderson, B.D.; Arkhipkin, D.; Averichev, G.S.; Bai, Y.; Balewski, J.; Barannikova, O.; Barnby, L.S.; Baudot, J.; Bekele, S.; Belaga, V.V.; Bellwied, R.; Berger, J.; Bezverkhny, B.I.; Bharadwaj, S.; Bhatia, V.S.; Bichsel, H.; Billmeier, A.; Bland, L.C.; Blyth, C.O.; Bonner, B.E.; Botje, M.; Boucham, A.; Brandin, A.; Bravar, A.; Bystersky, M.; Cadman, R.V.; Cai, X.Z.; Caines, H.; Calderon de la Barca Sanchez, M.; Carroll, J.; Castillo, J.; Cebra, D.; Chaloupka, P.; Chattopadhyay, S.; Chen, H.F.; Chen, Y.; Cheng, J.; Cherney, M.; Chikanian, A.; Christie, W.; Coffin, J.P.; Cormier, T.M.; Cramer, J.G.; Crawford, H.J.; Das, D.; Das, S.; de Moura, M.M.; Derevschikov, A.A.; Didenko, L.; Dietel, T.; Dong, W.J.; Dong, X.; Draper, J.E.; Du, F.; Dubey, A.K.; Dunin, V.B.; Dunlop, J.C.; Dutta Mazumdar, M.R.; Eckardt, V.; Edwards, W.R.; Efimov, L.G.; Emelianov, V.; Engelage, J.; Eppley, G.; Erazmus, B.; Estienne, M.; Fachini, P.; Faivre, J.; Fatemi, R.; Fedorisin, J.; Filimonov, K.; Filip, P.; Finch, E.; Fine, V.; Fisyak, Y.; Foley, K.J.; Fomenko, K.; Fu, J.; Gagliardi, C.A.; Gans, J.; Ganti, M.S.; Gaudichet, L.; Geurts, F.; Ghazikhanian, V.; Ghosh, P.; Gonzalez, J.E.; Grachov, O.; Grebenyuk, O.; Grosnick, D.; Guertin, S.M.; Gupta, A.; Gutierrez, T.D.; Hallman, T.J.; Hamed, A.; Hardtke, D.; Harris, J.W.; Heinz, M.; Henry, T.W.; Heppelmann, S.; Hippolyte, B.; Hirsch, A.; Hjort, E.; Hoffmann, G.W.; Huang, H.Z.; Huang, S.L.; Hughes, E.W.; Humanic, T.J.; Igo, G.; Ishihara, A.; Jacobs, P.; Jacobs, W.W.; Janik, M.; Jiang, H.; Jones, P.G.; Judd, E.G.; Kabana, S.; Kang, K.; Kaplan, M.; Keane, D.; Khodyrev, V.Yu; Kiryluk, J.; Kisiel, A.; Kislov, E.M.; Klay, J.; Klein, S.R.; Klyachko, A.; Koetke, D.D.; Kollegger, T.; Kopytine, M.; Kotchenda, L.; Kramer, M.; Kravtsov, P.; Kravtsov, V.I.; Krueger, K.; Kuhn, C.; Kulikov, A.I.; Kumar, A.; Kunz, C.L.; Kutuev, R.Kh.; Kuznetsov, A.A.; Lamont, M.A.C.; et al.

    2004-04-15

    We present STAR measurements of charged hadron production as a function of centrality in Au + Au collisions at {radical}s{sub NN} = 130 GeV. The measurements cover a phase space region of 0.2 < p{sub T} < 6.0 GeV/c in transverse momentum and 11 < {eta} < 1 in pseudorapidity. Inclusive transverse momentum distributions of charged hadrons in the pseudorapidity region 0.5 < |{eta}| < 1 are reported and compared to our previously published results for |{eta}| < 0.5. No significant difference is seen for inclusive p{sub T} distributions of charged hadrons in these two pseudorapidity bins. We measured dN/d{eta} distributions and truncated mean p{sub T} in a region of p{sub T} > P{sub T}{sup cut}, and studied the results in the framework of participant and binary scaling. No clear evidence is observed for participant scaling of charged hadron yield in the measured pT region. The relative importance of hard scattering process is investigated through binary scaling fraction of particle production.

  13. Centrality and pseudorapidity dependence of charged hadron production at intermediate p{sub T} in Au+Au collisions at {radical}s{sub NN} = 130 GeV

    SciTech Connect

    Adams, J.; Aggarwal, M.M.; Ahammed, Z.; Amonett, J.; Anderson, B.D.; Arkhipkin, D.; Averichev, G.S.; Bai, Y.; Balewski, J.; Barannikova, O.; Barnby, L.S.; Baudot, J.; Bekele, S.; Belaga, V.V.; Bellwied, R.; Berger, J.; Bezverkhny, B.I.; Bharadwaj, S.; Bhatia, V.S.; Bichsel, H.; Billmeier, A.; Bland, L.C.; Blyth, C.O.; Bonner, B.E.; Botje, M.; Boucham, A.; Brandin, A.; Bravar, A.; Bystersky, M.; Cadman, R.V.; Cai, X.Z.; Caines, H.; Calderon de la Barca Sanchez, M.; Carroll, J.; Castillo, J.; Cebra, D.; Chaloupka, P.; Chattopadhyay, S.; Chen, H.F.; Chen, Y.; Cheng, J.; Cherney, M.; Chikanian, A.; Christie, W.; Coffin, J.P.; Cormier, T.M.; Cramer, J.G.; Crawford, H.J.; Das, D.; Das, S.; de Moura, M.M.; Derevschikov, A.A.; Didenko, L.; Dietel, T.; Dong, W.J.; Dong, X.; Draper, J.E.; Du, F.; Dubey, A.K.; Dunin, V.B.; Dunlop, J.C.; Dutta Mazumdar, M.R.; Eckardt, V.; Edwards, W.R.; Efimov, L.G.; Emelianov, V.; Engelage, J.; Eppley, G.; Erazmus, B.; Estienne, M.; Fachini, P.; Faivre, J.; Fatemi, R.; Fedorisin, J.; Filimonov, K.; Filip, P.; Finch, E.; Fine, V.; Fisyak, Y.; Foley, K.J.; Fomenko, K.; Fu, J.; Gagliardi, C.A.; Gans, J.; Ganti, M.S.; Gaudichet, L.; Geurts, F.; Ghazikhanian, V.; Ghosh, P.; Gonzalez, J.E.; Grachov, O.; Grebenyuk, O.; Grosnick, D.; Guertin, S.M.; Gupta, A.; Gutierrez, T.D.; Hallman, T.J.; Hamed, A.; Hardtke, D.; Harris, J.W.; Heinz, M.; Henry, T.W.; Heppelmann, S.; Hippolyte, B.; Hirsch, A.; Hjort, E.; Hoffmann, G.W.; Huang, H.Z.; Huang, S.L.; Hughes, E.W.; Humanic, T.J.; Igo, G.; Ishihara, A.; Jacobs, P.; Jacobs, W.W.; Janik, M.; Jiang, H.; Jones, P.G.; Judd, E.G.; Kabana, S.; Kang, K.; Kaplan, M.; Keane, D.; Khodyrev, V.Yu; Kiryluk, J.; Kisiel, A.; Kislov, E.M.; Klay, J.; Klein, S.R.; Klyachko, A.; Koetke, D.D.; Kollegger, T.; Kopytine, M.; Kotchenda, L.; Kramer, M.; Kravtsov, P.; Kravtsov, V.I.; Krueger, K.; Kuhn, C.; Kulikov, A.I.; Kumar, A.; Kunz, C.L.; Kutuev, R.Kh.; Kuznetsov, A.A.; Lamont, M.A.C.; et al.

    2004-04-15

    We present STAR measurements of charged hadron production as a function of centrality in Au + Au collisions at {radical}s{sub NN} = 130 GeV. The measurements cover a phase space region of 0.2 < p{sub T} < 6.0 GeV/c in transverse momentum and -1 < {eta} < 1 in pseudorapidity. Inclusive transverse momentum distributions of charged hadrons in the pseudorapidity region 0.5 < |{eta}| < 1 are reported and compared to our previously published results for |{eta}| < 0.5. No significant difference is seen for inclusive p{sub T} distributions of charged hadrons in these two pseudorapidity bins. We measured dN/d{eta} distributions and truncated mean p{sub T} in a region of p{sub T} > p{sub T}{sup cut}, and studied the results in the framework of participant and binary scaling. No clear evidence is observed for participant scaling of charged hadron yield in the measured p{sub T} region. The relative importance of hard scattering process is investigated through binary scaling fraction of particle production.

  14. Density functional theory study of adsorption and dissociation of HfCl4 and H2O on Ge /Si(100)-(2×1): Initial stage of atomic layer deposition of HfO2 on SiGe surface

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Lu, Hong-Liang; Zhang, David Wei; Xu, Min; Ren, Jie; Zhang, Jian-Yun; Wang, Ji-Tao; Wang, Li-Kang

    2005-04-01

    We have investigated adsorption and dissociation of water and HfCl4 on Ge /Si(100)-(2×1) surface with density functional theory. The Si-Ge heterodimer and Ge-Ge homodimer are employed to represent the Si1-xGex surface. The activation energy for adsorption of water on Ge-Ge homodimer is much higher than that on Si-Ge heterodimer. No net activation barrier exists during the adsorption of HfCl4 on both SiGe surface dimers. The differences in the potential energy surface between reactions on Si-Ge and Ge-Ge dimers are due to different bond strengths. It should also be noticed that the activation energy for HfCl4 is quite flat, thus HfCl4 adsorbs and dissociates on Ge /Si(100)-(2×1) easily.

  15. Ohmic contact formation of metal/amorphous-Ge/n-Ge junctions with an anomalous modulation of Schottky barrier height

    SciTech Connect

    Liu, Hanhui; Wang, Peng; Qi, Dongfeng; Li, Xin; Han, Xiang; Wang, Chen; Chen, Songyan Li, Cheng; Huang, Wei

    2014-11-10

    The modulation of Schottky barrier height of metal/Ge inserting an amorphous Ge layer has been demonstrated. It is interested that the Schottky barrier height of Al/amorphous-Ge/n-Ge junctions is oscillated with increase of the a-Ge thickness from 0 to 10 nm, and when the thickness reaches above 10 nm, the Al/amorphous-Ge/n-Ge shows ohmic characteristics. Electron hopping through localized states of a-Ge layer, the alleviation of metal induced gap states, as well as the termination of dangling bonds at the amorphous-Ge/n-Ge interface are proposed to explain the anomalous modulation of Schottky barrier height.

  16. The revolution in SiGe: impact on device electronics

    NASA Astrophysics Data System (ADS)

    Harame, D. L.; Koester, S. J.; Freeman, G.; Cottrel, P.; Rim, K.; Dehlinger, G.; Ahlgren, D.; Dunn, J. S.; Greenberg, D.; Joseph, A.; Anderson, F.; Rieh, J.-S.; Onge, S. A. S. T.; Coolbaugh, D.; Ramachandran, V.; Cressler, J. D.; Subbanna, S.

    2004-03-01

    SiGe is having a major impact in device electronics. The most mature application is the SiGe BiCMOS technology which is in production throughout the world. The areas of most rapid growth are in CMOS where SiGe is being considered for a wide variety of elements including raised S/D, poly-SiGe Gates, in buffer layers to create a tensile strained Si layer, and as the conducting channel in MODFETs.

  17. 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.

  18. Investigation of GaInAs strain reducing layer combined with InAs quantum dots embedded in Ga(In)As subcell of triple junction GaInP/Ga(In)As/Ge solar cell.

    PubMed

    Li, Senlin; Bi, Jingfeng; Li, Mingyang; Yang, Meijia; Song, Minghui; Liu, Guanzhou; Xiong, Weiping; Li, Yang; Fang, Yanyan; Chen, Changqing; Lin, Guijiang; Chen, Wenjun; Wu, Chaoyu; Wang, Duxiang

    2015-01-01

    The InAs/GaAs quantum dots structure embedded in GaInP/Ga(In)As/Ge triple junction solar cell with and without Ga0.90In0.10As strain reducing layer was investigated. Conversion efficiency of 33.91% at 1,000 suns AM 1.5D with Ga0.90In0.10As strain reducing layer was demonstrated. A 1.19% improvement of the conversion efficiency was obtained via inserting the Ga0.90In0.10As strain reducing layer. The main contribution of this improvement was from the increase of the short-circuit current, which is caused by the reduction of the Shockley-Read-Hall recombination centers. Consequently, there was a decrease in open circuit voltage due to the lower thermal activation energy of confined carriers in Ga0.9In0.1As than GaAs and a reduction in the effective band gap of quantum dots. PMID:25852406

  19. The effect of the interlayer element on the exfoliation of layered Mo2AC (A = Al, Si, P, Ga, Ge, As or In) MAX phases into two-dimensional Mo2C nanosheets

    NASA Astrophysics Data System (ADS)

    Khazaei, Mohammad; Arai, Masao; Sasaki, Taizo; Estili, Mehdi; Sakka, Yoshio

    2014-02-01

    The experimental exfoliation of layered, ternary transition-metal carbide and nitride compounds, known as MAX phases, into two-dimensional (2D) nanosheets, is a great development in the synthesis of novel low-dimensional inorganic systems. Among the MAX phases, Mo-containing ones might be considered as the source for obtaining Mo2C nanosheets with potentially unique properties, if they could be exfoliated. Here, by using a set of first-principles calculations, we discuss the effect of the interlayer ‘A’ element on the exfoliation of Mo2AC (A = Al, Si, P, Ga, Ge, As or In) MAX phases into the 2D Mo2C nanosheets. Based on the calculated exfoliation energies and the elastic constants, we propose that Mo2InC with the lowest exfoliation energy and the highest elastic constant anisotropy between C11 and C33 might be a suitable compound for exfoliation into 2D Mo2C nanosheets.

  20. Enhanced Si-Ge interdiffusion in high phosphorus-doped germanium on silicon

    NASA Astrophysics Data System (ADS)

    Cai, Feiyang; Dong, Yuanwei; Tan, Yew Heng; Tan, Chuan Seng; (Maggie Xia, Guangrui

    2015-10-01

    Si-Ge interdiffusion with different P doping configurations was investigated. Significant interdiffusion happened when the Ge layers were doped with P in high 1018 cm-3 range, which resulted in a SiGe alloy region thicker than 150 nm after defect annealing cycles. With high P doped Ge, Si-Ge interdiffusivity is enhanced by 10-20 times in the xGe > 0.7 region compared with the control sample without P doping. We attribute this phenomenon to the much faster P transport towards the Ge seeding layers from the Ge side during the Ge layer growth, which increases the negatively charged vacancy concentrations and thus the interdiffusivity due to the Fermi effect in Si-Ge interdiffusion. This work is relevant to Ge-on-Si type device design, especially Ge-on-Si lasers.

  1. Investigation on the dominant key to achieve superior Ge surface passivation by GeOx based on the ozone oxidation

    NASA Astrophysics Data System (ADS)

    Wang, Xiaolei; Xiang, Jinjuan; Wang, Wenwu; Xiong, Yuhua; Zhang, Jing; Zhao, Chao

    2015-12-01

    The dominant key to achieve superior Ge surface passivation by GeOx interfacial layer is investigated based on ozone oxidation. The interface state density (Dit) measured from low temperature conduction method is found to decrease with increasing the GeOx thickness (0.26-1.06 nm). The X-ray photoelectron spectroscopy (XPS) is employed to demonstrate the interfacial structure of GeOx/Ge with different GeOx thicknesses. And the XPS results show that Ge3+ oxide component is responsible to the decrease of the Dit due to the effective passivation of Ge dangling bonds. Therefore, the formation of Ge3+ component is the dominant key to achieve low Dit for Ge gate stacks. Our work confirms that the same physical mechanism determines the Ge surface passivation by the GeOx regardless of the oxidation methods to grow the GeOx interfacial layer. As a result, to explore a growth process that can realize sufficient Ge3+ component in the GeOx interlayer as thin as possible is important to achieve both equivalent oxide thickness scaling and superior interfacial property simultaneously. This conclusion is helpful to engineer the optimization of the Ge gate stacks.

  2. Vertically Aligned Ge Nanowires on Flexible Plastic Films Synthesized by (111)-Oriented Ge Seeded Vapor-Liquid-Solid Growth.

    PubMed

    Toko, Kaoru; Nakata, Mitsuki; Jevasuwan, Wipakorn; Fukata, Naoki; Suemasu, Takashi

    2015-08-19

    Transfer-free fabrication of vertical Ge nanowires (NWs) on a plastic substrate is demonstrated using a vapor-liquid-solid (VLS) method. The crystal quality of Ge seed layers (50 nm thickness) prepared on plastic substrates strongly influenced the VLS growth morphology, i.e., the density, uniformity, and crystal quality of Ge NWs. The metal-induced layer exchange yielded a (111)-oriented Ge seed layer at 325 °C, which allowed for the VLS growth of vertically aligned Ge NWs. The Ge NW array had almost the same quality as that formed on a bulk Ge(111) substrate. Transmission electron microscopy demonstrated that the Ge NWs were defect-free single crystals. The present investigation paves the way for advanced electronic optical devices integrated on a low-cost flexible substrate. PMID:26230716

  3. Electronic and Thermoelectric Properties of Layered Sn- and Pb-Doped Ge2Sb2Te5 Alloys Using First Principle Calculations

    NASA Astrophysics Data System (ADS)

    Singh, Janpreet; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.

    2016-06-01

    A computational study on stable hexagonal phase of undoped, and Sn- and Pb-doped Ge2Sb2Te5 (GST) phase change materials has been carried out. The electronic structure, lattice dynamics and thermoelectric properties of doped GST have been extensively investigated using ab initio methods with virtual crystal approximation. The hexagonal symmetry of the GST is maintained with the addition of Sn and Pb dopants. The lattice parameters and atomic volume of the Sn-doped GST structure is larger than that of the undoped GST. Electronic band structure calculations show that there is an increase in band gap with the increase in the concentration of Sn (≤4.4 at.%). However, with the addition of a very small amount of Pb, there is a continuous decrease in lattice parameters and band gap values. The calculated energy band structure is then used in combination with the Boltzmann transport equation to calculate the thermoelectric parameters of GST and Sn- and Pb-doped materials. Seebeck coefficient ( S), electronic thermal conductivity ( κ e) and the thermoelectric figure-of-merit ( ZT) have been calculated with the help of BoltzTraP code. It was found that the thermoelectric properties of GST are enhanced with the addition of Sn.

  4. EXAFS Studies of Amorphous MoGe

    NASA Astrophysics Data System (ADS)

    Boyce, J. B.; Carter, W. L.; Geballe, T. H.; Claeson, T.

    1982-06-01

    Extended X-ray Absorption Fine Structure of amorphous and crystalline Mo-Ge samples sputter deposited on glass or kapton substrates was studied. Small local distortions were found in a substitutional b.c.c. Mo rich sample. A coordination in the range 5-7 and Ge-Mo distance of 2.65 A were estimated for an amorphous, intermediate composition Mo-Ge sample. The lack of superconductivity of some samples deposited on kapton was correlated to the presence of oxygen in the material.

  5. High Quality GaAs Growth by MBE on Si Using GeSi Buffers and Prospects for Space Photovoltaics

    NASA Technical Reports Server (NTRS)

    Carlin, J. A.; Ringel, S. A.; Fitzgerald, E. A.; Bulsara, M.

    2005-01-01

    III-V solar cells on Si substrates are of interest for space photovoltaics since this would combine high performance space cells with a strong, lightweight and inexpensive substrate. However, the primary obstacles blocking III-V/Si cells from achieving high performance to date have been fundamental materials incompatabilities, namely the 4% lattice mismatch between GaAs and Si, and the large mismatch in thermal expansion coefficient. In this paper, we report on the molecular beam epitaxial (MBE) growth and properties of GaAs layers and single junction GaAs cells on Si wafers which utilize compositionally graded GeSi Intermediate buffers grown by ultra-high vacuum chemical vapor deposition (UHVCVD) to mitigate the large lattice mismatch between GaAs and Si. Ga As cell structures were found to incorporate a threading dislocation density of 0.9-1.5 x 10 (exp 6) per square centimeter, identical to the underlying relaxed Ge cap of the graded buffer, via a combination of transmission electron microscopy, electron beam induced current, and etch pit density measurements. AlGaAs/GaAs double heterostructures wre grown on the GeSi/Si substrates for time-resolved photoluminescence measurements, which revealed a bulk GaAs minority carrier lifetime in excess of 10 ns, the highest lifetime ever reported for GaAs on Si. A series of growth were performed to ass3ss the impact of a GaAs buffer to a thickness of only 0.1 micrometer. Secondary ion mass spectroscopy studies revealed that there is negligible cross diffusion of Ga, As and Ge at he III-V/Ge interface, identical to our earlier findings for GaAs grown on Ge wafers using MBE. This indicates that there is no need for a buffer to "bury" regions of high autodopjing,a nd that either pn or np configuration cells are easily accomodated by these substrates. Preliminary diodes and single junction Al Ga As heteroface cells were grown and fabricated on the Ge/GeSi/Si substrates for the first time. Diodes fabricated on GaAs, Ge and Ge/Ge

  6. Comparative investigation of InGaP/InGaAs/Ge triple-junction solar cells using different Te-doped InGaP layers in tunnel junctions

    NASA Astrophysics Data System (ADS)

    Jung, Sang Hyun; Kim, Chang Zoo; Kim, Youngjo; Jun, Dong Hwan; Kang, Ho Kwan; Kim, Hogyoung

    2016-03-01

    Heavily tellurium (Te)-doped InGaP layers in tunnel junctions (TJs) grown by using metalorganic chemical vapor deposition (MOCVD) were investigated to improve the device performance of InGaP/InGaAs/Ge triple-junction solar cells. Three different doping techniques were employed to grow the Te-doped InGaP layers in the TJ; Te doping, Te and Si co-doping and Te pre-doping. Compared to other samples, the external quantum efficiency (EQE) profiles in the InGaP top cell were found to be higher for the sample with Te pre-doping. Under a concentrated light condition, higher fill factor (FF) and conversion efficiency were also observed for the sample with Te pre-doping. These indicate that the crystalline qualities of the upper TJ, composed of a p-GaAs/n-InGaP TJ, and the InGaP top cell were improved by using the Te pre-doping method.

  7. Reduction of critical current density for out-of-plane mode oscillation in a mag-flip spin torque oscillator using highly spin-polarized Co2Fe(Ga0.5Ge0.5) spin injection layer

    NASA Astrophysics Data System (ADS)

    Bosu, S.; Sepehri-Amin, H.; Sakuraba, Y.; Hayashi, M.; Abert, C.; Suess, D.; Schrefl, T.; Hono, K.

    2016-02-01

    We study spin torque oscillators comprised of a perpendicular spin injection layer (SIL) and a planar field generating layer to reveal the influence of the spin polarization of SIL material on the critical current density, JC, to induce microwave oscillation. Two systems with different SIL are compared: one with a highly spin-polarized Heusler alloy, Co2Fe(Ga0.5Ge0.5) (CFGG), and the other a prototypical Fe2Co alloy. Cross sectional scanning transmission electron microscopy observations show the B2-ordered structure in a 3-nm-thick CFGG SIL, a prerequisite for obtaining half-metallic transport properties. Current induced microwave oscillations are found at frequencies of ˜15 GHz for both systems. However, the current needed to cause the oscillations is ˜50% smaller for films with the CFGG SIL compared to those of the Fe2Co SIL. These results are in accordance with micromagnetic simulations that include spin accumulation at the SIL.

  8. Development of epitaxial growth technology for Ge1-xSnx alloy and study of its properties for Ge nanoelectronics

    NASA Astrophysics Data System (ADS)

    Nakatsuka, Osamu; Shimura, Yosuke; Takeuchi, Wakana; Taoka, Noriyuki; Zaima, Shigeaki

    2013-05-01

    We have recently developed an epitaxial growth technique for Ge1-xSnx layers with an especially high Sn content, and we investigated the crystalline properties of the Ge1-xSnx epitaxial layers. In this report, we describe our recent achievements for improving the crystalline quality of the epitaxial growth of Ge1-xSnx layers on various substrates. We also demonstrate the impacts of Sn incorporation on the defect and dopant behaviors and electrical properties of Ge1-xSnx epitaxial layers. Sn incorporation improves on the issue of unintentional hole generation due to vacancy defects and enhances the dopant activation of Ga atoms in the Ge matrix. In addition, we introduce a recent study of the optical properties of Ge1-xSnx epitaxial layers with very high Sn contents.

  9. Germanium–tin interdiffusion in strained Ge/GeSn multiple-quantum-well structure

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Dong, Yuan; Zhou, Qian; Tok, Eng Soon; Yeo, Yee-Chia

    2016-06-01

    The thermal stability and germanium–tin (Ge–Sn) interdiffusion properties were studied in epitaxial Ge/GeSn multiple-quantum-well (MQW) structure. No obvious interdiffusion was observed for annealing temperatures of 300 °C or below, while observable interdiffusion occurred for annealing temperatures of 380 °C and above. High-resolution x-ray diffraction was used to obtain the interdiffusion coefficient by analyzing the decrease rate of Ge/GeSn periodic satellite peaks. The interdiffusion coefficient is much higher, and the activation enthalpy of 1.21 eV is substantially lower in Ge/GeSn MQW structure than that previously reported in silicon–germanium (Si–Ge) systems. When the annealing temperature is increased to above 500 °C, Ge–Sn interdiffusion becomes severe. Some small pits appear on the surface, which should be related to Sn out-diffusion to the Ge cap layer, followed by Sn desorption from the top surface. This work provides insights into the Ge–Sn interdiffusion and Sn segregation behaviors in Ge/GeSn MQW structure, and the thermal budget that may be used for fabrication of devices comprising Ge/GeSn heterostructures.

  10. Crystallinity improvements of Ge waveguides fabricated by epitaxial lateral overgrowth

    NASA Astrophysics Data System (ADS)

    Oda, Katsuya; Okumura, Tadashi; Kasai, Junichi; Kako, Satoshi; Iwamoto, Satoshi; Arakawa, Yasuhiko

    2016-04-01

    Ge waveguides (WGs) were successfully fabricated on an SiO2 layer by combining epitaxial lateral overgrowth, chemical mechanical polishing (CMP), and reactive ion etching (RIE) of a Ge layer selectively grown on SiO2 patterns using low-pressure chemical vapor deposition. Selectivity was promoted by increasing the growth temperature; the length of the epitaxial lateral overgrown Ge layer reached 5 µm on the SiO2 layer under conditions of optimal selective growth at a temperature of 750 °C. The Ge layers were planarized using CMP down to a thickness of 1 µm, and then Ge WGs as active regions for light emitting devices were formed by using RIE on the planarized Ge layers. After defective regions around the Ge/Si interface were removed, 4-times-higher photoluminescence was obtained from the Ge WGs compared with one that contained the Ge/Si interface. These results indicate that this combined technique efficiently improved the performance of Ge light-emitting devices.

  11. Growth of highly strain-relaxed Ge1-xSnx/virtual Ge by a Sn precipitation controlled compositionally step-graded method

    NASA Astrophysics Data System (ADS)

    Takeuchi, Shotaro; Shimura, Yosuke; Nakatsuka, Osamu; Zaima, Shigeaki; Ogawa, Masaki; Sakai, Akira

    2008-06-01

    We have investigated Sn precipitation and strain relaxation behaviors in the growth of Ge1-xSnx layers on virtual Ge substrates (v-Ge) for strain engineering of Ge. By varying misfit strain at Ge1-xSnx/v-Ge and Ge1-ySny/Ge1-xSnx interfaces, we found that a critical misfit strain controls the onset of Sn precipitation at a given thickness of the Ge1-xSnx layer. A compositionally step-graded method, in which the critical misfit strain is taken into account, was applied to the growth of strain-relaxed Ge1-xSnx layers on v-Ge. Postdeposition annealing at each growth step led to lateral propagation of threading dislocations preexisting in the layer and originating from v-Ge, which resulted in high degree of strain relaxation. An epitaxial Ge layer was grown on the strain-relaxed Ge1-xSnx layer and an in-plane tensile strain of 0.68% was achieved.

  12. 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.

  13. Ge1-xSnx alloys pseudomorphically grown on Ge(001)

    NASA Astrophysics Data System (ADS)

    Ladrón de Guevara, H. Pérez; Rodríguez, A. G.; Navarro-Contreras, H.; Vidal, M. A.

    2003-12-01

    Ge1-xSnx alloys were grown on Ge(001) substrates in a conventional rf sputtering system. We determined the in-plane and in-growth lattice parameters, as well as the alloy bulk lattice parameter of the alloys for different Sn concentrations by high resolution x-ray diffraction. The Sn concentration was determined assuming Vegard's law for the alloy lattice parameter. At low concentrations, we observed that Ge1-xSnx layers have pseudomorphic characteristics for layer thickness from 320 to 680 nm. These characteristics of Ge1-xSnx layers agree with the People and Bean critical thickness model. This structural study opens the possibility of growing dislocation-free Ge1-xSnx alloys below the critical thickness.

  14. Status of GaAs/Ge solar cells

    NASA Technical Reports Server (NTRS)

    Iles, P. A.; Ho, F.; Yeh, Y. C. M.

    1991-01-01

    With experience at increasing production levels, GaAs/Ge cells are proving their effectiveness for some demanding missions. The experience in producing inactive-Ge structures should benefit parallel work on forming monolithic cascade cells using AlGaAs or GaAs top cell layers grown on Ge or other bottom cell materials. The adjustments needed to ensure that the GaAs/Ge interface is inactive are more likely to preserve the properties of a separately optimized bottom cell.

  15. GeSn pin diodes: from pure Ge to direct-gap materials

    NASA Astrophysics Data System (ADS)

    Gallagher, James; Senaratne, Charutha; Xu, Chi; Aoki, Toshihiro; Kouvetakis, John; Menendez, Jose

    2015-03-01

    Complete n - i - p Ge1-ySny diode structures (y =0-0.09) were fabricated on Si substrates with Sn concentrations covering the entire range between pure Ge and direct-gap materials. The structures typically consist of a thick (>1 μm) n + + Ge buffer layer grown by Gas Source Molecular Epitaxy using Ge4H10 and either P(SiH3)3 or P(GeH3)3 , followed by a GeSn intrinsic layer (~ 500 nm), grown by Chemical Vapor Deposition (CVD) using Ge3H8 and SnD4, and a GeSn p-type top layer (~ 200 nm) grown by CVD using Ge3H8,SnD4andB2H6. Temperature-dependence of the I - V characteristics of these diodes as well as the forward-bias dependence of their electroluminescence (EL) signal were investigated, making it possible for the first time to extract the compositional dependence of parameters such as band gaps, activation energies, and dark currents. The EL spectra are dominated by direct-gap emission, which shifts from 1590 nm to 2300 nm, in agreement with photoluminescence results. DOD AFOSR FA9550-12-1-0208 and DOD AFOSR FA9550-13-1-0022.

  16. Epi-cleaning of Ge/GeSn heterostructures

    NASA Astrophysics Data System (ADS)

    Di Gaspare, L.; Sabbagh, D.; De Seta, M.; Sodo, A.; Wirths, S.; Buca, D.; Zaumseil, P.; Schroeder, T.; Capellini, G.

    2015-01-01

    We demonstrate a very-low temperature cleaning technique based on atomic hydrogen irradiation for highly (1%) tensile strained Ge epilayers grown on metastable, partially strain relaxed GeSn buffer layers. Atomic hydrogen is obtained by catalytic cracking of hydrogen gas on a hot tungsten filament in an ultra-high vacuum chamber. X-ray photoemission spectroscopy, reflection high energy electron spectroscopy, atomic force microscopy, secondary ion mass spectroscopy, and micro-Raman showed that an O- and C-free Ge surface was achieved, while maintaining the same roughness and strain condition of the as-deposited sample and without any Sn segregation, at a process temperature in the 100-300 °C range.

  17. Epi-cleaning of Ge/GeSn heterostructures

    SciTech Connect

    Di Gaspare, L.; Sabbagh, D.; De Seta, M.; Sodo, A.; Wirths, S.; Buca, D.; Zaumseil, P.; Schroeder, T.; Capellini, G.

    2015-01-28

    We demonstrate a very-low temperature cleaning technique based on atomic hydrogen irradiation for highly (1%) tensile strained Ge epilayers grown on metastable, partially strain relaxed GeSn buffer layers. Atomic hydrogen is obtained by catalytic cracking of hydrogen gas on a hot tungsten filament in an ultra-high vacuum chamber. X-ray photoemission spectroscopy, reflection high energy electron spectroscopy, atomic force microscopy, secondary ion mass spectroscopy, and micro-Raman showed that an O- and C-free Ge surface was achieved, while maintaining the same roughness and strain condition of the as-deposited sample and without any Sn segregation, at a process temperature in the 100–300 °C range.

  18. Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films

    PubMed Central

    Bouška, M.; Pechev, S.; Simon, Q.; Boidin, R.; Nazabal, V.; Gutwirth, J.; Baudet, E.; Němec, P.

    2016-01-01

    Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers. PMID:27199107

  19. Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films.

    PubMed

    Bouška, M; Pechev, S; Simon, Q; Boidin, R; Nazabal, V; Gutwirth, J; Baudet, E; Němec, P

    2016-01-01

    Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers. PMID:27199107

  20. Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films

    NASA Astrophysics Data System (ADS)

    Bouška, M.; Pechev, S.; Simon, Q.; Boidin, R.; Nazabal, V.; Gutwirth, J.; Baudet, E.; Němec, P.

    2016-05-01

    Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers.

  1. New approach to the growth of low dislocation relaxed SiGe material

    NASA Astrophysics Data System (ADS)

    Powell, A. R.; Iyer, S. S.; LeGoues, F. K.

    1994-04-01

    In this growth process a new strain relief mechanism operates, whereby the SiGe epitaxial layer relaxes without the generation of threading dislocations within the SiGe layer. This is achieved by depositing SiGe on an ultrathin silicon on insulator (SOI) substrate with a superficial silicon thickness less than the SiGe layer thickness. Initially, the thin Si layer is put under tension due to an equalization of the strain between the Si and SiGe layers. Thereafter, the strain created in the thin Si layer relaxes by plastic deformation. Since the dislocations are formed and glide in the thin Si layer, no threading dislocation is ever introduced in to the upper SiGe material, which appeared dislocation free to the limit of the cross sectional transmission electron microscopy analysis. We thus have a method for producing very low dislocation, relaxes SiGe films with the additional benefit of an SOI substrate.

  2. Crystal orientation dependence of current-perpendicular-to-plane giant magnetoresistance of pseudo spin-valves with epitaxial Co{sub 2}Fe(Ge{sub 0.5}Ga{sub 0.5}) Heusler alloy layers

    SciTech Connect

    Chen, Jiamin; Hono, K.; Li, Songtian; Furubayashi, T. Takahashi, Y. K.

    2014-06-21

    The magnetoresistive (MR) properties of Co{sub 2}Fe(Ge{sub 0.5}Ga{sub 0.5}) (CFGG) Heusler alloy-based current-perpendicular-to-plane giant magnetoresistance pseudo-spin-valves (PSVs) are investigated. The PSV films are epitaxially grown on a sapphire (112{sup ¯}0) substrate with an Ag or Cu spacer layer, and their magnetoresistive properties are compared with those of PSV grown on MgO(001) substrates. For substrates with an Ag spacer, the PSV with the (001)[110]{sub CFGG}//(001)[010]{sub Ag} interface grown on MgO(001) exhibits a higher MR output compared with the (110)[001]{sub CFGG}//(111)[11{sup ¯}0]{sub Ag} interface grown on sapphire (112{sup ¯}0). In contrast, a higher MR output is obtained using a Cu spacer with the (110)[001]{sub CFGG}//(111)[11{sup ¯}0]{sub Cu} interface. These results demonstrate that the MR outputs depend upon the crystal orientation at the interface, and that interfaces with a small misfit tend to exhibit a larger MR output. This indicates the influence of crystal orientation as well as lattice mismatch upon the interfacial spin scattering asymmetry.

  3. Spin transport in p-Ge through a vertically stacked Ge/Fe3Si junction

    NASA Astrophysics Data System (ADS)

    Kawano, M.; Santo, K.; Ikawa, M.; Yamada, S.; Kanashima, T.; Hamaya, K.

    2016-07-01

    We experimentally show spin transport up to 125 K in a ˜40-nm-thick p-Ge(111) layer, epitaxially grown on a ferromagnetic Fe3Si. From the magnitude of the spin signals, the spin diffusion length of the p-Ge(111) layer at 10 K can be estimated to be approximately 50 nm. To understand the detectable spin transport in the p-Ge(111), we should consider the energy splitting between heavy-hole and light-hole bands at the L point.

  4. Novel Ge waveguide platform on Ge-on-insulator wafer for mid-infrared photonic integrated circuits.

    PubMed

    Kang, Jian; Takenaka, Mitsuru; Takagi, Shinichi

    2016-05-30

    We present Ge rib waveguide devices fabricated on a Ge-on-insulator (GeOI) wafer as a proof-of-concept Ge mid-infrared photonics platform. Numerical analysis revealed that the driving current for a given optical attenuation in a carrier-injection Ge waveguide device at a 1.95 μm wavelength can be approximately five times smaller than that in a Si device, enabling in-line carrier-injection Ge optical modulators based on free-carrier absorption. We prepared a GeOI wafer with a 2-μm-thick buried oxide layer (BOX) by wafer bonding. By using the GeOI wafer, we fabricated Ge rib waveguides. The Ge rib waveguides were transparent to 2 μm wavelengths and the propagation loss was found to be 1.4 dB/mm, which may have been caused by sidewall scattering. We achieved a negligible bend loss in the Ge rib waveguide, even with a 5 μm bend radius, owing to the strong optical confinement in the GeOI structure. We also formed a lateral p-i-n junction along the Ge rib waveguide to explore the capability of absorption modulation by carrier injection. By injecting current through the lateral p-i-n junction, we achieved optical intensity modulation in the 2 μm band based on the free-carrier absorption in Ge. PMID:27410108

  5. Towards simultaneous achievement of carrier activation and crystallinity in Ge and GeSn with heated phosphorus ion implantation: An optical study

    NASA Astrophysics Data System (ADS)

    D'Costa, Vijay Richard; Wang, Lanxiang; Wang, Wei; Lim, Sin Leng; Chan, Taw Kuei; Chua, Lye Hing; Henry, Todd; Zou, Wei; Hatem, Christopher; Osipowicz, Thomas; Tok, Eng Soon; Yeo, Yee-Chia

    2014-09-01

    We have investigated the optical properties of Ge and GeSn alloys implanted with phosphorus ions at 400 °C by spectroscopic ellipsometry from far-infrared to ultraviolet. The dielectric response of heated GeSn implants displays structural and transport properties similar to those of heated Ge implants. The far-infrared dielectric function of as-implanted Ge and GeSn shows the typical free carrier response which can be described by a single Drude oscillator. Bulk Ge-like critical points E1, E1 + Δ1, E0', and E2 are observed in the visible-UV dielectric function of heated Ge and GeSn indicating single crystalline quality of the as-implanted layers. Although the implantation at 400 °C recovers crystallinity in both Ge and GeSn, an annealing step is necessary to enhance the carrier activation.

  6. Similarity of Stranski-Krastanow growth of Ge/Si and SiGe/Si (001)

    SciTech Connect

    Norris, D. J.; Qiu, Y.; Walther, T.; Dobbie, A.; Myronov, M.

    2014-01-07

    This study investigates the onset of islanding (Stranski-Krastanow transition) in strained pure germanium (Ge) and dilute silicon-germanium (SiGe) alloy layers grown by chemical vapour deposition on Si(001) substrates. Integration of compositional profiles is compared to a novel method for quantification of X-ray maps acquired in cross-sectional scanning transmission electron microscopy, together with simulations of surface segregation of Ge. We show that Si{sub 1−x}Ge{sub x} alloys for germanium concentrations x ≤ 0.27 grow two-dimensionally and stay flat up to considerable layer thicknesses, while layers with concentrations in the range 0.28 < x ≤ 1 form islands after deposition of ∼3.0/x monolayers (=quarter unit cells in the diamond lattice, ML). The uncertainty in the amount of deposited material for pure Ge is ±(0.2–0.3) ML. Modelling shows that of the amount of germanium deposited, 0.7 ML segregate towards the free surface so that only ∼2.3/x ML are directly incorporated in the layer within a few nanometres, in good agreement with our measurements. For pure Ge (x = 1), this thickness is smaller than most values quoted in the literature, which we attribute to the high sensitivity of our method to fractional monolayer changes in the effective chemical width of such thin layers.

  7. Electrical characterization of p-GeSn/n-Ge diodes with interface traps under dc and ac regimes

    NASA Astrophysics Data System (ADS)

    Baert, B.; Gupta, S.; Gencarelli, F.; Loo, R.; Simoen, E.; Nguyen, N. D.

    2015-08-01

    In this work, the electrical properties of p-GeSn/n-Ge diodes are investigated in order to assess the impact of defects at the interface between Ge and GeSn using temperature-dependent current-voltage and capacitance-voltage measurements. These structures are made from GeSn epitaxial layers grown by CVD on Ge with in situ doping by Boron. As results, an average ideality factor of 1.2 has been determined and an activation energy comprised between 0.28 eV and 0.30 eV has been extracted from the temperature dependence of the reverse-bias current. Based on the comparison with numerical results obtained from device simulations, we explain this activation energy by the presence of traps located near the GeSn/Ge interface.

  8. Semiphenomenological method of analysis for intermediate-energy alpha-nucleus elastic scattering data

    SciTech Connect

    Ahmad, I.; Alvi, M.A.

    1983-12-01

    We propose a semiphenomenological method of analysis for intermediate energy ..cap alpha..-nucleus elastic scattering experiments and demonstrate its usefulness by analyzing available elastic ..cap alpha..-nucleus scattering data at 1.37 GeV.

  9. Properties of slow traps of ALD Al2O3/GeOx/Ge nMOSFETs with plasma post oxidation

    NASA Astrophysics Data System (ADS)

    Ke, M.; Yu, X.; Chang, C.; Takenaka, M.; Takagi, S.

    2016-07-01

    The realization of Ge gate stacks with a small amount of slow trap density as well as thin equivalent oxide thickness and low interface state density (Dit) is a crucial issue for Ge CMOS. In this study, we examine the properties of slow traps, particularly the location of slow traps, of Al2O3/GeOx/n-Ge and HfO2/Al2O3/GeOx/n-Ge MOS interfaces with changing the process and structural parameters, formed by atomic layer deposition (ALD) of Al2O3 and HfO2/Al2O3 combined with plasma post oxidation. It is found that the slow traps can locate in the GeOx interfacial layer, not in the ALD Al2O3 layer. Furthermore, we study the time dependence of channel currents in the Ge n-MOSFETs with 5-nm-thick Al2O3/GeOx/Ge gate stacks, with changing the thickness of GeOx, in order to further clarify the position of slow traps. The time dependence of the current drift and the effective time constant of slow traps do not change among the MOSFETs with the different thickness GeOx, demonstrating that the slow traps mainly exist near the interfaces between Ge and GeOx.

  10. Reduction of Schottky barrier height at metal/n-Ge interface by introducing an ultra-high Sn content Ge1-xSnx interlayer

    NASA Astrophysics Data System (ADS)

    Suzuki, Akihiro; Nakatsuka, Osamu; Shibayama, Shigehisa; Sakashita, Mitsuo; Takeuchi, Wakana; Kurosawa, Masashi; Zaima, Shigeaki

    2015-11-01

    We investigated the impact of introducing an ultra-high Sn content Ge1-xSnx interlayer on the electrical properties at the metal/Ge interface. We achieved epitaxial growth of a Ge1-xSnx thin layer with an ultra-high substitutional Sn content of up to 46% on a Ge(001) substrate by considering the misfit strain between Ge1-xSnx and Ge. From the current-voltage characteristics of Al/Ge1-xSnx/n-Ge Schottky diodes, we found an increase in the forward current density of the thermionic emission current with increasing Sn content in the Ge1-xSnx interlayer. The Schottky barrier height estimated in Al/Ge1-xSnx/n-Ge diodes decreases to 0.49 eV with an increase in the Sn content up to 46% of the Ge1-xSnx interlayer. The reduction of the barrier height may be due to the shift of the Fermi level pinning position at the metal/Ge interface with a Ge1-xSnx interlayer whose valence band edge is higher than that of Ge. This result enables the effective reduction of the contact resistivity by introducing a group-IV semiconductor alloy interlayer of Ge1-xSnx into the metal/n-Ge interface.

  11. Fabrication of GeSn-multiple quantum wells by overgrowth of Sn on Ge by using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Oliveira, F.; Fischer, I. A.; Benedetti, A.; Zaumseil, P.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.; Schulze, J.

    2015-12-01

    We report on the fabrication and structural characterization of epitaxially grown ultra-thin layers of Sn on Ge virtual substrates (Si buffer layer overgrown by a 50 nm thick Ge epilayer followed by an annealing step). Samples with 1 to 5 monolayers of Sn on Ge virtual substrates were grown using solid source molecular beam epitaxy and characterized by atomic force microscopy. We determined the critical thickness at which the transition from two-dimensional to three-dimensional growth occurs. This transition is due to the large lattice mismatch between Ge and Sn (≈14.7%). By depositing Ge on top of Sn layers, which have thicknesses at or just below the critical thickness, we were able to fabricate ultra-narrow GeSn multi-quantum-well structures that are fully embedded in Ge. We report results on samples with one and ten GeSn wells separated by 5 and 10 nm thick Ge spacer layers that were characterized by high resolution transmission electron microscopy and X-ray diffraction. We discuss the structure and material intermixing observed in the samples.

  12. Fabrication of GeSn-multiple quantum wells by overgrowth of Sn on Ge by using molecular beam epitaxy

    SciTech Connect

    Oliveira, F.; Fischer, I. A.; Schulze, J.; Benedetti, A.; Zaumseil, P.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.

    2015-12-28

    We report on the fabrication and structural characterization of epitaxially grown ultra-thin layers of Sn on Ge virtual substrates (Si buffer layer overgrown by a 50 nm thick Ge epilayer followed by an annealing step). Samples with 1 to 5 monolayers of Sn on Ge virtual substrates were grown using solid source molecular beam epitaxy and characterized by atomic force microscopy. We determined the critical thickness at which the transition from two-dimensional to three-dimensional growth occurs. This transition is due to the large lattice mismatch between Ge and Sn (≈14.7%). By depositing Ge on top of Sn layers, which have thicknesses at or just below the critical thickness, we were able to fabricate ultra-narrow GeSn multi-quantum-well structures that are fully embedded in Ge. We report results on samples with one and ten GeSn wells separated by 5 and 10 nm thick Ge spacer layers that were characterized by high resolution transmission electron microscopy and X-ray diffraction. We discuss the structure and material intermixing observed in the samples.

  13. Ultrathin (5 nm) SiGe-On-Insulator with high compressive strain (-2 GPa): From fabrication (Ge enrichment process) to in-depth characterizations

    NASA Astrophysics Data System (ADS)

    Glowacki, F.; Le Royer, C.; Morand, Y.; Pédini, J.-M.; Denneulin, T.; Cooper, D.; Barnes, J.-P.; Nguyen, P.; Rouchon, D.; Hartmann, J.-M.; Gourhant, O.; Baylac, E.; Campidelli, Y.; Barge, D.; Bonnin, O.; Schwarzenbach, W.

    2014-07-01

    300 mm ultrathin Silicon-On-Insulator (SOI) wafers with SiGe/Si stacks on top were used as pre-structures for the fabrication of 5 nm thick SiGe-On-Insulator (SGOI) substrates obtained by the Ge enrichment technique. Those substrates will be used as the channel of advanced Fully Depleted (FD) p-type Metal Oxide Semiconductor Field Effect Transistors (pMOSFET). We present in the first part the successful fabrication of 5 nm SGOI wafers. Various characterization techniques are used to investigate the Ge profile and the final strain in the fabricated 5 nm Si0.7Ge0.3 film. Secondary Ions Mass Spectrometry (SIMS) and Scanning Transmission Electron Microscopy (STEM) clearly show that the Ge content is very homogeneous (xGe = 30 ± 1%) in the SiGe layer. Raman spectroscopy and High Angle Annular Dark Field (HAADF) STEM both confirm that the 5 nm thick SiGe film is compressively strained (-2 GPa). The second part is dedicated to the sensitivity of the Ge enrichment process (based on numerical modelling). We investigate the impact of single and combined fluctuations of the pre-structure parameters (TSi, TSiGe,0, xGe,0) on the final SiGe layer (TSiGe, xGe).

  14. Acoustoelectric effects in very high-mobility p-SiGe/Ge/SiGe heterostructure

    SciTech Connect

    Drichko, I. L.; Diakonov, A. M.; Lebedeva, E. V.; Smirnov, I. Yu.; Mironov, O. A.; Kummer, M.; Kaenel, H. von

    2009-11-01

    Measurement results of the acoustoelectric effects [surface acoustic waves (SAW) attenuation and velocity] in a high-mobility p-SiGe/Ge/SiGe structure are presented. The structure was low-energy plasma-enhanced chemical vapor deposition grown with a two-dimensional (2D) channel buried in the strained Ge layer. The measurements were performed as a function of temperature (1.5-4.2 K) and magnetic field (up to 8.4 T) at different SAW intensities at frequencies 28 and 87 MHz. Shubnikov-de Haas-like oscillations of both SAW attenuation and the velocity change have been observed. Hole density and mobility, effective mass, quantum and transport relaxation times, as well as the Dingle temperature were measured with a method free of electric contacts. The effect of heating of the 2D hole gas by the electric field of the SAW was investigated. Energy relaxation time tau{sub e}psilon and the deformation potential constant determined.

  15. Role of nucleation sites on the formation of nanoporous Ge

    SciTech Connect

    Yates, B. R.; Darby, B. L.; Jones, K. S.; Elliman, R. G.

    2012-09-24

    The role of nucleation sites on the formation of nanoporous Ge was investigated. Three Ge films with different spherical or columnar pore morphologies to act as inherent nucleation sites were sputtered on (001) Ge. Samples were implanted 90 Degree-Sign from incidence at 300 keV with fluences ranging from 3.0 Multiplication-Sign 10{sup 15} to 3.0 Multiplication-Sign 10{sup 16} Ge{sup +}/cm{sup 2}. Electron microscopy investigations revealed varying thresholds for nanoporous Ge formation and exhibited a stark difference in the evolution of the Ge layers based on the microstructure of the initial film. The results suggest that the presence of inherent nucleation sites significantly alters the onset and evolution of nanoporous Ge.

  16. Au induced low-temperature formation of preferentially (111)-oriented crystalline Ge on insulator

    NASA Astrophysics Data System (ADS)

    Okamoto, Hayato; Kudo, Kohei; Nomitsu, Tatsushi; Mochii, Ryosuke; Moto, Kenta; Takakura, Kenichiro; Tsunoda, Isao

    2016-04-01

    The effects of Au insertion in solid-phase crystallization for amorphous Ge films on SiO2/Si substrates were investigated to achieve oriented crystalline Ge. After high-temperature annealing above 300 °C, Au atoms were highly diffused in the amorphous Ge layer. The resulting crystalline Ge consisted of random grains formed by crystal nucleation in the entire Ge region. However, when annealing temperature was decreased to below 250 °C, Au atoms were localized at their initial position even after a long annealing (20 h). Moreover, formation of preferentially (111)-oriented crystalline Ge was achieved without using the metal-induced layer-exchange crystallization method. These results suggest that crystal nucleation preferentially occurs at the amorphous Ge/Au interface, and subsequently the nucleus growth progresses into the Ge layer.

  17. Comments on intermediate-scale models

    NASA Astrophysics Data System (ADS)

    Ellis, J.; Enqvist, K.; Nanopoulos, D. V.; Olive, K.

    1987-04-01

    Some superstring-inspired models employ intermediate scales m1 of gauge symmetry breaking. Such scales should exceed 10 16 GeV in order to avoid prima facie problems with baryon decay through heavy particles and non-perturbative behaviour of the gauge couplings above mI. However, the intermediate-scale phase transition does not occur until the temperature of the Universe falls below O( mw), after which an enormous excess of entropy is generated. Moreover, gauge symmetry breaking by renormalization group-improved radiative corrections is inapplicable because the symmetry-breaking field has no renormalizable interactions at scales below mI. We also comment on the danger of baryon and lepton number violation in the effective low-energy theory.

  18. Interface and nanostructure evolution of cobalt germanides on Ge(001)

    SciTech Connect

    Grzela, T. Schubert, M. A.; Koczorowski, W.; Capellini, G.; Czajka, R.; Radny, M. W.; Curson, N.; Schofield, S. R.; Schroeder, T.

    2014-02-21

    Cobalt germanide (Co{sub x}Ge{sub y}) is a candidate system for low resistance contact modules in future Ge devices in Si-based micro and nanoelectronics. In this paper, we present a detailed structural, morphological, and compositional study on Co{sub x}Ge{sub y} formation on Ge(001) at room temperature metal deposition and subsequent annealing. Scanning tunneling microscopy and low energy electron diffraction clearly demonstrate that room temperature deposition of approximately four monolayers of Co on Ge(001) results in the Volmer Weber growth mode, while subsequent thermal annealing leads to the formation of a Co-germanide continuous wetting layer which evolves gradually towards the growth of elongated Co{sub x}Ge{sub y} nanostructures. Two types of Co{sub x}Ge{sub y} nanostructures, namely, flattop- and ridge-type, were observed and a systematic study on their evolution as a function of temperature is presented. Additional transmission electron microscopy and x-ray photoemission spectroscopy measurements allowed us to monitor the reaction between Co and Ge in the formation process of the Co{sub x}Ge{sub y} continuous wetting layer as well as the Co{sub x}Ge{sub y} nanostructures.

  19. Gate-stack engineering for self-organized Ge-dot/SiO2/SiGe-shell MOS capacitors

    NASA Astrophysics Data System (ADS)

    Lai, Wei-Ting; Yang, Kuo-Ching; Liao, Po-Hsiang; George, Tom; Li, Pei-Wen

    2016-02-01

    We report the first-of-its-kind, self-organized gate-stack heterostructure of Ge-dot/SiO2/SiGe-shell on Si fabricated in a single step through the selective oxidation of a SiGe nano-patterned pillar over a Si3N4 buffer layer on a Si substrate. Process-controlled tunability of the Ge-dot size (7.5‑90 nm), the SiO2 thickness (3‑4 nm), and as well the SiGe-shell thickness (2‑15 nm) has been demonstrated, enabling a practically-achievable core building block for Ge-based metal-oxide-semiconductor (MOS) devices. Detailed morphologies, structural, and electrical interfacial properties of the SiO2/Ge-dot and SiO2/SiGe interfaces were assessed using transmission electron microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Notably, NiGe/SiO2/SiGe and Al/SiO2/Ge-dot/SiO2/SiGe MOS capacitors exhibit low interface trap densities of as low as 3-5x10^11 cm^-2·eV^-1 and fixed charge densities of 1-5x10^11 cm^-2, suggesting good-quality SiO2/SiGe-shell and SiO2/Ge-dot interfaces. In addition, the advantage of having single-crystalline Si1-xGex shell (x > 0.5) in a compressive stress state in our self-aligned gate-stack heterostructure has great promise for possible SiGe (or Ge) MOS nanoelectronic and nanophotonic applications.

  20. 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.

  1. Vertical Ge and GeSn heterojunction gate-all-around tunneling field effect transistors

    NASA Astrophysics Data System (ADS)

    Schulze, Jörg; Blech, Andreas; Datta, Arnab; Fischer, Inga A.; Hähnel, Daniel; Naasz, Sandra; Rolseth, Erlend; Tropper, Eva-Maria

    2015-08-01

    We present experimental results on the fabrication and characterization of vertical Ge and GeSn heterojunction Tunneling Field Effect Transistors (TFETs). A gate-all-around process with mesa diameters down to 70 nm is used to reduce leakage currents and improve electrostatic control of the gate over the transistor channel. An ION = 88.4 μA/μm at VDS = VG = -2 V is obtained for a TFET with a 10 nm Ge0.92Sn0.08 layer at the source/channel junction. We discuss further possibilities for device improvements.

  2. 70 °C synthesis of high-Sn content (25%) GeSn on insulator by Sn-induced crystallization of amorphous Ge

    NASA Astrophysics Data System (ADS)

    Toko, K.; Oya, N.; Saitoh, N.; Yoshizawa, N.; Suemasu, T.

    2015-02-01

    Polycrystalline GeSn thin films are fabricated on insulating substrates at low temperatures by using Sn-induced crystallization of amorphous Ge (a-Ge). The Sn layer stacked on the a-Ge layer (100-nm thickness each) had two roles: lowering the crystallization temperature of a-Ge and composing GeSn. Slow annealing at an extremely low temperature of 70 °C allowed for a large-grained (350 nm) GeSn layer with a lattice constant of 0.590 nm, corresponding to a Sn composition exceeding 25%. The present investigation paves the way for advanced electronic optical devices integrated on a flexible plastic substrate as well as on a Si platform.

  3. Density and Capture Cross-Section of Interface Traps in GeSnO2 and GeO2 Grown on Heteroepitaxial GeSn.

    PubMed

    Gupta, Somya; Simoen, Eddy; Loo, Roger; Madia, Oreste; Lin, Dennis; Merckling, Clement; Shimura, Yosuke; Conard, Thierry; Lauwaert, Johan; Vrielinck, Henk; Heyns, Marc

    2016-06-01

    An imperative factor in adapting GeSn as the channel material in CMOS technology, is the gate-oxide stack. The performance of GeSn transistors is degraded due to the high density of traps at the oxide-semiconductor interface. Several oxide-gate stacks have been pursued, and a midgap Dit obtained using the ac conductance method, is found in literature. However, a detailed signature of oxide traps like capture cross-section, donor/acceptor behavior and profile in the bandgap, is not yet available. We investigate the transition region between stoichiometric insulators and strained GeSn epitaxially grown on virtual Ge substrates. Al2O3 is used as high-κ oxide and either Ge1-xSnxO2 or GeO2 as interfacial layer oxide. The interface trap density (Dit) profile in the lower half of the bandgap is measured using deep level transient spectroscopy, and the importance of this technique for small bandgap materials like GeSn, is explained. Our results provide evidence for two conclusions. First, an interface traps density of 1.7 × 10(13) cm(-2)eV(-1) close to the valence band edge (Ev + 0.024 eV) and a capture cross-section (σp) of 1.7 × 10(-18) cm(2) is revealed for GeSnO2. These traps are associated with donor states. Second, it is shown that interfacial layer passivation of GeSn using GeO2 reduces the Dit by 1 order of magnitude (2.6 × 10(12) cm(-2)eV(-1)), in comparison to GeSnO2. The results are cross-verified using conductance method and saturation photovoltage technique. The Dit difference is associated with the presence of oxidized (Sn(4+)) and elemental Sn in the interfacial layer oxide. PMID:27172051

  4. First-principles Study of Atomic Rearrangement in GeTe-S2 bTe3 Superlattice

    NASA Astrophysics Data System (ADS)

    Song, Young-Sun; Jhi, Seung-Hoon; CNPL Team

    GeTe-Sb2Te3 chalcogenide superlattices, known as interfacial phase change memories (iPCMs), have been claimed to outperform Ge-Sb-Te-based phase-change materials. Despite its great potential as next-generation non-volatile memory devices, we still lack clear knowledge of the phase change mechanism. According to a recent work, the phase change processes in iPCMs involve two-step atomic rearrangements of Ge-Te layers, but the detailed interatomic features still remain unresolved. In this work, we studied the nature of atomic layer rearrangements in iPCMs using first-principles calculations and the interatomic potential model. We used the climbing image nudged elastic band (CI-NEB) method to obtain the intermediate structures and energies during the rearrangement processes. Applying a simple interatomic potential model to in-between steps, we investigated the interatomic motion during the phase change process. We found that a few selected atomic pairs determine most the energy barrier and also the response to external pressures.

  5. Spontaneous Growth and Chemical Reduction Ability of Ge Nanoparticles

    PubMed Central

    Liu, Jun; Liang, Changhao; Tian, Zhenfei; Zhang, Shuyuan; Shao, Guosheng

    2013-01-01

    Forming colloidal solutions containing semiconductor quantum-sized nanoparticles (NPs) with clean surface has been a long-standing scientific challenge. In this contribution, we report a “top-down” method for the fabrication of Ge NPs by laser ablation of a Ge target in deionized water without adding any stabilizing reagents. The initial Ge NPs in amorphous structure showed spontaneous growth behavior by aging Ge colloids in deionized water under ambient temperature, which gradually evolved into a metastable tetragonal structure as an intermediate phase and then transformed into the stable cubic structure, being consistent with the Ostwald's rule of stages for the growth in a metastable system. The laser-induced initial Ge NPs demonstrate a unique and prominent size-dependent chemical reductive ability, which is evidenced by the rapid degradation of organic molecules such as chlorinated aromatic compounds, organic dyes, and reduction of heavy metal Cr(VI) ions.

  6. TiO2/GeOxNy stacked gate dielectrics for Ge-MOSFETs

    NASA Astrophysics Data System (ADS)

    Bera, M. K.; Mahata, C.; Chakraborty, A. K.; Nandi, S. K.; Tiwari, Jitendra N.; Hung, Jui-Yi; Maiti, C. K.

    2007-12-01

    In this work, we present the results of physical and electrical characterization of Ti-based high-k gate dielectrics on Ge substrates. Titanium tetrakis iso- propoxide (TTIP) was used as the organometallic source for the deposition of ultra-thin TiO2 films on p-Ge (1 0 0) at low temperature (<200 °C) by plasma enhanced chemical vapor deposition (PECVD) technique in a microwave (700 W, 2.45 GHz) plasma cavity discharge system at a pressure of ~65 Pa. The presence of an ultra-thin lossy GeO2 interfacial layer between the deposited high-k film and the substrate, results in frequency-dependent capacitance-voltage (C-V) characteristics in strong accumulation and a high interface state density (~1013 cm-2 eV-1). To improve the electrical properties, nitrogen engineering has been employed to convert the lossy GeO2 interfacial layer to its oxynitride, thus forming TiO2/GeOxNy/Ge stacked-gate structure with improved interface/electrical properties. Different N sources, such as NO, NH3 and NO/NH3, have been used for nitrogen engineering. XPS and Raman spectroscopy analyses have been used for surface morphological study. Electrical properties, such as gate leakage current density, interface state density, charge trapping, flatband voltage shift, etc, have been studied in detail for TiO2/GeOxNy/Ge MIS capacitors using the current-voltage (I-V), capacitance-voltage (C-V), conductance-voltage (G-V) and stress (both constant voltage and current) measurements. Although a significant improvement in electrical characteristics has been observed after nitridation in general, the formation of the interfacial GeOxNy layer, obtained from NO-plasma nitridation, is found to provide the maximum improvement among all the nitridation techniques used in this study. It is shown that the insertion of an ultra-thin oxynitride (GeOxNy) interfacial layer is advantageous for producing gate-quality TiO2 high-k dielectric stacks on Ge substrates.

  7. Intermediate Strength Gravitational Lensing

    SciTech Connect

    Irwin, John

    2005-03-17

    Weak lensing is found in the correlations of shear in {approx}10{sup 4} galaxy images, strong lensing is detected by the obvious distortion of a single galaxy image, whereas intermediate lensing requires detection of less obvious curvature in several neighboring galaxies. Small impact-parameter lensing causes a sextupole distortion whose orientation is correlated with the quadrupole distortion (shear). By looking within a field for the spatial correlation of this sextupole-quadrupole correlation, an intermediate lensing regime is observed. This technique requires correction for the sextupole as well as the quadrupole content of the PSF. We remove the HST PSF and uncover intermediate lensing in the Hubble deep fields. Correlations of the type expected are found.

  8. Raman study of strained Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Lin, Hai; Chen, Robert; Huo, Yijie; Kamins, Theodore I.; Harris, James S.

    2011-06-01

    The Ge-Ge longitudinal optical Raman peak has been measured in strained Ge1-xSnx alloy layers grown on top of relaxed InyGa1-yAs buffer layers on GaAs substrates by molecular beam epitaxy. The experimental result shows that the peak frequency shift increases linearly from the value for bulk Ge with the Sn fraction x and the strain ɛ, Δω = ω - ωGe = ax + bɛ. In these experiments alloy and strain contributions are decoupled and measured separately, and a and b are determined to be a = - 82 ± 4 cm-1 and b = - 563 ± 34 cm-1, over the entire composition and strain range investigated.

  9. Tensely strained GeSn alloys as optical gain media

    NASA Astrophysics Data System (ADS)

    Wirths, S.; Ikonic, Z.; Tiedemann, A. T.; Holländer, B.; Stoica, T.; Mussler, G.; Breuer, U.; Hartmann, J. M.; Benedetti, A.; Chiussi, S.; Grützmacher, D.; Mantl, S.; Buca, D.

    2013-11-01

    This letter presents the epitaxial growth and characterization of a heterostructure for an electrically injected laser, based on a strained GeSn active well. The elastic strain within the GeSn well can be tuned from compressive to tensile by high quality large Sn content (Si)GeSn buffers. The optimum combination of tensile strain and Sn alloying softens the requirements upon indirect to direct bandgap transition. We theoretically discuss the strain-doping relation for maximum net gain in the GeSn active layer. Employing tensile strain of 0.5% enables reasonable high optical gain values for Ge0.94Sn0.06 and even without any n-type doping for Ge0.92Sn0.08.

  10. Kesterite Cu2Zn(Sn,Ge)(S,Se)4 thin film with controlled Ge-doping for photovoltaic application.

    PubMed

    Zhao, Wangen; Pan, Daocheng; Liu, Shengzhong Frank

    2016-05-21

    Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm(2) without an anti-reflection layer. PMID:27121893

  11. Hispanic American Heritage, Intermediate.

    ERIC Educational Resources Information Center

    Shepherd, Mike

    This resource book features the cultural heritage of Hispanics living within the United States and includes ideas, materials, and activities to be used with students in the intermediate grades and middle school. This book explores the definition of the term "Hispanic Americans" and suggests a multilayered population with a variety of cultural…

  12. English 200: Intermediate Composition

    ERIC Educational Resources Information Center

    Ritter, Kelly

    2005-01-01

    "English 200: Intermediate Composition" is a program elective for English majors and a writing-intensive elective for nonmajors at Southern Connecticut State University (SCSU), a comprehensive institution of 11,000 undergraduate and graduate (master's level) students. English 200 is described in the departmental course catalog as a course "in…

  13. Water oxidation: Intermediate identification

    NASA Astrophysics Data System (ADS)

    Cowan, Alexander J.

    2016-08-01

    The slow kinetics of light-driven water oxidation on haematite is an important factor limiting the material's efficiency. Now, an intermediate of the water-splitting reaction has been identified offering hope that the full mechanism will soon be resolved.

  14. INTERMEDIATE READINGS IN TAGALOG.

    ERIC Educational Resources Information Center

    BOWEN, J. DONALD, ED.

    THE SECOND IN A SERIES OF TEXTS DESIGNED TO HELP THE STUDENT ACHIEVE AN UNDERSTANDING OF FILIPINO CULTURE AND ACQUIRE ENOUGH PROFICIENCY IN TAGALOG TO COMMUNICATE EASILY AND MEANINGFULLY, THESE INTERMEDIATE READINGS ARE COORDINATED WITH THE EDITOR'S "BEGINNING TAGALOG" (ED 014 696). INCLUDED IN PART I ARE READINGS WRITTEN ESPECIALLY FOR THIS TEXT…

  15. GLOSSARY TO INTERMEDIATE HINDI.

    ERIC Educational Resources Information Center

    Wisconsin Univ., Madison. Indian Language and Area Center.

    INCLUDED IN THIS GLOSSARY ARE THE VOCABULARY ITEMS FOR THE READINGS IN "INTERMEDIATE HINDI." THE ITEMS ARE ARRANGED BY SELECTION IN SERIAL ORDER. EACH ENTRY INCLUDES NAGARI (DEVANAGARI) SCRIPT SPELLING, A NOTATION OF THE FORM CLASS, AND A SHORT ENGLISH GLOSS. THESE TWO VOLUMES ARE ALSO AVAILABLE AS A SET FOR $7.00 FROM THE COLLEGE PRINTING…

  16. SPACE: Intermediate Level Modules.

    ERIC Educational Resources Information Center

    Indiana State Dept. of Education, Indianapolis. Center for School Improvement and Performance.

    These modules were developed to assist teachers at the intermediate level to move away from extensive skill practice and toward more meaningful interdisciplinary learning. This packet, to be used by teachers in the summer Extended Learning Program, provides detailed thematic lesson plans matched to the Indiana Curriculum Proficiency Guide. The…

  17. Intermediate Cambodian Reader.

    ERIC Educational Resources Information Center

    Huffman, Franklin E., Ed.; Proum, Im, Ed.

    This book is a sequel to the "Cambodian System of Writing and Beginning Reader." It is intended to serve as an intermediate reader to develop the student's ability to the point of reading Cambodian texts with the aid of a dictionary. Part One of the book consists of 37 readings, graded in length and difficulty, and selected to provide a wide range…

  18. Comet Ge-Wang

    NASA Astrophysics Data System (ADS)

    Ge, Yong-liang; Wang, Qi; Han, Tao

    1990-03-01

    Comet Ge-Wang (1988o) was discovered by GE Yong-liang and WANG Qi at Xinglong Station of Beijing Observatory on 1988 November 4. We collected 13 observations of this comet in China and abroad and calculated its orbit. It passed the perihelion on 1988 May 23. Ephemerides up to 1991 April are given.

  19. Comet Ge-Wang

    NASA Astrophysics Data System (ADS)

    Ge, Yong-Liang; Wang, Qi; Han, Tao

    1989-03-01

    Comet Ge-Wang (1988o) was discovered by GE Yong-liang and WANG Qi at Xinglong Station of Beijing Observatory on November 4, 1988. Thirteen observations of this comet were collected in China and abroad and calculated its orbit. It passed the perihelion on May 23, 1988. Ephemerides up to April 1991 are given.

  20. Structure of a passivated Ge surface prepared from aqueous solution.

    SciTech Connect

    Lyman, P. F.; Sakata, O.; Marasco, D, L.; Lee, T.-L.; Breneman, K. D.; Keane, D. T.; Bedzyk, M. J.; Materials Science Division; Northwestern Univ.; Univ. of Wisconsin at Milwaukee

    2000-08-10

    The structure of a passivating sulfide layer on Ge(001) was studied using X-ray standing waves and X-ray fluorescence. The sulfide layer was formed by reacting clean Ge substrates in (NH{sub 4}){sub 2}S solutions of various concentrations at 80{sup o}C. For each treatment, a sulfide layer containing approximately two to three monolayers (ML) of S was formed on the surface, and an ordered structure was found at the interface that contained approximately 0.4 ML of S. Our results suggest the rapid formation of a glassy GeS{sub x} layer containing 1.5-2.5 ML S residing atop a partially ordered interfacial layer of bridge-bonded S. The passivating reaction appears to be self-limited to 2-3 ML at this reaction temperature.

  1. Effect of temperature on the mutual diffusion of Ge/GaAs and GaAs/Ge

    NASA Astrophysics Data System (ADS)

    Bosi, Matteo; Attolini, Giovanni; Ferrari, Claudio; Frigeri, Cesare; Calicchio, Marco; Rossi, Francesca; Vad, Kálmán; Csik, Attila; Zolnai, Zsolt

    2011-03-01

    We studied the diffusion of Ge, As and Ga in GaAs/Ge and Ge/GaAs epilayers grown at different temperatures by metal-organic vapor phase epitaxy using iso-butylgermane, arsine and trimethylgallium in hydrogen atmosphere at low pressure. The use of low temperature buffer layers was investigated in order to overcome the diffusion problem. High-resolution X-ray diffraction and transmission electron microscopy were used to assess the crystal quality, while secondary neutral mass spectrometry has been employed to investigate diffusion profiles in the samples. As it is well known, the diffusivity of the atoms (e.g. Ga, As, Ge) and intermixing of layers during sample preparation strongly depend on the substrate temperature. We found that the use of a low temperature GaAs buffer layer reduced the diffusion in GaAs/Ge epitaxy at 600 °C; while a Ge low temperature buffer layer was not effective in reducing the interdiffusion in Ge/GaAs epitaxy at 700 °C.

  2. Antimony segregation in Ge and formation of n-type selectively doped Ge films in molecular beam epitaxy

    SciTech Connect

    Yurasov, D. V. Antonov, A. V.; Drozdov, M. N.; Schmagin, V. B.; Novikov, A. V.; Spirin, K. E.

    2015-10-14

    Antimony segregation in Ge(001) films grown by molecular beam epitaxy was studied. A quantitative dependence of the Sb segregation ratio in Ge on growth temperature was revealed experimentally and modeled theoretically taking into account both the terrace-mediated and step-edge-mediated segregation mechanisms. A nearly 5-orders-of-magnitude increase in the Sb segregation ratio in a relatively small temperature range of 180–350 °C was obtained, which allowed to form Ge:Sb doped layers with abrupt boundaries and high crystalline quality using the temperature switching method that was proposed earlier for Si-based structures. This technique was employed for fabrication of different kinds of n-type Ge structures which can be useful for practical applications like heavily doped n{sup +}-Ge films or δ-doped layers. Estimation of the doping profiles sharpness yielded the values of 2–5 nm per decade for the concentration gradient at the leading edge and 2–3 nm for the full-width-half-maximum of the Ge:Sb δ-layers. Electrical characterization of grown Ge:Sb structures revealed nearly full electrical activation of Sb atoms and the two-dimensional nature of charge carrier transport in δ-layers.

  3. Investigation of Ge1-xSnx/Ge with high Sn composition grown at low-temperature

    NASA Astrophysics Data System (ADS)

    Yu, I. S.; Wu, T. H.; Wu, K. Y.; Cheng, H. H.; Mashanov, V. I.; Nikiforov, A. I.; Pchelyakov, O. P.; Wu, X. S.

    2011-12-01

    We report on experimental investigations of the growth of Ge1-xSnx film with thickness above the critical thickness using Molecular Beam Epitaxy. A series of Ge1-xSnx films with various Sn compositions up to 14% are deposited on a Ge buffer layer for growth at low temperatures close to the melting point of Sn. Analysis of various measurements shows that the Ge1-xSnx film is defect free in the XTEM image and that Sn is distributed almost uniformly in the film for Sn compositions up to 9.3%. The Sn composition of the films is higher than the Sn composition that is theoretically predicted to cause the energy band of Ge to change from an indirect to a direct bandgap; thus, the present investigation provides a method for growing direct bandgap GeSn film, which is desired for use in applications involving optoelectronic devices.

  4. Ge/SiGe quantum wells on Si(111): Growth, structural, and optical properties

    SciTech Connect

    Gatti, E. Pezzoli, F.; Grilli, E.; Isa, F.; Chrastina, D.; Isella, G.; Müller Gubler, E.

    2014-07-28

    The epitaxial growth of Ge/Si{sub 0.15}Ge{sub 0.85} multiple quantum wells (MQWs) on Si(111) substrates is demonstrated. A 3 μm thick reverse, double-step virtual substrate with a final composition of Si{sub 0.10}Ge{sub 0.90} has been employed. High resolution XRD, TEM, AFM and defect etching analysis has been used for the study of the structural properties of the buffer and of the QWs. The QW stack is characterized by a threading dislocation density of about 3 × 10{sup 7 }cm{sup −2} and an interdiffusion layer at the well/barrier interface of 2.1 nm. The quantum confined energy levels of this system have been calculated using the k·p and effective mass approximation methods. The Ge/Si{sub 0.15}Ge{sub 0.85} MQWs have been characterized through absorption and photoluminescence measurements. The optical spectra have been compared with those of Ge/Si{sub 0.15}Ge{sub 0.85} QWs grown on Si(001) through a thick graded virtual substrate.

  5. Metastability and relaxation in tensile SiGe on Ge(001) virtual substrates

    SciTech Connect

    Frigerio, Jacopo; Lodari, Mario; Chrastina, Daniel Mondiali, Valeria; Isella, Giovanni; Bollani, Monica

    2014-09-21

    We systematically study the heteroepitaxy of SiGe alloys on Ge virtual substrates in order to understand strain relaxation processes and maximize the tensile strain in the SiGe layer. The degree of relaxation is measured by high-resolution x-ray diffraction, and surface morphology is characterized by atomic force microscopy. The results are analyzed in terms of a numerical model, which considers dislocation nucleation, multiplication, thermally activated glide, and strain-dependent blocking. Relaxation is found to be sensitive to growth rate and substrate temperature as well as epilayer misfit and thickness, and growth parameters are found which allow a SiGe film with over 4 GPa of tensile stress to be obtained.

  6. Modeling of intermediate phase growth

    SciTech Connect

    Umantsev, A.

    2007-01-15

    We introduced a continuum method for modeling of intermediate phase growth and numerically simulated three common experimental situations relevant to the physical metallurgy of soldering: growth of intermetallic compound layer from an unlimited amount of liquid and solid solders and growth of the compound from limited amounts of liquid solder. We found qualitative agreements with the experimental regimes of growth in all cases. For instance, the layer expands in both directions with respect to the base line when it grows from solid solder, and grows into the copper phase when the solder is molten. The quantitative agreement with the sharp-interface approximation was also achieved in these cases. In the cases of limited amounts of liquid solder we found the point of turnaround when the compound/solder boundary changed the direction of its motion. Although such behavior had been previously observed experimentally, the simulations revealed important information: the turnaround occurs approximately at the time of complete saturation of solder with copper. This result allows us to conclude that coarsening of the intermetallic compound structure starts only after the solder is practically saturated with copper.

  7. Characterization of ultrathin-body Germanium-on-insulator (GeOI) structures and MOSFETs on flipped Smart-Cut™ GeOI substrates

    NASA Astrophysics Data System (ADS)

    Yu, Xiao; Kang, Jian; Zhang, Rui; Takenaka, Mitsuru; Takagi, Shinichi

    2016-01-01

    A novel way to realize UTB GeOI substrates, where the high quality surface layers of Smart-Cut™ GeOI is utilized for UTB structure through a layer transfer technology by direct wafer bonding and a GeOI thinning process by the combination of RIE and thermal oxidation, is proposed and demonstrated. The physical properties of the proposed GeOI are systematically evaluated with the thickness down to around 10 nm. The proposed GeOI fabricated and thinned by the present method exhibits better crystal quality than the original one, with preserving the good GeOI thickness uniformity down to the UTB region. The electrical properties of the GeOI structures are also examined by using GeOI pMOSFETs, which are realized with the GeOI thickness down to 11 nm. It is found that the hole mobility of the flipped GeOI is higher at a given GeOI thickness than that of the original GeOI.

  8. Improvement of J(sc) in a Cu2ZnSnS4 Solar Cell by Using a Thin Carbon Intermediate Layer at the Cu2ZnSnS4/Mo Interface.

    PubMed

    Zhou, Fangzhou; Zeng, Fangqin; Liu, Xu; Liu, Fangyang; Song, Ning; Yan, Chang; Pu, Aobo; Park, Jongsung; Sun, Kaiwen; Hao, Xiaojing

    2015-10-21

    Back contact modification plays an important role in improving energy conversion efficiency of Cu2ZnSnS4 (CZTS) thin film solar cells. In this paper, an ultrathin carbon layer is introduced on molybdenum (Mo)-coated soda lime glass (SLG) prior to the deposition of CZTS precursor to improve the back contact and therefore enhance CZTS solar cell efficiency. By introducing this layer, the short circuit current (Jsc) and device conversion efficiency increase for both nonvacuum (sol-gel) and vacuum (sputtering) methods. Specifically, for the sol-gel based process, Jsc increases from 13.60 to 16.96 mA/cm(2) and efficiency from 4.47% to 5.52%, while for the sputtering based process, Jsc increases from 17.50 to 20.50 mA/cm(2) and efficiency from 4.10% to 5.20%. Furthermore, introduction of this layer does not lead to any deterioration of either open circuit voltage (Voc) or fill factor (FF). PMID:26418196

  9. Raman scattering from fully strained Ge1-xSnx (x<=0.22) alloys grown on Ge(001)2×1 by low-temperature molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Rojas-López, M.; Navarro-Contreras, H.; Desjardins, P.; Gurdal, O.; Taylor, N.; Carlsson, J. R. A.; Greene, J. E.

    1998-08-01

    Fully strained single-crystal Ge1-xSnx alloys (x⩽0.22) deposited on Ge(001)2×1 by low-temperature molecular beam epitaxy have been studied by Raman scattering. The results are characterized by a Ge-Ge longitudinal optical (LO) phonon line, which shifts to lower frequencies with increasing x. Samples capped with a 200-Å-thick Ge layer exhibit a second Ge-Ge LO phonon line whose position remains close to that expected from bulk Ge. For all samples, capped and uncapped, the frequency shift ΔωGeSn of the Ge-Ge LO phonon line from the Ge1-xSnx layer, with respect to the position for bulk Ge, is linear with the Sn fraction x (ΔωGeSn=-76.8x cm-1) over the entire composition range. Using the elastic constants, the Grüneisen parameter, and the shear phonon deformation parameter for Ge, we calculate the contribution of compressive strain to the total frequency shift to be Δωstrain=63.8x cm-1. Thus, the LO phonon shift in Ge1-xSnx due to substitutional-Sn-induced bond stretching in fully relaxed alloys is estimated to be Δωbond =-140.6x cm-1.

  10. Arsenic-terminated Ge(111): An ideal 1 x 1 surface

    SciTech Connect

    Bringans, R.D.; Uhrberg, R.I.G.; Bachrach, R.Z.; Northrup, J.E.

    1985-07-29

    Arsenic interaction with the Ge(111) surface results in the replacement of the outer Ge layer with an As layer. This system has a 1 x 1 symmetry and the calculated positions of the As atoms are very close to the positions expected from bulk bond lengths. Ge(111):As is thus a model ideal surface and a comparison is made of an experimental and a theoretical determination of its fully occupied surface band.

  11. Intermediate water recovery system

    NASA Technical Reports Server (NTRS)

    Deckman, G.; Anderson, A. R. (Editor)

    1973-01-01

    A water recovery system for collecting, storing, and processing urine, wash water, and humidity condensates from a crew of three aboard a spacecraft is described. The results of a 30-day test performed on a breadboard system are presented. The intermediate water recovery system produced clear, sterile, water with a 96.4 percent recovery rate from the processed urine. Recommendations for improving the system are included.

  12. Rutherford backscattering research on the strained SiGe/Si structure

    NASA Astrophysics Data System (ADS)

    Hu, J. H.; Fan, Y. L.; Gong, D. W.; Wang, X.; Zhou, Z. Y.

    1994-12-01

    The ion beam channeling technique has been used to characterize the SiGe/Si structure. It reveals different relative yield between <100> and <110> aligned spectra for strained SiGe layer, silicon buffer layer and silicon substrate which depends on different atomic arrangement.

  13. Gallium Arsenide Layers Grown by Molecular Beam Epitaxy on Single Crystalline Germanium Islands on Insulator

    NASA Astrophysics Data System (ADS)

    Takai, Mikio; Tanigawa, Takaho; Minamisono, Tadanori; Gamo, Kenji; Namba, Susumu

    1984-05-01

    Gallium arsenide (GaAs) layers have successfully been grown by molecular beam epitaxy on single crystalline germanium (Ge) islands, recrystallized by zone melting with SiO2 capping layers, on thermally-oxidized Si-wafers. The GaAs layers, grown on the single crystalline Ge islands, show smooth surfaces without any grain-boundaries, while those, grown on the Ge islands with grain-boundaries and on the SiO2, have grain-boundaries. The GaAs layers on the single crystalline Ge islands emit photoluminescence, the intensity of which is almost comparable to that of GaAs layers on bulk Ge crystals.

  14. Multilevel Ge-Se Film Based Resist Systems

    NASA Astrophysics Data System (ADS)

    Tai, K. L.; Vadimsky, R. G.; Ong, E.

    1982-06-01

    Multilevel resist systems based on Ge-Se films make possible the use of optical projection printers for printing 0.5-1.0μm features. The four multilevel resist systems considered employ either a photosensitive or a photopassive polymer layer for planarization. In bilevel schemes the surface of the Ge-Se film is reacted in a Ag(CN)i- containing solution to form a Ag2Se imaging layer. No reacted Ge-Se is used as a sacrificial layer in trilevel schemes. Ge-Se films are resistant to attack by oxygen plasma and therefore make good masks for pattern transfer by dry (reactive ion) etching, to a thick underlying photopassive polymer layer. Because of their high absorbance (a 105cm-1) in the ultraviolet and violet, Ge-Se patterns can also be used as exposure masks for transferring images to a thick underlying photosensitive polymer layer. The latter is "flood" exposed through the Ge-Se mask and wet developed. Both dry and wet processes provide steep wall-profile patterns in the polymer layer. The dry process provides superior feature size control while the wet process offers reduced processing cost. The exceptional lithographic performance exhibited by Ge-Se resist systems is attributed to a unique edge-sharpening effect; diffraction is compensated for by lateral silver diffusion in the Ag2Se layer. Patterns having 0.6μm lines and spaces are obtained over lcmXlcm fields with a defocus tolerance of 2.5μm using a standard Zeiss 10:1 reduction lens (N.A.=0.28, λ=436nm). Results indicate that optical lithography can practically print features in the size regime previously reserved for a-beam or x-ray based lithographic technologies.

  15. Method of producing buried porous silicon-geramanium layers in monocrystalline silicon lattices

    NASA Technical Reports Server (NTRS)

    Fathauer, Robert W. (Inventor); George, Thomas (Inventor); Jones, Eric W. (Inventor)

    1997-01-01

    Lattices of alternating layers of monocrystalline silicon and porous silicon-germanium have been produced. These single crystal lattices have been fabricated by epitaxial growth of Si and Si--Ge layers followed by patterning into mesa structures. The mesa structures are stain etched resulting in porosification of the Si--Ge layers with a minor amount of porosification of the monocrystalline Si layers. Thicker Si--Ge layers produced in a similar manner emitted visible light at room temperature.

  16. Fabrication of crystalline Ge thin films by co-deposition of Au and Ge at low substrate temperatures (<200 °C) without post annealing

    NASA Astrophysics Data System (ADS)

    Sugiyama, Takatoshi; Mishiba, Naoya; Kamiko, Masao; Kyuno, Kentaro

    2016-09-01

    Crystalline Ge thin films with (111) orientation are obtained by co-depositing Au and Ge on a substrate heated to ∼170 °C, with Au segregating at the film surface, which is desirable for selective etching. Although in the conventional metal-induced crystallization method using Au as a catalyst, a bilayer of Au and amorphous Ge layers have to be annealed for Ge to crystallize, the film in this study is already crystalline in the as-deposited state. The effective crystallization process implies the existence of a supercooled liquid alloy layer at the growth front.

  17. X-ray scattering studies of surfactant mediated epitaxial growth of Si/Ge/Si(001) heterostructures

    SciTech Connect

    Rodrigues, W.; Sakata, O.; Lee, T.-L.; Walko, D. A.; Marasco, D. L.; Bedzyk, M. J. [Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208

    2000-09-01

    The strain and morphology of Si/Ge films grown by surfactant mediated molecular beam epitaxy on Si(001) with Bi as the surfactant were studied with grazing-incidence x-ray diffraction, x-ray reflectivity, low-energy electron diffraction, and Auger electron spectroscopy. Bi is observed to prevent the intermixing of Ge and Si layers by inhibiting Ge segregation in Si. Without a surfactant the critical thickness of Ge/Si(001) is 3 monolayers (ML). Using Bi, two-dimensional growth of Ge is observed for films up to 10 ML in thickness, with the onset of strain relaxation occurring at 7 ML of Ge growth. At 10 ML, the top Ge atomic layers are only partially relaxed. This is achieved by introducing roughness at the interface of the Ge and Si layers. (c) 2000 American Institute of Physics.

  18. Possible source of intermediate ions over marine environment.

    PubMed

    Pawar, Sunil D; Gopalakrishnan, V

    2012-01-01

    Measurements of small, intermediate and large ions made onboard ORV Sagarkanya over the Arabian Sea in May-June 2003 during Arabian Sea Monsoon Experiment (ARMEX) are reported here. The daily averaged values of small-, intermediate-, and large-ion concentrations measured for 36 days during this cruise have been used for analysis. The analysis shows a weak positive correlation of 0.14 between intermediate- and large-ion concentrations, which indicates that the sources of these two types of ions are different over ocean surface. The negative correlation is observed between small- and intermediate-ion concentration for entire period of cruise. In addition, it is seen that the intermediate-ion concentration shows a very good (r = 0.58) and significant positive correlation with sea surface pressure. Based on good negative correlation between small- and intermediate-ion concentrations and good positive correlation between intermediate-ion concentration and sea surface pressure, it has been proposed that attachment of small ions to the ultrafine particles transported from upper troposphere to marine boundary layer is the main source of intermediate ions over ocean surface. This study supports the idea that the main source of ultrafine particles over marine boundary layer (MBL) is entrainment of aerosol particles from the free troposphere. PMID:22701357

  19. Possible Source of Intermediate Ions over Marine Environment

    PubMed Central

    Pawar, Sunil D.; Gopalakrishnan, V.

    2012-01-01

    Measurements of small, intermediate and large ions made onboard ORV Sagarkanya over the Arabian Sea in May-June 2003 during Arabian Sea Monsoon Experiment (ARMEX) are reported here. The daily averaged values of small-, intermediate-, and large-ion concentrations measured for 36 days during this cruise have been used for analysis. The analysis shows a weak positive correlation of 0.14 between intermediate- and large-ion concentrations, which indicates that the sources of these two types of ions are different over ocean surface. The negative correlation is observed between small- and intermediate-ion concentration for entire period of cruise. In addition, it is seen that the intermediate-ion concentration shows a very good (r = 0.58) and significant positive correlation with sea surface pressure. Based on good negative correlation between small- and intermediate-ion concentrations and good positive correlation between intermediate-ion concentration and sea surface pressure, it has been proposed that attachment of small ions to the ultrafine particles transported from upper troposphere to marine boundary layer is the main source of intermediate ions over ocean surface. This study supports the idea that the main source of ultrafine particles over marine boundary layer (MBL) is entrainment of aerosol particles from the free troposphere. PMID:22701357

  20. Ultrathin GeSn p-channel MOSFETs grown directly on Si(111) substrate using solid phase epitaxy

    NASA Astrophysics Data System (ADS)

    Maeda, Tatsuro; Jevasuwan, Wipakorn; Hattori, Hiroyuki; Uchida, Noriyuki; Miura, Shu; Tanaka, Masatoshi; Santos, Nuno D. M.; Vantomme, André; Locquet, Jean-Pierre; Lieten, Ruben R.

    2015-04-01

    Ultrathin GeSn layers with a thickness of 5.5 nm are fabricated on a Si(111) substrate by solid phase epitaxy (SPE) of amorphous GeSn layers with Sn concentrations up to 6.7%. We demonstrate well-behaved depletion-mode operation of GeSn p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) with an on/off ratio of more than 1000 owing to the ultrathin GeSn channel layer (5.5 nm). It is found that the on current increases significantly with increasing Sn concentration at the same gate overdrive, attributed to an increasing substitutional Sn incorporation in Ge. The GeSn (6.7%) layer sample shows approximately 90% enhancement in hole mobility in comparison with a pure Ge channel on Si.

  1. Structures of stable and metastable Ge2Sb2Te5, an intermetallic compound in GeTe-Sb2Te3 pseudobinary systems.

    PubMed

    Matsunaga, Toshiyuki; Yamada, Noboru; Kubota, Yoshiki

    2004-12-01

    The most widely used memory materials for rewritable phase-change optical disks are the GeTe-Sb2Te3 pseudobinary compounds. Among these compounds, Ge2Sb2Te5 crystallizes into a cubic close-packed structure with a six-layer period (metastable phase) in the non-thermal equilibrium state, and a trigonal structure with a nine-layer period (stable phase) in the thermal equilibrium state. The structure of the stable phase has Ge/Sb layers in which Ge and Sb are randomly occupied, as does the structure of the metastable phase, while the conventionally estimated structure had separate layers of Ge and Te. The metastable and stable phases are very similar in that Te and Ge/Sb layers stack alternately to form the crystal. The major differences between these phases are: (i) the stable phase has pairs of adjacent Te layers that are not seen in the metastable phase and (ii) only the metastable phase contains vacancies of ca 20 at. % in the Ge/Sb layers. PMID:15534378

  2. Impact of Ge profile on the performance of PNP SiGe HBT on thin film SOI

    NASA Astrophysics Data System (ADS)

    Misra, Prasanna K.; Qureshi, S.

    2012-10-01

    The pnp SiGe HBT on thin film SOI is investigated with different Ge profiles using 2D numerical simulations in MEDICI. The base current, collector current, DC current gain, AC voltage gain, unity current gain frequency and breakdown voltage is obtained for a 0.09 × 1.0 μm2 pnp SiGe HBT with triangular (0%-30%), trapezoidal (10%- 20%) and box (15%) Ge profiles in the base layer. The results obtained with the Ge profiles, has been analyzed and compared. The Ft BVCEO product for triangular, trapezoidal and box Ge profiles has been found as 190.8, 401, and 359.6 GHzV respectively. The tradeoff between voltage gain and unity current gain frequency for the Ge profiles has been analyzed. The simulation result suggests that the pnp SiGe HBT on thin film SOI with trapezoidal Ge profile is a potential candidate for the high speed complementary bipolar circuits that can be used in high performance mixed signal applications.

  3. Fabrication and ferromagnetism of Si-SiGe/MnGe core-shell nanopillars.

    PubMed

    Wang, Liming; Liu, Tao; Wang, Shuguang; Zhong, Zhenyang; Jia, Quanjie; Jiang, Zuimin

    2016-10-01

    Si-Si0.5Ge0.5/Mn0.08Ge0.92 core-shell nanopillar samples were fabricated on ordered Si nanopillar patterned substrates by molecular beam epitaxy at low temperatures. The magnetic properties of the samples are found to depend heavily on the growth temperature of the MnGe layer. The sample grown at a moderate temperature of 300 °C has the highest Curie temperature of 240 K as well as the strongest ferromagnetic signals. On the basis of the microstructural results, the ferromagnetic properties of the samples are believed to come from the intrinsic Mn-doped amorphous or crystalline Ge ferromagnetic phase rather than any intermetallic ferromagnetic compounds of Mn and Ge. After being annealed at a temperature of 500 °C, all the samples exhibit the same Curie temperature of 220 K, which is in sharp contrast to the different Curie temperature for the as-grown samples, and the ferromagnetism for the annealed samples comes from Mn5GeSi2 compounds which are formed during the annealing. PMID:27581545

  4. 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.

  5. First-Principles calculation of surface stress evolution of Ge quantum dots

    NASA Astrophysics Data System (ADS)

    Lu, Guang-Hong; Cuma, Martin; Liu, Feng

    2004-03-01

    Ge quantum dots (huts) form on Si(001) surface after growth of a wetting layer of 3-4 monolayers, having a highly ordered structure bounded by (105) facets. Surface stress/strain plays an important role in their stabilization. Recent experiments [1,2] of Ge growth on Si(105) surface have suggested a continuous evolution toward compression with increasing Ge coverage to stabilize Ge/Si(105) facets. However, quantitative information of surface stress of Ge/Si(105) facet, and hence the surface stress on Ge dots is still lacking, which causes a big gap in our understanding. Therefore, we have performed large-scale first-principles calculations to evaluate evolution of surface energy and surface stress in the Ge-covered Si (105) surface, as a function of Ge coverage. We show a very large tensile surface stress present in clean Si(105) surface induced by surface reconstruction, which continuously evolve toward compression with increasing Ge coverage, confirming the qualitative suggestion by experiments. Quantitatively, only moderate reduction of tensile surface stress occurs for the first two layers of Ge deposition, and the surface stress actually remains to be tensile until 5-layer of Ge coverage. This work is supported by DOE. [1] Y. Fujikawa, K. Akiyama, T. Nagao, T. Sakurai, M.G. Lagally, T. Hashimoto, Y. Morikawa, and K. Terakura, Phys. Rev. Lett. 88, 176101 (2002) [2] P. Raiteri,D.B. Migas, L. Miglio, A. Rastelli, and H. von Kanel, Phys. Rev. Lett. 88, 256103 (2002)

  6. Structural singularities in Ge(x)Te(100-x) films.

    PubMed

    Piarristeguy, A A; Micoulaut, M; Escalier, R; Jóvári, P; Kaban, I; van Eijk, J; Luckas, J; Ravindren, S; Boolchand, P; Pradel, A

    2015-08-21

    Structural and calorimetric investigation of Ge(x)Te(100-x) films over wide range of concentration 10 < x < 50 led to evidence two structural singularities at x ∼ 22 at. % and x ∼ 33-35 at. %. Analysis of bond distribution, bond variability, and glass thermal stability led to conclude to the origin of the first singularity being the flexible/rigid transition proposed in the framework of rigidity model and the origin of the second one being the disappearance of the undercooled region resulting in amorphous materials with statistical distributions of bonds. While the first singularity signs the onset of the Ge-Ge homopolar bonds, the second is related to compositions where enhanced Ge-Ge correlations at intermediate lengthscales (7.7 Å) are observed. These two threshold compositions correspond to recently reported resistance drift threshold compositions, an important support for models pointing the breaking of homopolar Ge-Ge bonds as the main phenomenon behind the ageing of phase change materials. PMID:26298140

  7. Formation of nickel germanide on SiO{sub 2}-capped n-Ge to lower its Schottky barrier height

    SciTech Connect

    Lin, Guangyang; Tang, Mengrao; Li, Cheng Huang, Shihao; Lu, Weifang; Wang, Chen; Yan, Guangming; Chen, Songyan

    2013-12-16

    In this Letter, NiGe/SiO{sub 2}/n-Ge ohmic contacts were demonstrated with Ge, rather than Ni, diffusion through the ion-implanted SiO{sub 2} films to form NiGe. The equivalent Schottky barrier height reduced from 0.58 eV for NiGe/n-Ge to ohmic contact. The anomalous diffusion behavior and accumulation of Ge in the SiO{sub 2} near the NiGe/SiO{sub 2} interface can be explained by vacancy-enhanced Ge diffusion. It is proposed that the presence of vacancies and Ge atoms embedded in the SiO{sub 2} layer play a significant role in the current enhancement by generation of multiple levels in the SiO{sub 2} band gap.

  8. Atomistic simulation of damage accumulation and amorphization in Ge

    SciTech Connect

    Gomez-Selles, Jose L. Martin-Bragado, Ignacio; Claverie, Alain; Benistant, Francis

    2015-02-07

    Damage accumulation and amorphization mechanisms by means of ion implantation in Ge are studied using Kinetic Monte Carlo and Binary Collision Approximation techniques. Such mechanisms are investigated through different stages of damage accumulation taking place in the implantation process: from point defect generation and cluster formation up to full amorphization of Ge layers. We propose a damage concentration amorphization threshold for Ge of ∼1.3 × 10{sup 22} cm{sup −3} which is independent on the implantation conditions. Recombination energy barriers depending on amorphous pocket sizes are provided. This leads to an explanation of the reported distinct behavior of the damage generated by different ions. We have also observed that the dissolution of clusters plays an important role for relatively high temperatures and fluences. The model is able to explain and predict different damage generation regimes, amount of generated damage, and extension of amorphous layers in Ge for different ions and implantation conditions.

  9. Advancing tandem solar cells by spectrally selective multilayer intermediate reflectors.

    PubMed

    Hoffmann, Andre; Paetzold, Ulrich W; Zhang, Chao; Merdzhanova, Tsvetelina; Lambertz, Andreas; Ulbrich, Carolin; Bittkau, Karsten; Rau, Uwe

    2014-08-25

    Thin-film silicon tandem solar cells are composed of an amorphous silicon top cell and a microcrystalline silicon bottom cell, stacked and connected in series. In order to match the photocurrents of the top cell and the bottom cell, a proper photon management is required. Up to date, single-layer intermediate reflectors of limited spectral selectivity are applied to match the photocurrents of the top and the bottom cell. In this paper, we design and prototype multilayer intermediate reflectors based on aluminum doped zinc oxide and doped microcrystalline silicon oxide with a spectrally selective reflectance allowing for improved current matching and an overall increase of the charge carrier generation. The intermediate reflectors are successfully integrated into state-of-the-art tandem solar cells resulting in an increase of overall short-circuit current density by 0.7 mA/cm(2) in comparison to a tandem solar cell with the standard single-layer intermediate reflector. PMID:25322181

  10. Intermediate connector for stacked organic light emitting devices

    DOEpatents

    D& #x27; Andrade, Brian

    2013-02-12

    A device is provided, having an anode, a cathode, and an intermediate connector disposed between the anode and the cathode. A first organic layer including an emissive sublayer is disposed between the anode and the intermediate connector, and a second including an emissive sublayer is disposed between the intermediate connector and the cathode. The intermediate connector includes a first metal having a work function lower than 4.0 eV and a second metal having a work function lower than 5.0 eV. The work function of the first metal is at least 0.5 eV less than the work function of the second metal. The first metal is in contact with a sublayer of the second organic layer that includes a material well adapted to receive holes from a low work function metal.

  11. GeO{sub 2}/Ge structure submitted to annealing in deuterium: Incorporation pathways and associated oxide modifications

    SciTech Connect

    Bom, N. M.; Soares, G. V.; Hartmann, S.; Bordin, A.; Radtke, C.

    2014-10-06

    Deuterium (D) incorporation in GeO{sub 2}/Ge structures following D{sub 2} annealing was investigated. Higher D concentrations were obtained for GeO{sub 2}/Ge samples in comparison to their SiO{sub 2}/Si counterparts annealed in the same conditions. Oxygen vacancies produced during the annealing step in D{sub 2} constitute defect sites for D incorporation, analogous to defects at the SiO{sub 2}/Si interfacial region. Besides D incorporation, volatilization of the oxide layer is also observed as a consequence of D{sub 2} annealing, especially in the high temperature regime of the present study (>450 °C). In parallel to this volatilization, the stoichiometry and chemical structure of remnant oxide are modified as well. These results evidence the broader impact of forming gas annealing in dielectric/Ge structures with respect to SiO{sub 2}/Si counterparts.

  12. Stark shift of the absorption spectra in Ge/Ge1-xSnx/Ge type-I single QW cell for mid-wavelength infra-red modulators

    NASA Astrophysics Data System (ADS)

    Yahyaoui, N.; Sfina, N.; Lazzari, J.-L.; Bournel, A.; Said, M.

    2015-09-01

    For mid-wavelength infra-red (MWIR) modulation or detection applications, we propose α-Sn rich Ge/Ge1-xSnx/Ge a type-I single quantum wells (SQW) partially strain compensated on Ge1-ySny relaxed layers grown onto (0 0 1)-oriented Ge substrate. Such elementary cells with W-like potential profiles of conduction and valence bands have been modeled by solving the one-dimensional Schrödinger equation under an applied external electrical field. First, strain effects on electrons, heavy holes (hh) and light holes (lh) energy bands for strained/relaxed Ge1-xSnx/Ge1-ySny heterointerfaces are investigated using the model-solid theory in the whole ranges (0 ⩽ x, y ⩽ 1) of Sn compositions. From the obtained band-discontinuities, band gaps and effective masses, Ge1-ySny/Ge/Ge0.80Sn0.20/Ge/Ge1-ySny cells are computed as a function of the Ge0.80Sn0.20 well width for three compositions of the Ge1-ySny buffer layer (y = 0.05, 0.07 and 0.09) in order to get the optimum quantum confinement of electrons and holes levels while keeping a reasonable amount of averaged strain in the cell. The electric field effect on the absorption spectra is given. An absorption coefficient in the 6× to 3 × 103 cm-1 range is reasonably obtained for a SQW at room temperature with a rather large Stark shift of the direct transition between 0.46 and 0.38 eV (i.e., λ = 3.26-2.70 μm) at large external fields (50 kV/cm). These characteristics are attractive for the design of MWIR optical modulators.

  13. Franz-Keldysh effect in GeSn pin photodetectors

    NASA Astrophysics Data System (ADS)

    Oehme, M.; Kostecki, K.; Schmid, M.; Kaschel, M.; Gollhofer, M.; Ye, K.; Widmann, D.; Koerner, R.; Bechler, S.; Kasper, E.; Schulze, J.

    2014-04-01

    The optical properties and the Franz-Keldysh effect at the direct band gap of GeSn alloys with Sn concentrations up to 4.2% at room temperature were investigated. The GeSn material was embedded in the intrinsic region of a Ge heterojunction photodetector on Si substrates. The layer structure was grown by means of ultra-low temperature molecular beam epitaxy. The absorption coefficient as function of photon energy and the direct bandgap energies were determined. In all investigated samples, the Franz-Keldysh effect can be observed. A maximum absorption ratio of 1.5 was determined for 2% Sn for a voltage swing of 3 V.

  14. Critical thickness for strain relaxation of Ge1-xSnx (x ≤ 0.17) grown by molecular beam epitaxy on Ge(001)

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Zhou, Qian; Dong, Yuan; Tok, Eng Soon; Yeo, Yee-Chia

    2015-06-01

    We investigated the critical thickness (hc) for plastic relaxation of Ge1-xSnx grown by molecular beam epitaxy. Ge1-xSnx films with various Sn mole fraction x (x ≤ 0.17) and different thicknesses were grown on Ge(001). The strain relaxation of Ge1-xSnx films and the hc were investigated by high-resolution x-ray diffraction and reciprocal space mapping. It demonstrates that the measured hc values of Ge1-xSnx layers are as much as an order of magnitude larger than that predicted by the Matthews and Blakeslee (M-B) model. The People and Bean (P-B) model was also used to predict the hc values in Ge1-xSnx/Ge system. The measured hc values for various Sn content follow the trend, but slightly larger than that predicted by the P-B model.

  15. On the compression behavior of Cr2GeC and V2GeC up to quasi-hydrostatic pressures of 50 GPa

    NASA Astrophysics Data System (ADS)

    Manoun, Bouchaib; Amini, Sharam; Gupta, Surojit; Saxena, Surendra K.; Barsoum, Michel W.

    2007-11-01

    Using a synchrotron x-ray radiation source and a diamond anvil cell we measured the functional dependences of the lattice parameters of Cr2GeC and V2GeC to quasi-hydrostatic pressures of the order of 50 GPa. Like other solids in this family of layered ternary carbides and nitrides, the bulk moduli are high and no phase transformations were observed. The bulk modulus of V2GeC (165 ± 2 GPa) is lower than that of Cr2GeC (182 ± 2 GPa). Replacing Ge by Al in V2GeC to form V2AlC leads to a 22% increase in bulk modulus. In contradistinction, the same substitution in Cr2GeC results in a 10% decrease in bulk modulus.

  16. Direct band gap optical emission from Ge islands grown on relaxed Si{sub 0.5}Ge{sub 0.5}/Si (100) substrate

    SciTech Connect

    Aluguri, R.; Manna, S.; Ray, S. K.

    2014-01-07

    Strained Ge islands have been grown on fully relaxed Si{sub 0.5}Ge{sub 0.5} substrate by pulsed laser ablation technique. The formation of strained Ge islands has been found for film with higher thickness following Stranski–Krastanov growth mechanism. The variation of strain with changing Ge layer thickness has been analyzed using Raman spectroscopy and high-resolution X-ray diffraction techniques. X-ray photoelectron spectra have shown the absence of any Si-Ge intermixing and oxidation of Ge films. A strong no-phonon photoluminescence emission from Ge islands has been observed, showing the superior optical characteristics of the islands grown on relaxed substrate.

  17. Direct synthesis of highly textured Ge on flexible polyimide films by metal-induced crystallization

    NASA Astrophysics Data System (ADS)

    Oya, N.; Toko, K.; Saitoh, N.; Yoshizawa, N.; Suemasu, T.

    2014-06-01

    The highly (111)-textured Ge thin film (50-nm thickness) is demonstrated on a flexible polyimide film via the low-temperature crystallization (325 °C) of amorphous Ge using Al as a catalyst. Covering the polyimide with insulators significantly improved the crystal quality of the resulting Ge layer. In particular, SiN covering led to 97% (111)-oriented Ge with grains 200 μm in size, two orders larger than the grain size of polycrystalline Ge directly formed on the polyimide film. This achievement will give a way to realize advanced electronic and optical devices simultaneously allowing for high performance, inexpensiveness, and flexibility.

  18. Direct synthesis of highly textured Ge on flexible polyimide films by metal-induced crystallization

    SciTech Connect

    Oya, N.; Toko, K. Suemasu, T.; Saitoh, N.; Yoshizawa, N.

    2014-06-30

    The highly (111)-textured Ge thin film (50-nm thickness) is demonstrated on a flexible polyimide film via the low-temperature crystallization (325 °C) of amorphous Ge using Al as a catalyst. Covering the polyimide with insulators significantly improved the crystal quality of the resulting Ge layer. In particular, SiN covering led to 97% (111)-oriented Ge with grains 200 μm in size, two orders larger than the grain size of polycrystalline Ge directly formed on the polyimide film. This achievement will give a way to realize advanced electronic and optical devices simultaneously allowing for high performance, inexpensiveness, and flexibility.

  19. Germanium Dumbbells in a New Superconducting Modification of BaGe3.

    PubMed

    Castillo, Rodrigo; Baranov, Alexey I; Burkhardt, Ulrich; Cardoso-Gil, Raul; Schnelle, Walter; Bobnar, Matej; Schwarz, Ulrich

    2016-05-01

    We report the high-pressure high-temperature synthesis (P = 15 GPa, T = 1300 K) of BaGe3(tI32) adopting a CaGe3-type crystal structure. Bonding analysis reveals layers of covalently bonded germanium dumbbells being involved in multicenter Ba-Ge interactions. Physical measurements evidence metal-type electrical conductivity and a transition to a superconducting state at 6.5 K. Chemical bonding and physical properties of the new modification are discussed in comparison to the earlier described hexagonal form BaGe3(hP8) with a columnar arrangement of Ge3 triangles. PMID:27064595

  20. Atom-probe and field emission electron spectroscope studies of Ge on Ir

    NASA Astrophysics Data System (ADS)

    Ashino, Makoto; Tomitori, Masahiko; Nishikawa, Osamu

    1993-04-01

    The combination of an atom-probe (AP) and a field emission electron spectroscope (FEES) was employed to investigate the electronic structure of Ge layers on an Ir substrate. Germanium forms a thin film with a fairly uniform thickness, possibly owing to a small activation energy for diffusion on Ir or the lattice matching between Ge and Ir. The FEES spectrum obtained from Ge layers thicker than 8-9 ML exhibits a semiconductive energy gap and a peak at 0.7 eV below the Fermi level as for Si on Mo. However, the minimum layer thickness to exhibit the semiconductive spectrum profile is significantly thicker than that for Si on Mo. The observed difference could be attributed to the layer structure of the deposited Ge and to the narrower energy gap of Ge than that of Si.

  1. Effect of mixed Ge/Si cross-linking on the physical properties of amorphous Ge-Si-Te networks

    SciTech Connect

    Gunasekera, K.; Boolchand, P.; Micoulaut, M.

    2014-04-28

    Amorphous Ge{sub x}Si{sub x}Te{sub 1−2x} glasses are studied as a function of composition by a combination of experimental and theoretical methods, allowing for a full description of the network structure in relationship with physico-chemical properties. Calorimetric and thermal measurements reveal that such glasses display an anomalous behavior across a range of compositions x{sub c1}=7.5% and intermediate phase, where network rigidity onsets as the content x of Group IV atoms (Ge, Si) are increased. The structural manifestation of these anomalies is understood from  {sup 119}Sn Mössbauer spectroscopy and First Principles Molecular Dynamics at selected compositions (Ge{sub 20}Te{sub 80}, Si{sub 20}Te{sub 80}, and Ge{sub 10}Si{sub 10}Te{sub 80}). The numerical models reveal the quite different roles played by the modifier or network cross-linker Ge or Si atoms, Si being more tetrahedral in sp{sup 3} geometry, whereas Mössbauer spectroscopy shows that the nature of chemical bonding is dramatically changed around x≃ 8%. The precise evolution of the local structure and chemical bonding ultimately allows understanding the origin of the intermediate phase in these complex tellurides.

  2. Three step double layers in the laboratory

    NASA Astrophysics Data System (ADS)

    Bailey, Andrew, III; Hershkowitz, Noah

    1988-01-01

    A new class of stationary double layer structure, with three or more distinct steps, is demonstrated in the laboratory. A large monotonic potential increase results from a series of smaller double layers. In many respects, these double layer structures resemble those inferred from satellite measurements of auroral double layers. This new class of double layer appears to depend on turbulence for its existence and to be a hybrid structure, intermediate between anomalous resistivity and BGK double layers.

  3. Synthesis of Ge nanocrystals embedded in a Si host matrix

    NASA Astrophysics Data System (ADS)

    Ngiam, Shih-Tung; Jensen, Klavs F.; Kolenbrander, K. D.

    1994-12-01

    The synthesis of a composite material consisting of Ge nanoclusters (greater than or equal to 2 nm in diameter) embedded in a Si host matrix is reported. The Ge nanoparticles are produced by pulsed laser ablation and are codeposited in a Si film simultaneously grown by chemical beam epitaxy using disilane. Scanning transmission electron microscopy, combined with energy-dispersive x-ray measurements, show that discrete Ge particles (greater than or equal to 2 nm diameter) are deposited within a polycrystalline Si host matrix. High-resolution transmission electron microscopy reveals that the paricles are crystalline with a lattice spacing corresponding to that of Ge. The enhancement of Si deposition rates from silanes in the presence of Ge, previously demonstrated in chemical vapor deposition of Si(1 - x)Ge(x) alloys, is shown to facilitate the growth of a Si layer around the Ge nanocrystals. The overall composition of the Ge cluster/Si host composite material is determined by Rutherford backscattering measurements.

  4. Tensile-Strained GeSn Metal-Oxide-Semiconductor Field-Effect Transistor Devices on Si(111) Using Solid Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Lieten, Ruben R.; Maeda, Tatsuro; Jevasuwan, Wipakorn; Hattori, Hiroyuki; Uchida, Noriyuki; Miura, Shu; Tanaka, Masatoshi; Locquet, Jean-Pierre

    2013-10-01

    We demonstrate tensile-strained GeSn metal-oxide-semiconductor field-effect transistor (MOSFET) devices on Si(111) substrates using solid phase epitaxy of amorphous GeSn layers. Amorphous GeSn layers are obtained by limiting the adatom surface mobility during deposition. Subsequent annealing transforms the amorphous layer into single-crystalline GeSn by solid phase epitaxy. Single-crystalline GeSn layers with 4.5% Sn and 0.33% tensile strain are fabricated on Si(111) substrates. To verify the structural quality of thin-film GeSn as a channel material, we fabricate ultrathin GeSn p-channel MOSFETs (pMOSFETs) on Si(111). We demonstrate junctionless depletion-mode operation of tensile-strained GeSn(111) pMOSFETs on Si substrates.

  5. Ge auto-doping and out-diffusion in InGaP grown on Ge substrate and their effects on the ordering of InGaP

    NASA Astrophysics Data System (ADS)

    Wu, Hong-Ming; Tsai, Shi-Jane; Ho, Hao-I.; Lin, Hao-Hsiung

    2016-03-01

    We report on the Ge auto-doping and out-diffusion in InGaP epilayer with Cu-Pt ordering grown on 4-in. Ge substrate. Ge profiles determined from secondary ion mass spectrometry indicate that the Ge out-diffusion depth is within 100 nm. However, the edge of the wafer suffers from stronger Ge gas-phase auto-doping than the center, leading to ordering deterioration in the InGaP epilayer. In the edge, we observed a residual Cu-Pt ordering layer left beneath the surface, suggesting that the ordering deterioration takes place after the deposition rather than during the deposition and In/Ga inter-diffusion enhanced by Ge vapor-phase auto-doping is responsible for the deterioration. We thus propose a di-vacancy diffusion model, in which the amphoteric Ge increases the di-vacancy density, resulting in a Ge density dependent diffusion. In the model, the In/Ga inter-diffusion and Ge out-diffusion are realized by the random hopping of In/Ga host atoms and Ge atoms to di-vacancies, respectively. Simulation based on this model well fits the Ge out-diffusion profiles, suggesting its validity. By comparing the Ge diffusion coefficient obtained from the fitting and the characteristic time constant of ordering deterioration estimated from the residual ordering layer, we found that the hopping rates of Ge and the host atoms are in the same order of magnitude, indicating that di-vacancies are bound in the vicinity of Ge atoms.

  6. Interfacial and electrical characteristics of Al2O3 gate dielectric on fully depleted SiGe on insulator

    NASA Astrophysics Data System (ADS)

    Di, Zengfeng; Zhang, Miao; Liu, Weili; Shen, Qinwo; Luo, Suhua; Song, Zhitang; Lin, Chenglu; Huang, Anping; Chu, Paul K.

    2005-06-01

    The interfacial and electrical characteristics of as-deposited or annealed A2O3 gate dielectric films grown on fully depleted SiGe-on-insulator are investigated. An interfacial layer composed of SiOx and GeOx is observed in the as-grown film. The interfacial silicate formation is effectively suppressed by GeOx formation. However, GeOx is reduced to Ge and extensive silicate formation occurs after annealing. The formation of silicate and disappearance of GeOx after annealing leads to a decrease in the density of the interfacial states.

  7. Magnetotransport Properties of Epitaxial Ge/AlAs Heterostructures Integrated on GaAs and Silicon.

    PubMed

    Hudait, Mantu K; Clavel, Michael; Goley, Patrick S; Xie, Yuantao; Heremans, Jean J

    2015-10-14

    The magnetotransport properties of epitaxial Ge/AlAs heterostructures with different growth conditions and substrate architectures have been studied under ±9 T magnetic field and at 390 mK temperature. Systematic mobility measurements of germanium (Ge) epilayers grown on GaAs substrates at growth temperatures from 350 to 450 °C allow us to extract a precise growth window for device-quality Ge, corroborated by structural and morphological properties. Our results on Si substrate using a composite metamorphic AlAs/GaAs buffer at 400 °C Ge growth temperature, show that the Ge/AlAs system can be tailored to have a single carrier transport while keeping the charge solely in the Ge layer. Single carrier transport confined to the Ge layer is demonstrated by the weak-localization quantum correction to the conductivity observed at low magnetic fields and 390 mK temperature. The weak localization effect points to a near-absence of spin-orbit interaction for carriers in the electronically active layer and is used here for the first time to pinpoint Ge as this active layer. Thus, the epitaxial Ge grown on Si using AlAs/GaAs buffer architecture is a promising candidate for next-generation energy-efficient fin field-effect transistor applications. PMID:26413844

  8. Analytical response function for planar Ge detectors

    NASA Astrophysics Data System (ADS)

    García-Alvarez, Juan A.; Maidana, Nora L.; Vanin, Vito R.; Fernández-Varea, José M.

    2016-04-01

    We model the response function (RF) of planar HPGe x-ray spectrometers for photon energies between around 10 keV and 100 keV. The RF is based on the proposal of Seltzer [1981. Nucl. Instrum. Methods 188, 133-151] and takes into account the full-energy absorption in the Ge active volume, the escape of Ge Kα and Kβ x-rays and the escape of photons after one Compton interaction. The relativistic impulse approximation is employed instead of the Klein-Nishina formula to describe incoherent photon scattering in the Ge crystal. We also incorporate a simple model for the continuous component of the spectrum produced by the escape of photo-electrons from the active volume. In our calculations we include external interaction contributions to the RF: (i) the incoherent scattering effects caused by the detector's Be window and (ii) the spectrum produced by photo-electrons emitted in the Ge dead layer that reach the active volume. The analytical RF model is compared with pulse-height spectra simulated using the PENELOPE Monte Carlo code.

  9. Conformational dynamics through an intermediate

    NASA Astrophysics Data System (ADS)

    Garai, Ashok; Zhang, Yaojun; Dudko, Olga K.

    2014-04-01

    The self-assembly of biological and synthetic nanostructures commonly proceeds via intermediate states. In living systems in particular, the intermediates have the capacity to tilt the balance between functional and potentially fatal behavior. This work develops a statistical mechanical treatment of conformational dynamics through an intermediate under a variable force. An analytical solution is derived for the key experimentally measurable quantity—the distribution of forces at which a conformational transition occurs. The solution reveals rich kinetics over a broad range of parameters and enables one to locate the intermediate and extract the activation barriers and rate constants.

  10. Stellar Laboratories: New GeV and Ge VI Oscillator Strengths and their Validation in the Hot White Dwarf RE0503-289

    NASA Technical Reports Server (NTRS)

    Rauch, T.; Werner, K.; Biemont, E.; Quinet, P.; Kruk, J. W.

    2013-01-01

    State-of-the-art spectral analysis of hot stars by means of non-LTE model-atmosphere techniques has arrived at a high level of sophistication. The analysis of high-resolution and high-S/N spectra, however, is strongly restricted by the lack of reliable atomic data for highly ionized species from intermediate-mass metals to trans-iron elements. Especially data for the latter has only been sparsely calculated. Many of their lines are identified in spectra of extremely hot, hydrogen-deficient post-AGB stars. A reliable determination of their abundances establishes crucial constraints for AGB nucleosynthesis simulations and, thus, for stellar evolutionary theory. Aims. In a previous analysis of the UV spectrum of RE 0503-289, spectral lines of highly ionized Ga, Ge, As, Se, Kr, Mo, Sn, Te, I, and Xe were identified. Individual abundance determinations are hampered by the lack of reliable oscillator strengths. Most of these identified lines stem from Ge V. In addition, we identified Ge VI lines for the first time. We calculated Ge V and Ge VI oscillator strengths in order to reproduce the observed spectrum. Methods. We newly calculated Ge V and Ge VI oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our non-LTE stellar-atmosphere models for the analysis of the Ge IV-VI spectrum exhibited in high-resolution and high-S/N FUV (FUSE) and UV (ORFEUS/BEFS, IUE) observations of RE 0503-289. Results. In the UV spectrum of RE 0503-289, we identify four Ge IV, 37 Ge V, and seven Ge VI lines. Most of these lines are identified for the first time in any star. We can reproduce almost all Ge IV, GeV, and Ge VI lines in the observed spectrum of RE 0503-289 (T(sub eff) = 70 kK, log g = 7.5) at log Ge = -3.8 +/- 0.3 (mass fraction, about 650 times solar). The Ge IV/V/VI ionization equilibrium, that is a very sensitive T(sub eff) indicator, is reproduced well. Conclusions. Reliable measurements and calculations of atomic data are a

  11. Low-temperature (180 °C) formation of large-grained Ge (111) thin film on insulator using accelerated metal-induced crystallization

    SciTech Connect

    Toko, K. Numata, R.; Oya, N.; Suemasu, T.; Fukata, N.; Usami, N.

    2014-01-13

    The Al-induced crystallization (AIC) yields a large-grained (111)-oriented Ge thin film on an insulator at temperatures as low as 180 °C. We accelerated the AIC of an amorphous Ge layer (50-nm thickness) by initially doping Ge in Al and by facilitating Ge diffusion into Al. The electron backscatter diffraction measurement demonstrated the simultaneous achievement of large grains over 10 μm and a high (111) orientation fraction of 90% in the polycrystalline Ge layer formed at 180 °C. This result opens up the possibility for developing Ge-based electronic and optical devices fabricated on inexpensive flexible substrates.

  12. Silver photo-diffusion and photo-induced macroscopic surface deformation of Ge33S67/Ag/Si substrate

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Y.; Asaoka, H.; Uozumi, Y.; Kondo, K.; Yamazaki, D.; Soyama, K.; Ailavajhala, M.; Mitkova, M.

    2016-08-01

    Ge-chalcogenide films show various photo-induced changes, and silver photo-diffusion is one of them which attracts lots of interest. In this paper, we report how silver and Ge-chalcogenide layers in Ge33S67/Ag/Si substrate stacks change under light exposure in the depth by measuring time-resolved neutron reflectivity. It was found from the measurement that Ag ions diffuse all over the matrix Ge33S67 layer once Ag dissolves into the layer. We also found that the surface was macroscopically deformed by the extended light exposure. Its structural origin was investigated by a scanning electron microscopy.

  13. Kesterite Cu2Zn(Sn,Ge)(S,Se)4 thin film with controlled Ge-doping for photovoltaic application

    NASA Astrophysics Data System (ADS)

    Zhao, Wangen; Pan, Daocheng; Liu, Shengzhong (Frank)

    2016-05-01

    Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm2 without an anti-reflection layer.Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm2 without an anti-reflection layer. Electronic supplementary information (ESI) available: The XRD patterns, chemical component analysis, top-view and cross-sectional images, and XPS of CZTGSSe thin films with different Ge content are exhibited. See DOI: 10.1039/c6nr00959j

  14. Epitaxial growth of highly compressively strained GeSn alloys up to 12.5% Sn

    NASA Astrophysics Data System (ADS)

    Oehme, M.; Buca, D.; Kostecki, K.; Wirths, S.; Holländer, B.; Kasper, E.; Schulze, J.

    2013-12-01

    This paper reports on the growth and characterization of highly compressive strained GeSn layers on thin strain relaxed Ge virtual substrates on Si wafers. Sn concentration up to 12.5%, which is about more than 10 times the thermal equilibrium predicted for GeSn binaries, are successfully epitaxially grown by ultra-low temperature (160 °C) molecular beam epitaxy. A minimum channeling yield of 9% evidence the high crystalline quality of the GeSn alloys while angular channeling scan demonstrate that all GeSn layers are fully pseudomorphic on the relaxed Ge virtual substrate. The strain analysis shows a deviation from the Vegard's law for Sn contents above 8%. The analysis is completed by the Raman mode dependence on the alloys composition.

  15. Intermediate BL Lac objects

    NASA Astrophysics Data System (ADS)

    Bondi, M.; Marchã, M. J. M.; Dallacasa, D.; Stanghellini, C.

    2001-08-01

    The 200-mJy sample, defined by Marchã et al., contains about 60 nearby, northern, flat-spectrum radio sources. In particular, the sample has proved effective at finding nearby radio-selected BL Lac objects with radio luminosities comparable to those of X-ray-selected objects, and low-luminosity flat-spectrum weak emission-line radio galaxies (WLRGs). The 200-mJy sample contains 23 BL Lac objects (including 6 BL Lac candidates) and 19 WLRGs. We will refer to these subsamples as the 200-mJy BL Lac sample and the 200-mJy WLRG sample, respectively. We have started a systematic analysis of the morphological pc-scale properties of the 200-mJy radio sources using VLBI observations. This paper presents VLBI observations at 5 and 1.6GHz of 14 BL Lac objects and WLRGs selected from the 200-mJy sample. The pc-scale morphology of these objects is briefly discussed. We derive the radio beaming parameters of the 200-mJy BL Lac objects and WLRGs and compare them with those of other BL Lac samples and with a sample of FR I radio galaxies. The overall broad-band radio, optical and X-ray properties of the 200-mJy BL Lac sample are discussed and compared with those of other BL Lac samples, radio- and X-ray-selected. We find that the 200-mJy BL Lac objects fill the gap between HBL and LBL objects in the colour-colour plot, and have intermediate αXOX as expected in the spectral energy distribution unification scenario. Finally, we briefly discuss the role of the WLRGs.

  16. Masonry. Performance Objectives. Intermediate Course.

    ERIC Educational Resources Information Center

    Thompson, Moses

    Several intermediate performance objectives and corresponding criterion measures are listed for each of 13 terminal objectives for an intermediate masonry course. These materials, developed for a two-semester (3 hours daily) course, are designed to provide the student with the skills and knowledge necessary for entry level employment in the field…

  17. Printing. Performance Objectives. Intermediate Course.

    ERIC Educational Resources Information Center

    Seivert, Chester

    Several intermediate performance objectives and corresponding criterion measures are listed for each of 13 terminal objectives for an intermediate printing course. The materials were developed for a two-semester (3 hours daily) course with specialized classroom, shop, and practical experiences designed to enable the student to develop proficiency…

  18. Welding. Performance Objectives. Intermediate Course.

    ERIC Educational Resources Information Center

    Vincent, Kenneth

    Several intermediate performance objectives and corresponding criterion measures are listed for each of nine terminal objectives for an intermediate welding course. The materials were developed for a 36-week (3 hours daily) course designed to prepare the student for employment in the field of welding. Electric welding and specialized (TIG & MIG)…

  19. SiGe/Si heterojunction internal photoemission long-wavelength infrared detectors fabricated by molecular beam epitaxy

    NASA Technical Reports Server (NTRS)

    Lin, True-Lon; Ksendzov, A.; Dejewski, Suzan M.; Jones, Eric W.; Fathauer, Robert W.; Krabach, Timothy N.; Maserjian, Joseph

    1991-01-01

    A new SiGe/Si heterojunction internal photoemission (HIP) long-wavelength infrared (LWIR) detector has been fabricated by molecular beam epitaxy (MBE). The detection mechanism of the SiGe/Si HIP detector is infrared absorption in the degenerately doped p+-SiGe layer followed by internal photoemission of photoexcited holes over a heterojunction barrier. By adjusting the Ge concentration in the SiGe layer, and, consequently, the valence band offset between SiGe and Si, the cutoff wavelength of SiGe HIP detectors can be extended into the LWIR (8-17-micron) regime. Detectors were fabricated by growing p+-SiGe layers using MBE on patterned p-type Si substrates. The SiGe layers were boron-doped, with concentrations ranging from 10 to the 19th/cu cm to 4 x 10 to the 20th/cu cm. Infrared absorption of 5-25 percent in a 30-nm-thick p+-SiGe layer was measured in the 3-20-micron range using a Fourier transform infrared spectrometer. Quantum efficiencies of 3-5 percent have been obtained from test devices in the 8-12-micron range.

  20. Magnetic order in the filled skutterudites RPt4Ge12 (R = Nd, Eu)

    NASA Astrophysics Data System (ADS)

    Nicklas, M.; Gumeniuk, R.; Schnelle, W.; Rosner, H.; Leithe-Jasper, A.; Steglich, F.; Grin, Yu

    2011-01-01

    Rare-earth metal filled skutterudites RPt4Ge12 with R=La-Nd, and Eu exhibit a variety of different ground states, e.g., conventional and unconventional superconductivity in LaPt4Ge12 and PrPt4Ge12, respectively, and intermediate valence behavior in CePt4Ge12. In this work we investigate the magnetic state of NdPt4Ge12 and EuPt4Ge12 by specific heat, dc-susceptibility and magnetization. NdPt4Ge12 shows two magnetic phase transitions at TN1 = 0.67 K and TN2 = 0.58 K, while EuPt4Ge12 displays a complex magnetic phase diagram below the magnetic ordering temperature of 1.78 K. The specific heat indicates that in NdPt4Ge12 the crystalline electric field (CEF) ground state of the Nd3+ is a quartet and that, as expected, in EuPt4Ge12 the Eu2+ state is fully degenerate.

  1. Facet engineering for SiGe/Si stressors in advanced CMOS technology

    NASA Astrophysics Data System (ADS)

    Kasim, Johnson; Reichel, Carsten; Dilliway, Gabriela; Bai, Bo; Zakowsky, Nadja

    2015-08-01

    A two-layer SiGe stressor was introduced for our CMOS technology containing a bottom layer with high Ge content to induce more stress to the channel and a top layer with lower Ge content for better nickel silicidation. However, even with the top lower Ge layer, defects were found after silicidation causing contact punch through. Since it is well known that the silicidation improves for Si, the SiGe top layer was replaced by a Si layer (Si-cap). Evaluation on 750 °C and 850 °C grown Si-cap was done. Different temperature grown Si-caps showed different growth behavior with morphology of the Si-cap grown at 850 °C completely different than that of the Si cap grown at 750 °C. There was a clear {3 1 1} facet formation for the higher temperature Si-cap resulting in a pinning effect to the spacer edge similar to that observed for the SiGe-cap. The faceted Si-cap improved silicidation and device parameters enabling the extension of this integration approach for SiGe/Si stressors to the more advanced technology nodes.

  2. Introduction of SiGe/Si heterojunction into novel multilayer tunnel FinFET

    NASA Astrophysics Data System (ADS)

    Morita, Yukinori; Fukuda, Koichi; Mori, Takahiro; Mizubayashi, Wataru; Migita, Shinji; Endo, Kazuhiko; O'uchi, Shin-ichi; Liu, Yongxun; Masahara, Meishoku; Matsukawa, Takashi; Ota, Hiroyuki

    2016-04-01

    A novel tunnel FinFET equipped with a SiGe/Si heterojunction and a multilayer fin-channel has been experimentally demonstrated. A high-quality SiGe layer is epitaxially grown on a heavily doped Si source as a tunnel junction. A FinFET-like hetero-multilayer channel with a trigate configuration significantly increases the drain current compared with conventional SiGe/Si heterojunction parallel-plate tunnel FETs.

  3. Raman scattering in Si/SiGe nanostructures: Revealing chemical composition, strain, intermixing, and heat dissipation

    SciTech Connect

    Mala, S. A.; Tsybeskov, L.; Lockwood, D. J.; Wu, X.; Baribeau, J.-M.

    2014-07-07

    We present a quantitative analysis of Raman scattering in various Si/Si{sub 1-x}Ge{sub x} multilayered nanostructures with well-defined Ge composition (x) and layer thicknesses. Using Raman and transmission electron microscopy data, we discuss and model Si/SiGe intermixing and strain. By analyzing Stokes and anti-Stokes Raman signals, we calculate temperature and discuss heat dissipation in the samples under intense laser illumination.

  4. Formation of GeSn alloy on Si(100) by low-temperature molecular beam epitaxy

    SciTech Connect

    Talochkin, A. B.; Mashanov, V. I.

    2014-12-29

    GeSn alloys grown on Si(100) by the low-temperature (100 °C) molecular beam epitaxy are studied using scanning tunneling microscopy and Raman spectroscopy. It is found that the effect of Sn as a surfactant modifies substantially the low-temperature growth mechanism of Ge on Si. Instead of the formation of small Ge islands surrounded by amorphous Ge, in the presence of Sn, the growth of pure Ge islands appears via the Stranski-Krastanov growth mode, and a partially relaxed Ge{sub 1−x}Sn{sub x} alloy layer with the high Sn-fraction up to 40 at. % is formed in the area between them. It is shown that the observed growth mode induced by high surface mobility of Sn and the large strain of the pseudomorphic state of Ge to Si ensures the minimum elastic-strain energy of the structure.

  5. Formation of GeSn alloy on Si(100) by low-temperature molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Talochkin, A. B.; Mashanov, V. I.

    2014-12-01

    GeSn alloys grown on Si(100) by the low-temperature (100 °C) molecular beam epitaxy are studied using scanning tunneling microscopy and Raman spectroscopy. It is found that the effect of Sn as a surfactant modifies substantially the low-temperature growth mechanism of Ge on Si. Instead of the formation of small Ge islands surrounded by amorphous Ge, in the presence of Sn, the growth of pure Ge islands appears via the Stranski-Krastanov growth mode, and a partially relaxed Ge1-xSnx alloy layer with the high Sn-fraction up to 40 at. % is formed in the area between them. It is shown that the observed growth mode induced by high surface mobility of Sn and the large strain of the pseudomorphic state of Ge to Si ensures the minimum elastic-strain energy of the structure.

  6. Phonon transport control by nanoarchitecture including epitaxial Ge nanodots for Si-based thermoelectric materials

    PubMed Central

    Yamasaka, Shuto; Nakamura, Yoshiaki; Ueda, Tomohiro; Takeuchi, Shotaro; Sakai, Akira

    2015-01-01

    Phonon transport in Si films was controlled using epitaxially-grown ultrasmall Ge nanodots (NDs) with ultrahigh density for the purpose of developing Si-based thermoelectric materials. The Si/Ge ND stacked structures, which were formed by the ultrathin SiO2 film technique, exhibited lower thermal conductivities than those of the conventional nanostructured SiGe bulk alloys, despite the stacked structures having a smaller Ge fraction. This came from the large thermal resistance caused by phonon scattering at the Si/Ge ND interfaces. The phonon scattering can be controlled by the Ge ND structure, which was independent of Si layer structure for carrier transport. These results demonstrate the effectiveness of ultrasmall epitaxial Ge NDs as phonon scattering sources, opening up a route for the realisation of Si-based thermoelectric materials. PMID:26434678

  7. Synthesis of Epitaxial Films Based on Ge-Si-Sn Materials with Ge/GeSn, Ge/GeSiSn, and GeSn/GeSiSn Heterojunctions

    NASA Astrophysics Data System (ADS)

    Timofeev, V. A.; Kokhanenko, A. P.; Nikiforov, A. I.; Mashanov, V. I.; Tuktamyshev, A. R.; Loshkarev, I. D.

    2015-11-01

    Results of investigations into the synthesis of heterostructures based on Ge-Si-Sn materials by the method of low-temperature molecular beam epitaxy are presented. The formation of epitaxial films during structure growth has been controlled by the reflection high-energy electron diffraction method. Films with Ge/GeSn, Ge/GeSiSn, and GeSn/GeSiSn heterojunctions are grown with Sn content changing from 2 to 10 % at temperatures in the interval 150-350°C. The stressed state, the composition, and the lattice parameter are studied by the x-ray diffraction method using Omega-scan curves and reciprocal space maps. A tensile strain in the Ge film during Ge/Ge0.9Sn0.1/Si structure growth has reached 0.86%.

  8. Periodic intermediate long wave equation: the undressing method

    SciTech Connect

    Lebedev, D.R.; Radul, A.O.

    1987-08-01

    The periodic equation of a two-layer liquid (periodic intermediate long wave equation) is studied by the undressing method using formal Volterra operators. The method is used to construct an infinite series of conservation laws; higher equations of the two-layer liquid are written down in Hamiltonian form; it is shown that the conservation laws are preserved by the higher equations; and an involution theorem is proved.

  9. Stability of intermediate phases forming on interaction of silicon and germanium with phosphorus and arsenic

    SciTech Connect

    Ugai, Ya.A.; Goncharov, E.G.; Sokolov, L.I.; Pshestanchik, V.R.

    1987-12-01

    By comparing the comparative stability of the intermediate phases in the systems Si(Ge)-P(As) we showed that for the compounds formed by adjacent components in the periodic system the determining factors in the interaction are the electronic configuration and the relative difference of the covalent radii.

  10. Density-functional theory molecular dynamics simulations of a-HfO2/Ge(100)(2 × 1) and a-ZrO2/Ge(100)(2 × 1) interface passivation.

    PubMed

    Chagarov, E A; Porter, L; Kummel, A C

    2016-02-28

    The structural properties of a-HfO2/Ge(2 × 1)-(001) and a-ZrO2/Ge(2 × 1)-(001) interfaces were investigated with and without a GeOx interface interlayer using density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic a-HfO2 and a-ZrO2 samples were generated using a hybrid classical-DFT MD "melt-and-quench" approach and tested against experimental properties. The oxide/Ge stacks were annealed at 700 K, cooled to 0 K, and relaxed providing the system with enough freedom to form realistic interfaces. For each high-K/Ge stack type, two systems with single and double interfaces were investigated. All stacks were free of midgap states; however, stacks with a GeO(x) interlayer had band-edge states which decreased the band gaps by 0%-30%. These band-edge states were mainly produced by under-coordinated Ge atoms in GeO(x) layer or its vicinity due to deformation, intermixing, and bond-breaking. The DFT-MD simulations show that electronically passive interfaces can be formed either directly between high-K dielectrics and Ge or with a monolayer of GeO2 if the processing does not create or properly passivate under-coordinated Ge atoms and Ge's with significantly distorted bonding angles. Comparison to the charge states of the interfacial atoms from DFT to experimental x-ray photoelectron spectroscopy results shows that while most studies of gate oxide on Ge(001) have a GeO(x) interfacial layer, it is possible to form an oxide/Ge interface without a GeO(x) interfacial layer. Comparison to experiments is consistent with the dangling bonds in the suboxide being responsible for midgap state formation. PMID:26931715

  11. Density-functional theory molecular dynamics simulations of a-HfO2/Ge(100)(2 × 1) and a-ZrO2/Ge(100)(2 × 1) interface passivation

    NASA Astrophysics Data System (ADS)

    Chagarov, E. A.; Porter, L.; Kummel, A. C.

    2016-02-01

    The structural properties of a-HfO2/Ge(2 × 1)-(001) and a-ZrO2/Ge(2 × 1)-(001) interfaces were investigated with and without a GeOx interface interlayer using density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic a-HfO2 and a-ZrO2 samples were generated using a hybrid classical-DFT MD "melt-and-quench" approach and tested against experimental properties. The oxide/Ge stacks were annealed at 700 K, cooled to 0 K, and relaxed providing the system with enough freedom to form realistic interfaces. For each high-K/Ge stack type, two systems with single and double interfaces were investigated. All stacks were free of midgap states; however, stacks with a GeOx interlayer had band-edge states which decreased the band gaps by 0%-30%. These band-edge states were mainly produced by under-coordinated Ge atoms in GeOx layer or its vicinity due to deformation, intermixing, and bond-breaking. The DFT-MD simulations show that electronically passive interfaces can be formed either directly between high-K dielectrics and Ge or with a monolayer of GeO2 if the processing does not create or properly passivate under-coordinated Ge atoms and Ge's with significantly distorted bonding angles. Comparison to the charge states of the interfacial atoms from DFT to experimental x-ray photoelectron spectroscopy results shows that while most studies of gate oxide on Ge(001) have a GeOx interfacial layer, it is possible to form an oxide/Ge interface without a GeOx interfacial layer. Comparison to experiments is consistent with the dangling bonds in the suboxide being responsible for midgap state formation.

  12. High efficiency GaAs/Ge monolithic tandem solar cells

    NASA Technical Reports Server (NTRS)

    Tobin, S. P.; Vernon, S. M.; Bajgar, C.; Haven, V. E.; Geoffroy, L. M.; Sanfacon, M. M.; Lillington, D. R.; Hart, R. E., Jr.

    1988-01-01

    Two-terminal monolithic tandem cells consisting of a GaAs solar cell grown epitaxially on a Ge solar cell substrate are very attractive for space applications. Tandem cells of GaAs grown by metal-organic chemical vapor deposition on thin Ge were investigated to address both higher efficiency and reduced weight. Two materials growth issues associated with this heteroepitaxial system, autodoping of the GaAs layers by Ge and diffusion of Ga and As into the Ge substrate, were addressed. The latter appears to result in information of an unintentional p-n junction in the Ge. Early simulator measurements gave efficiencies as high as 21.7 percent for 4 cm2 GaAs/Ge cells, but recent high-altitude testing has given efficiencies of 18 percent. Sources of errors in simulator measurements of two-terminal tandem cells are discussed. A limiting efficiency of about 36 percent for the tandem cell at AMO was calculated. Ways to improve the performance of present cells, primarily by increasing the Isc and Voc of the Ge cell, are proposed.

  13. Low temperature epitaxial growth of Ge on cube- textured Ni

    SciTech Connect

    GIARE, C; Palazzo, J; Goyal, Amit; WANG, G; LU, T

    2012-01-01

    Quasi- single crystal Ge films were grown on [001]<010> textured Ni substrate at a temperature of 350 oC using an insulating buffer layer of CaF2. A direct deposition of Ge on Ni at 350 oC was shown to alloy with Ni. From x- ray pole figure analysis, it was shown that Ge grew epitaxially with the same orientation as CaF2 and the dispersions in the out- of- plane and in- plane directions were found to be 1.7 0.1o and 6 1o, respectively. In the out- of- plane direction, Ge[111]||CaF2[111]||Ni[001]. In addition, the Ge consisted of four equivalent in- plane oriented domains such that two mutually orthogonal directions: Ge 211 and Ge 011 are parallel to mutually orthogonal directions: Ni 110 and Ni 110 , respectively of the Ni(001) surface. This was shown to be originated from the four equivalent in- plane oriented domains of CaF2 created to minimize the mismatch strain between CaF2 and Ni in those directions.

  14. Quantum Dot TiO2-Ge Solar Cells

    NASA Astrophysics Data System (ADS)

    Church, Carena; Muthuswamy, Elayaraja; Kauzlarich, Susan; Carter, Sue

    2014-03-01

    Colloidal germanium (Ge) quantum dots (CQDs) are attractive solar materials due to their low toxicity compared to Pb- or Cd- based nanocrystals (NC), low cost, and optimal, tunable bandgap for both increased IR response and potential power conversion efficiency (η) boosts from Multiple Exciton Generation (MEG). We report on the successful fabrication and characterization of spun-cast donor/acceptor type TiO2-Ge CQD solar cells utilizing Ge colloidal quantum dots (CQD) synthesized via a facile microwave method as the active layer. We find that our Ge QD size performance-related trends are similar to other QD systems studied. Additionally, our best heterojunction devices achieved short circuit currents (JSC) of 450 μA and open circuit voltages (VOC) of 0.335 V, resulting in η = 0.022 %. While this represents significant increases over previous Ge CQD PV (85 % over hybrid Ge-P3HT PV, 350 % over Ge NC PV), our photocurrents are still much lower than other NC systems. Analysis of intensity-dependent J-V characteristics reveal that our currents are limited by a space-charge region that forms leading to unbalanced charge extraction. We conclude by discussing a variety of film treatments and device structures we have tested to increase JSC.

  15. Ba2Sb4GeS10

    PubMed Central

    Geng, Lei

    2013-01-01

    The title quaternary compound, dibarium tetra­anti­mony germanium deca­sulfide, Ba2Sb4GeS10, crystallizes in a novel three-dimensional ∞ 3[Sb4GeS10]4− network structure, which is composed of triangular pyramidal SbS3 (site symmetry m..), distorted SbS5 (m..) polyhedra and regular GeS4 (-4..) tetra­hedra. The SbS3 and SbS5 units are connected with each other through corner- and edge-sharing, forming a Sb4S10 layer in the ab plane. The GeS4 tetra­hedra further bridge two neighbouring Sb4S10 layers, forming a three-dimensional ∞ 3[Sb4GeS10]4− network. The Ba2+ cation (..2) is located between two Sb4S10 layers and is coordinated by ten S atoms with Ba—S bond lengths in the range 3.2505 (9)–3.4121 (2) Å. PMID:23723748

  16. Structural investigations of the α12 Si–Ge superstructure

    PubMed Central

    Etzelstorfer, Tanja; Ahmadpor Monazam, Mohammad Reza; Cecchi, Stefano; Kriegner, Dominik; Chrastina, Daniel; Gatti, Eleonora; Grilli, Emanuele; Rosemann, Nils; Chatterjee, Sangam; Holý, Vaclav; Pezzoli, Fabio; Isella, Giovanni; Stangl, Julian

    2015-01-01

    This article1 reports the X-ray diffraction-based structural characterization of the α12 multilayer structure SiGe2Si2Ge2SiGe12 [d’Avezac, Luo, Chanier & Zunger (2012 ▶). Phys. Rev. Lett. 108, 027401], which is predicted to form a direct bandgap material. In particular, structural parameters of the superlattice such as thickness and composition as well as interface properties, are obtained. Moreover, it is found that Ge subsequently segregates into layers. These findings are used as input parameters for band structure calculations. It is shown that the direct bandgap properties depend very sensitively on deviations from the nominal structure, and only almost perfect structures can actually yield a direct bandgap. Photoluminescence emission possibly stemming from the superlattice structure is observed. PMID:26089750

  17. Large grain growth of Ge-rich Ge1-xSnx (x ≈ 0.02) on insulating surfaces using pulsed laser annealing in flowing water

    NASA Astrophysics Data System (ADS)

    Kurosawa, Masashi; Taoka, Noriyuki; Ikenoue, Hiroshi; Nakatsuka, Osamu; Zaima, Shigeaki

    2014-02-01

    We investigate Sn incorporation effects on the growth characteristics of Ge-rich Ge1-xSnx (x < 0.02) on SiO2 crystallized by pulsed laser annealing (PLA) in air and water. Despite the very low Sn content of 2%, Sn atoms within the GeSn layers play a role in preventing ablation and aggregation of the layers during these PLA. Raman and electron backscatter diffraction measurements demonstrate achievement of large-grain (˜800 nmϕ) growth of Ge0.98Sn0.02 polycrystals by using PLA in water. These polycrystals also show a tensile-strain of ˜0.68%. This result opens up the possibility for developing GeSn-based devices fabricated on flexible substrates as well as Si platforms.

  18. Effect of stacking sequence on crystallization in Al/a-Ge bilayer thin films

    SciTech Connect

    Zhang, Tianwei; Zhang, Weilin; Ma, Fei E-mail: kwxu@mail.xjtu.edu.cn; Huang, Yuhong; Xu, Kewei E-mail: kwxu@mail.xjtu.edu.cn

    2014-05-15

    Two types of bilayer thin films with different deposition sequences, i.e., amorphous Ge under Al (a-Ge/Al) and the inverse (Al/a-Ge), were prepared by magnetron sputtering at room temperature. In-situ and ex-situ thermal annealing were compared to study the effect of the stacking sequence on crystallization of amorphous Ge. Although metal-induced crystallization occurred in both cases at low temperature, layer exchange was observed only in a-Ge/Al. In fact, compressive stress could usually be produced when Ge atoms diffused into Al grain boundaries and crystallized there. In the a-Ge/Al system, the stress could be released through diffusion of Al atoms onto the surface and formation of hillocks. Thus, grain boundary (GB) mediated crystallization was dominant in the whole process and layer exchange occurred. However, in the Al/a-Ge system, it was difficult for stress to be relaxed because the Ge sublayer and substrate restricted the diffusion of Al atoms. GB-mediated crystallization was, therefore, considerably suppressed and interface-mediated crystallization was preferred without layer exchange. This leads to distinct morphologies of dendrites in the two systems.

  19. Charge trapping of Ge-nanocrystals embedded in TaZrO{sub x} dielectric films

    SciTech Connect

    Lehninger, D. Seidel, P.; Geyer, M.; Schneider, F.; Heitmann, J.; Klemm, V.; Rafaja, D.; Borany, J. von

    2015-01-12

    Ge-nanocrystals (NCs) were synthesized in amorphous TaZrO{sub x} by thermal annealing of co-sputtered Ge-TaZrO{sub x} layers. Formation of spherical shaped Ge-NCs with small variation of size, areal density, and depth distribution was confirmed by high-resolution transmission electron microscopy. The charge storage characteristics of the Ge-NCs were investigated by capacitance-voltage and constant-capacity measurements using metal-insulator-semiconductor structures. Samples with Ge-NCs exhibit a maximum memory window of 5 V by sweeping the bias voltage from −7 V to 7 V and back. Below this maximum, the width of the memory window can be controlled by the bias voltage. The fitted slope of the memory window versus bias voltage characteristics is very close to 1 for samples with one layer Ge-NCs. A second layer Ge-NCs does not result in a second flat stair in the memory window characteristics. Constant-capacity measurements indicate charge storage in trapping centers at the interfaces between the Ge-NCs and the surrounding materials (amorphous matrix/tunneling oxide). Charge loss occurs by thermal detrapping and subsequent band-to-band tunneling. Reference samples without Ge-NCs do not show any memory window.

  20. EVALUATION OF TRANSPORTATION OPTIONS FOR INTERMEDIATE NON DESTRUCTIVE EXAMINATIONS

    SciTech Connect

    Case, Susan; Hoggard, Gary

    2014-07-01

    Idaho National Laboratory (INL) shipments of irradiated experiments from the Advanced Test Reactor (ATR) to the Hot Fuels Examination Facility (HFEF) have historically been accomplished using the General Electric Model 2000 (GE 2000) Type B shipping container. Battelle Energy Alliance (BEA) concerns regarding the future availability and leasing and handling costs associated with the GE 2000 cask have warranted an evaluation of alternative shipping options. One or more of these shipping options may be utilized to perform non destructive examinations (NDE) such as neutron radiography and precision gamma scans of irradiated experiments at HFEF and then return the experiments to ATR for further irradiation, hereafter referred to as “intermediate NDE.”

  1. Sn-based Ge/Ge0.975Sn0.025/Ge p-i-n photodetector operated with back-side illumination

    NASA Astrophysics Data System (ADS)

    Chang, C.; Li, H.; Huang, S. H.; Cheng, H. H.; Sun, G.; Soref, R. A.

    2016-04-01

    We report an investigation of a GeSn-based p-i-n photodetector grown on a Ge wafer that collects light signal from the back of the wafer. Temperature dependent absorption measurements performed over a wide temperature range (300 K down to 25 K) show that (a) absorption starts at the indirect bandgap of the active GeSn layer and continues up to the direct bandgap of the Ge wafer, and (b) the peak responsivity increases rapidly at first with decreasing temperature, then increases more slowly, followed by a decrease at the lower temperatures. The maximum responsivity happens at 125 K, which can easily be achieved with the use of liquid nitrogen. The temperature dependence of the photocurrent is analyzed by taking into consideration of the temperature dependence of the electron and hole mobility in the active layer, and the analysis result is in reasonable agreement with the data in the temperature regime where the rapid increase occurs. This investigation demonstrates the feasibility of a GeSn-based photodiode that can be operated with back-side illumination for applications in image sensing systems.

  2. GeSn-on-insulator substrate formed by direct wafer bonding

    NASA Astrophysics Data System (ADS)

    Lei, Dian; Lee, Kwang Hong; Bao, Shuyu; Wang, Wei; Wang, Bing; Gong, Xiao; Tan, Chuan Seng; Yeo, Yee-Chia

    2016-07-01

    GeSn-on-insulator (GeSnOI) on Silicon (Si) substrate was realized using direct wafer bonding technique. This process involves the growth of Ge1-xSnx layer on a first Si (001) substrate (donor wafer) followed by the deposition of SiO2 on Ge1-xSnx, the bonding of the donor wafer to a second Si (001) substrate (handle wafer), and removal of the Si donor wafer. The GeSnOI material quality is investigated using high-resolution transmission electron microscopy, high-resolution X-ray diffraction (HRXRD), atomic-force microscopy, Raman spectroscopy, and spectroscopic ellipsometry. The Ge1-xSnx layer on GeSnOI substrate has a surface roughness of 1.90 nm, which is higher than that of the original Ge1-xSnx epilayer before transfer (surface roughness is 0.528 nm). The compressive strain of the Ge1-xSnx film in the GeSnOI is as low as 0.10% as confirmed using HRXRD and Raman spectroscopy.

  3. Chemical Bonding, Interfaces and Defects in Hafnium Oxide/Germanium Oxynitride Gate Stacks on Ge (100)

    SciTech Connect

    Oshima, Yasuhiro; Sun, Yun; Kuzum, Duygu; Sugawara, Takuya; Saraswat, Krishna C.; Pianetta, Piero; McIntyre, Paul C.; /Stanford U., Materials Sci. Dept.

    2008-10-31

    Correlations among interface properties and chemical bonding characteristics in HfO{sub 2}/GeO{sub x}N{sub y}/Ge MIS stacks were investigated using in-situ remote nitridation of the Ge (100) surface prior to HfO{sub 2} atomic layer deposition (ALD). Ultra thin ({approx}1.1 nm), thermally stable and aqueous etch-resistant GeO{sub x}N{sub y} interfaces layers that exhibited Ge core level photoelectron spectra (PES) similar to stoichiometric Ge{sub 3}N{sub 4} were synthesized. To evaluate GeO{sub x}N{sub y}/Ge interface defects, the density of interface states (D{sub it}) was extracted by the conductance method across the band gap. Forming gas annealed (FGA) samples exhibited substantially lower D{sub it} ({approx} 1 x 10{sup 12} cm{sup -2} eV{sup -1}) than did high vacuum annealed (HVA) and inert gas anneal (IGA) samples ({approx} 1x 10{sup 13} cm{sup -2} eV{sup -1}). Germanium core level photoelectron spectra from similar FGA-treated samples detected out-diffusion of germanium oxide to the HfO{sub 2} film surface and apparent modification of chemical bonding at the GeO{sub x}N{sub y}/Ge interface, which is related to the reduced D{sub it}.

  4. An observation of direct-gap electroluminescence in GaAs structures with Ge quantum wells

    SciTech Connect

    Aleshkin, V. Ya.; Dikareva, N. V.; Dubinov, A. A.; Zvonkov, B. N.; Kudryavtsev, K. E.; Nekorkin, S. M.

    2015-02-15

    A light-emitting diode structure based on GaAs with eight narrow Ge quantum wells is grown by laser sputtering. An electroluminescence line polarized predominately in the plane parallel to the constituent layers of the structure is revealed. The line corresponds to the direct optical transitions in momentum space in the Ge quantum wells.

  5. Characterization of extended defects in SiGe alloys formed by high dose Ge + implantation into Si

    NASA Astrophysics Data System (ADS)

    Cristiano, F.; Nejim, A.; de Mauduit, B.; Claverie, A.; Hemment, P. L. F.

    1996-12-01

    The synthesis of SiGe/Si heterostructures by Ge + ion implantation is reported. 400 keV Ge + ions were implanted at doses ranging from 3 × 10 16 to 10 × 10 16 ions/cm 2 into (001) Si wafers, followed by Si + amorphisation and low temperature Solid Phase Epitaxial Regrowth (SPER). TEM investigations show that strained alloys can be fabricated if the elastic strain energy ( Eel) of the SiGe layer does not exceed a critical value ( E' el) of about 300 mJ/m 2, which is independent of the implantation energy. Our analysis also suggests that "hairpin" dislocations are formed as strain relieving defects in relaxed structures. A "strain relaxation" model is proposed to explain their formation.

  6. Effect of temperature on layer separation by plasma hydrogenation

    SciTech Connect

    Di, Z. F.; Wang, Y. Q.; Nastasi, M.; Rossi, F.; Shao, L.; Thompson, P. E.

    2008-12-22

    We have studied hydrogen diffusion in plasma hydrogenated Si/SiGe/Si heterostructure at different temperatures. At low temperature, intrinsic point defects in the molecular beam epitaxy grown Si capping layer are found to compete with the buried strain SiGe layer for hydrogen trapping. The interaction of hydrogen with point defects affects the hydrogen long-range diffusion, and restricts the amount of hydrogen available for trapping by the SiGe layer. However, hydrogen trapping by the capping layer is attenuated with increasing hydrogenation temperature allowing more hydrogen to be trapped in the strain SiGe layer with subsequent surface blister formation. A potential temperature window for plasma hydrogenation induced layer separation is identified based on the combined considerations of trap-limited diffusion at low temperature and outdiffusion of H{sub 2} molecule together with the dissociation of Si-H bonds inside of H platelet at high temperature.

  7. Effect of temperature on layer separation by plasma-hydrogenation

    SciTech Connect

    Di, Zengfeng; Michael, Nastasi A; Wang, Yongqiang

    2008-01-01

    We have studied hydrogen diffusion in plasma hydrogenated Si/SiGe/Si heterostructure at different temperatures. At low temperature, intrinsic point defects in the molecular beam epitaxy grown Si capping layer are found to compete with the buried strain SiGe layer for hydrogen trapping. The interaction of hydrogen with point defects affects the hydrogen long-range diffusion, and restricts the amount of hydrogen available for trapping by the SiGe layer. However, hydrogen trapping by the capping layer is attenuated with increasing hydrogenation temperature allowing more hydrogen to be trapped in the strain SiGe layer with subsequent surface blister formation. A potential temperature window for plasma hydrogenation induced layer separation is identified based on the combined considerations of trap-limited diffusion at low temperature and outdiffusion of H{sub 2} molecule together with the dissociation of Si-H bonds inside of H platelet at high temperature.

  8. Elastic strain relaxation in axial Si/Ge whisker heterostructures

    SciTech Connect

    Hanke, M.; Eisenschmidt, C.; Werner, P.; Zakharov, N. D.; Syrowatka, F.; Heyroth, F.; Schaefer, P.; Konovalov, O.

    2007-04-15

    The elastic behavior of molecular beam epitaxy-grown SiGe/Si(111) nanowhiskers (NWs) has been studied by means of electron microscopy, x-ray scattering, and numerical linear elasticity theory. Highly brilliant synchrotron radiation was applied to map the diffusely scattered intensity near the asymmetric (115) reciprocal lattice point. The larger lattice parameter with respect to the Si matrix causes a lateral lattice expansion within embedded Ge layers. This enables a clear separation of scattering due to NWs and laterally confined areas aside. Finite element calculations prove a lateral lattice compression in the Si matrix close to the NW apex above buried threefold and single Ge layer stacks. This suggests an incorporation probability, which additionally depends on the radial position within heteroepitaxial NWs.

  9. Strained Germanium-Tin pMOSFET Fabricated on a Silicon-on-Insulator Substrate with Relaxed Ge Buffer

    NASA Astrophysics Data System (ADS)

    Su, Shao-Jian; Han, Gen-Quan; Zhang, Dong-Liang; Zhang, Guang-Ze; Xue, Chun-Lai; Wang, Qi-Ming; Cheng, Bu-Wen

    2013-11-01

    Germanium-tin (Ge1-xSnx) p-type metal-oxide-semiconductor field effect transistors (pMOSFETs) were fabricated using a strained Ge0.985Sn0.015 thin film that was epitaxially grown on a silicon-on-insulator substrate with a relaxed Ge buffer layer. The Ge buffer was deposited using a two-step chemical vapor deposition growth technique. The high quality Ge0.985Sn0.015 layer was grown by solid source molecular beam epitaxy. Ge0.985Sn0.015 pMOSFETs with Si surface passivation, TaN/HfO2 gate stack, and nickel stanogermanide [Ni(Ge1-xSnx)] source/drain were fabricated on the grown substrate. The device achieves an effective hole mobility of 182 cm2/V·s at an inversion carrier density of 1 × 1013 cm-2.

  10. Strange particle production at low and intermediate energies

    SciTech Connect

    Alam, M. Rafi; Athar, M. Sajjad; Simo, I. Ruiz; Vacas, M. J. Vicente

    2011-11-23

    The weak kaon production off the nucleon induced by neutrinos and antineutrinos is studied at low and intermediate energies of interest for some ongoing and future neutrino oscillation experiments. We develop a microscopical model based on the SU(3) chiral Lagrangians. The studied mechanisms are the main source of kaon production for neutrino energies up to 2 GeV for the various channels and the cross sections are large enough to be amenable to be measured by experiments such as Minerva, T2K and NOvA.

  11. Ge Nanocluster Enhanced Er Photoluminescence

    NASA Astrophysics Data System (ADS)

    Guzman, Julian; Chrzan, Daryl C.; Haller, Eugene E.

    2010-03-01

    We investigated the enhancement of the Er^3+ photoluminescence (PL) at 1540 nm by the incorporation of Ge nanoclusters into Er-doped silica using ion beams. We found that the Er^3+ PL enhancement is due to the presence of Ge and not to the radiation damage from the ion-implantation process. We determined that the Er^3+ PL depends on the Ge content, postgrowth annealing, and crystallinity of the Ge nanoclusters. Furthermore, we observed that the Er^3+ PL signal is maximized after annealing at 685 C for 1 h. This is the temperature at which Ge nanoclusters begin to crystallize. Transmission electron microscopy studies were conducted to determine the size distribution of the Ge nanoclusters. Moreover, extended X-ray absorption fine structure measurements performed at the Ge-K and Er-LIII edges revealed that there is negligible Ge-Er bonding. This suggests that Er is either fully oxidized or that it is not located in the Ge nanoclusters. Therefore, we believe that the energy transfer process from the Ge nanoclusters to the Er ions occurs through a non-optical resonant dipole transfer (F"orster ProcessfootnotetextT. F"orster, Discuss. Faraday Soc. 27, 7 (1959). similar to what has been proposed for the Si nanocrystal case.footnotetextM. Fujii, M. Yoshida, S. Hayashi, and K. Yamamoto, J. Appl. Phys. 84, 4525 (1998).

  12. Formation of ST12 phase Ge nanoparticles in ZnO thin films

    NASA Astrophysics Data System (ADS)

    Ceylan, Abdullah; Gumrukcu, Emre; Ozcan, Sadan

    2015-03-01

    In this work, we investigate the effects of reactive and nonreactive growth of ZnO on the rapid thermal annealing (RTA) induced formation of Ge nanoparticles (Ge-np) in ZnO: Ge nanocomposite thin films. The samples were deposited by sequential sputtering of ZnO and Ge thin film layers with a total thickness of about 600 nm on Si substrates followed by an ex-situ (RTA) at 600°C for 30, 60, 90, 120, 150, 180, and 210 s under forming gas atmosphere. In order for the reactive sputtering of ZnO layer, 5 mTorr Oxygen was introduced to the growth chamber. XRD and Raman analyses were utilized to investigate the effect of RTA time on the structural evolution of the samples. It has been realized that crystal structure of Ge nanoparticles is significantly affected by the growth method of the embedding ZnO layer. While reactive deposition of ZnO layers results in a mixture of diamond cubic (DC) and simple tetragonal (ST12) Ge-np, nonreactive deposition of ZnO layers leads to the formation of pure DC Ge-np upon RTA process. Formation of these two phases has been discussed based on the existence of native point defects such as oxygen vacancies and Zn interstitials.

  13. Model of cosmology and particle physics at an intermediate scale

    SciTech Connect

    Bastero-Gil, M.; Di Clemente, V.; King, S. F.

    2005-05-15

    We propose a model of cosmology and particle physics in which all relevant scales arise in a natural way from an intermediate string scale. We are led to assign the string scale to the intermediate scale M{sub *}{approx}10{sup 13} GeV by four independent pieces of physics: electroweak symmetry breaking; the {mu} parameter; the axion scale; and the neutrino mass scale. The model involves hybrid inflation with the waterfall field N being responsible for generating the {mu} term, the right-handed neutrino mass scale, and the Peccei-Quinn symmetry breaking scale. The large scale structure of the Universe is generated by the lightest right-handed sneutrino playing the role of a coupled curvaton. We show that the correct curvature perturbations may be successfully generated providing the lightest right-handed neutrino is weakly coupled in the seesaw mechanism, consistent with sequential dominance.

  14. Ferromagnetism in ion implanted amorphous and nanocrystalline MnxGe1-x

    NASA Astrophysics Data System (ADS)

    Verna, A.; Ottaviano, L.; Passacantando, M.; Santucci, S.; Picozzi, P.; D'Orazio, F.; Lucari, F.; de Biase, M.; Gunnella, R.; Berti, M.; Gasparotto, A.; Impellizzeri, G.; Priolo, F.

    2006-08-01

    The structural, electronic, and magnetic properties of a MnxGe1-x alloy prepared through room-temperature ion implantation ( 100keV , 2×1016ions/cm2 ) and subsequent 400°C annealing have been investigated with several experimental techniques. The as-implanted sample shows a quasi-Gaussian Mn concentration depth profile with a projected range (peak Mn concentration x≃12at./% ) at 55nm and end of range at 140nm . The structural investigation shows that the overall implanted Ge layer is amorphous. In particular, up to a depth of 60nm , the implanted layer is also porous and oxidized, whereas the deepest implanted region (60-140nm) is purely composed of amorphous Ge with Mn atoms diluted in it. This sample manifests magnetic hysteresis up to 20K and a strong nonlinear S-shaped magnetic response up to 150K . Upon annealing at 400°C , the top porous layer remains essentially amorphous, whereas partial reconstruction into Ge nanocrystals ( ˜10nm in diameter) occurs in the 60-140-nm -deep implanted region. Part of the Mn atoms, mainly belonging to the top porous layer, further diffuses toward the surface and forms chemical bonds with O contaminants, becoming magnetically inactive. The other Mn atoms, mainly in the region between 60 and 140nm from the surface, remain trapped in the residual amorphous matrix or in the Ge nanocrystals, whereas formation of Mn-Ge extrinsic phases (like Mn11Ge8 and Mn5Ge3 ) is excluded. The magnetic response of the annealed sample originates from the existence of a soft and a harder magnetic component, assigned to the dilution of Mn atoms in residual amorphous Ge and Ge nanocrystals, respectively. The hard component, attributable to a MnxGe1-x diluted magnetic semiconductor in nanocrystalline form, manifests magnetic hysteresis up to above 250K .

  15. Application of heterojunction to Si-based solar cells using photonic nanostructures coupled with vertically aligned Ge quantum dots

    NASA Astrophysics Data System (ADS)

    Takahashi, Isao; Hoshi, Yusuke; Tayagaki, Takeshi; Oikawa, Takafumi; Ohdaira, Keisuke; Usami, Noritaka

    2015-08-01

    We have recently developed a new structure for solar cells that consists of photonic nanostructures coupled with vertically aligned Ge quantum dots on a crystalline Si substrate. For the fabrication of a solar cell device, a heterojunction with a-Si:H was chosen because its processing temperature is less than 200 °C, at which point Ge atoms cannot diffuse into Si layers. In this study, we developed a guideline for the most appropriate cell structures to take advantage of the Ge layer by fabricating heterojunction solar cells with various structures. As a result, we confirmed that the carriers absorbed in Ge quantum dots contributed output current when Ge quantum dots are fabricated on the pn-junction side. Hence, the presence of built-in potential in a Ge dot layer was found to be necessary to extract the carriers generated in the Ge layer. In addition, carrier transport in Ge quantum dots is improved under conditions of reverse bias. Therefore, the electrical field in the Ge layer is a key parameter to improve solar cell performance in our proposed structure.

  16. Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe by solid-liquid-coexisting annealing of a-GeSn/c-Si structures

    NASA Astrophysics Data System (ADS)

    Sadoh, Taizoh; Chikita, Hironori; Matsumura, Ryo; Miyao, Masanobu

    2015-09-01

    Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe on Si substrates is strongly desired to realize advanced electronic and optical devices, which can be merged onto Si large-scale integrated circuits (LSI). To achieve this, annealing characteristics of a-GeSn/c-Si structures are investigated under wide ranges of the initial Sn concentrations (0%-26%) and annealing conditions (300-1000 °C, 1 s-48 h). Epitaxial growth triggered by SiGe mixing is observed after annealing, where the annealing temperatures necessary for epitaxial growth significantly decrease with increasing initial Sn concentration and/or annealing time. As a result, Ge-rich (˜80%) SiGe layers with Sn concentrations of ˜2% are realized by ultra-low temperature annealing (300 °C, 48 h) for a sample with the initial Sn concentration of 26%. The annealing temperature (300 °C) is in the solid-liquid coexisting temperature region of the phase diagram for Ge-Sn system. From detailed analysis of crystallization characteristics and composition profiles in grown layers, it is suggested that SiGe mixing is generated by a liquid-phase reaction even at ultra-low temperatures far below the melting temperature of a-GeSn. This ultra-low-temperature growth technique of Ge-rich SiGe on Si substrates is expected to be useful to realize next-generation LSI, where various multi-functional devices are integrated on Si substrates.

  17. Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe by solid-liquid-coexisting annealing of a-GeSn/c-Si structures

    SciTech Connect

    Sadoh, Taizoh Chikita, Hironori; Miyao, Masanobu; Matsumura, Ryo

    2015-09-07

    Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe on Si substrates is strongly desired to realize advanced electronic and optical devices, which can be merged onto Si large-scale integrated circuits (LSI). To achieve this, annealing characteristics of a-GeSn/c-Si structures are investigated under wide ranges of the initial Sn concentrations (0%–26%) and annealing conditions (300–1000 °C, 1 s–48 h). Epitaxial growth triggered by SiGe mixing is observed after annealing, where the annealing temperatures necessary for epitaxial growth significantly decrease with increasing initial Sn concentration and/or annealing time. As a result, Ge-rich (∼80%) SiGe layers with Sn concentrations of ∼2% are realized by ultra-low temperature annealing (300 °C, 48 h) for a sample with the initial Sn concentration of 26%. The annealing temperature (300 °C) is in the solid-liquid coexisting temperature region of the phase diagram for Ge-Sn system. From detailed analysis of crystallization characteristics and composition profiles in grown layers, it is suggested that SiGe mixing is generated by a liquid-phase reaction even at ultra-low temperatures far below the melting temperature of a-GeSn. This ultra-low-temperature growth technique of Ge-rich SiGe on Si substrates is expected to be useful to realize next-generation LSI, where various multi-functional devices are integrated on Si substrates.

  18. Effects of rapid thermal annealing on the structural and local atomic properties of ZnO: Ge nanocomposite thin films

    SciTech Connect

    Ceylan, Abdullah Ozcan, Sadan; Rumaiz, Abdul K.; Caliskan, Deniz; Ozbay, Ekmel; Woicik, J. C.

    2015-03-14

    We have investigated the structural and local atomic properties of Ge nanocrystals (Ge-ncs) embedded ZnO (ZnO: Ge) thin films. The films were deposited by sequential sputtering of ZnO and Ge thin film layers on z-cut quartz substrates followed by an ex-situ rapid thermal annealing (RTA) at 600 °C for 30, 60, and 90 s under forming gas atmosphere. Effects of RTA time on the evolution of Ge-ncs were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), hard x-ray photoelectron spectroscopy (HAXPES), and extended x-ray absorption fine structure (EXAFS). XRD patterns have clearly shown that fcc diamond phase Ge-ncs of sizes ranging between 18 and 27 nm are formed upon RTA and no Ge-oxide peak has been detected. However, cross-section SEM images have clearly revealed that after RTA process, Ge layers form varying size nanoclusters composed of Ge-ncs regions. EXAFS performed at the Ge K-edge to probe the local atomic structure of the Ge-ncs has revealed that as prepared ZnO:Ge possesses Ge-oxide but subsequent RTA leads to crystalline Ge structure without the oxide layer. In order to study the occupied electronic structure, HAXPES has been utilized. The peak separation between the Zn 2p and Ge 3d shows no significant change due to RTA. This implies little change in the valence band offset due to RTA.

  19. Kinetics of epitaxial growth of Si and SiGe films on (1 1 0) Si substrates

    NASA Astrophysics Data System (ADS)

    Sugiyama, N.; Moriyama, Y.; Nakaharai, S.; Tezuka, T.; Mizuno, T.; Takagi, S.

    2004-03-01

    The epitaxial growth of Si and SiGe layers on (1 1 0) Si substrates using UHV-CVD is studied with comparing that on (1 0 0) substrates. It is revealed that, while the growth rate on (1 1 0) surfaces is quite lower than that on (1 0 0) surfaces, the Ge content of SiGe is the same between (1 0 0) and (1 1 0) surfaces, meaning that the ratio of decomposition yields of source molecules for Si and Ge are same in both the (1 0 0) and (1 1 0) substrates. This characteristic is expected to lead to the epitaxial growth of SiGe films with uniform Ge content over the three-dimensional patterned structure, which can be utilized for vertical FET and Fin-FETs. Actually, it has been experimentally confirmed that the SiGe films grown over trench structures has a uniform Ge content.

  20. Electronic and material characterization of silicon-germanium and silicon-germanium-carbon epitaxial layers

    NASA Astrophysics Data System (ADS)

    Peterson, Jeffrey John

    This dissertation presents results of material and electronic characterization of strained SiGe and SiGeC epitaxial layers grown on (100) silicon using Atmospheric Pressure Chemical Vapor Deposition and Reduced Pressure Chemical Vapor Deposition. Fabrication techniques for SiGe and SiGeC are also presented. Materials characterization of epitaxial SiGe and SiGeC was done to characterize crystallinity using visual, microscopic, and Rutherford Backscattering (RBS) characterization. Surface roughness was characterized and found to correspond roughly with epitaxial crystal quality. Spectroscopic ellipsometry was used to study epitaxial layer composition and thickness, requiring development of models for nSiGe and nSiGeC versus composition (the first published for nSiGeC) and generation of ellipsometric nomograms. X-ray diffraction (XRD) measurements of epitaxial strain and relaxation showed Ge composition dominates the stress, although strain compensation due to C was observed. XRD, Raman, and Fourier Transform Infrared (FTIR) characterization were done to characterize substitutional C in SiGeC epitaxial layers, finding that C incorporation into SiGeC saturates for C contents >1%. Fabrication techniques for SiGe and SiGeC were examined. Low thermal budget processing of strained layers were investigated as well as fabrication techniques using advantageous material properties of SiGe and SiGeC. Ti/Al contacts were developed and characterized for electrical contact to SiGe and SiGeC. Schottky contacts of Pt silicide on SiGe and SiGeC was done; formation and resistivity were characterized. Four separate resistivity characterization structures have been fabricated using mesa-etch and Si etch-stop techniques. A NPN Heterojunction Bipolar transistor has been fabricated using successive mesa-etches and SiGe (or SiGeC) etch-stops. Electronic characterization of in-situ doped SiGe and SiGeC epitaxial layers was done to determine resistivity, mobility, and bandgap. Resistivities

  1. GeSn p-i-n waveguide photodetectors on silicon substrates

    NASA Astrophysics Data System (ADS)

    Peng, Yu-Hsiang; Cheng, H. H.; Mashanov, Vladimir I.; Chang, Guo-En

    2014-12-01

    We report an investigation on GeSn p-i-n waveguide photodetectors grown on a Ge-buffered Si wafer. In comparison with a reference Ge detector, the GeSn detector shows an enhanced responsivity in the measured energy range, mainly attributed to the smaller bandgap caused by Sn-alloying. Analysis of the quantum efficiency indicates that increasing the Sn content in the active layers can significantly shorten the required device length to achieve the maximum efficiency. The present investigation demonstrates the planar photodetectors desired for monolithic integration with electronic devices.

  2. Isotropic plasma etching of Ge Si and SiNx films

    DOE PAGESBeta

    Henry, Michael David; Douglas, Erica Ann

    2016-05-01

    This study reports on selective isotropic dry etching of chemically vapor deposited (CVD) Ge thin film, release layers using a Shibaura chemical downstream etcher (CDE) with NF3 and Ar based plasma chemistry. Relative etch rates between Ge, Si and SiNx are described with etch rate reductions achieved by adjusting plasma chemistry with O2. Formation of oxides reducing etch rates were measured for both Ge and Si, but nitrides or oxy-nitrides created using direct injection of NO into the process chamber were measured to increase Si and SiNx etch rates while retarding Ge etching.

  3. Charge storage characteristics and tunneling mechanism of amorphous Ge-doped HfOx films

    NASA Astrophysics Data System (ADS)

    Qiu, X. Y.; Zhang, S. Y.; Zhang, T.; Wang, R. X.; Li, L. T.; Zhang, Y.; Dai, J. Y.

    2016-09-01

    Amorphous Ge-doped HfOx films have been deposited on p-Si(100) substrates by means of RF magnetron sputtering. Microstructural investigations reveal the partial oxidation of doped Ge atoms in the amorphous HfOx matrix and the existence of HfSiOx interfacial layer. Capacitance-voltage hysteresis of the Ag-/Ge-doped HfOx/Si/Ag memory capacitor exhibits a memory window of 3.15 V which can maintain for >5 × 104 cycles. Current-voltage characteristics reveal that Poole-Frenkel tunneling is responsible for electron transport in the Ge-doped HfOx film.

  4. GeSn p-i-n waveguide photodetectors on silicon substrates

    SciTech Connect

    Peng, Yu-Hsiang; Chang, Guo-En; Cheng, H. H.; Mashanov, Vladimir I.

    2014-12-08

    We report an investigation on GeSn p-i-n waveguide photodetectors grown on a Ge-buffered Si wafer. In comparison with a reference Ge detector, the GeSn detector shows an enhanced responsivity in the measured energy range, mainly attributed to the smaller bandgap caused by Sn-alloying. Analysis of the quantum efficiency indicates that increasing the Sn content in the active layers can significantly shorten the required device length to achieve the maximum efficiency. The present investigation demonstrates the planar photodetectors desired for monolithic integration with electronic devices.

  5. Near-Infrared Photoluminescence Enhancement in Ge/CdS and Ge/ZnS Core/Shell Nanocrystals: Utilizing IV/II-VI Semiconductor Epitaxy

    SciTech Connect

    Guo, Yijun; Rowland, Clare E; Schaller, Richard D; Vela, Javier

    2014-08-26

    Ge nanocrystals have a large Bohr radius and a small, size-tunable band gap that may engender direct character via strain or doping. Colloidal Ge nanocrystals are particularly interesting in the development of near-infrared materials for applications in bioimaging, telecommunications and energy conversion. Epitaxial growth of a passivating shell is a common strategy employed in the synthesis of highly luminescent II–VI, III–V and IV–VI semiconductor quantum dots. Here, we use relatively unexplored IV/II–VI epitaxy as a way to enhance the photoluminescence and improve the optical stability of colloidal Ge nanocrystals. Selected on the basis of their relatively small lattice mismatch compared with crystalline Ge, we explore the growth of epitaxial CdS and ZnS shells using the successive ion layer adsorption and reaction method. Powder X-ray diffraction and electron microscopy techniques, including energy dispersive X-ray spectroscopy and selected area electron diffraction, clearly show the controllable growth of as many as 20 epitaxial monolayers of CdS atop Ge cores. In contrast, Ge etching and/or replacement by ZnS result in relatively small Ge/ZnS nanocrystals. The presence of an epitaxial II–VI shell greatly enhances the near-infrared photoluminescence and improves the photoluminescence stability of Ge. Ge/II–VI nanocrystals are reproducibly 1–3 orders of magnitude brighter than the brightest Ge cores. Ge/4.9CdS core/shells show the highest photoluminescence quantum yield and longest radiative recombination lifetime. Thiol ligand exchange easily results in near-infrared active, water-soluble Ge/II–VI nanocrystals. We expect this synthetic IV/II–VI epitaxial approach will lead to further studies into the optoelectronic behavior and practical applications of Si and Ge-based nanomaterials.

  6. Intermediate ions in the atmosphere

    NASA Astrophysics Data System (ADS)

    Tammet, Hannes; Komsaare, Kaupo; Hõrrak, Urmas

    2014-01-01

    Intermediate air ions are charged nanometer-sized aerosol particles with an electric mobility of about 0.03-0.5 cm2 V- 1 s- 1 and a diameter of about 1.5-7.5 nm. Intensive studies of new particle formation provided good knowledge about intermediate ions during burst events of atmospheric aerosol nucleation. Information about intermediate ions during quiet periods between the bursts remained poor. The new mobility analyzer SIGMA can detect air ions at concentrations of mobility fractions of about 1 cm- 3 and enables studying intermediate ions during quiet periods. It became evident that intermediate ions always exist in atmospheric air and should be considered an indicator and a mediator of aerosol nucleation. The annual average concentration of intermediate ions of one polarity in Tartu, Estonia, was about 40 cm- 3 while 5% of the measurements showed a concentration of less than 10 cm- 3. The fraction concentrations in logarithmic 1/8-decade mobility bins between 0.1 and 0.4 cm2 V- 1 s- 1 often dropped below 1 cm- 3. The bursts of intermediate ions at stations separated by around 100 km appeared to be correlated. The lifespan of intermediate ions in the atmosphere is a few minutes, and they cannot be carried by wind over long distances. Thus the observed long-range correlation of intermediate ions is explained by simultaneous changes in air composition in widely spaced stations. A certain amount of intermediate ion bursts, predominantly of negative polarity, are produced by the balloelectric effect at the splashing of water drops during rain. These bursts are usually excluded when speaking about new particle formation because the balloelectric particles are assumed not to grow to the size of the Aitken mode. The mobility distribution of balloelectric ions is uniform in shape in all measurements. The maximum is located at a mobility of about 0.2 cm2 V- 1 s- 1, which corresponds to the diameter of particles of about 2.5 nm.

  7. Pure, single crystal Ge nanodots formed using a sandwich structure via pulsed UV excimer laser annealing.

    PubMed

    Liao, Ting-Wei; Chen, Hung-Ming; Shen, Kuan-Yuan; Kuan, Chieh-Hsiung

    2015-04-24

    In this paper, a sandwich structure comprising a SiO2 capping layer, amorphous Germanium (a-Ge) nanodots (NDs), and a pit-patterned Silicon (Si) substrate is developed, which is then annealed by utilizing a pulsed ultraviolet excimer laser in order to fabricate an array of pure, single crystal Ge NDs at room temperature. A wide bandgap SiO2 capping layer is used as a transparent thermally isolated layer to prevent thermal loss and Si-Ge intermixing. The two-dimensional pit-patterned Si substrate is designed to confine the absorbed laser energy, reduce the melting point, and block the surface migration of the Ge. After optimizing the laser radiation parameters such that the laser energy density is 200 mJ cm(-2), the laser annealing period is 10 s, and the number of laser shots is 10, pure, single crystal Ge NDs that have both a regular arrangement and a uniform size distribution are obtained in the pits of the Si substrates. The Raman spectrum shows a highly symmetric Ge transversal optical peak with a full width at half maximum of 4.2 cm(-1) at 300.7 cm(-1), which is close to that of the original Ge wafer. In addition, the high-resolution transmission electron microscopy image for the Ge NDs and the corresponding selected area electron diffraction pattern shows a clear single crystalline structure without any impurities. PMID:25815515

  8. Pure, single crystal Ge nanodots formed using a sandwich structure via pulsed UV excimer laser annealing

    NASA Astrophysics Data System (ADS)

    Liao, Ting-Wei; Chen, Hung-Ming; Shen, Kuan-Yuan; Kuan, Chieh-Hsiung

    2015-04-01

    In this paper, a sandwich structure comprising a SiO2 capping layer, amorphous Germanium (a-Ge) nanodots (NDs), and a pit-patterned Silicon (Si) substrate is developed, which is then annealed by utilizing a pulsed ultraviolet excimer laser in order to fabricate an array of pure, single crystal Ge NDs at room temperature. A wide bandgap SiO2 capping layer is used as a transparent thermally isolated layer to prevent thermal loss and Si-Ge intermixing. The two-dimensional pit-patterned Si substrate is designed to confine the absorbed laser energy, reduce the melting point, and block the surface migration of the Ge. After optimizing the laser radiation parameters such that the laser energy density is 200 mJ cm-2, the laser annealing period is 10 s, and the number of laser shots is 10, pure, single crystal Ge NDs that have both a regular arrangement and a uniform size distribution are obtained in the pits of the Si substrates. The Raman spectrum shows a highly symmetric Ge transversal optical peak with a full width at half maximum of 4.2 cm-1 at 300.7 cm-1, which is close to that of the original Ge wafer. In addition, the high-resolution transmission electron microscopy image for the Ge NDs and the corresponding selected area electron diffraction pattern shows a clear single crystalline structure without any impurities.

  9. Synthesis of ZnO:Ge Thin Films via Plasma Gas Condensation

    NASA Astrophysics Data System (ADS)

    Ceylan, Abdullah; Ali, Janan; Ozcan, Sadan

    2013-03-01

    we introduce a new method for the synthesis of Ge nanoparticle embedded ZnO thin films that are considered to be a potential candidate for photovoltaic applications. As opposed to current techniques, for the independent preparation of Ge nanoparticles, Cluster Deposition Source (CDS) utilising gas condensation of sputtered Ge atoms is used. For the synthesis of ZnO thin film host material conventional sputtering is employed. In the proposed technique independently synthesized Ge nanoparticles and ZnO thin films are combined into a composite structure on Si. XRD patterns of the samples have revealed that Ge nanoparticles preferentially settle on (113) planes on top of the (002) oriented ZnO layer. It is realized that Ge nanoparticles with sizes ranging from 16 nm to 20 nm could be embedded into a well-defined ZnO matrix. In fact, TEM studies performed on Ge nanoparticles captured on a Cu grids have manifested that Ge reach to ZnO matrix as clusters composed of particles with sizes of about 7-8 nm and then eventually grow larger due to substrate heating implemented during capping layer deposition. Optical absorption measurements have revealed that Ge nanoparticle inclusion lead to an additional absorption edge at about 2.75 eV along with 3.17 eV edge resulting from ZnO host.

  10. 75 FR 47318 - GE Asset Management Incorporated and GE Investment Distributors, Inc.; Notice of Application and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-05

    ... COMMISSION GE Asset Management Incorporated and GE Investment Distributors, Inc.; Notice of Application and.... Applicants: GE Asset Management Incorporated (``GEAM'') and GE Investment Distributors, Inc. (``GEID....\\3\\ The Commission alleged in the complaint (``Complaint'') that, from 2000 to 2003, four...

  11. Growth and evolution of nickel germanide nanostructures on Ge(001)

    NASA Astrophysics Data System (ADS)

    Grzela, T.; Capellini, G.; Koczorowski, W.; Schubert, M. A.; Czajka, R.; Curson, N. J.; Heidmann, I.; Schmidt, Th; Falta, J.; Schroeder, T.

    2015-09-01

    Nickel germanide is deemed an excellent material system for low resistance contact formation for future Ge device modules integrated into mainstream, Si-based integrated circuit technologies. In this study, we present a multi-technique experimental study on the formation processes of nickel germanides on Ge(001). We demonstrate that room temperature deposition of ˜1 nm of Ni on Ge(001) is realized in the Volmer-Weber growth mode. Subsequent thermal annealing results first in the formation of a continuous NixGey wetting layer featuring well-defined terrace morphology. Upon increasing the annealing temperature to 300 °C, we observed the onset of a de-wetting process, characterized by the appearance of voids on the NixGey terraces. Annealing above 300 °C enhances this de-wetting process and the surface evolves gradually towards the formation of well-ordered, rectangular NixGey 3D nanostructures. Annealing up to 500 °C induces an Ostwald ripening phenomenon, with smaller nanoislands disappearing and larger ones increasing their size. Subsequent annealing to higher temperatures drives the Ni-germanide diffusion into the bulk and the consequent formation of highly ordered, {111} faceted Ni-Ge nanocrystals featuring an epitaxial relationship with the substrate Ni-Ge (101); (010) || Ge(001); (110).

  12. Growth and evolution of nickel germanide nanostructures on Ge(001).

    PubMed

    Grzela, T; Capellini, G; Koczorowski, W; Schubert, M A; Czajka, R; Curson, N J; Heidmann, I; Schmidt, Th; Falta, J; Schroeder, T

    2015-09-25

    Nickel germanide is deemed an excellent material system for low resistance contact formation for future Ge device modules integrated into mainstream, Si-based integrated circuit technologies. In this study, we present a multi-technique experimental study on the formation processes of nickel germanides on Ge(001). We demonstrate that room temperature deposition of ∼1 nm of Ni on Ge(001) is realized in the Volmer-Weber growth mode. Subsequent thermal annealing results first in the formation of a continuous NixGey wetting layer featuring well-defined terrace morphology. Upon increasing the annealing temperature to 300 °C, we observed the onset of a de-wetting process, characterized by the appearance of voids on the NixGey terraces. Annealing above 300 °C enhances this de-wetting process and the surface evolves gradually towards the formation of well-ordered, rectangular NixGey 3D nanostructures. Annealing up to 500 °C induces an Ostwald ripening phenomenon, with smaller nanoislands disappearing and larger ones increasing their size. Subsequent annealing to higher temperatures drives the Ni-germanide diffusion into the bulk and the consequent formation of highly ordered, {111} faceted Ni-Ge nanocrystals featuring an epitaxial relationship with the substrate Ni-Ge (101); (010) || Ge(001); (110). PMID:26335383

  13. Roles of Oxygen and Water Vapor in the Oxidation of Halogen Terminated Ge(111) Surfaces

    SciTech Connect

    Sun, Shiyu; Sun, Yun; Liu, Zhi; Lee, Dong-Ick; Pianette, Piero; /SLAC, SSRL

    2006-12-18

    The initial stage of the oxidation of Cl and Br terminated Ge(111) surfaces is studied using photoelectron spectroscopy. The authors perform controlled experiments to differentiate the effects of different factors in oxidation, and find that water vapor and oxygen play different roles. Water vapor effectively replaces the halogen termination layers with the hydroxyl group, but does not oxidize the surfaces further. In contrast, little oxidation is observed for Cl and Br terminated surfaces with dry oxygen alone. However, with the help of water vapor, oxygen oxidizes the surface by breaking the Ge-Ge back bonds instead of changing the termination layer.

  14. Evaluation of Dislocation Density of SiGe-on-Insulator Substrates using Enhanced Secco Etching Method

    NASA Astrophysics Data System (ADS)

    Sugiyama, Naoharu; Moriyama, Yoshihiko; Tezuka, Tsutomu; Mizuno, Tomohisa; Nakaharai, Shu; Usuda, Koji; Takagi, Sin-ichi

    2003-07-01

    The dislocation density in thin SiGe on Insulator layers is evaluated, for the first time, by the enhanced secco etching method. It is found that the dislocation density in SGOI layers formed by the Ge condensation method is 6× 103 cm-2. It has also been confirmed that the different types of defects are observed by the HF defect detection method. In addition, the origin of dislocations is discussed by the diagnosis of the variation of dislocation densities during the process steps in the Ge condensation technique.

  15. Diffusion and crystallization mechanisms of Ge /Au bilayer media for write-once optical disk

    NASA Astrophysics Data System (ADS)

    Wu, T. H.; Kuo, P. C.; Ou, S. L.; Chen, Jung-Po; Yen, Po-Fu; Jeng, Tzuan-Ren; Wu, Chih-Yuan; Huang, Der-Ray

    2008-01-01

    Ge /Au bilayer thin films were fabricated by magnetron sputtering method, the temperature dependence of resistance from room temperature to 500°C and concentration depth profiles are measured. From the temperature dependence of resistance measurement, we found two phase change phenomena which occurred at 175 and 360°C. The element concentration depth profiles of the as-deposited and recorded region indicate that the Au-Ge alloy is initially formed at the Ge /Au interface. The dominant diffusion element is Au atom and the diffusion path is from Au layer to Ge layer. The optimum simulated bit error rate value is about 1.4×0-6 at 9.0mW under two time high definition digital versatile disk (HD DVD) recording speed. The dynamic tests show that this Ge /Au bilayer films can be applied to one to two times HD DVD-R.

  16. Short, intermediate and mesoscopic range order in sulfur-rich binary glasses

    SciTech Connect

    Bychkov, E.; Miloshova, M.; Price, D.L.; Benmore, C.J.; Lorriaux, A.

    2008-09-29

    Pulsed neutron and high-energy X-ray diffraction, small-angle neutron scattering, Raman spectroscopy and DSC were used to study structural changes on the short, intermediate and mesoscopic range scale for sulfur-rich AsS{sub x} (x {ge} 1.5) and GeS{sub x} (x {ge} 2) glasses. Two structural regions were found in the both systems. (1) Between stoichiometric (As{sub 2}S{sub 3} and GeS{sub 2}) and 'saturated' (AsS{sub 2.2} and GeS{sub 2.7}) compositions, excessive sulfur atoms form sulfur dimers and/or short chains, replacing bridging sulfur in corner-sharing AsS{sub 3/2} and GeS{sub 4/2} units. (2) Above the 'saturated' compositions at [As] < 30.5 at.% and [Ge] < 27 at.%, sulfur rings and longer sulfur chains (especially in the AsS{sub x} system) appear in the glass network. The glasses become phase separated with the domains of 20-50 {angstrom}, presumably enriched with sulfur rings. The longer chains Sn are not stable and crystallize to c-S{sub 8} on ageing of a few days to several months, depending on composition.

  17. Multilayered Ge/SiGe Material in Microfabricated Thermoelectric Modules

    NASA Astrophysics Data System (ADS)

    Samarelli, A.; Llin, L. Ferre; Cecchi, S.; Chrastina, D.; Isella, G.; Etzelstorfer, T.; Stangl, J.; Gubler, E. Muller; Weaver, J. M. R.; Dobson, P.; Paul, D. J.

    2014-10-01

    Results for low dimensional p-type Ge/SiGe superlattices with Ge quantum wells of 3.43 nm are presented. A range of microfabricated test structures have been developed to characterise the cross-plane electrical and thermal properties of the Ge/SiGe heterostructures. These superlattices were directly grown on 100-mm-diameter silicon wafers by a chemical vapour deposition growth system with rates up to 6 nm/s. Quantum well and quantum mechanical tunnel barriers with dimensions down to nm have been designed, grown and tested; they demonstrate a ZT of 0.08 ± 0.011 and power factor of 1.34 ± 0.15 m W m-1 K-2 at 300 K. A complete microfabricated module using indium bump-bonding is reported together with preliminary results on unoptimised material and leg dimensions. Routes to optimise the material and modules are discussed.

  18. Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

    SciTech Connect

    Pinto, S.; Roldan Gutierrez, Manuel A; Ramos, M. M.D.; Gomes, M.J.M.; Molina, S. I.; Pennycook, Stephen J; Varela del Arco, Maria; Buljan, M.; Barradas, N.; Alves, E.; Chahboun, A.; Bernstorff, S.

    2012-01-01

    In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO{sub 2})/SiO{sub 2} multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO{sub 2}) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.

  19. Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

    SciTech Connect

    Pinto, S. R. C.; Ramos, M. M. D.; Gomes, M. J. M.; Buljan, M.; Chahboun, A.; Roldan, M. A.; Molina, S. I.; Bernstorff, S.; Varela, M.; Pennycook, S. J.; Barradas, N. P.; Alves, E.

    2012-04-01

    In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO{sub 2})/SiO{sub 2} multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO{sub 2}) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.

  20. Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

    NASA Astrophysics Data System (ADS)

    Pinto, S. R. C.; Buljan, M.; Chahboun, A.; Roldan, M. A.; Bernstorff, S.; Varela, M.; Pennycook, S. J.; Barradas, N. P.; Alves, E.; Molina, S. I.; Ramos, M. M. D.; Gomes, M. J. M.

    2012-04-01

    In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO2)/SiO2 multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO2) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.

  1. Ge growth on porous silicon: The effect of buffer porosity on the epilayer crystalline quality

    NASA Astrophysics Data System (ADS)

    Calabrese, G.; Baricordi, S.; Bernardoni, P.; De Salvador, D.; Ferroni, M.; Guidi, V.; Morandi, V.; Vincenzi, D.

    2014-09-01

    We report on the epitaxial growth of Ge virtual substrates directly on Si (001) and on different porosity porous silicon (pSi) buffers. Obtained results indicate that Ge grown on low porosity (22%) pSi buffer has a better crystalline quality compared to Ge grown on bulk Si and on higher porosity buffers. This result is attributed to the compliant nature of pSi and to its reduced Young's modulus, which leads to plastic tensile deformation of the 22% porosity buffer under the in-plane tensile stress introduced by Ge lattice. The same result is not observed for higher porosity buffers, this effect being attributed to the higher buffer fragility. A low porosity pSi layer can hence be used as buffer for the growth of Ge on Si virtual substrates with reduced dislocation content and for the growth of Ge based devices or the successive integration of III-V semiconductors on Si.

  2. Phase formation during Mn thin film reaction with Ge: Self-aligned germanide process for spintronics

    NASA Astrophysics Data System (ADS)

    Abbes, O.; Portavoce, A.; Le Thanh, V.; Girardeaux, C.; Michez, L.

    2013-10-01

    Interesting results have been reported concerning the magnetic properties of the Mn5Ge3 compound, opening the road to possibly create spin injectors in Ge. However, a process compatible with the Complementary Metal Oxide Semiconductor technology, allowing to produce a Mn5Ge3 layer on the active regions of Ge-based transistors has not been well established yet. Here, we report on the solid state reaction between a 50 nm-thick Mn film and amorphous Ge, aiming to investigate a similar process than the one (Salicide) used for contact production in the standard Si technology. In situ X-ray diffraction combined with ex situ structural and magnetic characterizations were used to identify and study phase formation during the Mn/Ge reaction.

  3. 193 nm Excimer laser processing of Si/Ge/Si(100) micropatterns

    NASA Astrophysics Data System (ADS)

    Gontad, F.; Conde, J. C.; Chiussi, S.; Serra, C.; González, P.

    2016-01-01

    193 nm Excimer laser assisted growth and crystallization of amorphous Si/Ge bilayer patterns with circular structures of 3 μm diameter and around 25 nm total thickness, is presented. Amorphous patterns were grown by Laser induced Chemical Vapor Deposition, using nanostencils as shadow masks and then irradiated with the same laser to induce structural and compositional modifications for producing crystalline SiGe alloys through fast melting/solidification cycles. Compositional and structural analyses demonstrated that pulses of 240 mJ/cm2 lead to graded SiGe alloys with Si rich discs of 2 μm diameter on top, a buried Ge layer, and Ge rich SiGe rings surrounding each feature, as predicted by previous numerical simulation.

  4. Intermediate depth seismicity - a reflection seismic approach

    NASA Astrophysics Data System (ADS)

    Haberland, C.; Rietbrock, A.

    2004-12-01

    During subduction the descending oceanic lithosphere is subject to metamorphic reactions, some of them associated with the release of fluids. It is now widely accepted, that these reactions and associated dehydration processes are directly related with the generation of intermediate depth earthquakes (dehydration embrittlement). However, the structure of the layered oceanic plate at depth and the location of the earthquakes relative to structural units of the subducting plate (sources within the oceanic crust and/or in the upper oceanic mantle lithosphere?) are still not resolved yet. This is in mainly due to the fact that the observational resolution needed to address these topics (in the range of only a few kilometers) is hardly achieved in field experiments and related studies. Here we study the wavefields of intermediate depth earthquakes typically observed by temporary networks in order to assess their high-resolution potential in resolving structure of the down going slab and locus of seismicity. In particular we study whether the subducted oceanic Moho can be detected by the analysis of secondary phases of local earthquakes (near vertical reflection). Due to the irregular geometry of sources and receivers we apply an imaging technique similar to diffraction stack migration. The method is tested using synthetic data both based on 2-D finite difference simulations and 3-D kinematic ray tracing. The accuracy of the hypocenter location and onset times crucial for the successful application of stacking techniques (coherency) was achieved by the use of relatively relocated intermediate depth seismicity. Additionally, we simulate the propagation of the wavefields at larger distance (wide angle) indicating the development of guided waves traveling in the low-velocity waveguide associated with the modeled oceanic crust. We also present application on local earthquake data from the South American subduction zone.

  5. Structure and infrared photoluminescence of GeSi nanocrystals formed by high temperature annealing of GeOx/SiO2 multilayers

    NASA Astrophysics Data System (ADS)

    Volodin, V. A.; Gambaryan, M. P.; Cherkov, A. G.; Stoffel, M.; Rinnert, H.; Vergnat, M.

    2016-08-01

    Germanium and GeSi nanocrystals were synthesized in SiGeO2 glass by high temperature annealings of GeOx(5 nm)/SiO2(5 nm) multilayers. According to electron microscopy data, the size distribution and stoichiometry of the nanocrystals depend on the annealing temperature (700, 800, or 900 °C). Spatial redistribution of Ge with the formation of large faceted nanocrystals located near the Si substrate and GeSi intermixing at the substrate/film interface were observed. In the case of the 900 °C annealed sample, we note that some nanocrystals have a pyramid-like shape. Infrared absorption spectroscopy demonstrates that intermixing takes place between the GeOx and SiO2 layers leading to the formation of SiGeO2 glass. Raman spectroscopy confirms the formation of Ge nanocrystals after annealing at 700 °C and GeSi nanocrystals after annealing at 800 and 900 °C. For all annealed samples, we report the observation of infrared photoluminescence (PL) at low temperatures in the spectral range 1300–2100 nm. The observation of PL at wavelengths close to 2000 nm may be due to defect-induced radiative transitions in the nanocrystals.

  6. Electronic properties of epitaxial Ge/AlAs heterostructures on Si and GaAs

    NASA Astrophysics Data System (ADS)

    Heremans, J. J.; Xie, Yuantao; Hudait, M. K.; Clavel, M.; Goley, P. S.

    Ge, with high electron and hole mobilities, has advantages over Si for low-power high-speed nanoscale logic. We report on the MBE growth of Ge/AlAs/GaAs and Ge/AlAs/GaAs/Si structures, where the Ge/AlAs band offsets provide carrier confinement inside the Ge layer. We studied the confinement of carriers in the Ge layer, the effect of the AlAs buffer layer, and the effects of a growth pause and growth temperature, correlated to structural and morphological properties. Magnetotransport and quantum transport measurements were obtained down to 390 mK and in magnetic fields up to 9 T. A weak-localization signal, in contrast to antilocalization, indicates absence of spin-orbit interaction and hence electron confinement in the Ge rather than in the III-V layers. For the Ge/AlAs/GaAs/Si structure a low-temperature sheet carrier density 1.4 x 1014 cm-2 and mobility 390 cm2/Vs were obtained, with similar values at 290 K, while at 200 K a maximum in mobility is reached of 470 cm2/Vs. For the Ge/AlAs/GaAs structures a mobility up to 260 cm2/Vs was obtained at 2 x 1013 cm-2 at 290 K. The Ge/AlAs/GaAs structures have also shown phonon-limited scattering vs temperature, attesting to the quality of interfaces. Supported by DOE DE-FG02-08ER46532, NSF ECCS-1348653, Intel Corp.

  7. Ba termination of Ge(001) studied with STM.

    PubMed

    Koczorowski, W; Grzela, T; Radny, M W; Schofield, S R; Capellini, G; Czajka, R; Schroeder, T; Curson, N J

    2015-04-17

    We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy. Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (∼0.15 ML) that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that the thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps to temperatures of 470, 570, 670 and 770 K although a gradual ordering of the Ba layer is observed at 570 K and above, accompanied by a decrease in Ba layer density. Annealing above 770 K produces the 2D surface alloy phase accompanied by strain relief through monolayer height trench formation. An annealing temperature of 1070 K sees a further change in surface morphology but retention of the 2D surface alloy characteristic. These results are discussed in view of their possible implications for future semiconductor integrated circuit technology. PMID:25797886

  8. Ba termination of Ge(001) studied with STM

    NASA Astrophysics Data System (ADS)

    Curson, Neil; Koczorowski, Wojciech; Grzela, Tomasz; Radny, Marian; Schofield, Steven; Capellini, Giovanni; Czajka, Ryszard; Schroeder, Thomas

    2015-03-01

    We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy (STM). Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (0.15 ML) such that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps up to 770 K with a gradual ordering of the Ba layer at 570 K and above and a decrease in Ba layer density. Annealing above 770 K produces the 2-D surface alloy phase accompanied by strain relief through monolayer height trench formation. At 1070 K the surface morphology changes again but remains a 2-D surface alloy. WK and NJC acknowledge EPSRC grant EP/I02865X/1. WK, MWR and R.C. acknowledge the Polish Ministry of Science and Higher Education for support (Project No. N-N202-195840).

  9. Ba termination of Ge(001) studied with STM

    NASA Astrophysics Data System (ADS)

    Koczorowski, W.; Grzela, T.; Radny, M. W.; Schofield, S. R.; Capellini, G.; Czajka, R.; Schroeder, T.; Curson, N. J.

    2015-04-01

    We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy. Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (∼0.15 ML) that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that the thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps to temperatures of 470, 570, 670 and 770 K although a gradual ordering of the Ba layer is observed at 570 K and above, accompanied by a decrease in Ba layer density. Annealing above 770 K produces the 2D surface alloy phase accompanied by strain relief through monolayer height trench formation. An annealing temperature of 1070 K sees a further change in surface morphology but retention of the 2D surface alloy characteristic. These results are discussed in view of their possible implications for future semiconductor integrated circuit technology.

  10. Influence of layer charge and charge distribution of smectites on the flow behaviour and swelling of bentonites

    USGS Publications Warehouse

    Christidis, G.E.; Blum, A.E.; Eberl, D.D.

    2006-01-01

    The influence of layer charge and charge distribution of dioctahedral smectites on the rheological and swelling properties of bentonites is examined. Layer charge and charge distribution were determined by XRD using the LayerCharge program [Christidis, G.E., Eberl, D.D., 2003. Determination of layer charge characteristics of smectites. Clays Clay Miner. 51, 644-655.]. The rheological properties were determined, after sodium exchange using the optimum amount of Na2CO3, from free swelling tests. Rheological properties were determined using 6.42% suspensions according to industrial practice. In smectites with layer charges of - 0.425 to - 0.470 per half formula unit (phfu), layer charge is inversely correlated with free swelling, viscosity, gel strength, yield strength and thixotropic behaviour. In these smectites, the rheological properties are directly associated with the proportion of low charge layers. By contrast, in low charge and high charge smectites there is no systematic relation between layer charge or the proportion of low charge layers and rheological properties. However, low charge smectites yield more viscous suspensions and swell more than high charge smectites. The rheological properties of bentonites also are affected by the proportion of tetrahedral charge (i.e. beidellitic charge), by the existence of fine-grained minerals having clay size, such as opal-CT and to a lesser degree by the ionic strength and the pH of the suspension. A new method for classification of smectites according to the layer charge based on the XRD characteristics of smecites is proposed, that also is consistent with variations in rheological properties. In this classification scheme the term smectites with intermediate layer charge is proposed. ?? 2006 Elsevier B.V. All rights reserved.

  11. Buried Porous Silicon-Germanium Layers in Monocrystalline Silicon Lattices

    NASA Technical Reports Server (NTRS)

    Fathauer, Robert W. (Inventor); George, Thomas (Inventor); Jones, Eric W. (Inventor)

    1998-01-01

    Monocrystalline semiconductor lattices with a buried porous semiconductor layer having different chemical composition is discussed and monocrystalline semiconductor superlattices with a buried porous semiconductor layers having different chemical composition than that of its monocrystalline semiconductor superlattice are discussed. Lattices of alternating layers of monocrystalline silicon and porous silicon-germanium have been produced. These single crystal lattices have been fabricated by epitaxial growth of Si and Si-Ge layers followed by patterning into mesa structures. The mesa structures are strain etched resulting in porosification of the Si-Ge layers with a minor amount of porosification of the monocrystalline Si layers. Thicker Si-Ge layers produced in a similar manner emitted visible light at room temperature.

  12. Compact intermediates in RNA folding

    SciTech Connect

    Woodson, S.A.

    2011-12-14

    Large noncoding RNAs fold into their biologically functional structures via compact yet disordered intermediates, which couple the stable secondary structure of the RNA with the emerging tertiary fold. The specificity of the collapse transition, which coincides with the assembly of helical domains, depends on RNA sequence and counterions. It determines the specificity of the folding pathways and the magnitude of the free energy barriers to the ensuing search for the native conformation. By coupling helix assembly with nascent tertiary interactions, compact folding intermediates in RNA also play a crucial role in ligand binding and RNA-protein recognition.

  13. Nuclear reactions at intermediate energies

    NASA Astrophysics Data System (ADS)

    Shyam, Radhey

    2016-05-01

    In the domain of Nuclear reactions at intermediate energies, the QCD coupling constant αs is large enough (~ 0.3 - 0.5) to render the perturbative calculational techniques inapplicable. In this regime the quarks are confined into colorless hadrons and it is expected that effective field theories of hadron interactions via exchange of hadrons, provide useful tools to describe such reactions. In this contribution we discuss the application of one such theory, the effective Lagrangian model, in describing the hadronic reactions at intermediate energies whose measurements are the focus of a vast international experimental program.

  14. Strain distributions and electronic property modifications in Si/Ge axial nanowire heterostructures

    SciTech Connect

    Swadener, John Gregory; Picraux, Samuel T

    2008-01-01

    Molecular dynamics simulations were carried out for Si/Ge axial nanowire heterostructures using modified effective atom method (MEAM) potentials. A Si-Ge MEAM interatomic cross potential was developed based on available experimental data and used for these studies. The atomic distortions and strain distributions near the Si/Ge interfaces are predicted for nanowires with their axes oriented along the [111] direction. The cases of 10 and 25 nm diameter SilGe biwires and of 25 nm diameter Si/Ge/Si axial heterostructures with the Ge disc 1 nm thick were studied. Substantial distortions in the height of the atoms adjacent to the interface were found for the biwires, but not for the Ge discs. Strains as high as 3.5% were found for the Ge disc and values of 2 to 2.5% were found at the Si and Ge interfacial layers in the biwires. Deformation potential theory was used to estimate the influence of the strains on the band gap, and reductions in band gap to as small as 40% of bulk values are predicted for the Ge discs. Localized regions of increased strain and resulting energy minima were also found within the Si/Ge biwire interfaces with the larger effects on the Ge side of the interface. The regions of strain maxima near and within the interfaces are anticipated to be useful for tailoring band gaps and producing quantum confinement of carriers. These results suggest nanowire heterostructures provide greater design flexibility in band structure modification than is possible with planar layer growth.

  15. ABA-alcohol is an intermediate in abscisic acid biosynthesis

    SciTech Connect

    Rock, C.D.; Zeevaart, J.A.D. )

    1990-05-01

    It has been established that ABA-aldehyde is a precursor to ABA. The ABA-deficient flacca and sitiens mutants of tomato are blocked in the conversion of ABA-aldehyde to ABA, and accumulate trans-ABA-alcohol. {sup 18}O-Labeling studies of ABA in flacca and sitiens show that these mutants synthesize a large percentage of ({sup 18}O)ABA which contains two {sup 18}O atoms in the carboxyl group. Furthermore, the mutants synthesize much greater amounts of trans-ABA-glucose ester (t-ABA-GE) compared with the wild type, and this ({sup 18}O)t-ABA-GE is also double labeled in the carboxyl group. Our interpretation of these data is that the {sup 18}O in ABA-aldehyde is trapped in the side chain by reduction to ({sup 18}O)ABA-alcohol, followed by isomerization to ({sup 18}O)t-ABA-alcohol and oxidation with {sup 18}O{sub 2} to ({sup 18}O)t-ABA. The ({sup 18}O)t-ABA is then rapidly converted to ({sup 18}O)t-ABA-GE. Because ({sup 18}O)ABA doubly labeled in the carboxyl group has been observed in small amounts in labeling experiments with several species, and various species have been shown to convert ABA-aldehyde to ABA-alcohol and t-ABA-alcohol, we propose that ABA-alcohol is an ABA intermediate in a shunt pathway.

  16. Antimony segregation in stressed SiGe heterostructures grown by molecular beam epitaxy

    SciTech Connect

    Drozdov, M. N.; Novikov, A. V.; Yurasov, D. V.

    2013-11-15

    The effects of the growth temperature, composition, and elastic strains in separate layers on the segregation of antimony are studied experimentally for stressed SiGe structures grown by molecular beam epitaxy. It is established that the growth conditions and parameters of the structures exert an interrelated influence on the segregation of Sb: the degree of the influence of the composition and elastic stresses in the SiGe layers on Sb segregation depends on the growth temperature. It is shown that usage of a method previously proposed by us for the selective doping of silicon structures with consideration for the obtained dependences of Sb segregation on the growth conditions and parameters of the SiGe layers makes it possible to form SiGe structures selectively doped with antimony.

  17. Ge-Au eutectic bonding of Ge {100} single crystals

    NASA Astrophysics Data System (ADS)

    Knowlton, W. B.; Itoh, K. M.; Beeman, J. W.; Emes, J. H.; Loretto, D.; Haller, E. E.

    1993-11-01

    We present preliminary results on the eutectic bonding between two {100} Ge single crystal surfaces using thin films of Au ranging from 900Å/surface to 300Å/surface and Pd (10% the thickness of Au). Following bonding, plan view optical microscopy (OM) of the cleaved interface of samples with Au thicknesses ≤ 500Å/surface show a eutectic morphology more conducive to phonon transmission through the bond interface. High resolution transmission electron microscopy (HRTEM) cross sectional interface studies of a 300Å/surface Au sample show <100> epitaxial growth of Ge. In sections of the bond, lattice continuity of the Ge is apparent through the interface. TEM studies also reveal <110> heteroepitaxial growth of Au with a Au-Ge lattice mismatch of less than 2%. Eutectic bonds with 200Å/surface Au have been attained with characterization pending. An optical polishing technique for Ge has been optimized to insure intimate contact between the Ge surfaces prior to bonding. Interferometry analysis of the optically polished Ge surface shows that surface height fluctuations lie within ±150Å across an interval of 1mm. Characterization of phonon transmission through the interface is discussed with respect to low temperature detection of ballistic phonons.

  18. Thermal Stability of Ge2Sb2Te5 in Contact with Ti and TiN

    NASA Astrophysics Data System (ADS)

    Venugopal, Vijayaharan A.; Ottaviani, Giampiero; Bresolin, Camillo; Erbetta, Davide; Modelli, Alberto; Varesi, Enrico

    2009-10-01

    The thermal stability of a Ge2Sb2Te5 chalcogenide layer in contact with titanium and titanium nitride metallic thin films has been investigated mainly using x-ray diffraction and elastic nuclear backscattering techniques. Without breaking vacuum, Ti and TiN have been deposited on Ge2Sb2Te5 material using magnetron sputtering. Thermal treatments have been performed in a 10-7 mbar vacuum furnace. On annealing up to 450°C, the TiN metallic film does not interact with the chalcogenide film, but at the same time adhesion problems and instabilities in contact resistance arise. To improve the adhesion and eventually stabilize the contact resistance, an interfacial Ti layer has been considered. At 300°C, a TiTe2 compound is formed by interacting with Te segregated from the Ge2Sb2Te5 layer. At higher temperatures, the Ti layer decomposes the chalcogenide film, forming several compounds tentatively identified as GeTe, Ge3Ti5, Ge5Ti6, TiTe2,, and Sb2Te3. It has been found that the properties of the Ge2Sb2Te5 film can be retained by controlling the decomposition rate of the chalcogenide layer, which is achieved by providing a limited supply of Ti and/or by depositing a Te-rich Ge2Sb2Te5 film.

  19. High-k gate stacks on low bandgap tensile strained Ge and GeSn alloys for field-effect transistors.

    PubMed

    Wirths, Stephan; Stange, Daniela; Pampillón, Maria-Angela; Tiedemann, Andreas T; Mussler, Gregor; Fox, Alfred; Breuer, Uwe; Baert, Bruno; San Andrés, Enrique; Nguyen, Ngoc D; Hartmann, Jean-Michel; Ikonic, Zoran; Mantl, Siegfried; Buca, Dan

    2015-01-14

    We present the epitaxial growth of Ge and Ge0.94Sn0.06 layers with 1.4% and 0.4% tensile strain, respectively, by reduced pressure chemical vapor deposition on relaxed GeSn buffers and the formation of high-k/metal gate stacks thereon. Annealing experiments reveal that process temperatures are limited to 350 °C to avoid Sn diffusion. Particular emphasis is placed on the electrical characterization of various high-k dielectrics, as 5 nm Al2O3, 5 nm HfO2, or 1 nmAl2O3/4 nm HfO2, on strained Ge and strained Ge0.94Sn0.06. Experimental capacitance-voltage characteristics are presented and the effect of the small bandgap, like strong response of minority carriers at applied field, are discussed via simulations. PMID:25531887

  20. Morphology and chemical composition of cobalt germanide islands on Ge(001)

    NASA Astrophysics Data System (ADS)

    Ewert, M.; Schmidt, Th; Flege, J. I.; Heidmann, I.; Grzela, T.; Klesse, W. M.; Foerster, M.; Aballe, L.; Schroeder, T.; Falta, J.

    2016-08-01

    The reactive growth of cobalt germanide on Ge(001) was investigated by means of in situ x-ray absorption spectroscopy photoemission electron microscopy (XAS-PEEM), micro-illumination low-energy electron diffraction (μ-LEED), and ex situ atomic force microscopy (AFM). At a Co deposition temperature of 670 °C, a rich morphology with different island shapes and dimensions is observed, and a correlation between island morphology and stoichiometry is found. By combining XAS-PEEM and μ-LEED, we were able to identify a large part of the islands to consist of CoGe2, with many of them having an unusual epitaxial relationship: CoGe2 [\\bar{1}10](111) \\parallel Ge [\\bar{1}10](001). Side facets with (112) and (113) orientation have been found for such islands. However, two additional phases were observed, most likely Co5Ge7 and CoGe. Comparing growth on Ge(001) single crystals and on Ge(001)/Si(001) epilayer substrates, the occurrence of these intermediate phases seems to be promoted by defects or residual strain.