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Sample records for ge liquid semiconductor

  1. Nanophase diagram of binary eutectic Au-Ge nanoalloys for vapor-liquid-solid semiconductor nanowires growth

    PubMed Central

    Lu, Haiming; Meng, Xiangkang

    2015-01-01

    Although the vapor-liquid-solid growth of semiconductor nanowire is a non-equilibrium process, the equilibrium phase diagram of binary alloy provides important guidance on the growth conditions, such as the temperature and the equilibrium composition of the alloy. Given the small dimensions of the alloy seeds and the nanowires, the known phase diagram of bulk binary alloy cannot be expected to accurately predict the behavior of the nanowire growth. Here, we developed a unified model to describe the size- and dimensionality-dependent equilibrium phase diagram of Au-Ge binary eutectic nanoalloys based on the size-dependent cohesive energy model. It is found that the liquidus curves reduce and shift leftward with decreasing size and dimensionality. Moreover, the effects of size and dimensionality on the eutectic composition are small and negligible when both components in binary eutectic alloys have the same dimensionality. However, when two components have different dimensionality (e.g. Au nanoparticle-Ge nanowire usually used in the semiconductor nanowires growth), the eutectic composition reduces with decreasing size. PMID:26053237

  2. Nanophase diagram of binary eutectic Au-Ge nanoalloys for vapor-liquid-solid semiconductor nanowires growth.

    PubMed

    Lu, Haiming; Meng, Xiangkang

    2015-06-08

    Although the vapor-liquid-solid growth of semiconductor nanowire is a non-equilibrium process, the equilibrium phase diagram of binary alloy provides important guidance on the growth conditions, such as the temperature and the equilibrium composition of the alloy. Given the small dimensions of the alloy seeds and the nanowires, the known phase diagram of bulk binary alloy cannot be expected to accurately predict the behavior of the nanowire growth. Here, we developed a unified model to describe the size- and dimensionality-dependent equilibrium phase diagram of Au-Ge binary eutectic nanoalloys based on the size-dependent cohesive energy model. It is found that the liquidus curves reduce and shift leftward with decreasing size and dimensionality. Moreover, the effects of size and dimensionality on the eutectic composition are small and negligible when both components in binary eutectic alloys have the same dimensionality. However, when two components have different dimensionality (e.g. Au nanoparticle-Ge nanowire usually used in the semiconductor nanowires growth), the eutectic composition reduces with decreasing size.

  3. Glass Transitions, Semiconductor-Metal Transitions, and Fragilities in Ge -V -Te (V =As , Sb) Liquid Alloys: The Difference One Element Can Make

    NASA Astrophysics Data System (ADS)

    Wei, Shuai; Coleman, Garrett J.; Lucas, Pierre; Angell, C. Austen

    2017-03-01

    Glass-transition temperatures (Tg ) and liquid fragilities are measured along a line of constant Ge content in the system Ge-As-Te, and contrasted with the lack of glass-forming ability in the twin system Ge-Sb-Te at the same Ge content. The one composition established as free of crystal contamination in the latter system shows a behavior opposite to that of a more covalent system. The comparison of Tg vs bond density in the three systems Ge-As-chalcogen differing in chalcogen, i.e., S, Se, or Te, shows that as the chalcogen becomes more metallic, i.e., in the order S semiconductor-to-metal (SC-M ) transitions, with their associated thermodynamic manifestations in relevant liquid alloys. The thermodynamic components, as seen previously, control liquid fragility and cause fragile-to-strong transitions during cooling. We tentatively conclude that liquid-state behavior in phase-change materials is controlled by liquid-liquid (LL) and SC-M transitions that have become submerged below the liquidus surface. In the case of the Ge-Te binary, a crude extrapolation to GeTe stoichiometry indicates that the SC-M transition lies about 20% below the melting point, suggesting a parallel with the intensely researched "hidden liquid-liquid transition" in supercooled water. In the water case, superfast crystallization initiates in the high-fragility domain some 4% above the LL transition temperature (TLL ) which is located at approximately 15% below the (ambient pressure) melting point.

  4. Modeling of Diffusion in Liquid Ge and Its Alloys

    NASA Technical Reports Server (NTRS)

    Stroud, David G.

    1998-01-01

    This report summarizes progress made on NASA Grant NAG3-1437, Modeling of diffusion in Liquid Ge and Its Alloys, which was in effect from January 15, 1993 through July 10, 1997. It briefly describes the purpose of the grant, and the work accomplished in simulations and other studies of thermophysical properties of liquid semiconductors and related materials. A list of publications completed with the support of the grant is also given.

  5. Vapor-liquid-solid growth of endotaxial semiconductor nanowires.

    PubMed

    Li, Shaozhou; Huang, Xiao; Liu, Qing; Cao, Xiehong; Huo, Fengwei; Zhang, Hua; Gan, Chee Lip

    2012-11-14

    Free-standing and in-plane lateral nanowires (NWs) grown by the vapor-liquid-solid (VLS) process have been widely reported. Herein, we demonstrate that the VLS method can be extended to the synthesis of horizontally aligned semiconductor NWs embedded in substrates. Endotaxial SiGe NWs were grown in silicon substrates by tuning the directional movement of the catalyst in the substrates. The location of the SiGe NWs can be controlled by the SiO(2) pattern on the silicon surface. By varying the growth conditions, the proportion of Ge in the obtained NWs can also be tuned. This approach opens up an opportunity for the spatial control of the NW growth in substrates and can potentially broaden the applications of NWs in new advanced fields.

  6. Moving liquids with light: Photoelectrowetting on semiconductors

    PubMed Central

    Arscott, Steve

    2011-01-01

    By linking semiconductor physics and wetting phenomena a brand new effect termed “photoelectrowetting-on-semiconductors” is demonstrated here for a conducting droplet resting on an insulator-semiconductor stack. Optical generation of carriers in the space-charge region of the underlying semiconductor alters the capacitance of the liquid-insulator-semiconductor stack; the result of this is a modification of the wetting contact angle of the droplet upon illumination using above band gap light. The effect is demonstrated using commercial silicon wafers, both n- and p-type having a doping range spanning four orders of magnitude (6×1014−8×1018 cm−3), coated with a commercial amorphous fluoropolymer insulating film (Teflon®). Impedance measurements confirm that the observations are semiconductor space-charge related effects. The impact of the work could lead to new silicon-based technologies in areas such as Laboratory-on-a-Chip, Microfluidics and Optofluidics. PMID:22355699

  7. Semiconductor liquid crystal composition and methods for making the same

    DOEpatents

    Alivisatos, A. Paul; Li, Liang-shi

    2005-04-26

    Semiconductor liquid crystal compositions and methods for making such compositions are disclosed. One embodiment of the invention is directed to a liquid crystal composition including a solvent and semiconductor particles in the solvent. The solvent and the semiconductor particles are in an effective amount in the liquid crystal composition to form a liquid crystal phase.

  8. Electrodeposition of metals and semiconductors in air- and water-stable ionic liquids.

    PubMed

    Zein el-Abedin, Sherif; Endres, Frank

    2006-01-16

    In addition to their stability, the advantages of air- and water-stable ionic liquids over chloroaluminate ionic liquids, which were intensively investigated in the past, are that they are easy to dry, purify, and handle. Moreover, some of these ionic liquids have an extremely large electrochemical window of more than 5 V, and hence they give access to the electrodeposition of many metals and semiconductors, such as Ta, Ti, Si, and Ge. The results to date for the electrodeposition of metals and semiconductors in the most popular air- and water-stable ionic liquids are presented.

  9. Thermodynamic properties of liquid Si and Ge

    NASA Technical Reports Server (NTRS)

    Shih, W.-H.; Stroud, D.

    1985-01-01

    Thermodynamic properties of liquid Si and Ge are calculated using standard variational techniques, with the hard-sphere system as a reference system. Third-order electron-ion pseudopotential contributions are included nonvariationally and are shown to have little effect on the free energy, although a larger one on the derivatives of the free energy. Two different model pseudopotentials are used and give similar results in good agreement with experiment.

  10. Electrical Properties of Reactive Liquid Crystal Semiconductors

    NASA Astrophysics Data System (ADS)

    McCulloch, Iain; Coelle, Michael; Genevicius, Kristijonas; Hamilton, Rick; Heckmeier, Michael; Heeney, Martin; Kreouzis, Theo; Shkunov, Maxim; Zhang, Weimin

    2008-01-01

    Fabrication of display products by low cost printing technologies such as ink jet, gravure offset lithography and flexography requires solution processable semiconductors for the backplane electronics. The products will typically be of lower performance than polysilicon transistors, but comparable to amorphous silicon. A range of prototypes are under development, including rollable electrophoretic displays, active matrix liquid crystal displays (AMLCD's), and flexible organic light-emitting diode (OLED) displays. Organic semiconductors that offer both electrical performance and stability with respect to storage and operation under ambient conditions are required. This work describes the initial evaluation of reactive mesogen semiconductors, which can polymerise within mesophase temperatures, “freezing in” the order in crosslinked domains. These crosslinked domains offer mechanical stability and are inert to solvent exposure in further processing steps. Reactive mesogens containing conjugated aromatic cores, designed to facilitate charge transport and provide good oxidative stability, were prepared and their liquid crystalline properties evaluated. Both time-of-flight and field effect transistor devices were prepared and their electrical characterisation reported.

  11. Electrochemical liquid-liquid-solid (ec-LLS) crystal growth: a low-temperature strategy for covalent semiconductor crystal growth.

    PubMed

    Fahrenkrug, Eli; Maldonado, Stephen

    2015-07-21

    details chosen for ec-LLS. Third, the rate of introduction of zero-valent materials into the liquid metal is precisely gated with a high degree of resolution by the applied potential/current. The intent of this Account is to summarize the key elements of ec-LLS identified to date, first contextualizing this method with respect to other semiconductor crystal growth methods and then highlighting some unique capabilities of ec-LLS. Specifically, we detail ec-LLS as a platform to prepare Ge and Si crystals from bulk- (∼1 cm(3)), micro- (∼10(-10) cm(3)), and nano-sized (∼10(-16) cm(3)) liquid metal electrodes in common solvents at low temperature. In addition, we describe our successes in the preparation of more compositionally complex binary covalent III-V semiconductors.

  12. Production of 35S for a Liquid Semiconductor Betavoltaic

    SciTech Connect

    Meier, David E.; Garnov, A. Y.; Robertson, J. D.; Kwon, J. W.; Wacharasindhu, T.

    2009-10-01

    The specific energy density from radioactive decay is five to six orders of magnitude greater than the specific energy density in conventional chemical battery and fuel cell technologies. We are currently investigating the use of liquid semiconductor based betavoltaics as a way to directly convert the energy of radioactive decay into electrical power and potentially avoid the radiation damage that occurs in solid state semiconductor devices due to non-ionizing energy loss. Sulfur-35 was selected as the isotope for the liquid semiconductor demonstrations because it can be produced in high specific activity and it is chemically compatible with known liquid semiconductor media.

  13. Phase diagram of nanoscale alloy particles used for vapor-liquid-solid growth of semiconductor nanowires.

    PubMed

    Sutter, Eli; Sutter, Peter

    2008-02-01

    We use transmission electron microscopy observations to establish the parts of the phase diagram of nanometer sized Au-Ge alloy drops at the tips of Ge nanowires (NWs) that determine their temperature-dependent equilibrium composition and, hence, their exchange of semiconductor material with the NWs. We find that the phase diagram of the nanoscale drop deviates significantly from that of the bulk alloy, which explains discrepancies between actual growth results and predictions on the basis of the bulk-phase equilibria. Our findings provide the basis for tailoring vapor-liquid-solid growth to achieve complex one-dimensional materials geometries.

  14. Growth and applications of GeSn-related group-IV semiconductor materials

    PubMed Central

    Zaima, Shigeaki; Nakatsuka, Osamu; Taoka, Noriyuki; Kurosawa, Masashi; Takeuchi, Wakana; Sakashita, Mitsuo

    2015-01-01

    We review the technology of Ge1−xSnx-related group-IV semiconductor materials for developing Si-based nanoelectronics. Ge1−xSnx-related materials provide novel engineering of the crystal growth, strain structure, and energy band alignment for realising various applications not only in electronics, but also in optoelectronics. We introduce our recent achievements in the crystal growth of Ge1−xSnx-related material thin films and the studies of the electronic properties of thin films, metals/Ge1−xSnx, and insulators/Ge1−xSnx interfaces. We also review recent studies related to the crystal growth, energy band engineering, and device applications of Ge1−xSnx-related materials, as well as the reported performances of electronic devices using Ge1−xSnx related materials. PMID:27877818

  15. Ab-initio calculations of semiconductor MgGeP{sub 2} and MgGeAs{sub 2}

    SciTech Connect

    Kocak, B.; Ciftci, Y.O.

    2016-05-15

    Highlights: • MgGeP{sub 2} and MgGeAs{sub 2} are semiconductor compounds. • MgGeP{sub 2} and MgGeAs{sub 2} are energetically, mechanically and dynamically stable. • The electronic charge density contour plot shows that the nature of bonding is a mixture of ionic-covalent. - Abstract: In this study, we focus on structural, electronic, elastic, lattice dynamic and optic properties of MgGeP{sub 2} and MgGeAs{sub 2} using ab-initio density-functional theory (DFT) within Armiento-Mattson 2005 (AM05) scheme of the generalized gradient approximation (GGA) for the exchange-correlation potential. Our computed structural results are in reasonable agreement with the literature. The band gap of these compounds is predicted to be direct. Our elastic results prove that these compounds are mechanically stable. The obtained phonon spectra of MgGeP{sub 2} and MgGeAs{sub 2} do not exhibit any significant imaginary branches using GGA-AM05 for the exchange-correlation approximation. Further analysis of the optical response of the dielectric functions, optical reflectivity, refractive index, extinction coefficient and electron energy loss delves into for the energy range of 0–22.5 eV. It motivated that there exists an optical polarization anisotropy of these compounds for optoelectronic device applications.

  16. Group IV semiconductor Ge integration with topological insulator Sb2Te3 for spintronic application

    NASA Astrophysics Data System (ADS)

    Zheng, Beining; Sun, Yu; Wu, Jie; Han, Mei; Wu, Xiaofeng; Huang, Keke; Feng, Shouhua

    2017-03-01

    Sb2Te3/Ge heterojunctions were grown on deoxidized GaAs (0 0 1) substrates by molecular beam epitaxy to explore a new type of spin torque device. Despite the large lattice mismatch between Ge and Sb2Te3, the films display highly uniform fabrication and good crystallinity, which have been confirmed by structural characterization. The band structures of Sb2Te3/Ge heterojunctions were investigated by x-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy. Small chemical shift of Sb 3d5/2 indicates that TI conducting surface is not destroyed, and Ge valence band bending contributes to Fermi level depinning. The band offset of Sb2Te3/Ge heterojunctions is different from common gate dielectric/Ge heterojunctions. The integral quality of the heterostructure reveals the potential of combining topological insulators with semiconductors for the advancement of spintronic devices.

  17. ‘Symbiotic’ semiconductors: unusual and counter-intuitive Ge/Si/O interactions

    NASA Astrophysics Data System (ADS)

    George, T.; Li, P. W.; Chen, K. H.; Peng, K. P.; Lai, W. T.

    2017-03-01

    Since the inception of the first transistors in the 1940s, the immense body of work on the Group IV semiconductors, Si and Ge, has spearheaded spectacular advances in modern integrated-circuit (IC) technology that has enabled a vast landscape of device applications in logic, memory, and computing. Although initially Si supplanted Ge as the material of choice for metal–oxide–semiconductor field-effect transistors, Ge-based devices are now breaking new ground. Widespread and innovative Ge-based applications exist in optoelectronics, communications, microelectro-mechanical systems, and energy harvesting/savings. On the fundamental, materials science front, while it is well known that Ge and Si are fully miscible in each other, the nature and extent of their attraction for each other has largely been unexplored. In this paper, we report a rather curious interplay between Ge and Si that occurs at high temperature (~900 °C) and that can be best described as ‘symbiotic’. Each element appears to facilitate reactions in the other which would otherwise not be possible. Oxygen intersititials also appear to play a major role in these reactions. Our experimental work has allowed us to classify four distinct regimes where these reactions occur. We describe these conditions and provide the necessary theoretical explanations for these results.

  18. Chitin Liquid-Crystal-Templated Oxide Semiconductor Aerogels.

    PubMed

    Chau, Trang The Lieu; Le, Dung Quang Tien; Le, Hoa Thi; Nguyen, Cuong Duc; Nguyen, Long Viet; Nguyen, Thanh-Dinh

    2017-09-13

    Chitin nanocrystals have been used as a liquid crystalline template to fabricate layered oxide semiconductor aerogels. Anisotropic chitin liquid crystals are transformed to sponge-like aerogels by hydrothermally cross-linked gelation and lyophilization-induced solidification. The hydrothermal gelation of chitin aqueous suspensions then proceeds with peroxotitanate to form hydrogel composites that recover to form aerogels after freeze-drying. The homogeneous peroxotitanate/chitin composites are calcined to generate freestanding titania aerogels that exhibit the nanostructural integrity of layered chitin template. Our extended investigations show that coassembling chitin nanocrystals with other metal-based precursors also yielded semiconductor aerogels of perovskite BaTiO3 and CuOx nanocrystals. The potential of these materials is great to investigate these chitin sponges for biomedicine and these semiconductor aerogels for photocatalysis, gas sensing, and other applications. Our results present a new aerogel templating method of highly porous, ultralight materials with chitin liquid crystals.

  19. Growth process and characterization of magnetic semiconductors based on GeMn alloy films

    NASA Astrophysics Data System (ADS)

    Pinto, N.; Morresi, L.; Murri, R.; D'Orazio, F.; Lucari, F.; Passacantando, M.; Picozzi, P.

    2004-05-01

    The growth mechanism of thin Ge1-xMnx/Ge(100) diluted magnetic semiconductor films have been studied by reflection high energy electron diffraction (RHEED) technique and correlated to the structural and magnetic properties of the films provided by X-ray diffraction (XRD) and magneto-optical Kerr effect (MOKE), respectively. The RHEED analysis evidenced a transition from a bi-dimensional to a three-dimensional growth mechanism at deposition temperature, TG, lower than 433 K while XRD characterization showed a polycrystalline structure with Ge grain size depending on TG. At low TG (343 K) all the Ge1-xMnx films behaved superparamagnetically, while at TG = 433 K hysteresis loops were observed, with a maximum Curie temperature of 250 K, for 0.027 < x < 0.044.

  20. Tricritical behavior of the two-dimensional intrinsically ferromagnetic semiconductor CrGeTe3

    NASA Astrophysics Data System (ADS)

    Lin, G. T.; Zhuang, H. L.; Luo, X.; Liu, B. J.; Chen, F. C.; Yan, J.; Sun, Y.; Zhou, J.; Lu, W. J.; Tong, P.; Sheng, Z. G.; Qu, Z.; Song, W. H.; Zhu, X. B.; Sun, Y. P.

    2017-06-01

    CrGeTe3 recently emerges as a new two-dimensional (2D) ferromagnetic semiconductor that is promising for spintronic device applications. Unlike CrSiTe3 whose magnetism can be understood using the 2D-Ising model, CrGeTe3 exhibits a smaller van der Waals gap and larger cleavage energy, which could lead to a transition of magnetic mechanism from 2D to 3D. To confirm this speculation, we investigate the critical behavior of CrGeTe3 around the second-order paramagnetic-ferromagnetic phase transition. We obtain the critical exponents estimated by several common experimental techniques including the modified Arrott plot, Kouvel-Fisher method, and critical isotherm analysis, which show that the magnetism of CrGeTe3 follows the tricritical mean-field model with the critical exponents β , γ , and δ of 0.240 ±0.006 , 1.000 ±0.005 , and 5.070 ±0.006 , respectively, at the Curie temperature of 67.9 K. We therefore suggest that the magnetic phase transition from 2D to 3D for CrGeTe3 should locate near a tricritical point. Our experiment provides a direct demonstration of the applicability of the tricritical mean-field model to a 2D ferromagnetic semiconductor.

  1. DFT calculations of magnetic anisotropy energy of Ge(1-x)Mn(x)Te ferromagnetic semiconductor.

    PubMed

    Łusakowski, A; Bogusławski, P; Story, T

    2015-06-10

    Density functional theory (DFT) calculations of the energy of magnetic anisotropy for diluted ferromagnetic semiconductor Ge(1-x)Mn(x)Te were performed using OpenMX package with fully relativistic pseudopotentials. The influence of hole concentration and magnetic ion neighbourhood on magnetic anisotropy energy is presented. Analysis of microscopic mechanism of magnetic anisotropy is provided, in particular the role of spin-orbit coupling, spin polarization and spatial changes of electron density are discussed. The calculations are in accordance with the experimental observation of perpendicular magnetic anisotropy in rhombohedral Ge(1-x)Mn(x)Te (1 1 1) thin layers.

  2. DFT calculations of magnetic anisotropy energy of Ge1-xMnxTe ferromagnetic semiconductor

    NASA Astrophysics Data System (ADS)

    Łusakowski, A.; Bogusławski, P.; Story, T.

    2015-06-01

    Density functional theory (DFT) calculations of the energy of magnetic anisotropy for diluted ferromagnetic semiconductor Ge1-xMnxTe were performed using OpenMX package with fully relativistic pseudopotentials. The influence of hole concentration and magnetic ion neighbourhood on magnetic anisotropy energy is presented. Analysis of microscopic mechanism of magnetic anisotropy is provided, in particular the role of spin-orbit coupling, spin polarization and spatial changes of electron density are discussed. The calculations are in accordance with the experimental observation of perpendicular magnetic anisotropy in rhombohedral Ge1-xMnxTe (1 1 1) thin layers.

  3. Semiconductor apparatus utilizing gradient freeze and liquid-solid techniques

    NASA Technical Reports Server (NTRS)

    Fleurial, Jean-Pierre (Inventor); Caillat, Thierry F. (Inventor); Borshchevsky, Alexander (Inventor)

    1998-01-01

    Transition metals of Group VIII (Co, Rh and Ir) have been prepared as semiconductor compounds with the general formula TSb.sub.3. The skutterudite-type crystal lattice structure of these semiconductor compounds and their enhanced thermoelectric properties results in semiconductor materials which may be used in the fabrication of thermoelectric elements to substantially improve the efficiency of the resulting thermoelectric device. Semiconductor materials having the desired skutterudite-type crystal lattice structure may be prepared in accordance with the present invention by using vertical gradient freezing techniques and/or liquid phase sintering techniques. Measurements of electrical and thermal transport properties of selected semiconductor materials prepared in accordance with the present invention, demonstrated high Hall mobilities (up to 1200 cm.sup.2.V.sup.-1.s.sup.-1) and good Seebeck coefficients (up to 150 .mu.VK.sup.-1 between 300.degree. C. and 700.degree. C.). Optimizing the transport properties of semiconductor materials prepared from elemental mixtures Co, Rh, Ir and Sb resulted in a substantial increase in the thermoelectric figure of merit (ZT) at temperatures as high as 400.degree. C. for thermoelectric elements fabricated from such semiconductor materials.

  4. Electroluminescence from metal-insulator-semiconductor tunneling diodes using compressively strained Ge on Si0.5Ge0.5 virtual substrates.

    PubMed

    Manna, Santanu; Aluguri, Rakesh; Das, Samaresh; Singha, Rajkumar; Ray, Samit K

    2013-11-18

    Direct band gap optical transition in compressively strained Ge film is demonstrated for the first time under current injection through a metal-insulator-semiconductor diode structure. The compressively strained Ge layer is grown on the relaxed Si0.5Ge0.5 substrate by solid source molecular beam epitaxy. The electroluminescence of direct band gap emission from strained Ge film and TO phonon assisted transition in Si and SiGe from the virtual substrate is observed under different current injections. The signature of heavy hole and light hole splitting in valence band is observed in the electroluminescence spectra from strained Ge layer. The temperature dependent electroluminescence characteristics have been studied over a temperature range of 10-300 K. AC frequency modulation for the Ge direct band electroluminescence has been studied to improve the emission efficiency over the DC bias.

  5. Design and Synthesis of Novel Liquid Crystals and Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Wang, Kunlun

    Liquid crystals have found wide applications due to their unique properties. In order to search for new nematic liquid crystal compounds with relatively low phase transition temperatures, a series of [1,2,3]-triazole-based mesogens and LC dimers were synthesized via the "Click Reaction" under mild conditions and their phase behavior will be presented. Meanwhile, hydrogen-bonded complexes mixed by benzonitrile derivatives and aromatic acetylenes are obtained and their thermal behavior examined. In order to achieve a better understanding of the influence of difluorination on the oligophenyls, a series of partially fluorinated oligomers were obtained and some of their physical properties are compared. Organic semiconductors possess many advantages compared to conventional inorganic semiconductors. Perfluorination was utilized in our molecular design for the synthesis of 1,3,5-triphenyl benzene derivatives and self-assembled crystals via nitrogen-iodine halogen bonding and the target molecules might show some interesting semicondocting properties.

  6. A method of studying the photoelectric properties of liquid semiconductors

    SciTech Connect

    Aivazov, A.A.; Budagyan, B.G.; Giorgadze, A.L.

    1985-09-01

    The authors propose a way of measuring the optical and photoelectric properties of liquid semiconductors. They have developed a high temperature apparatus with cuvettes that allow sufficient material to be loaded for heat treating the melt over the whole range of measurement temperatures. After fusion and heat treatment for 30 min, the melt is fed into the working chamber by the pressure exerted by the inert gas. The optical and photoeletric parameters are measured from the melt. This method has been used to measure the steady-state longitudinal photoconductivity of liquid selenium.

  7. Direct detection of sub-GeV dark matter with semiconductor targets

    NASA Astrophysics Data System (ADS)

    Essig, Rouven; Fernández-Serra, Marivi; Mardon, Jeremy; Soto, Adrián; Volansky, Tomer; Yu, Tien-Tien

    2016-05-01

    Dark matter in the sub-GeV mass range is a theoretically motivated but largely unexplored paradigm. Such light masses are out of reach for conventional nuclear recoil direct detection experiments, but may be detected through the small ionization signals caused by dark matter-electron scattering. Semiconductors are well-studied and are particularly promising target materials because their {O} (1 eV) band gaps allow for ionization signals from dark matter particles as light as a few hundred keV. Current direct detection technologies are being adapted for dark matter-electron scattering. In this paper, we provide the theoretical calculations for dark matter-electron scattering rate in semiconductors, overcoming several complications that stem from the many-body nature of the problem. We use density functional theory to numerically calculate the rates for dark matter-electron scattering in silicon and germanium, and estimate the sensitivity for upcoming experiments such as DAMIC and SuperCDMS. We find that the reach for these upcoming experiments has the potential to be orders of magnitude beyond current direct detection constraints and that sub-GeV dark matter has a sizable modulation signal. We also give the first direct detection limits on sub-GeV dark matter from its scattering off electrons in a semiconductor target (silicon) based on published results from DAMIC. We make available publicly our code, QEdark , with which we calculate our results. Our results can be used by experimental collaborations to calculate their own sensitivities based on their specific setup. The searches we propose will probe vast new regions of unexplored dark matter model and parameter space.

  8. Direct detection of sub-GeV dark matter with semiconductor targets

    DOE PAGES

    Essig, Rouven; Fernández-Serra, Marivi; Mardon, Jeremy; ...

    2016-05-09

    Dark matter in the sub-GeV mass range is a theoretically motivated but largely unexplored paradigm. Such light masses are out of reach for conventional nuclear recoil direct detection experiments, but may be detected through the small ionization signals caused by dark matter-electron scattering. Semiconductors are well-studied and are particularly promising target materials because their O(1 eV) band gaps allow for ionization signals from dark matter particles as light as a few hundred keV. Current direct detection technologies are being adapted for dark matter-electron scattering. In this paper, we provide the theoretical calculations for dark matter-electron scattering rate in semiconductors, overcomingmore » several complications that stem from the many-body nature of the problem. We use density functional theory to numerically calculate the rates for dark matter-electron scattering in silicon and germanium, and estimate the sensitivity for upcoming experiments such as DAMIC and SuperCDMS. We find that the reach for these upcoming experiments has the potential to be orders of magnitude beyond current direct detection constraints and that sub-GeV dark matter has a sizable modulation signal. We also give the first direct detection limits on sub-GeV dark matter from its scattering off electrons in a semiconductor target (silicon) based on published results from DAMIC. We make available publicly our code, QEdark, with which we calculate our results. Our results can be used by experimental collaborations to calculate their own sensitivities based on their specific setup. In conclusion, the searches we propose will probe vast new regions of unexplored dark matter model and parameter space.« less

  9. Direct detection of sub-GeV dark matter with semiconductor targets

    SciTech Connect

    Essig, Rouven; Fernández-Serra, Marivi; Mardon, Jeremy; Soto, Adrián; Volansky, Tomer; Yu, Tien -Tien

    2016-05-09

    Dark matter in the sub-GeV mass range is a theoretically motivated but largely unexplored paradigm. Such light masses are out of reach for conventional nuclear recoil direct detection experiments, but may be detected through the small ionization signals caused by dark matter-electron scattering. Semiconductors are well-studied and are particularly promising target materials because their O(1 eV) band gaps allow for ionization signals from dark matter particles as light as a few hundred keV. Current direct detection technologies are being adapted for dark matter-electron scattering. In this paper, we provide the theoretical calculations for dark matter-electron scattering rate in semiconductors, overcoming several complications that stem from the many-body nature of the problem. We use density functional theory to numerically calculate the rates for dark matter-electron scattering in silicon and germanium, and estimate the sensitivity for upcoming experiments such as DAMIC and SuperCDMS. We find that the reach for these upcoming experiments has the potential to be orders of magnitude beyond current direct detection constraints and that sub-GeV dark matter has a sizable modulation signal. We also give the first direct detection limits on sub-GeV dark matter from its scattering off electrons in a semiconductor target (silicon) based on published results from DAMIC. We make available publicly our code, QEdark, with which we calculate our results. Our results can be used by experimental collaborations to calculate their own sensitivities based on their specific setup. In conclusion, the searches we propose will probe vast new regions of unexplored dark matter model and parameter space.

  10. Template-free preparation of crystalline Ge nanowire film electrodes via an electrochemical liquid-liquid-solid process in water at ambient pressure and temperature for energy storage.

    PubMed

    Gu, Junsi; Collins, Sean M; Carim, Azhar I; Hao, Xiaoguang; Bartlett, Bart M; Maldonado, Stephen

    2012-09-12

    The direct electrodeposition of crystalline germanium (Ge) nanowire film electrodes from an aqueous solution of dissolved GeO(2) using discrete 'flux' nanoparticles capable of dissolving Ge(s) has been demonstrated. Electrodeposition of Ge at inert electrode substrates decorated with small (<100 nm), discrete indium (In) nanoparticles resulted in crystalline Ge nanowire films with definable nanowire diameters and densities without the need for a physical or chemical template. The Ge nanowires exhibited strong polycrystalline character as-deposited, with approximate crystallite dimensions of 20 nm and a mixed orientation of the crystallites along the length of the nanowire. Energy dispersive spectroscopic elemental mapping of individual Ge nanowires showed that the In nanoparticles remained at the base of each nanowire, indicating good electrical communication between the Ge nanowire and the underlying conductive support. As-deposited Ge nanowire films prepared on Cu supports were used without further processing as Li(+) battery anodes. Cycling studies performed at 1 C (1624 mA g(-1)) indicated the native Ge nanowire films supported stable discharge capacities at the level of 973 mA h g(-1), higher than analogous Ge nanowire film electrodes prepared through an energy-intensive vapor-liquid-solid nanowire growth process. The cumulative data show that ec-LLS is a viable method for directly preparing a functional, high-activity nanomaterials-based device component. The work presented here is a step toward the realization of simple processes that make fully functional energy conversion/storage technologies based on crystalline inorganic semiconductors entirely through benchtop, aqueous chemistry and electrochemistry without time- or energy-intensive process steps.

  11. High-efficiency metal-semiconductor-metal photodetectors on heteroepitaxially grown Ge on Si.

    PubMed

    Okyay, Ali K; Nayfeh, Ammar M; Saraswat, Krishna C; Yonehara, Takao; Marshall, Ann; McIntyre, Paul C

    2006-09-01

    We demonstrate extremely efficient germanium-on-silicon metal-semiconductor-metal photodetectors with responsivities (R) as high as 0.85 A/W at 1.55 microm and 2V reverse bias. Ge was directly grown on Si by using a novel heteroepitaxial growth technique, which uses multisteps of growth and hydrogen annealing to reduce surface roughness and threading dislocations that form due to the 4.2% lattice mismatch. Photodiodes on such layers exhibit reverse dark currents of 100 mA/cm2 and external quantum efficiency up to 68%. This technology is promising to realize monolithically integrated optoelectronics.

  12. Electron Liquids in Semiconductor Quantum Structures

    SciTech Connect

    Aron Pinczuk

    2009-05-25

    The groups led by Stormer and Pinczuk have focused this project on goals that seek the elucidation of novel many-particle effects that emerge in two-dimensional electron systems (2DES) as the result from fundamental quantum interactions. This experimental research is conducted under extreme conditions of temperature and magnetic field. From the materials point of view, the ultra-high mobility systems in GaAs/AlGaAs quantum structures continue to be at the forefront of this research. The newcomer materials are based on graphene, a single atomic layer of graphite. The graphene research is attracting enormous attention from many communities involved in condensed matter research. The investigated many-particle phenomena include the integer and fractional quantum Hall effect, composite fermions, and Dirac fermions, and a diverse group of electron solid and liquid crystal phases. The Stormer group performed magneto-transport experiments and far-infrared spectroscopy, while the Pinczuk group explores manifestations of such phases in optical spectra.

  13. Electron-microscopic microstructural examination of glassy Ge-Se semiconductors

    NASA Astrophysics Data System (ADS)

    Marikhin, V. A.; Mamontova, T. N.; Nikitin, V. A.

    1984-04-01

    The microstructure of glassy Ge-Se semiconductors was studied under an electron microscope, synthetic GeSe2 being an important representative of the Ge-Se system. Specimens of this material had been produced by heating a mixture of Ge with electrical resistivity of 50 ohm cm and 99.999% pure Se in a T-40-600 tubular vacuum furnace to 1000 C at a rate not exceeding 150 C/h and holding at this temperature for 40-50 h prior to quenching the melt at a rate within 100-200 C/s. Examination under a JEM-5Y microscope with an acceleration voltage up to 100 kV revealed microdomains (200-300 A) and minidomains (1000-2000 A) forming macrodomains (3-4 micron). This confirms the hypothesis, based on earlier laser spectrophotography and luminescence measurements, that these glassy materials are heterogeneous with inclusions of fine imperfect crystallites. The replicas indicate also that microdomains with unsaturated bonds and carrying electric charges may be forming during segregation of phases.

  14. Dynamical behavior of a dangling bond dimer on a hydrogenated semiconductor: Ge(001):H

    NASA Astrophysics Data System (ADS)

    Godlewski, Szymon; Kolmer, Marek; Lis, Jakub; Zuzak, Rafal; Such, Bartosz; Gren, Wojciech; Szymonski, Marek; Kantorovich, Lev

    2015-09-01

    We show that a dangling bond (DB) dimer on Ge(001):H exhibits a dynamical behavior when the empty states are imaged with scanning tunneling microscopy (STM) at liquid helium temperature. Large amplitude Ge atom vibrations are decisive in facilitating a specific appearance of the structure in the STM images. The underlying mechanism is unraveled using a theoretical model and calculations within the density functional theory framework. Furthermore, we demonstrate the ability to induce controlled switching of the DB dimer with noncontact atomic force microscope and the stabilizing role of the dimer-dimer interaction.

  15. 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.

  16. Rashba type band splittings in ferroelectric semiconductor α-GeTe(111)

    NASA Astrophysics Data System (ADS)

    Kim, Beomyoung; Oh, Hyungju; Kim, Yeongkwan; Denlinger, Jonathan; Kim, Changyoung

    There has been significant increase in the research of spin orbit coupling (SOC) induced exotic phenomena. The Rashba effect, theoretically predicted to exist, is one of the SOC related phenomena. The phenomenon was later experimentally observed in the surface states of metals and topological insulators as well as interfaces of hetero structures that have inversion symmetry breaking (ISB). Even bulk states with intrinsic ISB such as BiTeI is found to have Rashba split bands. It was very recently proposed that ferroelectric GeTe has Rashba effect in the bulk. This is a unique situation where ISB is provided not by the structure ISB but by an electrical polarization. We have performed angle-resolved photoemission spectroscopy (ARPES) on GeTe single crystals to investigate the unique bulk Rashba state. Our results indeed show the existence of a Rashba-type band splitting as theoretically predicted. We discuss various aspect of the Rashba states in ferroelectric semiconductor α-GeTe(111).

  17. Defect Characterization in SiGe/SOI Epitaxial Semiconductors by Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Ferragut, R.; Calloni, A.; Dupasquier, A.; Isella, G.

    2010-12-01

    The potential of positron annihilation spectroscopy (PAS) for defect characterization at the atomic scale in semiconductors has been demonstrated in thin multilayer structures of SiGe (50 nm) grown on UTB (ultra-thin body) SOI (silicon-on-insulator). A slow positron beam was used to probe the defect profile. The SiO2/Si interface in the UTB-SOI was well characterized, and a good estimation of its depth has been obtained. The chemical analysis indicates that the interface does not contain defects, but only strongly localized charged centers. In order to promote the relaxation, the samples have been submitted to a post-growth annealing treatment in vacuum. After this treatment, it was possible to observe the modifications of the defect structure of the relaxed film. Chemical analysis of the SiGe layers suggests a prevalent trapping site surrounded by germanium atoms, presumably Si vacancies associated with misfit dislocations and threading dislocations in the SiGe films.

  18. Structure of a molecular liquid GeI4

    NASA Astrophysics Data System (ADS)

    Fuchizaki, Kazuhiro; Sakagami, Takahiro; Kohara, Shinji; Mizuno, Akitoshi; Asano, Yuta; Hamaya, Nozomu

    2016-11-01

    A molecular liquid GeI4 is a candidate that undergoes a pressure-induced liquid-to-liquid phase transition. This study establishes the reference structure of the low-pressure liquid phase. Synchrotron x-ray diffraction measurements were carried out at several temperatures between the melting and the boiling points under ambient pressure. The molecule has regular tetrahedral symmetry, and the intramolecular Ge-I length of 2.51 Å is almost temperature-independent within the measured range. A reverse Monte Carlo (RMC) analysis is employed to find that the distribution of molecular centers remains self-similar against heating, and thus justifying the length-scaling method adopted in determining the density. The RMC analysis also reveals that the vertex-to-face orientation of the nearest molecules are not straightly aligned, but are inclined at about 20 degrees, thereby making the closest intermolecular I-I distance definitely shorter than the intramolecular one. The prepeak observed at  ˜1 Å-1 in the structural factor slightly shifts and increases in height with increasing temperature. The origin of the prepeak is clearly identified to be traces of the 111 diffraction peak in the crystalline state. The prepeak, assuming the residual spatial correlation between germanium sites in the densest direction, thus shifts toward lower wavenumbers with thermal expansion. The aspect that a relative reduction in molecular size associated with the volume expansion is responsible for the increase in the prepeak’s height is confirmed by a simulation, in which the molecular size is changed.

  19. Electron-Hole Condensation in Semiconductors: Electrons and holes condense into freely moving liquid metallic droplets, a plasma phase with novel properties.

    PubMed

    Jeffries, C D

    1975-09-19

    In Ge and Si, and also in Ge-Si alloys (74), there is extensive evidence for the stable binding of electrons and holes into a cold plasma of constant density, which undergoes a phase separation. Liquid metallic drops 1 to 300 microm in size are formed, with lifetimes ranging from 0.1 to 600 microsec. For Ge a surprising amount is known: the phase diagram, the surface energy, the work function, the decay kinetics. Much less is known for Si. There is good agreement between theoretical and experimental values of the liquid density, the critical density, the critical temperature, and the binding energy. The stability of the liquid phase is strikingly dependent on band structure. The multivalley structure and mass anisotropy of Si, Ge, and Ge-Si, together with their indirect band gap, are no doubt responsible for the observed stability in these crystals. In the similar semiconductor gallium phosphide, drops have not yet been observed, most likely because the high impurity content traps the excitons. In gallium arsenide the existence of drops is controversial (75). Undoubtedly drops will be found to exist in other semiconductors, perhaps at even higher temperatures. This is an exciting field for the experimentalist; new phenomena are being rapidly discovered, usually before they are predicted. For the theorist, the electron-hole drop is of high intrinsic interest. It represents the first example of a quantum liquid of constant density in a periodic crystal lattice. A number of challenging experimental and theoretical problems remain.

  20. Controlled Growth of Organic Semiconductor Films Using Liquid Crystal Solvents

    NASA Astrophysics Data System (ADS)

    Bufkin, Kevin; Ohlson, Brooks; Hillman, Ben; Johnson, Brad; Patrick, David

    2008-05-01

    Interest in using organic semiconductors in applications such as large area displays, photovoltaic devices, and RFID tags stems in part from their prospects for enabling significantly reduced manufacturing costs compared to traditional inorganic semiconductors. However many of the best performing prototype devices produced so far have involved expensive or time-consuming fabrication methods, such as the use of single crystals or thin films deposited under high vacuum conditions. We present a new approach for growing low molecular weight organic crystalline films at ambient conditions based on a vapor-liquid-solid growth mechanism using thermotropic nematic liquid crystal (LC) solvents. Tetracene is deposited via atmospheric-pressure sublimation onto substrates coated by a LC layer oriented using rubbed polyimide, producing films that are highly crystalline, with large grain sizes, and possessing macroscopic uniaxial orientation. This poster will describe the growth mechanism, discuss the effects of processing conditions such as LC layer thickness, substrate temperature and flux rate, and compare the results to a model of deposition-diffusion aggregation accounting for the finite thickness of the solvent layer.

  1. Controlled Growth of Organic Semiconductor Films Using Liquid Crystal Solvents

    NASA Astrophysics Data System (ADS)

    Bufkin, Kevin; Ohlson, Brooks; Hillman, Ben; Johnson, Brad; Patrick, David

    2008-03-01

    Interest in using organic semiconductors in applications such as large area displays, photovoltaic devices, and RFID tags stems in part from their prospects for enabling significantly reduced manufacturing costs compared to traditional inorganic semiconductors. However many of the best performing prototype devices produced so far have involved expensive or time-consuming fabrication methods, such as the use of single crystals or thin films deposited under high vacuum conditions. We present a new approach for growing low molecular weight organic crystalline films at ambient conditions based on a vapor-liquid-solid growth mechanism using thermotropic nematic liquid crystal (LC) solvents. Tetracene is deposited via atmospheric-pressure sublimation onto substrates coated by a LC layer oriented using rubbed polyimide, producing films that are highly crystalline, with large grain sizes, and possessing macroscopic uniaxial orientation. This poster will describe the growth mechanism, discuss the effects of processing conditions such as LC layer thickness, substrate temperature and flux rate, and compare the results to a model of diffusion limited aggregation accounting for the finite thickness of the solvent layer.

  2. Ab-initio calculation of ZnGeAs{sub 2} semiconductor

    SciTech Connect

    Tripathy, S. K. Kumar, V.

    2014-04-24

    The structural, electronic, optical and elastic properties of ZnGeAs{sub 2} semiconductor have been investigated using pseudopotential plane wave method within the density functional theory (DFT). The optimized lattice constants, energy gap and crystal field splitting parameter are calculated. The optical properties such as dielectric function, optical reflectivity,, extinction coefficient, absorption spectra, refractive index and electron energy loss spectrum have been studied. The values of bulk modulus (B), elastic constants (C{sub ij}), Young’s modulus (Y), Zener anisotropic factor (A), Poisson’s ratio (ν) and Debye temperature (Θ{sub D}) have been calculated. The calculated values of all these parameters are compared with the available experimental values and the values reported by different workers. A fairly good agreement has been found between them.

  3. Length mismatch in random semiconductor alloys. III. Crystalline and amorphous SiGe

    NASA Astrophysics Data System (ADS)

    Mousseau, Normand; Thorpe, M. F.

    1992-12-01

    In the third paper of this series on the length mismatch problem, we study binary semiconductor alloys in both their crystalline and amorphous forms. We have concentratred on SiGe alloys. Applying the theory developed in paper I, we obtain the mean length for both nearest and next-nearest neighbors as well as the nearest-neighbor length distribution for the crystalline alloy. We show that the theoretical results fall within the limits set by experiment. We check our analytical results against computer simulations. We examine the effect of amorphization on the internal strain, using the Wooten, Winer, and Weaire model, and find that the disorders due to the length mismatch and due to amorphization decouple.

  4. 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.

  5. Stability of Quasi-Two-Dimensional Electron-Hole Liquid in Semiconductor Structures of the Type-II

    NASA Astrophysics Data System (ADS)

    Vasilchenko, A. A.; Kopytov, G. F.; Krivobok, V. S.; Ermokhin, D. A.

    2017-02-01

    Analytical expressions are obtained for the energy of a quasi-two-dimensional electron-hole liquid (EHL) and the threshold value of the barrier height for electrons, above which formation of the direct EHL is impossible. It is shown that the state with a quasi-two-dimensional EHL can be energetically favorable in semiconductors with the anisotropy of masses and (or) a large number of equivalent valleys. A comparison of the calculation results with the experimental data for the Si/SiGe/Si structure is made.

  6. Investigation of Interface between Ge Electrodes and Ionic Liquid Electrolytes for Electric Double Layer Capacitors

    NASA Astrophysics Data System (ADS)

    Abeysinghe, R. M.; Oguchi, H.; Kuwano, H.

    2016-11-01

    This study discusses novel way of use of ionic liquids to develop Ge-based electrodes for electric double layer capacitors (EDLC). We found that ionic liquids change their electrochemical properties depending on the amount of the absorbed water. Wet ionic liquids work as solvents to dissolve Ge and make porous structures, whereas dry ones work as electrolytes of the EDLCs. The former property was used to increase surface area of the electrodes which is desired to increase the capacity of EDLCs. This method showed another advantage in contrast to the dry ionic liquids; wet ones could fill the complex Ge pores in parallel to porous structure formation. Finally, after porous formation, we dried the ionic liquid at 100 °C and prepared the EDLCs composed of Ge porous electrodes. Cyclic voltammetry and impedance measurements indicated that the obtained devices can work as EDLCs.

  7. A comparative first-principles study of the structural and electronic properties of the liquid Li-Si and Li-Ge alloys

    NASA Astrophysics Data System (ADS)

    Chiang, Han-Hsin; Kuo, Chin-Lung

    2017-02-01

    We have performed a comparative first-principles study on the structural and electronic properties of the liquid Li1-xSix and Li1-xGex alloys over a range of composition from x = 0.09 to 0.50. Our calculations showed that Si and Ge atoms can exhibit very distinct local bonding characteristics as they were alloyed with the Li atoms in the liquid state, where Si atoms tended to form a variety of covalent bonding configurations while Ge atoms predominantly appeared as the isolated anions in the liquid alloys. These differences in bonding characteristics were reflected in their electronic density of states, in which the liquid Li1-xGex alloys have a lower degree of s-p hybridization with narrower distributions of the 3s and 3p states than the liquid Li1-xSix alloys. Our calculations also showed that the optical conductivities of these two liquid alloys can undergo a transition from the Drude-like metallic nature to the semiconductor-like character as the Si/Ge content increases from 0.09 to 0.22. However, as the Si/Ge content further increases to 0.50, the liquid Li1-xGex alloys may transit to exhibit the Drude-like metallic nature, while the liquid Li1-xSix alloys can still hold the semiconductor-like character. Moreover, our calculations revealed that the dc conductivities of these liquid alloys are predominantly determined by the number of total electronic states at the Fermi level. As the liquid Li1-xSix alloys are within the composition range between 0.20 and 0.50, the increment of the states at the Fermi level with increasing the Si content is nearly identical to the amount of the Li states decreased, leading to an almost unchanged number of total electronic states at the Fermi level. However, since Ge atoms do not favor forming covalent bonding in the liquid alloys to keep the Fermi level at a minimum of the density of states, the liquid Li1-xGex alloys would have more electronic states at the Fermi level and thereby higher dc conductivities than the liquid Li1

  8. Structural properties of liquid Ge2Se3: A first-principles study

    NASA Astrophysics Data System (ADS)

    Le Roux, Sébastien; Zeidler, Anita; Salmon, Philip S.; Boero, Mauro; Micoulaut, Matthieu; Massobrio, Carlo

    2011-10-01

    The structural properties of liquid Ge2Se3were investigated by first-principles molecular dynamics using the Becke-Lee-Yang-Parr scheme for the treatment of the exchange-correlation functional in density functional theory. Our data for the total neutron structure factor and the total pair-distribution function are in excellent agreement with the experimental results. The structure is made predominantly (˜61%) from units comprising fourfold coordinated Ge atoms in the form of Ge-GeSe3 or Ge-Se4 motifs, but there is also a large variety of motifs in which Ge and Se are not fourfold and twofold coordinated, respectively. The miscoordinated atoms and homopolar bonds lead to a highly perturbed tetrahedral network, as reflected by diffusion coefficients that are larger than in the case of liquid GeSe2. The network does, nevertheless, exhibit intermediate range order which is associated with the Ge-Ge correlations and which manifests itself by a first sharp diffraction peak in the total neutron structure factor. The evolution of the properties of GexSe1-x liquids (0 ≤x≤ 1) with composition is discussed.

  9. "Liquid-liquid-solid"-type superoleophobic surfaces to pattern polymeric semiconductors towards high-quality organic field-effect transistors.

    PubMed

    Wu, Yuchen; Su, Bin; Jiang, Lei; Heeger, Alan J

    2013-12-03

    Precisely aligned organic-liquid-soluble semiconductor microwire arrays have been fabricated by "liquid-liquid-solid" type superoleophobic surfaces directed fluid drying. Aligned organic 1D micro-architectures can be built as high-quality organic field-effect transistors with high mobilities of >10 cm(2) ·V(-1) ·s(-1) and current on/off ratio of more than 10(6) . All these studies will boost the development of 1D microstructures of organic semiconductor materials for potential application in organic electronics. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Thermoelectric Effects on the Boundary of Solid and Liquid Phases of Ternary Semiconductors and Alloys of the A-12B-IVC-V13 Type,

    DTIC Science & Technology

    THERMOELECTRICITY, *SEMICONDUCTORS), (* SEEBECK EFFECT , SEMICONDUCTORS), LIQUIDS, PHASE STUDIES, COPPER COMPOUNDS, GERMANIUM COMPOUNDS, TELLURIDES, SELENIDES, TIN COMPOUNDS, SILVER COMPOUNDS, THERMAL CONDUCTIVITY, USSR

  11. Anomalous diffusion and non-monotonic relaxation processes in Ge-Se liquids

    NASA Astrophysics Data System (ADS)

    Yildirim, Can; Raty, Jean-Yves; Micoulaut, Matthieu

    2016-06-01

    We investigate the dynamical properties of liquid GexSe100-x as a function of Ge content by first-principles molecular dynamic simulations for a certain number of temperatures in the liquid state. The focus is set on ten compositions (where x ≤ 33%) encompassing the reported flexible to rigid and rigid to stressed-rigid transitions. We examine diffusion coefficients, diffusion activation energies, glassy relaxation behavior, and viscosity of these liquids from Van Hove correlation and intermediate scattering functions. At fixed temperature, all properties/functions exhibit an anomalous behavior with Ge content in the region 18%-22%, and provide a direct and quantitative link to the network rigidity.

  12. Interface-driven phase separation in multifunctional materials: The case of the ferromagnetic semiconductor GeMn

    NASA Astrophysics Data System (ADS)

    Arras, Emmanuel; Lançon, Frédéric; Slipukhina, Ivetta; Prestat, Éric; Rovezzi, Mauro; Tardif, Samuel; Titov, Andrey; Bayle-Guillemaud, Pascale; D'Acapito, Francesco; Barski, André; Favre-Nicolin, Vincent; Jamet, Matthieu; Cibert, Joël; Pochet, Pascal

    2012-03-01

    We use extensive first-principles simulations to show the major role played by interfaces in the mechanism of phase separation observed in semiconductor multifunctional materials. We make an analogy with the precipitation sequence observed in oversaturated AlCu alloys, and replace the Guinier-Preston zones in this new context. A class of materials, the α phases, is proposed to understand the formation of the coherent precipitates observed in the GeMn system. The interplay between formation and interface energies is analyzed for these phases and for the structures usually considered in the literature. The existence of the α phases is assessed with both theoretical and experimental arguments.

  13. Morphology and crystal phase evolution of GeO 2 in liquid phase deposition process

    NASA Astrophysics Data System (ADS)

    Jing, Chengbin; Sun, Wei; Wang, Wei; Li, Yi; Chu, Junhao

    2012-01-01

    Morphology and crystal phase evolution of GeO 2 in liquid phase deposition (LPD) process is investigated. Rod-like solid phases precipitate out of solution ahead of truncated cube-like phases. SEM, XRD and TEM analyses reveal that the two sorts of solid phases are tetragonal GeO 2 and hexagonal GeO 2, respectively. The tetragonal GeO 2 phases start to experience a re-dissolving process as soon as the hexagonal phases come into being. The prior precipitation of the rod-like phase arises from a relatively low solute saturation of tetragonal GeO 2. Fast growth of a tetragonal GeO 2 phase along [111] direction leads to development of a rod-like shape. The re-dissolving phenomenon does not agree with the classic growth kinetics of crystals but is strongly favored by our calculations based on thermodynamics. The GeO 2 solutes are released in a fluctuant way by germanate ions, which promotes the occurrence of the re-dissolution phenomenon. The current researches open a door for room-temperature LPD growth of not only the hexagonal GeO 2 particles and film but also the one-dimensional tetragonal GeO 2 product.

  14. The effect of dielectric constants on noble metal/semiconductor SERS enhancement: FDTD simulation and experiment validation of Ag/Ge and Ag/Si substrates.

    PubMed

    Wang, Tao; Zhang, Zhaoshun; Liao, Fan; Cai, Qian; Li, Yanqing; Lee, Shuit-Tong; Shao, Mingwang

    2014-02-11

    The finite-difference time-domain (FDTD) method was employed to simulate the electric field distribution for noble metal (Au or Ag)/semiconductor (Ge or Si) substrates. The simulation showed that noble metal/Ge had stronger SERS enhancement than noble metal/Si, which was mainly attributed to the different dielectric constants of semiconductors. In order to verify the simulation, Ag nanoparticles with the diameter of ca. 40 nm were grown on Ge or Si wafer (Ag/Ge or Ag/Si) and employed as surface-enhanced Raman scattering substrates to detect analytes in solution. The experiment demonstrated that both the two substrates exhibited excellent performance in the low concentration detection of Rhodamine 6G. Besides, the enhancement factor (1.3 × 10(9)) and relative standard deviation values (less than 11%) of Ag/Ge substrate were both better than those of Ag/Si (2.9 × 10(7) and less than 15%, respectively), which was consistent with the FDTD simulation. Moreover, Ag nanoparticles were grown in-situ on Ge substrate, which kept the nanoparticles from aggregation in the detection. To data, Ag/Ge substrates showed the best performance for their sensitivity and uniformity among the noble metal/semiconductor ones.

  15. Material degradation of liquid organic semiconductors analyzed by nuclear magnetic resonance spectroscopy

    SciTech Connect

    Fukushima, Tatsuya; Yamamoto, Junichi; Fukuchi, Masashi; Kaji, Hironori; Hirata, Shuzo; Jung, Heo Hyo; Adachi, Chihaya; Hirata, Osamu; Shibano, Yuki

    2015-08-15

    Liquid organic light-emitting diodes (liquid OLEDs) are unique devices consisting only of liquid organic semiconductors in the active layer, and the device performances have been investigated recently. However, the device degradation, especially, the origin has been unknown. In this study, we show that material degradation occurs in liquid OLEDs, whose active layer is composed of carbazole with an ethylene glycol chain. Nuclear magnetic resonance (NMR) experiments clearly exhibit that the dimerization reaction of carbazole moiety occurs in the liquid OLEDs during driving the devices. In contrast, cleavages of the ethylene glycol chain are not detected within experimental error. The dimerization reaction is considered to be related to the device degradation.

  16. As doping of Si-Ge-Sn epitaxial semiconductor materials on a commercial CVD reactor

    NASA Astrophysics Data System (ADS)

    Bhargava, Nupur; Margetis, Joe; Tolle, John

    2017-09-01

    In this work we present the As doping, via AsH3, of Ge1-x Sn x and SiyGe1-y-x Sn x alloys grown in a commercial RPCVD reactor. The composition, thickness, and resistivity of the layers were measured for varying AsH3 flows and AsH3 growth kinetics was discussed. We find that the addition of As to the lattice induces compressive strain in the layer despite a smaller covalent radius relative to Ge and Sn. N-type dopant incorporation and activation is compared for AsH3 and PH3-based processes, and we find that As incorporates more efficiently than P. As concentrations > 2 × 1020 cm-3 were achieved for both Ge1-x Sn x and SiyGe1-y-x Sn x with resistivity as low as 0.6 mΩ cm.

  17. An automatic liquid-nitrogen filling system for multiple Ge detectors

    SciTech Connect

    Koizumi, Mitsuo; Oshima, Masumi; Toh, Yosuke; Kimura, Atsushi; Kin, Tadahiro; Furutaka, Kazuyoshi; Murakami, Yukihiro; Osa, Akihiko; Ando, Shingo

    2009-01-15

    In order to reduce the time and effort of the daily task of refilling Dewar vessels of Ge detectors with liquid nitrogen (LN{sub 2}), we have developed an automatic LN{sub 2} filling system equipped with a LN{sub 2} plant. With this system, we were freed from the work of LN{sub 2} filling. Such an LN{sub 2} filling system is useful for moderate-scale Ge detector arrays consisting of fewer than 20 Ge detectors.

  18. Ether-like Si-Ge hydrides for applications in synthesis of nanostructured semiconductors and dielectrics.

    PubMed

    Tice, Jesse B; Weng, Change; Tolle, John; D'Costa, Vijay R; Singh, Rachna; Menendez, Jose; Kouvetakis, John; Chizmeshya, Andrew V G

    2009-09-14

    Hydrolysis reactions of silyl-germyl triflates are used to produce ether-like Si-Ge hydride compounds including H(3)SiOSiH(3) and the previously unknown O(SiH(2)GeH(3))(2). The structural, energetic and vibrational properties of the latter were investigated by experimental and quantum chemical simulation methods. A combined Raman, infrared and theoretical analysis indicated that the compound consists of an equal mixture of linear and gauche isomers in analogy to the butane-like H(3)GeSiH(2)SiH(2)GeH(3) with an exceedingly small torsional barrier of approximately 0.2 kcal mol(-1). This is also corroborated by thermochemistry simulations which indicate that the energy difference between the isomers is less than 1 kcal mol(-1). Proof-of-principle depositions of O(SiH(2)GeH(3))(2) at 500 degrees C on Si(100) yielded nearly stoichiometric Si(2)Ge(2)O materials, closely reflecting the composition of the molecular core. A complete characterization of the film by RBS, XTEM, Raman and IR ellipsometry revealed the presence of Si(0.30)Ge(0.70) quantum dots embedded within an amorphous matrix of Si-Ge-O suboxide, as required for the fabrication of high performance nonvolatile memory devices. The use of readily available starting materials coupled with facile purification and high yields also makes the above molecular approach an attractive synthesis route to H(3)SiOSiH(3) with industrial applications in the formation of Si-O-N high-k gate materials in high-mobility SiGe based transistors.

  19. Direct observation of both contact and remote oxygen scavenging of GeO{sub 2} in a metal-oxide-semiconductor stack

    SciTech Connect

    Fadida, S. Shekhter, P.; Eizenberg, M.; Cvetko, D.; Floreano, L.; Verdini, A.; Kymissis, I.

    2014-10-28

    In the path to incorporating Ge based metal-oxide-semiconductor into modern nano-electronics, one of the main issues is the oxide-semiconductor interface quality. Here, the reactivity of Ti on Ge stacks and the scavenging effect of Ti were studied using synchrotron X-ray photoelectron spectroscopy measurements, with an in-situ metal deposition and high resolution transmission electron microscopy imaging. Oxygen removal from the Ge surface was observed both in direct contact as well as remotely through an Al{sub 2}O{sub 3} layer. The scavenging effect was studied in situ at room temperature and after annealing. We find that the reactivity of Ti can be utilized for improved scaling of Ge based devices.

  20. A photoelectrochemical-thermal hydrogen producing cycle involving a semiconductor liquid junction cell

    NASA Astrophysics Data System (ADS)

    Gissler, W.

    A photoelectrochemical-thermal hydrogen producing cycle is proposed involving a semiconductor liquid junction solar cell. In contrast with direct photoelectrolysis, the proposal is based upon a photoelectrochemical oxidation or reduction of the n- or p-type semiconductor electrode respectively in an aqueous electrolyte. In subsequent thermal reaction steps the water splitting process is completed, and the semiconductor electrode is regenerated. The advantage of the method is that semiconductors of band gap energies which are well matched to the solar spectrum can be used and correspondingly high solar energy conversion efficiencies can be obtained. The drawback is that the electrode regeneration process is in general quite complicated. The method is demonstrated by using a trigonal selenium electrode which allows a relatively simple regeneration. First experimental results on the photoelectrochemical reaction step are reported.

  1. Photogeneration and enhanced charge transport in aligned smectic liquid crystalline organic semiconductor

    SciTech Connect

    Paul, Sanjoy; Ellman, Brett; Tripathi, Suvagata; Twieg, Robert J.

    2015-10-07

    Liquid crystalline organic semiconductors are emerging candidates for applications in electronic and photonic devices. One of the most attractive aspects of such materials is the potential, in principle, to easily control and manipulate the molecular alignment of the semiconductor over large length scales. Here, we explore the consequences of alignment in a model smectic liquid crystalline semiconductor, and find that the photogeneration efficiency is a strong function of incident polarization in aligned samples. A straightforward theory shows that such behavior is a general feature of aligned materials, regardless of the details of photophysics. Furthermore, we uncover tentative evidence that the mobility of aligned samples is substantially enhanced. Both of these phenomena are of significant technological importance.

  2. Activities of oxygen in liquid Cu-Sb and Cu-Ge alloys

    NASA Astrophysics Data System (ADS)

    Otsuka, Shinya; Matsumura, Yoshihiro; Kozuka, Zensaku

    1982-03-01

    In order to determine the activity coefficients of oxygen, γΩ in liquid Cu-Sb and Cu-Ge alloys at 1373 K as a function of alloy composition, the modified coulometric titrations, described previously, have been performed by using the galvanic cell: O in liquid Cu-Sb or Cu-Ge alloys/ZrO2 (+CaO)/Air, Pt. A pronounced point of inflection in the In γΩ vs alloy composition curve has been observed both for Cu-Sb and Cu-Ge alloys, as predicted by Jacob and Alcock’s quasichemical equation. The measured data itself, however, are significantly different from those predicted by their equation. The validity of Wagner’s solution model with one or two energy parameters has been also tested.

  3. Fabrication of Ta2O5/GeNx gate insulator stack for Ge metal-insulator-semiconductor structures by electron-cyclotron-resonance plasma nitridation and sputtering deposition techniques

    NASA Astrophysics Data System (ADS)

    Otani, Yohei; Itayama, Yasuhiro; Tanaka, Takuo; Fukuda, Yukio; Toyota, Hiroshi; Ono, Toshiro; Mitsui, Minoru; Nakagawa, Kiyokazu

    2007-04-01

    The authors have fabricated germanium (Ge) metal-insulator-semiconductor (MIS) structures with a 7-nm-thick tantalum pentaoxide (Ta2O5)/2-nm-thick germanium nitride (GeNx) gate insulator stack by electron-cyclotron-resonance plasma nitridation and sputtering deposition. They found that pure GeNx ultrathin layers can be formed by the direct plasma nitridation of the Ge surface without substrate heating. X-ray photoelectron spectroscopy revealed no oxidation of the GeNx layer after the Ta2O5 sputtering deposition. The fabricated MIS capacitor with a capacitance equivalent thickness of 4.3nm showed excellent leakage current characteristics. The interface trap density obtained by the modified conductance method was 4×1011cm-2eV-1 at the midgap.

  4. Influence of polymorphism on charge transport properties in isomers of fluorenone-based liquid crystalline semiconductors.

    PubMed

    Lincker, Frédéric; Attias, André-Jean; Mathevet, Fabrice; Heinrich, Benoît; Donnio, Bertrand; Fave, Jean-Louis; Rannou, Patrice; Demadrille, Renaud

    2012-03-28

    We measured the charge carrier mobilities for two isomers of fluorenone-based liquid crystalline organic semiconductors from their isotropic down to crystalline states through one or two mesophases. Improved charge transport properties of melt-processed crystalline films were obtained for the isomer exhibiting a highly ordered mesophase below its disordered smectic phase. This journal is © The Royal Society of Chemistry 2012

  5. The role of relative rate constants in determining surface state phenomena at semiconductor-liquid interfaces.

    PubMed

    Iqbal, Asif; Hossain, Md Sazzad; Bevan, Kirk H

    2016-10-26

    In this work, we present a theoretical study of surface state occupation statistics at semiconductor-liquid interfaces, as it pertains to the evolution of H2 and O2 through water splitting. Our approach combines semiclassical charge transport and electrostatics at the semiconductor-liquid junction, with a master rate equation describing surface state mediated electron/hole transfer. As a model system we have studied the TiO2-water junction in the absence of illumination, where it is shown that surface states might not always equilibrate with the semiconductor. Non-trivial electrostatics, for example including a shifting of the Mott-Schottky plateau in capacitive measurements, are explored when deep-level surface states partially equilibrate with the liquid. We also endeavor to explain observations of non-linearity present in Mott-Schottky plots, as they pertain to surface state occupation statistics. In general, it is intended that the results of this work will serve to further the use and development of quantitative device modeling techniques in the description of H2 evolution at semiconductor-liquid junctions.

  6. Semiconductor liquid junction photocell having a p-type photoactive electrode

    SciTech Connect

    Heller, A.; Lewerenz, H.J.; Miller, B.

    1982-08-10

    A semiconductor liquid junction photocell has a photovoltaic junction between a p-type photoactive electrode comprising InP or Si and an electrolyte comprising a redox couple selected from the group consisting of V2+/V3+, Nb4+/Nb5+, and Ti3+/Ti4+ produces a stable photocurrent output.

  7. Achieving low parasitic resistance in Ge p-channel metal-oxide-semiconductor field-effect transistors by ion implantation after germanidation

    NASA Astrophysics Data System (ADS)

    Hsin Chang, Wen; Ota, Hiroyuki; Maeda, Tatsuro

    2015-05-01

    The parasitic resistance (Rpara) of Ge p-channel metal-oxide-semiconductor field-effect transistors (p-MOSFETs) fabricated by ion implantation after germanidation (IAG) has been investigated by varying the drive-in annealing temperature. The lowest Rpara of 835 Ω µm was achieved after 450 °C drive-in annealing for 1 min. Boron segregation between NiGe and Ge induced by drive-in annealing has advantages in forming an abrupt metallic source/drain (S/D) junction and contributes to the decrease in Rpara. The appropriate process window for fabricating Ge p-MOSFETs by IAG was also given. IAG, a pathway for introducing a Ge channel into CMOS technology beyond the 10 nm node, was proved to be effective for reducing Rpara.

  8. Microstructure and magnetic behavior of Mn doped GeTe chalcogenide semiconductors based phase change materials

    NASA Astrophysics Data System (ADS)

    Adam, Adam Abdalla Elbashir; Cheng, Xiaomin; Abuelhassan, Hassan H.; Miao, Xiang Shui

    2017-06-01

    Phase-change materials (PCMs) are the most promising candidates to be used as an active media in the universal data storage and spintronic devices, due to their large differences in physical properties of the amorphous-crystalline phase transition behavior. In the present study, the microstructure, magnetic and electrical behaviors of Ge0.94Mn0.06Te thin film were investigated. The crystallographic structure of Ge0.94Mn0.06Te thin film was studied sing X-ray diffractometer (XRD) and High Resolution Transmission Electron Microscope (HR-TEM). The XRD pattern showed that the crystallization structure of the film was rhombohedral phase for GeTe with a preference (202) orientation. The HR-TEM image of the crystalline Ge0.94Mn0.06Te thin film demonstrated that, there were two large crystallites and small amorphous areas. The magnetization as a function of the magnetic field analyses of both amorphous and crystalline states showed the ferromagnetic hysteretic behaviors. Then, the hole carriers concentration of the film was measured and it found to be greater than 1021 cm-3 at room temperature. Moreover, the anomalous of Hall Effect (AHE) was clearly observed for the measuring temperatures 5, 10 and 50 K. The results demonstrated that the magnitude of AHE decreased when the temperature was increasing.

  9. Is Cd_1-xMn_xGeP2 A Ferromagnetic Semiconductor?

    NASA Astrophysics Data System (ADS)

    Zhao, Yu-Jun; Geng, W. T.; Freeman, A. J.; Oguchi, T.

    2001-03-01

    A great deal of effort is devoted to exploring high TC magnetic semico nductors. Very recently, experiments on chalcopyrite CdGeP2 with a hig h Mn concentration incorporated into its surface region was interpreted t o be a room temperature ferromagnet (FM).(G. A. Medvedkin, et al), Jpn. J. Appl. Phys. 39, L949 (2000) We investigated Cd_1-xMn_xGeP2 (x=3D1.0, 0.5, and 0.25) by the first-princ iples full-potential linearized augmented plane wave(Wimmer, Kra kauer, Weinert, and Freeman, PRB 24), 864 (1981). (FLAPW) and (B. Delley, J. Chem. Phys. , 2000 (in press))DMol^3 metho ds within LDA and GGA. The lattice constant of MnGeP2 is obtained from the ``CTB plus η=3Dη_tet" rule,(J. E. Jaffe and Alex Zunger, PRB, 29), 1882 (1984). The lattice constants for x=3D0.5 and 0.25 are interpolated from CdGeP2 and MnGeP_2, and are very clo se to the available experimental values. The internal structural paramete rs are fully optimized. As expected, it is found that E_AFM is much l ower than E_FM for x=3D1.0 (by ~200 meV/Mn). However, for x=3D 0.5 and 0.25, E_AFM is slightly lower (by tens of meV/Mn), in contras t to the experimental results. Possible causes of this difference are dis cussed.

  10. Combining experiment and optical simulation in coherent X-ray nanobeam characterization of Si/SiGe semiconductor heterostructures

    SciTech Connect

    Tilka, J. A.; Park, J.; Ahn, Y.; Pateras, A.; Sampson, K. C.; Savage, D. E.; Prance, J. R.; Simmons, C. B.; Coppersmith, S. N.; Eriksson, M. A.; Lagally, M. G.; Holt, M. V.; Evans, P. G.

    2016-07-06

    Here, the highly coherent and tightly focused x-ray beams produced by hard x-ray light sources enable the nanoscale characterization of the structure of electronic materials but are accompanied by significant challenges in the interpretation of diffraction and scattering patterns. X-ray nanobeams exhibit optical coherence combined with a large angular divergence introduced by the x-ray focusing optics. The scattering of nanofocused x-ray beams from intricate semiconductor heterostructures produces a complex distribution of scattered intensity. We report here an extension of coherent xray optical simulations of convergent x-ray beam diffraction patterns to arbitrary x-ray incident angles to allow the nanobeam diffraction patterns of complex heterostructures to be simulated faithfully. These methods are used to extract the misorientation of lattice planes and the strain of individual layers from synchrotron x-ray nanobeam diffraction patterns of Si/SiGe heterostructures relevant to applications in quantum electronic devices. The systematic interpretation of nanobeam diffraction patterns from semiconductor heterostructures presents a new opportunity in characterizing and ultimately designing electronic materials.

  11. Combining experiment and optical simulation in coherent X-ray nanobeam characterization of Si/SiGe semiconductor heterostructures

    DOE PAGES

    Tilka, J. A.; Park, J.; Ahn, Y.; ...

    2016-07-06

    Here, the highly coherent and tightly focused x-ray beams produced by hard x-ray light sources enable the nanoscale characterization of the structure of electronic materials but are accompanied by significant challenges in the interpretation of diffraction and scattering patterns. X-ray nanobeams exhibit optical coherence combined with a large angular divergence introduced by the x-ray focusing optics. The scattering of nanofocused x-ray beams from intricate semiconductor heterostructures produces a complex distribution of scattered intensity. We report here an extension of coherent xray optical simulations of convergent x-ray beam diffraction patterns to arbitrary x-ray incident angles to allow the nanobeam diffraction patternsmore » of complex heterostructures to be simulated faithfully. These methods are used to extract the misorientation of lattice planes and the strain of individual layers from synchrotron x-ray nanobeam diffraction patterns of Si/SiGe heterostructures relevant to applications in quantum electronic devices. The systematic interpretation of nanobeam diffraction patterns from semiconductor heterostructures presents a new opportunity in characterizing and ultimately designing electronic materials.« less

  12. Combining experiment and optical simulation in coherent X-ray nanobeam characterization of Si/SiGe semiconductor heterostructures

    SciTech Connect

    Tilka, J. A.; Park, J.; Ahn, Y.; Pateras, A.; Sampson, K. C.; Savage, D. E.; Lagally, M. G.; Evans, P. G.; Prance, J. R.; Simmons, C. B.; Coppersmith, S. N.; Eriksson, M. A.; Holt, M. V.

    2016-07-07

    The highly coherent and tightly focused x-ray beams produced by hard x-ray light sources enable the nanoscale characterization of the structure of electronic materials but are accompanied by significant challenges in the interpretation of diffraction and scattering patterns. X-ray nanobeams exhibit optical coherence combined with a large angular divergence introduced by the x-ray focusing optics. The scattering of nanofocused x-ray beams from intricate semiconductor heterostructures produces a complex distribution of scattered intensity. We report here an extension of coherent x-ray optical simulations of convergent x-ray beam diffraction patterns to arbitrary x-ray incident angles to allow the nanobeam diffraction patterns of complex heterostructures to be simulated faithfully. These methods are used to extract the misorientation of lattice planes and the strain of individual layers from synchrotron x-ray nanobeam diffraction patterns of Si/SiGe heterostructures relevant to applications in quantum electronic devices. The systematic interpretation of nanobeam diffraction patterns from semiconductor heterostructures presents a new opportunity in characterizing and ultimately designing electronic materials.

  13. Combining experiment and optical simulation in coherent X-ray nanobeam characterization of Si/SiGe semiconductor heterostructures

    SciTech Connect

    Tilka, J. A.; Park, J.; Ahn, Y.; Pateras, A.; Sampson, K. C.; Savage, D. E.; Prance, J. R.; Simmons, C. B.; Coppersmith, S. N.; Eriksson, M. A.; Lagally, M. G.; Holt, M. V.; Evans, P. G.

    2016-07-06

    Here, the highly coherent and tightly focused x-ray beams produced by hard x-ray light sources enable the nanoscale characterization of the structure of electronic materials but are accompanied by significant challenges in the interpretation of diffraction and scattering patterns. X-ray nanobeams exhibit optical coherence combined with a large angular divergence introduced by the x-ray focusing optics. The scattering of nanofocused x-ray beams from intricate semiconductor heterostructures produces a complex distribution of scattered intensity. We report here an extension of coherent xray optical simulations of convergent x-ray beam diffraction patterns to arbitrary x-ray incident angles to allow the nanobeam diffraction patterns of complex heterostructures to be simulated faithfully. These methods are used to extract the misorientation of lattice planes and the strain of individual layers from synchrotron x-ray nanobeam diffraction patterns of Si/SiGe heterostructures relevant to applications in quantum electronic devices. The systematic interpretation of nanobeam diffraction patterns from semiconductor heterostructures presents a new opportunity in characterizing and ultimately designing electronic materials.

  14. The structural, elastic, electronic and dynamical properties of chalcopyrite semiconductor BeGeAs2 from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Çiftci, Yasemin Ö.; Evecen, Meryem; Aldırmaz, Emine

    2017-01-01

    First-principles calculations for the structural, elastic, electronic and vibrational properties of BeGeAs2 with chalcopyrite structure have been reported in the frame work of the density functional theory. The calculated ground state properties are in good agreement with the available data. By considering the electronic band structure and electronic density of states calculation, it is found that this compound is a semiconductor which confirmed the previous work. Single-crystal elastic constants and related properties such as Young's modulus, Poisson ratio, shear modulus and bulk modulus have been predicted using the stress-finite strain technique. It can be seen from the calculated elastic constants that this compound is mechanically stable in the chalcopyrite structure. Pressure dependences of elastic constants and band gap are also reported. Finally, the phonon dispersion curves and total and partial density of states were calculated and discussed. The calculated phonon frequencies BeGeAs2 are positive, indicating the dynamical stability of the studied compound.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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 Al2O3 and HfO2. However, there has been much effort to deposit ternary oxides, such as perovskites (ABO3), 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.

  17. Semiconductor/Liquid Junctions: Molecular Manipulation of Interface Energetics.

    DTIC Science & Technology

    1980-11-21

    S. Wrighton. (Published: Acc. Chem. Res., 1979, 12, 303.) ONR-TR-3 "N-Type Molybdenum Diselenide-Based Liquid Junction Solar Cells : A Non-Aqueous...579. The high hts of our accomplishments in these areas are given in the paragraphs \\elow. N-Type MoY2/Liquid Electrolyte Junctions. N-type MoS2 and...examination of a wider range of redox reagents than is possible in H20; we found that both n-type MoS2 and MoSe 2 resist photoanodic decomposition in CH3CN

  18. Interactive Analysis of Gamm-ray Spectra from GE Semiconductor Detectors

    SciTech Connect

    Egger, Ann

    1997-09-25

    GAUSS IX is a tool to interactively analyze gamma-ray spectra from Ge Semicondutor detectors. The user has full control over the view of the spectrum being analyzed and the location of the peaks and peak regions. Analysis is performed at user request to the requested peak regions. The fit of a peak region can be previewed before archival or deletion. An iterative procedure is available for calibrating the energy and width equations.

  19. GAUSS IX. Interactive Analysis of Gamm-ray Spectra from GE Semiconductor Detectors

    SciTech Connect

    Egger, A.E.

    1997-01-01

    GAUSS IX is a tool to interactively analyze gamma-ray spectra from Ge Semicondutor detectors. The user has full control over the view of the spectrum being analyzed and the location of the peaks and peak regions. Analysis is performed at user request to the requested peak regions. The fit of a peak region can be previewed before archival or deletion. An iterative procedure is available for calibrating the energy and width equations.

  20. Soft liquid phase adsorption for fabrication of organic semiconductor films on wettability patterned surfaces.

    PubMed

    Watanabe, Satoshi; Akiyoshi, Yuri; Matsumoto, Mutsuyoshi

    2014-01-01

    We report a soft liquid-phase adsorption (SLPA) technique for the fabrication of organic semiconductor films on wettability-patterned substrates using toluene/water emulsions. Wettability-patterned substrates were obtained by the UV-ozone treatment of self-assembled monolayers of silane coupling agents on glass plates using a metal mask. Organic semiconductor polymer films were formed selectively on the hydrophobic part of the wettability-patterned substrates. The thickness of the films fabricated by the SLPA technique is significantly larger than that of the films fabricated by dip-coating and spin-coating techniques. The film thickness can be controlled by adjusting the volume ratio of toluene to water, immersion angle, immersion temperature, and immersion time. The SLPA technique allows for the direct production of organic semiconductor films on wettability-patterned substrates with minimized material consumption and reduced number of fabrication steps.

  1. Functionalization of the semiconductor surfaces of diamond (100), Si (100), and Ge (100) by cycloaddition of transition metal oxides: a theoretical prediction.

    PubMed

    Xu, Yi-Jun; Fu, Xianzhi

    2009-09-01

    The viability of functionalization of the semiconductor surfaces of diamond (100), Si (100), and Ge (100) by traditional [3 + 2] cycloaddition of transition metal oxides has been predicted using effective cluster models in the framework of density functional theory. The cycloaddition of transition metal oxides (OsO(4), RuO(4), and MnO(4)(-)) onto the X (100) (X = C, Si, and Ge) surface is much more facile than that of other molecular analogues including ethylene, fullerene, and single-walled carbon nanotubes because of the high reactivity of surface dimers of X (100). Our computational results demonstrate the plausibility that the well-known [3 + 2] cycloaddition of transition metal oxides to alkenes in organic chemistry can be employed as a new type of surface reaction to functionalize the semiconductor X (100) surface, which offers the new possibility for self-assembly or chemical functionalization of X (100) at low temperature. More importantly, the chemical functionalization of X (100) by cycloaddition of transition metal oxides provides the molecular basis for preparation of semiconductor-supported catalysts but also strongly advances the concept of using organic reactions to modify the solid surface, particularly to modify the semiconductor C (100), Si (100), and Ge (100) surfaces for target applications in numerous fields such as microelectronics and heterogeneous photocatalysis.

  2. Improvement in C-V characteristics of Ge metal-oxide semiconductor capacitor by H2O2 incorporated HCl pretreatment

    NASA Astrophysics Data System (ADS)

    Kamata, Yoshiki; Ino, Tsunehiro; Koyama, Masato; Nishiyama, Akira

    2008-02-01

    Electrical characteristics of high-κ /Ge metal-oxide semiconductor (MOS) capacitors pretreated with HCl or HF solutions are investigated, including the effect of H2O2 incorporation. HCl treatment is more effective than HF treatment for decreasing equivalent oxide thickness. H2O2 incorporation into HCl solution leads to dramatic decrease in the capacitance at inversion side. We have confirmed that residual metal impurities are reduced below 1010atoms/cm2 on the Ge surface after pretreatment with mixed solution of HCl and H2O2. We conclude that decrease in metal impurities at Ge surface is responsible for the superior C-V characteristic of Ge MOS capacitor.

  3. 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.

  4. Ferromagnets based on diamond-like semiconductors GaSb, InSb, Ge, and Si supersaturated with manganese or iron impurities during laser-plasma deposition

    SciTech Connect

    Demidov, E. S.; Podol'skii, V. V.; Lesnikov, V. P.; Sapozhnikov, M. V.; Druzhnov, D. M.; Gusev, S. N.; Gribkov, B. A.; Filatov, D. O.; Stepanova, Yu. S.; Levchuk, S. A.

    2008-01-15

    Properties of thin (30-100 nm) layers of diluted magnetic semiconductors based on diamond-like compounds III-V (InSb and GaSb) and elemental semiconductors Ge and Si doped with 3d impurities of manganese and iron up to 15% were measured and discussed. The layers were grown by laser-plasma deposition onto heated single-crystal gallium arsenide or sapphire substrates. The ferromagnetism of layers with the Curie temperature up to 500 K appeared in observations of the ferromagnetic resonance, anomalous Hall effect, and magneto-optic Kerr effect. The carrier mobility of diluted magnetic semiconductors is a hundred times larger than that of the previously known highest temperature magnetic semiconductors, i.e., copper and chromium chalcogenides. The difference between changes in the magnetization with temperature in diluted semiconductors based on III-V, Ge, and Si was discussed. A complex structure of the ferromagnetic resonance spectrum in Si:Mn/GaAs was observed. The results of magnetic-force microscopy showed a weak correlation between the surface relief and magnetic inhomogeneity, which suggests that the ferromagnetism is caused by the 3d-impurity solid solution, rather than ferromagnetic phase inclusions.

  5. High quality, giant crystalline-Ge stripes on insulating substrate by rapid-thermal-annealing of Sn-doped amorphous-Ge in solid-liquid coexisting region

    SciTech Connect

    Matsumura, Ryo; Kai, Yuki; Chikita, Hironori; Sadoh, Taizoh; Miyao, Masanobu

    2015-06-15

    Formation of large-grain (≥30 μm) Ge crystals on insulating substrates is strongly desired to achieve high-speed thin-film transistors. For this purpose, we propose the methods of Sn-doping into amorphous-Ge combined with rapid-thermal-annealing (RTA) in the solid-liquid coexisting temperature region for the Ge-Sn alloy system. The densities of micro-crystal-nuclei formed in this temperature region become low by tuning the RTA temperature close to the liquidus curve, which enhances the lateral growth of GeSn. Thanks to the very small segregation coefficient of Sn, almost all Sn atoms segregate toward edges of the stripes during growth. Agglomeration of GeSn degrades the surface morphologies; however, it is significantly improved by lowering the initial Sn concentration. As a result, pure Ge with large crystal grains (∼40 μm) with smooth surface are obtained by optimizing the initial Sn concentration as low as 3 ∼ 5%. Lateral growth lengths are further increased through decreasing the number of nuclei in stripes by narrowing stripe width. In this way, high-crystallinity giant Ge crystals (∼200 μm) are obtained for the stripe width of 3 μm. This “Si-seed free” technique for formation of large-grain pure Ge crystals is very useful to realize high-performance thin-film devices on insulator.

  6. Effects of Ge and Sn substitution on the metal-semiconductor transition and thermoelectric properties of Cu12Sb4S13 tetrahedrite.

    PubMed

    Kosaka, Yasufumi; Suekuni, Koichiro; Hashikuni, Katsuaki; Bouyrie, Yohan; Ohta, Michihiro; Takabatake, Toshiro

    2017-03-15

    The synthetic tetrahedrites Cu12-yTrySb4S13 (Tr: Mn, Fe, Co, Ni, Zn) have been extensively studied due to interest in metal-semiconductor transition as well as in superior thermoelectric performance. We have prepared Ge- and Sn-bearing tetrahedrites, Cu12-xMxSb4S13 (M = Ge, Sn; x ≤ 0.6), and investigated the effects of the substitutions on the phase transition and the thermoelectric properties. The substitutions of Ge and Sn for Cu suppress the metal-semiconductor transition and increase the electrical resistivity ρ and the positive thermopower S. This finding suggests that the phase transition is prevented by electron doping into the unoccupied states of the valence band. The variations of ρ, S, and magnetic susceptibility for the present systems correspond well with those for the system with Tr = Zn(2+), confirming the tetravalent states for Ge and Sn. The substitution of M(4+) for Cu(1+) decreases the power factor S(2)/ρ but enhances the dimensionless thermoelectric figure of merit ZT, due to reductions in both the charge carrier contribution and lattice contribution to the thermal conductivity. As a result, ZT has a maximum value of ∼0.65 at 665 K for x = 0.3-0.5 in Cu12-xMxSb4S13 with M = Ge and Sn.

  7. Infrared sensitive liquid crystal light valve with semiconductor substrate.

    PubMed

    Shcherbin, Konstantin; Gvozdovskyy, Igor; Evans, Dean R

    2016-02-10

    A liquid crystal light valve (LCLV) is an optically controlled spatial light modulator that allows recording of dynamic holograms. Almost all known LCLVs operate in the visible range of the spectrum. In the present work we demonstrate a LCLV operating in the infrared. The interaction of signal and pump waves is studied for different applied voltages, grating spacings, and intensities of the recording beams. A fourfold amplification of the weak signal beam is achieved. The amplitude of the refractive index modulation Δn=0.007 and nonlinear coupling constant n₂=-1  cm²/W are estimated from the experimental results. External phase modulation of one of the recording beams is used for a further transient increase of the signal beam gain.

  8. Interfacial trapping in an aged discotic liquid crystal semiconductor

    NASA Astrophysics Data System (ADS)

    Dawson, Nathan J.; Patrick, Michael S.; Paul, Sanjoy; Ellman, Brett; Semyonov, Alexander; Twieg, Robert J.; Matthews, Rachael; Pentzer, Emily; Singer, Kenneth D.

    2015-08-01

    This study reports on time-of-flight (TOF) hole mobility measurements in aged 2,3,6,7,10,11-Hexakis(pentyloxy)triphenylene columnar liquid crystals. In contrast to the original samples reported in 2006, homeotropically aligned samples yielded TOF transients with an extended non-exponential rise. The experimental data were fit to a simple model that accurately reproduces the TOF transients assuming delayed charge release from traps near the optically excited electrode. While interfacial trapping appears only in the aged materials, the bulk mobility is similar to the pristine material. The model addresses dispersive transport in quasi-one-dimensional materials, determines the charge carrier mobility in systems with interfacial traps, and provides a method for characterizing the traps.

  9. Electrostatic effect of Au nanoparticles on near-infrared photoluminescence from Si/SiGe due to nanoscale metal/semiconductor contact.

    PubMed

    Yin, Yefei; Wang, Ze; Wang, Shuguang; Bai, Yujie; Jiang, Zuimin; Zhong, Zhenyang

    2017-04-18

    Photoluminescence (PL) from Si and SiGe is comprehensively modified by Au NPs under excitation without surface plasmon resonance. Moreover, the PL sensitively depends on the size of the Au NPs, the excitation power and the thickness of the Si layer between the Au NPs and SiGe. A model is proposed in terms of the electrostatic effects of Au NPs naturally charged by electron transfer through the nanoscale metal/semiconductor Schottky junction without an external bias or external injection of carriers. The model accounts well for all the unique PL features. It also reveals that Au NPs can substantially modify the energy band structures, distribution and transition of carriers in the nanoscale region below the Au NPs. Our results demonstrate that Au NPs on semiconductors can efficiently modulate light-matter interaction.

  10. Electrostatic effect of Au nanoparticles on near-infrared photoluminescence from Si/SiGe due to nanoscale metal/semiconductor contact

    NASA Astrophysics Data System (ADS)

    Yin, Yefei; Wang, Ze; Wang, Shuguang; Bai, Yujie; Jiang, Zuimin; Zhong, Zhenyang

    2017-04-01

    Photoluminescence (PL) from Si and SiGe is comprehensively modified by Au NPs under excitation without surface plasmon resonance. Moreover, the PL sensitively depends on the size of the Au NPs, the excitation power and the thickness of the Si layer between the Au NPs and SiGe. A model is proposed in terms of the electrostatic effects of Au NPs naturally charged by electron transfer through the nanoscale metal/semiconductor Schottky junction without an external bias or external injection of carriers. The model accounts well for all the unique PL features. It also reveals that Au NPs can substantially modify the energy band structures, distribution and transition of carriers in the nanoscale region below the Au NPs. Our results demonstrate that Au NPs on semiconductors can efficiently modulate light–matter interaction.

  11. 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.

  12. Discotic liquid crystals: a new generation of organic semiconductors.

    PubMed

    Sergeyev, Sergey; Pisula, Wojciech; Geerts, Yves Henri

    2007-12-01

    Discotic (disc-like) molecules typically comprising a rigid aromatic core and flexible peripheral chains have been attracting growing interest because of their fundamental importance as model systems for the study of charge and energy transport and due to the possibilities of their application in organic electronic devices. This critical review covers various aspects of recent research on discotic liquid crystals, in particular, molecular design concepts, supramolecular structure, processing into ordered thin films and fabrication of electronic devices. The chemical structure of the conjugated core of discotic molecules governs, to a large extent, their intramolecular electronic properties. Variation of the peripheral flexible chains and of the aromatic core is decisive for the tuning of self-assembly in solution and in bulk. Supramolecular organization of discotic molecules can be effectively controlled by the choice of the processing methods. In particular, approaches to obtain suitable macroscopic orientations of columnar superstructures on surfaces, that is, planar uniaxial or homeotropic alignment, are discussed together with appropriate processing techniques. Finally, an overview of charge transport in discotic materials and their application in optoelectronic devices is given.

  13. Heat-Treatment-Induced Switching of Magnetic States in the Doped Polar Semiconductor Ge1‑xMnxTe

    NASA Astrophysics Data System (ADS)

    Kriener, M.; Nakajima, T.; Kaneko, Y.; Kikkawa, A.; Yu, X. Z.; Endo, N.; Kato, K.; Takata, M.; Arima, T.; Tokura, Y.; Taguchi, Y.

    2016-05-01

    Cross-control of a material property - manipulation of a physical quantity (e.g., magnetisation) by a nonconjugate field (e.g., electrical field) – is a challenge in fundamental science and also important for technological device applications. It has been demonstrated that magnetic properties can be controlled by electrical and optical stimuli in various magnets. Here we find that heat-treatment allows the control over two competing magnetic phases in the Mn-doped polar semiconductor GeTe. The onset temperatures Tc of ferromagnetism vary at low Mn concentrations by a factor of five to six with a maximum Tc ≈ 180 K, depending on the selected phase. Analyses in terms of synchrotron x-ray diffraction and energy dispersive x-ray spectroscopy indicate a possible segregation of the Mn ions, which is responsible for the high-Tc phase. More importantly, we demonstrate that the two states can be switched back and forth repeatedly from either phase by changing the heat-treatment of a sample, thereby confirming magnetic phase-change-memory functionality.

  14. Heat-Treatment-Induced Switching of Magnetic States in the Doped Polar Semiconductor Ge1-xMnxTe.

    PubMed

    Kriener, M; Nakajima, T; Kaneko, Y; Kikkawa, A; Yu, X Z; Endo, N; Kato, K; Takata, M; Arima, T; Tokura, Y; Taguchi, Y

    2016-05-10

    Cross-control of a material property - manipulation of a physical quantity (e.g., magnetisation) by a nonconjugate field (e.g., electrical field) - is a challenge in fundamental science and also important for technological device applications. It has been demonstrated that magnetic properties can be controlled by electrical and optical stimuli in various magnets. Here we find that heat-treatment allows the control over two competing magnetic phases in the Mn-doped polar semiconductor GeTe. The onset temperatures Tc of ferromagnetism vary at low Mn concentrations by a factor of five to six with a maximum Tc ≈ 180 K, depending on the selected phase. Analyses in terms of synchrotron x-ray diffraction and energy dispersive x-ray spectroscopy indicate a possible segregation of the Mn ions, which is responsible for the high-Tc phase. More importantly, we demonstrate that the two states can be switched back and forth repeatedly from either phase by changing the heat-treatment of a sample, thereby confirming magnetic phase-change-memory functionality.

  15. Heat-Treatment-Induced Switching of Magnetic States in the Doped Polar Semiconductor Ge1−xMnxTe

    PubMed Central

    Kriener, M.; Nakajima, T.; Kaneko, Y.; Kikkawa, A.; Yu, X. Z.; Endo, N.; Kato, K.; Takata, M.; Arima, T.; Tokura, Y.; Taguchi, Y.

    2016-01-01

    Cross-control of a material property - manipulation of a physical quantity (e.g., magnetisation) by a nonconjugate field (e.g., electrical field) – is a challenge in fundamental science and also important for technological device applications. It has been demonstrated that magnetic properties can be controlled by electrical and optical stimuli in various magnets. Here we find that heat-treatment allows the control over two competing magnetic phases in the Mn-doped polar semiconductor GeTe. The onset temperatures Tc of ferromagnetism vary at low Mn concentrations by a factor of five to six with a maximum Tc ≈ 180 K, depending on the selected phase. Analyses in terms of synchrotron x-ray diffraction and energy dispersive x-ray spectroscopy indicate a possible segregation of the Mn ions, which is responsible for the high-Tc phase. More importantly, we demonstrate that the two states can be switched back and forth repeatedly from either phase by changing the heat-treatment of a sample, thereby confirming magnetic phase-change-memory functionality. PMID:27160657

  16. Magnetoresistance control in granular Zn 1 - x - y CdxMnyGeAs2 nanocomposite ferromagnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Kilanski, L.; Fedorchenko, I. V.; Górska, M.; Ślawska-Waniewska, A.; Nedelko, N.; Podgórni, A.; Avdonin, A.; Lähderanta, E.; Dobrowolski, W.; Aronov, A. N.; Marenkin, S. F.

    2015-09-01

    We present studies of structural, magnetic, and electrical properties of Zn 1 - x - y CdxMnyGeAs2 nanocomposite ferromagnetic semiconductor samples with changeable chemical composition. The presence of MnAs clusters induces the studied alloy room temperature ferromagnetism with the Curie temperature, TC, around 305 K. The chemical composition of the chalcopyrite matrix controls the geometrical parameters of the clusters, inducing different magnetoresistance effects in the crystals. The presence of ferromagnetic clusters in the alloy induces either negative or positive magnetoresistance with different values. The Cd-content allows a change of magnetoresistance sign in our samples from negative (for x ≈ 0.85 ) to positive (for x ≈ 0.12 ). The negative magnetoresistance present in the samples with x ≈ 0.85 is observed at temperatures T < 25 K with maximum values of about -32% at T = 1.4 K and B = 13 T, strongly depending on the Mn content, y. The positive magnetoresistance present in the samples with x ≈ 0.12 is observed with maximum values not exceeding 50% at B = 13 T and T = 4.3 K, changing with the Mn content, y.

  17. Activities of oxygen in liquid Bi, Sn, and Ge from electrochemical measurements

    NASA Astrophysics Data System (ADS)

    Otsuka, Shinya; Sano, Toyokazu; Kozuka, Zensaku

    1981-09-01

    Modified coulometric titrations on the galvanic cell: O in liquid Bi, Sn or Ge/ZrO2( + CaO)/Air, Pt, were performed to determine the oxygen activities in liquid bismuth and tin at 973, 1073 and 1173 and in liquid germanium at 1233 and 1373 K. The standard Gibbs energy of solution of oxygen in liquid bismuth, tin and germanium for 1/2 O2 (1 atm) → O (1 at. pct) were determined respectively to be ΔG° (in Bi) = -24450 + 3.42 T (±200), cal· g-atom-1 = - 102310 + 14.29 T (±900), J·g-atom-1, ΔG° (in Sn) = -42140 + 4.90 T (±350), cal· g-aton-1 = -176300 + 20.52 T (± 1500), J-g-atom-1, ΔG° (inGe) = -42310 + 5.31 7 (±300), cal·g-atom-1 = -177020 + 22.21 T(± 1300), J· g-atom-1, where the reference state for dissolved oxygen was an infinitely dilute solution. It was reconfirmed that the modified coulometric titration method proposed previously by two of the present authors produced far more reliable results than those reported by other investigators.

  18. Reduction of (68)Ge activity containing liquid waste from (68)Ga PET chemistry in nuclear medicine and radiopharmacy by solidification.

    PubMed

    de Blois, Erik; Chan, Ho Sze; Roy, Kamalika; Krenning, Eric P; Breeman, Wouter A P

    PET with (68)Ga from the TiO2- or SnO2- based (68)Ge/(68)Ga generators is of increasing interest for PET imaging in nuclear medicine. In general, radionuclidic purity ((68)Ge vs. (68)Ga activity) of the eluate of these generators varies between 0.01 and 0.001%. Liquid waste containing low amounts of (68)Ge activity is produced by eluting the (68)Ge/(68)Ga generators and residues from PET chemistry. Since clearance level of (68)Ge activity in waste may not exceed 10 Bq/g, as stated by European Directive 96/29/EURATOM, our purpose was to reduce (68)Ge activity in solution from >10 kBq/g to <10 Bq/g; which implies the solution can be discarded as regular waste. Most efficient method to reduce the (68)Ge activity is by sorption of TiO2 or Fe2O3 and subsequent centrifugation. The required 10 Bq per mL level of (68)Ge activity in waste was reached by Fe2O3 logarithmically, whereas with TiO2 asymptotically. The procedure with Fe2O3 eliminates ≥90% of the (68)Ge activity per treatment. Eventually, to simplify the processing a recirculation system was used to investigate (68)Ge activity sorption on TiO2, Fe2O3 or Zeolite. Zeolite was introduced for its high sorption at low pH, therefore (68)Ge activity containing waste could directly be used without further interventions. (68)Ge activity containing liquid waste at different HCl concentrations (0.05-1.0 M HCl), was recirculated at 1 mL/min. With Zeolite in the recirculation system, (68)Ge activity showed highest sorption.

  19. Experimental and ab initio molecular dynamics study of the structure and physical properties of liquid GeTe

    NASA Astrophysics Data System (ADS)

    Weber, Hans; Schumacher, Mathias; Jóvári, Pál; Tsuchiya, Yoshimi; Skrotzki, Werner; Mazzarello, Riccardo; Kaban, Ivan

    2017-08-01

    GeTe is a prototypical phase-change material employed in data storage devices. In this work, the atomic structure of liquid GeTe is studied by x-ray and neutron diffraction in the temperature range from 1197 to 998 K. The dynamic viscosity is measured from 1273 to 953 K, which is 55 K below the solidification point, using an oscillating-cup viscometer. The density of liquid GeTe between 1293 and 973 K is determined by the high-energy γ -ray attenuation method. The experiments are complemented with ab initio molecular dynamics (AIMD) simulations based on density functional theory (DFT). Compatibility of the AIMD-DFT models with the diffraction data is proven by simultaneous fitting of all data sets in the frame of the reverse Monte Carlo simulation technique. It is shown that octahedral order dominates in liquid GeTe, although tetrahedral structures are also present. The viscosity of the equilibrium and weakly undercooled liquid GeTe obeys the Arrhenius law with a small activation energy of the order of 0.3 eV, which is indicative of a highly fragile liquid. The calculated density of states and electronic wave functions point to the existence of a pseudogap and localized electron states within the gap in the equilibrium liquid near the melting point as well as in the undercooled liquid.

  20. Ionic Liquid Activation of Amorphous Metal-Oxide Semiconductors for Flexible Transparent Electronic Devices

    DOE PAGES

    Pudasaini, Pushpa Raj; Noh, Joo Hyon; Wong, Anthony T.; ...

    2016-02-09

    To begin this abstract, amorphous metal-oxide semiconductors offer the high carrier mobilities and excellent large-area uniformity required for high performance, transparent, flexible electronic devices; however, a critical bottleneck to their widespread implementation is the need to activate these materials at high temperatures which are not compatible with flexible polymer substrates. The highly controllable activation of amorphous indium gallium zinc oxide semiconductor channels using ionic liquid gating at room temperature is reported. Activation is controlled by electric field-induced oxygen migration across the ionic liquid-semiconductor interface. In addition to activation of unannealed devices, it is shown that threshold voltages of a transistormore » can be linearly tuned between the enhancement and depletion modes. Finally, the first ever example of transparent flexible thin film metal oxide transistor on a polyamide substrate created using this simple technique is demonstrated. Finally, this study demonstrates the potential of field-induced activation as a promising alternative to traditional postdeposition thermal annealing which opens the door to wide scale implementation into flexible electronic applications.« less

  1. Ionic Liquid Activation of Amorphous Metal-Oxide Semiconductors for Flexible Transparent Electronic Devices

    SciTech Connect

    Pudasaini, Pushpa Raj; Noh, Joo Hyon; Wong, Anthony T.; Ovchinnikova, Olga S.; Haglund, Amanda V.; Dai, Sheng; Ward, Thomas Zac; Mandrus, David; Rack, Philip D.

    2016-02-09

    To begin this abstract, amorphous metal-oxide semiconductors offer the high carrier mobilities and excellent large-area uniformity required for high performance, transparent, flexible electronic devices; however, a critical bottleneck to their widespread implementation is the need to activate these materials at high temperatures which are not compatible with flexible polymer substrates. The highly controllable activation of amorphous indium gallium zinc oxide semiconductor channels using ionic liquid gating at room temperature is reported. Activation is controlled by electric field-induced oxygen migration across the ionic liquid-semiconductor interface. In addition to activation of unannealed devices, it is shown that threshold voltages of a transistor can be linearly tuned between the enhancement and depletion modes. Finally, the first ever example of transparent flexible thin film metal oxide transistor on a polyamide substrate created using this simple technique is demonstrated. Finally, this study demonstrates the potential of field-induced activation as a promising alternative to traditional postdeposition thermal annealing which opens the door to wide scale implementation into flexible electronic applications.

  2. Composite Zn1-x Cd x GeAs2 semiconductors: structural and electrical properties

    NASA Astrophysics Data System (ADS)

    Kilanski, L.; Reszka, A.; Górska, M.; Domukhovski, V.; Podgórni, A.; Kowalski, B. J.; Dobrowolski, W.; Fedorchenko, I. V.; Aronov, A. N.; Marenkin, S. F.

    2016-12-01

    We present the studies of structural, transport and magnetotransport properties of \\text{Z}{{\\text{n}}1-x} Cd x GeAs2 crystals with the chemical content changing from 0 to 1. The structural studies indicate that this alloy exists as a composite two-phase material in almost the entire range of average chemical compositions. The two phase nature of our samples does have a significant influence on the carrier transport and magnetotransport of the composite alloy. The change of the conductivity type is observed at room temperature, from p-type for x≤slant 0.18 to n-type for x  >  0.18, respectively. The Hall carrier mobility measured at room temperature decreases as a function of x from about 35 cm2 (V · s)-1 for the sample with x  =  0 down to 3 cm2 (V · s)-1 for the sample with x  =  0.233. For x  >  0.233 the Hall carrier mobility shows an increase with x, up to the highest value around 875 cm2 (V · s)-1 observed for the sample with x  =  1. Temperature dependent resistivity measurements indicate the presence of thermal activation of carriers with activation energy, E a, with values from 20 to 30 meV for all the studied samples. The temperature dependent Hall effect data show that the grain boundary limited transport is strong in all our samples. For the samples with x≥slant 0.833 the negative MR is observed at temperatures lower than 100 K and at low magnetic field values, B\\in ≤ft(-3;+3\\right) T. This effect is interpreted as a weak localization phenomenon with low values of phase coherence length, {{L}φ}<5 nm.

  3. Improved interface properties of Ge metal-oxide-semiconductor capacitor with TaTiO gate dielectric by using in situ TaON passivation interlayer

    NASA Astrophysics Data System (ADS)

    Ji, F.; Xu, J. P.; Liu, J. G.; Li, C. X.; Lai, P. T.

    2011-05-01

    TaON is in situ formed as a passivating interlayer in Ge metal-oxide-semiconductor (MOS) capacitors with high-k TaTiO gate dielectric fabricated simply by alternate sputtering of Ta and Ti. Also, postdeposition annealing is performed in wet N2 to suppress the growth of unstable GeOx at the Ge surface. As a result, excellent electrical properties of the Ge MOS devices are demonstrated, such as high equivalent dielectric constant (22.1), low interface-state density (7.3×1011 cm-2 eV), small gate leakage current (8.6×10-4 A cm-2 at Vg-Vfb=1 V), and high device reliability. Transmission electron microscopy and x-ray photoelectron spectroscopy support that all these should be attributed to the fact that the nitrogen barrier in the TaON interlayer can effectively block the interdiffusions of Ge and Ta, and the wet-N2 anneal can significantly suppress the growth of unstable low-k GeOx.

  4. Surface structure of the liquid Au[subscript 72]Ge[subscript 28] eutectic phase: X-ray reflectivity

    SciTech Connect

    Pershan, P.S.; Stoltz, S.E.; Mechler, S.; Shpyrko, O.G.; Grigoriev, A.Y.; Balagurusamy, V.S. K.; Lin, B.H.; Meron, M.

    2009-12-01

    The surface structure of the liquid phase of the Au{sub 72}Ge{sub 28} eutectic alloy has been measured using resonant and nonresonant x-ray reflectivity and grazing incidence x-ray diffraction. In spite of the significant differences in the surface tension of liquid Ge and Au the Gibbs adsorption enhancement of Ge concentration at the surface is minimal. This is in striking contrast to all the other binary alloys with large differences in the respective surface tensions measured up to date. In addition there is no evidence of the anomalous strong surface layering or in-plane crystalline order that has been reported for the otherwise quite similar liquid Au{sub 82}Si{sub 18} eutectic. Instead, the surface of eutectic Au{sub 72}Ge{sub 28} is liquidlike and the layering can be explained by the distorted crystal model with only slight modifications to the first layer.

  5. Realisation of magnetically and atomically abrupt half-metal/semiconductor interface: Co2FeSi0.5Al0.5/Ge(111)

    NASA Astrophysics Data System (ADS)

    Nedelkoski, Zlatko; Kuerbanjiang, Balati; Glover, Stephanie E.; Sanchez, Ana M.; Kepaptsoglou, Demie; Ghasemi, Arsham; Burrows, Christopher W.; Yamada, Shinya; Hamaya, Kohei; Ramasse, Quentin M.; Hasnip, Philip J.; Hase, Thomas; Bell, Gavin R.; Hirohata, Atsufumi; Lazarov, Vlado K.

    2016-11-01

    Halfmetal-semiconductor interfaces are crucial for hybrid spintronic devices. Atomically sharp interfaces with high spin polarisation are required for efficient spin injection. In this work we show that thin film of half-metallic full Heusler alloy Co2FeSi0.5Al0.5 with uniform thickness and B2 ordering can form structurally abrupt interface with Ge(111). Atomic resolution energy dispersive X-ray spectroscopy reveals that there is a small outdiffusion of Ge into specific atomic planes of the Co2FeSi0.5Al0.5 film, limited to a very narrow 1 nm interface region. First-principles calculations show that this selective outdiffusion along the Fe-Si/Al atomic planes does not change the magnetic moment of the film up to the very interface. Polarized neutron reflectivity, x-ray reflectivity and aberration-corrected electron microscopy confirm that this interface is both magnetically and structurally abrupt. Finally, using first-principles calculations we show that this experimentally realised interface structure, terminated by Co-Ge bonds, preserves the high spin polarization at the Co2FeSi0.5Al0.5/Ge interface, hence can be used as a model to study spin injection from half-metals into semiconductors.

  6. Realisation of magnetically and atomically abrupt half-metal/semiconductor interface: Co2FeSi0.5Al0.5/Ge(111).

    PubMed

    Nedelkoski, Zlatko; Kuerbanjiang, Balati; Glover, Stephanie E; Sanchez, Ana M; Kepaptsoglou, Demie; Ghasemi, Arsham; Burrows, Christopher W; Yamada, Shinya; Hamaya, Kohei; Ramasse, Quentin M; Hasnip, Philip J; Hase, Thomas; Bell, Gavin R; Hirohata, Atsufumi; Lazarov, Vlado K

    2016-11-21

    Halfmetal-semiconductor interfaces are crucial for hybrid spintronic devices. Atomically sharp interfaces with high spin polarisation are required for efficient spin injection. In this work we show that thin film of half-metallic full Heusler alloy Co2FeSi0.5Al0.5 with uniform thickness and B2 ordering can form structurally abrupt interface with Ge(111). Atomic resolution energy dispersive X-ray spectroscopy reveals that there is a small outdiffusion of Ge into specific atomic planes of the Co2FeSi0.5Al0.5 film, limited to a very narrow 1 nm interface region. First-principles calculations show that this selective outdiffusion along the Fe-Si/Al atomic planes does not change the magnetic moment of the film up to the very interface. Polarized neutron reflectivity, x-ray reflectivity and aberration-corrected electron microscopy confirm that this interface is both magnetically and structurally abrupt. Finally, using first-principles calculations we show that this experimentally realised interface structure, terminated by Co-Ge bonds, preserves the high spin polarization at the Co2FeSi0.5Al0.5/Ge interface, hence can be used as a model to study spin injection from half-metals into semiconductors.

  7. Realisation of magnetically and atomically abrupt half-metal/semiconductor interface: Co2FeSi0.5Al0.5/Ge(111)

    PubMed Central

    Nedelkoski, Zlatko; Kuerbanjiang, Balati; Glover, Stephanie E.; Sanchez, Ana M.; Kepaptsoglou, Demie; Ghasemi, Arsham; Burrows, Christopher W.; Yamada, Shinya; Hamaya, Kohei; Ramasse, Quentin M.; Hasnip, Philip J.; Hase, Thomas; Bell, Gavin R.; Hirohata, Atsufumi; Lazarov, Vlado K.

    2016-01-01

    Halfmetal-semiconductor interfaces are crucial for hybrid spintronic devices. Atomically sharp interfaces with high spin polarisation are required for efficient spin injection. In this work we show that thin film of half-metallic full Heusler alloy Co2FeSi0.5Al0.5 with uniform thickness and B2 ordering can form structurally abrupt interface with Ge(111). Atomic resolution energy dispersive X-ray spectroscopy reveals that there is a small outdiffusion of Ge into specific atomic planes of the Co2FeSi0.5Al0.5 film, limited to a very narrow 1 nm interface region. First-principles calculations show that this selective outdiffusion along the Fe-Si/Al atomic planes does not change the magnetic moment of the film up to the very interface. Polarized neutron reflectivity, x-ray reflectivity and aberration-corrected electron microscopy confirm that this interface is both magnetically and structurally abrupt. Finally, using first-principles calculations we show that this experimentally realised interface structure, terminated by Co-Ge bonds, preserves the high spin polarization at the Co2FeSi0.5Al0.5/Ge interface, hence can be used as a model to study spin injection from half-metals into semiconductors. PMID:27869132

  8. Carrier transport properties of the Group-IV ferromagnetic semiconductor Ge{sub 1-x}Fe{sub x} with and without boron doping

    SciTech Connect

    Ban, Yoshisuke Wakabayashi, Yuki; Akiyama, Ryota; Nakane, Ryosho; Tanaka, Masaaki

    2014-09-15

    We have investigated the transport and magnetic properties of group-IV ferromagnetic semiconductor Ge{sub 1-x}Fe{sub x} films (x = 1.0 and 2.3%) with and without boron doping grown by molecular beam epitaxy (MBE). In order to accurately measure the transport properties of 100-nm-thick Ge{sub 1-x}Fe{sub x} films, (001)-oriented silicon-on-insulator (SOI) wafers with an ultra-thin Si body layer (∼5 nm) were used as substrates. Owing to the low Fe content, the hole concentration and mobility in the Ge{sub 1-x}Fe{sub x} films were exactly estimated by Hall measurements because the anomalous Hall effect in these films was found to be negligibly small. By boron doping, we increased the hole concentration in Ge{sub 1-x}Fe{sub x} from ∼10{sup 18} cm{sup −3} to ∼10{sup 20} cm{sup −3} (x = 1.0%) and to ∼10{sup 19} cm{sup −3} (x = 2.3%), but no correlation was observed between the hole concentration and magnetic properties. This result presents a contrast to the hole-induced ferromagnetism in III-V ferromagnetic semiconductors.

  9. Thermal transport across high-pressure semiconductor-metal transition in Si and Si0.991Ge0.009

    DOE PAGES

    Hohensee, Gregory T.; Fellinger, Michael R.; Trinkle, Dallas R.; ...

    2015-05-07

    Time-domain thermoreflectance (TDTR) can be applied to metallic samples at high pressures in the diamond anvil cell (DAC) and provide non-contact measurements of thermal transport properties. We have performed regular and beam-offset TDTR to establish the thermal conductivities of Si and Si0.991Ge0.009 across the semiconductor-metal phase transition and up to 45 GPa. The thermal conductivities of metallic Si and Si(Ge) are comparable to aluminum and indicative of predominantly electronic heat carriers. Metallic Si and Si(Ge) have an anisotropy of approximately 1.4, similar to that of beryllium, due to the primitive hexagonal crystal structure. Furthermore, we used the Wiedemann-Franz law tomore » derive the associated electrical resistivity, and found it consistent with the Bloch-Gruneisen model.« less

  10. Strong anisotropy of magnetization and sign reversion of ordinary Hall coefficient in single crystal Ge{sub 1-x}Mn{sub x} magnetic semiconductor films

    SciTech Connect

    Deng, J. X.; Tian, Y. F.; He, S. M.; Bai, H. L.; Xu, T. S.; Yan, S. S.; Dai, Y. Y.; Chen, Y. X.; Liu, G. L.; Mei, L. M.

    2009-08-10

    Epitaxial single-crystal Ge{sub 1-x}Mn{sub x} ferromagnetic-semiconductor films were fabricated on Ge(001) substrates by molecular beam epitaxy. All the samples are ferromagnetic and have strong magnetic anisotropy indicated by different magnetization in plane and out of plane. The electrical transport of the films obeys Efros variable range hopping law in the low temperature range. Interestingly, a negative coefficient of the ordinary Hall effect of p-type carriers was found in the variable range hopping at low temperature. Anomalous Hall effect in Ge{sub 0.949}Mn{sub 0.051} film was observed below the Curie temperature, indicating the carrier-mediated intrinsic ferromagnetism.

  11. Thermal transport across high-pressure semiconductor-metal transition in Si and Si0.991Ge0.009

    NASA Astrophysics Data System (ADS)

    Hohensee, Gregory T.; Fellinger, Michael R.; Trinkle, Dallas R.; Cahill, David G.

    2015-05-01

    Time-domain thermoreflectance (TDTR) can be applied to metallic samples at high pressures in the diamond anvil cell and provide noncontact measurements of thermal transport properties. We have performed regular and beam-offset TDTR to establish the thermal conductivities of Si and Si0.991Ge0.009 across the semiconductor-metal phase transition and up to 45 GPa. The thermal conductivities of metallic Si and Si(Ge) are comparable to aluminum and indicative of predominantly electronic heat carriers. Metallic Si and Si(Ge) have an anisotropy of approximately 1.4, similar to that of beryllium, due to the primitive hexagonal crystal structure. We used the Wiedemann-Franz law to derive the associated electrical resistivity, and found it consistent with the Bloch-Grüneisen model.

  12. Controlling Axial p-n Heterojunction Abruptness Through Catalyst Alloying in Vapor-Liquid-Solid Grown Semiconductor Nanowires

    SciTech Connect

    Perea, Daniel E.; Schreiber, Daniel K.; Devaraj, Arun; Thevuthasan, Suntharampillai; Yoo, Jinkyoung; Dayeh, Shadi A.; Picraux, Samuel T.

    2012-07-30

    The p-n junction can be regarded as the most important electronic structure that is responsible for the ubiquity of semiconductor microelectronics today. Efforts to continually scale down the size of electronic components is guiding research to explore the use of nanomaterials synthesized from a bottom-up approach - group-IV semiconductor nanowires being one such material. However, Au-catalyzed synthesis of Si/Si1-x-Gex semiconductor nanowire heterojunctions using the commonly-used vapor-liquid-solid (VLS) growth technique results in diffuse heterojunction interfaces [1], leading to doubts of producing compositionally-sharp p-n junctions using this approach. However, we have recently reported the ability to increase Ge-Si nanowire heterojunction abruptness by VLS synthesis from a Au(1-x)Ga(x) catalyst alloy as shown by EDX analysis in an SEM [2]. In this work, we have extended the use of a AuGa catalyst alloy to produce more compositionally abrupt p-n junction interfaces compared to using pure Au as directly measured by atom probe tomography. As shown in Figure 1(a-b), individual Ge-Si heterostructured nanowires were grown vertically atop Ge(111) microposts. Direct growth on the microposts provides a facile approach to nanowire analysis which circumvents the need to use FIB-based sample preparation techniques. Both nanowires grown from pure Au and a AuGa catalyst alloy were analyzed. The corresponding 3D APT reconstruction of an individual heterostructured nanowire is shown in Figure 1(c) with the corresponding materials labeled. A 1-dimensional composition profile along the analysis direction in Figure 1(d) confirms an increase in heterojunction abruptness for nanowires grown from AuGa (~10nm) compared to nanowires grown from pure Au (~65nm). Analysis of the P distribution within the Si region (Figure 1(e)) indicates that P reaches a constant distribution over approximately 10nm when incorporated through the AuGa catalyst, whereas it continually increases over 100

  13. Magnetic Susceptibility of liquid Gd-NM (NM = Cu, Ga, Ge) alloys

    NASA Astrophysics Data System (ADS)

    Shimakura, Hironori; Tahara, Shuta; Okada, Tatsuya; Ohno, Satoru

    2017-08-01

    For rare earth alloys, the indirect interaction of RKKY is at work between rare-earth atoms. Therefore, the magnetism of them depends on the number of conduction electrons and the distance between rare-earth metals. In this work, to reveal the relationship between the number of conduction electrons and magnetic property of rare earth metal alloys, magnetic susceptibility measurements for liquid Gd-NM (NM = Cu, Ga, Ge) was performed by Faraday method. As the results, it was observed that the sign of paramagnetic Curie temperature of Cu-Gd alloys are positive at all composition, while Ga-Gd and Ge-Gd alloys show negative paramagnetic Curie temperature at certain composition. Moreover, it was indicated when the alloy at certain composition shows highest melting temperature, it has the lowest paramagnetic Curie temperature.

  14. Vapor-Liquid-Solid Etch of Semiconductor Surface Channels by Running Gold Nanodroplets

    PubMed Central

    Nikoobakht, Babak; Herzing, Andrew; Muramoto, Shin; Tersoff, Jerry

    2016-01-01

    We show that Au nanoparticles spontaneously move across the (001) surface of InP, InAs, and GaP when heated in the presence of water vapor. As they move, the particles etch crystallographically aligned grooves into the surface. We show that this process is a negative analog of the vapor-liquid-solid (VLS) growth of semiconductor nanowires: semiconductor dissolves into the catalyst, and reacts with water vapor at the catalyst surface to create volatile oxides, depleting the dissolved cations and anions and so sustaining the dissolution process. This VLS etching process provides a new tool for directed assembly of structures with sub-lithographic dimensions, as small as a few nanometers in diameter. Au particles above 100 nm in size do not exhibit this process but remain stationary, with oxide accumulating around the particles. PMID:26599639

  15. Metallization in the molten and solid state and phase diagrams of the GeSe2 and GeS2 under high pressure

    NASA Astrophysics Data System (ADS)

    Brazhkin, V. V.; Bychkov, E.; Kondrin, M. V.

    2014-12-01

    We found that under high pressure, the GeSe2 and GeS2 melts pass into the metallic state. In the vicinity of the melting curves, their metallization begins at 3.5 and 7 GPa, respectively. The position of the semiconductor-metal transition line on the phase diagram for GeSe2 liquid is established. The GeS2-II and GeSe2-III high-pressure crystalline modifications are semiconductors, whereas the GeSe2-III modification at pressures exceeding 3.5-4 GPa is a metal (σ ≈ 103 Ω-1 cm-1). The ( P, T) phase diagrams for these compounds are constructed in the pressure range up to 10 GPa. Metallization during the GeSe2-II-GeSe2-III transition is evidently responsible for the small jump of entropy and the corresponding almost vertical slope of the transition line.

  16. Liquid-crystal composites with controlled photoluminescence of CdSe/ZnS semiconductor quantum rods

    NASA Astrophysics Data System (ADS)

    Danilov, V. V.; Artem'ev, M. V.; Baranov, A. V.; Orlova, A. O.; Mukhina, M. V.; Khrebtov, A. I.

    2011-06-01

    Liquid-crystal (LC) composites based on a combination of different acrylates and pentylcyanobiphenyl and containing CdSe/ZnS semiconductor quantum nanorods have been investigated. Samples of electro-optical cells with planar or homeotropic structures (depending on the acrylate type) have been obtained. The morphology of LC composite formation has been studied using luminescence techniques. It is shown that these composites are gel-like LC media, where the formation of dispersed and network structures in the cells plays a stabilizing role. The role of the electron transfer reactions during polymerization and the features of the kinetics of the Freedericksz effect (reorientation in an electric field) are discussed.

  17. Memory characteristics of metal-oxide-semiconductor structures based on Ge nanoclusters-embedded GeO(x) films grown at low temperature.

    PubMed

    Lin, Tzu-Shun; Lou, Li-Ren; Lee, Ching-Ting; Tsai, Tai-Cheng

    2012-03-01

    The memory devices constructed from the Ge-nanoclusters embedded GeO(x) layer deposited by the laser-assisted chemical vapor deposition (LACVD) system were fabricated. The Ge nanoclusters were observed by a high-resolution transmission electron microscopy. Using the capacitance versus voltage (C-V) and the conductance versus voltage (G-V) characteristics measured under various frequencies, the memory effect observed in the C-V curves was dominantly attributed to the charge storage in the Ge nanoclusters. Furthermore, the defects existed in the deposited film and the interface states were insignificant to the memory performances. Capacitance versus time (C-t) measurement was also executed to evaluate the charge retention characteristics. The charge storage and retention behaviors of the devices demonstrated that the Ge nanoclusters grown by the LACVD system at low temperature are promising for memory device applications.

  18. Time-of-flight analysis of charge mobility in a Cu-phthalocyanine-based discotic liquid crystal semiconductor

    NASA Astrophysics Data System (ADS)

    Fujikake, Hideo; Murashige, Takeshi; Sugibayashi, Makiko; Ohta, Kazuchika

    2004-10-01

    We used a time-of-flight method to study the charge carrier mobility properties of a molecular-aligned discotic liquid crystal semiconductor based on Cu-phthalocyanine. The heated isotropic-phase semiconductor material was sandwiched between transparent electrodes coated onto glass substrates without conventional alignment layers. This was then cooled, and a discotic liquid crystal semiconductor cell was obtained, which we used to make mobility measurements. The material had a fixed molecular alignment due to the supercooling of the hexagonal columnar mesophase. It was clarified that the carrier mobility for electrons was as high as it was for holes at room temperature. The maximum value of negative charge mobility reached 2.60×10-3cm2/Vs, although negative carrier mobility is often much lower than positive carrier mobility in other organic semiconductors, including conventional Cu-phthalocyanine vacuum-deposited films.

  19. Improvement of growing of Ge QDs by the method of liquid phase epitaxy

    NASA Astrophysics Data System (ADS)

    Maronchuk, I. I.; Sanikovitch, D. D.; Cherkashin, A. S.; Nitchev, H.; Dimova-Malinovska, D.

    2017-01-01

    This paper reports on improvement of the technological conditions for nano-heteroepitaxial structures (NHES) growth with Ge quantum dots (QDs) by liquid phase epitaxial (LPE) method applying impulse cooling on the substrate (ICS) The physical and mathematic modeling of the processes of growth and the analysis of the thermodynamic status has been carried out to optimize the construction of the thermal unit, the located in it graphite cassette and of the thermal conditions. For the analysis the Solid Works Flow Simulation program is applied, which has a satisfactory accuracy of calculations of heat-transfer simulation. The analysis has revealed shortcomings in the construction of the equipment. Having in mind these results the equipment is reconstructed and new different elements of the thermal block are installed. Good agreement of the experimental and calculated temperature distribution in the process of NHES with Ge QDs growing is obtained. The grown Ge QDs have improved structure with homogeneous distribution and size and depth of the Quantum Wells. The experiments carried out show good reproducibility of the growing process confirming the correctness of the mathematic modeling.

  20. Charge transport in liquid crystalline smectic and discotic organic semiconductors: New results and experimental methodologies

    NASA Astrophysics Data System (ADS)

    Paul, Sanjoy

    Organic electronics offer the possibility of producing low cost, flexible, and large area electronics. Organic semiconductors (OSCs) (organic polymers and crystals), used in organic electronics, are promising materials for novel optical and electronic devices such as organic light emitting diodes, organic field effect transistors, organic sensors, and organic photovoltaics (OPVs). OSCs are composed of molecules weakly held together via van der Walls forces rather than covalent bonds as in the case of inorganic semiconductors such as Si. The combined effect of small wave function overlap, spatial and energetic disorder in organic semiconducting materials lead to localization of charge carriers and, in many cases, hopping conduction. OSCs also differ from conventional semiconductors in that charges photogeneration (e.g., in OPVs) proceeds via the production, diffusion, and dissociation of excitons. Liquid crystalline OSCs (LCOSCs) are semiconductors with phases intermediate between the highly ordered crystalline and completely disordered liquid phases. These materials offer many advantages including facile alignment and the opportunity to study the effects of differing intermolecular geometries on transfer integrals, disorder-induced trapping, charge mobilities, and photogeneration efficiency. In this dissertation work, we explored the photogeneration and charge transport mechanisms in a few model smectic and discotic LCs to better understand the governing principles of photogeneration and charge transport using conventional and novel methods based on the pulsed laser time-of-flight charge carrier transport technique. Four major interrelated topics were considered in this research. First, a sample of smectic LC was aligned in order to compare the resulting hole mobility to that of an unaligned sample, with the aim of understanding how the intermolecular alignment over large length scales affects the hopping probability. The role of the polarization of the

  1. Molecular dynamics simulation of the liquid crystalline semiconductor: 8-TTP-8

    NASA Astrophysics Data System (ADS)

    Yoneya, Makoto; Funahashi, Masahiro; Yokoyama, Hiroshi

    2009-02-01

    In this study, the structure and dynamics of a liquid crystalline semiconductor dioctylterthiophene system, 8-TTP-8, were examined by molecular dynamics simulations. We especially focus on the melting transition from the crystal to the liquid crystal smectic G phase. Simulations of the rotational autocorrelation functions show that the transition is characterized by the onset of rotation around the long molecular axis, while maintaining a hexagonal packing within the smectic layers. This implies that the stepwise decrease of the carrier mobility at the melting transition point may be caused by this rotational disordering. We also found the molecular diffusions (at a rate of D~0.9x-10m2/s) in the simulated SmG phase. All these characteristics of the simulated SmG phase, including the molecular diffusions, are similar to those of a rotator (plastic crystal) phase.

  2. Electroless Deposition of III-V Semiconductor Nanostructures from Ionic Liquids at Room Temperature.

    PubMed

    Lahiri, Abhishek; Borisenko, Natalia; Olschewski, Mark; Gustus, René; Zahlbach, Janine; Endres, Frank

    2015-09-28

    Group III-V semiconductor nanostructures are important materials in optoelectronic devices and are being researched in energy-related fields. A simple approach for the synthesis of these semiconductors with well-defined nanostructures is desired. Electroless deposition (galvanic displacement) is a fast and versatile technique for deposition of one material on another and depends on the redox potentials of the two materials. Herein we show that GaSb can be directly synthesized at room temperature by galvanic displacement of SbCl3 /ionic liquid on electrodeposited Ga, on Ga nanowires, and also on commercial Ga. In situ AFM revealed the galvanic displacement process of Sb on Ga and showed that the displacement process continues even after the formation of GaSb. The bandgap of the deposited GaSb was 0.9±0.1 eV compared to its usual bandgap of 0.7 eV. By changing the cation in the ionic liquid, the redox process could be varied leading to GaSb with different optical properties.

  3. Controlled Growth of Organic Semiconductor Films Using Electrospray Vapor-Liquid-Solid Deposition

    NASA Astrophysics Data System (ADS)

    Shaw, Daniel; Bufkin, Kevin; Johnson, Brad; Patrick, David

    2010-03-01

    Interest in low molecular weight organic semiconductors (OS) for applications such as light-emitting diodes, photovoltaics, and other technologies stems in part from their prospects for enabling significantly reduced manufacturing costs compared to traditional inorganic semiconductors. However many of the best performing prototype devices produced so far have involved expensive or time-consuming fabrication methods, such as the use of single crystals or thin films deposited under high vacuum conditions. New methods are needed capable of rapidly and inexpensively producing high quality polycrystalline films, preferably involving near-ambient conditions. This poster will present studies of one such approach based on an electrospray vapor-liquid-solid growth technique. The method produces polycrystalline OS films deposited via atmospheric-pressure sublimation from a carrier gas (argon) which is partially ionized by a corona discharge. Vapor-phase molecules are then attracted to a charged substrate coated with a thin liquid solvent layer, in which they dissolve and grow as crystals, producing films with large grain sizes. This poster will describe the electrostatic and hydrodynamic features of the deposition mechanism, and the growth kinetics of the resulting polycrystalline films.

  4. LArGe: Background suppression using liquid argon (LAr) scintillation for 0 νββ decay search with enriched germanium (Ge) detectors

    NASA Astrophysics Data System (ADS)

    Di Marco, M.; Peiffer, P.; Schönert, S.

    2007-10-01

    Measurements with a bare p-type high purity germanium diode (HPGe) submerged in a 19 kg liquid argon (LAr) scintillation detector at MPIK-Heidelberg are reported. The liquid argon-germanium system (LArGe) is operated as a 4 π anti-Compton spectrometer to suppress backgrounds in the HPGe. This R&D is carried out in the framework of the Gerda experiment which searches for 0 νββ decays with HPGe detectors enriched in 76Ge. The goal of this work is to develop a novel method to discriminate backgrounds in 0 νββ search which would ultimately allow to investigate the effective neutrino mass free of background events down to the inverse mass hierarchy scale. Other applications in low-background counting are expected.

  5. 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.

  6. High Electron Mobility Ge n-Channel Metal-Insulator-Semiconductor Field-Effect Transistors Fabricated by the Gate-Last Process with the Solid Source Diffusion Technique

    NASA Astrophysics Data System (ADS)

    Maeda, Tatsuro; Morita, Yukinori; Takagi, Shinichi

    2010-06-01

    We fabricate high-k/Ge n-channel metal-insulator-semiconductor field-effect transistors (MISFETs) by the gate-last process with the thermal solid source diffusion to achieve both of high quality source/drain (S/D) and gate stack. The n+/p junction formed by solid source diffusion technique of Sb dopant shows the excellent diode characteristics of ˜1.5×105 on/off ratio between +1 and -1 V and the quite low reverse current density of ˜4.1×10-4 A/cm2 at +1 V after the fabrication of high-k/Ge n-channel MISFETs that enable us to observe well-behaved transistor performances. The extracted electron mobility with the peak of 891 cm2/(V.s) is high enough to be superior to the Si universal electron mobility especially in low Eeff.

  7. Outstanding laser damage threshold in Li2MnGeS4 and tunable optical nonlinearity in diamond-like semiconductors.

    PubMed

    Brant, Jacilynn A; Clark, Daniel J; Kim, Yong Soo; Jang, Joon I; Weiland, Ashley; Aitken, Jennifer A

    2015-03-16

    The new Li2MnGeS4 and Li2CoSnS4 compounds result from employing a rational and simple design strategy that guides the discovery of diamond-like semiconductors (DLSs) with wide regions of optical transparency, high laser damage threshold, and efficient second-order optical nonlinearity. Single-crystal X-ray diffraction was used to solve and refine the crystal structures of Li2MnGeS4 and Li2CoSnS4, which crystallize in the noncentrosymmetric space groups Pna21 and Pn, respectively. Synchrotron X-ray powder diffraction (SXRPD) was used to assess the phase purity, and diffuse reflectance UV-vis-NIR spectroscopy was used to estimate the bandgaps of Li2MnGeS4 (Eg = 3.069(3) eV) and Li2CoSnS4 (Eg = 2.421(3) eV). In comparison with Li2FeGeS4, Li2FeSnS4, and Li2CoSnS4 DLSs, Li2MnGeS4 exhibits the widest region of optical transparency (0.60-25 μm) and phase matchability (≥1.6 μm). All four of the DLSs exhibit second-harmonic generation and are compared with the benchmark NLO material, AgGaSe2. Most remarkably, Li2MnGeS4 does not undergo two- or three-photon absorption upon exposure to a fundamental Nd:YAG beam (λ = 1.064 μm) and exhibits a laser damage threshold > 16 GW/cm(2).

  8. Structure and lattice dynamics of the wide band gap semiconductors MgSiN2 and MgGeN2

    NASA Astrophysics Data System (ADS)

    Râsander, M.; Quirk, J. B.; Wang, T.; Mathew, S.; Davies, R.; Palgrave, R. G.; Moram, M. A.

    2017-08-01

    We have determined the structural and lattice dynamical properties of the orthorhombic, wide band gap semiconductors MgSiN2 and MgGeN2 using density functional theory. In addition, we present the structural properties and Raman spectra of MgSiN2 powder. The structural properties and lattice dynamics of the orthorhombic systems are compared to those of wurtzite AlN. We find clear differences in the lattice dynamics between MgSiN2, MgGeN2 and AlN, for example, we find that the highest phonon frequency in MgSiN2 is about 100 cm-1 higher than the highest frequency in AlN, and that MgGeN2 is much softer. We also provide the Born effective charge tensors and dielectric tensors of MgSiN2, MgGeN2 and AlN. Phonon related thermodynamic properties, such as the heat capacity and the entropy, have also been evaluated and are found to be in very good agreement with available experimental results.

  9. Complementary metal-oxide semiconductor-compatible detector materials with enhanced 1550 nm responsivity via Sn-doping of Ge/Si(100)

    NASA Astrophysics Data System (ADS)

    Roucka, Radek; Beeler, Richard; Mathews, Jay; Ryu, Mee-Yi; Kee Yeo, Yung; Menéndez, José; Kouvetakis, John

    2011-05-01

    Previously developed methods used to grow Ge1-ySny alloys on Si are extended to Sn concentrations in the 1019-1020 cm-3 range. These concentrations are shown to be sufficient to engineer large increases in the responsivity of detectors operating at 1550 nm. The dopant levels of Sn are incorporated at temperatures in the 370-390 °C range, yielding atomically smooth layers devoid of threading defects at high growth rates of 15-30 nm/min. These conditions are far more compatible with complementary metal-oxide semiconductor processing than the high growth and processing temperatures required to achieve the same responsivity via tensile strain in pure Ge on Si. A detailed study of a detector based on a Sn-doped Ge layer with 0.25% (1.1 × 1020 cm-3) Sn range demonstrates the responsivity enhancement and shows much better I-V characteristics than previously fabricated detectors based on Ge1-ySny alloys with y = 0.02.

  10. Achievement of low parasitic resistance in Ge n-channel metal-oxide-semiconductor field-effect transistor using an embedded TiN-source/drain structure

    NASA Astrophysics Data System (ADS)

    Nagatomi, Y.; Tateyama, T.; Tanaka, S.; Yamamoto, K.; Wang, D.; Nakashima, H.

    2017-03-01

    We investigated the source/drain (S/D) parasitic resistance (R P) of a Ge n-channel metal-oxide-semiconductor field-effect transistor (n-MOSFET) with TiN-S/D. The R P was as high as ˜1400 Ω, which is attributed to a very thin amorphous interlayer (a-IL) at a TiN/Ge interface. To solve this problem, n-MOSFETs with an embedded S/D structure were fabricated, of which the S/D was formed by the etching of a Ge layer using 0.03%-H2O2 solution followed by TiN sputter deposition. The electrical performances were investigated for devices with etching depths in the range of 2-22 nm. The devices with etching depths of 2-5 nm did not work. The devices with etching depths of 12-15 nm showed a quite normal transistor operation, and the R P was as low as ˜130 Ω, which is comparable to that of a p-MOSFET with PtGe-S/D. However, R Ps of the devices with etching depths of ˜22 nm was considerably high. The reason for these results is discussed on the basis of an a-IL formation at the sidewall of the engraved S/D region.

  11. Study of the fundamental units of novel semiconductor materials: structures, energetics, and thermodynamics of the Ge-Sn and Si-Ge-Sn molecular systems.

    PubMed

    Ciccioli, A; Gigli, G

    2012-07-05

    The binary Ge(y)Sn(z) and ternary Si(x)Ge(y)Sn(z) molecular systems containing up to five atoms were investigated by means of density functional theory and coupled cluster calculations. The minimum energy structures were calculated and higher energy isomers are also proposed. The atomization energies of the ground state isomers were calculated by the CCSD(T) method with correlation consistent basis sets up to quadruple-ζ quality. The resulting values were extrapolated to the complete basis set limit and corrected by an approximate evaluation of the spin-orbit effect. Energetic properties such as binding, fragmentation and mixing energies, and HOMO-LUMO gap were analyzed as a function of the cluster size and composition. By using empirically adjusted atomization energies and DFT harmonic frequencies, the thermal functions were evaluated, and a thermodynamic database for the Si-Ge-Sn system was built, containing data for 55 gaseous species. On this basis, equilibrium calculations were performed in the temperature interval 1600-2200 K aimed at predicting the composition of the gas phase under various conditions. The results presented here can be of interest to improve the microscopic knowledge of Ge-Sn and Si-Ge-Sn materials, which are among the most promising candidates for advanced applications in the field of electronic and optoelectronic components, both as epitaxially grown layers and as nanocrystal quantum dots.

  12. Electronic functionalization of solid-to-liquid interfaces between organic semiconductors and ionic liquids: Realization of very high performance organic single-crystal transistors

    NASA Astrophysics Data System (ADS)

    Uemura, T.; Hirahara, R.; Tominari, Y.; Ono, S.; Seki, S.; Takeya, J.

    2008-12-01

    High-performance electronic function of current amplification is realized with the use of solid-to-liquid interfaces between organic semiconductors and ionic liquid. To hold in place the ionic liquid of 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide known for low viscosity and high ionic conductivity, an elastomeric well structure is fabricated with polydimethylsiloxane on which organic single crystals of rubrene are electrostatically attached. As the result of rapid formation of electric double layers in the ionic liquid interfacing, the high-mobility organic semiconductor crystals' fast-switching transistor function is demonstrated with the application of gate voltage, realizing the highest sheet transconductance, namely, amplifying performance, ever achieved.

  13. Controlling the assembly of chalcogenide anions in ionic liquids: from binary Ge/Se through ternary Ge/Sn/Se to binary Sn/Se frameworks.

    PubMed

    Lin, Yumei; Massa, Werner; Dehnen, Stefanie

    2012-10-15

    Seven compounds with binary or ternary Ge/Se, Ge/Sn/Se, or Sn/Se anionic substructures crystallized upon the ionothermal reactions of [K(4)(H(2)O)(3)][Ge(4)Se(10)] with SnCl(4)·5H(2)O or SnCl(2) in [BMMIm][BF(4)] or [BMIm][BF(4)] (BMMIm=1-butyl-2,3-dimethyl-imidazolium, BMIm=1-butyl-3-methyl-imidazolium). The products were obtained by subtly varying the reaction conditions; the nature and amount of an additional amine was the most important parameter in the product selection and in determining the Sn/Ge ratio in the isolated products. The crystal structures of these chalcogenides were based on complex anions with unprecedented topologies that varied from discrete clusters (0D) through 1D chain structures or 2D layers to 3D frameworks. The architecture and composition of the title compounds were well reflected by their optical absorption behavior. Herein, we report a convenient approach for the generation of chalcogenidometallate phases with fine-tunable electronic properties in ionic liquids, which have been inaccessible by traditional methods.

  14. Liquid-phase epitaxial growth of two-dimensional semiconductor hetero-nanostructures.

    PubMed

    Tan, Chaoliang; Zeng, Zhiyuan; Huang, Xiao; Rui, Xianhong; Wu, Xue-Jun; Li, Bing; Luo, Zhimin; Chen, Junze; Chen, Bo; Yan, Qingyu; Zhang, Hua

    2015-02-02

    Although many two-dimensional (2D) hybrid nanostructures are being prepared, the engineering of epitaxial 2D semiconductor hetero-nanostructures in the liquid phase still remains a challenge. The preparation of 2D semiconductor hetero-nanostructures by epitaxial growth of metal sulfide nanocrystals, including CuS, ZnS and Ni3S2, is achieved on ultrathin TiS2 nanosheets by a simple electrochemical approach by using the TiS2 crystal and metal foils. Ultrathin CuS nanoplates that are 50-120 nm in size and have a triangular/hexagonal shape are epitaxially grown on TiS2 nanosheets with perfect epitaxial alignment. ZnS and Ni3S2 nanoplates can be also epitaxially grown on TiS2 nanosheets. As a proof-of-concept application, the obtained 2D CuS-TiS2 composite is used as the anode in a lithium ion battery, which exhibits a high capacity and excellent cycling stability.

  15. One-step photoembossing for submicrometer surface relief structures in liquid crystal semiconductors.

    PubMed

    Liedtke, Alicia; Lei, Chunhong; O'Neill, Mary; Dyer, Peter E; Kitney, Stuart P; Kelly, Stephen M

    2010-06-22

    We report a new single-step method to directly imprint nanometer-scale structures on photoreactive organic semiconductors. A surface relief grating is spontaneously formed when a light-emitting, liquid crystalline, and semiconducting thin film is irradiated by patterned light generated using a phase mask. Grating formation requires no postannealing nor wet etching so there is potential for high-throughput fabrication. The structured film is cross-linked for robustness. Gratings deeper than the original film thickness are made with periods as small as 265 nm. Grating formation is attributed to mass transfer, enhanced by self-assembly, from dark to illuminated regions. A photovoltaic device incorporating the grating is discussed.

  16. Business diversification - In the businesses of desk calculator, semiconductor and liquid crystal

    NASA Astrophysics Data System (ADS)

    Asada, Atsushi

    This is a record of the lecture at the 27th Annual Meeting on Information Science and Technology. Lecturer, a staff member of Sharp, Corp., explained its business diversification. The Company started with electric appliances. After coping with the application of computer technology, it made a success in the business of desk calculator. Aiming at making calculator for personal use, it coped with the business in semiconductor, and developed its business in liquid crystal for making calculator thinner. Based on these businesses, it expanded its business in OA appliances, and developed the business in combining electric appliances and information including distribution and marketing. The businesses in the age of 1990s will be requested to provide services by customizing hardware, software and system with efforts to enhance valued-added to them.

  17. Spectroscopic Studies of Semiconductor Materials for Aggressive-scaled Micro- and Opto-electronic Devices: nc-SiO2, GeO2; ng-Si, Ge and ng-Transition metal (TM) oxides

    NASA Astrophysics Data System (ADS)

    Cheng, Cheng

    Non-crystalline thin film materials are widely used in the semiconductor industry (micro- and optoelectronics) and in green energy, e.g., photovolatic applications. This dissertation under-pins these device application with studies of their electronic structures using derivative X-ray Absorption Spectroscopy (XAS) and derivative Spectroscopic Ellipsometry (SE) for the first time to experimentally determine electronic and intrinsic defect structures. Differences between electron and hole mobilities in c- (and ng-Si) and c- (and ng- Ge), make Ge channels superior to Si channels in for aggressively scaled CMOS field effect transistors (FETs). Bonding between Si and Ge substrates and gate dielectric oxides is the focus this dissertation. The primary objective of this research is to measure and interpret by ab-initio theory the electronic and intrinsic electronic defect structures mirco-electronic thin film materials. This is accomplished for the first time by combining (i) derivative XAS TEY data obtained at the Stanford Synchrotron Radiation Light Source (SSRL) with (ii) derivative Spectroscopic Ellipsometry results obtained at the J.A. Woollam Co. laboratory. All the oxides were deposited in RPECVD system with in-line AES and RHEED. Thins films and gate stacks were annealed in RTA system in Ar to determine temperature dependent changes. 2nd derivative analysis is applied on XAS and SE spectra emphasizing the conduction band (CB) and virtual bound state (VBS) regimes. 2nd derivative SE spectra for ng-Si and ng-Ge each have 3 distinct regimes: (i) 3 excitons, (ii) 2 features in the CB edge region, and (iii) 3 additional exciton features above the IP. Excitonic spectral width provides conductivity electron masses (em0*) and hence electron mobilities. The wider the energy range, the higher the electron mobility in that CB. Spectra of high-K dielectrics have an additional energy regime between the CB edge regime, and the higher eV excitons. This regime has 4 intra-d state

  18. Effective passivation and high-performance metal-oxide-semiconductor devices using ultra-high-vacuum deposited high- κ dielectrics on Ge without interfacial layers

    NASA Astrophysics Data System (ADS)

    Chu, L. K.; Chu, R. L.; Lin, T. D.; Lee, W. C.; Lin, C. A.; Huang, M. L.; Lee, Y. J.; Kwo, J.; Hong, M.

    2010-09-01

    Without using any interfacial passivation layers, high- κ dielectric Y 2O 3, HfO 2, and Ga 2O 3(Gd 2O 3) [GGO], by electron beam evaporation in ultra-high-vacuum (UHV), have been directly deposited on Ge substrate. Comprehensive investigations have been carried out to study the oxide/Ge interfaces chemically, structurally, and electronically: hetero-structures of all the studied oxides on Ge are highly thermally stable with annealing to 500 °C, and their interfaces remain atomically sharp. The electrical analyses have been conducted on metal-oxide-semiconductor (MOS) devices, i.e. MOS capacitors (MOSCAPs) and MOS field-effect-transistors (MOSFETs). Dielectrics constants of the Y 2O 3, HfO 2, and GGO have been extracted to be ˜17, 20, and 13-15, respectively, indicating no interfacial layer formation with 500 °C annealing. A low interfacial density of states ( Dits), as low as 3 × 10 11 cm -2 eV -1, has been achieved for GGO/Ge near mid-gap along with a high Fermi-level movement efficiency as high as 80%. The GGO/Ge pMOSFETs with TiN as the metal gate have yielded very high-performances, in terms of 496 μA/μm, 178 μS/μm, and 389 cm 2/V s in saturation drain current density, maximum transconductance, and effective hole mobility, respectively. The gate width and gate length of the MOSFET are 10 μm and 1 μm.

  19. Effect of Remote Oxygen Scavenging on Electrical Properties of Ge-Based Metal-Oxide-Semiconductor Capacitors

    NASA Astrophysics Data System (ADS)

    Fadida, Sivan; Nyns, Laura; Van Elshocht, Sven; Eizenberg, Moshe

    2017-01-01

    Remote oxygen scavenging has been studied in a metal/high- k dielectric/GeO2/Ge stack, where a thin Ti layer inserted into the metal/high- k dielectric interface serves as the scavenger. First, we established that remote oxygen scavenging indeed occurs specifically in the studied HfO2/Al2O3/GeO2/Ge stack. It was also established that the source for oxygen is decomposition of the GeO2 layer. Then, the effect of remote oxygen scavenging of the GeO2 layer on the electrical characteristics of the metal/oxide/Ge capacitors was investigated. The electrical properties were studied in comparison with identical gate stacks with a Pt electrode, before and after annealing. Although a decrease in effective oxide thickness was demonstrated as a result of this process, clear degradation of the interface electrical quality was observed after scavenging. Initiation of the scavenging process was witnessed upon deposition of Ti at room temperature, emphasizing that this process could not be controlled.

  20. Enhanced ferromagnetic transition temperature induced by a microscopic structural rearrangement in the diluted magnetic semiconductor Ge1 -xMnxTe

    NASA Astrophysics Data System (ADS)

    Kriener, M.; Nakajima, T.; Kaneko, Y.; Kikkawa, A.; Hashizume, D.; Kato, K.; Takata, M.; Arima, T.; Tokura, Y.; Taguchi, Y.

    2017-06-01

    The correlation between magnetic properties and microscopic structural aspects in the diluted magnetic semiconductor Ge1 -xMnxTe is investigated by x-ray diffraction and magnetization as a function of the Mn concentration x . The occurrence of high ferromagnetic-transition temperatures in the rhombohedrally distorted phase of slowly cooled Ge1 -xMnxTe is shown to be directly correlated with the formation and coexistence of strongly distorted Mn-poor and weakly distorted Mn-rich regions. It is demonstrated that the weakly distorted phase fraction is responsible for the occurrence of high-transition temperatures in Ge1 -xMnxTe . When the Mn concentration becomes larger, the Mn-rich regions start to switch into the undistorted cubic structure, and the transition temperature is suppressed concurrently. By identifying suitable annealing conditions, we successfully increased the transition temperature to above 200 K for Mn concentrations close to the cubic phase. Structural data indicate that the weakly distorted phase fraction can be restored at the expense of the cubic regions upon the enhancement of the transition temperature, clearly establishing the direct link between high-transition temperatures and the weakly distorted Mn-rich phase fraction.

  1. Liquid-solid phase transition of Ge-Sb-Te alloy observed by in-situ transmission electron microscopy.

    PubMed

    Berlin, Katja; Trampert, Achim

    2016-11-05

    Melting and crystallization dynamics of the multi-component Ge-Sb-Te alloy have been investigated by in-situ transmission electron microscopy (TEM). Starting point of the phase transition study is an ordered hexagonal Ge1Sb2Te4 thin film on Si(111) where the crystal structure and the chemical composition are verified by scanning TEM and electron energy-loss spectroscopy, respectively. The in-situ observation of the liquid phase at 600°C including the liquid-solid and liquid-vacuum interfaces and their movements was made possible due to an encapsulation of the TEM sample. The solid-liquid interface during melting displays a broad and diffuse transition zone characterized by a vacancy induced disordered state. Although the velocities of interface movements are measured to be in the nanometer per second scale, both, for crystallization and solidification, the underlying dynamic processes are considerably different. Melting reveals linear dependence on time, whereas crystallization exhibits a non-linear time-dependency featuring a superimposed start-stop motion. Our results may provide valuable insight into the atomic mechanisms at interfaces during the liquid-solid phase transition of Ge-Sb-Te alloys.

  2. Bistable Spatial Light Modulator Using Guest-Host Liquid Crystal and Bi12GeO20 Photoconductive Crystal

    NASA Astrophysics Data System (ADS)

    Fujikake, Hideo; Takizawa, Kuniharu; Kikuchi, Hiroshi

    1993-02-01

    This paper describes a new bistable spatial light modulator consisting of a guest-host type of 90°-twisted nematic liquid crystal layer and a Bi12GeO20 photoconductor. The optical bistability is generated by an internal electro-optic feedback effect based on the nonlinear transmittance property of the guest-host liquid crystal layer and the photoconductive property of the Bi12GeO20 crystal. This device has various optical threshold functions, where the optical threshold level is easily controlled by varying the drive voltage of the device or its frequency. Optical image binarization and optical parallel logic operations based on optical bistability are realized by illuminating the liquid crystal layer with blue light. It has a limiting resolution of 25 lp/mm, and the rise and decay times of the device are approximately 30 ms and 90 ms, respectively.

  3. Liquid mixture detection by InGaAsP semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Zhu, Xiang; Cassidy, Daniel T.

    1997-01-01

    Compact liquid sensors were constructed by using the output of near-infrared semiconductor diode lasers to measure transmission. Multiple short external cavities were used to force diode lasers to provide a wide spectral coverage (approximately equals 72 nm) for the detection of broad absorption features of liquids. The transmission at discrete laser modes were processed by the principal component regression (PCR) and the partial least squares (PLS) algorithms. A root mean square error of prediction of 0.092% and a correlation coefficient R2 of 0.998 were obtained for the detection of water concentration in D2O. The rms value of 0.056% from 30 independent measurements of 0.5% water in D2P showed that the method was sensitive to detect 0.1% concentration difference. The application of the PCR and the PLS algorithms in the scheme was studied in a three mixture system of water, acetone and methanol in terms of optimizing factors and detection of 'outliers'. The limiting noise sources were determined by modeling synthetic data.

  4. Employing `Liquid Gap' Transistors to Examine the Mobility-Carrier Density Relation in Polymer and Single Crystal Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Frisbie, Daniel

    2009-03-01

    It is generally known that the carrier mobility in organic semiconductors can depend on carrier density, but the precise relationship hinges on the degree of structural order and the dielectric polarizability at the organic/dielectric interface. We have fabricated both single crystal and polymer transistors using the PDMS stamp approach pioneered by Podzorov and Rogers [1], where we have replaced the usual `air gap' in these structures with liquids having different dielectric constants. This structure allows us to examine transport in single crystals and polymer semiconductors as a function of tunable dielectric constant and also charge density. We find striking differences in transport behavior for organic single crystals versus polymer semiconductor films using these liquid dielectric transistors. For organic single crystals such as rubrene, the carrier mobility does not seem to be a function of charge density but does strongly depend on the liquid dielectric constant, in keeping with previous results reported by Morpurgo [2] on the effects of dielectric polarizability. For polymer semiconductors, the effect of charge density is overwhelming; there is a strong increase in charge mobility with increasing carrier concentration, following a power law. These results are already largely known, but the `liquid gap' transistors provide a convenient testbed for examining these effects side-by-side for different materials in the same device. We will describe the device fabrication and the nature of our results, as well as discuss the origins of the very different behavior for single crystals versus polymer semiconductor films. 1) Sundar, V.C., et al. Science 303 (2004) 1643. 2) Hulea, I. N., et al. Nature Mater. 5 (2006) 982.

  5. Assessment of Anisotropic Semiconductor Nanorod and Nanoplatelet Heterostructures with Polarized Emission for Liquid Crystal Display Technology

    SciTech Connect

    Cunningham, Patrick D.; Souza, João B.; Fedin, Igor; She, Chunxing; Lee, Byeongdu; Talapin, Dmitri V.

    2016-06-28

    Semiconductor nanorods can emit linear-polarized light at efficiencies over 80%. Polarization of light in these systems, confirmed through single-rod spectroscopy, can be explained on the basis of the anisotropy of the transition dipole moment and dielectric confinement effects. Here we report emission polarization in macroscopic semiconductor polymer composite films containing CdSe/CdS nanorods and colloidal CdSe nanoplatelets. Anisotropic nanocrystals dispersed in polymer films of poly butyl-co-isobutyl methacrylate (PBiBMA) can be stretched mechanically in order to obtain unidirectionally aligned arrays. A high degree of alignment, corresponding to an orientation factor of 0.87, was achieved and large areas demonstrated polarized emission, with the contrast ratio I-parallel to/I-perpendicular to= 5.6, making these films viable candidates for use in liquid crystal display (LCD) devices. To some surprise, we observed significant optical anisotropy and emission polarization for 2D CdSe nanoplatelets with the electronic structure of quantum wells. The aligned nanorod arrays serve as optical funnels, absorbing unpolarized light and re-emitting light from deep-green to red with quantum efficiencies over 90% and high degree of linear polarization. Our results conclusively demonstrate the benefits of anisotropic nanostructures for LCD backlighting. The polymer films with aligned CdSe/CdS dot-in-rod and rod-in-rod nanostructures show more than 2-fold enhancement of brightness compared to the emitter layers with randomly oriented nanostructures. This effect can be explained as the combination of linearly polarized luminescence and directional emission from individual nanostructures.

  6. First-principles calculations of Mg2X (X = Si, Ge, Sn) semiconductors with the calcium fluorite structure

    NASA Astrophysics Data System (ADS)

    Sandong, Guo

    2015-05-01

    The electronic structures of Mg2X (X = Si, Ge, Sn) have been calculated by using generalized gradient approximation, various screened hybrid functionals, as well as Tran and Blaha's modified Becke and Johnson exchange potential. It was found that the Tran and Blaha's modified Becke and Johnson exchange potential provides a more realistic description of the electronic structures and the optical properties of Mg2X (X = Si, Ge, Sn) than else exchange-correlation potential, and the theoretical gaps and dielectric functions of Mg2X (X = Si, Ge, Sn) are quite compatible with the experimental data. The elastic properties of Mg2X (X = Si, Ge, Sn) have also been studied in detail with the generalized gradient approximation, including bulk modulus, shear modulus, Young's modulus, Poisson's ratio, sound velocities, and Debye temperature. The phonon dispersions of Mg2X (X = Si, Ge, Sn) have been calculated within the generalized gradient approximation, suggesting no structural instability, and the measurable phonon heat capacity as a function of the temperature has been also calculated. Project supported by the Fundamental Research Funds for the Central Universities (No. 2013QNA32) and the National Natural Science Foundation of China (No. 11404391).

  7. Solar Energy Conversion and Environmental Remediation Using Inorganic Semiconductor-Liquid Interfaces: The Road Traveled and the Way Forward.

    PubMed

    Rajeshwar, Krishnan

    2011-06-02

    Unlike their solid-state counterparts, semiconductor-liquid junctions are versatile in that the incident solar energy can be stored in the form of chemical fuels. Another attractive application is the use of irradiated oxide semiconductor-coated surfaces for self-cleaning and antifogging. The theme of this history-tinged Guest Commentary centers on the question of what has been accomplished in the above "photoelectrochemical" schemes over the 35 year time frame from 1975 to 2010. Progress in this field was aided by the infusion of new concepts and contributions from the materials chemistry and physics communities. A related aspect of discussion is how the active semiconductor material has evolved both chemically and morphologically in these applications. It is shown that despite impressive research advances, only a handful of the above concepts (e.g., dye-sensitized solar photon conversion and self-cleaning and antifogging surfaces) have made the successful transition from the laboratory to the marketplace.

  8. Flow-Solution-Liquid-Solid Growth of Semiconductor Nanowires: A Novel Approach for Controlled Synthesis

    SciTech Connect

    Hollingsworth, Jennifer A.; Palaniappan, Kumaranand; Laocharoensuk, Rawiwan; Smith, Nickolaus A.; Dickerson, Robert M.; Casson, Joanna L.; Baldwin, Jon K.

    2012-06-07

    Semiconductor nanowires (SC-NWs) have potential applications in diverse technologies from nanoelectronics and photonics to energy harvesting and storage due to their quantum-confined opto-electronic properties coupled with their highly anisotropic shape. Here, we explore new approaches to an important solution-based growth method known as solution-liquid-solid (SLS) growth. In SLS, molecular precursors are reacted in the presence of low-melting metal nanoparticles that serve as molten fluxes to catalyze the growth of the SC-NWs. The mechanism of growth is assumed to be similar to that of vapor-liquid-solid (VLS) growth, with the clear distinctions of being conducted in solution in the presence of coordinating ligands and at relatively lower temperatures (<300 C). The resultant SC-NWs are soluble in common organic solvents and solution processable, offering advantages such as simplified processing, scale-up, ultra-small diameters for quantum-confinement effects, and flexible choice of materials from group III-V to groups II-VI, IV-VI, as well as truly ternary I-III-VI semiconductors as we recently demonstrates. Despite these advantages of SLS growth, VLS offers several clear opportunities not allowed by conventional SLS. Namely, VLS allows sequential addition of precursors for facile synthesis of complex axial heterostructures. In addition, growth proceeds relatively slowly compared to SLS, allowing clear assessments of growth kinetics. In order to retain the materials and processing flexibility afforded by SLS, but add the elements of controlled growth afforded by VLS, we transformed SLS into a flow based method by adapting it to synthesis in a microfluidic system. By this new method - so-called 'flow-SLS' (FSLS) - we have now demonstrated unprecedented fabrication of multi-segmented SC-NWs, e.g., 8-segmented CdSe/ZnSe defined by either compositionally abrupt or alloyed interfaces as a function of growth conditions. In addition, we have studied growth rates as a

  9. The strain induced band gap modulation from narrow gap semiconductor to half-metal on Ti{sub 2}CrGe: A first principles study

    SciTech Connect

    Li, Jia; Zhang, Zhidong; Lu, Zunming; Xie, Hongxian; Fang, Wei; Li, Shaomin; Liang, Chunyong; Yin, Fuxing

    2015-11-15

    The Heusler alloy Ti{sub 2}CrGe is a stable L2{sub 1} phase with antiferromagnetic ordering. With band-gap energy (∼ 0.18 eV) obtained from a first-principles calculation, it belongs to the group of narrow band gap semiconductor. The band-gap energy decreases with increasing lattice compression and disappears until a strain of −5%; moreover, gap contraction only occurs in the spin-down states, leading to half-metallic character at the −5% strain. The Ti{sub 1}, Ti{sub 2}, and Cr moments all exhibit linear changes in behavior within strains of −5%– +5%. Nevertheless, the total zero moment is robust for these strains. The imaginary part of the dielectric function for both up and down spin states shows a clear onset energy, indicating a corresponding electronic gap for the two spin channels.

  10. Theoretical comparison of Si, Ge, and GaAs ultrathin p-type double-gate metal oxide semiconductor transistors

    NASA Astrophysics Data System (ADS)

    Dib, Elias; Bescond, Marc; Cavassilas, Nicolas; Michelini, Fabienne; Raymond, Laurent; Lannoo, Michel

    2013-08-01

    Based on a self-consistent multi-band quantum transport code including hole-phonon scattering, we compare current characteristics of Si, Ge, and GaAs p-type double-gate transistors. Electronic properties are analyzed as a function of (i) transport orientation, (ii) channel material, and (iii) gate length. We first show that ⟨100⟩-oriented devices offer better characteristics than their ⟨110⟩-counterparts independently of the material choice. Our results also point out that the weaker impact of scattering in Ge produces better electrical performances in long devices, while the moderate tunneling effect makes Si more advantageous in ultimately scaled transistors. Moreover, GaAs-based devices are less advantageous for shorter lengths and do not offer a high enough ON current for longer gate lengths. According to our simulations, the performance switching between Si and Ge occurs for a gate length of 12 nm. The conclusions of the study invite then to consider ⟨100⟩-oriented double-gate devices with Si for gate length shorter than 12 nm and Ge otherwise.

  11. Planar-orientation polycrystalline thin film of liquid-crystalline organic semiconductor by template-directed self-assembly

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Fei; Iino, Hiroaki; Hanna, Jun-ichi

    2017-10-01

    We fabricated planar-orientation crystalline thin films of organic semiconductors, in which molecules sit parallel, i.e., “face-on”, on the substrate and favor vertical charge transport. Thanks to molecular orientation that is sensitive to surface properties and the self-organization of liquid crystals, planar-orientation crystalline thin films can be prepared by simply cooling a smectic liquid-crystalline organic semiconductor from isotropic temperature with the aid of a poly(vinyl alcohol) (PVA) microtemplate. The molecular orientation of crystalline thin films was investigated by polarized optical microscopy (POM) and X-ray diffraction (XRD) analysis, and the current–voltage characteristics of the films were studied in a diode configuration. The results showed high potential for device applications.

  12. Doniach Phase Diagram, Revisited: From Ferromagnet to Fermi Liquid in Pressurized CeRu[sub 2] Ge[sub 2

    SciTech Connect

    Suellow, S.; Aronson, M.C. ); Rainford, B.D. ); Haen, P. )

    1999-04-01

    We present the resistivity and ac susceptibility of CeRu[sub 2]Ge [sub 2] at pressures p up to 130thinspthinspkbar. Pressure transforms the system from a ferromagnet into a nonordering Fermi liquid (FL). The suppression of magnetic order at p[sub c]=67 kbar is accompanied by non-Fermi liquid (NFL) behavior. By comparing our results to isoelectronic CeRu[sub 2]( Ge[sub 1[minus]x]Si [sub x])[sub 2] we derive a unified hybridization J phase diagram for the entire material class. The phase diagram is characterized by the FL and Kondo energy scales T[sub FL] and T[sub K] , with the NFL behavior appearing at T[sub FL]=0 K , while T[sub K] remains finite and a smoothly increasing function of J . [copyright] [ital 1999] [ital The American Physical Society

  13. Doniach Phase Diagram, Revisited: From Ferromagnet to Fermi Liquid in Pressurized CeRu{sub 2} Ge{sub 2}

    SciTech Connect

    Suellow, S.; Aronson, M.C.; Rainford, B.D.; Haen, P.

    1999-04-01

    We present the resistivity and ac susceptibility of CeRu{sub 2}Ge {sub 2} at pressures p up to 130thinspthinspkbar. Pressure transforms the system from a ferromagnet into a nonordering Fermi liquid (FL). The suppression of magnetic order at p{sub c}=67 kbar is accompanied by non-Fermi liquid (NFL) behavior. By comparing our results to isoelectronic CeRu{sub 2}( Ge{sub 1{minus}x}Si {sub x}){sub 2} we derive a unified hybridization J phase diagram for the entire material class. The phase diagram is characterized by the FL and Kondo energy scales T{sub FL} and T{sub K} , with the NFL behavior appearing at T{sub FL}=0 K , while T{sub K} remains finite and a smoothly increasing function of J . {copyright} {ital 1999} {ital The American Physical Society}

  14. Generation of diluted magnetic semiconductor nanostructures by pulsed laser ablation in liquid

    NASA Astrophysics Data System (ADS)

    Savchuk, Ol. A.; Savchuk, A. I.; Stolyarchuk, I. D.; Tkachuk, P. M.; Garasym, V. I.

    2015-11-01

    Results of study of two members of diluted magnetic semiconductor (DMS) family, namely Cd1-xMnxTe and Zn1-xMnxO, which are in form of micro- and nanoparticles generated by pulsed laser ablation in liquid medium (PLAL), have been presented. The structural analysis using X-ray diffraction (XRD) of nanocrystals indicated that Mn has entered the AIIBVI lattice without changing the crystal structure and systematically substituted the A2+ ions in the lattice. Atomic force microscopy (AFM) gives information about surface morphology of the formed nanostructures. The scanning electron microscopy (SEM) clearly illustrates flower-like particles of Zn1-xMnxO, which consist of nanosheets and nanoleaves with average thickness about (5-8) nm. Obviously, these nanoobjects are responsible for the observed blue shift of the absorption edge in DMS nanostructures. In magneto-optical Faraday rotation spectra of both Cd1-xMnxTe and Zn1-xMnxO nanostructures there were exhibited peculiarities associated with s,p-d spin exchange interactions and confinement effect. It was observed almost linear dependence of the Faraday rotation as function of magnetic field strength for nanoparticles in contrast to the dependence with saturation in bulk case.

  15. Pressure dependence of the static structure of liquid GeTe based on ab initio molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Koura, Akihide; Shimojo, Fuyuki

    2017-08-01

    We have investigated the pressure dependence of the static structure of liquid GeTe based on ab initio molecular dynamics simulations. The pressure range is between ambient pressure and 250 GPa, and their temperatures between 1000 K and 4000 K, which keep the liquid state. In this study, we found two transition stages caused by the compression. At the first stage, below 12 GPa, atomic distances elongate and Peierls-type distortion is dissolved with increasing pressure. At the second stage, above 12 GPa, atomic distances shorten and the electronic states shows metallic.

  16. Dreams and Reality of Using Naked Ge Detectors in Liquid Nitrogen Status (Long-Term Stability) of GENIUS-TF

    NASA Astrophysics Data System (ADS)

    Krivosheina, Irina V.; Klapdor-Kleingrothaus, Hans V.

    2008-04-01

    GENIUS-TF-II is a setup of six naked high purity Ge detectors (15 kg) in liquid nitrogen in Gran Sasso. It has been installed in October, 2004 - after the first four naked Ge detectors had been installed on May 5, 2003 (GENIUS-TF-I). The GENIUS-Test-Facility (GENIUS-TF) is the first and up to now only setup ever testing the novel technique aiming at extreme background reduction in search for rare decays in particular underground. The goal of GENIUS-TF was to test some key operational parameters of the full GENIUS project in 1997.1-6 Simultaneous physical goal was to search for the annual modulation of the Dark Matter signal.12,25 After operation of GENIUS-TF over three years with finally six naked Ge detectors (15 kg) in liquid nitrogen in Gran Sasso we realize serious problems for realization of a full-size GENIUS-like experiment: 1. Background from 222Rn diffusing into the setup, on a level far beyond the expectation. 2. Limited long-term stability of naked detectors in liquid nitrogen as result of increasing leakage current. None of the six detectors is running after three years with the nominal leakage current. Three of the six detectors do not work any more at all. The results of our three years of investigation of the long-term stability casts serious doubt on the possibility to perform a full GENIUS project - or its copies GERDA or CAMEO/GEM.

  17. Enhanced photorefractive effect in liquid crystal structures co-doped with semiconductor quantum dots and metallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Anczykowska, A.; Bartkiewicz, S.; Nyk, M.; Myśliwiec, J.

    2011-11-01

    In this paper, we present strong enhancement of optical properties of hybrid liquid crystal structures functionalized with metallic and semiconductor nanoparticles. Several experiments done in two wave mixing experimental set-up have reported that diffraction efficiency can be improved by up to 14 times by introducing nanoparticles of cadmium selenide or gold into the photoconducting polymer adjacent to the liquid crystal layer. Our research may open up a possible route for the development of faster and more efficient holographic materials which can be used in dynamic data processing systems.

  18. Physical characteristics modification of a SiGe-HBT semiconductor device for performance improvement in a terahertz detecting system

    NASA Astrophysics Data System (ADS)

    Ghodsi, Hamed; Kaatuzian, Hassan

    2015-05-01

    In order to improve the performance of a pre-designed direct conversion terahertz detector which is implemented in a 0.25 μm-SiGe-BiCMOS process, we propose some slight modifications in the bipolar section of the SiGe device physical design. Comparison of our new proposed device and the previously reported device is done by SILVACO TCAD software simulation and we have used previous experimentally reported data to confirm our software simulations. Our proposed modifications in device structural design show a present device responsivity improvement of about 10% from 1 to 1.1 A/W while the bandwidth improvement is about 218 GHz. The minimum noise equivalent power at detector output is increased by about 14.3% and finally power consumption per pixel at the maximum responsivity is decreased by about 5%.

  19. Charge noise analysis of metal oxide semiconductor dual-gate Si/SiGe quantum point contacts

    SciTech Connect

    Kamioka, J.; Oda, S.; Kodera, T.; Takeda, K.; Obata, T.; Tarucha, S.

    2014-05-28

    The frequency dependence of conductance noise through a gate-defined quantum point contact fabricated on a Si/SiGe modulation doped wafer is characterized. The 1/f{sup 2} noise, which is characteristic of random telegraph noise, is reduced by application of a negative bias on the global top gate to reduce the local gate voltage. Direct leakage from the large global gate voltage also causes random telegraph noise, and therefore, there is a suitable point to operate quantum dot measurement.

  20. Improved electrical properties of Ge metal-oxide-semiconductor capacitors with high-k HfO2 gate dielectric by using La2O3 interlayer sputtered with/without N2 ambient

    NASA Astrophysics Data System (ADS)

    Xu, H. X.; Xu, J. P.; Li, C. X.; Lai, P. T.

    2010-07-01

    The electrical properties of n-Ge metal-oxide-semiconductor (MOS) capacitors with HfO2/LaON or HfO2/La2O3 stacked gate dielectric (LaON or La2O3 as interlayer) are investigated. It is found that better electrical performances, including lower interface-state density, smaller gate leakage current, smaller capacitance equivalent thickness, larger k value, and negligible C-V frequency dispersion, can be achieved for the MOS device with LaON interlayer. The involved mechanism lies in that the LaON interlayer can effectively block the interdiffusions of Ge, O, and Hf, thus suppressing the growth of unstable GeOx interlayer and improving the dielectric/Ge interface quality.

  1. Macroporous Semiconductors

    PubMed Central

    Föll, Helmut; Leisner, Malte; Cojocaru, Ala; Carstensen, Jürgen

    2010-01-01

    Pores in single crystalline semiconductors come in many forms (e.g., pore sizes from 2 nm to > 10 µm; morphologies from perfect pore crystal to fractal) and exhibit many unique properties directly or as nanocompounds if the pores are filled. The various kinds of pores obtained in semiconductors like Ge, Si, III-V, and II-VI compound semiconductors are systematically reviewed, emphasizing macropores. Essentials of pore formation mechanisms will be discussed, focusing on differences and some open questions but in particular on common properties. Possible applications of porous semiconductors, including for example high explosives, high efficiency electrodes for Li ion batteries, drug delivery systems, solar cells, thermoelectric elements and many novel electronic, optical or sensor devices, will be introduced and discussed.

  2. Lateral solidification of a liquid crystalline semiconductor film induced by temperature gradient

    NASA Astrophysics Data System (ADS)

    Hoshino, Tomoya; Ito, Hayato; Fujieda, Ichiro; Hanasaki, Tomonori

    2013-09-01

    Derivatives of [1]benzothieno[3,2-b]benzothiophene (BTBT) are attracting much attention as a highly soluble, highmobility semiconductor material for thin-film transistor applications. These small molecules are known to organize themselves into a single crystalline structure after spin coating or drop casting. Charge transport in a single crystal material is anisotropic in nature. Hence, it is desired to control its orientation during growth or recrystallization so that the source and drain electrodes of a transistor are to be placed along a faster transport direction. We propose to generate temperature gradient in a heated liquid crystalline thin film to induce lateral recrystallization. In experiment, we tried two methods. First, an aluminum plate with two narrow ridges was inserted between a temperature-controlled stage and a square silicon substrate with a 200nm-thick SiO2 and a spin-coated C8-BTBT film. We raised the temperature of the stage to 120oC and let it cool gradually. During cooling at around 105oC , the color of the sample started to change, indicating a phase change. This change proceeded from the corners of the film and in about 30 seconds, darker regions merged at the center of the substrate. Second, the sample was placed at the edge of the stage. In this case, the color change started from the protruding corner of the sample and proceeded toward the other end. Micrograph observation revealed that cracks were formed in these films and they were perpendicular to the direction of the phase change.

  3. Nature of an intermediate non-Fermi liquid state in Ge-substituted YbRh2Si2: Fermionized skyrmions, Lifshitz transition, skyrmion liquid, and Gruneisen ratio

    NASA Astrophysics Data System (ADS)

    Kim, Ki-Seok

    2012-10-01

    We propose a skyrmion liquid state for the non-Fermi liquid (NFL) phase in Ge-substituted YbRh2Si2, where skyrmions form their Fermi surface, argued to result from the strongly coupled nature between skyrmions and itinerant electrons. The fermionized skyrmion theory identifies the antiferromagnetic (AF) transition with the Lifshitz transition, where the quantum critical point (QCP) is characterized by the dynamical critical exponent z=2. Nonlocal interactions between skyrmions allow a critical line above the AF QCP, which originates from the Kondo-coupling effect with itinerant electrons. This critical line is described by the skyrmion liquid state, which results in Landau damping for spin fluctuations, thus characterized by z=3. As a result, the Gruneisen ratio is predicted to change from ˜T-1 at the AF QCP to ˜T-2/3 in the NFL phase.

  4. Pulsed-laser-induced damage in semiconductors Ge, ZnS, and ZnSe at 10.6um

    NASA Astrophysics Data System (ADS)

    Lefranc, Sebastian; Kudriavtsev, Eugene M.; Autric, Michel L.

    1998-04-01

    Laser irradiation induced damage to several materials of interest for use as 10.6 micrometers laser system windows is investigated in this paper. The irradiation source in these single shot experiments was a pulsed TEA CO2 laser. Damage initiation in semiconductors has been studied during the interaction by measuring the variation of the transmitted intensity of a He- Ne and a CO2 cw lasers through the samples. Results show that damages appear at the beginning of the laser-matter interaction process on both surfaces and in the bulk of the materials. The damaged materials have been characterized for various incident fluences by means of optical microscopy and scanning electron microscopy in terms of topography and morphology. The modified surface chemical analysis and the structural analysis have been carried out using energy dispersive x-ray and Raman spectroscopy.

  5. Investigation of size effects on the structure of liquid GeSe2 calculated via first-principles molecular dynamics.

    PubMed

    Micoulaut, Matthieu; Le Roux, Sébastien; Massobrio, Carlo

    2012-06-14

    The structural properties of liquid GeSe(2) have been calculated by first-principles molecular dynamics by using a periodic simulation box containing N = 480 atoms. This has allowed a comparison with previous results obtained on a smaller system size (N = 120) [M. Micoulaut, R. Vuilleumier, and C. Massobrio, Phys. Rev. B 79, 214205 (2009)]. In the domain of first-principles molecular dynamics, we obtain an assessment of system size effects of unprecedented quality. Overall, no drastic differences are found between the two sets of results, confirming that N = 120 is a suitable size to achieve a realistic description of this prototypical disordered network. However, for N = 480, short range properties are characterized by an increase of chemical order, the number of Ge tetrahedra coordinated to four Se atoms being larger. At the intermediate range order level, size effect mostly modify the low wavevector region (k ~1 Å(-1)) in the concentration-concentration partial structure factor.

  6. Thermal and Optical Modulation of the Carrier Mobility in OTFTs Based on an Azo-anthracene Liquid Crystal Organic Semiconductor.

    PubMed

    Chen, Yantong; Li, Chao; Xu, Xiuru; Liu, Ming; He, Yaowu; Murtaza, Imran; Zhang, Dongwei; Yao, Chao; Wang, Yongfeng; Meng, Hong

    2017-03-01

    One of the most striking features of organic semiconductors compared with their corresponding inorganic counterparts is their molecular diversity. The major challenge in organic semiconductor material technology is creating molecular structural motifs to develop multifunctional materials in order to achieve the desired functionalities yet to optimize the specific device performance. Azo-compounds, because of their special photoresponsive property, have attracted extensive interest in photonic and optoelectronic applications; if incorporated wisely in the organic semiconductor groups, they can be innovatively utilized in advanced smart electronic applications, where thermal and photo modulation is applied to tune the electronic properties. On the basis of this aspiration, a novel azo-functionalized liquid crystal semiconductor material, (E)-1-(4-(anthracen-2-yl)phenyl)-2-(4-(decyloxy)phenyl)diazene (APDPD), is designed and synthesized for application in organic thin-film transistors (OTFTs). The UV-vis spectra of APDPD exhibit reversible photoisomerizaton upon photoexcitation, and the thin films of APDPD show a long-range orientational order based on its liquid crystal phase. The performance of OTFTs based on this material as well as the effects of thermal treatment and UV-irradiation on mobility are investigated. The molecular structure, stability of the material, and morphology of the thin films are characterized by thermal gravimetric analysis (TGA), polarizing optical microscopy (POM), (differential scanning calorimetry (DSC), UV-vis spectroscopy, atomic force microscopy (AFM), and scanning tunneling microscopy (STM). This study reveals that our new material has the potential to be applied in optical sensors, memories, logic circuits, and functional switches.

  7. Ge{sub 0.83}Sn{sub 0.17} p-channel metal-oxide-semiconductor field-effect transistors: Impact of sulfur passivation on gate stack quality

    SciTech Connect

    Lei, Dian; Wang, Wei; Gong, Xiao E-mail: yeo@ieee.org; Liang, Gengchiau; Yeo, Yee-Chia E-mail: yeo@ieee.org; Zhang, Zheng; Pan, Jisheng; Tok, Eng-Soon

    2016-01-14

    The effect of room temperature sulfur passivation of the surface of Ge{sub 0.83}Sn{sub 0.17} prior to high-k dielectric (HfO{sub 2}) deposition is investigated. X-ray photoelectron spectroscopy (XPS) was used to examine the chemical bonding at the interface of HfO{sub 2} and Ge{sub 0.83}Sn{sub 0.17}. Sulfur passivation is found to be effective in suppressing the formation of both Ge oxides and Sn oxides. A comparison of XPS results for sulfur-passivated and non-passivated Ge{sub 0.83}Sn{sub 0.17} samples shows that sulfur passivation of the GeSn surface could also suppress the surface segregation of Sn atoms. In addition, sulfur passivation reduces the interface trap density D{sub it} at the high-k dielectric/Ge{sub 0.83}Sn{sub 0.17} interface from the valence band edge to the midgap of Ge{sub 0.83}Sn{sub 0.17}, as compared with a non-passivated control. The impact of the improved D{sub it} is demonstrated in Ge{sub 0.83}Sn{sub 0.17} p-channel metal-oxide-semiconductor field-effect transistors (p-MOSFETs). Ge{sub 0.83}Sn{sub 0.17} p-MOSFETs with sulfur passivation show improved subthreshold swing S, intrinsic transconductance G{sub m,int}, and effective hole mobility μ{sub eff} as compared with the non-passivated control. At a high inversion carrier density N{sub inv} of 1 × 10{sup 13 }cm{sup −2}, sulfur passivation increases μ{sub eff} by 25% in Ge{sub 0.83}Sn{sub 0.17} p-MOSFETs.

  8. Kinetics of liquid-mediated crystallization of amorphous Ge from multi-frame dynamic transmission electron microscopy

    SciTech Connect

    Santala, M. K. Campbell, G. H.; Raoux, S.

    2015-12-21

    The kinetics of laser-induced, liquid-mediated crystallization of amorphous Ge thin films were studied using multi-frame dynamic transmission electron microscopy (DTEM), a nanosecond-scale photo-emission transmission electron microscopy technique. In these experiments, high temperature gradients are established in thin amorphous Ge films with a 12-ns laser pulse with a Gaussian spatial profile. The hottest region at the center of the laser spot crystallizes in ∼100 ns and becomes nano-crystalline. Over the next several hundred nanoseconds crystallization continues radially outward from the nano-crystalline region forming elongated grains, some many microns long. The growth rate during the formation of these radial grains is measured with time-resolved imaging experiments. Crystal growth rates exceed 10 m/s, which are consistent with crystallization mediated by a very thin, undercooled transient liquid layer, rather than a purely solid-state transformation mechanism. The kinetics of this growth mode have been studied in detail under steady-state conditions, but here we provide a detailed study of liquid-mediated growth in high temperature gradients. Unexpectedly, the propagation rate of the crystallization front was observed to remain constant during this growth mode even when passing through large local temperature gradients, in stark contrast to other similar studies that suggested the growth rate changed dramatically. The high throughput of multi-frame DTEM provides gives a more complete picture of the role of temperature and temperature gradient on laser crystallization than previous DTEM experiments.

  9. Kinetics of liquid-mediated crystallization of amorphous Ge from multi-frame dynamic transmission electron microscopy

    SciTech Connect

    Santala, M. K.; Raoux, S.; Campbell, G. H.

    2015-12-24

    The kinetics of laser-induced, liquid-mediated crystallization of amorphous Ge thin films were studied using multi-frame dynamic transmission electron microscopy (DTEM), a nanosecond-scale photo-emission transmission electron microscopy technique. In these experiments, high temperature gradients are established in thin amorphous Ge films with a 12-ns laser pulse with a Gaussian spatial profile. The hottest region at the center of the laser spot crystallizes in ~100 ns and becomes nano-crystalline. Over the next several hundred nanoseconds crystallization continues radially outward from the nano-crystalline region forming elongated grains, some many microns long. The growth rate during the formation of these radial grains is measured with time-resolved imaging experiments. Crystal growth rates exceed 10 m/s, which are consistent with crystallization mediated by a very thin, undercooled transient liquid layer, rather than a purely solid-state transformation mechanism. The kinetics of this growth mode have been studied in detail under steady-state conditions, but here we provide a detailed study of liquid-mediated growth in high temperature gradients. Unexpectedly, the propagation rate of the crystallization front was observed to remain constant during this growth mode even when passing through large local temperature gradients, in stark contrast to other similar studies that suggested the growth rate changed dramatically. As a result, the high throughput of multi-frame DTEM provides gives a more complete picture of the role of temperature and temperature gradient on laser crystallization than previous DTEM experiments.

  10. Impacts of Ti on electrical properties of Ge metal-oxide-semiconductor capacitors with ultrathin high- k LaTiON gate dielectric

    NASA Astrophysics Data System (ADS)

    Xu, H. X.; Xu, J. P.; Li, C. X.; Chan, C. L.; Lai, P. T.

    2010-06-01

    Ge Metal-Oxide-Semiconductor (MOS) capacitors with LaON gate dielectric incorporating different Ti contents are fabricated and their electrical properties are measured and compared. It is found that Ti incorporation can increase the dielectric permittivity, and the higher the Ti content, the larger is the permittivity. However, the interfacial and gate-leakage properties become poorer as the Ti content increases. Therefore, optimization of Ti content is important in order to obtain a good trade-off among the electrical properties of the device. For the studied range of the Ti/La2O3 ratio, a suitable Ti/La2O3 ratio of 14.7% results in a high relative permittivity of 24.6, low interface-state density of 3.1×1011 eV-1 cm-2, and relatively low gate-leakage current density of 2.0×10-3 A cm-2 at a gate voltage of 1 V.

  11. Pattern dependency in selective epitaxy of B-doped SiGe layers for advanced metal oxide semiconductor field effect transistors

    NASA Astrophysics Data System (ADS)

    Hâllstedt, J.; Kolahdouz, M.; Ghandi, R.; Radamson, H. H.; Wise, R.

    2008-03-01

    This study presents investigations about the physical mechanisms, origin, and methods to control the pattern dependency in selective epitaxial growth of Si1-xGex (x=0.14-0.32) layers. It is shown with a comprehensive experimental study that the local Si coverage of individual chips on patterned wafers is the main parameter for the layer profile in the epitaxial growth. This was explained by the gas depletion of the growth species in the low velocity boundary layer over the wafer. The gas depletion radius around each oxide opening was in the centimeter range which is related to the boundary layer thickness. The results from these experiments were applied to grow Si0.75Ge0.25 layers with B concentration of 4×1020cm-3 selectively for elevated source and drains in fully depleted ultrathin body silicon on insulator p metal oxide semiconductor field effect transistor (p-MOSFET) devices. The epitaxy control was maintained over a wide range of device sizes by optimized process parameters in combination with a wafer pattern design consisting of dummy features causing a uniform gas depletion over the chips on the wafer.

  12. Colloidal synthesis and functional properties of quaternary Cu-based semiconductors: Cu2HgGeSe4

    NASA Astrophysics Data System (ADS)

    Li, Wenhua; Ibáñez, Maria; Cadavid, Doris; Zamani, Reza R.; Rubio-Garcia, Javier; Gorsse, Stéphane; Morante, Joan Ramon; Arbiol, Jordi; Cabot, Andreu

    2014-03-01

    Herein, a colloidal synthetic route to produce highly monodisperse Cu2HgGeSe4 (CHGSe) nanoparticles (NPs) is presented in detail. The high yield of the developed procedure allowed the production of CHGSe NPs at the gram scale. A thorough analysis of their structural and optical properties is shown. CHGSe NPs displayed poly-tetrahedral morphology and narrow size distributions with average size in the range of 10-40 nm and size dispersions below 10 %. A 1.6 eV optical band gap was measured by mean of UV-Vis. By adjusting the cation ratio, an effective control of their electrical conductivity is achieved. The prepared NPs are used as building blocks for the production of CHGSe bulk nanostructured materials. The thermoelectric properties of CHGSe nanomaterials are studied in the temperature range from 300 to 730 K. CHGSe nanomaterials reached electrical conductivities up to 5 × 104 S m-1, Seebeck coefficients above 100 μV K-1, and thermal conductivities below 1.0 W m-1 K-1 which translated into thermoelectric figures of merit up to 0.34 at 730 K.

  13. REMGa3Ge and RE3Ni3Ga8Ge3 (M = Ni, Co; RE = rare-earth element): new intermetallics synthesized in liquid gallium. X-ray, electron, and neutron structure determination and magnetism.

    PubMed

    Zhuravleva, Marina A; Pcionek, Robert J; Wang, Xiaoping; Schultz, Arthur J; Kanatzidis, Mercouri G

    2003-10-06

    New quaternary intermetallic phases REMGa(3)Ge (1) (RE = Y, Sm, Tb, Gd, Er, Tm; M = Ni, Co) and RE(3)Ni(3)Ga(8)Ge(3) (2) (RE = Sm, Gd) were obtained from exploratory reactions involving rare-earth elements (RE), transition metal (M), Ge, and excess liquid Ga the reactive solvent. The crystal structures were solved with single-crystal X-ray and electron diffraction. The crystals of 1 and 2 are tetragonal. Single-crystal X-ray data: YNiGa(3)Ge, a = 4.1748(10) A, c = 23.710(8) A, V = 413.24(2) A(3), I4/mmm, Z = 4; Gd(3)Ni(3)Ga(8)Ge(3), a = 4.1809(18) A, c = 17.035(11) A, V = 297.8(3) A(3), P4/mmm, Z = 1. Both compounds feature square nets of Ga atoms. The distribution of Ga and Ge atoms in the REMGa(3)Ge was determined with neutron diffraction. The neutron experiments revealed that in 1 the Ge atoms are specifically located at the 4e crystallographic site, while Ga atoms are at 4d and 8g. The crystal structures of these compounds are related and could be derived from the consecutive stacking of disordered [MGa](2) puckered layers, monatomic RE-Ge planes and [MGa(4)Ge(2)] slabs. Complex superstructures with modulations occurring in the ab-plane and believed to be associated with the square nets of Ga atoms were found by electron diffraction. The magnetic measurements show antiferromagnetic ordering of the moments located on the RE atoms at low temperature, and Curie-Weiss behavior at higher temperatures with the values of mu(eff) close to those expected for RE(3+) free ions.

  14. Does a network structure exist in molecular liquid SnI4 and GeI4?

    NASA Astrophysics Data System (ADS)

    Sakagami, Takahiro; Fuchizaki, Kazuhiro

    2017-04-01

    The existence of a network structure consisting of electrically neutral tetrahedral molecules in liquid SnI4 and GeI4 at ambient pressure was examined. The liquid structures employed for the examination were obtained from a reverse Monte Carlo analysis. The structures were physically interpreted by introducing an appropriate intermolecular interaction. A ‘bond’ was then defined as an intermolecular connection that minimizes the energy of intermolecular interaction. However, their ‘bond’ energy is too weak for the ‘bond’ and the resulting network structure to be defined statically. The vertex-to-edge orientation between the nearest molecules is so ubiquitous that almost all of the molecules in the system can take part in the network, which is reflected in the appearance of a prepeak in the structure factor.

  15. Liquid nitrogen tests of a Torus coil for the Jefferson Lab 12GeV accelerator upgrade

    SciTech Connect

    Fair, Ruben J.; Ghoshal, Probir K.; Bruhwel, Krister B.; Kashy, David H.; Machie, Danny; Bachimanchi, Ramakrishna; Taylor, William; Fischer, John W.; Legg, Robert A.; Powers, Jacob R.

    2015-06-01

    A magnet system consisting of six superconducting trapezoidal racetrack-type coils is being built for the Jefferson Lab 12-GeV accelerator upgrade project. The magnet coils are wound with Superconducting Super Collider-36 NbTi strand Rutherford cable soldered into a copper channel. Each superconducting toroidal coil is force cooled by liquid helium, which circulates in a tube that is in good thermal contact with the inside of the coil. Thin copper sheets are soldered to the helium cooling tube and enclose the superconducting coil, providing cooling to the rest of the coil pack. As part of a rigorous risk mitigation exercise, each of the six coils is cooled with liquid nitrogen (LN2) to 80 K to validate predicted thermal stresses, verify the robustness and integrity of electrical insulation, and evaluate the efficacy of the employed conduction cooling method. This paper describes the test setup, the tests performed, and the findings.

  16. Synthesis of doped semiconductor nanostructures using microemulsions and liquid crystals as templates

    NASA Astrophysics Data System (ADS)

    Panzarella, Tracy Heckler

    Semiconductor nanocrystals, also known as quantum dots (QDs), are a relatively new class of materials with unique size-dependent optical properties that enable the use of these materials in a variety of applications, including fluorescent labels for biomolecules, illumination and display technologies and photovoltaics. When the size of the QD is smaller than the mean separation of an optically excited electron-hole pair, or exciton, size-dependent fluorescence is observed as their emission peak shifts to larger wavelengths with increasing size. Doping of QDs with transition metals enables the tuning of their optoelectronic properties, leading to emission wavelengths longer than their bulk emission. The doping of QDs has recently garnered significant attention because it allows for the ability to tune the QD emission without changing its size. Currently, the most common method for synthesizing QDs involves the injection of organometallic precursors into hot coordinating solvents. To obtain monodisperse nanocrystals with this technique, instantaneous injection of the reactants, uniform nucleation over the entire reactor volume and perfect mixing are required. These conditions are difficult to achieve in practice, and even more difficult in a scaled-up reactor system necessary for commercial applications. The use of microemulsions as templates can enable the synthesis of semiconductor nanocrystals of uniform size and shape, and allow for scalability. The template used in this work consists of para-xylene as the continuous phase, water as the dispersed phase, and a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO37-PPO56-PEO37) block copolymer as the surfactant, with the reactants dissolved in the aqueous dispersed phase. Microemulsions formed by this technique, exhibit very slow droplet to droplet coalescence kinetics and allow for the growth of particles with narrow size distribution. A microemulsion template was used to synthesize Mn-doped Zn

  17. Deep-blue light emission with a wide-bandgap naphthalene-derivative liquid organic semiconductor host

    NASA Astrophysics Data System (ADS)

    Kobayashi, Naofumi; Kuwae, Hiroyuki; Oshima, Juro; Ishimatsu, Ryoichi; Tashiro, Shuya; Imato, Toshihiko; Adachi, Chihaya; Shoji, Shuichi; Mizuno, Jun

    2017-02-01

    We developed a novel naphthalene-derivative to function as a wide-bandgap liquid organic semiconductor (LOS) host material for the limited range of liquid deep-blue light-emitting materials that have been developed to date. The naphthalene-derivative, 1-naphthaleneacetic acid 2-ethylhexyl ester (NLQ) was synthesized as a LOS, by introducing an ethylhexyl group into naphthalene. 9,10-Diphenyl anthracene (DPA) was doped into NLQ as a guest deep-blue dye. From the absorption spectrum, the bandgap energy of NLQ was estimated to be 4.13 eV, indicating that NLQ has the widest bandgap energy of any such host material so far as we know. Deep-blue electroluminescence (EL) emission in a liquid state was obtained by doping DPA into NLQ. Light emission could be achieved by a combination of Förster resonance energy transfer and direct recombination of trapped holes and electrons because the bandgap energy of DPA is straddle by that of the wide-bandgap NLQ. Thus, NLQ is shown to be a promising wide-bandgap LOS host material, which allows deep-blue light emission and may have applications in liquid organic light-emitting diodes.

  18. Kinetics of liquid-mediated crystallization of amorphous Ge from multi-frame dynamic transmission electron microscopy

    DOE PAGES

    Santala, M. K.; Raoux, S.; Campbell, G. H.

    2015-12-24

    The kinetics of laser-induced, liquid-mediated crystallization of amorphous Ge thin films were studied using multi-frame dynamic transmission electron microscopy (DTEM), a nanosecond-scale photo-emission transmission electron microscopy technique. In these experiments, high temperature gradients are established in thin amorphous Ge films with a 12-ns laser pulse with a Gaussian spatial profile. The hottest region at the center of the laser spot crystallizes in ~100 ns and becomes nano-crystalline. Over the next several hundred nanoseconds crystallization continues radially outward from the nano-crystalline region forming elongated grains, some many microns long. The growth rate during the formation of these radial grains is measuredmore » with time-resolved imaging experiments. Crystal growth rates exceed 10 m/s, which are consistent with crystallization mediated by a very thin, undercooled transient liquid layer, rather than a purely solid-state transformation mechanism. The kinetics of this growth mode have been studied in detail under steady-state conditions, but here we provide a detailed study of liquid-mediated growth in high temperature gradients. Unexpectedly, the propagation rate of the crystallization front was observed to remain constant during this growth mode even when passing through large local temperature gradients, in stark contrast to other similar studies that suggested the growth rate changed dramatically. As a result, the high throughput of multi-frame DTEM provides gives a more complete picture of the role of temperature and temperature gradient on laser crystallization than previous DTEM experiments.« less

  19. Low-temperature growth of fully epitaxial CoFe/Ge/Fe3Si layers on Si for vertical-type semiconductor spintronic devices

    NASA Astrophysics Data System (ADS)

    Sakai, S.; Kawano, M.; Ikawa, M.; Sato, H.; Yamada, S.; Hamaya, K.

    2017-09-01

    We develop a low-temperature growth technique of epitaxial Ge layers on a body-centered-cubic ferromagnetic metal (bcc-FM), Fe3Si, by combining solid phase epitaxy (SPE) and molecular beam epitaxy (MBE). The insertion of an SPE-grown Ge layer enables two-dimensional epitaxial growth of Ge layers by MBE even at a growth temperature of ∼175 {}\\circ C. Thanks to the relatively flat surface of the Ge epilayers, we can obtain an epitaxial CoFe (bcc-FM) layer on top of the Ge layers, leading to the all-epitaxial CoFe/Ge/Fe3Si trilayer with a reasonable magnetization reversal process. We believe that the all-epitaxial CoFe/Ge/Fe3Si trilayer has great potential to be utilized as novel vertical-type Ge-channel spintronic devices.

  20. ZnMnO diluted magnetic semiconductor nanoparticles: Synthesis by laser ablation in liquids, optical and magneto-optical properties

    NASA Astrophysics Data System (ADS)

    Savchuk, A. I.; Perrone, A.; Lorusso, A.; Stolyarchuk, I. D.; Savchuk, O. A.; Shporta, O. A.

    2014-05-01

    Nanoparticles of ZnO and Zn1-xMnxO were synthesized by pulsed laser ablation in liquid medium (PLAL). Metal zinc target was used for preparing of pure ZnO nanostructures and Zn1-xMnxO ceramic plates served for preparing of ternary nanoparticles. As synthesized nanomaterials are characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy analysis (EDS), atomic force microscopy (AFM), UV-vis absorption, photoluminescence and Faraday rotation spectroscopy. SEM images showed a well-defined flower-like nanostructures. Absorption edge of Zn0.95Mn0.05O nanoparticles in colloid solution exhibits blue shift due to confinement effect. The observed photoluminescence peaks are attributed to the band-edge transitions and vacancies or defects. The Faraday rotation as a function of photon energy demonstrates behavior typical for diluted magnetic semiconductors (DMSs) in paramagnetic state.

  1. Determination of the electrical conductivity of liquid Ge(0.95)Si(0.05)

    NASA Technical Reports Server (NTRS)

    Rolin, T. D.; Szofran, F. R.

    1995-01-01

    We have measured the electrical conductivity of molten germanium-silicon Ge(0.95)Si(0.05) from the liquidus temperature (1050 C) up to 1220 C. The data were acquired with a unique apparatus which utilizes the standard four-probe technique. The basic unit consists of a fused silica enclosure that contains hermetic glass-to-tungsten seals that can support vacuum pressures down to 10(exp -7) Torr. With calibration, the measurement error for the low vapor pressure materials of this study was typically less than 7%. The temperature dependence of the electrical conductivity of a Ge(0.95)Si(0.05) melt was found to vary from approximately 22,300/ohm/cm at the liquidus temperature down to approximately 16,000/ohm/cm at 1220 C. The negative temperature coefficient as well as the magnitude of these data clearly indicate that the molten material is metallic in nature despite the semiconducting properties of the solid.

  2. Determination of the electrical conductivity of liquid Ge(0.95)Si(0.05)

    NASA Technical Reports Server (NTRS)

    Rolin, T. D.; Szofran, F. R.

    1995-01-01

    We have measured the electrical conductivity of molten germanium-silicon Ge(0.95)Si(0.05) from the liquidus temperature (1050 C) up to 1220 C. The data were acquired with a unique apparatus which utilizes the standard four-probe technique. The basic unit consists of a fused silica enclosure that contains hermetic glass-to-tungsten seals that can support vacuum pressures down to 10(exp -7) Torr. With calibration, the measurement error for the low vapor pressure materials of this study was typically less than 7%. The temperature dependence of the electrical conductivity of a Ge(0.95)Si(0.05) melt was found to vary from approximately 22,300/ohm/cm at the liquidus temperature down to approximately 16,000/ohm/cm at 1220 C. The negative temperature coefficient as well as the magnitude of these data clearly indicate that the molten material is metallic in nature despite the semiconducting properties of the solid.

  3. 200 A GeV Au + Au collisions serve a nearly perfect quark-gluon liquid.

    PubMed

    Song, Huichao; Bass, Steffen A; Heinz, Ulrich; Hirano, Tetsufumi; Shen, Chun

    2011-05-13

    A new robust method to extract the specific shear viscosity (η/s)(QGP) of a quark-gluon plasma (QGP) at temperatures T(c) < T ≲ 2T(c) from the centrality dependence of the eccentricity-scaled elliptic flow v2/ε measured in ultrarelativistic heavy-ion collisions is presented. Coupling viscous fluid dynamics for the QGP with a microscopic transport model for hadronic freeze-out we find for 200 A GeV Au + Au collisions that v2/ε is a universal function of multiplicity density (1/S)(dN(ch)/dy) that depends only on the viscosity but not on the model used for computing the initial fireball eccentricity ε. Comparing with measurements we find 1<4π(η/s)(QGP) < 2.5 where the uncertainty range is dominated by model uncertainties for the values of ε used to normalize the measured v2.

  4. Semiconductor electrodes. 32. n- and p-GaAs, n- and p-Si, and n-TiO/sub 2/ in liquid ammonia

    SciTech Connect

    Malpas, R.E.; Itaya, K.; Bard, A.J.

    1981-04-08

    The behavior of several n- and p-type semiconductors in liquid ammonia with 0.1 M KI as supporting electrolyte was investigated. The flat-band potentials were estimated from Schottky-Mott plots, and the current-potential curves with several redox couples (e.g., benzophenone, naphthalene, nitrobenzene) in the dark and under illumination were obtained. Photoinjection of solvated electrons at p-GaAs and p-Si was demonstrated, and the results with these materials were shown to be consistent with those from the Fermi level pinning model. Solvated electron photovoltaic cells with these semiconductors were also constructed.

  5. Dynamic gratings recording in liquid crystal light valve with semiconductor substrate

    NASA Astrophysics Data System (ADS)

    Shcherbin, Konstantin; Gvozdovskyy, Igor; Evans, Dean R.

    2016-03-01

    Liquid crystal light valve with GaAs substrate operating in the transmission mode in the infrared is studied. The nonlinear phase shift of the transmitted light wave is measured as a function of applied voltage. The dynamic grating recording is achieved. A fourfold amplification of the weak signal beam is reached. The gain is increased by means of proper tilting of the cell that increases an effective pretilt of the liquid crystal molecules. The amplitude of the refractive index modulation and nonlinear coupling constant are estimated from the experimental results.

  6. Molecular approaches to p- and n-nanoscale doping of Ge 1-ySn y semiconductors: Structural, electrical and transport properties

    NASA Astrophysics Data System (ADS)

    Xie, Junqi; Tolle, J.; D'Costa, V. R.; Weng, C.; Chizmeshya, A. V. G.; Menendez, J.; Kouvetakis, J.

    2009-08-01

    We report the development of practical doping protocols via designer molecular sources to create n- and p-type doped Ge 1-ySn y layers grown directly upon Si(1 0 0). These materials will have applications in the fabrication of advanced PIN devices that are intended to extend the infrared optical response beyond that of Ge by utilizing the Sn composition as an additional design parameter. Highly controlled and efficient n-doping of single-layer structures is achieved using custom built P(GeH 3) 3 and As(GeH 3) 3, precursors containing preformed Ge-As and Ge-P near-tetrahedral bonding arrangements compatible with the structure of the host Ge-Sn lattice. Facile substitution and complete activation of the P and As atoms at levels ˜10 17-10 19 cm -3 is obtained via in situ depositions at low temperatures (350 °C). Acceptor doping is readily achieved using conventional diborane yielding carrier concentrations between 10 17-10 19 cm -3 under similar growth conditions. Full activation of the as-grown dopant concentrations is demonstrated by combined SIMS and Hall experiments, and corroborated using a contactless spectroscopic ellipsometry approach. RTA processing of the samples leads to a significant increase in carrier mobility comparable to that of bulk Ge containing similar doping levels. The alloy scattering contribution appears to be negligible for electron carrier concentrations beyond 10 19 cm -3 in n-type samples and hole concentrations beyond 10 18 cm -3 in p-type samples. A comparative study using the classical lower-order hydrides PH 3 and AsH 3 produced n-doped films with carrier densities (up to 9 × 10 19 cm -3) similar to those afforded by P(GeH 3) 3 and As(GeH 3) 3. However, early results indicate that the simpler PH 3 and AsH 3 sources yield materials with inferior morphology and microstructure. Calculations of surface energetics using bond enthalpies suggest that the latter massive compounds bind to the surface via strong Ge-Ge bonds and likely act as

  7. Synthesis and Structural and Optical Properties of Ga(As1-xPx)Ge3 and (GaP)yGe5-2y Semiconductors Using Interface-Engineered Group IV Platforms.

    PubMed

    Wallace, Patrick M; Sims, Patrick E; Xu, Chi; Poweleit, Christian D; Kouvetakis, John; Menéndez, José

    2017-09-26

    Epitaxial synthesis of Ga(As1-xPx)Ge3 alloys on Si(100) substrates is demonstrated using chemical vapor deposition reactions of [D2GaN(CH3)2]2 with P(GeH3)3 and As(GeH3)3 precursors. These compounds are chosen to promote the formation of GaAsGe3 and GaPGe3 building blocks which interlink to produce the desired crystalline product. Ge-rich (GaP)yGe5-2y analogues have also been grown with tunable Ge contents up to 90% by reactions of P(GeH3)3 with [D2GaN(CH3)2]2 under similar deposition protocols. In both cases, the crystal growth utilized Ge1-xSix buffer layers whose lattice constants were specifically tuned as a function of composition to allow perfect lattice matching with the target epilayers. This approach yielded single-phase materials with excellent crystallinity devoid of mismatch-induced dislocations. The lattice parameters of Ga(As1-xPx)Ge3 interpolated among the Ge, GaAs, and GaP end members, corroborating the Rutherford backscattering measurements of the P/As ratio. A small deviation from the Vegard's law that depends on the As/P ratio was observed and corroborated by ab initio calculations. Raman scattering shows evidence for the existence of Ga-As and Ga-P bonds in the Ge matrix. The As-rich samples exhibited photoluminescence with wavelengths similar to those observed for pure GaAsGe3, indicating that the emission profile does not change in any measurable manner by replacing As by P over a broad range up to x = 0.2. Furthermore, the photoluminescence (PL) data suggested a large negative bowing of the band gap as expected on account of a strong valence band localization on the As atoms. Spectroscopic ellipsometry measurements of the dielectric function revealed a distinct direct gap transition that closely matches the PL emission energy. These measurements also showed that the absorption coefficients can be systematically tuned as a function of composition, indicating possible applications of the new materials in optoelectronics, including photovoltaics.

  8. Topological characteristics of bonds in SiO{sub 2} and GeO{sub 2} oxide systems upon a glass-liquid transition

    SciTech Connect

    Ozhovan, M. I.

    2006-11-15

    Using the Angell model of broken bonds (configurons), configuron clustering in a topologically disordered lattice (network) of amorphous SiO{sub 2} and GeO{sub 2} upon a glass-liquid transition is considered. It is shown that the glass-liquid transition is accompanied by the formation of a macroscopic (percolation) configuron cluster penetrating the entire bulk of the material and possessing fractal geometry. The glass-liquid (overcooled liquid) percolation phase transition in the amorphous substance is accompanied by a change in the Hausdorff dimension of the bond network structure for configurons from the three-dimensional Euclidean dimension in the glassy state to a fractal dimension of 2.55 {+-} 0.05 in the liquidlike state. Contrary to the kinetic character of the liquid-glass transition, the glass-transition temperature is a thermodynamic parameter of the amorphous substance, depending parametrically on the cooling rate.

  9. Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals.

    PubMed

    Carey, Benjamin J; Ou, Jian Zhen; Clark, Rhiannon M; Berean, Kyle J; Zavabeti, Ali; Chesman, Anthony S R; Russo, Salvy P; Lau, Desmond W M; Xu, Zai-Quan; Bao, Qiaoliang; Kevehei, Omid; Gibson, Brant C; Dickey, Michael D; Kaner, Richard B; Daeneke, Torben; Kalantar-Zadeh, Kourosh

    2017-02-17

    A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (∼1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes.

  10. Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals

    NASA Astrophysics Data System (ADS)

    Carey, Benjamin J.; Ou, Jian Zhen; Clark, Rhiannon M.; Berean, Kyle J.; Zavabeti, Ali; Chesman, Anthony S. R.; Russo, Salvy P.; Lau, Desmond W. M.; Xu, Zai-Quan; Bao, Qiaoliang; Kevehei, Omid; Gibson, Brant C.; Dickey, Michael D.; Kaner, Richard B.; Daeneke, Torben; Kalantar-Zadeh, Kourosh

    2017-02-01

    A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (~1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes.

  11. Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals

    PubMed Central

    Carey, Benjamin J.; Ou, Jian Zhen; Clark, Rhiannon M.; Berean, Kyle J.; Zavabeti, Ali; Chesman, Anthony S. R.; Russo, Salvy P.; Lau, Desmond W. M.; Xu, Zai-Quan; Bao, Qiaoliang; Kavehei, Omid; Gibson, Brant C.; Dickey, Michael D.; Kaner, Richard B.; Daeneke, Torben; Kalantar-Zadeh, Kourosh

    2017-01-01

    A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (∼1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes. PMID:28211538

  12. Fabrication of tensile-strained single-crystalline GeSn on transparent substrate by nucleation-controlled liquid-phase crystallization

    NASA Astrophysics Data System (ADS)

    Oka, Hiroshi; Amamoto, Takashi; Koyama, Masahiro; Imai, Yasuhiko; Kimura, Shigeru; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2017-01-01

    We developed a method of forming single-crystalline germanium-tin (GeSn) alloy on transparent substrates that is based on liquid-phase crystallization. By controlling and designing nucleation during the melting growth process, a highly tensile-strained single-crystalline GeSn layer was grown on a quartz substrate without using any crystal-seeds or catalysts. The peak field-effect hole mobility of 423 cm2/V s was obtained for a top-gate single-crystalline GeSn MOSFET on a quartz substrate with a Sn content of 2.6%, indicating excellent crystal quality and mobility enhancement due to Sn incorporation and tensile strain.

  13. Characterization and control of ZnGeN2 cation lattice ordering

    NASA Astrophysics Data System (ADS)

    Blanton, Eric W.; He, Keliang; Shan, Jie; Kash, Kathleen

    2017-03-01

    ZnGeN2 and other heterovalent ternary semiconductors have important potential applications in optoelectronics, but ordering of the cation sublattice, which can affect the band gap, lattice parameters, and phonons, is not yet well understood. Here the effects of growth and processing conditions on the ordering of the ZnGeN2 cation sublattice were investigated using x-ray diffraction and Raman spectroscopy. Polycrystalline ZnGeN2 was grown by exposing solid Ge to Zn and NH3 vapors at temperatures between 758 °C and 914 °C. Crystallites tended to be rod-shaped, with growth rates higher along the c-axis. The degree of ordering, from disordered, wurtzite-like x-ray diffraction spectra to orthorhombic, with space group Pna21, increased with increasing growth temperature, as evidenced by the appearance of superstructure peaks and peak splittings in the diffraction patterns. Annealing disordered, low-temperature-grown ZnGeN2 at 850 °C resulted in increased cation ordering. Growth of ZnGeN2 on a liquid Sn-Ge-Zn alloy at 758 °C showed an increase in the tendency for cation ordering at a lower growth temperature, and resulted in hexagonal platelet-shaped crystals. The trends shown here may help to guide understanding of the synthesis and characterization of other heterovalent ternary nitride semiconductors as well as ZnGeN2.

  14. Dispersions of Semiconductor Nanoparticles in Thermotropic Liquid Crystal: From Optical Modification to Assisted Self-Assembly

    NASA Astrophysics Data System (ADS)

    Rodarte, Andrea L.

    The interaction of semiconducting quantum dot nanoparticles (QDs) within thermotropic liquid crystalline (LC) materials are studied in this thesis. LC materials are ideal for bottom-up organization of nanoparticles as an active matrix that can be externally manipulated via electric or magnetic fields. In addition, the optical properties of QDs can be modified by the surrounding LC resulting in novel devices such as a quantum dot/liquid crystal laser. The first system studies the dispersion of spherical nanoparticles in the phase. The dispersion is investigated with the use of polarized optical microscopy, fluorescence microscopy and confocal scanning microscopy. Quantum dots well dispersed in the isotropic phase are expelled from ordered domains of LC at the phase transition. Under controlled conditions, the majority of QDs in the system can form ordered three dimensional assemblies that are situated at defect points in the liquid crystal. The internal order of the assemblies is probed utilizing Forster resonance energy transfer (FRET), combined with small angle X-ray scattering (SAXS). Furthermore, the location of these assemblies can be predetermined with the use of beads as defect nucleation points in the cell. The interaction of QDs in a cholesteric liquid crystal (CLC) is also investigated. The reflection band created by the periodic change of index of refraction in a planar aligned CLC acts as a 1-D photonic cavity when the CLC is doped with a low concentration of QDs. A Cano-wedge cell varies the pitch of the CLC leading to the formation of Grandjean steps. This spatially tunes the photonic stop band, changing the resonance condition and continuously altering both the emission wavelength and polarization state of the QD ensemble. Using high resolution spatially and spectrally resolved photoluminescence measurements, the emission is shown to be elliptically polarized and that the tilt of the ellipse, while dependent on the emission wavelength, additionally

  15. Growing 3C-SiC heteroepitaxial layers on α-SiC substrate by vapour-liquid-solid mechanism from the Al-Ge-Si ternary system

    NASA Astrophysics Data System (ADS)

    Lorenzzi, Jean; Ferro, Gabriel; Cauwet, François; Souliere, Véronique; Carole, Davy

    2011-03-01

    In this work, we present and compare the results obtained from different Si-based melts (Ge-Si, Al-Si and Al-Ge-Si) for growing SiC layers on α-SiC substrate by vapour-liquid-solid (VLS) mechanism. It was found that, depending on melt composition, the deposit could be either a complete 3C or α-SiC layer or even a mixture of these polytypes. The binary Al-Si melt leads systematically to a highly p-type homoepitaxial α-SiC deposit while Ge-Si melt gives a non-intentional n-type doped layers of either 3C or 6H polytypes depending on growth conditions. However, highly p-type doped 3C heteroepitaxial deposit can be obtained if a small amount of Al is added to the Ge-Si binary liquid phase. This means that the VLS mechanism is very flexible and allows growing either n- or p-type SiC layers of 3C or 6H polytypes.

  16. Phase separation and exchange biasing in the ferromagnetic IV-VI semiconductor Ge{sub 1-x}Mn{sub x}Te

    SciTech Connect

    Lechner, R. T.; Springholz, G.; Hassan, M.; Groiss, H.; Kirchschlager, R.; Stangl, J.; Hrauda, N.; Bauer, G.

    2010-07-12

    Ferromagnetic Ge{sub 1-x}Mn{sub x}Te grown by molecular beam epitaxy with Mn content of x{sub Mn}approx =0.5 is shown to exhibit a strong tendency for phase separation. At higher growth temperatures apart from the cubic Ge{sub 0.5}Mn{sub 0.5}Te, a hexagonal MnTe and a rhombohedral distorted Ge{sub 0.83}Mn{sub 0.17}Te phase is formed. This coexistence of antiferromagnetic MnTe and ferromagnetic Ge{sub 0.5}Mn{sub 0.5}Te results in magnetic exchange-bias effects.

  17. Genetic-Algorithm Discovery of a Direct-Gap and Optically Allowed Superstructure from Indirect-Gap Si and Ge Semiconductors

    NASA Astrophysics Data System (ADS)

    D'Avezac, Mayeul; Luo, Jun-Wei; Chanier, Thomas; Zunger, Alex

    2012-01-01

    Combining two indirect-gap materials—with different electronic and optical gaps—to create a direct gap material represents an ongoing theoretical challenge with potentially rewarding practical implications, such as optoelectronics integration on a single wafer. We provide an unexpected solution to this classic problem, by spatially melding two indirect-gap materials (Si and Ge) into one strongly dipole-allowed direct-gap material. We leverage a combination of genetic algorithms with a pseudopotential Hamiltonian to search through the astronomic number of variants of Sin/Gem/…/Sip/Geq superstructures grown on (001) Si1-xGex. The search reveals a robust configurational motif—SiGe2Si2Ge2SiGen on (001) SixGe1-x substrate (x≤0.4) presenting a direct and dipole-allowed gap resulting from an enhanced Γ-X coupling at the band edges.

  18. Influence of the oxidizing species on the Ge dangling bonds at the (100)Ge/GeO2 interface

    NASA Astrophysics Data System (ADS)

    Baldovino, Silvia; Molle, Alessandro; Fanciulli, Marco

    2010-05-01

    The nature of the defects present at various Ge/GeO2 interfaces has been investigated by means of electrically detected magnetic resonance (EDMR) spectroscopy. GeO2 thin films were grown by atomic oxygen, ozone, and molecular oxygen exposure. The defect microstructure is sensitive to the oxidizing species, i.e., to the oxidation mechanism. Different EDMR spectra are correlated with the specific electrical response of the corresponding Ge/GeO2 metal-oxide-semiconductor structures.

  19. Nanoscale strain distributions in embedded SiGe semiconductor devices revealed by precession electron diffraction and dual lens dark field electron holography

    SciTech Connect

    Wang, Y. Y.; Cooper, D.; Bernier, N.; Rouviere, J.; Murray, C. E.; Bruley, J.

    2015-01-26

    The detailed strain distributions produced by embedded SiGe stressor structures are measured at high spatial resolution with high precision, with dual lens dark field electron holography and precession electron diffraction. Shear strain and lattice rotation within the crystalline lattice are observed at the boundaries between the SiGe and Si regions. The experimental results are compared to micromechanical modeling simulations to understand the mechanisms of elastic relaxation on all the modes of deformation at a sub-micron length scale.

  20. MSM-Metal Semiconductor Metal Photo-detector Using Black Silicon Germanium (SiGe) for Extended Wavelength Near Infrared Detection

    DTIC Science & Technology

    2012-09-01

    for Si1–xGex/Si MSM photodiodes. (a) 15% Ge with and without 5 mW light(red) and (b) 30% Ge MSM device with 5 (green) and 10 mW lights ( Lavender ...device with 5 (green) and 10 mW lights ( Lavender ). The clear dependence of the response on the optical power of the illumination source is evident

  1. Photoluminescence and electroluminescence from Ge/strained GeSn/Ge quantum wells

    NASA Astrophysics Data System (ADS)

    Lin, Chung-Yi; Huang, Chih-Hsiung; Huang, Shih-Hsien; Chang, Chih-Chiang; Liu, C. W.; Huang, Yi-Chiau; Chung, Hua; Chang, Chorng-Ping

    2016-08-01

    Ge/strained GeSn/Ge quantum wells are grown on a 300 mm Si substrate by chemical vapor deposition. The direct bandgap emission from strained GeSn is observed in the photoluminescence spectra and is enhanced by Al2O3/SiO2 passivation due to the field effect. The electroluminescence of the direct bandgap emission of strained GeSn is also observed from the Ni/Al2O3/GeSn metal-insulator-semiconductor tunneling diodes. Electroluminescence is a good indicator of GeSn material quality, since defects in GeSn layers degrade the electroluminescence intensity significantly. At the accumulation bias, the holes in the Ni gate electrode tunnel to the strained n-type GeSn layer through the ultrathin Al2O3 and recombine radiatively with electrons. The emission wavelength of photoluminescence and electroluminescence can be tuned by the Sn content.

  2. Electrical property and structural analysis of amphoteric impurity Ge doped GaSe crystal grown by liquid phase growth

    NASA Astrophysics Data System (ADS)

    Sato, Y.; Zhao, S.; Maeda, K.; Tanabe, T.; Oyama, Y.

    2017-06-01

    In order to improve conversion efficiency of THz wave generation, Germanium (Ge)-doped gallium selenide (GaSe) single crystals have been grown by Temperature Difference Method under Controlled Vapor Pressure (TDM-CVP). In this article, electrical property and lattice constant of Ge doped GaSe (GaSe:Ge) crystal are compared with that of not-intentionally doped GaSe crystal. Compared with non-doped GaSe crystal, carrier concentration p was decreased by Ge-doping (not-intentionally doped GaSe p = 3.2 ×1015 cm-3 at 255 K, GaSe:Ge p = 4.9 ×1014 cm-3 at 255 K). In addition, it has been confirmed that lattice constant of GaSe crystal increased with doping Ge concentration increased.

  3. Supercritical supersaturations and ultrafast cooling of the growth solution in liquid-phase epitaxy of semiconductors

    NASA Astrophysics Data System (ADS)

    Abramov, A. V.; Deryagin, N. G.; Tret'yakov, D. N.

    1996-04-01

    A method for accomplishing ultrafast cooling is proposed which makes possible supercritical supersaturations of the growth solution in liquid-phase epitaxy. Growth boat designs providing cooling rates as high as 0268-1242/11/4/025/img1 are considered. The temperatures of contact, 0268-1242/11/4/025/img2, of a GaAs substrate with a Ga-based solution and of a Si substrate with a Sn-based growth solution, calculated for various substrate 0268-1242/11/4/025/img3 and solution temperatures 0268-1242/11/4/025/img4, are in good agreement with experimental values. The maximum attainable supercooling is markedly increased to as high as 0268-1242/11/4/025/img5 for the Ga - As system, when the growth solution is subjected to ultrafast cooling. The prospects of using the method for fabricating heterostructures with a large lattice mismatch are discussed.

  4. Studies of Water V. Five Phonons in Protonic Semiconductor Lattice Model of Pure Liquid Water

    NASA Astrophysics Data System (ADS)

    Jie, Binbin; Sah, Chihtang

    2017-07-01

    We report physics based confirmation (~1% RMS deviation), by existing experimental data, of proton-prohol (proton-hole) ion product (pH) and mobilities in pure liquid water (0-100{}{{o}}C, 1-atm pressure) anticipated from our melted-ice Hexagonal-Close-Packed (H{}2O){}4 Lattice Model. Five phonons are identified. (1) A propagating protonic phonon (520.9 meV from lone-pair-blue-shifted stretching mode of isolated water molecule) absorbed to generate a proton-prohol pair or detrap a tightly-bound proton. (2) Two (173.4 and 196.6 meV) bending-breathing protonic-proholic or protonic phonons absorbed during de-trapping-limited proton or proton-prohol mobilities. (3) Two propagating oxygenic-wateric Debye-Dispersive phonons (30.3 and 27.5 meV) absorbed during scattering-limited proton or proton-prohol mobilities. Summer School in Theoretical Physics funded by the National Natural Science Foundation of China, on Soft Materials Physics, hosted by the Physics Department of Xiamen University, China, during August 1 to 14, 2016. This was also just presented at the 2017 March Meeting (March 14 to 16) of the American Physical Society in New Orleans, USA.

  5. Liquid detection with InGaAsP semiconductor lasers having multiple short external cavities.

    PubMed

    Zhu, X; Cassidy, D T

    1996-08-20

    A liquid detection system consisting of a diode laser with multiple short external cavities (MSXC's) is reported. The MSXC diode laser operates single mode on one of 18 distinct modes that span a range of 72 nm. We selected the modes by setting the length of one of the external cavities using a piezoelectric positioner. One can measure the transmission through cells by modulating the injection current at audio frequencies and using phase-sensitive detection to reject the ambient light and reduce 1/f noise. A method to determine regions of single-mode operation by the rms of the output of the laser is described. The transmission data were processed by multivariate calibration techniques, i.e., partial least squares and principal component regression. Water concentration in acetone was used to demonstrate the performance of the system. A correlation coefficient of R(2) = 0.997 and 0.29% root-mean-square error of prediction are found for water concentration over the range of 2-19%.

  6. Electrical properties of Ge metal-oxide-semiconductor capacitors with high-k La2O3 gate dielectric incorporated by N or/and Ti

    NASA Astrophysics Data System (ADS)

    Huoxi, Xu; Jingping, Xu

    2016-06-01

    LaON, LaTiO and LaTiON films are deposited as gate dielectrics by incorporating N or/and Ti into La2O3 using the sputtering method to fabricate Ge MOS capacitors, and the electrical properties of the devices are carefully examined. LaON/Ge capacitors exhibit the best interface quality, gate leakage property and device reliability, but a smaller k value (14.9). LaTiO/Ge capacitors exhibit a higher k value (22.7), but a deteriorated interface quality, gate leakage property and device reliability. LaTiON/Ge capacitors exhibit the highest k value (24.6), and a relatively better interface quality (3.1 × 1011 eV-1 cm-2), gate leakage property (3.6 × 10-3 A/cm2 at V g = 1 V + V fb) and device reliability. Therefore, LaTiON is more suitable for high performance Ge MOS devices as a gate dielectric than LaON and LaTiO materials. Project supported by the National Natural Science Foundation of China (No. 61274112), the Natural Science Foundation of Hubei Province (No. 2011CDB165), and the Scientific Research Program of Huanggang Normal University (No. 2012028803).

  7. Enhanced charge storage capability of Ge/GeO(2) core/shell nanostructure.

    PubMed

    Yuan, C L; Lee, P S

    2008-09-03

    A Ge/GeO(2) core/shell nanostructure embedded in an Al(2)O(3) gate dielectrics matrix was produced. A larger memory window with good data retention was observed in the fabricated metal-insulator-semiconductor (MIS) capacitor for Ge/GeO(2) core/shell nanoparticles compared to Ge nanoparticles only, which is due to the high percentage of defects located on the surface and grain boundaries of the GeO(2) shell. We believe that the findings presented here provide physical insight and offer useful guidelines to controllably modify the charge storage properties of indirect semiconductors through defect engineering.

  8. Two-Dimensional Crystallization of Rylene Diimide Based n-Type Semiconductors Tuned by the Dimensions of the Aromatic Core at the Liquid-Solid Interface.

    PubMed

    Guo, Zongxia; Yu, Ping; Sun, Kai; Wang, Wenpin; Wei, Yuhan; Li, Zhibo

    2017-05-18

    The investigation of semiconductors at the surface provides opportunities to observe and understand the mechanism of molecular interaction for the design of semiconductors so that organic electronics with good performance can be built. Herein, the 2D crystallization of rylene diimide based n-type semiconductors (i.e., 1-4) was explored at the liquid-highly oriented pyrolytic graphite interface by means of scanning tunneling microscopy. Rylene diimides 1-3 with increased aromatic dimensions show different surface crystallization behaviors and distinguished 2D patterns. The surface chirality was also found to be directly affected by the aromatic dimensions. The 2D patterns and the surface chirality could also be tuned by the nature of the solvent. In addition, molecular symmetry was found to be of great important for the formation of long-range ordered 2D monolayers. This investigation highlights the importance of the rational design of molecular dimensions and geometrical symmetry in achieving determined 2D nanopatterns on surfaces, especially for the rylene diimide based n-type semiconductors. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Tuning Bandgap of p-Type Cu2Zn(Sn, Ge)(S, Se)4 Semiconductor Thin Films via Aqueous Polymer-Assisted Deposition.

    PubMed

    Yi, Qinghua; Wu, Jiang; Zhao, Jie; Wang, Hao; Hu, Jiapeng; Dai, Xiao; Zou, Guifu

    2017-01-18

    Bandgap engineering of kesterite Cu2Zn(Sn, Ge)(S, Se)4 with well-controlled stoichiometric composition plays a critical role in sustainable inorganic photovoltaics. Herein, a cost-effective and reproducible aqueous solution-based polymer-assisted deposition approach is developed to grow p-type Cu2Zn(Sn, Ge)(S, Se)4 thin films with tunable bandgap. The bandgap of Cu2Zn(Sn, Ge)(S, Se)4 thin films can be tuned within the range 1.05-1.95 eV using the aqueous polymer-assisted deposition by accurately controlling the elemental compositions. One of the as-grown Cu2Zn(Sn, Ge)(S, Se)4 thin films exhibits a hall coefficient of +137 cm(3)/C. The resistivity, concentration and carrier mobility of the Cu2ZnSn(S, Se)4 thin film are 3.17 ohm·cm, 4.5 × 10(16) cm(-3), and 43 cm(2)/(V·S) at room temperature, respectively. Moreover, the Cu2ZnSn(S, Se)4 thin film when used as an active layer in a solar cell leads to a power conversion efficiency of 3.55%. The facile growth of Cu2Zn(Sn, Ge)(S, Se)4 thin films in an aqueous system, instead of organic solvents, provides great promise as an environmental-friendly platform to fabricate a variety of single/multi metal chalcogenides for the thin film industry and solution-processed photovoltaic devices.

  10. Structural, elastic, electronic and optical properties of the novel quaternary diamond-like semiconductors Cu2MgSiS4 and Cu2MgGeS4

    NASA Astrophysics Data System (ADS)

    Bedjaoui, A.; Bouhemadou, A.; Aloumi, S.; Khenata, R.; Bin-Omran, S.; Al-Douri, Y.; Saad Saoud, F.; Bensalem, S.

    2017-08-01

    The structural, elastic, electronic and optical properties of two newly synthetized quaternary diamond-like semiconductors Cu2MgSiS4 and Cu2MgGeS4 were studied in detail using two complementary first-principles approaches. The calculated equilibrium structural parameters are in good agreement with the available experimental data. Single-crystal and polycrystalline elastic moduli and their related properties, including elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, elastic anisotropy indexes, Pugh's criterion, elastic wave velocities and Debye temperature, were predicted. We find that the inclusion of the electronic exchange-correlation through the newly developed Tran-Blaha modified Becke-Johnson potential (TB-mBJ) improves the description of the electronic structure. The TB-mBJ yields a direct band gap (Γ-Γ) of 2.64 and 1.54 eV for Cu2MgSiS4 and Cu2MgGeS4, respectively. Frequency dependence of the dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity, energy loss function and optical conductivity were predicted and the origin of the observed electronic transitions were assigned.

  11. Structural, electronic and kinetic properties of the phase-change material Ge2Sb2Te5 in the liquid state.

    PubMed

    Schumacher, Mathias; Weber, Hans; Jóvári, Pál; Tsuchiya, Yoshimi; Youngs, Tristan G A; Kaban, Ivan; Mazzarello, Riccardo

    2016-06-08

    Phase-change materials exhibit fast and reversible transitions between an amorphous and a crystalline state at high temperature. The two states display resistivity contrast, which is exploited in phase-change memory devices. The technologically most important family of phase-change materials consists of Ge-Sb-Te alloys. In this work, we investigate the structural, electronic and kinetic properties of liquid Ge2Sb2Te5 as a function of temperature by a combined experimental and computational approach. Understanding the properties of this phase is important to clarify the amorphization and crystallization processes. We show that the structural properties of the models obtained from ab initio and reverse Monte Carlo simulations are in good agreement with neutron and X-ray diffraction experiments. We extract the kinetic coefficients from the molecular dynamics trajectories and determine the activation energy for viscosity. The obtained value is shown to be fully compatible with our viscosity measurements.

  12. Structural, electronic and kinetic properties of the phase-change material Ge2Sb2Te5 in the liquid state

    NASA Astrophysics Data System (ADS)

    Schumacher, Mathias; Weber, Hans; Jóvári, Pál; Tsuchiya, Yoshimi; Youngs, Tristan G. A.; Kaban, Ivan; Mazzarello, Riccardo

    2016-06-01

    Phase-change materials exhibit fast and reversible transitions between an amorphous and a crystalline state at high temperature. The two states display resistivity contrast, which is exploited in phase-change memory devices. The technologically most important family of phase-change materials consists of Ge-Sb-Te alloys. In this work, we investigate the structural, electronic and kinetic properties of liquid Ge2Sb2Te5 as a function of temperature by a combined experimental and computational approach. Understanding the properties of this phase is important to clarify the amorphization and crystallization processes. We show that the structural properties of the models obtained from ab initio and reverse Monte Carlo simulations are in good agreement with neutron and X-ray diffraction experiments. We extract the kinetic coefficients from the molecular dynamics trajectories and determine the activation energy for viscosity. The obtained value is shown to be fully compatible with our viscosity measurements.

  13. Structural, electronic and kinetic properties of the phase-change material Ge2Sb2Te5 in the liquid state

    PubMed Central

    Schumacher, Mathias; Weber, Hans; Jóvári, Pál; Tsuchiya, Yoshimi; Youngs, Tristan G. A.; Kaban, Ivan; Mazzarello, Riccardo

    2016-01-01

    Phase-change materials exhibit fast and reversible transitions between an amorphous and a crystalline state at high temperature. The two states display resistivity contrast, which is exploited in phase-change memory devices. The technologically most important family of phase-change materials consists of Ge-Sb-Te alloys. In this work, we investigate the structural, electronic and kinetic properties of liquid Ge2Sb2Te5 as a function of temperature by a combined experimental and computational approach. Understanding the properties of this phase is important to clarify the amorphization and crystallization processes. We show that the structural properties of the models obtained from ab initio and reverse Monte Carlo simulations are in good agreement with neutron and X-ray diffraction experiments. We extract the kinetic coefficients from the molecular dynamics trajectories and determine the activation energy for viscosity. The obtained value is shown to be fully compatible with our viscosity measurements. PMID:27272222

  14. Synthesis of New Sr3RE2(Ge3O9)2 (RE=La, Y) cyclogermanates by liquid-phase precursor methods

    NASA Astrophysics Data System (ADS)

    Melkozerova, Marina A.; Lipina, Olga A.; Baklanova, Yana V.; Tyutyunnik, Alexander P.; Zubkov, Vladimir G.

    2017-04-01

    New cyclogermanates Sr3RE2(Ge3O9)2 (RE=La, Y) with Ca3Y2(Si3O9)2 cyclosilicate structure type have been prepared by two liquid-phase precursor routes: the citrate and the Pechini methods. The phase composition, morphology and optical properties of the intermediate and final products have been characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectance spectroscopy (DRS). The thermogravimetric (TGA) and differential thermal analyses (DTA) were used to study the thermal decomposition of the precursors. The powder XRD measurements indicate that the phase formation of Sr3RE2(Ge3O9)2 (RE=La, Y) (S.G. C2/c, Z=4) takes place after 20 h annealing at 800 °C. The DRS data revealed that the cyclogermanates are promising optical hosts.

  15. Improved efficiency of GaInP/(In)GaAs/Ge solar cells using textured liquid-phase-deposited (LPD) ZnO

    NASA Astrophysics Data System (ADS)

    Lei, Po-Hsun; Lin, Chia-Te; Ye, Sheng-Jhan

    2013-03-01

    This study presents a proposal for textured ZnO grown by liquid phase deposition (LPD) to improve the efficiency of GaInP/(In)GaAs/Ge solar cells. The experimental and calculated results show that the photocurrent density and conversion efficiency of GaInP/(In)GaAs/Ge solar cells with a textured liquid-phase-deposited zinc oxide (LPD-ZnO) window layer are dependent on the root-mean-square (RMS) roughness of LPD-ZnO, as determined by the hydrochloric acid (HCl) concentration and deposition temperature. The optimal RMS-roughness range for textured LPD-ZnO is 90-100 nm. The GaInP/(In)GaAs/Ge solar cells with the 95 nm LPD-ZnO window layer have a higher open circuit voltage (2.41 V), short circuit current density (14.88 mA cm-2), and conversion efficiency (29.8%) than those without the LPD-ZnO textured window layer. They also have high external quantum efficiency at light wavelengths between 300 and 1000 nm because of high photocurrent density, resulting from the low reflectivity between air and textured LPD-ZnO. Additionally, the temperature characteristics for GaInP/(In)GaAs/Ge solar cells without and with the textured LPD-ZnO window layer are similar, indicating that ambient temperature does not degrade the solar cells with the textured LPD-ZnO window layer while they are operating outside.

  16. A Solution-Processable Liquid-Crystalline Semiconductor for Low-Temperature-Annealed Air-Stable N-Channel Field-Effect Transistors.

    PubMed

    Ozdemir, Resul; Choi, Donghee; Ozdemir, Mehmet; Kim, Hyekyoung; Kostakoğlu, Sinem Tuncel; Erkartal, Mustafa; Kim, Hyungsug; Kim, Choongik; Usta, Hakan

    2017-04-05

    A new solution-processable and air-stable liquid-crystalline n-channel organic semiconductor (2,2'-(2,8-bis(5-(2-octyldodecyl)thiophen-2-yl)indeno[1,2-b]fluorene-6,12-diylidene)dimalononitrile, α,ω-2OD-TIFDMT) with donor-acceptor-donor (D-A-D) π conjugation has been designed, synthesized, and fully characterized. The new semiconductor exhibits a low LUMO energy (-4.19 eV) and a narrow optical bandgap (1.35 eV). The typical pseudo-focal-conic fan-shaped texture of a hexagonal columnar liquid-crystalline (LC) phase was observed over a wide temperature range. The spin-coated semiconductor thin films show the formation of large (≈0.5-1 μm) and highly crystalline platelike grains with edge-on molecular orientations. Low-temperature-annealed (50 °C) top-contact/bottom-gate OFETs have provided good electron mobility values as high as 0.11 cm(2)  (V s)(-1) and high Ion /Ioff ratios of 10(7) to 10(8) with excellent ambient stability. This indicates an enhancement of two orders of magnitude (100×) when compared with the β-substituted parent semiconductor, β-DD-TIFDMT (2,2'-(2,8-bis(3-dodecylthiophen-2-yl)indeno[1,2-b]fluorene-6,12-diylidene)dimalononitrile). The current rational alkyl-chain engineering route offers great advantages for D-A-D π-core coplanarity in addition to maintaining good solubility in organic solvents, and leads to favorable optoelectronic/physicochemical characteristics. These remarkable findings demonstrate that α,ω-2OD-TIFDMT is a promising semiconductor material for the development of n-channel OFETs on flexible plastic substrates and LC-state annealing of the columnar liquid crystals can lower the electron mobility for transistor-type charge transport. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Optical phonons in the wurtzstannite Cu2ZnGeS4 semiconductor: Polarized Raman spectroscopy and first-principle calculations

    NASA Astrophysics Data System (ADS)

    Guc, M.; Litvinchuk, A. P.; Levcenko, S.; Izquierdo-Roca, V.; Fontané, X.; Valakh, M. Ya.; Arushanov, E.; Pérez-Rodríguez, A.

    2014-05-01

    The vibrational properties of the wurtzstannite Cu2ZnGeS4 are studied experimentally by polarized Raman scattering in off-resonant and resonant conditions and theoretically by ab initio lattice dynamics calculations. Twenty-nine modes from 45 Raman active theoretically predicted have been experimentally detected and identified, including polar A1(TO),A1(LO), and B1(TO+LO)/B2(TO+LO) and nonpolar A2 symmetry phonon modes from measurements on (2 1 0) and (0 0 1) crystallographic planes of Cu2ZnGeS4 single crystals. The lattice dynamics calculations provide a full picture of the zone center phonon spectrum and allow the assignment of experimentally observed lines to first- and second-order lattice vibrations. Using resonance Raman conditions, a strong enhancement of the A1(LO) modes with the highest longitudinal-transversal spiting is observed.

  18. Influence of uniaxial strain in Si and Ge p-type double-gate metal-oxide-semiconductor field effect transistors

    NASA Astrophysics Data System (ADS)

    Moussavou, Manel; Cavassilas, Nicolas; Dib, Elias; Bescond, Marc

    2015-09-01

    We theoretically investigate the impact of uniaxial strain in extremely thin Si and Ge p-type double-gate transistors. Quantum transport modeling is treated using a 6-band k.p Hamiltonian and the non-equilibrium Green's function formalism including phonon scattering. Based on this framework, we analyze the influence of strain on current characteristics considering different transport directions and gate lengths. Our results first confirm the superiority of Ge over Si in long devices (15 nm gate length) for which best electrical performances are obtained considering channels along <110 > with a uni-axial compressive strain. For this configuration, Si devices suffer from inter-subband coupling which generates a strong hole-phonon scattering. Material dominance is reversed for shorter devices (7 nm gate length) where the small effective masses of Ge deteriorate the off-regime of the nano-transistor regardless of strain and crystallographic options. Due to weaker hole-phonon-scattering, <100 > -Si devices with a tensile strain are interestingly found to be more competitive than their <110 > -compressive counterparts. These results show that Si is still the most relevant material to reach the ultimate nanometer scale. More importantly, the same tensile strain can be considered to boost performances of both p- and n-type planar transistors which would lead to a significant simplification of the technological strain manufacturing.

  19. Metastable Ge1-xCx alloy nanowires.

    PubMed

    Kim, Byung-Sung; Lee, Jae-Hyun; Son, Kiseok; Hwang, Sung Woo; Choi, Byoung Lyong; Lee, Eun Kyung; Kim, Jong Min; Whang, Dongmok

    2012-02-01

    Carbon-containing alloy materials such as Ge(1-x)C(x) are attractive candidates for replacing silicon (Si) in the semiconductor industry. The addition of carbon to diamond lattice not only allows control over the lattice dimensions, but also enhances the electrical properties by enabling variations in strain and compositions. However, extremely low carbon solubility in bulk germanium (Ge) and thermodynamically unfavorable Ge-C bond have hampered the production of crystalline Ge(1-x)C(x) alloy materials in an equilibrium growth system. Here we successfully synthesized high-quality Ge(1-x)C(x) alloy nanowires (NWs) by a nonequilibrium vapor-liquid-solid (VLS) method. The carbon incorporation was controlled by NW growth conditions and the position of carbon atoms in the Ge matrix (at substitutional or interstitial sites) was determined by the carbon concentration. Furthermore, the shrinking of lattice spacing caused by substitutional carbon offered the promising possibility of band gap engineering for photovoltaic and optoelectronic applications.

  20. Semiconductor heterostructure

    NASA Technical Reports Server (NTRS)

    Hovel, Harold John (Inventor); Woodall, Jerry MacPherson (Inventor)

    1978-01-01

    A technique for fabricating a semiconductor heterostructure by growth of a ternary semiconductor on a binary semiconductor substrate from a melt of the ternary semiconductor containing less than saturation of at least one common ingredient of both the binary and ternary semiconductors wherein in a single temperature step the binary semiconductor substrate is etched, a p-n junction with specific device characteristics is produced in the binary semiconductor substrate by diffusion of a dopant from the melt and a region of the ternary semiconductor of precise conductivity type and thickness is grown by virtue of a change in the melt characteristics when the etched binary semiconductor enters the melt.

  1. Semiconductor structure

    NASA Technical Reports Server (NTRS)

    Hovel, Harold J. (Inventor); Woodall, Jerry M. (Inventor)

    1979-01-01

    A technique for fabricating a semiconductor heterostructure by growth of a ternary semiconductor on a binary semiconductor substrate from a melt of the ternary semiconductor containing less than saturation of at least one common ingredient of both the binary and ternary semiconductors wherein in a single temperature step the binary semiconductor substrate is etched, a p-n junction with specific device characteristics is produced in the binary semiconductor substrate by diffusion of a dopant from the melt and a region of the ternary semiconductor of precise conductivity type and thickness is grown by virtue of a change in the melt characteristics when the etched binary semiconductor enters the melt.

  2. Semiconductor nanowires: Controlled growth and thermal properties

    NASA Astrophysics Data System (ADS)

    Wu, Yiying

    This dissertation presents an experimental study of the controlled growth of semiconductor nanowires and their thermophysical properties. The synthesis of nanowires was based on the well-known Vapor-Liquid-Solid (VLS) mechanism in which the growth of nanowire is initiated by a nanosized liquid droplet. The prepared nanowires are single-crystalline with certain preferred growth direction. Nanowires with different compositions have been synthesized, including Si, Ge, boron and MgB2. The control of nanowire composition, diameter and orientation has also been achieved. In addition, a Pulsed Laser Ablation-Chemical Vapor Deposition (PLA-CVD) hybrid process was developed to synthesize Si/SiGe longitudinally superlattice nanowires. The thermal conductivity of individual pure Si nanowire and Si/SiGe nanowire was measured using a microfabricated suspended device over a temperature range of 20--320 K. The thermal conductivities of individual 22, 37, 56, and 115 nm diameter single crystalline intrinsic Si nanowires were much lower than the bulk value due to the strong phonon boundary scattering. Except for the 22 nm diameter nanowire, theoretical predictions using a modified Callaway model fit the experimental data very well. The data for the 22 nm diameter wire suggest that changes in phonon dispersion due to confinement can cause additional thermal conductivity reduction. The Si/SiGe superlattice nanowires with diameters of 83 run and 58 nm were also measured. Their thermal conductivities are smaller than pure Si nanowire with similar diameter, as well as Si/SiGe superlattice thin film with comparable period. Both the alloying scattering and the boundary scattering are believed to contribute to this reduction. Size dependent melting-recrystallization study of the carbon-sheathed semiconductor Ge nanowires was carried out in in-situ high temperature transmission electron microscope (TEM). Significant depression in melting temperature with decreasing size of the nanowires as

  3. Impact of dispersion forces on the atomic structure of a prototypical network-forming disordered system: The case of liquid GeSe2

    NASA Astrophysics Data System (ADS)

    Lampin, Evelyne; Bouzid, Assil; Ori, Guido; Boero, Mauro; Massobrio, Carlo

    2017-07-01

    A set of structural properties of liquid GeSe2 are calculated by using first-principles molecular dynamics and including, for the first time, van der Waals dispersion forces. None of the numerous atomic-scale simulations performed in the past on this prototypical disordered network-forming material had ever accounted for dispersion forces in the expression of the total energy. For this purpose, we employed either the Grimme-D2 or the maximally localized Wannier function scheme. We assessed the impact of dispersion forces on properties such as partial structure factors, pair correlation functions, bond angle distribution, and number of corner vs edge sharing connections. The maximally localized Wannier function scheme is more reliable than the Grimme-D2 scheme in reproducing existing first-principles results. In particular, the Grimme-D2 scheme worsens the agreement with experiments in the case of the Ge-Ge pair correlation function. Our study shows that the impact of dispersion forces on disordered chalcogenides has to be considered with great care since it cannot be necessarily the same when adopting different recipes.

  4. Enhanced determination of abscisic acid (ABA) and abscisic acid glucose ester (ABA-GE) in Cistus albidus plants by liquid chromatography-mass spectrometry in tandem mode.

    PubMed

    López-Carbonell, Marta; Gabasa, Marta; Jáuregui, Olga

    2009-04-01

    An improved, quick and simple method for the extraction and quantification of the phytohormones (+)-abscisic acid (ABA) and its major glucose conjugate, abscisic acid glucose ester (ABA-GE) in plant samples is described. The method includes the addition of deuterium-labeled internal standards to the leaves at the beginning of the extraction for quantification, a simple extraction/centrifugation process and the injection into the liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS-MS) system in multiple reaction monitoring mode (MRM). Quality parameters of the method (detection limits, repeatability, reproducibility and linearity) have been studied. The objective of this work is to show the applicability of this method for quantifying the endogenous content of both ABA and ABA-GE in Cistus albidus plants that have been grown during an annual cycle under Mediterranean field conditions. Leaf samples from winter plants have low levels of ABA which increase in spring and summer showing two peaks that corresponded to April and August. These increases are coincident with the high temperature and solar radiation and the low RWC and RH registered along the year. On the other hand, the endogenous levels of ABA-GE increase until maximum values in July just before the ABA content reaches its highest concentration, decreasing in August and during autumn and winter. Our results suggest that the method is useful for quantifying both compounds in this plant material and represents the advantage of a short-time sample preparation with a high accuracy and viability.

  5. Effect of Silicon on Activity Coefficients of Siderophile Elements (P, Au, Pd, As, Ge, Sb, and In) in Liquid Fe, with Application to Core Formation

    NASA Technical Reports Server (NTRS)

    Righter, K.; Pando, K.; Danielson, L. R.; Humayun, M.; Righter, M.; Lapen, T.; Boujibar, A.

    2016-01-01

    Earth's core contains approximately 10 percent light elements that are likely a combination of S, C, Si, and O, with Si possibly being the most abundant. Si dissolved into Fe liquids can have a large effect on the magnitude of the activity coefficient of siderophile elements (SE) in Fe liquids, and thus the partitioning behavior of those elements between core and mantle. The effect of Si can be small such as for Ni and Co, or large such as for Mo, Ge, Sb, As. The effect of Si on many siderophile elements is unknown yet could be an important, and as yet unquantified, influence on the core-mantle partitioning of SE. Here we report new experiments designed to quantify the effect of Si on the partitioning of P, Au, Pd, and many other SE between metal and silicate melt. The results will be applied to Earth, for which we have excellent constraints on the mantle siderophile element concentrations.

  6. Strain and lattice orientation distribution in SiN/Ge complementary metal–oxide–semiconductor compatible light emitting microstructures by quick x-ray nano-diffraction microscopy

    SciTech Connect

    Chahine, G. A.; Schülli, T. U.; Zoellner, M. H.; Guha, S.; Reich, C.; Zaumseil, P.; Capellini, G.; Richard, M.-I.; Schroeder, T.

    2015-02-16

    This paper presents a study of the spatial distribution of strain and lattice orientation in CMOS-fabricated strained Ge microstripes using high resolution x-ray micro-diffraction. The recently developed model-free characterization tool, based on a quick scanning x-ray diffraction microscopy technique can image strain down to levels of 10{sup −5} (Δa/a) with a spatial resolution of ∼0.5 μm. Strain and lattice tilt are extracted using the strain and orientation calculation software package X-SOCS. The obtained results are compared with the biaxial strain distribution obtained by lattice parameter-sensitive μ-Raman and μ-photoluminescence measurements. The experimental data are interpreted with the help of finite element modeling of the strain relaxation dynamics in the investigated structures.

  7. SEMICONDUCTOR DEVICES: Small-signal model parameter extraction for microwave SiGe HBTs based on Y- and Z-parameter characterization

    NASA Astrophysics Data System (ADS)

    Jun, Fu

    2009-08-01

    High frequency intrinsic small-signal model parameter extraction for microwave SiGe heterojunction bipolar transistors is studied, with a focus on the main feedback elements including the emitter series resistor, internal and external base-collector capacitors as well as the base series resistor, all of which are important in determining the behavior of the device equivalent circuit. In accordance with the respective features of definition of the Y- and Z-parameters, a novel combined use of them succeeds in reasonably simplifying the device equivalent circuit and thus decoupling the extraction of base-collector capacitances from other model parameters. As a result, a very simple direct extraction method is proposed. The proposed method is applied for determining the SiGe HBT small-signal model parameters by taking numerically simulated Y- and Z-parameters as nominal “measurement data" with the help of a Taurus-device simulator. The validity of the method is preliminarily confirmed by the observation of certain linear relations of device frequency behavior as predicted by the corresponding theoretical analysis. Furthermore, the extraction results can be used to reasonably account for the dependence of the extracted model parameters on device geometry and process parameters, reflecting the explicit physical meanings of parameters, and especially revealing the distributed nature of the base series resistor and its complex interactions with base-collector capacitors. Finally, the accuracy of our model parameter extraction method is further validated by comparing the modeled and simulated S-parameters as a function of frequency.

  8. Trap density of GeNx/Ge interface fabricated by electron-cyclotron-resonance plasma nitridation

    NASA Astrophysics Data System (ADS)

    Fukuda, Yukio; Otani, Yohei; Toyota, Hiroshi; Ono, Toshiro

    2011-07-01

    We have investigated GeNx/Ge interface properties using Si3N4(7 nm)/GeNx(2 nm)/Ge metal-insulator-semiconductor structures fabricated by the plasma nitridation of Ge substrates using an electron-cyclotron-resonance-generated nitrogen plasma. The interface trap density (Dit) measured by the conductance method is found to be distributed symmetrically in the Ge band gap with a minimum Dit value lower than 3 × 1011 cm-2eV-1 near the midgap. This result may lead to the development of processes for the fabrication of p- and n-Ge Schottky-barrier (SB) source/drain metal-insulator-semiconductor field-effect transistors using chemically and thermally robust GeNx dielectrics as interlayers for SB source/drain contacts and high-κ gate dielectrics.

  9. Metal-Insulator-Semiconductor Photodetectors

    PubMed Central

    Lin, Chu-Hsuan; Liu, Chee Wee

    2010-01-01

    The major radiation of the Sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III–V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows. PMID:22163382

  10. Metal-insulator-semiconductor photodetectors.

    PubMed

    Lin, Chu-Hsuan; Liu, Chee Wee

    2010-01-01

    The major radiation of the sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III-V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows.

  11. Improving the electrical properties of lanthanum silicate films on ge metal oxide semiconductor capacitors by adopting interfacial barrier and capping layers.

    PubMed

    Choi, Yu Jin; Lim, Hajin; Lee, Suhyeong; Suh, Sungin; Kim, Joon Rae; Jung, Hyung-Suk; Park, Sanghyun; Lee, Jong Ho; Kim, Seong Gyeong; Hwang, Cheol Seong; Kim, HyeongJoon

    2014-05-28

    The electrical properties of La-silicate films grown by atomic layer deposition (ALD) on Ge substrates with different film configurations, such as various Si concentrations, Al2O3 interfacial passivation layers, and SiO2 capping layers, were examined. La-silicate thin films were deposited using alternating injections of the La[N{Si(CH3)3}2]3 precursor with O3 as the La and O precursors, respectively, at a substrate temperature of 310 °C. The Si concentration in the La-silicate films was further controlled by adding ALD cycles of SiO2. For comparison, La2O3 films were also grown using [La((i)PrCp)3] and O3 as the La precursor and oxygen source, respectively, at the identical substrate temperature. The capacitance-voltage (C-V) hysteresis decreased with an increasing Si concentration in the La-silicate films, although the films showed a slight increase in the capacitance equivalent oxide thickness. The adoption of Al2O3 at the interface as a passivation layer resulted in lower C-V hysteresis and a low leakage current density. The C-V hysteresis voltages of the La-silicate films with Al2O3 passivation and SiO2 capping layers was significantly decreased to ∼0.1 V, whereas the single layer La-silicate film showed a hysteresis voltage as large as ∼1.0 V.

  12. Superconducting contacts to Ge/Si core/shell nanowires

    NASA Astrophysics Data System (ADS)

    Su, Zhaoen; Zarassi, Azarin; Patil, Dharamraj; Frolov, Sergey; Hocevar, Moira; Nguyen, Minh; Yoo, Jinkyoung; Dayeh, Shadi

    2015-03-01

    Ge/Si core/shell nanowires are hosts to one dimensional hole gas. The spin-orbit interaction is expected to be much larger than that in electron systems such as InSb and InAs. Therefore, Ge/Si nanowires have great potential to demonstrate helical liquid. When strong superconductivity is induced in the nanowire, robust topological superconductivity may form in the system. We will show how to achieve semiconductor-superconductor contacts to the nanowire. The effects of a few surface cleaning methods and annealing process on the contact resistance will be shown. Superconducting contacts of NbTiN, Al, Ti and their combinations are studied. NbTiN may be suitable for hybrid device carrying Majorana fermions for its high critical temperature and magnetic field. Supercurrent through Josephson junctions with these contacts is measured.

  13. Interfacial kinetics in nanosized Au/Ge films: An in situ TEM study

    NASA Astrophysics Data System (ADS)

    Kryshtal, Aleksandr P.; Minenkov, Alexey A.; Ferreira, Paulo J.

    2017-07-01

    We investigate the morphology and crystalline structure of Au/Ge films in a wide range of temperatures by in situ TEM heating. Au/Ge films with Au mass thickness of 0.2-0.3 nm and Ge thickness of 5 nm were produced in vacuum by the sequential deposition of components on a carbon substrate at room temperature. It has been shown that particles with an average size of 4 nm, formed by Au film de-wetting, melt on the germanium substrate at temperatures 110-160 °C, which are below the eutectic temperature for the bulk. The effect of crystallization-induced capillary motion of liquid eutectic particles over Ge surface has been found in this work. Formation of metastable fcc phase of Ge has been observed at the liquid-germanium interface and behind the moving particle. Formation of a liquid phase with its subsequent crystallization at the metal-semiconductor interface seems to play a key role in the metal-induced crystallization effect.

  14. Thermal transport across high-pressure semiconductor-metal transition in Si and Si0.991Ge0.009

    SciTech Connect

    Hohensee, Gregory T.; Fellinger, Michael R.; Trinkle, Dallas R.; Cahill, David G.

    2015-05-07

    Time-domain thermoreflectance (TDTR) can be applied to metallic samples at high pressures in the diamond anvil cell (DAC) and provide non-contact measurements of thermal transport properties. We have performed regular and beam-offset TDTR to establish the thermal conductivities of Si and Si0.991Ge0.009 across the semiconductor-metal phase transition and up to 45 GPa. The thermal conductivities of metallic Si and Si(Ge) are comparable to aluminum and indicative of predominantly electronic heat carriers. Metallic Si and Si(Ge) have an anisotropy of approximately 1.4, similar to that of beryllium, due to the primitive hexagonal crystal structure. Furthermore, we used the Wiedemann-Franz law to derive the associated electrical resistivity, and found it consistent with the Bloch-Gruneisen model.

  15. The Packing of Helical and Zigzag Chains and Distribution of Interstitial Voids in Expanded Liquid Se near the Semiconductor to Metal Transition

    NASA Astrophysics Data System (ADS)

    Maruyama, Kenji; Hiroi (Sato), Satoshi; Endo, Hirohisa; Hoshino, Hideoki; Odagaki, Takashi; Hensel, Friedrich

    2017-08-01

    The reverse Monte Carlo (RMC) and Voronoi-Delaunay (VD) void analyses were applied to study the modification of chain geometries near the semiconductor (SC) to metal (M) transition in expanded liquid Se along the isochore of d = 3.4 g/cm3. Fluctuations of dihedral angles with increasing temperature and pressure cause modification of the helical (H) chain to the planar zigzag (Z) chain conformations. The distribution of voids size (rV ) supported by chain segments and distances to the 4th 6th neighbor atoms on the chain segments provide information on the stacking of planar zigzag chains compensated by empty space (L-voids, rV 3.6 Å) which leads to the formation of metallic domains. Near SC-M transition region the number fraction NZ/NH for Z and H chain segments increases.

  16. Organic Field-Effect Transistors Based on a Liquid-Crystalline Polymeric Semiconductor using SU-8 Gate Dielectrics on Flexible Substrates

    PubMed Central

    Tetzner, Kornelius; Bose, Indranil R.; Bock, Karlheinz

    2014-01-01

    In this work, the insulating properties of poly(4-vinylphenol) (PVP) and SU-8 (MicroChem, Westborough, MA, USA) dielectrics are analyzed and compared with each other. We further investigate the performance behavior of organic field-effect transistors based on a semiconducting liquid-crystal polymer (LCP) using both dielectric materials and evaluate the results regarding the processability. Due to the lower process temperature needed for the SU-8 deposition, the realization of organic transistors on flexible substrates is demonstrated showing comparable charge carrier mobilities to devices using PVP on glass. In addition, a µ-dispensing procedure of the LCP on SU-8 is presented, improving the switching behavior of the organic transistors, and the promising stability data of the SU-8/LCP stack are verified after storing the structures for 60 days in ambient air showing negligible irreversible degradation of the organic semiconductor. PMID:28788243

  17. A method to form semiconductor quantum dot (QD) thin films by igniting a flame at air-liquid interface: CdS and WO3.

    PubMed

    Jadhav, Aarti H; Patil, Sagar H; Sathaye, Shivaram D; Patil, Kashinath R

    2015-02-01

    We reveal an easy, inexpensive, efficient one stepflame synthesis of semiconductor/metal oxide thin films at air-liquid interface, subsequently, transferred on suitable substrate. The method has been illustrated by the formation of CdS and WO3 QDs thin films. The features of the present method are (1) Growth of thin films consisting of0.5-2.0nm sized Quantum Dots (QDs)/(ultra-small nanoparticles) in a short time, at the air-liquid interface which can be suitably transferred by a well-known Blodgett technique to an appropriate substrate, (2) The method is suitable to apply layer by layer (LbL) technique to increase the film thickness as well as forming various compositions as revealed by AFM measurements. The films are characterized for their structure (SAED), morphology (TEM), optical properties (UV-Vis.) and photoluminescence (PL). Possible mechanism of formation of QDs thin film and effect of capping in case of CdS QDs is discussed.

  18. Photoluminescence and electroluminescence from Ge/strained GeSn/Ge quantum wells

    SciTech Connect

    Lin, Chung-Yi; Chang, Chih-Chiang; Huang, Chih-Hsiung; Huang, Shih-Hsien; Liu, C. W.; Huang, Yi-Chiau; Chung, Hua; Chang, Chorng-Ping

    2016-08-29

    Ge/strained GeSn/Ge quantum wells are grown on a 300 mm Si substrate by chemical vapor deposition. The direct bandgap emission from strained GeSn is observed in the photoluminescence spectra and is enhanced by Al{sub 2}O{sub 3}/SiO{sub 2} passivation due to the field effect. The electroluminescence of the direct bandgap emission of strained GeSn is also observed from the Ni/Al{sub 2}O{sub 3}/GeSn metal-insulator-semiconductor tunneling diodes. Electroluminescence is a good indicator of GeSn material quality, since defects in GeSn layers degrade the electroluminescence intensity significantly. At the accumulation bias, the holes in the Ni gate electrode tunnel to the strained n-type GeSn layer through the ultrathin Al{sub 2}O{sub 3} and recombine radiatively with electrons. The emission wavelength of photoluminescence and electroluminescence can be tuned by the Sn content.

  19. Optically and electrically controlled circularly polarized emission from cholesteric liquid crystal materials doped with semiconductor quantum dots.

    PubMed

    Bobrovsky, Alexey; Mochalov, Konstantin; Oleinikov, Vladimir; Sukhanova, Alyona; Prudnikau, Anatol; Artemyev, Mikhail; Shibaev, Valery; Nabiev, Igor

    2012-12-04

    Novel types of electro- and photoactive quantum dot-doped cholesteric materials have been engineered. UV-irradiation or electric field application allows one to control the degree of circular polarization and intensity of fluorescence emission by prepared quantum dot-doped liquid crystal films. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. 200 A GeV Au+Au Collisions Serve a Nearly Perfect Quark-Gluon Liquid

    SciTech Connect

    Song Huichao; Bass, Steffen A.; Heinz, Ulrich; Shen, Chun; Hirano, Tetsufumi

    2011-05-13

    A new robust method to extract the specific shear viscosity ({eta}/s){sub QGP} of a quark-gluon plasma (QGP) at temperatures T{sub c}GeV Au+Au collisions that v{sub 2}/{epsilon} is a universal function of multiplicity density (1/S)(dN{sub ch}/dy) that depends only on the viscosity but not on the model used for computing the initial fireball eccentricity {epsilon}. Comparing with measurements we find 1<4{pi}({eta}/s){sub QGP}<2.5 where the uncertainty range is dominated by model uncertainties for the values of {epsilon} used to normalize the measured v{sub 2}.

  1. Contact resistivity decrease at a metal/semiconductor interface by a solid-to-liquid phase transitional metallo-organic silver.

    PubMed

    Shin, Dong-Youn; Seo, Jun-Young; Kang, Min Gu; Song, Hee-eun

    2014-09-24

    We present a new approach to ensure the low contact resistivity of a silver paste at a metal/semiconductor interface over a broad range of peak firing temperatures by using a solid-to-liquid phase transitional metallo-organic silver, that is, silver neodecanoate. Silver nanoclusters, thermally derived from silver neodecanoate, are readily dissolved into the melt of metal oxide glass frit even at low temperatures, at which point the molten metal oxide glass frit lacks the dissociation capability of bulk silver into Ag(+) ions. In the presence of O(2-) ions in the melt of metal oxide glass frit, the redox reaction from Ag(+) to Ag(0) augments the noble-metal-assisted etching capability to remove the passivation layer of silicon nitride. Moreover, during the cooling stage, the nucleated silver atoms enrich the content of silver nanocolloids in the solidified metal oxide glass layer. The resulting contact resistivity of silver paste with silver neodecanoate at the metal/semiconductor interface thus remains low-between 4.12 and 16.08 mΩ cm(2)-whereas without silver neodecanoate, the paste exhibits a contact resistivity between 2.61 and 72.38 mΩ cm(2) in the range of peak firing temperatures from 750 to 810 °C. The advantage of using silver neodecanoate in silver paste becomes evident in that contact resistivity remains low over the broad range of peak firing temperatures, thus providing greater flexibility with respect to the firing temperature required in silicon solar cell applications.

  2. New Semiconductor Devices

    NASA Astrophysics Data System (ADS)

    Balestra, F.

    2008-11-01

    A review of recently emerging semiconductor devices for nanoelectronic applications is given. For the end of the international technology roadmap for semiconductors, very innovative materials, technologies and nanodevice architectures will be needed. Silicon on insulator-based devices seem to be the best candidates for the ultimate integration of integrated circuits on silicon. The flexibility of the silicon on insulator-based structure and the possibility to realize new device architectures allow to obtain optimum electrical properties for low power and high performance circuits. These transistors are also very interesting for high frequency and memory applications. The performance and physical mechanisms are addressed in single- and multi-gate thin film Si, SiGe and Ge metal-oxide-semiconductor field-effect-transistors. The impact of tensile or compressive uniaxial and biaxial strains in the channel, of high k materials and metal gates as well as metallic Schottky source-drain architectures are discussed. Finally, the interest of advanced beyond-CMOS (complementary MOS) nanodevices for long term applications, based on nanowires, carbon electronics or small slope switch structures are presented.

  3. Semiconductor detectors in nuclear and particle physics

    SciTech Connect

    Rehak, P.; Gatti, E.

    1992-12-31

    Semiconductor detectors for elementary particle physics and nuclear physics in the energy range above 1 GeV are briefly reviewed. In these two fields semiconductor detectors are used mainly for the precise position sensing. In a typical experiment, the position of a fast charged particle crossing a relatively thin semiconductor detector is measured. The position resolution achievable by semiconductor detectors is compared with the resolution achievable by gas filled position sensing detectors. Semiconductor detectors are divided into two groups: Classical semiconductor diode detectors and semiconductor memory detectors. Principles of the signal formation and the signal read-out for both groups of detectors are described. New developments of silicon detectors of both groups are reported.

  4. Molten Au/Ge alloy migration in Ge nanowires.

    PubMed

    Liu, Qian; Zou, Rujia; Wu, Jianghong; Xu, Kaibing; Lu, Aijiang; Bando, Yoshio; Golberg, Dmitri; Hu, Junqing

    2015-05-13

    Herein, we report time-resolved in situ transmission electron microscopy observation of Au particle melting at a Ge nanowire tip, subsequent forming of Au/Ge alloy liquid, and its migrating within the Ge nanowire. The migration direction and position of the Au/Ge liquid can be controlled by the applied voltage and the migration speed shows a linear deceleration in the nanowire. In a migration model proposed, the relevant dynamic mechanisms (electromigration, thermodiffusion, and viscous force, etc.) are discussed in detail. This work associated with the liquid mass transport in the solid nanowires should provide new insights into the crystal growth, interface engineering, and fabrication of the heterogeneous nanostructure-based devices.

  5. Contactless processing of SiGe-melts in EML under reduced gravity.

    PubMed

    Luo, Yuansu; Damaschke, Bernd; Schneider, Stephan; Lohöfer, Georg; Abrosimov, Nikolay; Czupalla, Matthias; Samwer, Konrad

    2016-01-01

    The processing of semiconductors based on electromagnetic levitation is a challenge, because this kind of materials shows a poor electrical conductivity. Here, we report the results of measurements of the thermophysical properties obtained recently from highly doped semiconductors Si1-x Ge x under microgravity conditions in the framework of parabola flight campaigns. Due to the limited time of about 20 s of microgravity especially Ge-rich samples with low melting temperatures were investigated. The measurements were performed contactlessly by video techniques with subsequent digital image processing. Linear and volume thermal expansion coefficients were measured hereby from image data. An anomaly of volume changes near the solidus temperature is visible. Viscosity and surface tension were determined by the oscillating drop technique using optic and electronic data. It was observed that the alloying of Si into Ge increases the surface tension of the melts. The viscosity is following an Arrhenius equation and shows a crossover temperature which separates simple liquid at high temperatures from cooperative liquid at low temperatures.

  6. Effect of Ge autodoping during III-V MOVPE growth on Ge substrates

    NASA Astrophysics Data System (ADS)

    Barrutia, Laura; Barrigón, Enrique; García, Iván; Rey-Stolle, Ignacio; Algora, Carlos

    2017-10-01

    During the MOVPE growth of III-V layers on Ge substrates, Ge atoms can be evaporated or etched from the back of the wafer and reach the growth surface, becoming incorporated into the epilayers. This is the so-called Ge autodoping effect, which we have studied through a set of growth experiments of GaInP and Ga(In)As layers lattice matched to Ge substrates, which have been characterized by Secondary Ion Mass Spectroscopy. The role of V/III ratio and growth rate on Ge autodoping has been studied and a MOVPE reactor pre-conditioning prior to the epitaxial growth of III-V semiconductor layers that mitigates this Ge autodoping has been identified. In addition, the use of 2-in. versus 4-in. Ge substrates has been compared and the use of a Si3N4 backside coating for the Ge substrates has been evaluated.

  7. Zinc oxide based diluted magnetic semiconductor nanoparticles: Synthesis by laser ablation in liquids, microstructural and optical properties

    SciTech Connect

    Savchuk, Andriy I.; Stolyarchuk, Ihor D.; Savchuk, Oleksandr A.; Makoviy, Vitaliy V.; Smolinsky, Mykhailo M.; Shporta, Oleksandra A.; Perrone, Alessio

    2013-12-04

    Nanoparticles of ZnO and ZnO doped with transition metals (Mn, Co) were synthesized by laser ablation in liquid medium. Scanning electron microscopy (SEM) showed formation of nanostructures with different shapes. Atomic force microscopy (AFM) gives information about surface morphology of the formed nanostructures. Absorption edge of ZnO, ZnO:Mn and ZnO:Co colloidal nanoparticles exhibits blue shift due to confinement effect. In photoluminescence spectra three peaks are attributed to the band-edge transitions and defect states. The Faraday rotation in ZnO:Mn nanoparticles gives evidence for paramagnetic behavior at room temperature.

  8. Si, Ge, and SiGe quantum wires and quantum dots

    NASA Astrophysics Data System (ADS)

    Pearsall, T. P.

    This document is part of subvolume C3 'Optical Properties' of volume 34 'Semiconductor quantum structures' of Landolt-Börnstein, Group III, Condensed Matter, on the optical properties of quantum structures based on group IV semiconductors. It discusses Si, Ge, and SiGe quantum wire and quantum dot structures, the synthesis of quantum wires and quantum dots, and applications of SiGe quantum-dot structures as photodetectors, light-emitting diodes, for optical amplification and as Si quantum-dot memories.

  9. Strongly-disordered hybridization and non-Fermi liquid behavior in CePt4Ge12-xSbx studied with thermoelectric power

    NASA Astrophysics Data System (ADS)

    White, Benjamin; Huang, Kevin; Maple, M. Brian

    2014-03-01

    Non-Fermi liquid (NFL) behavior is commonly associated with the presence of a nearby quantum critical point, but can also be observed in other scenarios. In a clean system, hybridization between localized and itinerant electron states can be characterized by a single Kondo temperature TK, but introducing chemical disorder can lead to a wide distribution of TK values. Given sufficient disorder, the resulting distribution will tend to include an appreciable number of localized electron states which are characterized by TK ~ 0 K, and NFL behavior emerges. A Kondo-disorder type of NFL behavior was recently reported in the filled skutterudite system CePt4Ge12-xSbx in the vicinity of x = 1 . We performed a study of the thermoelectric power S(T) for this system and observed an evolution of S(T) with x that is dramatic and broadly consistent with the boundaries of the proposed phase diagram. The effect of disordered hybridization is clearly observed in a low-temperature feature in S(T) in the range 0 . 5 <= x <= 1 . 5 and NFL behavior is also observed at x = 1. These results clearly demonstrate how sensitively S(T) is able to probe a Kondo disorder system. Research was performed with support from the US DOE grant DE-FG02-04-ER46105.

  10. Metabonomic study on the plasma of streptozotocin-induced diabetic rats treated with Ge Gen Qin Lian Decoction by ultra high performance liquid chromatography-mass spectrometry.

    PubMed

    Zhang, Qiyun; Xu, Guoliang; Li, Jia; Guo, Xiaofeng; Wang, Hong; Li, Bingtao; Tu, Jun; Zhang, Huashan

    2016-02-20

    Changes in endogenous metabolites in the plasma of streptozotocin (STZ)-induced diabetic rats treated with Ge Gen Qin Lian Decoction (GGQLD) were studied. The endogenous compounds in plasma were detected using ultra high performance liquid chromatography coupled with quadrupole-time-of-flight tandem mass spectrometry (UHPLC-Q-TOF-MS). Rats were divided into three groups: control, model, and administration (4.95g crude drug/kg body weight). After the final administration, plasma samples from the three groups were analyzed using metabonomics. The three sample groups could be clearly distinguished. The administration group exhibited a distinct return to the levels of phytosphingosine and dihydrosphingosine of the control group according to the principal component analysis score, and the corresponding biomarkers were defined. Significant changes in endogenous metabolites, such as dihydrosphingosine, phytosphingosine, cholylglycine, and pantothenic acid, were identified in STZ-induced diabetic rats. These biochemical changes are associated with the metabolism of sphingolipids, fats, and acetyl coenzyme-A, which could be useful to further investigate the characteristics of STZ-induced diabetes mellitus and the therapeutic mechanism of action of GGQLD. This metabonomic analysis could provide a useful starting point toelucidate the therapeutic effects and mechanism of action of GGQLD in diabetes mellitus.

  11. Chemically Derivatized Semiconductor Photoelectrodes.

    DTIC Science & Technology

    1982-01-04

    as Si, Ge, and GaAs derivatized with reagents based on ferrocene such as those represented by I and II. Work with p-type semiconductor photoelectrode...Concerning n-type Si it was found that EtOH/0.1 M En-Bu4N)C104 solutions containing A = ferrocene and A+ = ferri-- cinium result in a constant output of...electrical energy from an illuminated photoelectrochemical device configured as in Scheme II.(20) The ferrocene captures the photogenerated h+ at a rate -4

  12. The Longwave Silicon Chip - Integrated Plasma-Photonics in Group IV And III-V Semiconductors

    DTIC Science & Technology

    2013-10-01

    infrared, nanophotonics, semiconductor lasers , spasers, optical waveguiding, optical sensors, modulators, optical switches, photodetectors, quantum wells ...a Si-based lattice-matched room-temperature SiGeSn/GeSn/SiGeSn multi- quantum - well mid-infrared laser diode”, Optics Express, vol. 19, pp. 19957...GeSn/SiGeSn multi- quantum - well laser diodes, first-principles band theory of all SiGeSn alloys, Fano nano-membrane devices, ultralow-energy MOS

  13. Spectral and dielectric properties of nematic liquid crystal doped semiconductor quantum dots CdSe/ZnS

    NASA Astrophysics Data System (ADS)

    Kurachkina, M. A.; Shcherbinin, D. P.; Konshina, E. A.

    2015-06-01

    We investigated the absorption and luminescence spectra and the low-frequency spectra of dielectric losses of the nematic liquid crystal (NLC) suspensions with quantum dots (QDs) CdSe/ZnS with a core diameter of 3.5 nm and 5.0 nm. The changing of luminescence intensity and dielectric losses in the region below 103 Hz were observed as result variation of a concentration and a QDs size in the spectra of NLC/QDs suspensions in comparison with the pure NLC. Luminescence quenching of the NLC and the increase of dielectric loss in the spectra were found with the increasing CdSe/ZnS concentration in interval between 0.07 - 0.3 wt. %.

  14. Materials science: Screen printing of 2D semiconductors

    NASA Astrophysics Data System (ADS)

    Kim, Young Duck; Hone, James

    2017-04-01

    Atomically thin semiconductors have been made by transferring the oxide 'skin' of a liquid metal to substrates. This opens the way to the low-cost mass production of 2D semiconductors at the sizes needed for electronics applications.

  15. Temperature-independent hole mobility of a smectic liquid-crystalline semiconductor based on band-like conduction.

    PubMed

    Funahashi, Masahiro; Ishii, Tomohiko; Sonoda, Akinari

    2013-08-26

    A liquid-crystalline (LC) phenylterthiophene derivative, which exhibited an ordered smectic phase at room temperature, was purified by vacuum sublimation under a flow of nitrogen. During the sublimation process, thin plates with sizes of 1 mm grew on the surface of the vacuum tube. The crystals exhibited the same X-ray diffraction patterns as the ordered smectic phase of the LC state that was formed through a conventional recrystallization process by using organic solvents. Because of the removal of chemical impurities, the hole mobility in the ordered smectic phase of the vacuum-grown thin plates increased to 1.2×10(-1) cm(2) V(-1) s(-1) at room temperature, whereas that of the LC precipitates was 7×10(-2) cm(2) V(-1) s(-1). The hole mobility in the ordered smectic phase of the vacuum-sublimated sample was temperature-independent between 400 and 220 K. The electric-field dependence of the hole mobility was also very small within this temperature range. The temperature dependence of hole mobility was well-described by the Hoesterey-Letson model. The hole-transport characteristics indicate that band-like conduction affected by the localized states, rather than a charge-carrier-hopping mechanism, is a valid mechanism for hole transport in an ordered smectic phase.

  16. Investigation of Ge1-xSnx/Ge quantum-well structures as optical gain media

    NASA Astrophysics Data System (ADS)

    Sun, Li-Chou; Li, Hui; Cheng, H. H.; Chang, Guo-En

    2016-11-01

    An efficient Si-based laser is one of the most important components for photonic integrated circuits to break the bottleneck of data transport over optical networks. The main challenge is to create gain media based on group-IV semiconductors. Here we present an investigation of using low-dimensional Ge1-xSnx/Ge quantum-well (QW) structures pseudomorphically grown on Ge-buffered Si substrates as optical gain media for efficient Si-based lasers. Epitaxial growth of Ge1-xSnx/Ge QW structures on Ge-buffer Si substrate was carried out using low-temperature molecular beam epitaxy techniques. The light emission properties of the grown Ge1-xSnx/Ge QW structure were studied using photoluminescence spectroscopy, and clear redshifts of emission peaks were observed. Theoretical analysis of band structures indicates that Ge1-xSnx well sandwiched by Ge barriers can form type-I alignment at D point with a sufficient potential barrier height to confine carriers in the Ge1-xSnx well, thereby enhancing efficient electron-hole direct recombination. Our calculations also show that the energy difference between the lowest D-conduction subband and L conduction subband can be reduced with increasing Sn content, thereby enabling optical gain. These results suggest that Ge1-xSnx/Ge QW structures are promising for optical gain media to develop efficient Si-based light emitters.

  17. Dye Sensitization of Semiconductor Particles

    SciTech Connect

    Hartland, G. V.

    2003-01-13

    In this project electron transfer at semiconductor liquid interfaces was examined by ultrafast time-resolved and steady-state optical techniques. The experiments primarily yielded information about the electron transfer from titanium dioxide semiconductor particles to absorbed molecules. The results show that the rate of electron transfer depends on the structure of the molecule, and the crystalline phase of the particle. These results can be qualitatively explained by Marcus theory for electron transfer.

  18. Formation and Stabilization of Single-Crystalline Metastable AuGe Phases in Ge Nanowires

    SciTech Connect

    Sutter, E.; Sutter, P.

    2011-07-22

    We use in situ observations by variable temperature transmission electron microscopy on AuGe alloy drops at the tips of Ge nanowires (NWs) with systematically varying composition to demonstrate the controlled formation of metastable solid phases integrated in NWs. The process, which operates in the regime of vapor-liquid-solid growth, involves a size-dependent depression of the alloy liquidus at the nanoscale that leads to extremely Ge-rich AuGe melts at low temperatures. During slow cooling, these liquid AuGe alloy drops show pronounced departures from equilibrium, i.e., a frustrated phase separation of Ge into the adjacent solid NW, and ultimately crystallize as single-crystalline segments of metastable {gamma}-AuGe. Our findings demonstrate a general avenue for synthesizing NW heterostructures containing stable and metastable solid phases, applicable to a wide range of materials of which NWs form by the vapor-liquid-solid method.

  19. Pseudomorphic GeSn/Ge(001) quantum wells: Examining indirect band gap bowing

    SciTech Connect

    Tonkikh, Alexander A.; Eisenschmidt, Christian; Schmidt, Georg; Talalaev, Vadim G.; Zakharov, Nikolay D.; Werner, Peter; Schilling, Joerg

    2013-07-15

    A study of the bandgap character of compressively strained GeSn{sub 0.060-0.091}/Ge(001) quantum wells grown by molecular beam epitaxy is reported. The built-in strain in GeSn wells leads to an increased separation between L and {Gamma} conduction band minima. The prevalent indirect interband transitions in GeSn were probed by photoluminescence spectroscopy. As a result we could simulate the L-valley bowing parameter in GeSn alloys, b{sub L} = 0.80 {+-} 0.06 eV at 10 K. From this we conclude that even compressively strained GeSn/Ge(001) alloys could become direct band gap semiconductors at the Sn-fraction higher than 17.0 at. %.

  20. Semiconductor sensors

    NASA Technical Reports Server (NTRS)

    Gatos, Harry C. (Inventor); Lagowski, Jacek (Inventor)

    1977-01-01

    A semiconductor sensor adapted to detect with a high degree of sensitivity small magnitudes of a mechanical force, presence of traces of a gas or light. The sensor includes a high energy gap (i.e., .about. 1.0 electron volts) semiconductor wafer. Mechanical force is measured by employing a non-centrosymmetric material for the semiconductor. Distortion of the semiconductor by the force creates a contact potential difference (cpd) at the semiconductor surface, and this cpd is determined to give a measure of the force. When such a semiconductor is subjected to illumination with an energy less than the energy gap of the semiconductors, such illumination also creates a cpd at the surface. Detection of this cpd is employed to sense the illumination itself or, in a variation of the system, to detect a gas. When either a gas or light is to be detected and a crystal of a non-centrosymmetric material is employed, the presence of gas or light, in appropriate circumstances, results in a strain within the crystal which distorts the same and the distortion provides a mechanism for qualitative and quantitative evaluation of the gas or the light, as the case may be.

  1. Semiconductor photoelectrochemistry

    NASA Technical Reports Server (NTRS)

    Buoncristiani, A. M.; Byvik, C. E.

    1983-01-01

    Semiconductor photoelectrochemical reactions are investigated. A model of the charge transport processes in the semiconductor, based on semiconductor device theory, is presented. It incorporates the nonlinear processes characterizing the diffusion and reaction of charge carriers in the semiconductor. The model is used to study conditions limiting useful energy conversion, specifically the saturation of current flow due to high light intensity. Numerical results describing charge distributions in the semiconductor and its effects on the electrolyte are obtained. Experimental results include: an estimate rate at which a semiconductor photoelectrode is capable of converting electromagnetic energy into chemical energy; the effect of cell temperature on the efficiency; a method for determining the point of zero zeta potential for macroscopic semiconductor samples; a technique using platinized titanium dioxide powders and ultraviolet radiation to produce chlorine, bromine, and iodine from solutions containing their respective ions; the photoelectrochemical properties of a class of layered compounds called transition metal thiophosphates; and a technique used to produce high conversion efficiency from laser radiation to chemical energy.

  2. Survey of cryogenic semiconductor devices

    SciTech Connect

    Talarico, L.J.; McKeever, J.W.

    1996-04-01

    Improved reliability and electronic performance can be achieved in a system operated at cryogenic temperatures because of the reduction in mechanical insult and in disruptive effects of thermal energy on electronic devices. Continuing discoveries of new superconductors with ever increasing values of T{sub c} above that of liquid nitrogen temperature (LNT) have provided incentive for developing semiconductor electronic systems that may also operate in the superconductor`s liquid nitrogen bath. Because of the interest in high-temperature superconductor (HTS) devices, liquid nitrogen is the cryogen of choice and LNT is the temperature on which this review is focused. The purpose of this survey is to locate and assemble published information comparing the room temperature (298 K), performance of commercially available conventional and hybrid semiconductor device with their performance at LNT (77K), to help establish their candidacy as cryogenic electronic devices specifically for use at LNT. The approach to gathering information for this survey included the following activities. Periodicals and proceedings were searched for information on the behavior of semiconductor devices at LNT. Telephone calls were made to representatives of semiconductor industries, to semiconductor subcontractors, to university faculty members prominent for their research in the area of cryogenic semiconductors, and to representatives of the National Aeronautics and Space Administration (NASA) and NASA subcontractors. The sources and contacts are listed with their responses in the introduction, and a list of references appears at the end of the survey.

  3. Recent developments in semiconductor gamma-ray detectors

    SciTech Connect

    Luke, Paul N.; Amman, Mark; Tindall, Craig; Lee, Julie S.

    2003-10-28

    The successful development of lithium-drifted Ge detectors in the 1960's marked the beginning of the significant use of semiconductor crystals for direct detection and spectroscopy of gamma rays. In the 1970's, high-purity Ge became available, which enabled the production of complex detectors and multi-detector systems. In the following decades, the technology of semiconductor gamma-ray detectors continued to advance, with significant developments not only in Ge detectors but also in Si detectors and room-temperature compound-semiconductor detectors. In recent years, our group at Lawrence Berkeley National Laboratory has developed a variety of gamma ray detectors based on these semiconductor materials. Examples include Ge strip detectors, lithium-drifted Si strip detectors, and coplanar-grid CdZnTe detectors. These advances provide new capabilities in the measurement of gamma rays, such as the ability to perform imaging and the realization of highly compact spectroscopy systems.

  4. First-principles study of defect formation in the photovoltaic semiconductors Cu2GeS3 and Cu2ZnGeS4 for comparison with Cu2SnS3, Cu2ZnSnS4, and CuInSe2

    NASA Astrophysics Data System (ADS)

    Nishihara, Hironori; Maeda, Tsuyoshi; Shigemi, Akio; Wada, Takahiro

    2017-04-01

    The formation energies of neutral Cu, Ge, and S vacancies in monoclinic Cu2GeS3 and those of neutral Cu, Zn, Ge, and S vacancies in kesterite-type Cu2ZnGeS4 were evaluated by first-principles pseudopotential calculations using plane-wave basis functions. The calculations were performed at typical points in a schematic ternary phase diagram of a Cu–Ge–S system for Cu2GeS3 and in Cu–(Zn1/2Ge1/2)–S and Cu29S16–ZnS–GeS2 pseudoternary phase diagrams for Cu2ZnGeS4. The results have been compared with those for Cu2SnS3, Cu2ZnSnS4, and CuInSe2 calculated with the same version of the CASTEP program code. The results indicate that Cu vacancies are easily formed in Cu2GeS3 and Cu2ZnGeS4 under the Cu-poor condition as in the cases of Cu2SnS3, Cu2ZnSnS4, and CuInSe2, suggesting that Cu2GeS3 and Cu2ZnGeS4 are also preferable p-type absorber materials for thin-film solar cells. Desirable preparation conditions of these thin films for photovoltaic application are discussed using the calculated formation energies of antisite defects.

  5. Simulated characteristics of a heterojunction phototransistor with Ge1-xSnx alloy as base

    NASA Astrophysics Data System (ADS)

    Kumar, Dur Vesh; Pandey, Ankit Kumar; Basu, Rikmantra; Sharma, Anuj K.

    2016-12-01

    Groups III-V compound semiconductors and their alloys are the main photodetecting elements for the entire fiber optic telecommunication band. However, the recent successful growth of GeSnx alloy on Ge virtual substrates on Si platform makes the group IV alloys a potential competitor. GeSnx alloy shows direct band gap and has an absorption coefficient almost 10 times higher than that of Ge. The photonic devices are complementary metal-oxide-semiconductor compatible. We have considered an n-Ge/p+-GeSnx/n-GeSnx heterojunction phototransistor (HPT) and studied the variations of terminal currents by considering the Gummel Poon model of HPT, and values of optical and current gains, photocurrent, and responsivity have been obtained. The performance of the device as a photodetector at fiber optic communication wavelengths seems quite encouraging to justify the use of GeSn-based HPTs as a replacement of III-IV semiconductor-based photodetectors.

  6. Heterogeneous integration of SiGe/Ge and III-V for Si photonics

    NASA Astrophysics Data System (ADS)

    Takenaka, Mitsuru; Kim, Younghyun; Han, Jaehoon; Kang, Jian; Ikku, Yuki; Cheng, Yongpeng; Park, Jinkwon; Takagi, Shinichi

    2016-05-01

    The heterogeneous integration of SiGe/Ge and III-V semiconductors gives us an opportunity to enhance functionalities of Si photonics platform through their superior material properties which lack in Si. In this paper we discuss what SiGe/Ge and III-V can bring to Si photonics. We have predicted that the light effective hole mass in strained SiGe results in the enhanced the free-carrier effects such as the plasma dispersion effect and free-carrier absorption. We observed significantly larger free-carrier absorption in the SiGe optical modulator than in the control Si device. By fabricating asymmetric Mach-Zehnder interferometer (MZI) SiGe optical modulators, the enhancement of the plasma dispersion effect in strained SiGe has been successfully demonstrated. Mid-infrared integrated photonics based on Ge waveguides on Si have also been investigated. Since Ge is transparent to the entire mid-infrared range, Ge photonic integrated circuits on the Ge-on-Insulator (GeOI) wafer are quite attractive. We have successfully fabricated the GeOI wafer with 2-μm-thick buried oxide (BOX) layer by wafer bonding. The passive waveguide components based on Ge strip waveguides have been demonstrated on the GeOI. We have also demonstrated carrier-injection Ge variable optical attenuators. We have proposed and investigate the III-V CMOS photonics platform by using the III-V on Insulator (IIIV- OI) on a Si wafer. The strong optical confinement in the III-V-OI enables us to achieve high-performance photonic devices. We have successfully demonstrated InGaAsP MZI optical switch with the low on-state crosstalk on the III-V-OI. Ultra-low dark current waveguide InGaAs PDs integrated with an InP grating coupler are also achieved.

  7. Novel growth techniques of group-IV based semiconductors on insulator for next-generation electronics

    NASA Astrophysics Data System (ADS)

    Miyao, Masanobu; Sadoh, Taizoh

    2017-05-01

    Recent progress in the crystal growth of group-IV-based semiconductor-on-insulators is reviewed from physical and technological viewpoints. Liquid-phase growth based on SiGe-mixing-triggered rapid-melting growth enables formation of hybrid (100) (110) (111)-orientation Ge-on-insulator (GOI) structures, which show defect-free GOI with very high carrier mobility (˜1040 cm2 V-1 s-1). Additionally, SiGe mixed-crystals with laterally uniform composition were obtained by eliminating segregation phenomena during the melt-back process. Low-temperature solid-phase growth has been explored by combining this process with ion-beam irradiation, additional doping of group-IV elements, metal induced lateral crystallization with/without electric field, and metal-induced layer exchange crystallization. These efforts have enabled crystal growth on insulators below 400 °C, achieving high carrier mobility (160-320 cm2 V-1 s-1). Moreover, orientation-controlled SiGe and Ge films on insulators have been obtained below the softening temperatures of conventional plastic films (˜300 °C). Detailed characterization provides an understanding of physical phenomena behind these crystal growth techniques. Applying these methods when fabricating next-generation electronics is also discussed.

  8. Axial Ge/Si nanowire heterostructure tunnel FETs

    SciTech Connect

    Picraux, Sanuel T; Daych, Shadi A

    2010-01-01

    The vapor-liquid-solid (VLS) growth of semiconductor nanowires allows doping and composition modulation along their axis and the realization of axial 1 D heterostructures. This provides additional flexibility in energy band-edge engineering along the transport direction which is difficult to attain by planar materials growth and processing techniques. We report here on the design, growth, fabrication, and characterization of asymmetric heterostructure tunnel field-effect transistors (HTFETs) based on 100% compositionally modulated Si/Ge axial NWs for high on-current operation and low ambipolar transport behavior. We discuss the optimization of band-offsets and Schottky barrier heights for high performance HTFETs and issues surrounding their experimental realization. Our HTFET devices with 10 nm PECVD SiN{sub x} gate dielectric resulted in a measured current drive exceeding 100 {mu}A/{mu}m (I/{pi}D) and 10{sup 5} I{sub on}/I{sub off} ratios.

  9. Non-equilibrium induction of tin in germanium: towards direct bandgap Ge(1-x)Sn(x) nanowires.

    PubMed

    Biswas, Subhajit; Doherty, Jessica; Saladukha, Dzianis; Ramasse, Quentin; Majumdar, Dipanwita; Upmanyu, Moneesh; Singha, Achintya; Ochalski, Tomasz; Morris, Michael A; Holmes, Justin D

    2016-04-20

    The development of non-equilibrium group IV nanoscale alloys is critical to achieving new functionalities, such as the formation of a direct bandgap in a conventional indirect bandgap elemental semiconductor. Here, we describe the fabrication of uniform diameter, direct bandgap Ge(1-x)Sn(x) alloy nanowires, with a Sn incorporation up to 9.2 at.%, far in excess of the equilibrium solubility of Sn in bulk Ge, through a conventional catalytic bottom-up growth paradigm using noble metal and metal alloy catalysts. Metal alloy catalysts permitted a greater inclusion of Sn in Ge nanowires compared with conventional Au catalysts, when used during vapour-liquid-solid growth. The addition of an annealing step close to the Ge-Sn eutectic temperature (230 °C) during cool-down, further facilitated the excessive dissolution of Sn in the nanowires. Sn was distributed throughout the Ge nanowire lattice with no metallic Sn segregation or precipitation at the surface or within the bulk of the nanowires. The non-equilibrium incorporation of Sn into the Ge nanowires can be understood in terms of a kinetic trapping model for impurity incorporation at the triple-phase boundary during growth.

  10. Non-equilibrium induction of tin in germanium: towards direct bandgap Ge1-xSnx nanowires

    NASA Astrophysics Data System (ADS)

    Biswas, Subhajit; Doherty, Jessica; Saladukha, Dzianis; Ramasse, Quentin; Majumdar, Dipanwita; Upmanyu, Moneesh; Singha, Achintya; Ochalski, Tomasz; Morris, Michael A.; Holmes, Justin D.

    2016-04-01

    The development of non-equilibrium group IV nanoscale alloys is critical to achieving new functionalities, such as the formation of a direct bandgap in a conventional indirect bandgap elemental semiconductor. Here, we describe the fabrication of uniform diameter, direct bandgap Ge1-xSnx alloy nanowires, with a Sn incorporation up to 9.2 at.%, far in excess of the equilibrium solubility of Sn in bulk Ge, through a conventional catalytic bottom-up growth paradigm using noble metal and metal alloy catalysts. Metal alloy catalysts permitted a greater inclusion of Sn in Ge nanowires compared with conventional Au catalysts, when used during vapour-liquid-solid growth. The addition of an annealing step close to the Ge-Sn eutectic temperature (230 °C) during cool-down, further facilitated the excessive dissolution of Sn in the nanowires. Sn was distributed throughout the Ge nanowire lattice with no metallic Sn segregation or precipitation at the surface or within the bulk of the nanowires. The non-equilibrium incorporation of Sn into the Ge nanowires can be understood in terms of a kinetic trapping model for impurity incorporation at the triple-phase boundary during growth.

  11. Room Temperature Ferromagnetic Mn:Ge(001)

    PubMed Central

    Lungu, George Adrian; Stoflea, Laura Elena; Tanase, Liviu Cristian; Bucur, Ioana Cristina; Răduţoiu, Nicoleta; Vasiliu, Florin; Mercioniu, Ionel; Kuncser, Victor; Teodorescu, Cristian-Mihail

    2014-01-01

    We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001), heated at relatively high temperature (starting with 250 °C). The samples were characterized by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID), and magneto-optical Kerr effect (MOKE). Samples deposited at relatively elevated temperature (350 °C) exhibited the formation of ~5–8 nm diameter Mn5Ge3 and Mn11Ge8 agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe~2.5 phase, or manganese diluted into the Ge(001) crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm) deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge–Ge dimers on Ge(001). The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed. PMID:28788444

  12. Vapor-liquid-solid epitaxial growth of Si1-xGex alloy nanowires. Composition dependence on precursor reactivity and morphology control for vertical forests

    SciTech Connect

    Choi, S. G.; Manandhar, P.; Picraux, S. T.

    2015-07-07

    The growth of high-density group IV alloy nanowire forests is critical for exploiting their unique functionalities in many applications. Here, the compositional dependence on precursor reactivity and optimized conditions for vertical growth are studied for Si1- x Ge x alloy nanowires grown by the vapor-liquid-solid method. The nanowire composition versus gas partial-pressure ratio for germane-silane and germane-disilane precursor combinations is obtained at 350°C over a wide composition range (0.05 ≤ x ≤ 0.98) and a generalized model to predict composition for alloy nanowires is developed based on the relative precursor partial pressures and reactivity ratio. In combination with germane, silane provides more precise compositional control at high Ge concentrations (x > 0.7), whereas disilane greatly increases the Si concentration for a given gas ratio and enables more precise alloy compositional control at small Ge concentrations (x < 0.3). Vertically oriented, non-kinking nanowire forest growth on Si (111) substrates is then discussed for silane/germane over a wide range of compositions, with temperature and precursor partial pressure optimized by monitoring the nanowire growth front using in-situ optical reflectance. For high Ge compositions (x ≈ 0.9), a “two-step” growth approach with nucleation at higher temperatures results in nanowires with high-density and uniform vertical orientation. Furthermore, increasing Si content (x ≈ 0.8), the optimal growth window is shifted to higher temperatures, which minimizes nanowire kinking morphologies. For Si-rich Si1- x Ge x alloys (x ≈ 0.25), vertical nanowire growth is enhanced by single-step, higher-temperature growth at reduced pressures.

  13. Strain-induced growth of SiO2 dots by liquid phase deposition

    NASA Astrophysics Data System (ADS)

    Liu, C. W.; Hsu, B.-C.; Chen, K.-F.; Lee, M. H.; Shie, C.-R.; Chen, Pang-Shiu

    2003-01-01

    Silicon dioxide dots are deposited on the Si cap layers of self-assembled Ge dots using a liquid phase deposition method. The Si capping layer directly above the Ge dots has a tensile strain, while the Si cap on the wetting layer is not strained. The tensile strain can enhance the silicon dioxide nucleation and deposition on Si surface, and SiO2 dots are directly formed on the top of Ge dots with the SiO2 wetting layers between the dots. The step height and base width of the dots increase with the deposition time. A metal-oxide-semiconductor photodetector is fabricated using the liquid-phase-deposited oxide, and has a responsivity of 0.08 mA/W at 1550 nm.

  14. Photoelectroconversion by Semiconductors: A Physical Chemistry Experiment.

    ERIC Educational Resources Information Center

    Fan, Qinbai; And Others

    1995-01-01

    Presents an experiment designed to give students some experience with photochemistry, electrochemistry, and basic theories about semiconductors. Uses a liquid-junction solar cell and illustrates some fundamental physical and chemical principles related to light and electricity interconversion as well as the properties of semiconductors. (JRH)

  15. Photoelectroconversion by Semiconductors: A Physical Chemistry Experiment.

    ERIC Educational Resources Information Center

    Fan, Qinbai; And Others

    1995-01-01

    Presents an experiment designed to give students some experience with photochemistry, electrochemistry, and basic theories about semiconductors. Uses a liquid-junction solar cell and illustrates some fundamental physical and chemical principles related to light and electricity interconversion as well as the properties of semiconductors. (JRH)

  16. New developments in nanoparticle-liquid crystal composites: from magic-sized semiconductor nanoclusters to alignment pattern formation via nanoparticle stenciling

    NASA Astrophysics Data System (ADS)

    Mirzaei, Javad; Sawatzky, Ryan; Sharma, Anshul; Urbanski, Martin; Yu, Kui; Kitzerow, Heinz-S.; Hegmann, Torsten

    2012-03-01

    We here report on the alignment and electro-optic properties of nematic liquid crystals (LCs) either containing nanoscale particles as additives or featuring particles patterned on substrates. The investigated nematic LCs or LC dispersions are doped or in contact with magic-sized semiconductor CdSe nanocrystals (MSNCs) or silane- and alkylthiol monolayercapped gold nanoparticles. Three single-sized CdSe quantum dots capped with myristic acid exhibiting bright bandgap photoluminescence (PL) at λmax ~ 463 nm were tested as additives. Two of the quantum dots only vary in the amount of defects as indicated by different bandgap and deep trap PL. The third MSNC sample is compositionally different, doped with Zn. These MSNCs with almost identical sizes were doped at different concentrations (1-5 wt%) into the nematic phase of the 2-phenylpyrimidine-based LC1. Only the Zn-doped MSNCs showed the formation of birefringent stripes surrounded by areas of homeotropic alignment between plain glass slides at all concentrations as observed for many other nanoparticle-doped nematic LCs reported earlier by our group. In polyimide-coated glass slides favoring planar orientation of the nematic director, planar alignment was observed. Similarly, siloxane-coated gold nanoparticle additives with narrow size distribution, but larger size, show homeotropic alignment between plain glass and planar alignment in rubbed polyimide-coated cells. Surprisingly then, we succeeded in creating alignment patterns using smaller, ~2 nm alkylthiol-capped gold nanoparticles using a process called stenciling that allowed us to generate patterns of homeotropic alignment in a continuum of planar alignment of the nematic LC. Finally, electro-optic investigations on some of these samples revealed that only the Zn-doped magic-sized MSNCs significantly lower the dielectric anisotropy as well as the splay elastic constant of the nematic host, despite identical size and surface functionality of the three used

  17. Creating semiconductor metafilms with designer absorption spectra

    PubMed Central

    Kim, Soo Jin; Fan, Pengyu; Kang, Ju-Hyung; Brongersma, Mark L.

    2015-01-01

    The optical properties of semiconductors are typically considered intrinsic and fixed. Here we leverage the rapid developments in the field of optical metamaterials to create ultrathin semiconductor metafilms with designer absorption spectra. We show how such metafilms can be constructed by placing one or more types of high-index semiconductor antennas into a dense array with subwavelength spacings. It is argued that the large absorption cross-section of semiconductor antennas and their weak near-field coupling open a unique opportunity to create strongly absorbing metafilms whose spectral absorption properties directly reflect those of the individual antennas. Using experiments and simulations, we demonstrate that near-unity absorption at one or more target wavelengths of interest can be achieved in a sub-50-nm-thick metafilm using judiciously sized and spaced Ge nanobeams. The ability to create semiconductor metafilms with custom absorption spectra opens up new design strategies for planar optoelectronic devices and solar cells. PMID:26184335

  18. Thermodynamic modeling of the Ge-La binary system

    NASA Astrophysics Data System (ADS)

    Liu, Miao; Li, Chang-rong; Du, Zhen-min; Guo, Cui-ping; Niu, Chun-ju

    2012-08-01

    The Ge-La binary system was critically assessed by means of the calculation of phase diagram (CALPHAD) technique. The associate model was used for the liquid phase containing the constituent species Ge, La, Ge3La5, and Ge1.7La. The terminal solid solution diamond-(Ge) with a small solubility of La was described using the substitutional model, in which the excess Gibbs energy was formulated with the Redlich-Kister equation. The compounds with homogeneity ranges, α(Ge1.7La), β(Ge1.7La), and (GeLa), were modeled using two sublattices as α(Ge,La)1.7La, β(Ge,La)1.7La, and (Ge,La)(Ge,La), respectively. The intermediate phases with no solubility ranges, Ge4La5, Ge3La4, Ge3La5, and GeLa3, were treated as stoichiometric compounds. The three allotropic modifications of La, dhcp-La, fcc-La, and bcc-La, were kept as pure element phases since no solubility of Ge in La was reported. A set of self-consistent thermodynamic parameters of the Ge-La binary system was obtained. The calculation results agree well with the available experimental data from literatures.

  19. Chemical pressure effects on magnetism in the quantum spin liquid candidates Yb2X2O7 (X =Sn, Ti, Ge)

    NASA Astrophysics Data System (ADS)

    Dun, Z. L.; Lee, M.; Choi, E. S.; Hallas, A. M.; Wiebe, C. R.; Gardner, J. S.; Arrighi, E.; Freitas, R. S.; Arevalo-Lopez, A. M.; Attfield, J. P.; Zhou, H. D.; Cheng, J. G.

    2014-02-01

    The linear and nonlinear ac susceptibility measurements of Yb-pyrochlores, Yb2X2O7 (X =Sn, Ti, and Ge), show transitions with a ferromagnetic nature at 0.13 and 0.25 K for Yb2Sn2O7 and Yb2Ti2O7, respectively, and an antiferromagnetic ordering at 0.62 K for Yb2Ge2O7. These systematical results (i) provided information about the nature of the unconventional magnetic ground state in Yb2Ti2O7; (ii) realized a distinct antiferromagnetic ordering state in Yb2Ge2O7; and (iii) demonstrated that the application of chemical pressure through the series of Yb-pyrochlores can efficiently perturb the fragile quantum spin fluctuations of the Yb3+ ions and lead to very different magnetic ground states.

  20. Fabrication of normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors by photo-electrochemical gate recess etching in ionic liquid

    NASA Astrophysics Data System (ADS)

    Zhang, Zhili; Qin, Shuangjiao; Fu, Kai; Yu, Guohao; Li, Weiyi; Zhang, Xiaodong; Sun, Shichuang; Song, Liang; Li, Shuiming; Hao, Ronghui; Fan, Yaming; Sun, Qian; Pan, Gebo; Cai, Yong; Zhang, Baoshun

    2016-08-01

    We characterized an ionic liquid (1-butyl-3-methylimidazolium nitrate, C8H15N3O3) as a photo-electrochemical etchant for fabricating normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Using the ionic liquid, we achieved an etching rate of ˜2.9 nm/min, which is sufficiently low to facilitate good etching control. The normally-off AlGaN/GaN MIS-HEMT was fabricated with an etching time of 6 min, with the 20 nm low-pressure chemical vapor deposition (LPCVD) silicon nitride (Si3N4) gate dielectric exhibiting a threshold voltage shift from -10 to 1.2 V, a maximum drain current of more than 426 mA/mm, and a breakdown voltage of 582 V.

  1. Hopping conduction in polycrystalline semiconductors

    NASA Astrophysics Data System (ADS)

    Sharma, R. P.; Shukla, A. K.; Kapoor, A. K.; Srivastava, R.; Mathur, P. C.

    1985-03-01

    Measurements of dc conductivity (sigma) on polycrystalline semiconductors, viz., InSb, Si, and CdTe, have been reported in the temperature range 77-300 K. The conduction mechanism near liquid-nitrogen temperature has been identified as the hopping of charge carriers from the charged trap centers to empty traps near the Fermi level.

  2. Electrochemical impedance spectroscopy for quantitative interface state characterization of planar and nanostructured semiconductor-dielectric interfaces

    NASA Astrophysics Data System (ADS)

    Meng, Andrew C.; Tang, Kechao; Braun, Michael R.; Zhang, Liangliang; McIntyre, Paul C.

    2017-10-01

    The performance of nanostructured semiconductors is frequently limited by interface defects that trap electronic carriers. In particular, high aspect ratio geometries dramatically increase the difficulty of using typical solid-state electrical measurements (multifrequency capacitance- and conductance-voltage testing) to quantify interface trap densities (D it). We report on electrochemical impedance spectroscopy (EIS) to characterize the energy distribution of interface traps at metal oxide/semiconductor interfaces. This method takes advantage of liquid electrolytes, which provide conformal electrical contacts. Planar Al2O3/p-Si and Al2O3/p-Si0.55Ge0.45 interfaces are used to benchmark the EIS data against results obtained from standard electrical testing methods. We find that the solid state and EIS data agree very well, leading to the extraction of consistent D it energy distributions. Measurements carried out on pyramid-nanostructured p-Si obtained by KOH etching followed by deposition of a 10 nm ALD-Al2O3 demonstrate the application of EIS to trap characterization of a nanostructured dielectric/semiconductor interface. These results show the promise of this methodology to measure interface state densities for a broad range of semiconductor nanostructures such as nanowires, nanofins, and porous structures.

  3. Van der Waals Effects on semiconductor clusters.

    PubMed

    Li, Haisheng; Chen, Weiguang; Han, Xiaoyu; Li, Liben; Sun, Qiang; Guo, Zhengxiao; Jia, Yu

    2015-09-30

    Van der Waals (vdW) interactions play an important role on semiconductors in nanoscale. Here, we utilized first-principles calculations based on density functional theory to demonstrate the growth mode transition from prolate to multiunit configurations for Gen (n = 10-50) clusters. In agreement with the injected ion drift tube techniques that "clusters with n < 70 can be thought of as loosely bound assemblies of small strongly bound fragments (such as Ge7 and Ge10 )," we found these stable fragments are connected by Ge6 , Ge9 , or Ge10 unit (from bulk diamond), via strong covalent bonds. Our calculated cations usually fragment to Ge7 and Ge10 clusters, in accordance with the experiment results that the spectra Ge7 and Ge10 correspond to the mass abundance spectra. By controlling a germanium cluster with vdW interactions parameters in the program or not, we found that the vdW effects strengthen the covalent bond from different units more strikingly than that in a single unit. With more bonds between units than the threadlike structures, the multiunit structures have larger vdW energies, explaining why the isolated nanowires are harder to produce. © 2015 Wiley Periodicals, Inc.

  4. Stress originating from nanovoids in hydrogenated amorphous semiconductors

    NASA Astrophysics Data System (ADS)

    Wang, Zumin; Flötotto, David; Mittemeijer, Eric J.

    2017-03-01

    Structural inhomogeneities in the form of voids of nanometer sizes (nanovoids) have long been known to be present in hydrogenated amorphous semiconductors (Si, Ge). The physical and electrical properties of hydrogenated amorphous semiconductors can be pronouncedly influenced by the presence and characteristics of such nanovoids. In this work, by measuring in situ the intrinsic stress developments during deposition of pure, amorphous and of hydrogenated amorphous semiconductor (Si, Ge) thin films, under the same conditions in ultrahigh vacuum and on a comparative basis, a major source of tensile stress development could be ascribed to the occurrence of nanovoids in a-Si:H and a-Ge:H. The measurements allowed a quantitative evaluation of the surface stress acting along the surface of the nanovoids: 1.1-1.9 N/m for a-Si:H and 0.9-1.9 N/m for a-Ge:H.

  5. Impact of post deposition annealing in the electrically active traps at the interface between Ge(001) substrates and LaGeOx films grown by molecular beam deposition

    NASA Astrophysics Data System (ADS)

    Molle, Alessandro; Baldovino, Silvia; Fanciulli, Marco; Tsoutsou, Dimitra; Golias, Evangelos; Dimoulas, Athanasios

    2011-10-01

    Changes in the electron trapping at the interface between Ge substrates and LaGeOx films grown by atomic O assisted molecular beam deposition are inferred upon post deposition annealing treatment on the as-deposited films from electrically detected magnetic resonance (EDMR) spectroscopy and from the electrical response of Pt/LaGeOx/Ge metal oxide semiconductor (MOS) capacitors. The improved electrical performance of the MOS capacitors upon annealing is consistent with the EDMR detected reduction of oxide defects which are associated with GeO species in the LaGeOx layer as evidenced by x-ray photoelectron spectroscopy.

  6. Retention of the Zn-Zn bond in [Ge9 Zn-ZnGe9 ](6-) and Formation of [(Ge9 Zn)-(Ge9 )-(ZnGe9 )](8-) and Polymeric 1∞ [-(Ge9 Zn)(2-) -]1.

    PubMed

    Mayer, Kerstin; Jantke, Laura-Alice; Schulz, Stephan; Fässler, Thomas F

    2017-02-20

    Reactions of Zn(I)2 L2 (where L=[HC(PPh2 NPh)](-) ) with solutions of the Zintl phase K4 Ge9 in liquid ammonia lead to retention of the Zn-Zn bond and formation of the anion [(η(4) -Ge9 )Zn-Zn(η(4) -Ge9 )](6-) , representing the first complex with a Zn-Zn unit carrying two cluster entities. The trimeric anion [(η(4) -Ge9 )Zn{μ2 (η(1) :η(1) Ge9 )}Zn(η(4) -Ge9 )](8-) forms as a side product, indicating that oxidation reactions also take place. The reaction of Zn2 Cp*2 (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) with K4 Ge9 in ethylenediamine yielded the linear polymeric unit 1∞ {[Zn[μ2 (η(4) :η(1) Ge9 )]}(2-) with the first head-to-tail arrangement of ten-atom closo-clusters. All anions were obtained and structurally characterized as [A(2.2.2-crypt)](+) salts (A=K, Rb). Copious computational analyses at a DFT-PBE0/def2-TZVPP/PCM level of theory confirm the experimental structures and support the stability of the two hypothetical ten vertex cluster fragments closo-[Ge9 Zn](2-) and (paramagnetic) [Ge9 Zn](3-) .

  7. Ge/SiGe for silicon photonics

    NASA Astrophysics Data System (ADS)

    Ishikawa, Yasuhiko

    2017-01-01

    Near-infrared Ge photonic devices on a Si platform are presented toward low-cost, low-energy and high-capacity optical communications. Using Ge epitaxial layers selectively grown by chemical vapor deposition on Si-on-insulator layers, Ge photodiodes (PDs) of vertical pin structures are integrated with Si optical waveguides. The integrated Ge PDs show high responsivities as large as 0.8 A/W at 1.55 μm with the 3-dB cutoff frequency more than 10 GHz. SiGe/Ge heterostructures have potential applications to higher-performance devices. One application is to low-noise and low-voltage avalanche photodiodes (APDs), where a SiGe layer is inserted at the interface between the optical absorption layer of Ge and the carrier-multiplication layer of Si or Ge. The band discontinuity at the interface enhances the impact ionization for photo-generated carriers injected via SiGe. Fabricated APDs show an enhanced multiplication gain. The other application of SiGe is to a stressor to control the direct bandgap of Ge. As a proof of concept, a tensile-strained Si0.2Ge0.8 overlayer is shown to induce a compressive stress in the underlying Ge mesa stripe, leading to a blue shift in the absorption edge of Ge.

  8. Thermophysical Property Measurements of Molten Semiconductors in 1-g and Reduced-g Condition

    NASA Technical Reports Server (NTRS)

    Rhim, Won-Kyu

    1999-01-01

    Understanding and controlling the formation kinetics of varieties of crystal imperfections such as point defects, non uniform distribution of doping atoms, and impurity atoms in growing crystals are very important. Theoretical (numerical) modeling of the crystal growth process is an essential step to achieving these objectives. In order to obtain reliable modeling results, input parameters, i.e. various thermophysical parameters, must be accurate. The importance of accurate thermophysical properties of semiconductors in crystal growth cannot be overly emphasized. The total hemispherical emissivity, for instance, has a dramatic impact on the thermal environment. It determines the radiative emission from the surface of the melt which determines to a large extent the profile of the solidified crystal. In order to understand the convection and the turbulence in a melt, viscosity becomes an important parameter. The liquid surface tension determines the shape of the liquid-atmosphere interface near the solid-liquid-atmosphere triple point. Currently used values for these parameters are rather inaccurate, and this program intends to provide more reliable measurements of these thermophysical properties. Thus, the objective of this program is in the accurate measurements of various thermophysical properties which can be reliably used in the modeling of various crystal growth processes. In this program, thermophysical properties of molten semiconductors, such as Si, Ge, Si-Ge, and InSb will be measured as a function of temperature using the High Temperature Electrostatic Levitator at JPL. Each material will be doped by different kinds of impurities at various doping levels. Thermophysical properties which will be measured include: density, thermal expansion coefficient, surface tension, viscosity, specific heat, hemispherical total emissivity, and perhaps electrical and thermal conductivities. Many molten semiconductors are chemically reactive with crucibles. As a result

  9. Method of physical vapor deposition of metal oxides on semiconductors

    DOEpatents

    Norton, David P.

    2001-01-01

    A process for growing a metal oxide thin film upon a semiconductor surface with a physical vapor deposition technique in a high-vacuum environment and a structure formed with the process involves the steps of heating the semiconductor surface and introducing hydrogen gas into the high-vacuum environment to develop conditions at the semiconductor surface which are favorable for growing the desired metal oxide upon the semiconductor surface yet is unfavorable for the formation of any native oxides upon the semiconductor. More specifically, the temperature of the semiconductor surface and the ratio of hydrogen partial pressure to water pressure within the vacuum environment are high enough to render the formation of native oxides on the semiconductor surface thermodynamically unstable yet are not so high that the formation of the desired metal oxide on the semiconductor surface is thermodynamically unstable. Having established these conditions, constituent atoms of the metal oxide to be deposited upon the semiconductor surface are directed toward the surface of the semiconductor by a physical vapor deposition technique so that the atoms come to rest upon the semiconductor surface as a thin film of metal oxide with no native oxide at the semiconductor surface/thin film interface. An example of a structure formed by this method includes an epitaxial thin film of (001)-oriented CeO.sub.2 overlying a substrate of (001) Ge.

  10. Narrow band gap amorphous silicon semiconductors

    DOEpatents

    Madan, A.; Mahan, A.H.

    1985-01-10

    Disclosed is a narrow band gap amorphous silicon semiconductor comprising an alloy of amorphous silicon and a band gap narrowing element selected from the group consisting of Sn, Ge, and Pb, with an electron donor dopant selected from the group consisting of P, As, Sb, Bi and N. The process for producing the narrow band gap amorphous silicon semiconductor comprises the steps of forming an alloy comprising amorphous silicon and at least one of the aforesaid band gap narrowing elements in amount sufficient to narrow the band gap of the silicon semiconductor alloy below that of amorphous silicon, and also utilizing sufficient amounts of the aforesaid electron donor dopant to maintain the amorphous silicon alloy as an n-type semiconductor.

  11. Formation and Decay of Electron-Hole Plasma Clusters in a Direct-Gap Semiconductor CuCl

    NASA Astrophysics Data System (ADS)

    Jiang, Lei; Wu, Ming-Wei; Nagai, M.; Kuwata-Gonokami, M.

    2003-10-01

    The master equation for the cluster-size distribution function is solved numerically to investigate the electron-hole droplet formation claimed to be discovered in the direct-gap CuCl excited by picosecond laser pulses [Nagai et al. Phys. Rev. Lett. 86 (2001) 5795 J. Lumin. 100 (2002) 233]. Our result shows that for the excitation in the experiment, the average number of pairs per cluster (ANPC) is only around 5.2, much smaller than that (106 typically for Ge) of the well studied electron-hole droplet in indirect-gap semiconductors such as Ge and Si. These results indicate that what measured in CuCl by Nagai et al. may not come from the EHD formed from exciton gas, instead possibly come from some bubbles of excitons in metallic liquid.

  12. Hypersonic modes in nanophononic semiconductors.

    PubMed

    Hepplestone, S P; Srivastava, G P

    2008-09-05

    Frequency gaps and negative group velocities of hypersonic phonon modes in periodically arranged composite semiconductors are presented. Trends and criteria for phononic gaps are discussed using a variety of atomic-level theoretical approaches. From our calculations, the possibility of achieving semiconductor-based one-dimensional phononic structures is established. We present results of the location and size of gaps, as well as negative group velocities of phonon modes in such structures. In addition to reproducing the results of recent measurements of the locations of the band gaps in the nanosized Si/Si{0.4}Ge{0.6} superlattice, we show that such a system is a true one-dimensional hypersonic phononic crystal.

  13. Tensile strain in Ge membranes induced by SiGe nanostressors

    NASA Astrophysics Data System (ADS)

    Barget, Michael R.; Lodari, Mario; Borriello, Mauro; Mondiali, Valeria; Chrastina, Daniel; Bollani, Monica; Bonera, Emiliano

    2016-09-01

    The monolithic integration of photonic functionality into silicon microtechnology is widely advanced. Yet, there is no final solution for the realization of a light source compatible with the prevailing complementary metal-oxide-semiconductor technology. A lot of research effort focuses on germanium (Ge) on silicon (Si) heterostructures and tensile strain application to Ge is accepted as one feasible route to make Ge an efficient light emitter. Prior work has documented the special suitability of Ge membranes to reach the high tensile strain. We present a top-down approach for the creation of SiGe stressors on Ge micro-bridges and compare the obtained strain to the case of an attached bulk-like Ge layer. We could show that the Ge influenced by a SiGe stressor is under tensile strain; absolute strain values are of the order of 0.7% for both micro-bridge and bulk. The relative strain induced by the nanostructures in the micro-bridge is 1.3% due to the high sharing of elastic energy between nanostructures and bridges.

  14. Formation mechanisms of nano and microcones by laser radiation on surfaces of Si, Ge, and SiGe crystals

    PubMed Central

    2013-01-01

    In this work we study the mechanisms of laser radiation interaction with elementary semiconductors such as Si and Ge and their solid solution SiGe. As a result of this investigation, the mechanisms of nanocones and microcones formation on a surface of semiconductor were proposed. We have shown the possibility to control the size and the shape of cones both by the laser. The main reason for the formation of nanocones is the mechanical compressive stresses due to the atoms’ redistribution caused by the gradient of temperature induced by strongly absorbed laser radiation. According to our investigation, the nanocone formation mechanism in semiconductors is characterized by two stages. The first stage is characterized by formation of a p-n junction for elementary semiconductors or of a Ge/Si heterojunction for SiGe solid solution. The generation and redistribution of intrinsic point defects in elementary semiconductors and Ge atoms concentration on the irradiated surface of SiGe solid solution in temperature gradient field take place at this stage due to the thermogradient effect which is caused by strongly absorbed laser radiation. The second stage is characterized by formation of nanocones due to mechanical plastic deformation of the compressed Ge layer on Si. Moreover, a new 1D-graded band gap structure in elementary semiconductors due to quantum confinement effect was formed. For the formation of microcones Ni/Si structure was used. The mechanism of the formation of microcones is characterized by two stages as well. The first stage is the melting of Ni film after irradiation by laser beam and formation of Ni islands due to surface tension force. The second step is the melting of Ni and subsequent manifestations of Marangoni effect with the growth of microcones. PMID:23735193

  15. Ion implantation and low temperature properties of metal-semiconductor alloys

    NASA Astrophysics Data System (ADS)

    Xiao-Xing, Xi; Da-Wei, Zhou; Guang-Lin, Zhao; Qi-Ze, Ran; Jia-Rui, Liu; Wei-Yan, Guan

    1987-09-01

    We review the experimental work on ion implantation with respect to superconductivity and electrical resistivity of metal-semiconductor alloys carried out at the Institute of Physics of Academia Sinica. Samples studied included liquid-quenched AlSiGe ribbons and Al thin films. The liquid-quenched ribbons with a superconducting transition temperature Tc of 3.2 K were implanted with H or H 2 ions at room temperature and a decrease of Tc was observed. The ribbons were also implanted with Si ions at liquid nitrogen temperature, resulting in a higher onset of transition at about 4 K. We also implanted Si ions into Al thin films at room temperature up to 5 at.% Si. The Tc of the films increased from 1.5 to 1.9 K and the temperature-dependence of resistivity was changed from T5 to a T3-dependence within 30-50 K. The superconductivity of Al-semiconductor alloys was proved to be strongly influenced by the disorder, which depends crucially on the implantation temperature.

  16. Controlled growth of semiconductor crystals

    DOEpatents

    Bourret-Courchesne, Edith D.

    1992-01-01

    A method for growth of III-V, II-VI and related semiconductor single crystals that suppresses random nucleation and sticking of the semiconductor melt at the crucible walls. Small pieces of an oxide of boron B.sub.x O.sub.y are dispersed throughout the comminuted solid semiconductor charge in the crucible, with the oxide of boron preferably having water content of at least 600 ppm. The crucible temperature is first raised to a temperature greater than the melt temperature T.sub.m1 of the oxide of boron (T.sub.m1 =723.degree. K. for boron oxide B.sub.2 O.sub.3), and the oxide of boron is allowed to melt and form a reasonably uniform liquid layer between the crucible walls and bottom surfaces and the still-solid semiconductor charge. The temperature is then raised to approximately the melt temperature T.sub.m2 of the semiconductor charge material, and crystal growth proceeds by a liquid encapsulated, vertical gradient freeze process. About half of the crystals grown have a dislocation density of less than 1000/cm.sup.2. If the oxide of boron has water content less than 600 ppm, the crucible material should include boron nitride, a layer of the inner surface of the crucible should be oxidized before the oxide of boron in the crucible charge is melted, and the sum of thicknesses of the solid boron oxide layer and liquid boron oxide layer should be at least 50 .mu.m.

  17. Controlled growth of semiconductor crystals

    DOEpatents

    Bourret-Courchesne, E.D.

    1992-07-21

    A method is disclosed for growth of III-V, II-VI and related semiconductor single crystals that suppresses random nucleation and sticking of the semiconductor melt at the crucible walls. Small pieces of an oxide of boron B[sub x]O[sub y] are dispersed throughout the comminuted solid semiconductor charge in the crucible, with the oxide of boron preferably having water content of at least 600 ppm. The crucible temperature is first raised to a temperature greater than the melt temperature T[sub m1] of the oxide of boron (T[sub m1]=723 K for boron oxide B[sub 2]O[sub 3]), and the oxide of boron is allowed to melt and form a reasonably uniform liquid layer between the crucible walls and bottom surfaces and the still-solid semiconductor charge. The temperature is then raised to approximately the melt temperature T[sub m2] of the semiconductor charge material, and crystal growth proceeds by a liquid encapsulated, vertical gradient freeze process. About half of the crystals grown have a dislocation density of less than 1000/cm[sup 2]. If the oxide of boron has water content less than 600 ppm, the crucible material should include boron nitride, a layer of the inner surface of the crucible should be oxidized before the oxide of boron in the crucible charge is melted, and the sum of thicknesses of the solid boron oxide layer and liquid boron oxide layer should be at least 50 [mu]m. 7 figs.

  18. 73Ge-NQR study of heavy-fermion compound CeNi2Ge2

    NASA Astrophysics Data System (ADS)

    Kawasaki, S.; Sada, T.; Miyoshi, T.; Kotegawa, H.; Mukuda, H.; Kitaoka, Y.; Kobayashi, T. C.; Fukuhara, T.; Maezawa, K.; Itoh, K. M.; Haller, E. E.

    2007-03-01

    We report 73Ge-nuclear-quadrupole resonance (NQR) study of heavy-fermion compound CeNi2Ge2. The temperature dependence of the 73Ge nuclear-spin-lattice-relaxation rate 1/T1 indicates the development of magnetic correlations and the formation of a Fermi-liquid state at temperatures lower than TFL=0.4 K, where 1/T1T is constant. The 1/T1T decrease below TcNQR=0.1 K, whereas resistance decreases below Tconset=0.2 K and does not become zero. These results indicate CeNi2Ge2 closely locates to a superconducting quantum critical point.

  19. Development of high-resolution liquid-argon and -xenon detectors for 1 MeV-20 GeV gamma rays

    NASA Astrophysics Data System (ADS)

    Hademenos, G. J.; Fenyves, E. J.; Cline, David B.; Atac, Muzaffer

    1989-04-01

    A new concept in gamma ray detection is under development by the University of Texas at Dallas and the University of California, Los Angeles collaboration. Liquid-argon and -xenon detectors, used simultaneously as drift ionization chambers and as scintillation counters, combine the high energy resolution of ionization chambers and the high time resolution of scintillation counters with the very high spatial resolution and particle-track-imaging capability of liquid drift chambers. The detectors are characterized by their event-by-event processing and decision-making feature. Together with gas drift chambers and plastic scintillators, these detectors will be capable of carrying out gamma-ray and charged-particle measurements on accelerators, detecting cosmic gamma rays and charged particles in space-based experiments and observing high-energy particles deep underground. In addition to this, liquid-xenon detectors can be applied to high-resolution medical imaging of gamma rays.

  20. Semiconductor Crystal Growth in Static and Rotating Magnetic fields

    NASA Technical Reports Server (NTRS)

    Volz, Martin

    2004-01-01

    Magnetic fields have been applied during the growth of bulk semiconductor crystals to control the convective flow behavior of the melt. A static magnetic field established Lorentz forces which tend to reduce the convective intensity in the melt. At sufficiently high magnetic field strengths, a boundary layer is established ahead of the solid-liquid interface where mass transport is dominated by diffusion. This can have a significant effect on segregation behavior and can eliminate striations in grown crystals resulting from convective instabilities. Experiments on dilute (Ge:Ga) and solid solution (Ge-Si) semiconductor systems show a transition from a completely mixed convective state to a diffusion-controlled state between 0 and 5 Tesla. In HgCdTe, radial segregation approached the diffusion limited regime and the curvature of the solid-liquid interface was reduced by a factor of 3 during growth in magnetic fields in excess of 0.5 Tesla. Convection can also be controlled during growth at reduced gravitational levels. However, the direction of the residual steady-state acceleration vector can compromise this effect if it cannot be controlled. A magnetic field in reduced gravity can suppress disturbances caused by residual transverse accelerations and by random non-steady accelerations. Indeed, a joint program between NASA and the NHMFL resulted in the construction of a prototype spaceflight magnet for crystal growth applications. An alternative to the suppression of convection by static magnetic fields and reduced gravity is the imposition of controlled steady flow generated by rotating magnetic fields (RMF)'s. The potential benefits of an RMF include homogenization of the melt temperature and concentration distribution, and control of the solid-liquid interface shape. Adjusting the strength and frequency of the applied magnetic field allows tailoring of the resultant flow field. A limitation of RMF's is that they introduce deleterious instabilities above a

  1. Process for forming shaped group III-V semiconductor nanocrystals, and product formed using process

    DOEpatents

    Alivisatos, A. Paul; Peng, Xiaogang; Manna, Liberato

    2001-01-01

    A process for the formation of shaped Group III-V semiconductor nanocrystals comprises contacting the semiconductor nanocrystal precursors with a liquid media comprising a binary mixture of phosphorus-containing organic surfactants capable of promoting the growth of either spherical semiconductor nanocrystals or rod-like semiconductor nanocrystals, whereby the shape of the semiconductor nanocrystals formed in said binary mixture of surfactants is controlled by adjusting the ratio of the surfactants in the binary mixture.

  2. Process for forming shaped group II-VI semiconductor nanocrystals, and product formed using process

    DOEpatents

    Alivisatos, A. Paul; Peng, Xiaogang; Manna, Liberato

    2001-01-01

    A process for the formation of shaped Group II-VI semiconductor nanocrystals comprises contacting the semiconductor nanocrystal precursors with a liquid media comprising a binary mixture of phosphorus-containing organic surfactants capable of promoting the growth of either spherical semiconductor nanocrystals or rod-like semiconductor nanocrystals, whereby the shape of the semiconductor nanocrystals formed in said binary mixture of surfactants is controlled by adjusting the ratio of the surfactants in the binary mixture.

  3. Carrier Density Modulation in Ge Heterostructure by Ferroelectric Switching

    SciTech Connect

    Ponath, Patrick; Fredrickson, Kurt; Posadas, Agham B.; Ren, Yuan; Vasudevan, Rama K.; Okatan, Mahmut Baris; Jesse, Stephen; Aoki, Toshihiro; McCartney, Martha; Smith, David J.; Kalinin, Sergei V.; Lai, Keji; Demkov, Alexander A.

    2015-01-14

    The development of nonvolatile logic through direct coupling of spontaneous ferroelectric polarization with semiconductor charge carriers is nontrivial, with many issues, including epitaxial ferroelectric growth, demonstration of ferroelectric switching, and measurable semiconductor modulation. Here we report a true ferroelectric field effect carrier density modulation in an underlying Ge(001) substrate by switching of the ferroelectric polarization in the epitaxial c-axis-oriented BaTiO3 (BTO) grown by molecular beam epitaxy (MBE) on Ge. Using density functional theory, we demonstrate that switching of BTO polarization results in a large electric potential change in Ge. Aberration-corrected electron microscopy confirms the interface sharpness, and BTO tetragonality. Electron-energy-loss spectroscopy (EELS) indicates the absence of any low permittivity interlayer at the interface with Ge. Using piezoelectric force microscopy (PFM), we confirm the presence of fully switchable, stable ferroelectric polarization in BTO that appears to be single domain. Using microwave impedance microscopy (MIM), we clearly demonstrate a ferroelectric field effect.

  4. First-principles calculations on the origin of ferromagnetism in transition-metal doped Ge

    NASA Astrophysics Data System (ADS)

    Shinya, Hikari; Fukushima, Tetsuya; Masago, Akira; Sato, Kazunori; Katayama-Yoshida, Hiroshi

    2017-09-01

    Many researchers have shown an interest in Ge-based dilute magnetic semiconductors (DMSs) due to potential advantages for semiconductor spintronics applications. There has been great discussion about mechanisms of experimentally observed ferromagnetism in (Ge,Fe) and (Ge,Mn). We investigate the electronic structures, structural stabilities, magnetic exchange coupling constants, and Curie temperature of Ge-based DMSs, and clarify origins of the ferromagnetism, on the basis of density functional theory calculations. In both the (Ge,Fe) and (Ge,Mn) cases, the inhomogeneous distribution of the magnetic impurities plays an important role to determine the magnetic states; however, physical mechanisms of the ferromagnetism in these two materials are completely different. By the spinodal nanodecomposition, the Fe impurities in Ge gather together with keeping the diamond structure, so that the number of the first-nearest-neighbor Fe pairs with strong ferromagnetic interaction increases. Therefore, the Curie temperature drastically increases with the progress of the annealing. Our cluster expansion method clearly reveals that the other ordered compounds with different crystal structures such as Ge3Mn5 and Ge8Mn11 are easily generated in the (Ge,Mn) system. The estimated Curie temperature of Ge3Mn5 is in agreement with the observed Curie temperature in experiments. It should be considered that the precipitation of the ferromagnetic Ge3Mn5 clusters is an origin of high Curie temperature in (Ge,Mn).

  5. Buoyant convection during the growth of compound semiconductors by the liquid-encapsulated Czochralski process with an axial magnetic field and with a non-axisymmetric temperature

    SciTech Connect

    Ma, N.; Walker, J.S.

    1995-12-31

    This paper treats the buoyant convection of a molten semiconductor in a cylindrical crucible with a vertical axis, with a uniform vertical magnetic field, and with a non-axisymmetric temperature. Most previous treatments of melt motions with vertical magnetic fields have assumed that the temperature and buoyant convection were axisymmetric. In reality, the temperature and resultant buoyant convection often deviate significantly from axisymmetry. For a given non-axisymmetric temperature, the electromagnetic suppression of the axisymmetric part of the buoyant convection is stronger than that of the non-axisymmetric part, so that the deviation from an axisymmetric melt motion increases as the magnetic field strength is increased. The non-axisymmetric part of the buoyant convection includes relatively strong azimuthal velocities adjacent to the electrically insulating vertical crucible wall, because this wall blocks the radial electric currents needed to suppress azimuthal velocities.

  6. Photocatalysis Using Semiconductor Nanoclusters

    SciTech Connect

    Thurston, T.R.; Wilcoxon,J.P.

    1999-01-21

    We report on experiments using nanosize MoS{sub 2} to photo-oxidize organic pollutants in water using visible light as the energy source. We have demonstrated that we can vary the redox potentials and absorbance characteristics of these small semiconductors by adjusting their size, and our studies of the photooxidation of organic molecules have revealed that the rate of oxidation increases with increasing bandgap (i.e. more positive valence band and more negative conduction band potentials). Because these photocatalysis reactions can be performed with the nanoclusters fully dispersed and stable in solution, liquid chromatography can be used to determine both the intermediate reaction products and the state of the nanoclusters during the reaction. We have demonstrated that the MoS{sub 2} nanoclusters remain unchanged during the photooxidation process by this technique. We also report on studies of MoS{sub 2} nanoclusters deposited on TiO{sub 2} powder.

  7. Epitaxial Growth of GeGaAs.

    DTIC Science & Technology

    1981-06-01

    liquid solvent for epitaxial growth of Ge. Because of the finite solubility of GaAs in Pb (7 x 10-4 atomic fraction at 500°C) relatively fast initial...mixture of Pb and Sn was used as a melt. The solubility of Ge in a PbSn eutetic mixture is significantly higher than the solubility of Ge in pure Pb...shallow donor acceptor levels. Addition of a deep level to the crystal lat- tice at this point would further pin the fermi level near mid-gap

  8. Engineering optical properties of semiconductor metafilm superabsorbers

    NASA Astrophysics Data System (ADS)

    Kim, Soo Jin; Fan, Pengyu; Kang, Ju-Hyung; Brongersma, Mark L.

    2016-04-01

    Light absorption in ultrathin layer of semiconductor has been considerable interests for many years due to its potential applications in various optical devices. In particular, there have been great efforts to engineer the optical properties of the film for the control of absorption spectrums. Whereas the isotropic thin films have intrinsic optical properties that are fixed by materials' properties, metafilm that are composed by deep subwavelength nano-building blocks provides significant flexibilities in controlling the optical properties of the designed effective layers. Here, we present the ultrathin semiconductor metafilm absorbers by arranging germanium (Ge) nanobeams in deep subwavelength scale. Resonant properties of high index semiconductor nanobeams play a key role in designing effective optical properties of the film. We demonstrate this in theory and experimental measurements to build a designing rule of efficient, controllable metafilm absorbers. The proposed strategy of engineering optical properties could open up wide range of applications from ultrathin photodetection and solar energy harvesting to the diverse flexible optoelectronics.

  9. Codoped direct-gap semiconductor scintillators

    DOEpatents

    Derenzo, Stephen Edward [Pinole, CA; Bourret-Courchesne, Edith [Berkeley, CA; Weber, Marvin J [Danville, CA; Klintenberg, Mattias K [Berkeley, CA

    2008-07-29

    Fast, bright inorganic scintillators at room temperature are based on radiative electron-hole recombination in direct-gap semiconductors, e.g. CdS and ZnO. The direct-gap semiconductor is codoped with two different impurity atoms to convert the semiconductor to a fast, high luminosity scintillator. The codopant scheme is based on dopant band to dopant trap recombination. One dopant provides a significant concentration of carriers of one type (electrons or holes) and the other dopant traps carriers of the other type. Examples include CdS:In,Te; CdS:In,Ag; CdS:In,Na; ZnO:Ga,P; ZnO:Ga,N; ZnO:Ga,S; and GaN:Ge,Mg.

  10. Codoped direct-gap semiconductor scintillators

    DOEpatents

    Derenzo, Stephen E.; Bourret-Courchesne, Edith; Weber, Marvin J.; Klintenberg, Mattias K.

    2006-05-23

    Fast, bright inorganic scintillators at room temperature are based on radiative electron-hole recombination in direct-gap semiconductors, e.g. CdS and ZnO. The direct-gap semiconductor is codoped with two different impurity atoms to convert the semiconductor to a fast, high luminosity scintillator. The codopant scheme is based on dopant band to dopant trap recombination. One dopant provides a significant concentration of carriers of one type (electrons or holes) and the other dopant traps carriers of the other type. Examples include CdS:In,Te; CdS:In,Ag; CdS:In,Na; ZnO:Ga,P; ZnO:Ga,N; ZnO:Ga,S; and GaN:Ge,Mg.

  11. Indoor test for thermal performance of the GE TC-100 liquid solar collector eight- and ten-tube configuration. [Marshall Space Flight Center solar simulator

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The thermal performance of a liquid solar collector was tested in eight- and ten-tube configurations under simulated conditions. A time constant test and an incident angle modifier test were also conducted to determine the transient and incident angle effects on the collector. Performance loss with accessory covers is demonstrated. The gross collector area is about 17.4 ft sq without manifold and 19.1 ft sq with manifold. The collector weight is approximately 60 pounds empty and 75 pounds with manifold.

  12. One-dimensional quantum matter: gold-induced nanowires on semiconductor surfaces.

    PubMed

    Dudy, L; Aulbach, J; Wagner, T; Schäfer, J; Claessen, R

    2017-09-15

    Interacting electrons confined to only one spatial dimension display a wide range of unusual many-body quantum phenomena, ranging from Peierls instabilities to the breakdown of the canonical Fermi liquid paradigm to even unusual spin phenomena. The underlying physics is not only of tremendous fundamental interest, but may also have bearing on device functionality in future micro- and nanoelectronics with lateral extensions reaching the atomic limit. Metallic adatoms deposited on semiconductor surfaces may form self-assembled atomic nanowires, thus representing highly interesting and well-controlled solid-state realizations of such 1D quantum systems. Here we review experimental and theoretical investigations on a few selected prototypical nanowire surface systems, specifically Ge(0 0 1)-Au and Si(hhk)-Au, and the search for 1D quantum states in them. We summarize the current state of research and identify open questions and issues.

  13. Coated semiconductor devices for neutron detection

    DOEpatents

    Klann, Raymond T.; McGregor, Douglas S.

    2002-01-01

    A device for detecting neutrons includes a semi-insulated bulk semiconductor substrate having opposed polished surfaces. A blocking Schottky contact comprised of a series of metals such as Ti, Pt, Au, Ge, Pd, and Ni is formed on a first polished surface of the semiconductor substrate, while a low resistivity ("ohmic") contact comprised of metals such as Au, Ge, and Ni is formed on a second, opposed polished surface of the substrate. In one embodiment, n-type low resistivity pinout contacts comprised of an Au/Ge based eutectic alloy or multi-layered Pd/Ge/Ti/Au are also formed on the opposed polished surfaces and in contact with the Schottky and ohmic contacts. Disposed on the Schottky contact is a neutron reactive film, or coating, for detecting neutrons. The coating is comprised of a hydrogen rich polymer, such as a polyolefin or paraffin; lithium or lithium fluoride; or a heavy metal fissionable material. By varying the coating thickness and electrical settings, neutrons at specific energies can be detected. The coated neutron detector is capable of performing real-time neutron radiography in high gamma fields, digital fast neutron radiography, fissile material identification, and basic neutron detection particularly in high radiation fields.

  14. Band-Gap Engineering at a Semiconductor-Crystalline Oxide Interface

    SciTech Connect

    Jahangir-Moghadam, Mohammadreza; Ahmadi-Majlan, Kamyar; Shen, Xuan; Droubay, Timothy; Bowden, Mark; Chrysler, Matthew; Su, Dong; Chambers, Scott A.; Ngai, Joseph H.

    2015-02-09

    The epitaxial growth of crystalline oxides on semiconductors provides a pathway to introduce new functionalities to semiconductor devices. Key to integrating the functionalities of oxides onto semiconductors is controlling the band alignment at interfaces between the two materials. Here we apply principles of band gap engineering traditionally used at heterojunctions between conventional semiconductors to control the band offset between a single crystalline oxide and a semiconductor. Reactive molecular beam epitaxy is used to realize atomically abrupt and structurally coherent interfaces between SrZrxTi1-xO₃ and Ge, in which the band gap of the former is enhanced with Zr content x. We present structural and electrical characterization of SrZrxTi1-xO₃-Ge heterojunctions and demonstrate a type-I band offset can be achieved. These results demonstrate that band gap engineering can be exploited to realize functional semiconductor crystalline oxide heterojunctions.

  15. Band-Gap Engineering at a Semiconductor-Crystalline Oxide Interface

    DOE PAGES

    Jahangir-Moghadam, Mohammadreza; Ahmadi-Majlan, Kamyar; Shen, Xuan; ...

    2015-02-09

    The epitaxial growth of crystalline oxides on semiconductors provides a pathway to introduce new functionalities to semiconductor devices. Key to integrating the functionalities of oxides onto semiconductors is controlling the band alignment at interfaces between the two materials. Here we apply principles of band gap engineering traditionally used at heterojunctions between conventional semiconductors to control the band offset between a single crystalline oxide and a semiconductor. Reactive molecular beam epitaxy is used to realize atomically abrupt and structurally coherent interfaces between SrZrxTi1-xO₃ and Ge, in which the band gap of the former is enhanced with Zr content x. We presentmore » structural and electrical characterization of SrZrxTi1-xO₃-Ge heterojunctions and demonstrate a type-I band offset can be achieved. These results demonstrate that band gap engineering can be exploited to realize functional semiconductor crystalline oxide heterojunctions.« less

  16. Optical Properties of Small Band Gap Semiconductors Subject to Laser Excitation. Nonlinear Infrared Properties of Semiconductors.

    DTIC Science & Technology

    1982-01-01

    the Ill-V semiconductors with large spin -orbit splitting . These included GaAs, G&Sb, InAs, AlSb as w ll as Ge. The theory was further extended to...includle Lhe effects of the spin orbit split -off valence band in publication 12. E. 7hory of Pump and Probe Experiments To develop an understanding of the...James and D. L. Smith, "Absorption of High-Intensity 002 Laser Light in p-Type Semiconductors with Small Spin -Orbit Splittings ", J. Appi. Phys. S2

  17. Fermi level dependent native defect formation: Consequences for metal-semiconductor and semiconductor-semiconductor interfaces

    SciTech Connect

    Walukiewicz, W.

    1988-02-01

    The amphoteric native defect model of the Schottky barrier formation is used to analyze the Fermi level pinning at metal/semiconductor interfaces for submonolayer metal coverages. It is assumed that the energy required for defect generation is released in the process of surface back-relaxation. Model calculations for metal/GaAs interfaces show a weak dependence of the Fermi level pinning on the thickness of metal deposited at room temperature. This weak dependence indicates a strong dependence of the defect formation energy on the Fermi level, a unique feature of amphoteric native defects. This result is in very good agreement with experimental data. It is shown that a very distinct asymmetry in the Fermi level pinning on p- and n-type GaAs observed at liquid nitrogen temperatures can be understood in terms of much different recombination rates for amphoteric native defects in those two types of materials. Also, it is demonstrated that the Fermi level stabilization energy, a central concept of the amphoteric defect system, plays a fundamental role in other phenomena in semiconductors such as semiconductor/semiconductor heterointerface intermixing and saturation of free carrier concentration. 33 refs., 6 figs.

  18. Impact of post deposition annealing in the electrically active traps at the interface between Ge(001) substrates and LaGeO{sub x} films grown by molecular beam deposition

    SciTech Connect

    Molle, Alessandro; Baldovino, Silvia; Fanciulli, Marco; Tsoutsou, Dimitra; Golias, Evangelos; Dimoulas, Athanasios

    2011-10-15

    Changes in the electron trapping at the interface between Ge substrates and LaGeO{sub x} films grown by atomic O assisted molecular beam deposition are inferred upon post deposition annealing treatment on the as-deposited films from electrically detected magnetic resonance (EDMR) spectroscopy and from the electrical response of Pt/LaGeO{sub x}/Ge metal oxide semiconductor (MOS) capacitors. The improved electrical performance of the MOS capacitors upon annealing is consistent with the EDMR detected reduction of oxide defects which are associated with GeO species in the LaGeO{sub x} layer as evidenced by x-ray photoelectron spectroscopy.

  19. 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.

  20. Carrier transport in Ge nanowires / Si substrate heterojunction

    NASA Astrophysics Data System (ADS)

    Lee, E.-K.; Kamenev, B.; Tsybeskov, L.; Sharma, S.; Kamins, T. I.

    2006-03-01

    Semiconductor nanowires (NWs) attached to lattice-mismatched single-crystal substrates form quasi-one-dimensional (QOD) heterojunctions (HJs) where efficient structural relaxation might occur due to high surface-to-volume ratio. Current-voltage characteristics in Ge NW/(p+)Si samples with nearly micron-long Ge NWs exhibit metal-type conductivity with ohmic behavior and little conductivity temperature dependence. In contrast, Ge NW/(n+)Si samples display significant change in conductivity as a function of temperature with an activation energy up to 200 meV. In a narrow temperature interval near 150 K we observed current instabilities and oscillations for Ge NW/(n+)Si. At higher temperatures we find negative differential photoconductivity at low forward biases. Our experimental results are explained using a model of nearly ideal Si substrate/Ge NW hetero-interfaces.

  1. INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Two-stage liquid phase epitaxy for fabrication of buried InGaAsP/InP heterostructures

    NASA Astrophysics Data System (ADS)

    Procházková, O.; Novotný, J.; Šrobár, F.

    1988-11-01

    The technology of growth of buried heterojunction lasers emitting at 1.3 μm and some of their physical properties are described. Mesa stripes 8-μm wide were formed on heteroepitaxial wafers grown by liquid phase epitaxy at 630°C. They were buried by a second process at a lower temperature (590°C). The threshold current was about 100 mA and the temperature sensitivity was characterized by a parameter amounting to about 60 K. Single-mode lasing was observed occasionally.

  2. Electrolysis of a molten semiconductor

    NASA Astrophysics Data System (ADS)

    Yin, Huayi; Chung, Brice; Sadoway, Donald R.

    2016-08-01

    Metals cannot be extracted by electrolysis of transition-metal sulfides because as liquids they are semiconductors, which exhibit high levels of electronic conduction and metal dissolution. Herein by introduction of a distinct secondary electrolyte, we reveal a high-throughput electro-desulfurization process that directly converts semiconducting molten stibnite (Sb2S3) into pure (99.9%) liquid antimony and sulfur vapour. At the bottom of the cell liquid antimony pools beneath cathodically polarized molten stibnite. At the top of the cell sulfur issues from a carbon anode immersed in an immiscible secondary molten salt electrolyte disposed above molten stibnite, thereby blocking electronic shorting across the cell. As opposed to conventional extraction practices, direct sulfide electrolysis completely avoids generation of problematic fugitive emissions (CO2, CO and SO2), significantly reduces energy consumption, increases productivity in a single-step process (lower capital and operating costs) and is broadly applicable to a host of electronically conductive transition-metal chalcogenides.

  3. Rotator phases in narrow-gap semiconductors

    SciTech Connect

    Price, D.L.; Saboungi, M.L.; Fortner, J.; Richardson, J.W.; Howells, W.S.

    1993-12-01

    Zintl compounds of lead and tin with the heavier alkali metals are semiconductors with surprising and unusual properties in both solid and liquid states. These are ascribed to the formation of tetrahedral complex anions arising from charge transfer and covalent bonding around the polyvalent metal ions. The tetrahedra exhibit both rotational and translational order, leading to a variety of complex dynamical behaviors in both solid and liquid phases. The changes in order have dramatic effects on electrical transport properties.

  4. Electrorotation and Electroorientation of Semiconductor Nanowires.

    PubMed

    García-Sánchez, Pablo; Ramos, Antonio

    2017-08-29

    A number of experimental studies have shown electric-field manipulation of nanowires dispersed in liquids. We demonstrate from first-principles that the electrical response of semiconductor nanowires in liquids must be described by considering, at least, two mechanisms for interfacial polarization: the classical Maxwell-Wagner interfacial polarization and the formation of an electrical double layer. We compare the theoretical predictions with our experimental data and with data published elsewhere and show that both mechanisms play an important role.

  5. Dilute ferromagnetic semiconductors prepared by the combination of ion implantation with pulse laser melting

    NASA Astrophysics Data System (ADS)

    Zhou, Shengqiang

    2015-07-01

    Combining semiconducting and ferromagnetic properties, dilute ferromagnetic semiconductors (DFS) have been under intensive investigation for more than two decades. Mn doped III-V compound semiconductors have been regarded as the prototype of DFS from both experimental and theoretic investigations. The magnetic properties of III-V:Mn can be controlled by manipulating free carriers via electrical gating, as for controlling the electrical properties in conventional semiconductors. However, the preparation of DFS presents a big challenge due to the low solubility of Mn in semiconductors. Ion implantation followed by pulsed laser melting (II-PLM) provides an alternative to the widely used low-temperature molecular beam epitaxy (LT-MBE) approach. Both ion implantation and pulsed-laser melting occur far enough from thermodynamic equilibrium conditions. Ion implantation introduces enough dopants and the subsequent laser pulse deposit energy in the near-surface region to drive a rapid liquid-phase epitaxial growth. Here, we review the experimental study on preparation of III-V:Mn using II-PLM. We start with a brief description about the development of DFS and the physics behind II-PLM. Then we show that ferromagnetic GaMnAs and InMnAs films can be prepared by II-PLM and they show the same characteristics of LT-MBE grown samples. Going beyond LT-MBE, II-PLM is successful to bring two new members, GaMnP and InMnP, into the family of III-V:Mn DFS. Both GaMnP and InMnP films show the signature of DFS and an insulating behavior. At the end, we summarize the work done for Ge:Mn and Si:Mn using II-PLM and present suggestions for future investigations. The remarkable advantage of II-PLM approach is its versatility. In general, II-PLM can be utilized to prepare supersaturated alloys with mismatched components.

  6. Electrochemical impedance spectroscopy for quantitative interface state characterization of planar and nanostructured semiconductor-dielectric interfaces.

    PubMed

    Meng, Andrew C; Tang, Kechao; Braun, Michael; Zhang, Liangliang; McIntyre, Paul C

    2017-08-04

    The performance of nanostructured semiconductors is frequently limited by interface defects that trap electronic carriers. However, high aspect ratio geometries dramatically increase the difficulty of using typical solid-state electrical measurements (multifrequency capacitance- and conductance-voltage testing) to quantify interface trap densities (D<sub>it</sub>). We report on electrochemical impedance spectroscopy (EIS) with liquid electrolytes providing conformal electrical contact to characterize the energy distribution of interface traps at metal oxide/semiconductor interfaces. Planar Al<sub>2</sub>O<sub>3</sub>/p-Si and Al<sub>2</sub>O<sub>3</sub>/p-Si<sub>0.55</sub>Ge<sub>0.45</sub> interfaces are used to benchmark the EIS data against results obtained from standard electrical testing methods. We find that the solid state and EIS data agree very well, leading to the extraction of consistent Dit energy distributions. Measurements carried out on pyramid-nanostructured p-Si obtained by KOH etching followed by deposition of a 10 nm ALD-Al<sub>2</sub>O<sub>3</sub>, demonstrate the application of EIS to trap characterization of a nanostructured dielectric/semiconductor interface. These results show the promise of this methodology to measure interface state densities for a broad range of semiconductor nanostructures such as nanowires, nanofins, and porous structures. © 2017 IOP Publishing Ltd.

  7. Photoelectrosynthesis at semiconductor electrodes

    SciTech Connect

    Nozik, A. J.

    1980-12-01

    The general principles of photoelectrochemistry and photoelectrosynthesis are reviewed and some new developments in photoelectrosynthesis are discussed. Topics include energetics of semiconductor-electrolyte interfaces(band-edge unpinning); hot carrier injection at illuminated semiconductor-electrolyte junctions; derivatized semiconductor electrodes; particulate photoelectrochemical systems; layered compounds and other new materials; and dye sensitization. (WHK)

  8. Semiconductor ohmic contact

    NASA Technical Reports Server (NTRS)

    Hawrylo, F. Z.; Kressel, H.

    1977-01-01

    Contact formed on p-type surface of semiconductor laser has several advantages: highly conductive degenerate region and narrow band gap provides surface for good metal-to-semiconductor contact; lattice parameter of GaAs is 5.6533 A; improved lattice match eases interface strain which reduces interface cracking of semiconductor material.

  9. Preparation of III-V semiconductor nanocrystals

    DOEpatents

    Alivisatos, A.P.; Olshavsky, M.A.

    1996-04-09

    Nanometer-scale crystals of III-V semiconductors are disclosed. They are prepared by reacting a group III metal source with a group V anion source in a liquid phase at elevated temperature in the presence of a crystallite growth terminator such as pyridine or quinoline. 4 figs.

  10. Preparation of III-V semiconductor nanocrystals

    DOEpatents

    Alivisatos, A. Paul; Olshavsky, Michael A.

    1996-01-01

    Nanometer-scale crystals of III-V semiconductors are disclosed, They are prepared by reacting a group III metal source with a group V anion source in a liquid phase at elevated temperature in the presence of a crystallite growth terminator such as pyridine or quinoline.

  11. Strong emission of terahertz radiation from nanostructured Ge surfaces

    NASA Astrophysics Data System (ADS)

    Kang, Chul; Leem, Jung Woo; Maeng, Inhee; Kim, Tae Heon; Lee, Jong Seok; Yu, Jae Su; Kee, Chul-Sik

    2015-06-01

    Indirect band gap semiconductors are not efficient emitters of terahertz radiation. Here, we report strong emission of terahertz radiation from germanium wafers with nanostructured surfaces. The amplitude of THz radiation from an array of nano-bullets (nano-cones) is more than five (three) times larger than that from a bare-Ge wafer. The power of the terahertz radiation from a Ge wafer with an array of nano-bullets is comparable to that from n-GaAs wafers, which have been widely used as a terahertz source. We find that the THz radiation from Ge wafers with the nano-bullets is even more powerful than that from n-GaAs for frequencies below 0.6 THz. Our results suggest that introducing properly designed nanostructures on indirect band gap semiconductor wafers is a simple and cheap method to improve the terahertz emission efficiency of the wafers significantly.

  12. Strong emission of terahertz radiation from nanostructured Ge surfaces

    SciTech Connect

    Kang, Chul; Maeng, Inhee; Kee, Chul-Sik; Leem, Jung Woo; Yu, Jae Su; Kim, Tae Heon; Lee, Jong Seok

    2015-06-29

    Indirect band gap semiconductors are not efficient emitters of terahertz radiation. Here, we report strong emission of terahertz radiation from germanium wafers with nanostructured surfaces. The amplitude of THz radiation from an array of nano-bullets (nano-cones) is more than five (three) times larger than that from a bare-Ge wafer. The power of the terahertz radiation from a Ge wafer with an array of nano-bullets is comparable to that from n-GaAs wafers, which have been widely used as a terahertz source. We find that the THz radiation from Ge wafers with the nano-bullets is even more powerful than that from n-GaAs for frequencies below 0.6 THz. Our results suggest that introducing properly designed nanostructures on indirect band gap semiconductor wafers is a simple and cheap method to improve the terahertz emission efficiency of the wafers significantly.

  13. Photoluminescence measurements of high Sn-content Ge1-ySny and Ge1 - x - ySixSny grown on Ge-buffered Si

    NASA Astrophysics Data System (ADS)

    Yeo, Yung Kee; Harris, Thomas R.; Wang, Buguo; Ryu, Mee-Yi; Kouvetakis, John

    2015-03-01

    The optical properties of newly developed, high Sn-content Ge1-ySny and Ge1 - x - ySixSny thin films grown on Ge-buffered Si have been characterized using temperature-dependent and laser power-dependent photoluminescence (PL) measurements. The results show two distinct PL peaks related to both the direct (Γ) and indirect (L) bandgap transitions. Furthermore, the measured separation energy between the direct and indirect bandgap related PL peaks for Ge0.948Sn0.052 sample is only about 30 meV compared to the value of 140 meV for bulk Ge. This study shows a very encouraging result toward producing Ge- and Si-based direct bandgap semiconductors, whose predicted indirect-to-direct bandgap crossover could be near 6% Sn. Clear competition between the two transitions is also observed as a function of temperature and laser power. Overall, this work represents an extensive PL characterization of Ge1-ySny and Ge1 - x - ySixSny materials over a wide compositional range and should be useful for the development of next-generation optoelectronic devices. Author to whom correspondence should be addressed. Electronic mail: thomas.harris.ctr@afit.edu

  14. INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Liquid phase epitaxial growth of GaInAsP/InP laser structures

    NASA Astrophysics Data System (ADS)

    Nohavica, D.; Têminová, J.; Berková, D.; Zagrádková, M.; Kortan, I.; Zelinka, I.; Walachová, I.; Malina, V.

    1988-11-01

    A modified single-phase liquid phase epitaxy method was developed on the basis of a novel variant of the growth boat. The method was used to grow GaInAsP/InP double heterostructures for lasers emitting at 1.3 and 1.55 μm. The main properties of wide-contact diodes (radiation power and threshold current density) were adopted as the characteristics of the quality of heterostructures characterized by different configurations of active and guiding layers. The quality of the structure was confirmed by the fabrication of laser diodes of the following types: stripe with oxide insulation, clad-ridge waveguide, and double-channel planar buried.

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

    SciTech Connect

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

    2016-04-07

    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 ∼ 10{sup 5 }cm{sup −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)).

  16. Tensile-strained Ge/SiGe quantum-well photodetectors on silicon substrates with extended infrared response.

    PubMed

    Chang, Guo-En; Chen, Shao-Wei; Cheng, H H

    2016-08-08

    We report on tensile-strained Ge/Si0.11Ge0.89 quantum-well (QW) metal-semiconductor-metal (MSM) photodetectors on Si substrates. A tensile strain of 0.21% is introduced into the Ge wells by growing the QW stack on in-situ annealed Ge-on-Si virtual substrates (VS). The optical characterization of Ge/Si0.11Ge0.89 QW MSM photodetectors indicates that the optical response increases to a wavelength of 1.5 μm or higher owing to the strain-induced direct bandgap shrinkage. Analysis of the band structure by using a k · p model suggests that by optimizing the tensile strain and Ge well width, tensile-strained Ge/SiGe QW photodetectors can be designed to cover the telecommunication C-band and beyond for optical telecommunications and on-chip interconnection.

  17. Cubic Rashba Spin-Orbit Interaction of a Two-Dimensional Hole Gas in a Strained-Ge /SiGe Quantum Well

    NASA Astrophysics Data System (ADS)

    Moriya, Rai; Sawano, Kentarou; Hoshi, Yusuke; Masubuchi, Satoru; Shiraki, Yasuhiro; Wild, Andreas; Neumann, Christian; Abstreiter, Gerhard; Bougeard, Dominique; Koga, Takaaki; Machida, Tomoki

    2014-08-01

    The spin-orbit interaction (SOI) of a two-dimensional hole gas in the inversion symmetric semiconductor Ge is studied in a strained-Ge /SiGe quantum well structure. We observe weak antilocalization (WAL) in the magnetoconductivity measurement, revealing that the WAL feature can be fully described by the k-cubic Rashba SOI theory. Furthermore, we demonstrate electric field control of the Rashba SOI. Our findings reveal that the heavy hole (HH) in strained Ge is a purely cubic Rashba system, which is consistent with the spin angular momentum mj=±3/2 nature of the HH wave function.

  18. Unitary lens semiconductor device

    DOEpatents

    Lear, K.L.

    1997-05-27

    A unitary lens semiconductor device and method are disclosed. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors. 9 figs.

  19. Unitary lens semiconductor device

    DOEpatents

    Lear, Kevin L.

    1997-01-01

    A unitary lens semiconductor device and method. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors.

  20. Theoretical Investigations of Si-Ge Alloys in P42/ncm Phase: First-Principles Calculations

    PubMed Central

    Ma, Zhenyang; Liu, Xuhong; Yu, Xinhai; Shi, Chunlei; Yan, Fang

    2017-01-01

    The structural, mechanical, anisotropic, electronic and thermal properties of Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase are investigated in this work. The calculations have been performed with an ultra-soft pseudopotential by using the generalized gradient approximation and local density approximation in the framework of density functional theory. The achieved results for the lattice constants and band gaps of P42/ncm-Si and P42/ncm-Ge in this research have good accordance with other results. The calculated elastic constants and elastic moduli of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase are better than that of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/mnm phase. The Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase exhibit varying degrees of mechanical anisotropic properties in Poisson’s ratio, shear modulus, Young’s modulus, and universal anisotropic index. The band structures of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase show that they are all indirect band gap semiconductors with band gap of 1.46 eV, 1.25 eV, 1.36 eV and 1.00 eV, respectively. In addition, we also found that the minimum thermal conductivity κmin of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase exhibit different degrees of anisotropic properties in (001), (010), (100) and (01¯0) planes. PMID:28772964

  1. In Situ Characterization of Ge Nanocrystals Near the Growth Temperature

    SciTech Connect

    Sharp, I.D.; Xu, Q.; Liao, C.Y.; Chrzan, D.C.; Haller, E.E.; Yi, D.O.; Beeman, J.W.; Liliental-Weber, Z.; Yu, K.M.; Zakharov, D.N.; Ager, J.W. III

    2005-06-30

    We present in situ electron diffraction data indicating that Ge nanocrystals embedded in a silica matrix can be solid at temperatures exceeding the bulk Ge melting point. Supercooling is observed when returning from temperatures above the melting point of the Ge nanocrystals. Since melting point hysteresis is observed, it is not clear if nanoclusters are solid or liquid during the initial growth process. Raman spectra of as-grown nanocrystals give a measure of compressive stress and in-situ Raman spectroscopy further confirms the presence of crystalline Ge above 800 deg. C.

  2. In Situ Characterization of Ge Nanocrystals Near the Growth Temperature

    NASA Astrophysics Data System (ADS)

    Sharp, I. D.; Xu, Q.; Yi, D. O.; Liao, C. Y.; Beeman, J. W.; Liliental-Weber, Z.; Yu, K. M.; Zakharov, D. N.; Ager, J. W.; Chrzan, D. C.; Haller, E. E.

    2005-06-01

    We present in situ electron diffraction data indicating that Ge nanocrystals embedded in a silica matrix can be solid at temperatures exceeding the bulk Ge melting point. Supercooling is observed when returning from temperatures above the melting point of the Ge nanocrystals. Since melting point hysteresis is observed, it is not clear if nanoclusters are solid or liquid during the initial growth process. Raman spectra of as-grown nanocrystals give a measure of compressive stress and in-situ Raman spectroscopy further confirms the presence of crystalline Ge above 800 °C.

  3. Simultaneous determination of puerarin, daidzin, daidzein, paeoniflorin, albiflorin, liquiritin and liquiritigenin in rat plasma and its application to a pharmacokinetic study of Ge-Gen Decoction by a liquid chromatography-electrospray ionization-tandem mass spectrometry.

    PubMed

    Yan, Yan; Chai, Cheng-Zhi; Wang, Da-Wei; Wu, Jie; Xiao, Hong-He; Huo, Li-Xia; Zhu, Dan-Ni; Yu, Bo-Yang

    2014-07-01

    A liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method was developed and validated for simultaneous determination of seven constituents including puerarin, daidzin, daidzein, paeoniflorin, albiflorin, liquiritin and liquiritigenin in rat plasma using schisandrin as the internal standard (IS). The plasma samples were pretreated by a one-step direct protein precipitation with acetonitrile. The chromatographic separation was carried out on a C18 column with a gradient mobile phase consisting of acetonitrile and water (containing 0.1% formic acid and 5mM ammonium acetate). All analytes and IS were quantitated through electrospray ionization in positive ion multiple reaction monitoring (MRM) mode. The mass transitions were as follows: m/z 417.5→297.2 for puerarin, m/z 417.1→255.2 for daidzin, m/z 255.2→152.4 for daidzein, m/z 498.1→179.3 for paeoniflorin, m/z 481.1→197.3 for albiflorin, m/z 436.2→257.3 for liquiritin, m/z 257.2→137.3 for liquiritigenin and m/z 415.0→384.2 for IS, respectively. All calibration curves exhibited good linearity (r>0.9979) over a wide concentration range for all components. The intra-day and inter-day precisions (RSD) at three different levels were both less than 14.3% and the accuracies (RE) ranged from -13.2% to 14.8%. The extraction recoveries of the seven compounds ranged from 72.9% to 117.4%. The validated method was successfully applied to pharmacokinetic study of the seven components in female rat plasma after oral administration of Ge-Gen Decoction aqueous extract. Copyright © 2014 Elsevier B.V. All rights reserved.

  4. Stability and electronic properties of SiGe-based 2D layered structures

    NASA Astrophysics Data System (ADS)

    Jamdagni, Pooja; Kumar, Ashok; Thakur, Anil; Pandey, Ravindra; Ahluwalia, P. K.

    2015-01-01

    The structural and electronic properties of the in-plane hybrids consisting of siligene (SiGe), and its derivatives in both mono and bilayer forms are investigated within density functional theory. Among several pristine and hydrogenated configurations, the so-called chair conformation is energetically favorable for monolayers. On the other hand, the bilayer siligane (HSiGeH) prefers AB-stacked chair conformation and bilayer siligone (HSiGe) prefers AA-stacked buckled conformation. In SiGe, the Dirac-cone character is predicted to be retained. HSiGe is a magnetic semiconductor with a band gap of ˜0.6 eV. The electronic properties show tunability under mechanical strain and transverse electric field; (i) the energy gap opens up in the SiGe bilayer, (ii) a direct-to-indirect gap transition is predicted by the applied strain in the HSiGeH bilayer, and (iii) a semiconductor-to-metal transition is predicted for HSiGe and HSiGeH bilayers under the application of strain and electric field, thus suggesting SiGe and its derivatives to be a potential candidate for electronic devices at nanoscale.

  5. Strong room temperature electroluminescence from lateral p-SiGe/i-Ge/n-SiGe heterojunction diodes on silicon-on-insulator substrate

    NASA Astrophysics Data System (ADS)

    Lin, Guangyang; Yi, Xiaohui; Li, Cheng; Chen, Ningli; Zhang, Lu; Chen, Songyan; Huang, Wei; Wang, Jianyuan; Xiong, Xihuan; Sun, Jiaming

    2016-10-01

    A lateral p-Si0.05Ge0.95/i-Ge/n-Si0.05Ge0.95 heterojunction light emitting diode on a silicon-on-insulator (SOI) substrate was proposed, which is profitable to achieve higher luminous extraction compared to vertical junctions. Due to the high carrier injection ratio of heterostructures and optical reflection at the SiO2/Si interface of the SOI, strong room temperature electroluminescence (EL) at around 1600 nm from the direct bandgap of i-Ge with 0.30% tensile strain was observed. The EL peak intensity of the lateral heterojunction is enhanced by ˜4 folds with a larger peak energy than that of the vertical Ge p-i-n homojunction, suggesting that the light emitting efficiency of the lateral heterojunction is effectively improved. The EL peak intensity of the lateral heterojunction, which increases quadratically with injection current density, becomes stronger for diodes with a wider i-Ge region. The CMOS compatible fabrication process of the lateral heterojunctions paves the way for the integration of the light source with the Ge metal-oxide-semiconductor field-effect-transistor.

  6. Process modules for GeSn nanoelectronics with high Sn-contents

    NASA Astrophysics Data System (ADS)

    Schulte-Braucks, C.; Glass, S.; Hofmann, E.; Stange, D.; von den Driesch, N.; Hartmann, J. M.; Ikonic, Z.; Zhao, Q. T.; Buca, D.; Mantl, S.

    2017-02-01

    This paper systematically studies GeSn n-FETs, from individual process modules to a complete device. High-k gate stacks and NiGeSn metallic contacts for source and drain are characterized in independent experiments. To study both direct and indirect bandgap semiconductors, a range of 0-14.5 at.% Sn-content GeSn alloys are investigated. Special emphasis is placed on capacitance-voltage (C-V) characteristics and Schottky-barrier optimization. GeSn n-FET devices are presented including temperature dependent I-V characteristics. Finally, as an important step towards implementing GeSn in tunnel-FETs, negative differential resistance in Ge0.87Sn0.13 tunnel-diodes is demonstrated at cryogenic temperatures. The present work provides a base for further optimization of GeSn FETs and novel tunnel FET devices.

  7. Advanced Semiconductor Devices

    NASA Astrophysics Data System (ADS)

    Shur, Michael S.; Maki, Paul A.; Kolodzey, James

    2007-06-01

    I. Wide band gap devices. Wide-Bandgap Semiconductor devices for automotive applications / M. Sugimoto ... [et al.]. A GaN on SiC HFET device technology for wireless infrastructure applications / B. Green ... [et al.]. Drift velocity limitation in GaN HEMT channels / A. Matulionis. Simulations of field-plated and recessed gate gallium nitride-based heterojunction field-effect transistors / V. O. Turin, M. S. Shur and D. B. Veksler. Low temperature electroluminescence of green and deep green GaInN/GaN light emitting diodes / Y. Li ... [et al.]. Spatial spectral analysis in high brightness GaInN/GaN light emitting diodes / T. Detchprohm ... [et al.]. Self-induced surface texturing of Al2O3 by means of inductively coupled plasma reactive ion etching in Cl2 chemistry / P. Batoni ... [et al.]. Field and termionic field transport in aluminium gallium arsenide heterojunction barriers / D. V. Morgan and A. Porch. Electrical characteristics and carrier lifetime measurements in high voltage 4H-SiC PiN diodes / P. A. Losee ... [et al.]. Geometry and short channel effects on enhancement-mode n-Channel GaN MOSFETs on p and n- GaN/sapphire substrates / W. Huang, T. Khan and T. P. Chow. 4H-SiC Vertical RESURF Schottky Rectifiers and MOSFETs / Y. Wang, P. A. Losee and T. P. Chow. Present status and future Directions of SiGe HBT technology / M. H. Khater ... [et al.]Optical properties of GaInN/GaN multi-quantum Wells structure and light emitting diode grown by metalorganic chemical vapor phase epitaxy / J. Senawiratne ... [et al.]. Electrical comparison of Ta/Ti/Al/Mo/Au and Ti/Al/Mo/Au Ohmic contacts on undoped GaN HEMTs structure with AlN interlayer / Y. Sun and L. F. Eastman. Above 2 A/mm drain current density of GaN HEMTs grown on sapphire / F. Medjdoub ... [et al.]. Focused thermal beam direct patterning on InGaN during molecular beam epitaxy / X. Chen, W. J. Schaff and L. F. Eastman -- II. Terahertz and millimeter wave devices. Temperature-dependent microwave performance of

  8. Physico-chemical and electrical properties of rapid thermal oxides on Ge-rich SiGe heterolayers

    NASA Astrophysics Data System (ADS)

    Das, R.; Bera, M. K.; Chakraborty, S.; Saha, S.; Woitok, J. F.; Maiti, C. K.

    2006-11-01

    Rapid thermal oxidation of high-Ge content (Ge-rich) Si 1- xGe x ( x = 0.85) layers in dry O 2 ambient has been investigated. High-resolution X-ray diffraction (HRXRD) and strain-sensitive two-dimensional reciprocal space mapping X-ray diffractometry (2D-RSM) are employed to investigate strain relaxation and composition of as-grown SiGe alloy layers. Characterizations of ultra thin oxides (˜6-8 nm) have been performed using Fourier transform infrared spectroscopy (FTIR) and high-resolution X-ray photoelectron spectroscopy (HRXPS). Formation of mixed oxide i.e., (SiO 2 + GeO 2) and pile-up of Ge at the oxide/Si 1- xGe x interface have been observed. Enhancement in Ge segregation and reduction of oxide thickness with increasing oxidation temperature are reported. Interface properties and leakage current behavior of the rapid thermal oxides have been studied by capacitance-voltage (C-V) and current-voltage (J-V) techniques using metal-oxide-semiconductor capacitor (MOSCAP) structures and the results are reported.

  9. Remote interfacial dipole scattering and electron mobility degradation in Ge field-effect transistors with GeO x /Al2O3 gate dielectrics

    NASA Astrophysics Data System (ADS)

    Wang, Xiaolei; Xiang, Jinjuan; Wang, Shengkai; Wang, Wenwu; Zhao, Chao; Ye, Tianchun; Xiong, Yuhua; Zhang, Jing

    2016-06-01

    Remote Coulomb scattering (RCS) on electron mobility degradation is investigated experimentally in Ge-based metal-oxide-semiconductor field-effect-transistors (MOSFETs) with GeO x /Al2O3 gate stacks. It is found that the mobility increases with greater GeO x thickness (7.8-20.8 Å). The physical origin of this mobility dependence on GeO x thickness is explored. The following factors are excluded: Coulomb scattering due to interfacial traps at GeO x /Ge, phonon scattering, and surface roughness scattering. Therefore, the RCS from charges in gate stacks is studied. The charge distributions in GeO x /Al2O3 gate stacks are evaluated experimentally. The bulk charges in Al2O3 and GeO x are found to be negligible. The density of the interfacial charge is  +3.2  ×  1012 cm-2 at the GeO x /Ge interface and  -2.3  ×  1012 cm-2 at the Al2O3/GeO x interface. The electric dipole at the Al2O3/GeO x interface is found to be  +0.15 V, which corresponds to an areal charge density of 1.9  ×  1013 cm-2. The origin of this mobility dependence on GeO x thickness is attributed to the RCS due to the electric dipole at the Al2O3/GeO x interface. This remote dipole scattering is found to play a significant role in mobility degradation. The discovery of this new scattering mechanism indicates that the engineering of the Al2O3/GeO x interface is key for mobility enhancement and device performance improvement. These results are helpful for understanding and engineering Ge mobility enhancement.

  10. 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

  11. Lasing from Glassy Ge Quantum Dots in Crystalline Si

    PubMed Central

    2016-01-01

    Semiconductor light-emitters compatible with standard Si integration technology (SIT) are of particular interest for overcoming limitations in the operating speed of microelectronic devices. Light sources based on group IV elements would be SIT-compatible, but suffer from the poor optoelectronic properties of bulk Si and Ge. Here we demonstrate that epitaxially grown Ge quantum dots (QDs) in a defect-free Si matrix show extraordinary optical properties if partially amorphized by Ge-ion bombardment (GIB). In contrast to conventional SiGe nanostructures, these QDs exhibit dramatically shortened carrier lifetimes and negligible thermal quenching of the photoluminescence (PL) up to room temperature. Microdisk resonators with embedded GIB-QDs exhibit threshold behavior as well as a superlinear increase of the integrated PL intensity with concomitant line width narrowing as the pump power increases. These findings demonstrate light amplification by stimulated emission in a fully SIT-compatible group IV nanosystem. PMID:26937421

  12. Coherent spectroscopy of semiconductors.

    PubMed

    Cundiff, Steven T

    2008-03-31

    The coherent optical response of semiconductors has been the subject of substantial research over the last couple of decades. The interest has been motivated by unique aspects of the interaction between light and semiconductors that are revealed by coherent techniques. The ability to probe the dynamics of charge carriers has been a significant driver. This paper presents a review of selected results in coherent optical spectroscopy of semiconductors.

  13. Semiconductor microcavity lasers

    SciTech Connect

    Gourley, P.L.; Wendt, J.R.; Vawter, G.A.; Warren, M.E.; Brennan, T.M.; Hammons, B.E.

    1994-02-01

    New kinds of semiconductor microcavity lasers are being created by modern semiconductor technologies like molecular beam epitaxy and electron beam lithography. These new microcavities exploit 3-dimensional architectures possible with epitaxial layering and surface patterning. The physical properties of these microcavities are intimately related to the geometry imposed on the semiconductor materials. Among these microcavities are surface-emitting structures which have many useful properties for commercial purposes. This paper reviews the basic physics of these microstructured lasers.

  14. Absorption of light dark matter in semiconductors

    NASA Astrophysics Data System (ADS)

    Hochberg, Yonit; Lin, Tongyan; Zurek, Kathryn M.

    2017-01-01

    Semiconductors are by now well-established targets for direct detection of MeV to GeV dark matter via scattering off electrons. We show that semiconductor targets can also detect significantly lighter dark matter via an absorption process. When the dark matter mass is above the band gap of the semiconductor (around an eV), absorption proceeds by excitation of an electron into the conduction band. Below the band gap, multiphonon excitations enable absorption of dark matter in the 0.01 eV to eV mass range. Energetic dark matter particles emitted from the sun can also be probed for masses below an eV. We derive the reach for absorption of a relic kinetically mixed dark photon or pseudoscalar in germanium and silicon, and show that existing direct detection results already probe new parameter space. With only a moderate exposure, low-threshold semiconductor target experiments can exceed current astrophysical and terrestrial constraints on sub-keV bosonic dark matter.

  15. Liquid-phase epitaxy of the (Si{sub 2}){sub 1−x−y}(Ge{sub 2}){sub x}(GaAs){sub y} substitutional solid solution (0 ≤ x ≤ 0.91, 0 ≤ y ≤ 0.94) and their electrophysical properties

    SciTech Connect

    Saidov, A. S. Usmonov, Sh. N. Saidov, M. S.

    2015-04-15

    (Si{sub 2}){sub 1−x−y}(Ge{sub 2}){sub x}(GaAs){sub y} substitutional solid solutions (0 ≤ x ≤ 0.91, 0 ≤ y ≤ 0.94) are grown by liquid-phase epitaxy from a Pb-based solution-melt on Si substrates with the (111) crystallographic orientation. The chemical composition of the epitaxial films is studied by X-rays probe microanalysis, and the distribution profile of solid solution components is determined. Spectral dependences of the photosensitivity and photoluminescence of the n-Si-p(Si{sub 2}){sub 1−x−y}(Ge{sub 2}){sub x}(GaAs){sub y} heterostructures are studied at room and liquid-nitrogen temperatures. Two maxima are found in the photoluminescence spectra of the (Si{sub 2}){sub 1−x−y}(Ge{sub 2}){sub x}(GaAs){sub y} films (0 ≤ x ≤ 0.91, 0 ≤ y ≤ 0.94) against the background of a broad emission spectrum. The fundamental maximum with an energy of 1.45 eV is caused by the band-to-band recombination of solid solution carriers, and an additional maximum with an energy of 1.33 eV is caused by the recombination of carriers with the participation of impurity levels of the Si-Si bond (Si{sub 2} is covalently coupled with the tetrahedral lattice of the solid solution host)

  16. Semiconductor bridge (SCB) detonator

    DOEpatents

    Bickes, R.W. Jr.; Grubelich, M.C.

    1999-01-19

    The present invention is a low-energy detonator for high-density secondary-explosive materials initiated by a semiconductor bridge (SCB) igniter that comprises a pair of electrically conductive lands connected by a semiconductor bridge. The semiconductor bridge is in operational or direct contact with the explosive material, whereby current flowing through the semiconductor bridge causes initiation of the explosive material. Header wires connected to the electrically-conductive lands and electrical feed-throughs of the header posts of explosive devices, are substantially coaxial to the direction of current flow through the SCB, i.e., substantially coaxial to the SCB length. 3 figs.

  17. Semiconductor bridge (SCB) detonator

    DOEpatents

    Bickes, Jr., Robert W.; Grubelich, Mark C.

    1999-01-01

    The present invention is a low-energy detonator for high-density secondary-explosive materials initiated by a semiconductor bridge igniter that comprises a pair of electrically conductive lands connected by a semiconductor bridge. The semiconductor bridge is in operational or direct contact with the explosive material, whereby current flowing through the semiconductor bridge causes initiation of the explosive material. Header wires connected to the electrically-conductive lands and electrical feed-throughs of the header posts of explosive devices, are substantially coaxial to the direction of current flow through the SCB, i.e., substantially coaxial to the SCB length.

  18. Interconnected semiconductor devices

    DOEpatents

    Grimmer, Derrick P.; Paulson, Kenneth R.; Gilbert, James R.

    1990-10-23

    Semiconductor layer and conductive layer formed on a flexible substrate, divided into individual devices and interconnected with one another in series by interconnection layers and penetrating terminals.

  19. Growth and Optical Properties of Direct Band Gap Ge/Ge0.87Sn0.13 Core/Shell Nanowire Arrays.

    PubMed

    Assali, S; Dijkstra, A; Li, A; Koelling, S; Verheijen, M A; Gagliano, L; von den Driesch, N; Buca, D; Koenraad, P M; Haverkort, J E M; Bakkers, E P A M

    2017-03-08

    Group IV semiconductor optoelectronic devices are now possible by using strain-free direct band gap GeSn alloys grown on a Ge/Si virtual substrate with Sn contents above 9%. Here, we demonstrate the growth of Ge/GeSn core/shell nanowire arrays with Sn incorporation up to 13% and without the formation of Sn clusters. The nanowire geometry promotes strain relaxation in the Ge0.87Sn0.13 shell and limits the formation of structural defects. This results in room-temperature photoluminescence centered at 0.465 eV and enhanced absorption above 98%. Therefore, direct band gap GeSn grown in a nanowire geometry holds promise as a low-cost and high-efficiency material for photodetectors operating in the short-wave infrared and thermal imaging devices.

  20. Replacement of Ge in GeTe by [Ag +Sb] and rare earths: effect on thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Levin, E. M.; Hanson, M.; Hanus, R.; Schmidt-Rohr, K.

    2013-03-01

    High-efficiency p-type Te-Sb-Ge-Ag (TAGS) thermoelectric materials are based on the GeTe narrow-band self-dopant semiconductor where Ge can be replaced by up to 16 at.% [Ag +Sb]. To understand the effect of Ge replacement by 4 at.% [Ag +Sb] as well as rare earths atoms, we have synthesized and studied XRD, thermopower, electrical resistivity, thermal conductivity, and 125Te NMR of GeTe and Ag2Sb2Ge46-xRxTe50 with R =Gd, Dy and x = 1, 2. At 700 K, GeTe exhibits a thermopower of +146 μVK-1 and a large power factor, 42 μWcm-1K-2. Replacement of Ge by [Ag +Sb] and rare earths enhances the thermopower, but slightly reduces the power factor due to an increase in electrical resistivity. The thermal conductivity at 300 K of all alloys studied is reduced by a factor of two compared to GeTe. 125Te NMR spin-lattice relaxation time and resonance frequency reflect changes in carrier concentration. However, decrease of thermal conductivity due to carriers and increase of electrical resistivity are mostly due to a reduction of carrier mobility and indicate strong scattering produced by [Ag +Sb] and rare earth atoms. At 700 K, the thermoelectric figure of merit of GeTe is 0.8, whereas that in Ag2Sb2Ge45Dy1Te50 is much larger, 1.2, due to a reduction in thermal conductivity. Enhancement of thermopower is discussed within a model of energy filtering.

  1. Orange Zinc Germanate with Metallic Ge-Ge Bonds as a Chromophore-Like Center for Visible-Light-Driven Water Splitting.

    PubMed

    Qian, Ling; Chen, Jian Fu; Li, Yu Hang; Wu, Long; Wang, Hai Feng; Chen, Ai Ping; Hu, P; Zheng, Li Rong; Yang, Hua Gui

    2015-09-21

    The efficiency of solar-energy-conversion devices depends on the absorption region and intensity of the photon collectors. Organic chromophores, which have been widely stabilized on inorganic semiconductors for light trapping, are limited by the interface between the chromophore and semiconductor. Herein we report a novel orange zinc germanate (Zn-Ge-O) with a chromophore-like structure, by which the absorption region can be dramatically expanded. Structural characterizations and theoretical calculations together reveal that the origin of visible-light response can be attributed to the unusual metallic Ge-Ge bonds which act in a similar way to organic chromophores. Benefiting from the enhanced light harvest, the orange Zn-Ge-O demonstrates superior capacity for solar-driven hydrogen production.

  2. Closely packed Ge quantum dots in ITO matrix: influence of Ge crystallization on optical and electrical properties

    NASA Astrophysics Data System (ADS)

    Car, Tihomir; Nekić, Nikolina; Jerčinović, Marko; Salamon, Krešimir; Bogdanović-Radović, Iva; Delač Marion, Ida; Dasović, Jasna; Dražić, Goran; Ivanda, Mile; Bernstorff, Sigrid; Pivac, Branko; Kralj, Marko; Radić, Nikola; Buljan, Maja

    2016-06-01

    In the present work, a method for the low-temperature production of the material consisting of closely packed Ge QDs embedded in ITO matrix is described. The films are produced by magnetron sputtering deposition followed by thermal annealing. It is shown that the conductivity and optical properties of the films depend on the structure, Ge content in the ITO matrix as well as on the annealing conditions. The conductivity of the films changes up to seven orders of magnitude in dependence on the annealing conditions, and it shows transformation from semiconductor to metallic behavior. The optical properties are also strongly affected by the preparation and annealing conditions, so both conductivity and optical properties can be controllably manipulated. In addition, the crystallization of Ge is found to occur already at 300 °C, which is significantly lower than the crystallization temperature of Ge produced by the same method in silica and alumina matrices.

  3. Mobility anisotropy of two-dimensional semiconductors

    NASA Astrophysics Data System (ADS)

    Lang, Haifeng; Zhang, Shuqing; Liu, Zhirong

    2016-12-01

    The carrier mobility of anisotropic two-dimensional semiconductors under longitudinal acoustic phonon scattering was theoretically studied using deformation potential theory. Based on the Boltzmann equation with the relaxation time approximation, an analytic formula of intrinsic anisotropic mobility was derived, showing that the influence of effective mass on mobility anisotropy is larger than those of deformation potential constant or elastic modulus. Parameters were collected for various anisotropic two-dimensional materials (black phosphorus, Hittorf's phosphorus, BC2N , MXene, TiS3, and GeCH3) to calculate their mobility anisotropy. It was revealed that the anisotropic ratio is overestimated by the previously described method.

  4. Resistive switching memory characteristics of Ge/GeO x nanowires and evidence of oxygen ion migration

    NASA Astrophysics Data System (ADS)

    Prakash, Amit; Maikap, Siddheswar; Rahaman, Sheikh Ziaur; Majumdar, Sandip; Manna, Santanu; Ray, Samit K.

    2013-05-01

    The resistive switching memory of Ge nanowires (NWs) in an IrO x /Al2O3/Ge NWs/SiO2/p-Si structure is investigated. Ge NWs with an average diameter of approximately 100 nm are grown by the vapor-liquid-solid technique. The core-shell structure of the Ge/GeO x NWs is confirmed by both scanning electron microscopy and high-resolution transmission electron microscopy. Defects in the Ge/GeO x NWs are observed by X-ray photoelectron spectroscopy. Broad photoluminescence spectra from 10 to 300 K are observed because of defects in the Ge/GeO x NWs, which are also useful for nanoscale resistive switching memory. The resistive switching mechanism in an IrO x /GeO x /W structure involves migration of oxygen ions under external bias, which is also confirmed by real-time observation of the surface of the device. The porous IrO x top electrode readily allows the evolved O2 gas to escape from the device. The annealed device has a low operating voltage (<4 V), low RESET current (approximately 22 μA), large resistance ratio (>103), long pulse read endurance of >105 cycles, and good data retention of >104 s. Its performance is better than that of the as-deposited device because the GeO x film in the annealed device contains more oxygen vacancies. Under SET operation, Ge/GeO x nanofilaments (or NWs) form in the GeO x film. The diameter of the conducting nanofilament is approximately 40 nm, which is calculated using a new method.

  5. Semiconductor nanomembranes: a platform for new properties via strain engineering

    PubMed Central

    2012-01-01

    New phenomena arise in single-crystal semiconductors when these are fabricated in very thin sheets, with thickness at the nanometer scale. We review recent research on Si and Ge nanomembranes, including the use of elastic strain sharing, layer release, and transfer, that demonstrate new science and enable the fabrication of materials with unique properties. Strain engineering produces new strained forms of Si or Ge not possible in nature, new layered structures, defect-free SiGe sheets, and new electronic band structure and photonic properties. Through-membrane elastic interactions cause the double-sided ordering of epitaxially grown nanostressors on Si nanomembranes, resulting in a spatially and periodically varying strain field in the thin crystalline semiconductor sheet. The inherent influence of strain on the band structure creates band gap modulation, thereby creating effectively a single-element electronic superlattice. Conversely, large-enough externally applied strain can make Ge a direct-band gap semiconductor, giving promise for Group IV element light sources. PMID:23153167

  6. Semiconductor nanomembranes: a platform for new properties via strain engineering.

    PubMed

    Cavallo, Francesca; Lagally, Max G

    2012-11-15

    New phenomena arise in single-crystal semiconductors when these are fabricated in very thin sheets, with thickness at the nanometer scale. We review recent research on Si and Ge nanomembranes, including the use of elastic strain sharing, layer release, and transfer, that demonstrate new science and enable the fabrication of materials with unique properties. Strain engineering produces new strained forms of Si or Ge not possible in nature, new layered structures, defect-free SiGe sheets, and new electronic band structure and photonic properties. Through-membrane elastic interactions cause the double-sided ordering of epitaxially grown nanostressors on Si nanomembranes, resulting in a spatially and periodically varying strain field in the thin crystalline semiconductor sheet. The inherent influence of strain on the band structure creates band gap modulation, thereby creating effectively a single-element electronic superlattice. Conversely, large-enough externally applied strain can make Ge a direct-band gap semiconductor, giving promise for Group IV element light sources.

  7. Crystalline nanostructures on Ge surfaces induced by ion irradiation

    NASA Astrophysics Data System (ADS)

    Ou, Xin; Facsko, Stefan

    2014-12-01

    Besides conventional low efficiency lithographic techniques broad ion beam irradiation is a simple and potentially mass productive technique to fabricate nanoscale patterns on various semiconductor surfaces. The main drawback of this method is that the irradiated semiconductor surfaces are amorphized, which strongly limits the potential application of these nanostructures in electronic and optoelectronic devices. In this work we report that high-quality crystalline nanostructure patterns are formed on Ge surfaces via Ar+ irradiation at elevated temperatures. This pattern formation process resembles the pattern formation in homoepitaxy. Therefore, the process is discussed based on a 'reverse epitaxy' mechanism.

  8. Flexible germanium nanomembrane metal-semiconductor-metal photodiodes

    SciTech Connect

    Kim, Munho; Seo, Jung-Hun; Yu, Zongfu; Ma, Zhenqiang; Zhou, Weidong

    2016-08-01

    We demonstrate flexible Ge nanomembrane (Ge NM) based metal-semiconductor-metal photodiodes. The effect of uniaxial tensile strain on Ge NM based photodiodes was investigated using bending fixtures. Dark current density is decreased from 21.5 to 4.8 mA/cm{sup 2} at 3 V by a tensile strain of 0.42% while photon responsivity is increased from 0.2 to 0.45 A/W at the wavelength of 1.5 μm. Enhanced responsivity is also observed at longer wavelengths up to 1.64 μm. The uniaxial tensile strain effectively reduces the direct bandgap energy of the Ge NM, leading to a shift of the absorption edge toward a longer wavelength.

  9. Bonded semiconductor substrate

    DOEpatents

    Atwater, Jr.; Harry A. , Zahler; James M.

    2010-07-13

    Ge/Si and other nonsilicon film heterostructures are formed by hydrogen-induced exfoliation of the Ge film which is wafer bonded to a cheaper substrate, such as Si. A thin, single-crystal layer of Ge is transferred to Si substrate. The bond at the interface of the Ge/Si heterostructures is covalent to ensure good thermal contact, mechanical strength, and to enable the formation of an ohmic contact between the Si substrate and Ge layers. To accomplish this type of bond, hydrophobic wafer bonding is used, because as the invention demonstrates the hydrogen-surface-terminating species that facilitate van der Waals bonding evolves at temperatures above 600.degree. C. into covalent bonding in hydrophobically bound Ge/Si layer transferred systems.

  10. Band-gap engineering at a semiconductor - crystalline oxide interface

    NASA Astrophysics Data System (ADS)

    Ahmadi-Majlan, Kamyar; Jahangir-Moghadam, Mohammadreza; Shen, Xuan; Droubay, Timothy; Bowden, Mark; Chrysler, Matthew; Su, Dong; Chambers, Scott A.; Ngai, Joseph H.

    2015-03-01

    Abstract: The epitaxial growth of crystalline oxides on semiconductors provides a pathway to introduce new functionalities to semiconductor devices. Key to electrically coupling crystalline oxides with semiconductors to realize functional behavior is controlling the manner in which their bands align at interfaces. Here we apply principles of band gap engineering traditionally used at heterojunctions between conventional semiconductors to control the band offset between a single crystalline oxide and a semiconductor. Reactive molecular beam epitaxy is used to realize atomically abrupt and structurally coherent interfaces between SrZrxTi1 -xO3 and Ge, in which the band-gap of the former is enhanced with Zr content x. We present structural and electrical characterization of SrZrxTi1 -xO3-Ge heterojunctions for x = 0.2 to 0.75 and demonstrate the band offset can be tuned from type-II to type-I, with the latter being verified using photoemission measurements. The type-I band offset provides a platform to integrate the dielectric, ferroelectric and ferromagnetic functionalities of oxides with semiconducting devices.

  11. Molecular Semiconductors: An Introduction

    NASA Astrophysics Data System (ADS)

    de Mello, John; Halls, Jonathan James Michael

    2005-10-01

    Introducing the fundamental ideas and concepts behind organic semiconductors, this book provides a clear impression of the broad range of research activities currently underway. Aimed specifically at new entrant doctoral students from a wide variety of backgrounds, including chemistry, physics, electrical engineering and materials science, it also represents an ideal companion text to undergraduate courses in organic semiconductors.

  12. Characterisation of diode-connected SiGe BiCMOS HBTs for space applications

    NASA Astrophysics Data System (ADS)

    Venter, Johan; Sinha, Saurabh; Lambrechts, Wynand

    2016-02-01

    Silicon-germanium (SiGe) bipolar complementary metal-oxide semiconductor (BiCMOS) transistors have vertical doping profiles reaching deeper into the substrate when compared to lateral CMOS transistors. Apart from benefiting from high-speed, high current gain and low-output resistance due to its vertical profile, BiCMOS technology is increasingly becoming a preferred technology for researchers to realise next-generation space-based optoelectronic applications. BiCMOS transistors have inherent radiation hardening, to an extent predictable cryogenic performance and monolithic integration potential. SiGe BiCMOS transistors and p-n junction diodes have been researched and used as a primary active component for over the last two decades. However, further research can be conducted with diode-connected heterojunction bipolar transistors (HBTs) operating at cryogenic temperatures. This work investigates these characteristics and models devices by adapting standard fabrication technology components. This work focuses on measurements of the current-voltage relationship (I-V curves) and capacitance-voltage relationships (C-V curves) of diode-connected HBTs. One configuration is proposed and measured, which is emitterbase shorted. The I-V curves are measured for various temperature points ranging from room temperature (300 K) to the temperature of liquid nitrogen (77 K). The measured datasets are used to extract a model of the formed diode operating at cryogenic temperatures and used as a standard library component in computer aided software designs. The advantage of having broad-range temperature models of SiGe transistors becomes apparent when considering implementation of application-specific integrated circuits and silicon-based infrared radiation photodetectors on a single wafer, thus shortening interconnects and lowering parasitic interference, decreasing the overall die size and improving on overall cost-effectiveness. Primary applications include space-based geothermal

  13. Al and Ge simultaneous oxidation using neutral beam post-oxidation for formation of gate stack structures

    SciTech Connect

    Ohno, Takeo; Nakayama, Daiki; Samukawa, Seiji

    2015-09-28

    To obtain a high-quality Germanium (Ge) metal–oxide–semiconductor structure, a Ge gate stacked structure was fabricated using neutral beam post-oxidation. After deposition of a 1-nm-thick Al metal film on a Ge substrate, simultaneous oxidation of Al and Ge was carried out at 300 °C, and a Ge oxide film with 29% GeO{sub 2} content was obtained by controlling the acceleration bias power of the neutral oxygen beam. In addition, the fabricated AlO{sub x}/GeO{sub x}/Ge structure achieved a low interface state density of less than 1 × 10{sup 11 }cm{sup −2 }eV{sup −1} near the midgap.

  14. EDITORIAL: Oxide semiconductors

    NASA Astrophysics Data System (ADS)

    Kawasaki, M.; Makino, T.

    2005-04-01

    Blue or ultraviolet semiconducting light-emitting diodes have the potential to revolutionize illumination systems in the near-future. Such industrial need has propelled the investigation of several wide-gap semiconducting materials in recent years. Commercial applications include blue lasers for DVD memory and laser printers, while military applications are also expected. Most of the material development has so far been focused on GaN (band gap 3.5 eV at 2 K), and ZnSe (2.9 eV) because these two representative direct transition semiconductors are known to be bright emitting sources. GaN and GaN-based alloys are emerging as the winners in this field because ZnSe is subject to defect formation under high current drive. On the other hand, another II-VI compound, ZnO, has also excited substantial interest in the optoelectronics-oriented research communities because it is the brightest emitter of all, owing to the fact that its excitons have a 60 meV binding energy. This is compared with 26 meV for GaN and 20 meV for ZnSe. The stable excitons could lead to laser action based on their recombination even at temperatures well above room temperature. ZnO has additional major properties that are more advantageous than other wide-gap materials: availability of large area substrates, higher energy radiation stability, environmentally-friendly ingredients, and amenability to wet chemical etching. However, ZnO is not new to the semiconductor field as exemplified by several studies made during the 1960s on structural, vibrational, optical and electrical properties (Mollwo E 1982 Landolt-Boernstein New Series vol 17 (Berlin: Springer) p 35). In terms of devices, the luminescence from light-emitting diode structures was demonstrated in which Cu2O was used as the p-type material (Drapak I T 1968 Semiconductors 2 624). The main obstacle to the development of ZnO has been the lack of reproducible p-type ZnO. The possibility of achieving epitaxial p-type layers with the aid of thermal

  15. Monolayer germanium monochalcogenides (GeS/GeSe) as cathode catalysts in nonaqueous Li-O2 batteries.

    PubMed

    Ji, Yujin; Dong, Huilong; Yang, Mingye; Hou, Tingjun; Li, Youyong

    2017-08-09

    The development of novel cathode catalysts is of great importance to the practical applications of nonaqueous lithium oxygen (Li-O2) batteries. Here by using first-principles calculations, we revealed the catalytic mechanism and evaluated the catalytic activity of monolayer germanium monochalcogenides (2D-GeXs, X = S/Se) as cathode catalytic materials. For 2D-GeXs, Li4O4 with a ring-like structure is the final discharge product. The free energy diagram demonstrates that 2D-GeSe is more energetically favorable than 2D-GeS due to its considerably lower oxygen reduction reaction (ORR) overpotential (0.94 V) and oxygen evolution reaction (OER) overpotential (1.30 V), which originate from its weaker binding with LiO2 and stronger binding with the inserted Li atom. The analyses on electronic properties elucidate that the final product of Li4O4 on 2D-GeSe induces the semiconductor to semi-metal transition. Our results reflect that 2D-GeSe is an excellent candidate as a cathode material in nonaqueous Li-O2 batteries, while 2D-GeS is not appropriate.

  16. Optical absorption in highly strained Ge/SiGe quantum wells: The role of Γ→ Δ scattering

    NASA Astrophysics Data System (ADS)

    Lever, L.; Ikonić, Z.; Valavanis, A.; Kelsall, R. W.; Myronov, M.; Leadley, D. R.; Hu, Y.; Owens, N.; Gardes, F. Y.; Reed, G. T.

    2012-12-01

    We report the observation of the quantum-confined Stark effect in Ge/SiGe multiple quantum well heterostructures grown on Si0.22Ge0.78 virtual substrates. The large compressive strain in the Ge quantum well layers caused by the lattice mismatch with the virtual substrate results in a blue shift of the direct absorption edge, as well as a reduction in the Γ-valley scattering lifetime because of strain-induced splittings of the conduction band valleys. We investigate theoretically the Γ-valley carrier lifetimes by evaluating the Γ →L and Γ →Δ scattering rates in strained Ge/SiGe semiconductor heterostructures. These scattering rates are used to determine the lifetime broadening of excitonic peaks and the indirect absorption in simulated absorption spectra, which are compared with measured absorption spectra for quantum well structures with systematically varied dimensions. We find that Γ →Δ scattering is significant in compressively strained Ge quantum wells and that the Γ-valley electron lifetime is less than 50 fs in the highly strained structures reported here, where Γ →Δ scattering accounted for approximately half of the total scattering rate.

  17. 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).

  18. Mn-doped Ge and Si: A Review of the Experimental Status

    PubMed Central

    Zhou, Shengqiang; Schmidt, Heidemarie

    2010-01-01

    Diluted ferromagnetic semiconductors (FMS) are in the focus of intense research due to their potential applications in spintronics and their striking new physical properties. So far Mn-doped III-V compound semiconductors such as GaMnAs are the most important and best understood ones, but they are ferromagnetic only at well below room temperature. An interesting alternative could be magnetic semiconductors based on elemental semiconductors, also owing to their compatibility with Si microelectronics. In the last decades, considerable amount of work has been devoted to fabricate Mn-doped Ge and Si FMS. In this article, the structural, magnetic and magneto-transport properties of Mn-doped Ge and Si will be reviewed. PMID:28883369

  19. Liquid Contact Luminescence from Semiconductor Laser Materials

    DTIC Science & Technology

    1997-01-09

    Young, P.S. Zory, and D.P. Bour, Layer Diodes and Applications, Kurt I. Linden , Prasad R. Akkapeddi, Editors, Proc. SPIE 2682, 136 (1996). 129 130...Grove, P.S. Zory, H.K. Choi, and G.W. Turner, Laser Diodes and Applications, Kurt L Linden , Prasad R. Akkapeddi, Editors, Proc. SPIE 2382, 244 (1995...equivalent circuit model developed for PAL is shown in Figure 2-13. Cox CdI . Rsod~n Rf D iode j ,h10o Figure 2-13. Schematic diagram of the PAL

  20. Single and coupled quantum wells: SiGe

    NASA Astrophysics Data System (ADS)

    Usami, N.; Shiraki, Y.

    This document is part of subvolume C3 'Optical Properties' of volume 34 'Semiconductor quantum structures' of Landolt-Börnstein, Group III, Condensed Matter, on the optical properties of quantum structures based on group IV semiconductors. It discusses single and coupled quantum wells based on SiGe. Topics include the photoluminescence from SiGe/Si quantum wells (spectral features, dependence on excitation power and temperature), effects of quantum confinement, post-growth annealing, electric fields and external stress, the Fermi-edge singularity, time-resolved photoluminescence, growth mode transition, type-II strained Si quantum wells, coupled quantum wells, electroluminescence, interband absorption and intraband absorption, second-harmonic generation, and phonon modes.

  1. Quasi-perpetual discharge behaviour in p-type Ge-air batteries.

    PubMed

    Ocon, Joey D; Kim, Jin Won; Abrenica, Graniel Harne A; Lee, Jae Kwang; Lee, Jaeyoung

    2014-11-07

    Metal-air batteries continue to become attractive energy storage and conversion systems due to their high energy and power densities, safer chemistries, and economic viability. Semiconductor-air batteries - a term we first define here as metal-air batteries that use semiconductor anodes such as silicon (Si) and germanium (Ge) - have been introduced in recent years as new high-energy battery chemistries. In this paper, we describe the excellent doping-dependent discharge kinetics of p-type Ge anodes in a semiconductor-air cell employing a gelled KOH electrolyte. Owing to its Fermi level, n-type Ge is expected to have lower redox potential and better electronic conductivity, which could potentially lead to a higher operating voltage and better discharge kinetics. Nonetheless, discharge measurements demonstrated that this prediction is only valid at the low current regime and breaks down at the high current density region. The p-type Ge behaves extremely better at elevated currents, evident from the higher voltage, more power available, and larger practical energy density from a very long discharge time, possibly arising from the high overpotential for surface passivation. A primary semiconductor-air battery, powered by a flat p-type Ge as a multi-electron anode, exhibited an unprecedented full discharge capacity of 1302.5 mA h gGe(-1) (88% anode utilization efficiency), the highest among semiconductor-air cells, notably better than new metal-air cells with three-dimensional and nanostructured anodes, and at least two folds higher than commercial Zn-air and Al-air cells. We therefore suggest that this study be extended to doped-Si anodes, in order to pave the way for a deeper understanding on the discharge phenomena in alkaline metal-air conversion cells with semiconductor anodes for specific niche applications in the future.

  2. Preparation methodologies and nano/microstructural evaluation of metal/semiconductor thin films.

    PubMed

    Chen, Zhiwen; Jiao, Zheng; Wu, Minghong; Shek, Chan-Hung; Wu, C M Lawrence; Lai, Joseph K L

    2012-01-01

    Metal/semiconductor thin films are a class of unique materials that are widespread technological applications, particularly in the field of microelectronic devices. Assessment strategies of fractal and tures are of fundamental importance in the development of nano/microdevices. This review presents the preparation methodologies and nano/microstructural evaluation of metal/semiconductor thin films including Au/Ge bilayer films and Pd-Ge alloy thin films, which show in the form of fractals and nanocrystals. Firstly, the extended version of Au/Ge thin films for the fractal crystallization of amorphous Ge and the formation of nanocrystals developed with improved micro- and nanostructured features are described in Section 2. Secondly, the nano/microstructural characteristics of Pd/Ge alloy thin films during annealing have been investigated in detail and described in Section 3. Finally, we will draw the conclusions from the present work as shown in Section 4. It is expected that the preparation methodologies developed and the knowledge of nano/microstructural evolution gained in metal/semiconductor thin films, including Au/Ge bilayer films and Pd-Ge alloy thin films, will provide an important fundamental basis underpinning further interdisciplinary research in these fields such as physics, chemistry, materials science, and nanoscience and nanotechnology, leading to promising exciting opportunities for future technological applications involving these thin films.

  3. A Computer-Automated Temperature Control System for Semiconductor Measurements.

    DTIC Science & Technology

    1979-11-01

    D -A079 055 ILLINOIS UNIV AT URBANA-CHAMPAIGN DEPT OF ELECTRICAL -ETC F/ 14NC/UE2UOAE EPRAUECNRL YTMFRSMIOOC T INOV 79 RN SWITZER ,PC CHAN ’ C T SAH...of semiconductor devices and Materials . Temperature is monitored by a type T thermocouple embedded in a heat sink surrounding the sample. Liquid...semiconductor materials are dependent in some manner on temperature. One example is the rate of thermal emission of trapped holes or electrons from

  4. The coupling of thermochemistry and phase diagrams for Group 3-5 semiconductor systems

    NASA Astrophysics Data System (ADS)

    Anderson, T. J.

    Progress in the third year of this research program has been achieved in three basic areas: measurement of component activities with solid state galvanic cells, thermochemistry and phase diagram assessments, and computation of complex equilibria applied to chemical vapor deposition of compound semiconductors. The activity of In in In-Bi alloys was measured as a function of temperature and composition with a galvanic cell using yttria stabilized zirconia as the solid electrolyte. The activity of Ga in Ga-Bi alloys was determined in a similar solid-state galvanic cell. Coulometric titrations were performed to adjust the composition of Al in Al-In melts. Significant positive deviations were measured in In-rich compositions. Similar titrations were performed in the Al-Sb system. Complex reaction equilibria computations were performed on the Ga-In-As-Cl-H-Si-O and Ge-N-Cl-H system. The first system is important in hydride CVD of Ga(x)In(1-x)As for optoelectronic device applications. The work included the first application of a sensitivity analysis, that suggested the need for an improved thermochemical data base. The effect of various operating parameters on the deposited alloy composition was also studied. In addition, the effect of adding HCl to the mixing zone, the use of liquid Ga-In solution source zone, and the unintentional incorporation of Si were examined. The results of the predictions were verified with experiments by members of our group. Chemical equilibrium calculations were also performed on the Ge-N-Cl-H system to model CVD of Ge3N4.

  5. Effective Schottky Barrier Height Lowering of Metal/n-Ge with a TiO2/GeO2 Interlayer Stack.

    PubMed

    Kim, Gwang-Sik; Kim, Sun-Woo; Kim, Seung-Hwan; Park, June; Seo, Yujin; Cho, Byung Jin; Shin, Changhwan; Shim, Joon Hyung; Yu, Hyun-Yong

    2016-12-28

    A perfect ohmic contact formation technique for low-resistance source/drain (S/D) contact of germanium (Ge) n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) is developed. A metal-interlayer-semiconductor (M-I-S) structure with an ultrathin TiO2/GeO2 interlayer stack is introduced into the contact scheme to alleviate Fermi-level pinning (FLP), and reduce the electron Schottky barrier height (SBH). The TiO2 interlayer can alleviate FLP by preventing formation of metal-induced gap states (MIGS) with its very low tunneling resistance and series resistance and can provide very small electron energy barrier at the metal/TiO2 interface. The GeO2 layer can induce further alleviation of FLP by reducing interface state density (Dit) on Ge which is one of main causes of FLP. Moreover, the proposed TiO2/GeO2 stack can minimize interface dipole formation which induces the SBH increase. The M-I-S structure incorporating the TiO2/GeO2 interlayer stack achieves a perfect ohmic characteristic, which has proved unattainable with a single interlayer. FLP can be perfectly alleviated, and the SBH of the metal/n-Ge can be tremendously reduced. The proposed structure (Ti/TiO2/GeO2/n-Ge) exhibits 0.193 eV of effective electron SBH which achieves 0.36 eV of SBH reduction from that of the Ti/n-Ge structure. The proposed M-I-S structure can be suggested as a promising S/D contact technique for nanoscale Ge n-channel transistors to overcome the large electron SBH problem caused by severe FLP.

  6. Producing Silicon Carbide for Semiconductor Devices

    NASA Technical Reports Server (NTRS)

    Hsu, G. C.; Rohatgi, N. K.

    1986-01-01

    Processes proposed for production of SiC crystals for use in semiconductors operating at temperatures as high as 900 degrees C. Combination of new processes produce silicon carbide chips containing epitaxial layers. Chips of SiC first grown on porous carbon matrices, then placed in fluidized bed, where additional layer of SiC grows. Processes combined to yield complete process. Liquid crystallization process used to make SiC particles or chips for fluidized-bed process.

  7. Grade Equivalent Scores: To GE or Not to GE.

    ERIC Educational Resources Information Center

    Cole, Nancy S.

    The advantages and disadvantages of grade equivalent (GE) scores are explored, including appropriate uses for GE type scores and how to bring current GE scales closer to the type of information educators appear to desire. Although GE scores are not an equal interval scale, not comparable across school subjects, and do not indicate the grade level…

  8. Photoluminescence study of high density Si quantum dots with Ge core

    SciTech Connect

    Kondo, K. Makihara, K.; Ikeda, M.; Miyazaki, S.

    2016-01-21

    Si quantum dots (Si-QDs) with Ge core were self-assembled on thermally grown SiO{sub 2} from alternate thermal decomposition of pure SiH{sub 4} and GeH{sub 4} diluted with He. When the sample was excited by the 979 nm line of a semiconductor laser, fairly broad photoluminescence (PL) spectra in the region of 0.6–0.8 eV were observed at room temperature. The observed PL spectra suggested that radiative recombination of photo-generated carriers through quantized states of Ge core is the dominant pathway for the emission from the dots, reflecting the type II energy band discontinuity between the Si clad and Ge core. We also found that P-δ doping to Ge core plays an important role in recombination through the quantized states in the valence band of Ge core and P donor levels.

  9. Electronic and magnetic properties of Ga, Ge, P and Sb doped monolayer arsenene

    NASA Astrophysics Data System (ADS)

    Bai, M.; Zhang, W. X.; He, C.

    2017-07-01

    In this paper, the structural, electronic, and magnetic properties of Ga, Ge, P and Sb doped monolayer arsenene have been systematically investigated by first-principles calculations based on density functional theory. The properties of monolayer arsenene can be effectively tuned by substitutional doping. Especially, the dopant Ga could lead to an indirect-to-direct bandgap transition and doping a Ge atom could exhibit dilute magnetic semiconductor property. In addition, the second Ge atom slightly prefers to occupy the next nearest-neighbor site of As atom to form the complex substituted defect (GeAs - As - GeAs) in As30Ge2 system and is found to be anti-ferromagnetic coupling. The diverse electronic and magnetic properties highlight the potential applications of monolayer arsenene in electronics, optoelectronics and spintronics.

  10. Room Temperature Ferromagnetic, Anisotropic, Germanium Rich FeGe(001) Alloys.

    PubMed

    Lungu, George A; Apostol, Nicoleta G; Stoflea, Laura E; Costescu, Ruxandra M; Popescu, Dana G; Teodorescu, Cristian M

    2013-02-21

    Ferromagnetic FexGe1-x with x = 2%-9% are obtained by Fe deposition onto Ge(001) at high temperatures (500 °C). Low energy electron diffraction (LEED) investigation evidenced the preservation of the (1 × 1) surface structure of Ge(001) with Fe deposition. X-ray photoelectron spectroscopy (XPS) at Ge 3d and Fe 2p core levels evidenced strong Fe diffusion into the Ge substrate and formation of Ge-rich compounds, from FeGe₃ to approximately FeGe₂, depending on the amount of Fe deposited. Room temperature magneto-optical Kerr effect (MOKE) evidenced ferromagnetic ordering at room temperature, with about 0.1 Bohr magnetons per Fe atom, and also a clear uniaxial magnetic anisotropy with the in-plane easy magnetization axis. This compound is a good candidate for promising applications in the field of semiconductor spintronics.

  11. 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.

  12. Electric-field controlled ferromagnetism in MnGe magnetic quantum dots

    PubMed Central

    Xiu, Faxian; Wang, Yong; Zou, Jin; Wang, Kang L.

    2011-01-01

    Electric-field control of ferromagnetism in magnetic semiconductors at room temperature has been actively pursued as one of the important approaches to realize practical spintronics and non-volatile logic devices. While Mn-doped III-V semiconductors were considered as potential candidates for achieving this controllability, the search for an ideal material with high Curie temperature (Tc>300 K) and controllable ferromagnetism at room temperature has continued for nearly a decade. Among various dilute magnetic semiconductors (DMSs), materials derived from group IV elements such as Si and Ge are the ideal candidates for such materials due to their excellent compatibility with the conventional complementary metal-oxide-semiconductor (CMOS) technology. Here, we review recent reports on the development of high-Curie temperature Mn0.05Ge0.95 quantum dots (QDs) and successfully demonstrate electric-field control of ferromagnetism in the Mn0.05Ge0.95 quantum dots up to 300 K. Upon the application of gate-bias to a metal-oxide-semiconductor (MOS) capacitor, the ferromagnetism of the channel layer (i.e. the Mn0.05Ge0.95 quantum dots) was modulated as a function of the hole concentration. Finally, a theoretical model based upon the formation of magnetic polarons has been proposed to explain the observed field controlled ferromagnetism. PMID:22110869

  13. Electric-field controlled ferromagnetism in MnGe magnetic quantum dots.

    PubMed

    Xiu, Faxian; Wang, Yong; Zou, Jin; Wang, Kang L

    2011-01-01

    Electric-field control of ferromagnetism in magnetic semiconductors at room temperature has been actively pursued as one of the important approaches to realize practical spintronics and non-volatile logic devices. While Mn-doped III-V semiconductors were considered as potential candidates for achieving this controllability, the search for an ideal material with high Curie temperature (T(c)>300 K) and controllable ferromagnetism at room temperature has continued for nearly a decade. Among various dilute magnetic semiconductors (DMSs), materials derived from group IV elements such as Si and Ge are the ideal candidates for such materials due to their excellent compatibility with the conventional complementary metal-oxide-semiconductor (CMOS) technology. Here, we review recent reports on the development of high-Curie temperature Mn(0.05)Ge(0.95) quantum dots (QDs) and successfully demonstrate electric-field control of ferromagnetism in the Mn(0.05)Ge(0.95) quantum dots up to 300 K. Upon the application of gate-bias to a metal-oxide-semiconductor (MOS) capacitor, the ferromagnetism of the channel layer (i.e. the Mn(0.05)Ge(0.95) quantum dots) was modulated as a function of the hole concentration. Finally, a theoretical model based upon the formation of magnetic polarons has been proposed to explain the observed field controlled ferromagnetism.

  14. Shell morphology and Raman spectra of epitaxial Ge-SixGe1-x and Si-SixGe1-x core-shell nanowires

    NASA Astrophysics Data System (ADS)

    Wen, Feng; Dillen, David C.; Kim, Kyounghwan; Tutuc, Emanuel

    2017-06-01

    We investigate the shell morphology and Raman spectra of epitaxial Ge-SixGe1-x and Si-SixGe1-x core-shell nanowire heterostructures grown using a combination of a vapor-liquid-solid (VLS) growth mechanism for the core, followed by in-situ epitaxial shell growth using ultra-high vacuum chemical vapor deposition. Cross-sectional transmission electron microscopy reveals that the VLS growth yields cylindrical Ge, and Si nanowire cores grown along the ⟨111⟩, and ⟨110⟩ or ⟨112⟩ directions, respectively. A hexagonal cross-sectional morphology is observed for Ge-SixGe1-x core-shell nanowires terminated by six {112} facets. Two distinct morphologies are observed for Si-SixGe1-x core-shell nanowires that are either terminated by four {111} and two {100} planes associated with the ⟨110⟩ growth direction or four {113} and two {111} planes associated with the ⟨112⟩ growth direction. We show that the Raman spectra of Si- SixGe1-x are correlated with the shell morphology thanks to epitaxial growth-induced strain, with the core Si-Si mode showing a larger red shift in ⟨112⟩ core-shell nanowires compared to their ⟨110⟩ counterparts. We compare the Si-Si Raman mode value with calculations based on a continuum elasticity model coupled with the lattice dynamic theory.

  15. Si-Ge-metal ternary phase diagram calculations

    NASA Technical Reports Server (NTRS)

    Fleurial, J. P.; Borshchevsky, A.

    1990-01-01

    Solution crystal growth and doping conditions of Si-Ge alloys used for high-temperature thermoelectric generation are determined here. Liquid-phase epitaxy (LPE) has been successfully employed recently to obtain single-crystalline homogeneous layers of Si-Ge solid solutions from a liquid metal solvent. Knowledge of Si-Ge-metallic solvent ternary phase diagrams is essential for further single-crystal growth development. Consequently, a thermodynamic equilibrium model was used to calculate the phase diagrams of the Si-Ge-M systems, including solid solubilities, where M is Al, Ga, In, Sn, Pb, Sb, or Bi. Good agreement between calculated liquidus and solidus data and experimental DTA and microprobe results was obtained. The results are used to compare the suitability of the different systems for crystal growth (by LPE-type process).

  16. Slow Light Semiconductor Laser

    DTIC Science & Technology

    2015-02-02

    we demonstrate a semiconductor laser with a spectral linewidth of 18 kHz in the telecom band around 1:55um. The views, opinions and/or findings...we demonstrate a semiconductor laser with a spectral linewidth of 18 kHz in the telecom band around 1:55um. Further, the large intracavity field...hybrid Si/III- V platforms Abstract The semiconductor laser is the principal light source powering the world-wide optical fiber network . Ever

  17. Introduction to Semiconductor Devices

    NASA Astrophysics Data System (ADS)

    Brennan, Kevin F.

    2005-03-01

    This volume offers a solid foundation for understanding the most important devices used in the hottest areas of electronic engineering today, from semiconductor fundamentals to state-of-the-art semiconductor devices in the telecommunications and computing industries. Kevin Brennan describes future approaches to computing hardware and RF power amplifiers, and explains how emerging trends and system demands of computing and telecommunications systems influence the choice, design and operation of semiconductor devices. In addition, he covers MODFETs and MOSFETs, short channel effects, and the challenges faced by continuing miniaturization. His book is both an excellent senior/graduate text and a valuable reference for practicing engineers and researchers.

  18. Electrolysis of a molten semiconductor

    DOE PAGES

    Yin, Huayi; Chung, Brice; Sadoway, Donald R.

    2016-08-24

    Metals cannot be extracted by electrolysis of transition-metal sulfides because as liquids they are semiconductors, which exhibit high levels of electronic conduction and metal dissolution. Herein by introduction of a distinct secondary electrolyte, we reveal a high-throughput electro-desulfurization process that directly converts semiconducting molten stibnite (Sb2S3) into pure (99.9%) liquid antimony and sulfur vapour. At the bottom of the cell liquid antimony pools beneath cathodically polarized molten stibnite. At the top of the cell sulfur issues from a carbon anode immersed in an immiscible secondary molten salt electrolyte disposed above molten stibnite, thereby blocking electronic shorting across the cell. Inmore » conclusion, as opposed to conventional extraction practices, direct sulfide electrolysis completely avoids generation of problematic fugitive emissions (CO2, CO and SO2), significantly reduces energy consumption, increases productivity in a single-step process (lower capital and operating costs) and is broadly applicable to a host of electronically conductive transition-metal chalcogenides.« less

  19. Electrolysis of a molten semiconductor

    PubMed Central

    Yin, Huayi; Chung, Brice; Sadoway, Donald R.

    2016-01-01

    Metals cannot be extracted by electrolysis of transition-metal sulfides because as liquids they are semiconductors, which exhibit high levels of electronic conduction and metal dissolution. Herein by introduction of a distinct secondary electrolyte, we reveal a high-throughput electro-desulfurization process that directly converts semiconducting molten stibnite (Sb2S3) into pure (99.9%) liquid antimony and sulfur vapour. At the bottom of the cell liquid antimony pools beneath cathodically polarized molten stibnite. At the top of the cell sulfur issues from a carbon anode immersed in an immiscible secondary molten salt electrolyte disposed above molten stibnite, thereby blocking electronic shorting across the cell. As opposed to conventional extraction practices, direct sulfide electrolysis completely avoids generation of problematic fugitive emissions (CO2, CO and SO2), significantly reduces energy consumption, increases productivity in a single-step process (lower capital and operating costs) and is broadly applicable to a host of electronically conductive transition-metal chalcogenides. PMID:27553525

  20. Electrolysis of a molten semiconductor

    SciTech Connect

    Yin, Huayi; Chung, Brice; Sadoway, Donald R.

    2016-08-24

    Metals cannot be extracted by electrolysis of transition-metal sulfides because as liquids they are semiconductors, which exhibit high levels of electronic conduction and metal dissolution. Herein by introduction of a distinct secondary electrolyte, we reveal a high-throughput electro-desulfurization process that directly converts semiconducting molten stibnite (Sb2S3) into pure (99.9%) liquid antimony and sulfur vapour. At the bottom of the cell liquid antimony pools beneath cathodically polarized molten stibnite. At the top of the cell sulfur issues from a carbon anode immersed in an immiscible secondary molten salt electrolyte disposed above molten stibnite, thereby blocking electronic shorting across the cell. In conclusion, as opposed to conventional extraction practices, direct sulfide electrolysis completely avoids generation of problematic fugitive emissions (CO2, CO and SO2), significantly reduces energy consumption, increases productivity in a single-step process (lower capital and operating costs) and is broadly applicable to a host of electronically conductive transition-metal chalcogenides.

  1. Photoelectrochemistry of Semiconductor Nanowire Arrays

    SciTech Connect

    Mallouk, Thomas E; Redwing, Joan M

    2009-11-10

    This project supported research on the growth and photoelectrochemical characterization of semiconductor nanowire arrays, and on the development of catalytic materials for visible light water splitting to produce hydrogen and oxygen. Silicon nanowires were grown in the pores of anodic aluminum oxide films by the vapor-liquid-solid technique and were characterized electrochemically. Because adventitious doping from the membrane led to high dark currents, silicon nanowire arrays were then grown on silicon substrates. The dependence of the dark current and photovoltage on preparation techniques, wire diameter, and defect density was studied for both p-silicon and p-indium phosphide nanowire arrays. The open circuit photovoltage of liquid junction cells increased with increasing wire diameter, reaching 350 mV for micron-diameter silicon wires. Liquid junction and radial p-n junction solar cells were fabricated from silicon nano- and microwire arrays and tested. Iridium oxide cluster catalysts stabilized by bidentate malonate and succinate ligands were also made and studied for the water oxidation reaction. Highlights of this project included the first papers on silicon and indium phosphide nanowire solar cells, and a new procedure for making ligand-stabilized water oxidation catalysts that can be covalently linked to molecular photosensitizers or electrode surfaces.

  2. GE STEM Teacher's Conference

    NASA Image and Video Library

    2017-07-13

    Teachers participate in the Rocketry Engineering Design Challenge during the 2017 GE Foundation High School STEM Integration Conference at the Center for Space Education at NASA's Kennedy Space Center. High school teachers from across the country took part in the week-long conference, which is designed to explore effective ways for teachers, schools and districts from across the country to integrate STEM throughout the curriculum. The conference is a partnership between GE Foundation and the National Science Teachers Association.

  3. Two-stage model of nanocone formation on a surface of elementary semiconductors by laser radiation

    PubMed Central

    2012-01-01

    In this work, we study the mechanism of nanocone formation on a surface of elementary semiconductors by Nd:YAG laser radiation. Our previous investigations of SiGe and CdZnTe solid solutions have shown that nanocone formation mechanism is characterized by two stages. The first stage is characterized by formation of heterostructure, for example, Ge/Si heterostructure from SiGe solid solutions, and the second stage is characterized by formation of nanocones by mechanical plastic deformation of the compressed Ge layer on Si due to mismatch of Si and Ge crystalline lattices. The mechanism of nanocone formation for elementary semiconductors is not clear until now. Therefore, the main goal of our investigations is to study the stages of nanocone formation in elementary semiconductors. A new mechanism of p-n junction formation by laser radiation in the elementary semiconductor as a first stage of nanocone formation is proposed. We explain this effect by the following way: p-n junction is formed by generation and redistribution of intrinsic point defects in temperature gradient field – the thermogradient effect, which is caused by strongly absorbed laser radiation. According to the thermogradient effect, interstitial atoms drift towards the irradiated surface, but vacancies drift to the opposite direction – in the bulk of semiconductor. Since interstitials in Ge crystal are of n-type and vacancies are known to be of p-type, a n-p junction is formed. The mechanism is confirmed by the appearance of diode-like current–voltage characteristics after i-Ge irradiation crystal by laser radiation. The mechanism in Si is confirmed by conductivity type inversion and increased microhardness of Si crystal. The second stage of nanocone formation is laser heating up of top layer enriched by interstitial atoms with its further plastic deformation due to compressive stress caused by interstitials in the top layer and vacancies in the buried layer. PMID:22849869

  4. Isotopically controlled semiconductors

    SciTech Connect

    Haller, E.E.

    2004-11-15

    A review of recent research involving isotopically controlled semiconductors is presented. Studies with isotopically enriched semiconductor structures experienced a dramatic expansion at the end of the Cold War when significant quantities of enriched isotopes of elements forming semiconductors became available for worldwide collaborations. Isotopes of an element differ in nuclear mass, may have different nuclear spins and undergo different nuclear reactions. Among the latter, the capture of thermal neutrons which can lead to neutron transmutation doping, can be considered the most important one for semiconductors. Experimental and theoretical research exploiting the differences in all the properties has been conducted and will be illustrated with selected examples. Manuel Cardona, the longtime editor-in-chief of Solid State Communications has been and continues to be one of the major contributors to this field of solid state physics and it is a great pleasure to dedicate this review to him.

  5. Semiconductor Solar Superabsorbers

    PubMed Central

    Yu, Yiling; Huang, Lujun; Cao, Linyou

    2014-01-01

    Understanding the maximal enhancement of solar absorption in semiconductor materials by light trapping promises the development of affordable solar cells. However, the conventional Lambertian limit is only valid for idealized material systems with weak absorption, and cannot hold for the typical semiconductor materials used in solar cells due to the substantial absorption of these materials. Herein we theoretically demonstrate the maximal solar absorption enhancement for semiconductor materials and elucidate the general design principle for light trapping structures to approach the theoretical maximum. By following the principles, we design a practical light trapping structure that can enable an ultrathin layer of semiconductor materials, for instance, 10 nm thick a-Si, absorb > 90% sunlight above the bandgap. The design has active materials with one order of magnitude less volume than any of the existing solar light trapping designs in literature. This work points towards the development of ultimate solar light trapping techniques. PMID:24531211

  6. Physics of Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Brütting, Wolfgang

    2005-08-01

    Filling the gap in the literature currently available, this book presents an overview of our knowledge of the physics behind organic semiconductor devices. Contributions from 18 international research groups cover various aspects of this field, ranging from the growth of organic layers and crystals, their electronic properties at interfaces, their photophysics and electrical transport properties to the application of these materials in such different devices as organic field-effect transistors, photovoltaic cells and organic light-emitting diodes. From the contents: * Excitation Dynamics in Organic Semiconductors * Organic Field-Effect Transistors * Spectroscopy of Organic Semiconductors * Interfaces between Organic Semiconductors and Metals * Analysis and Modeling of Devices * Exciton Formation and Energy Transfer in Organic Light Emitting Diodes * Deposition and Characterization

  7. Electrically coupling complex oxides to semiconductors: A route to novel material functionalities

    DOE PAGES

    Ngai, J. H.; Ahmadi-Majlan, K.; Moghadam, J.; ...

    2017-01-12

    Complex oxides and semiconductors exhibit distinct yet complementary properties owing to their respective ionic and covalent natures. By electrically coupling complex oxides to traditional semiconductors within epitaxial heterostructures, enhanced or novel functionalities beyond those of the constituent materials can potentially be realized. Essential to electrically coupling complex oxides to semiconductors is control of the physical structure of the epitaxially grown oxide, as well as the electronic structure of the interface. In this paper, we discuss how composition of the perovskite A- and B-site cations can be manipulated to control the physical and electronic structure of semiconductor—complex oxide heterostructures. Two prototypicalmore » heterostructures, Ba1-xSrxTiO3/Ge and SrZrxTi1-xO3/Ge, will be discussed. In the case of Ba1-xSrxTiO3/Ge, we discuss how strain can be engineered through A-site composition to enable the re-orientable ferroelectric polarization of the former to be coupled to carriers in the semiconductor. In the case of SrZrxTi1-xO3/Ge we discuss how B-site composition can be exploited to control the band offset at the interface. Finally, analogous to heterojunctions between compound semiconducting materials, control of band offsets, i.e., band-gap engineering, provides a pathway to electrically couple complex oxides to semiconductors to realize a host of functionalities.« less

  8. Gold-induced nanowires on the Ge(100) surface yield a 2D and not a 1D electronic structure

    NASA Astrophysics Data System (ADS)

    de Jong, N.; Heimbuch, R.; Eliëns, S.; Smit, S.; Frantzeskakis, E.; Caux, J.-S.; Zandvliet, H. J. W.; Golden, M. S.

    2016-06-01

    Atomic nanowires on semiconductor surfaces induced by the adsorption of metallic atoms have attracted a lot of attention as possible hosts of the elusive, one-dimensional Tomonaga-Luttinger liquid. The Au/Ge(100) system in particular is the subject of controversy as to whether the Au-induced nanowires do indeed host exotic, 1D (one-dimensional) metallic states. In light of this debate, we report here a thorough study of the electronic properties of high quality nanowires formed at the Au/Ge(100) surface. The high-resolution ARPES data show the low-lying Au-induced electronic states to possess a dispersion relation that depends on two orthogonal directions in k space. Comparison of the E (kx,ky) surface measured using high-resolution ARPES to tight-binding calculations yields hopping parameters in the two different directions that differ by approximately factor of two. Additionally, by pinpointing the Au-induced surface states in the first, second, and third surface Brillouin zones and analyzing their periodicity in k||, the nanowire propagation direction seen clearly in STM can be imported into the ARPES data. We find that the larger of the two hopping parameters corresponds, in fact, to the direction perpendicular to the nanowires (tperp). This proves that the Au-induced electron pockets possess a two-dimensional, closed Fermi surface, and this firmly places the Au/Ge(100) nanowire system outside potential hosts of a Tomonaga-Luttinger liquid. We combine these ARPES data with scanning tunneling spectroscopic measurements of the spatially resolved electronic structure and find that the spatially straight—wirelike—conduction channels observed up to energies of order one electron volt below the Fermi level do not originate from the Au-induced states seen in the ARPES data. The former are rather more likely to be associated with bulk Ge states that are localized to the subsurface region. Despite our proof of the 2D (two-dimentional) nature of the Au

  9. SILICON CARBIDE FOR SEMICONDUCTORS

    DTIC Science & Technology

    This state-of-the-art survey on silicon carbide for semiconductors includes a bibliography of the most important references published as of the end...of 1964. The various methods used for growing silicon carbide single crystals are reviewed, as well as their properties and devices fabricated from...them. The fact that the state of-the-art of silicon carbide semiconductors is not further advanced may be attributed to the difficulties of growing

  10. Predictive simulations of semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Galli, Giulia

    2005-03-01

    Ab-initio simulations are playing an increasingly important role in understanding matter at the nanoscale and in predicting with controllable, quantitative accuracy the novel and complex properties of nanomaterials. A microscopic, fundamental understanding of nanoscale phenomena is very much in demand, as experimental investigations are sometimes controversial and usually they cannot be explained on the basis of simple models. In this talk, ab-initio molecular dynamics simulations and quantum monte carlo calculations of semiconductor nanoparticles will be presented, with focus on electronic and optical properties and on the microscopic structure of surfaces at the nanoscale. The characterization of nanoscale surfaces and interfaces is of paramount importance to predict the function of nanomaterials, and eventually their assembly into macroscopic solids, and it is still very challenging from an experimental standpoint, due to the lack of appropriate imaging techniques. The presentation will focus on Si, Ge, SiC nanoparticles and nanodiamond, and in addition we will discuss several results for II-VI dots and rods. (*) Work done in collaboration with G.Cicero, E.Draeger, J.Grossman, F.Gygi, D.Prendergast, A.Puzder, J.-Y.Raty, F.Reboredo, E.Schwegler, A.Williamson This work was performed under the auspices of the US Department of Energy by the University of California at the LLNL under contract no W-7405-Eng-48

  11. Carrier Density Modulation in Ge Heterostructure by Ferroelectric Switching

    DOE PAGES

    Ponath, Patrick; Fredrickson, Kurt; Posadas, Agham B.; ...

    2015-01-14

    The development of nonvolatile logic through direct coupling of spontaneous ferroelectric polarization with semiconductor charge carriers is nontrivial, with many issues, including epitaxial ferroelectric growth, demonstration of ferroelectric switching, and measurable semiconductor modulation. Here we report a true ferroelectric field effect carrier density modulation in an underlying Ge(001) substrate by switching of the ferroelectric polarization in the epitaxial c-axis-oriented BaTiO3 (BTO) grown by molecular beam epitaxy (MBE) on Ge. Using density functional theory, we demonstrate that switching of BTO polarization results in a large electric potential change in Ge. Aberration-corrected electron microscopy confirms the interface sharpness, and BTO tetragonality. Electron-energy-lossmore » spectroscopy (EELS) indicates the absence of any low permittivity interlayer at the interface with Ge. Using piezoelectric force microscopy (PFM), we confirm the presence of fully switchable, stable ferroelectric polarization in BTO that appears to be single domain. Using microwave impedance microscopy (MIM), we clearly demonstrate a ferroelectric field effect.« less

  12. Laser cooling in semiconductors (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Zhang, Jun

    2017-06-01

    Laser cooling of semiconductor is very important topic in science researches and technological applications. Here we will report our progresses on laser cooling in semiconductors. By using of strong coupling between excitons and longitudinal optical phonons (LOPs), which allows the resonant annihilation of multiple LOPs in luminescence up-conversion processes, we observe a net cooling by about 40 K starting from 290 kelvin with 514-nm pumping and about 15 K starting from100 K with 532-nm pumping in a semiconductor using group-II-VI cadmium sulphide nanobelts. We also discuss the thickness dependence of laser cooing in CdS nanobelts, a concept porotype of semiconductor cryocooler and possibility of laser cooling in II-VI semiconductor family including CdSSe、CdSe, CdSe/ZnTe QDs and bulk CdS et al., Beyond II-VI semiconductor, we will present our recent progress in laser cooling of organic-inorganic perovskite materials, which show a very big cooling power and external quantum efficiency in 3D and 2D case. Further more, we demonstrate a resolved sideband Raman cooling of a specific LO phonon in ZnTe, in which only one specific phonon resonant with exciton can be cooled or heated. In the end, we will discuss the nonlinear anti-Stokes Raman and anti-Stokes photoluminescence upcoversion in very low temperature as low as down to liquid 4.2 K. In this case, the anti-Stokes resonance induces a quadratic power denpendece of anti-Stokes Raman and anti-Stokes PL. We proposed a CARS-like process to explain it. This nonlinear process also provides a possible physics picture of ultra-low temperatures phonon assisted photoluminescence and anti-Stokes Raman process.

  13. Transfer-free synthesis of highly ordered Ge nanowire arrays on glass substrates

    NASA Astrophysics Data System (ADS)

    Nakata, M.; Toko, K.; Jevasuwan, W.; Fukata, N.; Saitoh, N.; Yoshizawa, N.; Suemasu, T.

    2015-09-01

    Vertically aligned Ge nanowires (NWs) are directly synthesized on glass via vapor-liquid-solid (VLS) growth using chemical-vapor deposition. The use of the (111)-oriented Ge seed layer, formed by metal-induced crystallization at 325 °C, dramatically improved the density, uniformity, and crystal quality of Ge NWs. In particular, the VLS growth at 400 °C allowed us to simultaneously achieve the ordered morphology and high crystal quality of the Ge NW array. Transmission electron microscopy demonstrated that the resulting Ge NWs had no dislocations or stacking faults. Production of high-quality NW arrays on amorphous insulators will promote the widespread application of nanoscale devices.

  14. Lattice-Matched Semiconductor Layers on Single Crystalline Sapphire Substrate

    NASA Technical Reports Server (NTRS)

    Choi, Sang; King, Glen; Park, Yeonjoon

    2009-01-01

    SiGe is an important semiconductor alloy for high-speed field effect transistors (FETs), high-temperature thermoelectric devices, photovoltaic solar cells, and photon detectors. The growth of SiGe layer is difficult because SiGe alloys have different lattice constants from those of the common Si wafers, which leads to a high density of defects, including dislocations, micro-twins, cracks, and delaminations. This innovation utilizes newly developed rhombohedral epitaxy of cubic semiconductors on trigonal substrates in order to solve the lattice mismatch problem of SiGe by using trigonal single crystals like sapphire (Al2O3) as substrate to give a unique growth-orientation to the SiGe layer, which is automatically controlled at the interface upon sapphire (0001). This technology is different from previous silicon on insulator (SOI) or SGOI (SiGe on insulator) technologies that use amorphous SiO2 as the growth plane. A cubic semiconductor crystal is a special case of a rhombohedron with the inter-planar angle, alpha = 90 deg. With a mathematical transformation, all rhombohedrons can be described by trigonal crystal lattice structures. Therefore, all cubic lattice constants and crystal planes (hkl) s can be transformed into those of trigonal crystal parameters. These unique alignments enable a new opportunity of perfect lattice matching conditions, which can eliminate misfit dislocations. Previously, these atomic alignments were thought to be impossible or very difficult. With the invention of a new x-ray diffraction measurement method here, growth of cubic semiconductors on trigonal crystals became possible. This epitaxy and lattice-matching condition can be applied not only to SiGe (111)/sapphire (0001) substrate relations, but also to other crystal structures and other materials, including similar crystal structures which have pointgroup rotational symmetries by 120 because the cubic (111) direction has 120 rotational symmetry. The use of slightly miscut (less than

  15. Reverse Epitaxy of Ge: Ordered and Faceted Surface Patterns

    NASA Astrophysics Data System (ADS)

    Ou, Xin; Keller, Adrian; Helm, Manfred; Fassbender, Jürgen; Facsko, Stefan

    2013-07-01

    Normal incidence ion irradiation at elevated temperatures, when amorphization is prevented, induces novel nanoscale patterns of crystalline structures on elemental semiconductors by a reverse epitaxial growth mechanism: on Ge surfaces irradiation at temperatures above the recrystallization temperature of 250°C leads to self-organized patterns of inverse pyramids. Checkerboard patterns with fourfold symmetry evolve on the Ge (100) surface, whereas on the Ge (111) surface, isotropic patterns with a sixfold symmetry emerge. After high-fluence irradiations, these patterns exhibit well-developed facets. A deterministic nonlinear continuum equation accounting for the effective surface currents due to an Ehrlich-Schwoebel barrier for diffusing vacancies reproduces remarkably well our experimental observations.

  16. High-performance Ge-on-Si photodetectors

    NASA Astrophysics Data System (ADS)

    Michel, Jurgen; Liu, Jifeng; Kimerling, Lionel C.

    2010-08-01

    The past decade has seen rapid progress in research into high-performance Ge-on-Si photodetectors. Owing to their excellent optoelectronic properties, which include high responsivity from visible to near-infrared wavelengths, high bandwidths and compatibility with silicon complementary metal-oxide-semiconductor circuits, these devices can be monolithically integrated with silicon-based read-out circuits for applications such as high-performance photonic data links and infrared imaging at low cost and low power consumption. This Review summarizes the major developments in Ge-on-Si photodetectors, including epitaxial growth and strain engineering, free-space and waveguide-integrated devices, as well as recent progress in Ge-on-Si avalanche photodetectors.

  17. Semiconductor microlasers with intracavity microfluidics for biomedical applications

    SciTech Connect

    Gourley, P.L.; McDonald, A.E.

    1997-03-01

    Microfabricated electro-optical-mechanical systems are expected to play an important role in future biomedical, biochemical and environmental technologies. Semiconductor photonic materials and devices are attractive components of such systems because of their ability to generate, transmit, modulate, and detect light. In this paper the authors report investigations of light-emitting semiconductor/glass microcavities filled with simple fluids. They examine surface tension for transporting liquids into the intracavity space and study the influence of the liquid on the spectral emission of the microcavity.

  18. Dislocation-free Ge Nano-crystals via Pattern Independent Selective Ge Heteroepitaxy on Si Nano-Tip Wafers

    PubMed Central

    Niu, Gang; Capellini, Giovanni; Schubert, Markus Andreas; Niermann, Tore; Zaumseil, Peter; Katzer, Jens; Krause, Hans-Michael; Skibitzki, Oliver; Lehmann, Michael; Xie, Ya-Hong; von Känel, Hans; Schroeder, Thomas

    2016-01-01

    The integration of dislocation-free Ge nano-islands was realized via selective molecular beam epitaxy on Si nano-tip patterned substrates. The Si-tip wafers feature a rectangular array of nanometer sized Si tips with (001) facet exposed among a SiO2 matrix. These wafers were fabricated by complementary metal-oxide-semiconductor (CMOS) compatible nanotechnology. Calculations based on nucleation theory predict that the selective growth occurs close to thermodynamic equilibrium, where condensation of Ge adatoms on SiO2 is disfavored due to the extremely short re-evaporation time and diffusion length. The growth selectivity is ensured by the desorption-limited growth regime leading to the observed pattern independence, i.e. the absence of loading effect commonly encountered in chemical vapor deposition. The growth condition of high temperature and low deposition rate is responsible for the observed high crystalline quality of the Ge islands which is also associated with negligible Si-Ge intermixing owing to geometric hindrance by the Si nano-tip approach. Single island as well as area-averaged characterization methods demonstrate that Ge islands are dislocation-free and heteroepitaxial strain is fully relaxed. Such well-ordered high quality Ge islands present a step towards the achievement of materials suitable for optical applications. PMID:26940260

  19. Dislocation-free Ge Nano-crystals via Pattern Independent Selective Ge Heteroepitaxy on Si Nano-Tip Wafers.

    PubMed

    Niu, Gang; Capellini, Giovanni; Schubert, Markus Andreas; Niermann, Tore; Zaumseil, Peter; Katzer, Jens; Krause, Hans-Michael; Skibitzki, Oliver; Lehmann, Michael; Xie, Ya-Hong; von Känel, Hans; Schroeder, Thomas

    2016-03-04

    The integration of dislocation-free Ge nano-islands was realized via selective molecular beam epitaxy on Si nano-tip patterned substrates. The Si-tip wafers feature a rectangular array of nanometer sized Si tips with (001) facet exposed among a SiO2 matrix. These wafers were fabricated by complementary metal-oxide-semiconductor (CMOS) compatible nanotechnology. Calculations based on nucleation theory predict that the selective growth occurs close to thermodynamic equilibrium, where condensation of Ge adatoms on SiO2 is disfavored due to the extremely short re-evaporation time and diffusion length. The growth selectivity is ensured by the desorption-limited growth regime leading to the observed pattern independence, i.e. the absence of loading effect commonly encountered in chemical vapor deposition. The growth condition of high temperature and low deposition rate is responsible for the observed high crystalline quality of the Ge islands which is also associated with negligible Si-Ge intermixing owing to geometric hindrance by the Si nano-tip approach. Single island as well as area-averaged characterization methods demonstrate that Ge islands are dislocation-free and heteroepitaxial strain is fully relaxed. Such well-ordered high quality Ge islands present a step towards the achievement of materials suitable for optical applications.

  20. Dislocation-free Ge Nano-crystals via Pattern Independent Selective Ge Heteroepitaxy on Si Nano-Tip Wafers

    NASA Astrophysics Data System (ADS)

    Niu, Gang; Capellini, Giovanni; Schubert, Markus Andreas; Niermann, Tore; Zaumseil, Peter; Katzer, Jens; Krause, Hans-Michael; Skibitzki, Oliver; Lehmann, Michael; Xie, Ya-Hong; von Känel, Hans; Schroeder, Thomas

    2016-03-01

    The integration of dislocation-free Ge nano-islands was realized via selective molecular beam epitaxy on Si nano-tip patterned substrates. The Si-tip wafers feature a rectangular array of nanometer sized Si tips with (001) facet exposed among a SiO2 matrix. These wafers were fabricated by complementary metal-oxide-semiconductor (CMOS) compatible nanotechnology. Calculations based on nucleation theory predict that the selective growth occurs close to thermodynamic equilibrium, where condensation of Ge adatoms on SiO2 is disfavored due to the extremely short re-evaporation time and diffusion length. The growth selectivity is ensured by the desorption-limited growth regime leading to the observed pattern independence, i.e. the absence of loading effect commonly encountered in chemical vapor deposition. The growth condition of high temperature and low deposition rate is responsible for the observed high crystalline quality of the Ge islands which is also associated with negligible Si-Ge intermixing owing to geometric hindrance by the Si nano-tip approach. Single island as well as area-averaged characterization methods demonstrate that Ge islands are dislocation-free and heteroepitaxial strain is fully relaxed. Such well-ordered high quality Ge islands present a step towards the achievement of materials suitable for optical applications.

  1. Radiative decay rates of impurity states in semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Turkov, Vadim K.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

    2015-10-01

    Doped semiconductor nanocrystals is a versatile material base for contemporary photonics and optoelectronics devices. Here, for the first time to the best of our knowledge, we theoretically calculate the radiative decay rates of the lowest-energy states of donor impurity in spherical nanocrystals made of four widely used semiconductors: ZnS, CdSe, Ge, and GaAs. The decay rates were shown to vary significantly with the nanocrystal radius, increasing by almost three orders of magnitude when the radius is reduced from 15 to 5 nm. Our results suggest that spontaneous emission may dominate the decay of impurity states at low temperatures, and should be taken into account in the design of advanced materials and devices based on doped semiconductor nanocrystals.

  2. Radiative decay rates of impurity states in semiconductor nanocrystals

    SciTech Connect

    Turkov, Vadim K.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

    2015-10-15

    Doped semiconductor nanocrystals is a versatile material base for contemporary photonics and optoelectronics devices. Here, for the first time to the best of our knowledge, we theoretically calculate the radiative decay rates of the lowest-energy states of donor impurity in spherical nanocrystals made of four widely used semiconductors: ZnS, CdSe, Ge, and GaAs. The decay rates were shown to vary significantly with the nanocrystal radius, increasing by almost three orders of magnitude when the radius is reduced from 15 to 5 nm. Our results suggest that spontaneous emission may dominate the decay of impurity states at low temperatures, and should be taken into account in the design of advanced materials and devices based on doped semiconductor nanocrystals.

  3. Optical and Phototransport Properties of Hydrogenated Amorphous Semiconductors

    NASA Astrophysics Data System (ADS)

    Li, Yuan-Min

    1990-01-01

    A study of the optical and phototransport properties of hydrogenated, tetrahedrally bonded amorphous semiconductor films produced by the radio frequency glow discharge technique is presented. The first part of this thesis reports an extensive investigation of hydrogenated and hydrogenated -fluorinated amorphous Si-Ge alloys, a-Si_{1-x}Ge_{x}:H and a-Si_{1-x}Ge_ {x}:H:F. The optical and vibrational properties of the two sets of alloys are described and compared. The photoconductivity of these materials is discussed with focus on the following two questions: (1) the drastic deterioration of the photoconductivity of a -Si_{1-x}Ge_{x }:H with increasing x; (2) the improved photoconductive response etamutau (quantum efficiency-mobility-lifetime product) in the fluoride {SiF_4 + GeF_4 + H_2 } derived alloys over that of the hydride {SiH_4 + GeH_4} derived alloys of roughly 50 at.% Ge, or with a bandgap near 1.4 eV. The phototransport properties of a-Si_ {1-x}Ge_{x}:H and a-Si _{1-x}Ge_{x }:H:F are analyzed in light of information provided by various types of electronic and structural characterization. Some specific models for the electronic band structure, charge transport, and recombination are probed. It is concluded that a uniform increase in the gap density of states can only partially account for the severe quality degradation of a a-Si_ {1-x}Ge_{x}:H(:F) relative to a-Si:H. The inferior photosensitivity of a-SiGe:H(:F) is caused, in part, by an increase in structural heterogeneity. Possible enhancement of recombination of excess carriers in the alloys due to clustered and/or charged defects, tunneling recombination, and reduced bandgap is assessed. The efficacy of hydrogen and fluorine in determining the properties of a-SiGe alloys is evaluated. It is found that the replacement of hydrogen by fluorine in a-SiGe can not be responsible for the observed improvement of etamu tau in the fluoride-derived a-Si_{0.5}Ge_{0.5}:H:F over the hydride-derived a-Si_ {0.5}Ge_{0

  4. Investigation of Defect Free SiGe Nanowire Biosensor Modified by Dual Plasma Technology.

    PubMed

    Chen, Yi-Ming; Chang, Tai-Yuan; Lai, Chiung-Hui; Chang, Kow-Ming; Chen, Chu-Feng; Lai, Yi-Lung; Whang, Allen Jong-Woei; Lai, Hui-Lung; Hsu, Terng-Ren

    2016-02-01

    Semiconductor nanowires (NWs) have been extensively investigated and discussed in various fields due to their unique physical properties. In this paper, we successfully produce SiGe NWs biosensor by VLSI technology. We propose the dual plasma technology with CF4 plasma pre-treatment and N2 plasma post-treatment for repairs of defects as well as optimization of SiGe NWs biosensor. The results indicate that sensitivity (S) of the biosensor with dual plasma technology has significantly improved at least 32.8%, suitable for producing industrial SiGe NWs biosensor in the future.

  5. Method of doping a semiconductor

    DOEpatents

    Yang, Chiang Y.; Rapp, Robert A.

    1983-01-01

    A method for doping semiconductor material. An interface is established between a solid electrolyte and a semiconductor to be doped. The electrolyte is chosen to be an ionic conductor of the selected impurity and the semiconductor material and electrolyte are jointly chosen so that any compound formed from the impurity and the semiconductor will have a free energy no lower than the electrolyte. A potential is then established across the interface so as to allow the impurity ions to diffuse into the semiconductor. In one embodiment the semiconductor and electrolyte may be heated so as to increase the diffusion coefficient.

  6. GE STEM Teacher's Conference

    NASA Image and Video Library

    2017-07-13

    Teachers prepare to demonstrate the projects they built for the Rocketry Engineering Design Challenge during the 2017 GE Foundation High School STEM Integration Conference at the Center for Space Education at NASA's Kennedy Space Center. High school teachers from across the country took part in the week-long conference, which is designed to explore effective ways for teachers, schools and districts from across the country to integrate STEM throughout the curriculum. The conference is a partnership between GE Foundation and the National Science Teachers Association.

  7. GE STEM Teacher's Conference

    NASA Image and Video Library

    2017-07-13

    Education Specialists Lynn Dotson, left, of the NASA Public Engagement Center, and Lester Morales, right, of Texas State University's NASA STEM Educator Professional Development Collaborative, explain the Rocketry Engineering Design Challenge to teachers participating in the 2017 GE Foundation High School STEM Integration Conference at the Center for Space Education at NASA's Kennedy Space Center. High school teachers from across the country took part in the week-long conference, which is designed to explore effective ways for teachers, schools and districts from across the country to integrate STEM throughout the curriculum. The conference is a partnership between GE Foundation and the National Science Teachers Association.

  8. Hydrogen in semiconductors

    SciTech Connect

    Haller, E.E. Lawrence Berkeley Lab., CA )

    1990-06-01

    After an incubation'' period in the 1970's and early 80's, during which the first hydrogen related centers were discovered and characterized in ultra-pure germanium, a sharp increase of research activity occurred after the discovery of shallow acceptor passivation in crystalline silicon. The aim of this review is to convey an insight into the rich, multifaceted physics and materials science which has emerged from the vast variety of experimental and theoretical studies of hydrogen in semiconductors. In order to arrive at the current understanding of hydrogen related phenomena in a logical way, each chapter will start with a brief review of the major experimental and theoretical advances of the past few years. Those who are interested to learn more about this fascinating area of semiconductor research are referred to reviews, to a number of conference proceedings volumes, and to an upcoming book which will contain authoritative chapters on most aspects of hydrogen in crystalline semiconductors. Some of the early art of semiconductor device processing can finally be put on a scientific foundation and new ways of arriving at advanced device structures begin to use what we have learned from the basic studies of hydrogen in semiconductors. 92 refs., 8 figs.

  9. Applications and use of in-situ chemical sensors in semiconductor manufacturing

    NASA Astrophysics Data System (ADS)

    Tolliver, Donald L.; Atkinson, George H.

    1997-07-01

    The use of in-situ chemical sensors in semiconductor wafer fabrication will increase significantly over the next five years. Advanced gas phase and liquid phase real time, non contaminating chemical sensors will be applied in four major categories of use. These four areas of application are: (1) Upstream measurements of trace contaminants in high purity process gases and liquids. (2) In-the-chamber or in-the- process bath measurements of chemical species of on line active process tools. (3) Real time, on line, downstream measurements of gas phase and liquid phase effluents coming from semiconductor wafer process tools. (4) Semiconductor industrial hygiene and safety monitors for toxic substances in the work place. This paper will review each of these major applications for both gases and liquids as they will need to be integrated into semiconductor wafer manufacturing over time. Some existing sensor applications currently exist. This review will focus extensively on in-situ real time chemical monitoring sensors.

  10. Properties of Semiconducting Ru_2Ge_3

    NASA Technical Reports Server (NTRS)

    Fleurial, Jean-Pierre; Borshchevsky, Alex

    1993-01-01

    Transport properties of large single crystalline samples of Ru_2Ge_3 grown from the melt have been investigated in a 25-1000 C temperature range. A diffusionless transition between 500 and 550C from a high temperature tetragonal structure to a low temperature orthorhombic structure was clearly observed. Results showed that both the low temperature orthorhombic and the high temperature structural tetragonal phase are semiconductors. Some anisotropy of the transport coefficients was determined by measuring the samples in orientations parallel and perpendicular to the preferential direction of crystal growth. Large Seebeck coefficient (up to 400 microVK^(-1)) and low thermal conductivity (as low as 20x10^(-3) Wcm^(-1)K^(-1)) were achieved for the low temperature orthorhombic phase. Difficulties in preparing heavily doped samples and low Hall mobilities have limited values for the maximum figure of merit to 0.5 x 10^(-3) K^(-1) at 500 C.

  11. Raman spectral shift versus strain and composition in GeSn layers with 6%-15% Sn content

    NASA Astrophysics Data System (ADS)

    Gassenq, A.; Milord, L.; Aubin, J.; Pauc, N.; Guilloy, K.; Rothman, J.; Rouchon, D.; Chelnokov, A.; Hartmann, J. M.; Reboud, V.; Calvo, V.

    2017-03-01

    GeSn alloys are the subject of intense research activities as these group IV semiconductors present direct bandgap behaviors for high Sn contents. Today, the control of strain becomes an important challenge to improve GeSn devices. Strain micro-measurements are usually performed by Raman spectroscopy. However, different relationships linking the Raman spectral shifts to the built-in strain can be found in the literature. They were deduced from studies on low Sn content GeSn layers (i.e., xSn < 8%) or on GeSiSn layers. In this work, we have calibrated the GeSn Raman relationship for really high Sn content GeSn binaries (6 < xSn < 15%). We have used fully strained GeSn layers and fully relaxed GeSn under-etched microstructures to clearly differentiate the contributions of strain and chemical composition on the Ge-Ge Raman spectral shift. We have shown that the GeSn Raman-strain coefficient for high Sn contents is higher compared with that for pure Ge.

  12. Transition region width of nanowire hetero- and pn-junctions grown using vapor-liquid-solid processes

    NASA Astrophysics Data System (ADS)

    Li, Na; Tan, Teh Y.; Gösele, U.

    2008-03-01

    The transition region width of nanowire heterojunctions and pn-junctions grown using vapor-liquid-solid (VLS) processes has been modeled. With two constituents or dopants I and II, the achievable width or abruptness of the junctions is attributed to the residual I atom/molecule stored in the liquid droplet at the onset of introducing II to grow the junction, and the stored I atom/molecule consumption into the subsequently grown crystal layers. The model yields satisfactory quantitative fits to a set of available Si-Ge junction data. Moreover, the model provides a satisfactory explanation to the relative junction width or abruptness differences between elemental and compound semiconductor junction cases, as well as a guideline for achieving the most desirable pn-junction widths.

  13. Morphology control and optical properties of SiGe nanostructures grown on glass substrate

    NASA Astrophysics Data System (ADS)

    Chang, Hsu-Kai; Lee, Si-Chen

    2012-02-01

    With the rapid progress of nanotechnology, nanostructures with different morphologies have been realized, which may be very promising to enhance the performance of semiconductor devices. In this study, SiGe nanostructures with several kinds of configurations have been synthesized through a chemical vapor deposition process. By controlling growth conditions, different SiGe nanostructures can be easily tuned. Structures and compositions of the nanostructures were determined by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The optical properties of various SiGe nanostructures revealed some dependence with their morphologies, which may be suitable for solar cell applications. The control of the SiGe morphology on nanoscale provides a convenient route to produce diverse SiGe nanostructures and creates new opportunities to realize the integration of future devices.

  14. Morphology control and optical properties of SiGe nanostructures grown on glass substrate

    PubMed Central

    2012-01-01

    With the rapid progress of nanotechnology, nanostructures with different morphologies have been realized, which may be very promising to enhance the performance of semiconductor devices. In this study, SiGe nanostructures with several kinds of configurations have been synthesized through a chemical vapor deposition process. By controlling growth conditions, different SiGe nanostructures can be easily tuned. Structures and compositions of the nanostructures were determined by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The optical properties of various SiGe nanostructures revealed some dependence with their morphologies, which may be suitable for solar cell applications. The control of the SiGe morphology on nanoscale provides a convenient route to produce diverse SiGe nanostructures and creates new opportunities to realize the integration of future devices. PMID:22369313

  15. Ohmic contact on n-type Ge using Yb-germanide

    SciTech Connect

    Zheng Zhiwei; Liu Ming; Ku, Teng-Chieh; Chin, Albert

    2012-11-26

    Poor ohmic contact by Fermi-level pinning to valence band (E{sub V}) edge is one of the major challenges for germanium (Ge) n-type metal-oxide-semiconductor field-effect transistor (nMOSFET). Using low work-function rare-earth ytterbium (Yb), good ohmic contact on n-type Ge with alleviated Fermi-level pinning was demonstrated. Such ohmic behavior depends strongly on the germanide formation condition, where much degraded ohmic contact at 600 Degree-Sign C rapid thermal annealing is due to the lower Yb/Ge composition found by energy-dispersive x-ray spectroscopy. The ohmic behavior of Yb-germanide/n-type-Ge has high potential for future high-performance Ge nMOSFET application.

  16. Yttrium passivation of defects in GeO2 and GeO2/Ge interfaces

    NASA Astrophysics Data System (ADS)

    Li, Hongfei; Robertson, John

    2017-01-01

    Alloying amorphous GeO2 with Y2O3 has been found experimentally to improve its chemical stability and electrical reliability as a gate dielectric in Ge-based field effect transistors. The mechanism is explained here based on density functional calculations. The GeO2 reliability problem is correlated with oxygen deficiency defects, which generate gap states near the band-edges of the underlying Ge. These can be passivated through Y doping. This shifts the defect gap state out of the gap up into the GeO2 conduction band, thus effectively passivating gap states in the GeO2 layer.

  17. Semiconductor surface protection material

    NASA Technical Reports Server (NTRS)

    Packard, R. D. (Inventor)

    1973-01-01

    A method and a product for protecting semiconductor surfaces is disclosed. The protective coating material is prepared by heating a suitable protective resin with an organic solvent which is solid at room temperature and converting the resulting solution into sheets by a conventional casting operation. Pieces of such sheets of suitable shape and thickness are placed on the semiconductor areas to be coated and heat and vacuum are then applied to melt the sheet and to drive off the solvent and cure the resin. A uniform adherent coating, free of bubbles and other defects, is thus obtained exactly where it is desired.

  18. New unorthodox semiconductor devices

    NASA Astrophysics Data System (ADS)

    Board, K.

    1985-12-01

    A range of new semiconductor devices, including a number of structures which rely entirely upon new phenomena, are discussed. Unipolar two-terminal devices, including impurity-controlled barriers and graded composition barriers, are considered, as are new transistor structures, including the hot-electron camel transistor, the planar-doped barrier transistor, the thermionic emission transistor, and the permeable base transistor. Regenerative switching devices are addressed, including the metal-tunnel insulator-semiconductor switch, the polysilicon switch, MIS, and MISIM switching structures, and the triangular-barrier switch. Heterostructure devices are covered, including the heterojunction bipolar transistor, the selectively doped heterojunction transistor, heterojunction lasers, and quantum-well structures.

  19. GUARD RING SEMICONDUCTOR JUNCTION

    DOEpatents

    Goulding, F.S.; Hansen, W.L.

    1963-12-01

    A semiconductor diode having a very low noise characteristic when used under reverse bias is described. Surface leakage currents, which in conventional diodes greatly contribute to noise, are prevented from mixing with the desired signal currents. A p-n junction is formed with a thin layer of heavily doped semiconductor material disposed on a lightly doped, physically thick base material. An annular groove cuts through the thin layer and into the base for a short distance, dividing the thin layer into a peripheral guard ring that encircles the central region. Noise signal currents are shunted through the guard ring, leaving the central region free from such currents. (AEC)

  20. Quantum Transport in Semiconductors

    DTIC Science & Technology

    1991-10-01

    SRS i 91 4. TITLE AND SUBTITLE Quantum Transport in Semiconductors 5. FUNDING NUMBER söMtos-rizk-ooss 6. AUTHOR(S) D. K. Ferry ©fte ELECTE...OF ABSTRACT UL NSN 7540-01-280-5500 O 1 9 Standard Form 298 (Rev. 2-89) Presented by ANSI Std «9-18 298-102 Final Report Quantum Transport in... Quantum Transport in Semiconductor Devices This final report describes a program of research investigating quantum effects which become important in

  1. X-ray characterization of Ge dots epitaxially grown on nanostructured Si islands on silicon-on-insulator substrates

    PubMed Central

    Zaumseil, Peter; Kozlowski, Grzegorz; Yamamoto, Yuji; Schubert, Markus Andreas; Schroeder, Thomas

    2013-01-01

    On the way to integrate lattice mismatched semiconductors on Si(001), the Ge/Si heterosystem was used as a case study for the concept of compliant substrate effects that offer the vision to be able to integrate defect-free alternative semiconductor structures on Si. Ge nanoclusters were selectively grown by chemical vapour deposition on Si nano-islands on silicon-on-insulator (SOI) substrates. The strain states of Ge clusters and Si islands were measured by grazing-incidence diffraction using a laboratory-based X-ray diffraction technique. A tensile strain of up to 0.5% was detected in the Si islands after direct Ge deposition. Using a thin (∼10 nm) SiGe buffer layer between Si and Ge the tensile strain increases to 1.8%. Transmission electron microscopy studies confirm the absence of a regular grid of misfit dislocations in such structures. This clear experimental evidence for the compliance of Si nano-islands on SOI substrates opens a new integration concept that is not only limited to Ge but also extendable to semiconductors like III–V and II–VI materials. PMID:24046490

  2. Screenable contact structure and method for semiconductor devices

    DOEpatents

    Ross, Bernd

    1980-08-26

    An ink composition for deposition upon the surface of a semiconductor device to provide a contact area for connection to external circuitry is disclosed, the composition comprising an ink system containing a metal powder, a binder and vehicle, and a metal frit. The ink is screened onto the semiconductor surface in the desired pattern and is heated to a temperature sufficient to cause the metal frit to become liquid. The metal frit dissolves some of the metal powder and densifies the structure by transporting the dissolved metal powder in a liquid sintering process. The sintering process typically may be carried out in any type of atmosphere. A small amount of dopant or semiconductor material may be added to the ink systems to achieve particular results if desired.

  3. Hole mobility degradation by remote Coulomb scattering and charge distribution in Al2O3/GeO x gate stacks in bulk Ge pMOSFET with GeO x grown by ozone oxidation

    NASA Astrophysics Data System (ADS)

    Zhou, Lixing; Wang, Xiaolei; Ma, Xueli; Xiang, Jinjuan; Yang, Hong; Zhao, Chao; Ye, Tianchun; Wang, Wenwu

    2017-06-01

    Hole mobility degradation due to remote Coulomb scattering (RCS) from fixed charges of GeO x /Al2O3 gate stacks is experimentally investigated in bulk Ge p-type metal-oxide-semiconductor field effect transistor (pMOSFET), with GeO x grown by ozone oxidation. The hole mobility at 77 K is found to increase with GeO x thickness. The phonon scattering can be ignored at 77 K and the surface roughness scattering is insignificant at a low inversion carrier concentration. This indicates that the RCS is responsible for mobility degradation. Therefore, the fixed charges are investigated in terms of RCS. The charge distribution in GeO x /Al2O3 gate stacks is experimentally estimated. The bulk charge in GeO x and Al2O3 is negligible. The densities of interface charges are  +3.22  ×  1012 cm-2 and  -2.57  ×  1012 cm-2 at the GeO x /Ge and Al2O3/GeO x interface, respectively. The electric dipole at the Al2O3/GeO x interface is  +0.17 eV, corresponding to charge area density of 1.76  ×  1013 cm-2. Consequently, the dipole at the Al2O3/GeO x interface plays a dominant role in the mobility degradation. Our results show that the investigation of charges in a gate stack is valuable for enhancing device performance.

  4. Structural Mapping of Functional Ge Layers Grown on Graded SiGe Buffers for sub-10 nm CMOS Applications Using Advanced X-ray Nanodiffraction.

    PubMed

    Richard, Marie-Ingrid; Zoellner, Marvin H; Chahine, Gilbert A; Zaumseil, Peter; Capellini, Giovanni; Häberlen, Maik; Storck, Peter; Schülli, Tobias U; Schroeder, Thomas

    2015-12-09

    We report a detailed advanced materials characterization study on 40 nm thick strained germanium (Ge) layers integrated on 300 mm Si(001) wafers via strain-relaxed silicon-germanium (SiGe) buffer layers. Fast-scanning X-ray microscopy is used to directly image structural inhomogeneities, lattice tilt, thickness, and strain of a functional Ge layer down to the sub-micrometer scale with a real space step size of 750 μm. The structural study shows that the metastable Ge layer, pseudomorphically grown on Si(0.3)Ge(0.7), exhibits an average compressive biaxial strain of -1.27%. By applying a scan area of 100 × 100 μm(2), we observe microfluctuations of strain, lattice tilt, and thickness of ca. ±0.03%, ±0.05°, and ±0.8 nm, respectively. This study confirms the high materials homogeneity of the compressively strained Ge layer realized by the step-graded SiGe buffer approach on 300 mm Si wafers. This presents thus a promising materials science approach for advanced sub-10 nm complementary metal oxide-semiconductor applications based on strain-engineered Ge transistors to outperform current Si channel technologies.

  5. Effective passivation of defects in Ge-rich SiGe-on-insulator substrates by Al 2O 3 deposition and subsequent post-annealing

    NASA Astrophysics Data System (ADS)

    Yang, Haigui; Iyota, Masatoshi; Ikeura, Shogo; Wang, Dong; Nakashima, Hiroshi

    2011-06-01

    A method of Al 2O 3 deposition and subsequent post-deposition annealing (Al 2O 3-PDA) was proposed to passivate electrically active defects in Ge-rich SiGe-on-insulator (SGOI) substrates, which were fabricated using Ge condensation by dry oxidation. The effect of Al 2O 3-PDA on defect passivation was clarified by surface analysis and electrical evaluation. It was found that Al 2O 3-PDA could not only suppress the surface reaction during Al-PDA in our previous work [Yang H, Wang D, Nakashima H, Hirayama K, Kojima S, Ikeura S. Defect control by Al-deposition and the subsequent post-annealing for SiGe-on-insulator substrates with different Ge fractions. Thin Solid Films 2010; 518: 2342-5.], but could also effectively passivate p-type defects generated during Ge condensation. The concentration in the range of 10 16-10 18 cm -3 for defect-induced acceptors and holes in Ge-rich SGOI drastically decreased after Al 2O 3-PDA. As a result of defect passivation, the electrical characteristics of both back-gate p-channel and n-channel metal-oxide-semiconductor field-effect transistors fabricated on Ge-rich SGOI were greatly improved after Al 2O 3-PDA.

  6. A low-temperature fabricated gate-stack structure for Ge-based MOSFET with ferromagnetic epitaxial Heusler-alloy/Ge electrodes

    NASA Astrophysics Data System (ADS)

    Fujita, Yuichi; Yamada, Michihiro; Nagatomi, Yuta; Yamamoto, Keisuke; Yamada, Shinya; Sawano, Kentarou; Kanashima, Takeshi; Nakashima, Hiroshi; Hamaya, Kohei

    2016-06-01

    A possible low-temperature fabrication process of a gate-stack for Ge-based spin metal-oxide-semiconductor field-effect transistor (MOSFET) is investigated. First, since we use epitaxial ferromagnetic Heusler alloys on top of the phosphorous doped Ge epilayer as spin injector and detector, we need a dry etching process to form Heusler-alloy/n+-Ge Schottky-tunnel contacts. Next, to remove the Ge epilayers damaged by the dry etching process, the fabricated structures are dipped in a 0.03% diluted H2O2 solution. Finally, Al/SiO2/GeO2/Ge gate-stack structures are fabricated at 300 °C as a top gate-stack structure. As a result, the currents in the Ge-MOSFET fabricated here can be modulated by applying gate voltages even by using the low-temperature formed gate-stack structures. This low-temperature fabrication process can be utilized for operating Ge spin MOSFETs with a top gate electrode.

  7. Structural study of Ge/GaAs thin films

    NASA Astrophysics Data System (ADS)

    Lazarov, V. K.; Lari, L.; Lytvyn, P. M.; Kholevchuk, V. V.; Mitin, V. F.

    2012-07-01

    Ge/GaAs heterostructure research is largely motivated by the application of this material in solar cells, metal-oxide-semiconductor field-effect transistors, mm-wave mixer diodes, temperature sensors and photodetectors. Therefore, understanding of how the properties of Ge/GaAs heterostructure depend on its preparation (growth) is of importance for various high-efficiency devices. In this work, by using thermal Ge evaporation on GaAs(100), we studied structural properties of these films as a function of the deposition rate. Film grains size and morphology show strong dependence of the deposition rate. Low deposition rates results in films with large crystal grains and rough surface. At high deposition rates films become flatter and their crystal grains size decreases, while at very high deposition rates films become amorphous. Cross-sectional TEM of the films show that the Ge films are granular single crystal epitaxially grown on GaAs. The Ge/GaAs interface is atomically abrupt and free from misfit dislocations. Stacking faults along the [111] directions that originate at the interface were also observed. Finally by using the Kelvin probe microscopy we show that work function changes are related to the grain structure of the film.

  8. Bonding and electronics of the MoTe2/Ge interface under strain

    NASA Astrophysics Data System (ADS)

    Szary, Maciej J.; Michalewicz, Marek T.; Radny, Marian W.

    2017-05-01

    Understanding the interface formation of a conventional semiconductor with a monolayer of transition-metal dichalcogenides provides a necessary platform for the anticipated applications of dichalcogenides in electronics and optoelectronics. We report here, based on the density functional theory, that under in-plane tensile strain, a 2H semiconducting phase of the molybdenum ditelluride (MoTe2) monolayer undergoes a semiconductor-to-metal transition and in this form bonds covalently to bilayers of Ge stacked in the [111] crystal direction. This gives rise to the stable bonding configuration of the MoTe2/Ge interface with the ±K valley metallic, electronic interface states exclusively of a Mo 4 d character. The atomically sharp Mo layer represents therefore an electrically active (conductive) subsurface δ -like two-dimensional profile that can exhibit a valley-Hall effect. Such system can develop into a key element of advanced semiconductor technology or a novel device concept.

  9. 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.

  10. Properties of infrared doped semiconductor Mie resonators (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Lewi, Tomer; Iyer, Prasad P.; Butakov, Nikita A.; Schuller, Jon A.

    2015-09-01

    Dielectric optical antenna resonators have recently emerged as a viable alternative to plasmonic resonators for metamaterials and nanophotonic devices, due to their ability to support multipolar Mie resonances with low losses. In this work, we experimentally investigate the mid-infrared Mie resonances in Si and Ge subwavelength spherical particles. In particular, we leverage the electronic and optical properties of these semiconductors in the mid-infrared range to design and tune Mie resonators through free-carrier refraction. Si and Ge semiconductor spheres of varying sizes of 0.5-4 μm were fabricated using femtosecond laser ablation. Using single particle infrared spectroscopy, we first demonstrate size-dependent Si and Ge Mie resonances spanning the entire mid-infrared (2-16 μm) spectral range. Subsequently we show that the Mie resonances can be tuned by varying material properties rather than size or geometry. We experimentally demonstrate doping-dependent resonance frequency shifts that follow simple Drude models of free-carrier refraction. We show that Ge particles exhibit a stronger doping dependence than Si due to the smaller effective mass of the free carriers. Using the unique size and doping dispersion of the electric and magnetic dipole modes, we identify and demonstrate a size regime where these modes are spectrally overlapping. We also demonstrate the emergence of plasmonic resonances for high doping levels and long wavelengths. These findings demonstrate the potential for tuning infrared semiconductor Mie resonances by optically or electrically modulating charge carrier densities, thus providing an excellent platform for tunable electromagnetic metamaterials.

  11. Growth strategies to control tapering in Ge nanowires

    SciTech Connect

    Periwal, P.; Baron, T. Salem, B.; Bassani, F.; Gentile, P.

    2014-04-01

    We report the effect of PH{sub 3} on the morphology of Au catalyzed Ge nanowires (NWs). Ge NWs were grown on Si (111) substrate at 400 °C in the presence of PH{sub 3}, using vapor-liquid-solid method by chemical vapor deposition. We show that high PH{sub 3}/GeH{sub 4} ratio causes passivation at NW surface. At high PH{sub 3} concentration phosphorous atoms attach itself on NW surface and form a self-protection coating that prevents conformal growth and leads to taper free nanostructures. However, in case of low PH{sub 3} flux the combination of axial and radial growth mechanism occurs resulting in conical structure. We have also investigated axial PH{sub 3}-intrinsic junctions in Ge NWs. The unusual NW shape is attributed to a combination of catalyzed, uncatalyzed and diffusion induced growth.

  12. 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

  13. Kansas Advanced Semiconductor Project

    SciTech Connect

    Baringer, P.; Bean, A.; Bolton, T.; Horton-Smith, G.; Maravin, Y.; Ratra, B.; Stanton, N.; von Toerne, E.; Wilson, G.

    2007-09-21

    KASP (Kansas Advanced Semiconductor Project) completed the new Layer 0 upgrade for D0, assumed key electronics projects for the US CMS project, finished important new physics measurements with the D0 experiment at Fermilab, made substantial contributions to detector studies for the proposed e+e- international linear collider (ILC), and advanced key initiatives in non-accelerator-based neutrino physics.

  14. Physics of Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Brütting, Wolfgang

    2004-05-01

    Organic semiconductors are of steadily growing interest as active components in electronics and optoelectronics. Due to their flexibility, low cost and ease-of-production they represent a valid alternative to conventional inorganic semiconductor technology in a number of applications, such as flat panel displays and illumination, plastic integrated circuits or solar energy conversion. Although first commercial applications of this technology are being realized nowadays, there is still the need for a deeper scientific understanding in order to achieve optimum device performance.This special issue of physica status solidi (a) tries to give an overview of our present-day knowledge of the physics behind organic semiconductor devices. Contributions from 17 international research groups cover various aspects of this field ranging from the growth of organic layers and crystals, their electronic properties at interfaces, their photophysics and electrical transport properties to the application of these materials in different devices like organic field-effect transistors, photovoltaic cells and organic light-emitting diodes.Putting together such a special issue one soon realizes that it is simply impossible to fully cover the whole area of organic semiconductors. Nevertheless, we hope that the reader will find the collection of topics in this issue useful for getting an up-to-date review of a field which is still developing very dynamically.

  15. Semiconductor Nanocrystal Photonics

    DTIC Science & Technology

    2005-08-31

    Hahn, H. Du, and T. D. Krauss, "Photoluminescence enhancement of colloidal semiconductor quantum dots embedded in a monolithic microcavity," Appl... DBRs ). The colloidal NC suspension was spun-coat into a 95-nm thick layer in the center of the cavity and then the other layers forming the top DBR

  16. Amorphous semiconductor solar cell

    DOEpatents

    Dalal, Vikram L.

    1981-01-01

    A solar cell comprising a back electrical contact, amorphous silicon semiconductor base and junction layers and a top electrical contact includes in its manufacture the step of heat treating the physical junction between the base layer and junction layer to diffuse the dopant species at the physical junction into the base layer.

  17. Chemically Derivatized Semiconductor Photoelectrodes.

    ERIC Educational Resources Information Center

    Wrighton, Mark S.

    1983-01-01

    Deliberate modification of semiconductor photoelectrodes to improve durability and enhance rate of desirable interfacial redox processes is discussed for a variety of systems. Modification with molecular-based systems or with metals/metal oxides yields results indicating an important role for surface modification in devices for fundamental study…

  18. Properties of nanocones formed on a surface of semiconductors by laser radiation: quantum confinement effect of electrons, phonons, and excitons

    PubMed Central

    2011-01-01

    On the basis of the analysis of experimental results, a two-stage mechanism of nanocones formation on the irradiated surface of semiconductors by Nd:YAG laser is proposed for elementary semiconductors and solid solutions, such as Si, Ge, SiGe, and CdZnTe. Properties observed are explained in the frame of quantum confinement effect. The first stage of the mechanism is characterized by the formation of a thin strained top layer, due to redistribution of point defects in temperature-gradient field induced by laser radiation. The second stage is characterized by mechanical plastic deformation of the stained top layer leading to arising of nanocones, due to selective laser absorption of the top layer. The nanocones formed on the irradiated surface of semiconductors by Nd:YAG laser possessing the properties of 1D graded bandgap have been found for Si, Ge, and SiGe as well, however QD structure in CdTe was observed. The model is confirmed by "blue shift" of bands in photoluminescence spectrum, "red shift" of longitudinal optical line in Raman back scattering spectrum of Ge crystal, appearance of Ge phase in SiGe solid solution after irradiation by the laser at intensity 20 MW/cm2, and non-monotonous dependence of Si crystal micro-hardness as function of the laser intensity. PMID:22060172

  19. Multi-junction, monolithic solar cell using low-band-gap materials lattice matched to GaAs or Ge

    DOEpatents

    Olson, Jerry M.; Kurtz, Sarah R.; Friedman, Daniel J.

    2001-01-01

    A multi-junction, monolithic, photovoltaic solar cell device is provided for converting solar radiation to photocurrent and photovoltage with improved efficiency. The solar cell device comprises a plurality of semiconductor cells, i.e., active p/n junctions, connected in tandem and deposited on a substrate fabricated from GaAs or Ge. To increase efficiency, each semiconductor cell is fabricated from a crystalline material with a lattice constant substantially equivalent to the lattice constant of the substrate material. Additionally, the semiconductor cells are selected with appropriate band gaps to efficiently create photovoltage from a larger portion of the solar spectrum. In this regard, one semiconductor cell in each embodiment of the solar cell device has a band gap between that of Ge and GaAs. To achieve desired band gaps and lattice constants, the semiconductor cells may be fabricated from a number of materials including Ge, GaInP, GaAs, GaInAsP, GaInAsN, GaAsGe, BGaInAs, (GaAs)Ge, CuInSSe, CuAsSSe, and GaInAsNP. To further increase efficiency, the thickness of each semiconductor cell is controlled to match the photocurrent generated in each cell. To facilitate photocurrent flow, a plurality of tunnel junctions of low-resistivity material are included between each adjacent semiconductor cell. The conductivity or direction of photocurrent in the solar cell device may be selected by controlling the specific p-type or n-type characteristics for each active junction.

  20. Structural properties of Ge on SrTiO{sub 3} (001) surface and Ge/SrTiO{sub 3} interface

    SciTech Connect

    Pu, Long; Wang, Jianli Tang, Gang; Zhang, Junting

    2015-03-14

    Germanium−perovskite oxide heterostructures have a strong potential for next-generation low-voltage and low-leakage metal-oxide semiconductor field-effect transistors. We investigated the atomic structure and electronic properties of Ge on perfect and defective (001) SrTiO{sub 3} by first-principle calculations. The specific adsorption sites at the initial growth stage and the atomic structure of Ge on the SrTiO{sub 3} (001) substrate have been systematically investigated. The surface grand potential was calculated and compared as a function of the relative chemical potential. The complete surface phase diagram was presented. The energetically favorable interfaces were pointed out among the atomic arrangements of the Ge/SrTiO{sub 3} (001) interfaces. The atomic structure and electronic properties of the intrinsic point defects were calculated and analyzed for the Ge/SrTiO{sub 3} (001) interfaces.

  1. Comparative study of GeO2/Ge and SiO2/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy

    DOE PAGES

    Mori, Daichi; Oka, Hiroshi; Hosoi, Takuji; ...

    2016-09-02

    The energy difference between the oxide and bulk peaks in X-ray photoelectron spectroscopy (XPS) spectra was investigated in this paper for both GeO2/Ge and SiO2/Si structures with thickness-controlled water films. This was achieved by obtaining XPS spectra at various values of relative humidity (RH) of up to ~15%. The increase in the energy shift is more significant for thermal GeO2 on Ge than for thermal SiO2 on Si above ~10-4% RH, which is due to the larger amount of water molecules that infiltrate into the GeO2 film to form hydroxyls. Analyzing the origins of this energy shift, we propose thatmore » the positive charging of a partially hydroxylated GeO2 film, which is unrelated to X-ray irradiation, causes the larger energy shift for GeO2/Ge than for SiO2/Si. A possible microscopic mechanism of this intrinsic positive charging is the emission of electrons from adsorbed water species in the suboxide layer of the GeO2 film to the Ge bulk, leaving immobile cations or positively charged states in the oxide. Finally, this may be related to the reported negative shift of flat band voltages in metal-oxide-semiconductor diodes with an air-exposed GeO2 layer.« less

  2. Comparative study of GeO2/Ge and SiO2/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Mori, Daichi; Oka, Hiroshi; Hosoi, Takuji; Kawai, Kentaro; Morita, Mizuho; Crumlin, Ethan J.; Liu, Zhi; Watanabe, Heiji; Arima, Kenta

    2016-09-01

    The energy difference between the oxide and bulk peaks in X-ray photoelectron spectroscopy (XPS) spectra was investigated for both GeO2/Ge and SiO2/Si structures with thickness-controlled water films. This was achieved by obtaining XPS spectra at various values of relative humidity (RH) of up to ˜15%. The increase in the energy shift is more significant for thermal GeO2 on Ge than for thermal SiO2 on Si above ˜10-4% RH, which is due to the larger amount of water molecules that infiltrate into the GeO2 film to form hydroxyls. Analyzing the origins of this energy shift, we propose that the positive charging of a partially hydroxylated GeO2 film, which is unrelated to X-ray irradiation, causes the larger energy shift for GeO2/Ge than for SiO2/Si. A possible microscopic mechanism of this intrinsic positive charging is the emission of electrons from adsorbed water species in the suboxide layer of the GeO2 film to the Ge bulk, leaving immobile cations or positively charged states in the oxide. This may be related to the reported negative shift of flat band voltages in metal-oxide-semiconductor diodes with an air-exposed GeO2 layer.

  3. Comparative study of GeO{sub 2}/Ge and SiO{sub 2}/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy

    SciTech Connect

    Mori, Daichi; Kawai, Kentaro; Morita, Mizuho; Arima, Kenta; Oka, Hiroshi; Hosoi, Takuji; Watanabe, Heiji; Crumlin, Ethan J.; Liu, Zhi

    2016-09-07

    The energy difference between the oxide and bulk peaks in X-ray photoelectron spectroscopy (XPS) spectra was investigated for both GeO{sub 2}/Ge and SiO{sub 2}/Si structures with thickness-controlled water films. This was achieved by obtaining XPS spectra at various values of relative humidity (RH) of up to ∼15%. The increase in the energy shift is more significant for thermal GeO{sub 2} on Ge than for thermal SiO{sub 2} on Si above ∼10{sup −4}% RH, which is due to the larger amount of water molecules that infiltrate into the GeO{sub 2} film to form hydroxyls. Analyzing the origins of this energy shift, we propose that the positive charging of a partially hydroxylated GeO{sub 2} film, which is unrelated to X-ray irradiation, causes the larger energy shift for GeO{sub 2}/Ge than for SiO{sub 2}/Si. A possible microscopic mechanism of this intrinsic positive charging is the emission of electrons from adsorbed water species in the suboxide layer of the GeO{sub 2} film to the Ge bulk, leaving immobile cations or positively charged states in the oxide. This may be related to the reported negative shift of flat band voltages in metal-oxide-semiconductor diodes with an air-exposed GeO{sub 2} layer.

  4. 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%.

  5. Phonons in Ge nanowires

    NASA Astrophysics Data System (ADS)

    Peelaers, H.; Partoens, B.; Peeters, F. M.

    2009-09-01

    The phonon spectra of thin freestanding, hydrogen passivated, Ge nanowires are calculated by ab initio techniques. The effect of confinement on the phonon modes as caused by the small diameters of the wires is investigated. Confinement causes a hardening of the optical modes and a softening of the longitudinal acoustic modes. The stability of the nanowires, undoped or doped with B or P atoms, is investigated using the obtained phonon spectra. All considered wires were stable, except for highly doped, very thin nanowires.

  6. Hot Carrier Dynamics in the X Valley in Si and Ge Measured by Pump-IR-Probe Absorption Spectroscopy

    NASA Technical Reports Server (NTRS)

    Wang, W. B.; Cavicchia, M. A.; Alfano, R. R.

    1996-01-01

    Si is the semiconductor of choice for nanoelectronic roadmap into the next century for computer and other nanodevices. With growing interest in Si, Ge, and Si(sub m)Ge(sub n) strained superlattices, knowledge of the carrier relaxation processes in these materials and structures has become increasingly important. The limited time resolution for earlier studies of carrier dynamics in Ge and Si, performed using Nd:glass lasers, was not sufficient to observe the fast cooling processes. In this paper, we present a direct measurement of hot carrier dynamics in the satellite X valley in Si and Ge by time-resolved infrared(IR) absorption spectroscopy, and show the potential of our technique to identify whether the X valley is the lowest conduction valley in semiconductor materials and structures.

  7. Carrier-lifetime-controlled selective etching process for semiconductors using photochemical etching

    DOEpatents

    Ashby, Carol I. H.; Myers, David R.

    1992-01-01

    The minority carrier lifetime is significantly much shorter in semiconductor materials with very high impurity concentrations than it is in semiconductor materials with lower impurity concentration levels. This phenomenon of reduced minority carrier lifetime in semiconductor materials having high impurity concentration is utilized to advantage for permitting highly selective semiconductor material etching to be achieved using a carrier-driven photochemical etching reaction. Various means may be employed for increasing the local impurity concentration level in specific near-surface regions of a semiconductor prior to subjecting the semiconductor material to a carrier-driven photochemical etching reaction. The regions having the localized increased impurity concentration form a self-aligned mask inhibiting photochemical etching at such localized regions while the adjacent regions not having increased impurity concentrations are selectively photochemically etched. Liquid- or gas-phase etching may be performed.

  8. Distinct local electronic structure and magnetism for Mn in amorphous Si and Ge

    SciTech Connect

    Zeng, Li; Cao, J. X.; Helgren, E.; Karel, J.; Arenholz, E.; Ouyang, Lu; Smith, David J.; Wu, R. Q.; Hellman, F.

    2010-06-01

    Transition metals such as Mn generally have large local moments in covalent semiconductors due to their partially filled d shells. However, Mn magnetization in group-IV semiconductors is more complicated than often recognized. Here we report a striking crossover from a quenched Mn moment (<0.1 {mu}{sub B}) in amorphous Si (a-Si) to a large distinct local Mn moment ({ge}3{mu}{sub B}) in amorphous Ge (a-Ge) over a wide range of Mn concentrations (0.005-0.20). Corresponding differences are observed in d-shell electronic structure and the sign of the Hall effect. Density-functional-theory calculations show distinct local structures, consistent with different atomic density measured for a-Si and a-Ge, respectively, and the Mn coordination number N{sub c} is found to be the key factor. Despite the amorphous structure, Mn in a-Si is in a relatively well-defined high coordination interstitial type site with broadened d bands, low moment, and electron (n-type) carriers, while Mn in a-Ge is in a low coordination substitutional type site with large local moment and holes (p-type) carriers. Moreover, the correlation between N{sub c} and the magnitude of the local moment is essentially independent of the matrix; the local Mn moments approach zero when N{sub c} > 7 for both a-Si and a-Ge.

  9. Lattice-matched heteroepitaxy of wide gap ternary compound semiconductors

    NASA Technical Reports Server (NTRS)

    Bachmann, Klaus J.

    1993-01-01

    A variety of applications are identified for heteroepitaxial structures of wide gap I-III-VI(sub 2) and II-IV-V(sub 2) semiconductors, and are assessed in comparison with ternary III-V alloys and other wide gap materials. Non-linear optical applications of the I-III-VI(sub 2) and II-IV-V(sub 2) compound heterostructures are discussed, which require the growth of thick epitaxial layers imposing stringent requirements on the conditions of heteroepitaxy. In particular, recent results concerning the MOCVD growth of ZnSi(x)Ge(1-x)P2 alloys lattice matching Si or GaP substrates are reviewed. Also, heterostructures of Cu(z)Ag(1-z)GaS2 alloys that lattice-match Si, Ge, GaP, or GaAs substrates are considered in the context of optoelectronic devices operating in the blue wavelength regime. Since under the conditions of MOCVD, metastable alloys of the II-IV-V(sub 2) compounds and group IV elements are realized, II-IV-V(sub 2) alloys may also serve as interlayers in the integration of silicon and germanium with exactly lattice-matched tetrahedrally coordinated compound semiconductors, e.g. ZnSi(x)Ge(1-x)P2.

  10. Lattice-matched heteroepitaxy of wide gap ternary compound semiconductors

    NASA Technical Reports Server (NTRS)

    Bachmann, Klaus J.

    1992-01-01

    A variety of applications are identified for heteroepitaxial structures of wide gap I-III-VI2 and II-IV-V2 semiconductors, and are assessed in comparison with ternary III-V alloys and other wide gap materials. Non-linear optical applications of the I-III-VI2 and II-IV-V2 compound heterostructures are discussed, which require the growth of thick epitaxial layers imposing stringent requirements on the conditions of heteroepitaxy. In particular, recent results concerning the MOCVD growth of ZnSi(x)Ge(1-x)P2 alloys lattice-matching Si or GaP substrates are reviewed. Also, heterostructures of Cu(z)Ag(1-z)GaS2 alloys that lattice-match Si, Ge, GaP or GaAs substrates are considered in the context of optoelectronic devices operating in the blue wavelength regime. Since under the conditions of MOCVD, metastable alloys of the II-IV-V2 compounds and group IV elements are realized, II-IV-V2 alloys may also serve as interlayers in the integration of silicon and germanium with exactly lattice-matched tetrahedrally coordinated compound semiconductors, e.g. ZnSi(x)Ge(1-x)P2.

  11. Optical transmittance and reflectance studies and evidence of weak electron-phonon interaction in Type-I Ge clathrate Ba8Ga16Ge30

    NASA Astrophysics Data System (ADS)

    Udono, Haruhiko; Imai, Motoharu; Kojima, Shuhei; Kume, Tetsuji; Tanigaki, Katsumi; Tajima, Hiroyuki

    2017-05-01

    The optical properties of ternary type-I Ge clathrate Ba8Ga16Ge30 are investigated by optical reflectance and transmittance measurements. The refractive index and extinction coefficient are calculated from the reflectance spectrum via the modified Kramers-Kronig analysis method between 0.5 and 3.2 eV. The photon energy dependence of the optical absorption coefficient reveals that Ba8Ga16Ge30 is an indirect band gap semiconductor with a gap energy Eg of 0.69 eV at 5.7 K and 0.66 eV at 285 K. The temperature dependence of Eg can be satisfactorily described by an equation based on the Bose-Einstein statistics model. When compared with those of common elemental, III-V, and II-VI semiconductors, the small temperature coefficient dEg/dT of the Ba8Ga16Ge30 can be considered to represent the weak electron-phonon interaction in the Ba8Ga16Ge30 clathrate.

  12. Light amplification using semiconductors

    SciTech Connect

    Dupuis, R.D.

    1987-06-01

    During the summer of 1953, John von Neumann discussed his ideas concerning light amplification using semiconductors with Edward Teller. In September of that year, von Neumann sent a manuscript containing his ideas and calculations on this subject to Teller for his comments. To the best of our knowledge, von Neumann did not take time to work further on these ideas, and the manuscript remained unpublished. These previously unpublished writings of John von Neumann on the subject of light amplification in semiconductors are printed as a service to the laser community. While von Neumann's original manuscript and his letter to Teller are available to anyone who visits the Library of Congress, it is much more convenient to have this paper appear in an archival journal.

  13. Semiconductor radiation detector

    DOEpatents

    Patt, Bradley E.; Iwanczyk, Jan S.; Tull, Carolyn R.; Vilkelis, Gintas

    2002-01-01

    A semiconductor radiation detector is provided to detect x-ray and light photons. The entrance electrode is segmented by using variable doping concentrations. Further, the entrance electrode is physically segmented by inserting n+ regions between p+ regions. The p+ regions and the n+ regions are individually biased. The detector elements can be used in an array, and the p+ regions and the n+ regions can be biased by applying potential at a single point. The back side of the semiconductor radiation detector has an n+ anode for collecting created charges and a number of p+ cathodes. Biased n+ inserts can be placed between the p+ cathodes, and an internal resistor divider can be used to bias the n+ inserts as well as the p+ cathodes. A polysilicon spiral guard can be implemented surrounding the active area of the entrance electrode or surrounding an array of entrance electrodes.

  14. Stretchable Organic Semiconductor Devices.

    PubMed

    Qian, Yan; Zhang, Xinwen; Xie, Linghai; Qi, Dianpeng; Chandran, Bevita K; Chen, Xiaodong; Huang, Wei

    2016-11-01

    Stretchable electronics are essential for the development of intensely packed collapsible and portable electronics, wearable electronics, epidermal and bioimplanted electronics, 3D surface compliable devices, bionics, prosthesis, and robotics. However, most stretchable devices are currently based on inorganic electronics, whose high cost of fabrication and limited processing area make it difficult to produce inexpensive, large-area devices. Therefore, organic stretchable electronics are highly attractive due to many advantages over their inorganic counterparts, such as their light weight, flexibility, low cost and large-area solution-processing, the reproducible semiconductor resources, and the easy tuning of their properties via molecular tailoring. Among them, stretchable organic semiconductor devices have become a hot and fast-growing research field, in which great advances have been made in recent years. These fantastic advances are summarized here, focusing on stretchable organic field-effect transistors, light-emitting devices, solar cells, and memory devices.

  15. Thermosize potentials in semiconductors

    NASA Astrophysics Data System (ADS)

    Karabetoglu, S.; Sisman, A.

    2017-09-01

    A thermosize junction consists of two different sized structures made using the same material. Classical and quantum thermosize effects (CTSEs and QTSEs), which are opposite to each other, induce a thermosize potential in a thermosize junction. A semi-analytical method is proposed to calculate thermosize potentials in wide ranges of degeneracy and confinement by considering both CTSEs and QTSEs in thermosize junctions made using semiconductors. Dependencies of thermosize potential on temperature, size, and degeneracy are examined. It is shown that a potential difference in millivolt scale can be induced as a combined effect of CTS and QTS. The highest potential is obtained in nondegenerate limit where the full analytical solution is obtained. The model can be used to design semiconductor thermosize devices for a possible experimental verification of CTSEs and QTSEs, which may lead to new nano energy conversion devices.

  16. Three dimensional strained semiconductors

    DOEpatents

    Voss, Lars; Conway, Adam; Nikolic, Rebecca J.; Leao, Cedric Rocha; Shao, Qinghui

    2016-11-08

    In one embodiment, an apparatus includes a three dimensional structure comprising a semiconductor material, and at least one thin film in contact with at least one exterior surface of the three dimensional structure for inducing a strain in the structure, the thin film being characterized as providing at least one of: an induced strain of at least 0.05%, and an induced strain in at least 5% of a volume of the three dimensional structure. In another embodiment, a method includes forming a three dimensional structure comprising a semiconductor material, and depositing at least one thin film on at least one surface of the three dimensional structure for inducing a strain in the structure, the thin film being characterized as providing at least one of: an induced strain of at least 0.05%, and an induced strain in at least 5% of a volume of the structure.

  17. PREFACE: Functionalized Liquid Liquid Interfaces

    NASA Astrophysics Data System (ADS)

    Girault, Hubert; Kornyshev, Alexei A.; Monroe, Charles W.; Urbakh, Michael

    2007-09-01

    Most natural processes take place at interfaces. For this reason, surface science has been a focal point of modern research. At solid-liquid interfaces one can induce various species to adsorb or react, and thus may study interactions between the substrate and adsorbates, kinetic processes, optical properties, etc. Liquid-liquid interfaces, formed by immiscible liquids such as water and oil, have a number of distinctive features. Both sides of the interface are amenable to detailed physical and chemical analysis. By chemical or electrochemical means, metal or semiconductor nanoparticles can be formed or localised at the interface. Surfactants can be used to tailor surface properties, and also to place organic molecular or supermolecular constructions at the boundary between the liquids. Electric fields can be used to drive ions from one fluid to another, or even change the shape of the interface itself. In many cases, both liquids are optically transparent, making functionalized liquid-liquid interfaces promising for various optical applications based on the transmission or reflection of light. An advantage common to most of these systems is self-assembly; because a liquid-liquid interface is not mechanically constrained like a solid-liquid interface, it can easily access its most stable state, even after it has been driven far from equilibrium. This special issue focuses on four modes of liquid-liquid interfacial functionalization: the controlled adsorption of molecules or nanoparticles, the formation of adlayers or films, electrowetting, and ion transfer or interface-localized reactions. Interfacial adsorption can be driven electrically, chemically, or mechanically. The liquid-liquid interface can be used to study how anisotropic particles orient at a surface under the influence of a field, how surfactants interact with other adsorbates, and how nanoparticles aggregate; the transparency of the interface also makes the chirality of organic adsorbates amenable to

  18. Tunable semiconductor lasers

    NASA Technical Reports Server (NTRS)

    Taghavi-Larigani, Shervin (Inventor); Vanzyl, Jakob J. (Inventor); Yariv, Amnon (Inventor)

    2006-01-01

    Tunable semiconductor lasers are disclosed requiring minimized coupling regions. Multiple laser embodiments employ ring resonators or ring resonator pairs using only a single coupling region with the gain medium are detailed. Tuning can be performed by changing the phase of the coupling coefficient between the gain medium and a ring resonator of the laser. Another embodiment provides a tunable laser including two Mach-Zehnder interferometers in series and a reflector coupled to a gain medium.

  19. Metal Contacts in Semiconductors.

    DTIC Science & Technology

    1983-11-01

    surfaces, Pnotoelectron spe troscopy, Auger electron spectro- I scopy, Schottky barriers, ohmic contacts, Defects in semiconductors, Cadmium * telluride...Indium phosphide, Gallium arsenide, Gallium Selenide . j 20. ABSTR ACT (roothat ow rees esh " neceay and td..ity by block -. b*w) SThe application of...angstroms. Also, provided one eliminates the systems where cadmium outdiffusion into high work function metals occurs then good agreement between the

  20. Chemically Derivatized Semiconductor Photoelectrodes.

    DTIC Science & Technology

    1983-06-01

    Journal of Chemical Education . l.i LA. Is. KEY WOROS (Coneinuo onm Few*,@*.oldsI noede eeand identify by block number) semiconductors, photoelectrodes...Massachusetts Institute of Technology Cambridge, Massachusetts 02139 Prepared for publication in the Journal of Chemical Education June 1, 1983 Reproduction...use of metals or metal oxides coated onto the photoelectrode surface. [Prepared for publication in the Journal of Chemical Education .

  1. Semiconductor projectile impact detector

    NASA Technical Reports Server (NTRS)

    Shriver, E. L. (Inventor)

    1977-01-01

    A semiconductor projectile impact detector is described for use in determining micrometeorite presence, as well as its flux and energy comprising a photovoltaic cell which generates a voltage according to the light and heat emitted by the micrometeorites upon impact. A counter and peak amplitude measuring device were used to indicate the number of particules which strike the surface of the cell as well as the kinetic energy of each of the particles.

  2. Isotopically controlled semiconductors

    SciTech Connect

    Haller, Eugene E.

    2006-06-19

    The following article is an edited transcript based on the Turnbull Lecture given by Eugene E. Haller at the 2005 Materials Research Society Fall Meeting in Boston on November 29, 2005. The David Turnbull Lectureship is awarded to recognize the career of a scientist who has made outstanding contributions to understanding materials phenomena and properties through research, writing, and lecturing, as exemplified by the life work of David Turnbull. Haller was named the 2005 David Turnbull Lecturer for his 'pioneering achievements and leadership in establishing the field of isotopically engineered semiconductors; for outstanding contributions to materials growth, doping and diffusion; and for excellence in lecturing, writing, and fostering international collaborations'. The scientific interest, increased availability, and technological promise of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled semiconductor crystals. This article reviews results obtained with isotopically controlled semiconductor bulk and thin-film heterostructures. Isotopic composition affects several properties such as phonon energies, band structure, and lattice constant in subtle, but, for their physical understanding, significant ways. Large isotope-related effects are observed for thermal conductivity in local vibrational modes of impurities and after neutron transmutation doping. Spectacularly sharp photoluminescence lines have been observed in ultrapure, isotopically enriched silicon crystals. Isotope multilayer structures are especially well suited for simultaneous self- and dopant-diffusion studies. The absence of any chemical, mechanical, or electrical driving forces makes possible the study of an ideal random-walk problem. Isotopically controlled semiconductors may find applications in quantum computing, nanoscience, and spintronics.

  3. Semiconductor Properties Near Interfaces.

    DTIC Science & Technology

    1980-07-31

    electron multi- plication with a scintillation counter. This detECtor , described in the appendix, provides very low background without sacrifice of...k ADA095 858 UNIVERSITY OF SOUTHERN CALIFORNIA LOS ANGELES F/G 20/12I SEMICONDUCTOR PROPERTIES NEAR INTERFACES.(U) JUL GO0 DB WITTRY. S Y YIN, F GUO...improvements in the Ion Microprobe Mass Analyzer; in the course of the investioations in improved inn detector was developed and a microcomrnu*e

  4. Semiconductor Diamond Technology

    DTIC Science & Technology

    1991-12-31

    hidrogen at the maximum pressure showed only very faint -second order spots. Annealing of thee samples to 1000*C restored the (2x0) configura.-tion...semiconductor contact also provides a suitable vehicle for electrical characterization of the device material. However, it has been observed that the...nature of the plasma activated diamond deposition processes provides a very useful and flexible vehicle for device fabrication sequences. Other workers

  5. Semiconductor Ion Implanters

    SciTech Connect

    MacKinnon, Barry A.; Ruffell, John P.

    2011-06-01

    In 1953 the Raytheon CK722 transistor was priced at $7.60. Based upon this, an Intel Xeon Quad Core processor containing 820,000,000 transistors should list at $6.2 billion. Particle accelerator technology plays an important part in the remarkable story of why that Intel product can be purchased today for a few hundred dollars. Most people of the mid twentieth century would be astonished at the ubiquity of semiconductors in the products we now buy and use every day. Though relatively expensive in the nineteen fifties they now exist in a wide range of items from high-end multicore microprocessors like the Intel product to disposable items containing 'only' hundreds or thousands like RFID chips and talking greeting cards. This historical development has been fueled by continuous advancement of the several individual technologies involved in the production of semiconductor devices including Ion Implantation and the charged particle beamlines at the heart of implant machines. In the course of its 40 year development, the worldwide implanter industry has reached annual sales levels around $2B, installed thousands of dedicated machines and directly employs thousands of workers. It represents in all these measures, as much and possibly more than any other industrial application of particle accelerator technology. This presentation discusses the history of implanter development. It touches on some of the people involved and on some of the developmental changes and challenges imposed as the requirements of the semiconductor industry evolved.

  6. Semiconductor Ion Implanters

    NASA Astrophysics Data System (ADS)

    MacKinnon, Barry A.; Ruffell, John P.

    2011-06-01

    In 1953 the Raytheon CK722 transistor was priced at 7.60. Based upon this, an Intel Xeon Quad Core processor containing 820,000,000 transistors should list at 6.2 billion! Particle accelerator technology plays an important part in the remarkable story of why that Intel product can be purchased today for a few hundred dollars. Most people of the mid twentieth century would be astonished at the ubiquity of semiconductors in the products we now buy and use every day. Though relatively expensive in the nineteen fifties they now exist in a wide range of items from high-end multicore microprocessors like the Intel product to disposable items containing `only' hundreds or thousands like RFID chips and talking greeting cards. This historical development has been fueled by continuous advancement of the several individual technologies involved in the production of semiconductor devices including Ion Implantation and the charged particle beamlines at the heart of implant machines. In the course of its 40 year development, the worldwide implanter industry has reached annual sales levels around 2B, installed thousands of dedicated machines and directly employs thousands of workers. It represents in all these measures, as much and possibly more than any other industrial application of particle accelerator technology. This presentation discusses the history of implanter development. It touches on some of the people involved and on some of the developmental changes and challenges imposed as the requirements of the semiconductor industry evolved.

  7. Spin Transport in Semiconductor heterostructures

    SciTech Connect

    Domnita Catalina Marinescu

    2011-02-22

    The focus of the research performed under this grant has been the investigation of spin transport in magnetic semiconductor heterostructures. The interest in these systems is motivated both by their intriguing physical properties, as the physical embodiment of a spin-polarized Fermi liquid, as well as by their potential applications as spintronics devices. In our work we have analyzed several different problems that affect the spin dynamics in single and bi-layer spin-polarized two-dimensional (2D) systems. The topics of interests ranged from the fundamental aspects of the electron-electron interactions, to collective spin and charge density excitations and spin transport in the presence of the spin-orbit coupling. The common denominator of these subjects is the impact at the macroscopic scale of the spin-dependent electron-electron interaction, which plays a much more subtle role than in unpolarized electron systems. Our calculations of several measurable parameters, such as the excitation frequencies of magneto-plasma modes, the spin mass, and the spin transresistivity, propose realistic theoretical estimates of the opposite-spin many-body effects, in particular opposite-spin correlations, that can be directly connected with experimental measurements.

  8. Numerical calculation of strain-N+-Ge1- x Sn x /P+-δGe1- x Sn x /N--Ge1- y - z Si y Sn z /P+-Ge1- y - z Si y Sn z heterojunction tunnel field-effect transistor

    NASA Astrophysics Data System (ADS)

    Wang, Suyuan; Zheng, Jun; Xue, Chunlai; Li, Chuanbo; Zuo, Yuhua; Cheng, Buwen; Wang, Qiming

    2017-05-01

    In this work, we present a theoretical calculation of the insertion of a δ-doping layer in double gate N+-Ge1- x Sn x /N-Ge1- y - z Si y Sn z /P+-Ge1- y - z Si y Sn z heterojunction p-type tunnel field-effect transistors (PTFETs) by semiconductor device simulation. The compositions of Ge1- x Sn x and Ge1- y - z Si y Sn z and the optimization of the δ-layer are analyzed in detail. It is shown that the use of narrow-bandgap Ge1- x Sn x in the source region and large-bandgap Ge1- y - z Si y Sn z in the drain region is favorable for increasing the on-state current (I ON) and suppressing the ambipolar effect. The P+ δ-layer in the Ge1- x Sn x considerably improves the PTFET performance compared with other structures. The best I ON of 69.56 µA/µm and the subthreshold swing (SS) of 22 mV/dec were achieved at a low applied voltage of -0.5 V.

  9. Review paper: Transparent amorphous oxide semiconductor thin film transistor

    NASA Astrophysics Data System (ADS)

    Kwon, Jang-Yeon; Lee, Do-Joong; Kim, Ki-Bum

    2011-03-01

    Thin film transistors (TFTs) with oxide semiconductors have drawn great attention in the last few years, especially for large area electronic applications, such as high resolution active matrix liquid crystal displays (AMLCDs) and active matrix organic light-emitting diodes (AMOLEDs), because of their high electron mobility and spatial uniform property. This paper reviews and summarizes recent emerging reports that include potential applications, oxide semiconductor materials, and the impact of the fabrication process on electrical performance. We also address the stability behavior of such devices under bias/illumination stress and critical factors related to reliability, such as the gate insulator, the ambient and the device structure.

  10. Superconductor-semiconductor hybrid devices, circuits, and systems

    SciTech Connect

    Kroger, H.; Hilbert, C.; Gibson, D.A.; Ghoshal, U.; Smith, L.N.

    1989-08-01

    The discovery of superconductors whose critical temperatures are above liquid nitrogen temperature has prompted considerable interest in hybrid superconducting-semiconducting electronics applications. This paper reviews the efforts to hybridize these technologies. Some of these efforts have already been demonstrated on a laboratory scale; others are at present just theoretical proposals. Hybridization is possible on the system, circuit, and device levels. The authors review studies of the applications of superconductors for interconnecting semiconductor systems and combining semiconductor and superconductor devices to enhance the performance of both digital and analog systems. Novel circuit combinations of superconducting and semiconducting devices are mentioned, as are proposal to combine these materials on the device level.

  11. Giant Seebeck effect in Ge-doped SnSe

    PubMed Central

    Gharsallah, M.; Serrano-Sánchez, F.; Nemes, N. M.; Mompeán, F. J.; Martínez, J. L.; Fernández-Díaz, M. T.; Elhalouani, F.; Alonso, J. A.

    2016-01-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit. PMID:27251233

  12. Giant Seebeck effect in Ge-doped SnSe

    NASA Astrophysics Data System (ADS)

    Gharsallah, M.; Serrano-Sánchez, F.; Nemes, N. M.; Mompeán, F. J.; Martínez, J. L.; Fernández-Díaz, M. T.; Elhalouani, F.; Alonso, J. A.

    2016-06-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit.

  13. Giant Seebeck effect in Ge-doped SnSe.

    PubMed

    Gharsallah, M; Serrano-Sánchez, F; Nemes, N M; Mompeán, F J; Martínez, J L; Fernández-Díaz, M T; Elhalouani, F; Alonso, J A

    2016-06-02

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit.

  14. Excitonic correlation in the Mott crossover regime in Ge

    NASA Astrophysics Data System (ADS)

    Sekiguchi, Fumiya; Shimano, Ryo

    2015-04-01

    Exciton Mott transition (EMT) in Ge was investigated by using optical-pump and terahertz-probe spectroscopy. From the quantitative analysis of optical conductivity and dielectric function, we evaluated the densities of unbound electron-hole pairs and excitons after the photoexcitation, from which we determined the ionization ratio of excitons α. The Mott crossover density region in Ge was elucidated from the density dependence of α in the temperature range above the critical temperature of electron-hole droplets. The 1 s -2 p excitonic transition energy hardly shifted with increasing density toward the EMT. Combined with the similar results recently observed in bulk Si, we suggest that the robustness of excitonic correlation against the Coulomb screening is a universal feature in bulk semiconductors in the Mott crossover regime.

  15. Semiconductor Alloy Theory.

    DTIC Science & Technology

    1986-01-14

    ftoc*o~ow7 and Idenify’ by block nam. bor) Electron mobility , Lattice Relaxation, Bond Length, Bond Energy, Mixing Enthalpies, Band Structure, Core...including: (1) generalization of Brooks’ formula for alloy-scattering limited electron mobility to including multiple bands and indirect gaps, (2...calculation of SiGe alloys band structure, electron mobility and core-exciton binding energy and • :linewidth, (3) comprehensive calculation of bond

  16. A global Ge isotope budget

    NASA Astrophysics Data System (ADS)

    Baronas, J. Jotautas; Hammond, Douglas E.; McManus, James; Wheat, C. Geoffrey; Siebert, Christopher

    2017-04-01

    We present measurements of Ge isotope composition and ancillary data for samples of river water, low- and high-temperature hydrothermal fluids, and seawater. The dissolved δ74Ge composition of analyzed rivers ranges from 2.0 to 5.6‰, which is significantly heavier than previously determined values for silicate rocks (δ74Ge = 0.4-0.7‰, Escoube et al., Geostand. Geoanal. Res., 36(2), 2012) from which dissolved Ge is primarily derived. An observed negative correlation between riverine Ge/Si and δ74Ge signatures suggests that the primary δ74Ge fractionation mechanism during rock weathering is the preferential incorporation of light isotopes into secondary weathering products. High temperature (>150 °C) hydrothermal fluids analyzed in this study have δ74Ge of 0.7-1.6‰, most likely fractionated during fluid equilibration with quartz in the reaction zone. Low temperature (25-63 °C) hydrothermal fluids are heavier (δ74Ge between 2.9‰ and 4.1‰) and most likely fractionated during Ge precipitation with hydrothermal clays. Seawater from the open ocean has a δ74Gesw value of 3.2 ± 0.4‰, and is indistinguishable among the different ocean basins at the current level of precision. This value should be regulated over time by the isotopic balance of Ge sources and sinks, and a new compilation of these fluxes is presented, along with their estimated isotopic compositions. Assuming steady-state, non-opal Ge sequestration during sediment authigenesis likely involves isotopic fractionation Δ74Gesolid-solution that is -0.6 ± 1.8‰.

  17. Raman Imaging in Semiconductor Physics: Applications to Microelectronic Materials and Devices

    NASA Astrophysics Data System (ADS)

    Tiberj, Antoine; Camassel, Jean

    The unique versatility of micro-Raman spectroscopy (\\upmu RS) in semiconductor physics remains in Raman imaging. Numerous applications cover the whole development of modern electronic and optoelectronic devices: from semiconductor growth to advanced device inspection tools. In this chapter, a wide variety of semiconductors (SiC, graphene, GaN, GaAs, SiGe, strained Si, sSOI, SGOI) and devices (FETs, lasers, MEMS) are addressed. First, it will be shown how Raman mapping enables to check the crystalline quality, the composition, the doping, and the uniformity of as-grown semiconductors. Then, we will focus on the most popular application in microelectronics: strain measurements either at the device or at the full wafer scale. Finally, we will show how \\upmu RS imaging can be used for final device inspection through the temperature mapping of operating devices (FETs, lasers, actuators).

  18. Operation of Ge- and GaAs-tunnel diodes under the influence of electron beams

    NASA Astrophysics Data System (ADS)

    El-Basit, W. Abd; Awad, Z. I. M.; Kamh, S. A.; Soliman, F. A. S.

    2017-02-01

    Nuclear radiation plays a very negative role in the semiconductor devices functionality, mainly when particular semiconductor devices are exposed to an extreme type of radiation. Tunneling is an important aspect of charge transport in semiconductor and molecular devices. So, the effect of electron irradiation on the current-voltage (I-V) characteristics of Germanium (Ge) and Gallium Arsenide (GaAs) tunneling diodes are reported at room temperature before and after irradiation. Electrons exposure, up to 3.73 My, of the tunnel diodes leads to a pronounced change in their electrical characteristics where the rate of change of the peak- and valley-currents, for Ge and GaAs tunnel diodes, due to electron exposure are shown to be about +53.6, +142 µA/MGy and +29.4, +53.6 µA/MGy, respectively. On the other hand, for the same irradiation doses, the rate of change of the valley- and forward-voltages and output power are shown to be about -44.9, -15.9 and -6.7 mW/MGy, for Ge tunnel diodes, respectively. While, GaAs samples, reported values of -81, -83 mV/MGy and -11.6 mW/MGy are observed. Besides, the peak to valley current ratio of both Ge- and GaAs TDs are proved to decrease due to electrons exposure, with damping ratios of about 78 and 81%, respectively.

  19. Operation of Ge- and GaAs-tunnel diodes under the influence of electron beams

    NASA Astrophysics Data System (ADS)

    El-Basit, W. Abd; Awad, Z. I. M.; Kamh, S. A.; Soliman, F. A. S.

    2017-06-01

    Nuclear radiation plays a very negative role in the semiconductor devices functionality, mainly when particular semiconductor devices are exposed to an extreme type of radiation. Tunneling is an important aspect of charge transport in semiconductor and molecular devices. So, the effect of electron irradiation on the current-voltage (I-V) characteristics of Germanium (Ge) and Gallium Arsenide (GaAs) tunneling diodes are reported at room temperature before and after irradiation. Electrons exposure, up to 3.73 My, of the tunnel diodes leads to a pronounced change in their electrical characteristics where the rate of change of the peak- and valley-currents, for Ge and GaAs tunnel diodes, due to electron exposure are shown to be about +53.6, +142 µA/MGy and +29.4, +53.6 µA/MGy, respectively. On the other hand, for the same irradiation doses, the rate of change of the valley- and forward-voltages and output power are shown to be about -44.9, -15.9 and -6.7 mW/MGy, for Ge tunnel diodes, respectively. While, GaAs samples, reported values of -81, -83 mV/MGy and -11.6 mW/MGy are observed. Besides, the peak to valley current ratio of both Ge- and GaAs TDs are proved to decrease due to electrons exposure, with damping ratios of about 78 and 81%, respectively.

  20. 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.