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Sample records for ge liquid semiconductor

  1. Monte Carlo studies of liquid semiconductor surfaces - Si and Ge

    NASA Technical Reports Server (NTRS)

    Wang, Z. Q.; Stroud, D.

    1988-01-01

    The liquid-vapor interface of Si and Ge, and of Si doped with impurities is studied using the empirical Stillinger-Weber two- and three-body potentials. The surface tension of the pure elements is calculated by use of a direct evaluation of the free energy required to create the surface. For Si, both the surface tension and its temperature derivative are in good agreement with experiment. To within numerical accuracy, the free surfaces of both Si and Ge have a monotonically decreasing density, with a 10-90 percent surface width of about 2.2 A in both cases. When large and small model impurities are introduced into pure liquid Si, they are found in the simulations to migrate, respectively, towards the surface and away from the surface. This behavior is consistent with the interpretation that impurities with atoms larger than Si tend to lower the surface tension.

  2. 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

  3. Optical conductivity for liquid semiconductors

    NASA Astrophysics Data System (ADS)

    Jain, Manish; Ko, Eunjung; Derby, J. J.; Chelikowsky, James

    2002-03-01

    We present calculations for the optical conductivity of several semiconductor liquids: SiGe, GaAs, CdTe, and ZnTe. We perform ab initio molecular dynamics for these liquids. The required interatomic forces are determined using the pseudopotential density functional method. We determine the optical conductivity by considering ensemble averages of the liquid state within the Kubo-Greenwood formalism. In the liquid phase, CdTe and ZnTe exhibit properties that are different from III-V and group IV semiconductors. CdTe and ZnTe remain semiconducting unlike SiGe and GaAs, which are metallic in the melt. These differences in optical conductivities are explained in terms of differences in the microstructure of the liquids. We also verify an empirical rule by Joffe and Regel. Their rule predicts the liquid will remain semiconducting if the short range order of the melt resembles that of the crystalline phase.

  4. Semiconductor nanorod liquid crystals

    SciTech Connect

    Li, Liang-shi; Walda, Joost; Manna, Liberato; Alivisatos, A. Paul

    2002-01-28

    Rodlike molecules form liquid crystalline phases with orientational order and positional disorder. The great majority of materials in which liquid crystalline phases have been observed are comprised of organic molecules or polymers, even though there has been continuing and growing interest in inorganic liquid crystals. Recent advances in the control of the sizes and shapes of inorganic nanocrystals allow for the formation of a broad class of new inorganic liquid crystals. Here we show the formation of liquid crystalline phases of CdSe semiconductor nanorods. These new liquid crystalline phases may have great importance for both application and fundamental study.

  5. 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.

  6. Optical Absorption in Liquid Semiconductors

    NASA Astrophysics Data System (ADS)

    Bell, Florian Gene

    and the proportionality to Tl concentration. The ionic model satisfactorily explains the observed concentration and temperature dependence of the absorption. It also provides for the first time, a universal explanation of the exponential edge in liquid semiconductors where charged defects are present, and provides a means of measuring the concentration of ions when the absorption can be calibrated.

  7. Semiconductor liquid-junction solar cell

    SciTech Connect

    Parkinson, B.A.

    1982-10-29

    A semiconductor liquid junction photocell in which the photocell is in the configuration of a light concentrator and in which the electrolytic solution both conducts current and facilitates the concentration of incident solar radiation onto the semiconductor. The photocell may be in the configuration of a non-imaging concentrator such as a compound parabolic concentrator, or an imaging concentrator such as a lens.

  8. A Pseudopotential Approach to Compute Thermodynamic Properties of Liquid Semiconductors

    NASA Astrophysics Data System (ADS)

    Prajapati, Anand; Thakor, Pankaj; Sonvane, Yogesh

    2015-03-01

    This paper deals with the theoretical approach for calculating the thermodynamical properties viz. Enthalpy(E),Entropy(S) and Helmholtz free energy(F) of some liquid semiconductors (Si, Ga, Ge, In, Sn, Tl, Bi, As, Se, Te and Sb). The Gibbs-Bogoliubov(GB) variational method is applied to compute the thermodynamical properties. Our well established model potential is used to define the electron-ion interaction. Charged Hard Sphere (CHS) reference system is used to describe the structural contribution to the Helmholtz free energy in the liquid phase. Local field correction function proposed by Farid et al is adopted to see the screening effect. Lastly, our newly constructed model potential is an effective one to produce the data of thermodynamical properties of some liquid semiconductor.

  9. 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

  10. 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.

  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. PMID:26132141

  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. Magnetic Mn5Ge3 nanocrystals embedded in crystalline Ge: a magnet/semiconductor hybrid synthesized by ion implantation

    PubMed Central

    2012-01-01

    The integration of ferromagnetic Mn5Ge3 with the Ge matrix is promising for spin injection in a silicon-compatible geometry. In this paper, we report the preparation of magnetic Mn5Ge3 nanocrystals embedded inside the Ge matrix by Mn ion implantation at elevated temperature. By X-ray diffraction and transmission electron microscopy, we observe crystalline Mn5Ge3 with variable size depending on the Mn ion fluence. The electronic structure of Mn in Mn5Ge3 nanocrystals is a 3d6 configuration, which is the same as that in bulk Mn5Ge3. A large positive magnetoresistance has been observed at low temperatures. It can be explained by the conductivity inhomogeneity in the magnetic/semiconductor hybrid system. PMID:23009168

  14. Metastability of Au-Ge liquid nanocatalysts: Ge vapor-liquid-solid nanowire growth far below the bulk eutectic temperature.

    PubMed

    Adhikari, Hemant; Marshall, Ann F; Goldthorpe, Irene A; Chidsey, Christopher E D; McIntyre, Paul C

    2007-12-01

    The vapor-liquid-solid mechanism of nanowire (NW) growth requires the presence of a liquid at one end of the wire; however, Au-catalyzed Ge nanowire growth by chemical vapor deposition can occur at approximately 100 degrees C below the bulk Au-Ge eutectic. In this paper, we investigate deep sub-eutectic stability of liquid Au-Ge catalysts on Ge NWs quantitatively, both theoretically and experimentally. We construct a binary Au-Ge phase diagram that is valid at the nanoscale and show that equilibrium arguments, based on capillarity, are inconsistent with stabilization of Au-Ge liquid at deep sub-eutectic temperatures, similar to those used in Ge NW growth. Hot-stage electron microscopy and X-ray diffraction are used to test the predictions of nanoscale phase equilibria. In addition to Ge supersaturation of the Au-Ge liquid droplet, which has recently been invoked as an explanation for deep sub-eutectic Ge NW growth, we find evidence of a substantial kinetic barrier to Au solidification during cooling below the nanoscale Au-Ge eutectic temperature. PMID:19206662

  15. Synthesis and characterization of group IV semiconductor nanowires by vapor-liquid-solid growth

    NASA Astrophysics Data System (ADS)

    Lew, Kok-Keong

    There is currently intense interest in one-dimensional nanostructures, such as nanotubes and nanowires, due to their potential to test fundamental concepts of dimensionality and to serve as building blocks for nanoscale devices. Vapor-liquid-solid (VLS) growth, which is one of the most common fabrication methods, has been used to produce single crystal semiconductor nanowires such as silicon (Si), germanium (Ge), and gallium arsenide (GaAs). In the VLS growth of Group IV semiconductor nanowires, a metal, such as gold (Au) is used as a catalyst agent to nucleate whisker growth from a Si-containing (silane (SIH4)) or Ge-containing vapor (germane (GeH 4)). Au and Si/Ge form a liquid alloy that has a eutectic temperature of around 360°C, which, upon supersaturation, nucleates the growth of a Si or Ge wire. The goal of this work is to develop a more fundamental understanding of VLS growth kinetics and intentional doping of Group IV semiconductor nanowires in order to better control the properties of the nanowires. The fabrication of p-type and n-type Si nanowires will be studied via the addition of dopant gases such as diborane (B2H 6), trimethylboron (TMB), and phosphine (PH3) during growth. The use of gaseous dopant sources provides more flexibility in growth, particularly for the fabrication of p-n junctions and structures with axial dopant variations (e.g. p+-p- p+). The study is then extended to fabricate SiGe alloy nanowires by mixing SiH4 and GeH4. Bandgap engineering in Si/SiGe heterostructures can lead to novel devices with improved performance compared to those made entirely of Si. The scientific findings will lead to a better understanding of the fabrication of Si/SiGe axial and radial heterostructure nanowires for functional nanowire device structures, such as heterojunction bipolar transistors (HBTs) and high electron mobility transistors (HEMTs). Eventually, the central theme of this research is to provide a scientific knowledge base and foundation for

  16. Liquid-Phase Electroepitaxy of Semiconductors

    NASA Astrophysics Data System (ADS)

    Dost, Sadik

    The chapter presents a review of the growth of single-crystal bulk semiconductors by liquid-phase electroepitaxy (LPEE). Following a short introduction, early modeling and theoretical studies on LPEE are briefly introduced. Recent experimental results on LPEE growth of GaAs/GaInAs single crystals under a static applied magnetic field are discussed in detail. The results of three-dimensional numerical simulations carried out for LPEE growth of GaAs under various electric and magnetic field levels are presented. The effect of magnetic field nonuniformities is numerically examined. Crystal growth experiments show that the application of a static magnetic field in LPEE growth of GaAs increases the growth rate very significantly. A continuum model to predict such high growth rates is also presented. The introduction of a new electric mobility in the model, i.e., the electromagnetic mobility, allows accurate predictions of both the growth rate and the growth interface shape. Space limitation required the citation of a limited number of references related to LPEE [29.1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73]. For details of many aspects of the LPEE growth process and its historical developments, the reader is referred to these references and also others cited therein.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    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.

  18. First principles simulations of liquid semiconductors: Electronic, structural and dynamic properties

    NASA Astrophysics Data System (ADS)

    Godlevsky, Vitaliy

    We develop ab initio molecular dynamics simulation technique to examine liquid semiconductors. Our methods use quantum interatomic forces, computed within the pseudopotential-density functional method (PDFM). In our work, we study typical representatives of IV, III-V and II-VI materials: Si, Ge, GaAs and CdTe. We show that, upon melting, IV and III-V semiconductors experience semiconductor → metal transition, while more ionic II-VI compounds remain semiconductors in the melt. Metallic type conductivity of liquid IV and III-V materials results from the structural changes of the systems in the melt. In our simulations, "open" zinc-blende (diamond for Si and Ge) structures transform into a more close-packed configuration during solid → liquid transition. Their coordination number, equal to 4 in the crystalline phase, changes to ˜6 in the liquid. We demonstrate that this leads to the breaking of covalent bonds and delocalization of electrons. According to our results, the density of states function of liquid IV and III-V semiconductors has a well defined "free electron" character. For these materials, the electrical conductivity jumps by one to two orders of magnitude during melting. This is opposite to the behavior of the majority of II-VI compounds. In our work, we examine CdTe, typical II-VI semiconductor. Although the dc conductivity of CdTe increases by a factor of 40 as it melts, this material remains a semiconductor in the liquid: its electrical conductivity increases with the temperature. At variance with IV and III-V semiconductors, liquid CdTe retains its tetrahedral environment with the coordination number of ˜4. We discover that a significant number of anion-cation bonds are conserved in liquid CdTe as opposed to IV and III-V materials. This is in agreement with the small entropy change observed in the melting process of CdTe. In our simulations, we find that further heating of molten CdTe results in significant structural changes with a

  19. 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.

  20. Atomically precise semiconductor--graphene and hBN interfaces by Ge intercalation.

    PubMed

    Verbitskiy, N I; Fedorov, A V; Profeta, G; Stroppa, A; Petaccia, L; Senkovskiy, B; Nefedov, A; Wöll, C; Usachov, D Yu; Vyalikh, D V; Yashina, L V; Eliseev, A A; Pichler, T; Grüneis, A

    2015-01-01

    The full exploration of the potential, which graphene offers to nanoelectronics requires its integration into semiconductor technology. So far the real-world applications are limited by the ability to concomitantly achieve large single-crystalline domains on dielectrics and semiconductors and to tailor the interfaces between them. Here we show a new direct bottom-up method for the fabrication of high-quality atomically precise interfaces between 2D materials, like graphene and hexagonal boron nitride (hBN), and classical semiconductor via Ge intercalation. Using angle-resolved photoemission spectroscopy and complementary DFT modelling we observed for the first time that epitaxially grown graphene with the Ge monolayer underneath demonstrates Dirac Fermions unaffected by the substrate as well as an unperturbed electronic band structure of hBN. This approach provides the intrinsic relativistic 2D electron gas towards integration in semiconductor technology. Hence, these new interfaces are a promising path for the integration of graphene and hBN into state-of-the-art semiconductor technology. PMID:26639608

  1. Strained Si, SiGe, and Ge channels for high-mobility metal-oxide-semiconductor field-effect transistors

    NASA Astrophysics Data System (ADS)

    Lee, Minjoo L.; Fitzgerald, Eugene A.; Bulsara, Mayank T.; Currie, Matthew T.; Lochtefeld, Anthony

    2005-01-01

    This article reviews the history and current progress in high-mobility strained Si, SiGe, and Ge channel metal-oxide-semiconductor field-effect transistors (MOSFETs). We start by providing a chronological overview of important milestones and discoveries that have allowed heterostructures grown on Si substrates to transition from purely academic research in the 1980's and 1990's to the commercial development that is taking place today. We next provide a topical review of the various types of strain-engineered MOSFETs that can be integrated onto relaxed Si1-xGex, including surface-channel strained Si n- and p-MOSFETs, as well as double-heterostructure MOSFETs which combine a strained Si surface channel with a Ge-rich buried channel. In all cases, we will focus on the connections between layer structure, band structure, and MOS mobility characteristics. Although the surface and starting substrate are composed of pure Si, the use of strained Si still creates new challenges, and we shall also review the literature on short-channel device performance and process integration of strained Si. The review concludes with a global summary of the mobility enhancements available in the SiGe materials system and a discussion of implications for future technology generations.

  2. 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.

  3. 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.

  4. Investigation of redox processes at semiconductor electrode liquid junctions

    SciTech Connect

    Koval, C.A.

    1990-08-01

    Research in fundamental aspects of photoelectrochemical cells has been in the following areas: chemical probes for hot carrier processes, electrostatic theory for describing electrical interactions at interfaces, and kinetics of electron transfer at ideal semiconductor solution interfaces. Our goal is to achieve a better understanding of dark and photo-induced current flow at the semiconductor electrode/redox electrolyte interface (SEI) so that devices and processes utilizing this interface for solar energy conversion can be developed or improved. Our most important accomplishment has been the development of a redox system capable of detecting hot electrons at the p-InP/acetonitrile interface. Also, we have examined electrostatic theory for the image potential of an ion as a function of distance from the SEI. Finally, our group was one of the first to realize that the 2-dimensional metal chalcogenides (MC) are excellent materials for fundamental studies of electron transfer at the SEI. One of the chief potential advantages for use of MC's is the formation of semiconductor/liquid junctions with nearly ideal electrochemical properties. 27 refs., 1 fig.

  5. 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.

  6. Emergence of competing magnetic interactions induced by Ge doping in the semiconductor FeGa3

    NASA Astrophysics Data System (ADS)

    Alvarez-Quiceno, J. C.; Cabrera-Baez, M.; Ribeiro, R. A.; Avila, M. A.; Dalpian, G. M.; Osorio-Guillén, J. M.

    2016-07-01

    FeGa3 is an unusual intermetallic semiconductor that presents intriguing magnetic responses to the tuning of its electronic properties. When doped with Ge, the system evolves from diamagnetic to paramagnetic to ferromagnetic ground states that are not well understood. In this work, we have performed a joint theoretical and experimental study of FeGa3 -xGex using density functional theory and magnetic susceptibility measurements. For low Ge concentrations we observe the formation of localized moments on some Fe atoms and, as the dopant concentration increases, a more delocalized magnetic behavior emerges. The magnetic configuration strongly depends on the dopant distribution, leading even to the appearance of antiferromagnetic interactions in certain configurations.

  7. 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. PMID:22900746

  8. Vertically Aligned Ge Nanowires on Flexible Plastic Films Synthesized by (111)-Oriented Ge Seeded Vapor-Liquid-Solid Growth.

    PubMed

    Toko, Kaoru; Nakata, Mitsuki; Jevasuwan, Wipakorn; Fukata, Naoki; Suemasu, Takashi

    2015-08-19

    Transfer-free fabrication of vertical Ge nanowires (NWs) on a plastic substrate is demonstrated using a vapor-liquid-solid (VLS) method. The crystal quality of Ge seed layers (50 nm thickness) prepared on plastic substrates strongly influenced the VLS growth morphology, i.e., the density, uniformity, and crystal quality of Ge NWs. The metal-induced layer exchange yielded a (111)-oriented Ge seed layer at 325 °C, which allowed for the VLS growth of vertically aligned Ge NWs. The Ge NW array had almost the same quality as that formed on a bulk Ge(111) substrate. Transmission electron microscopy demonstrated that the Ge NWs were defect-free single crystals. The present investigation paves the way for advanced electronic optical devices integrated on a low-cost flexible substrate. PMID:26230716

  9. Magnetic Interactions in the Diluted Magnetic Semiconductor Mn_xGe_1-x

    NASA Astrophysics Data System (ADS)

    Erwin, Steven C.; Hellberg, C. Stephen

    2001-03-01

    Much current debate has focused on the origins of ferromagnetism in III-V magnetic semiconductors. Less attention has been paid to magnetically doped Group-IV semiconductors, although they have been predicted to have Curie temperatures of the same order [1]. We use density-functional theoretical (DFT) methods to study the electronic structure and magnetic interactions in Mn_xGe_1-x, the first such elemental magnetic semiconductor to be realized experimentally [2]. We use ordered supercells to simulate 6% Mn concentration, and calculate total energies within DFT for a variety of positional and magnetic arrangements of Mn at fixed concentration. We then fit these energies to a Heisenberg model to extract the spin coupling constants. The result is a strong but very short-ranged antiferromagnetic interaction between Mn atoms, and a weaker but longer-ranged ferromagnetic interaction. The ferromagnetic interaction dominates at all Mn-Mn distances beyond nearest neighbor. [1] T. Dietl et al., Science 287, 1019 (2000). [2] Y.D. Park, J. Mattson, A. Hanbicki, and B. Jonker (unpublished).

  10. 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.

  11. Quest for high-Curie temperature MnxGe1-x diluted magnetic semiconductors for room-temperature spintronics applications

    NASA Astrophysics Data System (ADS)

    Nie, Tianxiao; Tang, Jianshi; Wang, Kang L.

    2015-09-01

    In this paper, we report the non-equilibrium growth of various Mn-doped Ge dilute magnetic semiconductor nanostructures using molecular-beam epitaxy, including quantum dots, nanodisks and nanowires. Their detailed structural and magnetic properties are characterized. By comparing the results with those in MnxGe1-x thin films, it is affirmed that the use of nanostructures helps eliminate crystalline defects and meanwhile enhance the carrier-mediate ferromagnetism from substantial quantum confinements. Our systematic studies provide a promising platform to build nonvolatile spinFET and other novel spintronic devices based upon dilute magnetic semiconductor nanostructures.

  12. Semiconductor-doped liquid-core optical fiber.

    PubMed

    Hreibi, Ali; Gérôme, Frédéric; Auguste, Jean-Louis; Zhang, Yu; Yu, William W; Blondy, Jean-Marc

    2011-05-01

    A semiconductor liquid-core optical fiber has been made by simply filling the hollow core of a capillary waveguide with nanoparticles suspended in toluene media. Under a low continuous optical power excitation at 532 nm, the emission of PbSe particles was clearly demonstrated in the infrared region and then partially maintained in the core of the fiber by the total internal reflection mechanism. Finally, due to the guided propagation, which results in multiple absorption effects, a linear shift of the emission peak toward longer wavelengths was observed (~0.32 nm/cm). As a proof of concept, this original demonstration of visible-to-infrared conversion could lead to the development of active fibered devices at wavelengths not covered by the conventional rare-earth ion doping. PMID:21540972

  13. Metal-induced assembly of a semiconductor island lattice: Ge truncated pyramids on Au-patterned Si.

    PubMed

    Robinson, J T; Liddle, J A; Minor, A; Radmilovic, V; Yi, D O; Greaney, P Alex; Long, K N; Chrzan, D C; Dubon, O D

    2005-10-01

    We report the two-dimensional alignment of semiconductor islands using rudimentary metal patterning to control nucleation and growth. In the Ge on Si system, a square array of submicron Au dots on the Si (001) surface induces the assembly of deposited Ge adatoms into an extensive island lattice. Remarkably, these highly ordered Ge islands form between the patterned Au dots and are characterized by a unique truncated pyramidal shape. A model based on patterned diffusion barriers explains the observed ordering and establishes general criteria for the broader applicability of such a directed assembly process to quantum dot ordering. PMID:16218739

  14. Intrinsic carrier effects in HfO2-Ge metal-insulator-semiconductor capacitors

    NASA Astrophysics Data System (ADS)

    Dimoulas, A.; Vellianitis, G.; Mavrou, G.; Evangelou, E. K.; Sotiropoulos, A.

    2005-05-01

    Germanium metal-insulator-semiconductor capacitors with HfO2 or other high-κ gate dielectrics show unusual low frequency behavior of the high frequency (1 kHz or higher) capacitance-voltage characteristics when biased in inversion. Here, we provide evidence that this effect is partly due to the high intrinsic carrier concentration ni in Ge. We show in particular that the ac conductance in inversion is thermally activated and it is governed either by generation-recombination processes in depletion, varying proportional to ni or by diffusion-limited processes varying as ni2, depending on whether the temperature is below or above 45 °C, respectively. From these measurements, we also show that the minority carrier response time in Ge is very short, in the microsecond range (much shorter than in Si), depending inversely proportional to ni at room temperature. This means that due to high ni, the inversion charge is built fast in response to high frequency signals at the gate, inducing the observed low frequency behavior.

  15. 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.

  16. Liquid GeBr/sub 4/. II. Molecular packing and liquid structure

    SciTech Connect

    Ludwig, K.F. Jr.; Wilson, L.; Warburton, W.K.; Bienenstock, A.I.

    1987-07-01

    Anomalous scattering data from 1-GeBr/sub 4/ are compared with theoretical predictions and with several models. Published hard-sphere RISM calculations of the pair correlation functions accurately predict the features of the experimental distribution functions, but discrepancies between theory and experiment are larger than the experimental uncertainty. New calculations with more realistic potentials are needed. The total structure factor of 1-GeBr/sub 4/ contains a prepeak which is due largely, but not exclusively, to correlations between molecular centers (i.e., germanium atoms). Modeling results indicate that there is strong interlocking of molecules in the liquid and that the Br--Br structure factor is largely determined by the packing of the halogen atoms with the germanium atoms effectively fitting in tetrahedral interstices. Models based on the monoclinic crystal of SnBr/sub 4/ agree better with the liquid data than models based on the cubic crystal of c-GeBr/sub 4/, suggesting that GeBr/sub 4/ undergoes a change in short-range molecular packing on melting.

  17. Liquid-state semiconductor p-n junction at 903 K

    NASA Astrophysics Data System (ADS)

    Sasaki, Yasushi; Hirano, Yoshihiko; Iguchi, Manabu; Ishii, Kuniyoshi

    2006-12-01

    A liquid-state semiconductor p-n junction has been fabricated by applying the liquid phase separation of the monotectic Sb-Sb2S3 system at 903K. Electrical conduction types of liquid semiconductor of Sb-S alloy and S2S3-x consisting of the immiscible system are found to be p and n types, respectively, from measured absolute Seebeck coefficients. The p-n junction was formed by the liquid Sb--S alloy and Sb2S3-x; this is confirmed from the asymmetric current-voltage characteristics or its behavior is rectified. The formation of the liquid-state p-n junction in liquid semiconductors has great prospects in the next-generation direct thermal-to-electrical energy conversion materials.

  18. Room-temperature local ferromagnetism and its nanoscale expansion in the ferromagnetic semiconductor Ge1–xFex

    NASA Astrophysics Data System (ADS)

    Wakabayashi, Yuki K.; Sakamoto, Shoya; Takeda, Yuki-Haru; Ishigami, Keisuke; Takahashi, Yukio; Saitoh, Yuji; Yamagami, Hiroshi; Fujimori, Atsushi; Tanaka, Masaaki; Ohya, Shinobu

    2016-03-01

    We investigate the local electronic structure and magnetic properties of the group-IV-based ferromagnetic semiconductor, Ge1‑xFex (GeFe), using soft X-ray magnetic circular dichroism. Our results show that the doped Fe 3d electrons are strongly hybridized with the Ge 4p states, and have a large orbital magnetic moment relative to the spin magnetic moment; i.e., morb/mspin ≈ 0.1. We find that nanoscale local ferromagnetic regions, which are formed through ferromagnetic exchange interactions in the high-Fe-content regions of the GeFe films, exist even at room temperature, well above the Curie temperature of 20–100 K. We observe the intriguing nanoscale expansion of the local ferromagnetic regions with decreasing temperature, followed by a transition of the entire film into a ferromagnetic state at the Curie temperature.

  19. Room-temperature local ferromagnetism and its nanoscale expansion in the ferromagnetic semiconductor Ge1-xFex.

    PubMed

    Wakabayashi, Yuki K; Sakamoto, Shoya; Takeda, Yuki-Haru; Ishigami, Keisuke; Takahashi, Yukio; Saitoh, Yuji; Yamagami, Hiroshi; Fujimori, Atsushi; Tanaka, Masaaki; Ohya, Shinobu

    2016-01-01

    We investigate the local electronic structure and magnetic properties of the group-IV-based ferromagnetic semiconductor, Ge1-xFex (GeFe), using soft X-ray magnetic circular dichroism. Our results show that the doped Fe 3d electrons are strongly hybridized with the Ge 4p states, and have a large orbital magnetic moment relative to the spin magnetic moment; i.e., morb/mspin ≈ 0.1. We find that nanoscale local ferromagnetic regions, which are formed through ferromagnetic exchange interactions in the high-Fe-content regions of the GeFe films, exist even at room temperature, well above the Curie temperature of 20-100 K. We observe the intriguing nanoscale expansion of the local ferromagnetic regions with decreasing temperature, followed by a transition of the entire film into a ferromagnetic state at the Curie temperature. PMID:26996202

  20. Room-temperature local ferromagnetism and its nanoscale expansion in the ferromagnetic semiconductor Ge1–xFex

    PubMed Central

    Wakabayashi, Yuki K.; Sakamoto, Shoya; Takeda, Yuki-haru; Ishigami, Keisuke; Takahashi, Yukio; Saitoh, Yuji; Yamagami, Hiroshi; Fujimori, Atsushi; Tanaka, Masaaki; Ohya, Shinobu

    2016-01-01

    We investigate the local electronic structure and magnetic properties of the group-IV-based ferromagnetic semiconductor, Ge1−xFex (GeFe), using soft X-ray magnetic circular dichroism. Our results show that the doped Fe 3d electrons are strongly hybridized with the Ge 4p states, and have a large orbital magnetic moment relative to the spin magnetic moment; i.e., morb/mspin ≈ 0.1. We find that nanoscale local ferromagnetic regions, which are formed through ferromagnetic exchange interactions in the high-Fe-content regions of the GeFe films, exist even at room temperature, well above the Curie temperature of 20–100 K. We observe the intriguing nanoscale expansion of the local ferromagnetic regions with decreasing temperature, followed by a transition of the entire film into a ferromagnetic state at the Curie temperature. PMID:26996202

  1. Magnetic-field-induced ferroelectric polarization reversal in the multiferroic Ge(1-x)Mn(x)Te semiconductor.

    PubMed

    Przybylińska, H; Springholz, G; Lechner, R T; Hassan, M; Wegscheider, M; Jantsch, W; Bauer, G

    2014-01-31

    Ge(1-x)Mn(x)Te is shown to be a multiferroic semiconductor, exhibiting both ferromagnetic and ferroelectric properties. By ferromagnetic resonance we demonstrate that both types of order are coupled to each other. As a result, magnetic-field-induced ferroelectric polarization reversal is achieved. Switching of the spontaneous electric dipole moment is monitored by changes in the magnetocrystalline anisotropy. This also reveals that the ferroelectric polarization reversal is accompanied by a reorientation of the hard and easy magnetization axes. By tuning the GeMnTe composition, the interplay between ferromagnetism and ferroelectricity can be controlled. PMID:24580486

  2. Semiconductor arrays with multiplexer readout for gamma-ray imaging: results for a 48 × 48 Ge array

    NASA Astrophysics Data System (ADS)

    Barber, H. B.; Augustine, F. L.; Barrett, H. H.; Dereniak, E. L.; Matherson, K. L.; Meyers, T. J.; Perry, D. L.; Venzon, J. E.; Woolfenden, J. M.; Young, E. T.

    1994-12-01

    We are developing a new kind of gamma-ray imaging device that has sub-millimeter spatial resolution and excellent energy resolution. The device is composed of a slab of semiconductor detector partitioned into an array of detector cells by photolithography and connected to a monolithic circuit chip called a multiplexer (MUX) for readout. Our application is for an ultra-high-resolution SPECT system for functional brain imaging using an injected radiotracer. We report here on results obtained with a Hughes 48 × 48 Ge PIN-photodiode array with MUX readout, originally developed as an infrared focal-plane-array imaging sensor. The device functions as an array of individual gamma-ray detectors with minimal interpixel crosstalk. Linearity of energy response is excellent up to at least 140 keV. The array exhibits excellent energy resolution, ˜ 2 keV at ≤ 140 keV or 1.5% FWHM at 140 keV. The energy resolution is dominated by MUX readout noise and so should improve with MUX optimization for gamma-ray detection. The spatial resolution of the 48 × 48 Ge array is essentially the same as the pixel spacing, 125 μm. The quantum efficiency is limited by the thin Ge detector (0.25 mm), but this approach is readily applicable to thicker Ge detectors and room-temperature semiconductor detectors such as CdTe, HgI 2 and CdZnTe.

  3. Electronic band structures of Ge1-xSnx semiconductors: A first-principles density functional theory study

    NASA Astrophysics Data System (ADS)

    Lee, Ming-Hsien; Liu, Po-Liang; Hong, Yung-An; Chou, Yen-Ting; Hong, Jia-Yang; Siao, Yu-Jin

    2013-02-01

    We conduct first-principles total-energy density functional calculations to study the band structures in Ge1-xSnx infrared semiconductor alloys. The norm-conserving optimized pseudopotentials of Ge and Sn have been constructed for electronic structure calculations. The composition-bandgap relationships in Ge1-xSnx lattices are evaluated by a detailed comparison of structural models and their electronic band structures. The critical Sn composition related to the transition from indirect- to direct-gap in Ge1-xSnx alloys is estimated to be as low as x ˜ 0.016 determined from the parametric fit. Our results show that the crossover Sn concentration occurs at a lower critical Sn concentration than the values predicted from the absorption measurements. However, early results indicate that the reliability of the critical Sn concentration from such measurements is hard to establish, since the indirect gap absorption is much weaker than the direct gap absorption. We find that the direct band gap decreases exponentially with the Sn composition over the range 0 0.375, in very good agreement with the theoretical observed behavior [D. W. Jenkins and J. D. Dow, Phys. Rev. B 36, 7994, 1987]. For homonuclear and heteronuclear complexes of Ge1-xSnx alloys, the indirect band gap at L-pointis is found to decrease homonuclear Ge-Ge bonds or increase homonuclear Sn-Sn bonds as a result of the reduced L valley. All findings agree with previously reported experimental and theoretical results. The analysis suggests that the top of valence band exhibits the localization of bond charge and the bottom of the conduction band is composed of the Ge 4s4p and/or Sn 5s5p atomic orbits.

  4. 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.

  5. Tensile-Strained GeSn Metal-Oxide-Semiconductor Field-Effect Transistor Devices on Si(111) Using Solid Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Lieten, Ruben R.; Maeda, Tatsuro; Jevasuwan, Wipakorn; Hattori, Hiroyuki; Uchida, Noriyuki; Miura, Shu; Tanaka, Masatoshi; Locquet, Jean-Pierre

    2013-10-01

    We demonstrate tensile-strained GeSn metal-oxide-semiconductor field-effect transistor (MOSFET) devices on Si(111) substrates using solid phase epitaxy of amorphous GeSn layers. Amorphous GeSn layers are obtained by limiting the adatom surface mobility during deposition. Subsequent annealing transforms the amorphous layer into single-crystalline GeSn by solid phase epitaxy. Single-crystalline GeSn layers with 4.5% Sn and 0.33% tensile strain are fabricated on Si(111) substrates. To verify the structural quality of thin-film GeSn as a channel material, we fabricate ultrathin GeSn p-channel MOSFETs (pMOSFETs) on Si(111). We demonstrate junctionless depletion-mode operation of tensile-strained GeSn(111) pMOSFETs on Si substrates.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    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.

  8. 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.

  9. Capacitance-voltage characteristics of Si and Ge nanomembrane based flexible metal-oxide-semiconductor devices under bending conditions

    NASA Astrophysics Data System (ADS)

    Cho, Minkyu; Seo, Jung-Hun; Park, Dong-Wook; Zhou, Weidong; Ma, Zhenqiang

    2016-06-01

    Metal-oxide-semiconductor (MOS) device is the basic building block for field effect transistors (FET). The majority of thin-film transistors (TFTs) are FETs. When MOSFET are mechanically bent, the MOS structure will be inevitably subject to mechanical strain. In this paper, flexible MOS devices using single crystalline Silicon (Si) and Germanium (Ge) nanomembranes (NM) with SiO2, SiO, and Al2O3 dielectric layers are fabricated on a plastic substrate. The relationships between semiconductor nanomembranes and various oxide materials are carefully investigated under tensile/compressive strain. The flatband voltage, threshold voltage, and effective charge density in various MOS combinations revealed that Si NM-SiO2 configuration shows the best interface charge behavior, while Ge NM-Al2O3 shows the worst. This investigation of flexible MOS devices can help us understand the impact of charges in the active region of the flexible TFTs and capacitance changes under the tensile/compressive strains on the change in electrical characteristics in flexible NM based TFTs.

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

    NASA Astrophysics Data System (ADS)

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

    2000-11-01

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

  11. Diffusion mass transport in liquid phase epitaxial growth of semiconductors

    SciTech Connect

    Dost, S.; Qin, Z.; Kimura, M.

    1996-12-01

    A numerical simulation model for the mass transport occurring during the liquid phase epitaxial growth of AlGaAs is presented. The mass transport equations in the liquid and solid phases, and the relationships between concentrations and temperature obtained from the phase diagram constitute the governing equations. These equations together with appropriate interface and boundary conditions were solved numerically by the Finite Element Method. Numerical results show the importance of diffusion into the solid phase, affecting the composition of grown layers. Simulation results agree with experiments.

  12. 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.

  13. Strained germanium-tin (GeSn) p-channel metal-oxide-semiconductor field-effect-transistors (p-MOSFETs) with ammonium sulfide passivation

    NASA Astrophysics Data System (ADS)

    Wang, Lanxiang; Su, Shaojian; Wang, Wei; Gong, Xiao; Yang, Yue; Guo, Pengfei; Zhang, Guangze; Xue, Chunlai; Cheng, Buwen; Han, Genquan; Yeo, Yee-Chia

    2013-05-01

    High-mobility strained Ge0.958Sn0.042 p-channel metal-oxide-semiconductor field-effect-transistors (p-MOSFETs) with ammonium sulfide [(NH4)2S] surface passivation were demonstrated. A ˜10 nm thick fully-strained single crystalline GeSn layer was epitaxially grown on Ge (1 0 0) substrate as the channel layer. (NH4)2S surface passivation was performed for the GeSn surface, followed by gate stack formation. Ge0.958Sn0.042 p-MOSFETs with (NH4)2S passivation show decent electrical characteristics and a peak effective mobility of 509 cm2/V s, which is the highest reported peak mobility obtained for GeSn channel p-MOSFETs so far.

  14. Growth and magnetic properties of IV-VI diluted magnetic semiconductor Ge{sub 1-x}Cr{sub x}Te

    SciTech Connect

    Fukuma, Y.; Taya, T.; Miyawaki, S.; Irisa, T.; Asada, H.; Koyanagi, T.

    2006-04-15

    IV-VI diluted magnetic semiconductor Ge{sub 1-x}Cr{sub x}Te films were grown on BaF{sub 2} substrates by molecular-beam epitaxy. The Ge{sub 1-x}Cr{sub x}Te film up to x=0.103 is single phase as determined by reflection high-energy electron diffraction and x-ray diffraction measurements. The optical band gap decreases with increasing Cr composition. Ferromagnetic order of the Ge{sub 1-x}Cr{sub x}Te films is characterized by direct magnetization and anomalous Hall effect measurements.

  15. 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. PMID:26906379

  16. 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.

  17. Oriented Liquid Crystalline Polymer Semiconductor Films with Large Ordered Domains.

    PubMed

    Xue, Xiao; Chandler, George; Zhang, Xinran; Kline, R Joseph; Fei, Zhuping; Heeney, Martin; Diemer, Peter J; Jurchescu, Oana D; O'Connor, Brendan T

    2015-12-01

    Large strains are applied to liquid crystalline poly(2,5-bis(3-tetradecylthiophen-2yl)thieno(3,2-b)thiophene) (pBTTT) films when held at elevated temperatures resulting in in-plane polymer alignment. We find that the polymer backbone aligns significantly in the direction of strain, and that the films maintain large quasi-domains similar to that found in spun-cast films on hydrophobic surfaces, highlighted by dark-field transmission electron microscopy imaging. The highly strained films also have nanoscale holes consistent with dewetting. Charge transport in the films is then characterized in a transistor configuration, where the field effect mobility is shown to increase in the direction of polymer backbone alignment, and decrease in the transverse direction. The highest saturated field-effect mobility was found to be 1.67 cm(2) V(-1) s(-1), representing one of the highest reported mobilities for this material system. The morphology of the oriented films demonstrated here contrast significantly with previous demonstrations of oriented pBTTT films that form a ribbon-like morphology, opening up opportunities to explore how differences in molecular packing features of oriented films impact charge transport. Results highlight the role of grain boundaries, differences in charge transport along the polymer backbone and π-stacking direction, and structural features that impact the field dependence of charge transport. PMID:26552721

  18. 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. PMID:17982517

  19. 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.

  20. Design and control of Ge-based metal-oxide-semiconductor interfaces for high-mobility field-effect transistors with ultrathin oxynitride gate dielectrics

    NASA Astrophysics Data System (ADS)

    Minoura, Yuya; Kasuya, Atsushi; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2013-07-01

    High-quality Ge-based metal-oxide-semiconductor (MOS) stacks were achieved with ultrathin oxynitride (GeON) gate dielectrics. An in situ process based on plasma nitridation of the base germanium oxide (GeO2) surface and subsequent metal electrode deposition was proven to be effective for suppressing electrical deterioration induced by the reaction at the metal/insulator interface. The electrical properties of the bottom GeON/Ge interface were further improved by both low-temperature oxidation for base GeO2 formation and high-temperature in situ vacuum annealing after plasma nitridation of the base oxide. Based on the optimized in situ gate stack fabrication process, very high inversion carrier mobility (μhole: 445 cm2/Vs, μelectron: 1114 cm2/Vs) was demonstrated for p- and n-channel Ge MOSFETs with Al/GeON/Ge gate stacks at scaled equivalent oxide thickness down to 1.4 nm.

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

    Energy Science and Technology Software Center (ESTSC)

    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.

  2. Temperature dependent shape transformation of Ge nanostructures by the vapor-liquid-solid method

    NASA Astrophysics Data System (ADS)

    Das, K.; Chakraborty, A. K.; NandaGoswami, M. L.; Shingha, R. K.; Dhar, A.; Coleman, K. S.; Ray, S. K.

    2007-04-01

    A vapor-liquid-solid method has been used to study the temperature dependent growth mechanism of Ge nanostructures on Au-coated Si (100) substrates. The formation of Ge nanodots, nanorods, and nanowires has been observed at different growth temperatures. The diameter of grown nanowires is found to be varying from 40 to 80 nm and that of nanorods from 70 to 90 nm, respectively. A comparative study has been done on three types of samples using x-ray diffraction and Raman spectroscopy. Photoluminescence spectra of grown nanostructures exhibit a broad emission band around 2.6 eV due to oxide related defect states.

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

    DOE PAGESBeta

    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 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

  4. Synthesis and fundamental studies of (H3Ge)xSiH4-x molecules: precursors to semiconductor hetero- and nanostructures on Si.

    PubMed

    Ritter, Cole J; Hu, Changwu; Chizmeshya, Andrew V G; Tolle, John; Klewer, Douglas; Tsong, Ignatius S T; Kouvetakis, John

    2005-07-13

    The synthesis of the entire silyl-germyl sequence of molecules (H(3)Ge)(x)SiH(4)(-)(x) (x = 1-4) has been demonstrated. These include the previously unknown (H(3)Ge)(2)SiH(2), (H(3)Ge)(3)SiH, and (H(3)Ge)(4)Si species as well as the H(3)GeSiH(3) analogue which is obtained in practical high-purity yields as a viable alternative to disilane and digermane for semiconductor applications. The molecules are characterized by FTIR, multinuclear NMR, mass spectrometry, and Rutherford backscattering. The structural, thermochemical, and vibrational properties are studied using density functional theory. A detailed comparison of the experimental and theoretical data is used to corroborate the synthesis of specific molecular structures. The (H(3)Ge)(x)SiH(4)(-)(x) family of compounds described here is not only of intrinsic molecular interest but also provides a unique route to a new class of Si-based semiconductors including epitaxial layers and coherent islands (quantum dots), with Ge-rich stoichiometries SiGe, SiGe(2), SiGe(3), and SiGe(4) reflecting the Si/Ge content of the corresponding precursor. The layers grow directly on Si(100) at unprecedented low temperatures of 300-450 degrees C and display homogeneous compositional and strain profiles, low threading defect densities, and atomically planar surfaces circumventing entirely the need for conventional graded compositions or lift-off technologies. The activation energies of all Si-Ge hydride reactions on Si(100) (E(a) approximately 1.5-2.0 eV) indicate high reactivity profiles with respect to H(2) desorption, consistent with the low growth temperatures of the films. The quantum dots are obtained exclusively at higher temperatures (T > 500 degrees C) and represent a new family of Ge-rich compositions with narrow size distribution, defect-free microstructures, and homogeneous, precisely tuned elemental content at the atomic level. PMID:15998091

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

    PubMed

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

    2015-12-01

    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 analogue of the vapor-liquid-solid (VLS) growth of semiconductor nanowires: the 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 thus sustaining the dissolution process. This VLS etching process provides a new tool for directed assembly of structures with sublithographic 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

  6. Investigation of Ge nanocrytals in a metal-insulator-semiconductor structure with a HfO2/SiO2 stack as the tunnel dielectric

    NASA Astrophysics Data System (ADS)

    Wang, Shiye; Liu, Weili; Wan, Qing; Dai, J. Y.; Lee, P. F.; Suhua, Luo; Shen, Qinwo; Zhang, Miao; Song, Zhitang; Lin, Chenglu

    2005-03-01

    A metal-insulator-semiconductor (MIS) structure containing a HfO2 control gate, a Ge nanocrystal-embedded HfO2 dielectric and a HfO2/SiO2 stack layer as tunnel oxide, was fabricated by an electron-beam evaporation method. High-resolution transmission electron microscopy study revealed that the HfO2/SiO2 stack layer minimized Ge penetration, leading to the formation of Ge nanocrystals that are self-aligned between the tunnel oxide and the capping HfO2 layer. Influence of different annealing conditions on the formation and distribution of Ge nanocrystals was studied. Current-voltage (I -V) and capacitance-voltage (C-V) measurements revealed promising electrical characteristics of the MIS structure, and relatively high stored charge density of 1012cm-2 was achieved.

  7. 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.

  8. 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.

  9. Electronic structure and charge injection at interface between electrode and liquid-crystalline semiconductor

    NASA Astrophysics Data System (ADS)

    Toda, Tohru; Hanna, Jun-ichi; Tani, Tadaaki

    2007-01-01

    The measurement and analysis of the current-voltage characteristics of a liquid-crystalline organic semiconductor 2-(4'-octyphenyl)-6-dodecyloxynaphthalene (8-PNP-O12) in contact with electrodes of Pt, Au, ITO, Cr, and Al (in the order of work function) have revealed that the injection of holes from the electrodes of Pt, Au, and indium tin oxide to 8-PNP-O12 takes place according to the Richardson-Schottky model and that an electric double layer is formed at the interface between each of these electrodes and 8-PNP-O12, making it difficult to inject holes from the former to the latter.

  10. Spatially resolved charge transport study in discotic liquid crystalline organic semiconductors

    NASA Astrophysics Data System (ADS)

    Paul, Sanjoy; Semyonov, Alexander; Dawson, Nathan J.; Singer, Kenneth D.; Twieg, Robert J.; Ellman, Brett

    Spatially resolved time-of-flight photogeneration and mobility have been measured on a discotic liquid crystalline organic semiconductor using scanning time-of-flight microscopy (STOFm). STOFm simultaneously obtains time-of-flight transients and polarized transmittance across the sample. Various shapes in time-of-flight transients were observed and extracted charge transport parameters such as photogeneration efficiency, mobility, and trapping show significant spatial variation. In some cases these can be linked to electrode surface inhomogeneities. Detailed measurement methodology, experimental results and challenges in their analysis will be discussed.

  11. Photoluminescence study of p-type CdGeAs2 ordered semiconductor crystals

    NASA Astrophysics Data System (ADS)

    McCrae, J. E.; Hengehold, R. L.; Yeo, Y. K.; Ohmer, M. C.; Schunemann, P. G.

    1997-01-01

    Results of a photoluminescence (PL) study as a function of excitation laser power, sample temperature, crystal orientation, and polarization are reported for the nonlinear optical material CdGeAs2. One broad weak PL peak near 0.38 eV, and another somewhat narrower and often far brighter PL peak near 0.55 eV were found at 4 K. The high energy PL peak shifts first towards lower, then higher, and back to lower energies again as the temperature increases from 2.2 to 295 K. This high energy peak is attributed to donor-acceptor pair dominant transitions at low temperatures, but it is attributed to band-to-band dominant transitions at higher temperatures. Strongly polarized PL was observed with the E field of the PL parallel to the material's c axis, and a polarization ratio as high as 6:1 was obtained.

  12. 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.

  13. 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

  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

    2016-01-01

    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

  15. Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe by solid-liquid-coexisting annealing of a-GeSn/c-Si structures

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe on Si substrates is strongly desired to realize advanced electronic and optical devices, which can be merged onto Si large-scale integrated circuits (LSI). To achieve this, annealing characteristics of a-GeSn/c-Si structures are investigated under wide ranges of the initial Sn concentrations (0%-26%) and annealing conditions (300-1000 °C, 1 s-48 h). Epitaxial growth triggered by SiGe mixing is observed after annealing, where the annealing temperatures necessary for epitaxial growth significantly decrease with increasing initial Sn concentration and/or annealing time. As a result, Ge-rich (˜80%) SiGe layers with Sn concentrations of ˜2% are realized by ultra-low temperature annealing (300 °C, 48 h) for a sample with the initial Sn concentration of 26%. The annealing temperature (300 °C) is in the solid-liquid coexisting temperature region of the phase diagram for Ge-Sn system. From detailed analysis of crystallization characteristics and composition profiles in grown layers, it is suggested that SiGe mixing is generated by a liquid-phase reaction even at ultra-low temperatures far below the melting temperature of a-GeSn. This ultra-low-temperature growth technique of Ge-rich SiGe on Si substrates is expected to be useful to realize next-generation LSI, where various multi-functional devices are integrated on Si substrates.

  16. 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.

  17. Simulations of Liquid III-V and II-VI Semiconductors: Semiconducting versus Metallic Behavior.

    NASA Astrophysics Data System (ADS)

    Godlevsky, V.

    2000-03-01

    All III-V group semiconductors exhibit metallic behavior when melted. The coordination number of these materials changes from 4 in the bulk to ~ 6 in the liquid phase. With the increase of the coordination number and compositional disorder common to liquid III-V semiconductors, the covalent bonds of these materials are predominantly replaced by metallic bonds. Electron delocalization and high atomic randomization result in a large entropy change during the solidarrowliquid transition. Unlike III-V compounds, a number of II-VI semiconductors (e.g. CdTe, ZnTe and HgS) experience a semiconductorarrowsemiconductor transition upon melting. These compounds retain their fourfold coordination in the liquid phase. In our work, we perform ab initio simulations of liquid GaAs (l-GaAs) and CdTe (l-CdTe), as representatives of III-V and II-VI materials.(V. Godlevsky, J. Derby, and J.R. Chelikowsky, Phys. Rev. Lett. 81), 4959 (1998) As opposed to the more close-packed l-GaAs, l-CdTe has an open fourfold structure. Besides the coordination number, l-CdTe also retains some of its crystalline compositional features (e.g. there are fewer ``wrong'' bond defects than in l-GaAs). In l-CdTe, the density of states has a dip at the Fermi level indicating the semiconducting character of electrical conductivity in this material. The d.c. conductivity in l-CdTe is by two orders of magnitude lower than that in l-GaAs. The small change in the structural order and electron delocalization is in good agreement with the small entropy change observed experimentally during the melting of CdTe. As the temperature increases further, l-CdTe undergoes a fourfold-sixfold transition accompanied by the disappearing of band gap. The d.c. conductivity of sixfold coordinated l-CdTe is by an order of magnitude larger than the d.c. conductivity of fourfold coordinated l-CdTe.(V. Godlevsky, M. Jain, J. Derby, and J.R. Chelikowsky, Phys. Rev. B, 60), 8640 (1999)

  18. 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.

  19. IV-VI diluted magnetic semiconductor Ge{sub 1-x}Mn{sub x}Te epilayer grown by molecular beam epitaxy

    SciTech Connect

    Fukuma, Y.; Goto, K.; Senba, S.; Miyawaki, S.; Asada, H.; Koyanagi, T.; Sato, H.

    2008-03-01

    Growth of the IV-VI diluted magnetic semiconductor Ge{sub 1-x}Mn{sub x}Te by molecular beam epitaxy is reported. The epitaxial growth of Ge{sub 1-x}Mn{sub x}Te (x=0.13) on BaF{sub 2} (111) with a GeTe buffer layer is confirmed by x-ray diffraction and reflection high-energy electron diffraction. The ferromagnetic order is clearly established by the magnetization and magnetotransport measurements. The Curie temperature of 100 K is obtained for the hole concentration of 7.86x10{sup 20} cm{sup -3}. The existence of the strong p-d exchange which gives rise to the ferromagnetic order is revealed by the hard x-ray photoemission measurements.

  20. 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.

  1. 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.

  2. Cation ordering and physicochemical characterization of the quaternary diamond-like semiconductor Ag{sub 2}CdGeS{sub 4}

    SciTech Connect

    Brunetta, Carl D.; Minsterman, William C.; Lake, Charles H.; Aitken, Jennifer A.

    2012-03-15

    The quaternary diamond-like semiconductor, Ag{sub 2}CdGeS{sub 4}, was synthesized via high-temperature solid-state synthesis as well as structurally and physicochemically characterized. Single crystal X-ray diffraction provided a model for Ag{sub 2}CdGeS{sub 4} in the orthorhombic, noncentrosymmetric space group Pna2{sub 1} with a=13.7415(8) A, b=8.0367(5) A and c=6.5907(4) A, in contrast to a previously published model in Pmn2{sub 1} from the Rietveld analysis of laboratory X-ray powder diffraction data. The Pna2{sub 1} space group is supported by the Rietveld analysis of synchrotron X-ray powder diffraction data. Differential thermal analysis suggests that Ag{sub 2}CdGeS{sub 4} exists in two polymorphs. Optical diffuse reflectance UV/vis/NIR spectroscopy indicates that the orange compound is a semiconductor with a band gap of 2.32 eV. Optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and inductively coupled plasma optical emission spectroscopy were used to further characterize the material. - Graphical abstract: The structure of the diamond-like semiconductor Ag{sub 2}CdGeS{sub 4} has been solved and refined in the orthorhombic noncentrosymmetric space group Pna2{sub 1}. A view down the a-axis shows that all MS{sub 4} tetrahedra are pointing in the same direction along the c-axis. The structure can be derived from that of lonsdaleite. Highlights: Black-Right-Pointing-Pointer The structure of Ag{sub 2}CdGeS{sub 4} is solved from single crystal X-ray diffraction. Black-Right-Pointing-Pointer The structure is supported by the Rietveld analysis of synchrotron diffraction data. Black-Right-Pointing-Pointer Ag{sub 2}CdGeS{sub 4} is a semiconductor with an optical band gap of 2.32 eV. Black-Right-Pointing-Pointer Additional characterization is reported.

  3. Influence of Temperature Variation on Field Effect Transistor Properties Using a Solution-Processed Liquid Crystalline Semiconductor, 8TNAT8.

    PubMed

    Monobe, Hirosato; Kimoto, Masaomi; Shimizu, Yo

    2016-04-01

    In this study, we used a liquid crystalline (LC) semiconductor, 8TNAT8, solution (e.g., 0.1 wt% in toluene) for forming an organic semiconductor layer by solution casting method, and fabricated bottom-gate/bottom-contact type field effect transistors (FETs). These LC semiconductors show FET characteristic properties and have high carrier mobility of 0.01 cm2 V-1 s-1. We have investigated the surface morphology and the influence of temperature variation on LC FET properties across the phase transition from crystal to mesophase of a LC semiconductor, 8TNAT8. In the most cases, FET mobility was irreversibly decreased after. temperature heat stress above the melting point of 8TNAT8, owing to the morphological change of LC layer. PMID:27451617

  4. 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

    2015-02-01

    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. PMID:25530025

  5. 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.

  6. A wave packet model for electron transfer and its implications for the semiconductor-liquid interface

    SciTech Connect

    Smith, B.B.; Nozik, A.J.

    1999-11-11

    This paper establishes the computational feasibility and examines the implications of a particular technique for simulations of time dependent electron transfer (ET) at semiconductor-liquid interfaces (SLIs). The methodology uses a one electron formalism employing wave packets, pseudopotentials, and molecular dynamics, which the authors dub WPMD. They describe a detailed mechanism for SLI ET by using the methodology. The model is versatile enough to address conventional SLI ET, surface state and adsorption mediated ET, photoexcited ET, and ET between quantum dots and other microstructures. They contrast the perspectives of their WPMD model of SLI ET with those in traditional literature and find substantial differences. The use of standard Landau-Zener theory for SLI ET is found particularly problematic.

  7. Hole Confinement and 1/ f Noise Characteristics of SiGe Double-Quantum-Well p-Type Metal-Oxide-Semiconductor Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Lin, Yu Min; Wu, San Lein; Chang, Shoou Jinn; Chen, Pang Shiu; Liu, Chee Wee

    2006-05-01

    A working p-type SiGe double-quantum-well metal-oxide-semiconductor field effect transistor (DQW-pMOSFETs) has been fabricated and characterized. The upper quantum well with 15%-Ge acts as an induced-carrier buffer to slow holes into the Si surface channel and increases the number of high-mobility holes in the 30%-Ge well at the bottom under high gate voltage by improving carrier confinement. DQW devices with a thinner Si-spacer layer between the two SiGe quantum wells exhibit an improved effective hole mobility and wider gate voltage swings but also reduced 1/ f noise levels than Si-controlled pMOSFETs. The DQW has an enhanced carrier confinement compared to a single quantum-well (SQW) device; however, the degradation of mobility and transconductance observed in a sample DQW indicates that this poor transport mechanism may result from an additional hole scattering effect at the Si/SiGe interface.

  8. Standardization of 68Ge/68Ga Using Three Liquid Scintillation Counting Based Methods

    PubMed Central

    Zimmerman, B. E.; Cessna, J. T.; Fitzgerald, R.

    2008-01-01

    A solution containing 68Ge in equilibrium with its daughter, 68Ga, has been standardized for the first time at the National Institute of Standards and Technology (NIST) using 3 liquid scintillation-based techniques: live-timed 4πβ -γ anticoincidence (LTAC) counting, the Triple-to-Double Coincidence Ratio (TDCR) method, and 3H-standard efficiency tracing with the CIEMAT1/NIST (CNET) method. The LTAC technique is much less dependent on level scheme data and model-dependent parameters and was thus able to provide a reference activity concentration value for the master solution with a combined standard uncertainty of about 0.3 %. The other two methods gave activity concentration values with respective differences from the reference value of +1.2 % and −1.5 %, which were still within the experimental uncertainties. Measurements made on the NIST “4π”γ secondary standard ionization chamber allowed for the determination of calibration factors for that instrument, allowing future calibrations to be made for 68Ge/68Ga without the need for a primary measurement. The ability to produce standardized solutions of 68Ge presents opportunities for the development of a number of NIST-traceable calibration sources with very low (<1 %) relative standard uncertainties that can be used in diagnostic medical imaging. PMID:27096126

  9. Epitaxial GeSn film formed by solid phase epitaxy and its application to Yb{sub 2}O{sub 3}-gated GeSn metal-oxide-semiconductor capacitors with sub-nm equivalent oxide thickness

    SciTech Connect

    Lee, Ching-Wei; Wu, Yung-Hsien; Hsieh, Ching-Heng; Lin, Chia-Chun

    2014-11-17

    Through the technique of solid phase epitaxy (SPE), an epitaxial Ge{sub 0.955}Sn{sub 0.045} film was formed on a Ge substrate by depositing an amorphous GeSn film followed by a rapid thermal annealing at 550 °C. A process that uses a SiO{sub 2} capping layer on the amorphous GeSn film during SPE was proposed and it prevents Sn precipitation from occurring while maintaining a smooth surface due to the reduced surface mobility of Sn atoms. The high-quality epitaxial GeSn film was observed to have single crystal structure, uniform thickness and composition, and tiny surface roughness with root mean square of 0.56 nm. With a SnO{sub x}-free surface, Yb{sub 2}O{sub 3}-gated GeSn metal-oxide-semiconductor (MOS) capacitors with equivalent oxide thickness (EOT) of 0.55 nm were developed. A small amount of traps inside the Yb{sub 2}O{sub 3} was verified by negligible hysteresis in capacitance measurement. Low leakage current of 0.4 A/cm{sup 2} at gate bias of flatband voltage (V{sub FB})-1 V suggests the high quality of the gate dielectric. In addition, the feasibility of using Yb{sub 2}O{sub 3} to well passivate GeSn surface was also evidenced by the small interface trap density (D{sub it}) of 4.02 × 10{sup 11} eV{sup −1} cm{sup −2}, which can be attributed to smooth GeSn surface and Yb{sub 2}O{sub 3} valency passivation. Both leakage current and D{sub it} performance outperform other passivation techniques at sub-nm EOT regime. The proposed epitaxial GeSn film along with Yb{sub 2}O{sub 3} dielectric paves an alternative way to enable high-performance GeSn MOS devices.

  10. Nitride-Based UV Metal-Insulator-Semiconductor Photodetector with Liquid-Phase-Deposition Oxide

    NASA Astrophysics Data System (ADS)

    Hwang, J. D.; Yang, Gwo Huei; Yang, Yuan Yi; Yao, Pin Cuan

    2005-11-01

    A low-temperature (30-40°C), low-cost and reliable method of liquid phase deposition (LPD) has been employed to grow SiO2 layers on GaN. The LPD process uses a supersaturated acid aqueous solution of hydrofluosilicic (H2SiF6) as a source liquid and an aqueous solution of boric acid (H3BO3) as a deposition rate controller. In this study, the LPD SiO2 was prepared at 40°C with concentrations of H2SiF6 and H3BO3 at 0.2 and 0.01 M, respectively. The minimum interface-trap density, Dit, of a metal-insulator-semiconductor (MIS) capacitor with a structure of Al/20 nm LPD-SiO2/n-GaN was estimated to be 8.4× 1011 cm-2 V-1. Furthermore, a MIS photodetector with a 10-nm-thick LPD-SiO2 layer has been fabricated successfully. The dark current density was as low as 4.41× 10-6 A/cm2 for an applied field of 4 MV/cm. A maximum responsivity of 0.112 A/W was observed for incident ultraviolet light of 366 nm with an intensity of 4.15 mW/cm2. Defect-assisted tunneling was invoked to explain these results.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    PubMed

    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∥/I⊥ = 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. PMID:27203222

  14. 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

  15. Vapor-liquid-soild growth of group IV (Si, Ge, Si1-xGe x) single and heterostructured nanowires

    NASA Astrophysics Data System (ADS)

    Minassian, Sharis

    In this thesis, an alternative Si source, disilane (Si2H 6) has been investigated which is of interest since it is more reactive than SiH4 and therefore may enable higher growth rates at lower temperature and lower partial pressures. The lower thermal stability of Si 2H6 could also be an advantage to enable the growth of Si 1-xGex nanowires over the entire composition range at lower temperatures which are more compatible with the range of conditions typically used for Ge nanowire growth and in turn may enable the fabrication of different types of heterostructures. To fulfill the objective of this research, a systematic study has been developed to explore the growth of group IV (Si, Ge, and Si 1-xGex alloy) single and heterostructured nanowires from Si2H6 and GeH4 precursors. First, the growth kinetics of individual SiNWs from Si2H 6 was investigated by examining the effects of growth parameters on their growth rate. The results were compared to that obtained with SiH 4. In addition, to gain a better insight into the SiNW growth process, the results were also compared with Si films deposited under similar conditions inside the same reactor. Overall compared to SiH4, the use of Si 2H6 enabled higher growth rates for both SiNWs and Si films. For both gases, a nonlinearity was observed in the growth rate of nanowire as a function of gas partial pressure which was explained by a simple decomposition mechanism including the adsorption, desorption and incorporation of precursor molecule on the Au droplet surface. The apparent activation energy of the process was found to be identical for both gases under the conditions examined in the present study, suggesting similar rate-determining step in the nanowire growth process from the two precursors. Upon completion of studies on SiNW growth, the synthesis parameter space was then determined for undoped GeNWs and the influence of growth conditions on their morphology as well as their growth rate was examined. It was found that

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  17. A systematic study of the optical and electrical properties of Ge1-ySny and Ge1-x-ySixSn y semiconductor alloys

    NASA Astrophysics Data System (ADS)

    Harris, Thomas R.

    In order to fully utilize newly developed Ge1-ySny and Ge1-x-ySixSny materials for new novel optoelectronic devices, the optical and electrical properties of these alloys were investigated using photoluminescence (PL) and Hall-effect measurements. Direct bandgap PL emission was observed from almost all the samples, making them very promising candidates for Si-based light emitting devices. T-dependent PL studies also indicate that the indirect-to-direct bandgap transition of Ge1-ySny alloys might take place at a much lower Sn content than the theory predicts. T-dependent Hall-effect measurements showed both degenerate parallel conducting layers as well as a conductivity type change from p to n at around 370-435 K, which could affect the operation of devices made from these materials. Etch studies were performed to determine the properties of the epilayers alone. Reasonable results for the average volume carrier density in the film were obtained. It was also found that there exists high level of surface states at the surface of almost all the samples. These studies should be very useful for the development of practical devices based on Ge1-ySny alloys.

  18. Optimization of SiGe selective epitaxy for source/drain engineering in 22 nm node complementary metal-oxide semiconductor (CMOS)

    NASA Astrophysics Data System (ADS)

    Wang, G. L.; Moeen, M.; Abedin, A.; Kolahdouz, M.; Luo, J.; Qin, C. L.; Zhu, H. L.; Yan, J.; Yin, H. Z.; Li, J. F.; Zhao, C.; Radamson, H. H.

    2013-09-01

    SiGe has been widely used for source/drain (S/D) engineering in pMOSFETs to enhance channel mobility. In this study, selective Si1-xGex growth (0.25 ≤ x ≤ 0.35) with boron concentration of 1-3 × 1020 cm-3 in the process for 22 nm node complementary metal-oxide semiconductor (CMOS) has been investigated and optimized. The growth parameters were carefully tuned to achieve deposition of high quality and highly strained material. The thermal budget was decreased to 800 °C to suppress dopant diffusion, to minimize Si loss in S/D recesses, and to preserve the S/D recess shape. Two layers of Si1-xGex were deposited: a bottom layer with high Ge content (x = 0.35) which filled the recess and a cap layer with low Ge content (x = 0.25) which was elevated in the S/D regions. The elevated SiGe cap layer was intended to be consumed during the Ni-silicidation process in order to avoid strain reduction in the channel region arising from strain relaxation in SiGe S/D. In this study, a kinetic gas model was also applied to predict the pattern dependency of the growth and to determine the epi-profile in different transistor arrays. The input parameters include growth temperature, partial pressures of reactant gases, and chip layout. By using this model, the number of test wafers for epitaxy experiments can be decreased significantly. When the epitaxy process parameters can be readily predicted by the model for epi-profile control in an advanced chip design, fast and cost-effective process development can be achieved.

  19. Designer hydride routes to 'Si-Ge'/(Gd,Er)2O3/Si(1 1 1) semiconductor-on-insulator heterostructures

    NASA Astrophysics Data System (ADS)

    Watkins, Tylan; Jiang, Liying; Smith, D. J.; Chizmeshya, A. V. G.; Menendez, J.; Kouvetakis, J.

    2011-12-01

    We demonstrate Si-Ge integration on engineered M2O3/Si(1 1 1) (M = Gd,Er) dielectric buffer layers using non-traditional chemical precursors that provide new levels of functionality within the deposition process. Stoichiometric Si0.50Ge0.50 alloys and pure Si heterostructures are grown epitaxially via ultra-low-temperature chemical vapor deposition using SiH3GeH3 and Si3H8/Si4H10, respectively. In the case of Si on Gd2O3, an optimal growth processing window in the range of 500-600 °C was found to yield planar layers with monocrystalline structures via a proposed coincidence lattice matching mechanism (2aSi-aGd2O3), while for the SiGe system (2% lattice mismatch) comparable quality films with fully relaxed strain states are deposited at a lower temperature range of 420-450 °C. Extension of this growth process to Si on Er2O3 yields remarkably high-quality layers in spite of the even larger ~3% lattice mismatch. In all cases, the Si-Ge overlayers are found to primarily adopt an A-B-A epitaxial alignment with respect to the M2O3 buffered Si(1 1 1). A comparative study of the Si growth using Si3H8 and Si4H10 indicates that both compounds provide an efficient and straightforward process for semiconductor growth on Gd2O3/Si(1 1 1), which appears to be more viable than conventional approaches from the point of view of scalability and volume.

  20. 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.

  1. Strained Germanium-Tin (GeSn) P-Channel Metal-Oxide-Semiconductor Field-Effect Transistors Featuring High Effective Hole Mobility

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Yan, Jing; Wang, Hongjuan; Cheng, Buwen; Han, Genquan

    2015-06-01

    Compressively strained and p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) are fabricated with low-temperature surface passivation. High crystallinity GeSn films epitaxially grown on a Ge(001) substrate are used for the device fabrication. The impacts of the Sn composition on the subthreshold swing , threshold voltage , on-state current , and effective hole mobility of the devices are investigated. GeSn pMOSFETs with different Sn compositions show a similar , indicating almost the same midgap density of interface states . A positive shift of with an increase of the Sn composition is observed. A pMOSFET exhibits a significant improvement in as compared to a device with a lower Sn composition, which is due to the superior hole mobility in a device with a higher Sn composition. pMOSFETs achieve a peak effective hole mobility of , which is much higher than that of devices. The enhancement of the compressive strain and chemical effect in the channel region with increased Sn composition leads to an improvement of.

  2. Important role of the non-uniform Fe distribution for the ferromagnetism in group-IV-based ferromagnetic semiconductor GeFe

    SciTech Connect

    Wakabayashi, Yuki K.; Ohya, Shinobu; Ban, Yoshisuke; Tanaka, Masaaki

    2014-11-07

    We investigate the growth-temperature dependence of the properties of the group-IV-based ferromagnetic semiconductor Ge{sub 1−x}Fe{sub x} films (x = 6.5% and 10.5%), and reveal the correlation of the magnetic properties with the lattice constant, Curie temperature (T{sub C}), non-uniformity of Fe atoms, stacking-fault defects, and Fe-atom locations. While T{sub C} strongly depends on the growth temperature, we find a universal relationship between T{sub C} and the lattice constant, which does not depend on the Fe content x. By using the spatially resolved transmission-electron diffractions combined with the energy-dispersive X-ray spectroscopy, we find that the density of the stacking-fault defects and the non-uniformity of the Fe concentration are correlated with T{sub C}. Meanwhile, by using the channeling Rutherford backscattering and particle-induced X-ray emission measurements, we clarify that about 15% of the Fe atoms exist on the tetrahedral interstitial sites in the Ge{sub 0.935}Fe{sub 0.065} lattice and that the substitutional Fe concentration is not correlated with T{sub C}. Considering these results, we conclude that the non-uniformity of the Fe concentration plays an important role in determining the ferromagnetic properties of GeFe.

  3. Liquid phase electroepitaxial bulk growth of binary and ternary alloy semiconductors under external magnetic field

    NASA Astrophysics Data System (ADS)

    Sheibani, Hamdi

    2002-01-01

    Liquid Phase Electroepitaxy (LPEE) and is a relatively new, promising technique for producing high quality, thick compound semiconductors and their alloys. The main objectives are to reduce the adverse effect of natural convection and to determine the optimum growth conditions for reproducible desired crystals for the optoelectronic and electronic device industry. Among the available techniques for suppressing the adverse effect of natural convection, the application of an external magnetic field seems the most feasible one. The research work in this dissertation consists of two parts. The first part is focused on the design and development of a state of the art LPEE facility with a novel crucible design, that can produce bulk crystals of quality higher than those achieved by the existing LPEE system. A growth procedure was developed to take advantage of this novel crucible design. The research of the growth of InGaAs single crystals presented in this thesis will be a basis for the future LPEE growth of other important material and is an ideal vehicle for the development of a ternary crystal growth process. The second part of the research program is the experimental study of the LPEE growth process of high quality bulk single crystals of binary/ternary semiconductors under applied magnetic field. The compositional uniformity of grown crystals was measured by Electron Probe Micro-analysis (EPMA) and X-ray microanalysis. The state-of-the-art LPEE system developed at University of Victoria, because of its novel design features, has achieved a growth rate of about 4.5 mm/day (with the application of an external fixed magnetic field of 4.5 KGauss and 3 A/cm2 electric current density), and a growth rate of about 11 mm/day (with 4.5 KGauss magnetic field and 7 A/cm2 electric current density). This achievement is simply a breakthrough in LPEE, making this growth technique absolutely a bulk growth technique and putting it in competition with other bulk growth techniques

  4. 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).

  5. Elastic, vibrational and thermodynamic properties of α-Sn based group IV semiconductors and GeC under pressure

    NASA Astrophysics Data System (ADS)

    Souadkia, M.; Bennecer, B.; Kalarasse, F.

    2013-11-01

    We present first-principles calculations of the structural, elastic, vibrational and thermodynamic properties of SnSi, SnGe, SnC and GeC. We employ the density-functional perturbation theory (DFPT) within the local density approximation in conjunction with the quasi-harmonic approximation. The calculated lattice parameters, which are obtained by minimizing the total energy, are in the range of those reported in the literature for the binary compounds and in good agreement with the measured ones for the elemental components. Our results for the elastic properties show that c44 softens as pressure increases for SnSi and SnGe. The phonon spectra, the density of states and the Born effective charge at zero pressure are calculated and the phonon frequencies are positive. A pressure induced soft transverse acoustic phonon mode is identified at the zone boundary X point of the Brillouin zone at pressure of 12.95 and 12.45 GPa for SnSi and SnGe respectively. The linear expansion coefficient for the elemental components is calculated and compared to experiment. The temperature and pressure dependence of the thermal expansion, the overall Grüneisen parameter, the bulk modulus and the heat capacity is predicted. The thermal expansion coefficient decreases with increasing pressure and does not show any negative behavior for GeC and this is due to the positive transverse acoustic mode Grüneisen parameters. Our results for SnxGe alloys using the supercell method indicate that the variation of the Grüneisen parameter and the thermal expansion with concentration has the same trend and the bulk modulus softens.

  6. 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.

  7. 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.

  8. Micropipe healing in SiC wafers by liquid-phase epitaxy in Si Ge melts

    NASA Astrophysics Data System (ADS)

    Filip, O.; Epelbaum, B.; Bickermann, M.; Winnacker, A.

    2004-10-01

    Liquid-phase epitaxy (LPE) of silicon carbide (SiC) was shown to be an effective technique to overgrow micropipe defects (MP) in SiC wafers prepared by the physical vapour transport (PVT) technique. Growth close to thermodynamic equilibrium, e.g. low supersaturation, provides a favourable condition for effective MP healing. Therefore, the aim of this work was to grow epitaxial layers from strongly diluted Si-based solutions. Using the method of horizontal dipping, the dependence of MP elimination efficiency on Si-Ge flux composition and on the crystallographic orientation (on- and off-axis) of the SiC wafer was investigated. High-quality single crystalline SiC layers of a thickness up to 10 μm were grown with the growth rate of 0.5 μm/h. On off-oriented wafers, stepped growth morphology was observed independent of the melt composition. Micropipes with the diameter below 5 μm were closed with an efficiency of about 80%. SEM investigations as well as inspection under reflected/transmitted light did not show any specific distortion of the growth morphology at the micropipe healing place.

  9. Numerical study of liquid phase diffusion growth of SiGe subjected to accelerated crucible rotation

    NASA Astrophysics Data System (ADS)

    Sekhon, M.; Lent, B.; Dost, S.

    2016-03-01

    The effect of accelerated crucible rotation technique (ACRT) on liquid phase diffusion (LPD) growth of SixGe1-x crystal has been investigated numerically. Transient, axisymmetric simulations have been carried out for triangular and trapezoidal ACRT cycles. Natural convection driven flow in the early growth hours is found to be modified by the ACRT induced Ekman flow. Results also reveal that a substantial mixing in the solution can be induced by the application of ACRT in the later hours of growth which is otherwise a diffusion dominated growth period for LPD growth technique. A comparison is drawn to the cases of stationary crucible and crucible rotating at a constant speed examined previously for this growth system by Sekhon and Dost (J. Cryst. Growth 430 (2015) 63). It is found that a superior interface flattening effect and radial compositional uniformity along the growth interface can be accomplished by employing ACRT at 12 rpm than that which could be achieved by using steady crucible rotation at 25 rpm, owing to the higher time averaged growth velocity achieved in the former case. Furthermore, minor differences are also predicted in the results obtained for trapezoidal and triangular ACRT cycles.

  10. 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.

  11. Infrared nonlinear optical properties of lithium-containing diamond-like semiconductors Li2ZnGeSe4 and Li2ZnSnSe4.

    PubMed

    Zhang, Jian-Han; Clark, Daniel J; Brant, Jacilynn A; Sinagra, Charles W; Kim, Yong Soo; Jang, Joon I; Aitken, Jennifer A

    2015-06-28

    Two new lithium-containing diamond-like semiconductors, Li2ZnGeSe4 and Li2ZnSnSe4, have been prepared by high-temperature, solid-state synthesis. Single crystal X-ray diffraction reveals that both compounds adopt the wurtz-kesterite structure type, crystallizing in the noncentrosymmetric space group Pn. X-ray powder diffraction coupled with Rietveld refinement indicates the high degree of phase purity in which the materials are prepared. Both compounds display optical bandgaps around 1.8 eV, wide optical transparency windows from 0.7 to 25 μm and type-I phase matched second harmonic generation starting at 2500 nm and persisting deeper into the infrared. Using the Kurtz powder method, the second-order nonlinear optical coefficient, χ((2)), was estimated to be 19 and 23 pm V(-1) for Li2ZnGeSe4 and Li2ZnSnSe4, respectively. Using a 1064 nm incident laser beam with a pulse width (τ) of 30 ps both compounds exhibit a laser damage threshold of 0.3 GW cm(-2), which is higher than that of the AgGaSe2 reference material measured under identical conditions. Differential thermal analysis shows that the title compounds are stable up to 684 and 736 °C, respectively. These properties collectively demonstrate that Li2ZnGeSe4 and Li2ZnSnSe4 have great potential for applications in tunable laser systems, especially in the infrared and even up to the terahertz regime. Electronic structure calculations using a plane-wave pseudopotential method within density functional theory provide insight regarding the nature of the bandgap and bonding. PMID:26006322

  12. 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

  13. ``Seedless'' vapor-liquid-solid growth of Si and Ge nanowires: The origin of bimodal diameter distributions

    NASA Astrophysics Data System (ADS)

    Dailey, Eric; Drucker, Jeff

    2009-03-01

    We identify a previously uncharacterized vapor-liquid-solid growth mode that can produce small diameter, epitaxial ⟨110⟩ oriented Si and Ge nanowires (NWs). Disilane or digermane pyrolysis evolves H2 causing the monolayer thick Au/Si(111) layer between three dimensional Au seeds to dewet and form small Au islands. Under some conditions, these small islands facilitate "seedless" growth of small diameter NWs distinct from larger NWs that grow from the deposited seeds leading to a bimodal diameter distribution. We identify the precursor pressures and growth temperature regimes for which Si and Ge NW growth occurs in the absence of deposited seeds from the dewetted Au/Si(111) layer.

  14. Study on Momentum Density in Semiconductor Alloys GeC and SnC by Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Amrane, N.

    The independent particle model (IPM) coupled with empirical pseudopotential method (EPM) was used to compute the thermalized positron charge densities in specific family of binary tetrahedrally coordinated crystals of formula ANB8-N. Initial results show a clear asymmetrical positron charge distribution relative to the bond center. It is observed that the positron density is maximum in the open interstices and is excluded not only from the ion cores but also to a considerable degree from the valence bonds. Electron-positron momentum densities are calculated for the (001, 110) planes. The results are used to analyze the positron effects in GeC and SnC. Our computational technique provides the theoretical means of interpreting the k-space densities obtained experimentally using the two-dimensional angular correlation of annihilation radiation (2D-ACAR).

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

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

    DOE PAGESBeta

    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

  1. Synthesis and properties of Si and SiGe/Si nanowires

    NASA Astrophysics Data System (ADS)

    Redwing, Joan M.; Lew, Kok-Keong; Bogart, Timothy E.; Pan, Ling; Dickey, Elizabeth C.; Carim, A. H.; Wang, Yanfeng; Cabassi, Marco A.; Mayer, Theresa S.

    2004-06-01

    The fabrication of semiconductor nanowires, in which composition, size and conductivity can be controlled in both the radial and axial direction of the wire is of interest for fundamental studies of carrier confinement as well as nanoscale device development. In this study, group IV semiconductor nanowires, including Si, Ge and SixGe1-x alloy nanowires were fabricated by vapor-liquid-solid (VLS) growth using gaseous precursors. In the VLS process, gold is used to form a liquid alloy with Si and Ge which, upon supersaturation, precipitates a semiconductor nanowire. Nanoporous alumina membranes were used as templates for the VLS growth process, in order to control the diameter of the nanowires over the range from 45 nm to 200 nm. Intentional p-type and n-type doping was achieved through the addition of either trimethylboron, diborane or phosphine gas during nanowire growth. The electrical properties of undoped and intentionally doped silicon nanowires were characterized using field-assisted assembly to align and position the wires onto pre-patterned test bed structures. The depletion characteristics of back-gated nanowire structures were used to determine conductivity type and qualitatively compare dopant concentration. SiGe and SiGe/Si axial heterostructure nanowires were also prepared through the addition of germane gas during VLS growth. The Ge concentration in the wires was controllable over the range from 12 % to 25% by varying the inlet GeH4/SiH4 ratio.

  2. 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.

  3. 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

  4. Evolution of ferromagnetic and non-Fermi-liquid states with doping: The case of Ru-doped UCoGe

    NASA Astrophysics Data System (ADS)

    Vališka, Michal; Pospíšil, Jiří; Diviš, Martin; Prokleška, Jan; Sechovský, Vladimír; Abd-Elmeguid, Mohsen M.

    2015-07-01

    We have investigated the impact of Ru substitution for Co on the behavior of the ferromagnetic superconductor UCoGe by performing x-ray diffraction, magnetization, specific heat, and electrical resistivity measurements on polycrystalline samples of the UCo1 -xRuxGe series (0 ≥x ≤0.9 ) . The initial Ru substitution up to x ≈0.1 leads to a simultaneous sharp increase of the Curie temperature and spontaneous magnetization up to maximum values of TC=8.6 K and MS=0.1 μB per formula unit, respectively, whereas superconductivity vanishes already for x ≈0.03 . Further increase of the Ru content beyond x ≈0.1 leads to a precipitous decrease of both TC and MS towards a ferromagnetic quantum critical point (QCP) at xcr=0.31 . Consequently, the T -x magnetic phase diagram consists of a well-developed ferromagnetic dome. We discuss the evolution of ferromagnetism with x on the basis of band structure changes due to varying 5 f -ligand hybridization. This scenario is supported by the results of electronic structure calculations and consideration of the simplified periodic Anderson model. The analysis of the temperature dependencies of the electrical resistivity and heat capacity at low temperatures of the samples in the vicinity of the QCP reveals a non-Fermi-liquid behavior and assigns the ferromagnetic quantum phase transition to be most likely of a continuous Hertz-Millis type.

  5. Facile liquid phase deposition of thick reflective GeO2 film for hollow waveguide delivery of CO2 laser radiation

    NASA Astrophysics Data System (ADS)

    Jing, Chengbin; Hou, Jinxia; Xu, Xinguang; Zhang, Yongheng

    2008-02-01

    A new idea of using LPD (liquid phase deposition) to prepare a GeO2 thick reflective film for hollow waveguide delivery of CO2 laser radiation was investigated in this work. The LPD process was achieved by designedly adding acid to GeO2-aqueous ammonia. The addition of acid could induce the transformation of germanate ions into GeO2 solutes, leading to the deposition of a GeO2 ceramic film when the concentration of GeO2 solute is higher than its saturation solubility. It was found that the highest film growth rate occurred at a pH value of 3, while a film with low surface roughness and good adhesion to the substrate was produced at a pH value of 2 and the film could be converted to a smooth, compact hexagonal GeO2 film by heat treatment at 1120 °C for 30 min. Two abnormal dispersion bands within 7.6-9 μm and 9.6-11.2 μm were mainly caused by the silica glass substrate and the GeO2 film, respectively. The film was thick enough to achieve the total reflectance of the CO2 laser radiation. The use of this GeO2 film in a hollow waveguide structure for CO2 laser radiation delivery is discussed based on the transmission loss and the feasibility of the deposition of the GeO2 film inside silica capillary tubes. The results show that the hollow waveguides with low transmission loss are most likely fabricated at a low cost using the LPD-derived GeO2 reflective film.

  6. Effects of degradation on the performance of a triphenylene based liquid crystal organic semiconductor

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    We report on time-of-flight (TOF) hole mobility measurements in an aged discotic columnar liquid crystal, Hexakis(pentyloxy)triphenylene (HAT5). The experimental data was fit to an interfacial trapping model based on Van de Walle's approximations. The theory accurately reproduces the TOF transients of delayed charge release near the optically excited material/electrode interface. Interfacial trapping appears only in the aged materials, but the bulk mobility is the same as that of the pristine material. We also discuss preliminary results of TOF photocurrent transients of HAT5 exposed to ozone.

  7. Enhancement of photoluminescence from n-type tensile-strained GeSn wires on an insulator fabricated by lateral liquid-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Shimura, Takayoshi; Matsue, Masahiro; Tominaga, Kohei; Kajimura, Keiko; Amamoto, Takashi; Hosoi, Takuji; Watanabe, Heiji

    2015-11-01

    We investigated the optical properties of undoped and n-type GeSn wires fabricated by a lateral liquid-phase epitaxial method. The Sn concentration was approximately 0.5% in the region from the seed to near the wire end. Moreover, the Sn concentration increased to 6% at the wire end, whereas Si diffusion from the seed was enhanced and extended to 200 μm from the seed. Tensile strain gradually decreased from 0.5% close the seed to 0.25% at the wire end. The photoluminescence (PL) peak was red-shifted by Sn incorporation into the Ge wires, and a PL peak at 0.66 eV was observed from the wire end. Upon n-type doping, the PL intensity of the GeSn layers was significantly enhanced to approximately 10 times higher than that of the undoped GeSn wires.

  8. 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.

  9. n-Type silicon photoelectrochemistry in methanol: Design of a 10.1% efficient semiconductor/liquid junction solar cell

    PubMed Central

    Gronet, Chris M.; Lewis, Nathan S.; Cogan, George; Gibbons, James

    1983-01-01

    n-Type Si electrodes in MeOH solvent with 0.2 M (1-hydroxyethyl)ferrocene, 0.5 mM (1-hydroxyethyl)ferricenium, and 1.0 M LiClO4 exhibit air mass 2 conversion efficiencies of 10.1% for optical energy into electricity. We observe open-circuit voltages of 0.53 V and short-circuit quantum efficiencies for electron flow of nearly unity. The fill factor of the cell does not decline significantly with increases in light intensity, indicating substantial reduction in efficiency losses in MeOH solvent compared to previous nonaqueous n-Si systems. Matte etch texturing of the Si surface decreases surface reflectivity and increases photocurrent by 50% compared to shiny, polished Si samples. The high values of the open-circuit voltage observed are consistent with the presence of a thin oxide layer, as in a Schottky metal-insulator-semiconductor device, which yields decreased surface recombination and increased values of open-circuit voltage and short-circuit current. The n-Si system was shown to provide sustained photocurrent at air mass 2 levels (20 mA/cm2) for charge through the interface of >2,000 C/cm2. The n-Si/MeOH system represents a liquid junction cell that has exceeded the 10% barrier for conversion of optical energy into electricity. PMID:16593280

  10. Indium-Tin-Oxide Metal-Insulator-Semiconductor GaN Ultraviolet Photodetectors Using Liquid-Phase-Deposition Oxide

    NASA Astrophysics Data System (ADS)

    Yang, Gow-Huei; Hwang, Jun-Dar; Lan, Chih-Hsueh; Chan, Chien-Mao; Chen, Hone-Zem; Chang, Shoou-Jinn

    2007-08-01

    A low-cost and reliable SiO2 insulating layer was successfully deposited onto GaN by liquid-phase deposition (LPD) using supersaturated H2SiF6 and H3BO3 solutions. The interface-trap density, Dit, was estimated to be 1.2× 1012 cm-2 eV-1 for the as-grown, not annealed LPD-SiO2 layers. It was found that the leakage current density was 2.06× 10-5 A/cm2 at a negative bias of 10 V for the as-grown Al/20 nm LPD-SiO2/GaN metal-insulator-semiconductor (MIS) capacitors. It was also found that the LPD-SiO2 layer could be used to suppress the dark current of nitride-based photodetectors. A large photocurrent to dark-current contrast ratio higher than four orders of magnitude and a maximum responsivity of 0.65 A/W were observed from the fabricated indium-tin-oxide (ITO)/LPD-SiO2/GaN MIS UV photodetectors. These results could be explained by defect-assisted tunneling.

  11. Characterization of supercooled liquid Ge2Sb2Te5 and its crystallization by ultrafast-heating calorimetry.

    PubMed

    Orava, J; Greer, A L; Gholipour, B; Hewak, D W; Smith, C E

    2012-04-01

    Differential scanning calorimetry (DSC) is widely used to study the stability of amorphous solids, characterizing the kinetics of crystallization close to the glass-transition temperature T(g). We apply ultrafast DSC to the phase-change material Ge(2)Sb(2)Te(5) (GST) and show that if the range of heating rates is extended to more than 10(4) K s(-1), the analysis can cover a wider temperature range, up to the point where the crystal growth rate approaches its maximum. The growth rates that can be characterized are some four orders of magnitude higher than in conventional DSC, reaching values relevant for the application of GST as a data-storage medium. The kinetic coefficient for crystal growth has a strongly non-Arrhenius temperature dependence, revealing that supercooled liquid GST has a high fragility. Near T(g) there is evidence for decoupling of the crystal-growth kinetics from viscous flow, matching the behaviour for a fragile liquid suggested by studies on oxide and organic systems. PMID:22426461

  12. 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%. PMID:21102889

  13. 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

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

    SciTech Connect

    d'Avezac, M.; Luo, J. W.; Chanier, T.; Zunger, A.

    2012-01-13

    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 Si{sub n}/Ge{sub m}/.../Si{sub p}/Ge{sub q} superstructures grown on (001) Si{sub 1-x}Ge{sub x}. The search reveals a robust configurational motif - SiGe{sub 2}Si{sub 2}Ge{sub 2}SiGe{sub n} on (001) Si{sub x}Ge{sub 1-x} substrate (x {le} 0.4) presenting a direct and dipole-allowed gap resulting from an enhanced {Gamma}-X coupling at the band edges.

  15. 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.

  16. Liquid crystalline phthalocyanines as a self-assembling organic semiconductor for solution-processing thin film devices

    NASA Astrophysics Data System (ADS)

    Miyake, Y.; Hori, T.; Yoshida, H.; Monobe, H.; Fujii, A.; Ozaki, M.; Shimizu, Y.

    2011-03-01

    A liquid crystalline phthalocyanine semiconductor, 1, 4, 8, 11, 15, 18, 22, 25-hexahexylphthalocyanine (C6PcH2) was studied on the drift mobility of charged carriers by a Time-Of-Flight (TOF) method. It was found that this compound exhibits an ambipolar nature for charge transport and the hole and electron mobilities were determined to be in the order of 10-1 cm2 V-1 s-1 for polydomain films of the hexagonal disordered columnar (Colhd) mesophase. This is comparable to that of the octyl homologue (C8PcH2) reported by Hanna et al. However, C6PcH2 did not show any tendency to form the homeotropic alignment between ITO-coated glass substrates, though C8PcH2 so clearly and easily does. Clear decay curves of the transient photocurrents could be obtained in TOF measurements even for polydomain films of the crystalline solid phase to give a strongly temperature-dependent mobility of holes which reaches to 1.1 cm2 V-1 s-1 at room temperature (RT) as the temperature goes down, whilst the electron mobility slightly increases to be 0.5 cm2 V-1 s-1at RT. This compound could easily form thin films by spin-coating technique with the toluene solution and a simple bulk-heterojunction thin film solar cell was fabricated to give a good performance such as 3.1 % of power conversion efficiency and > 70 % of external quantum efficiency.

  17. Enhancement of mobility in ultra-thin-body GeOI p-channel metal–oxide–semiconductor field effect transistors with Si-passivated back interfaces

    NASA Astrophysics Data System (ADS)

    Chang, Wen-Hsin; Irisawa, Toshifumi; Ishii, Hiroyuki; Hattori, Hiroyuki; Takagi, Hideki; Kurashima, Yuichi; Maeda, Tatsuro

    2016-09-01

    Ultra-thin-body (UTB) germanium-on-insulator (GeOI) substrates with Si-passivated back interfaces have been fabricated by using advanced epitaxial-lift-off (ELO) technology. Performance of UTB GeOI p-MOSFETs with body thickness (T body) in the 4–16 nm range has also been characterized. Si-passivated back interfaces have been fabricated and found to be effective in mitigating the unpleasant hole-mobility degradation in the UTB GeOI regime owing to the suppression of the back interface scattering.

  18. Absorbance and Photoluminescence of Si, Ge, and MoS{sub 2} Nanoparticles Studied by Liquid Chromatography

    SciTech Connect

    Provencio, P.P.; Samara, G.A.; Wilcoxon, J.P,

    1999-07-12

    The authors have successfully synthesized highly crystalline, size-selected indirect band-gap nanocrystals (NC) of Si, Ge and MoS{sub 2} in the size range 2-10 nm in inverse micelles and studied their optical absorption and photoluminescence (PL) properties using liquid chromatography. Room temperature, visible PL from these nanocrystals was demonstrated in the range 700-350 nm (1.8-3.5 eV). their experimental results are interpreted in terms of the corresponding electronic structure of the bulk materials and it is demonstrated that these nanocrystals retain bulk-like electronic character to sizes as small as 2 nm, but the absorbance energies are strongly blue-shifted by quantum confinement. The experimental results on Si-NCs are also compared to earlier work on Si clusters grown by other techniques and to the predictions of various model calculations. Currently, the wide variations in the theoretical predictions of the various models along with considerable uncertainties in experimental size determination for clusters less than 3-4 nm, make it difficult to select the best model.

  19. 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.

  20. 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.

  1. Semiconductor-based experiments for neutrinoless double beta decay search

    NASA Astrophysics Data System (ADS)

    Barnabé Heider, Marik; Gerda Collaboration

    2012-08-01

    Three experiments are employing semiconductor detectors in the search for neutrinoless double beta (0νββ) decay: COBRA, Majorana and GERDA. COBRA is studying the prospects of using CdZnTe detectors in terms of achievable energy resolution and background suppression. These detectors contain several ββ emitters and the most promising for 0νββ-decay search is 116Cd. Majorana and GERDA will use isotopically enriched high purity Ge detectors to search for 0νββ-decay of 76Ge. Their aim is to achieve a background ⩽10-3 counts/(kgṡyṡkeV) at the Q improvement compared to the present state-of-art. Majorana will operate Ge detectors in electroformed-Cu vacuum cryostats. A first cryostat housing a natural-Ge detector array is currently under preparation. In contrast, GERDA is operating bare Ge detectors submerged in liquid argon. The construction of the GERDA experiment is completed and a commissioning run started in June 2010. A string of natural-Ge detectors is operated to test the complete experimental setup and to determine the background before submerging the detectors enriched in 76Ge. An overview and a comparison of these three experiments will be presented together with the latest results and developments.

  2. Synthesis in ionic liquids : [Bi{sub 2}Te{sub 2}Br](AlCl{sub 4}), a direct gap semiconductor with a cationic framework.

    SciTech Connect

    Biswas, K.; Zhang, Q.; Chung, I.; Song, J.-H.; Androulaksi, J.; Freeman, A. J.; Kanatzidis, M. G.; Materials Science Division; Northwestern Univ.

    2010-01-01

    The Lewis acidic ionic liquid EMIMBr-AlCl{sub 3} (EMIM = 1-ethyl-3-methylimidazolium) allows a novel synthetic route to the semiconducting layered metal chalcogenides halide [Bi{sub 2}Te{sub 2}Br](AlCl{sub 4}) and its Sb analogue. [Bi{sub 2}Te{sub 2}Br](AlCl{sub 4}) is a direct band gap, strongly anisotropic semiconductor and consists of cationic infinite layers of [Bi{sub 2}Te{sub 2}Br]{sup +} and [AlCl{sub 4}]{sup -} anions inserted between the layers.

  3. 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).

  4. (Chemical probes of charge transfer at semiconductor/liquid junctions). Technical report for May 15, 1984-January 15, 1985

    SciTech Connect

    Koval, C.A.

    1985-01-01

    A study of the effects of surface energetics and surface oxide layers on the cyclic voltametry of metallocenes at nonilluminated p- and n-InP electrodes has been completed. Nearly ideal semiconductor/solution interfaces can be prepared, it was concluded, and the voltammetry of metallocenes is a way to probe electron transfer across this interface under different surface energetic conditions. Single crystals of WSe/sub 2/ were grown by chemical vapor transport. A computer program was written to collect voltametric data and calculated convoluted currents, and it is used to examine the kinetics of charge transfer across the semiconductor solution interface. (LEW)

  5. Fabrication and electrical characterization of homo- and hetero-structure Si/SiGe nanowire Tunnel Field Effect Transistor grown by vapor-liquid-solid mechanism

    NASA Astrophysics Data System (ADS)

    Brouzet, V.; Salem, B.; Periwal, P.; Alcotte, R.; Chouchane, F.; Bassani, F.; Baron, T.; Ghibaudo, G.

    2016-04-01

    We demonstrate the fabrication and electrical characterization of Ω -gate Tunnel Field Effect Transistors (TFET) based on p-Si/i-Si/n+Si0.7Ge0.3 heterostructure nanowires grown by Chemical Vapor Deposition (CVD) using the vapor-liquid-solid (VLS) mechanism. The electrical performances of the p-Si/i-Si/n+Si0.7Ge0.3 heterostructure TFET device are presented and compared to Si and Si0.7Ge0.3 homostructure nanowire TFETs. We observe an improvement of the electrical performances of TFET with p-Si/i-Si/n+Si0.7Ge0.3 heterostructure nanowire (HT NW). The optimized devices present an Ion current of about 245 nA at VDS = -0.5 V and VGS = -3 V with a subthreshold swing around 135 mV/dec. Finally, we show that the electrical results are in good agreement with numerical simulation using Kane's Band-to-Band Tunneling model.

  6. Field-induced spin-flop in antiferromagnetic semiconductors with commensurate and incommensurate magnetic structures: Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS).

    PubMed

    Brant, Jacilynn A; dela Cruz, Clarina; Yao, Jinlei; Douvalis, Alexios P; Bakas, Thomas; Sorescu, Monica; Aitken, Jennifer A

    2014-12-01

    Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS), which are among the first magnetic semiconductors with the wurtz-kesterite structure, exhibit antiferromagnetism with TN ≈ 6 and 4 K, respectively. Both compounds undergo a conventional metamagnetic transition that is accompanied by a hysteresis; a reversible spin-flop transition is dominant. On the basis of constant-wavelength neutron powder diffraction data, we propose that LIGS and LITS exhibit collinear magnetic structures that are commensurate and incommensurate with propagation vectors km = [1/2, 1/2, 1/2] and [0, 0, 0.546(1)], respectively. The two compounds exhibit similar magnetic phase diagrams, as the critical fields are temperature-dependent. The nuclear structures of the bulk powder samples were verified using time-of-flight neutron powder diffraction along with synchrotron X-ray powder diffraction. (57)Fe and (119)Sn Mössbauer spectroscopy confirmed the presence of Fe(2+) and Sn(4+) as well as the number of crystallographically unique positions. LIGS and LITS are semiconductors with indirect and direct bandgaps of 1.42 and 1.86 eV, respectively, according to optical diffuse-reflectance UV-vis-NIR spectroscopy. PMID:25397682

  7. 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

    2016-01-01

    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

  8. 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.

  9. Charge-Doping-Driven Evolution of Magnetism and Non-Fermi-Liquid Behavior in the Filled Skutterudite CePt4Ge12-xSbx

    NASA Astrophysics Data System (ADS)

    Nicklas, M.; Kirchner, S.; Borth, R.; Gumeniuk, R.; Schnelle, W.; Rosner, H.; Borrmann, H.; Leithe-Jasper, A.; Grin, Yu.; Steglich, F.

    2012-12-01

    The filled skutterudite compound CePt4Ge12 is situated close to the border between the intermediate valence of Ce and heavy-fermion behavior. Substitution of Ge by Sb drives the system into a strongly correlated and, ultimately, upon further increasing the Sb concentration, an antiferromagnetically ordered state. Our experiments evidence a delicate interplay of emerging Kondo physics and the formation of a local 4f moment. An extended non-Fermi-liquid region, which can be understood in the framework of a Kondo-disorder model, is observed. Band-structure calculations support the conclusion that the physical properties are governed by the interplay of electron supply via Sb substitution and the concomitant volume effects.

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. Chemical probes of charge transfer at semiconductor/liquid junctions. Technical report, January 16, 1985-January 15, 1986

    SciTech Connect

    Koval, C.A.

    1986-01-01

    We attempted to obtain quantitative, non-mass-transfer limited current density vs. potential relationships for a select group of metallocenes. A reproducible procedure for poising the solution redox potential and measuring currents in stirred solutions was developed as well as software programs for data analysis and graphical representation. Even though both p-type and n-type InP electrodes exhibit regions of relative stability, it now appears that this material will not be suitable for detailed kinetic studies. The currents seem to be dominated by leakage phenomena and changes in the thickness of surface oxide which tend to obscure redox processes inherent to the semiconductor solution interface itself.

  15. Analysis of lateritic material from Cerro Impacto by instrumental neutron activation employing a low-energy photon semiconductor and a high-energy Ge(Li) detector

    SciTech Connect

    LaBrecque, J.J.; Beusen, J.M.; Van Grieken, R.E.

    1986-01-01

    Nineteen elements were determined in four different grain size fractions of a bulk geological material from Cerro Impacto for a study of the physical (mechanical) concentration process of different elements based upon the hardness of the different minerals. The analysis was performed by excitation of the sample with a high, slow neutron flux followed by gamma-ray spectroscopy with both a conventional Ge(Li) high-energy detector and a low-energy photon detector (LEPD). The accuracy of this method was studied with the use of two standard reference materials, SY-2 and SY-3, which are similar to the real samples. The values determined were also compared with a secondary target x-ray fluorescence method for all the elements that were suitable to both methods. Actually, the x-ray fluorescence method was found to be more complementary than competitive. 10 refs., 2 figs., 4 tabs.

  16. 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.

  17. Coherent magnetic semiconductor nanodot arrays

    PubMed Central

    2011-01-01

    In searching appropriate candidates of magnetic semiconductors compatible with mainstream Si technology for future spintronic devices, extensive attention has been focused on Mn-doped Ge magnetic semiconductors. Up to now, lack of reliable methods to obtain high-quality MnGe nanostructures with a desired shape and a good controllability has been a barrier to make these materials practically applicable for spintronic devices. Here, we report, for the first time, an innovative growth approach to produce self-assembled and coherent magnetic MnGe nanodot arrays with an excellent reproducibility. Magnetotransport experiments reveal that the nanodot arrays possess giant magneto-resistance associated with geometrical effects. The discovery of the MnGe nanodot arrays paves the way towards next-generation high-density magnetic memories and spintronic devices with low-power dissipation. PMID:21711627

  18. Studies of photocorrosion and passivation of n-GaAs based semiconductor/liquid junction photoelectrochemical cells

    NASA Astrophysics Data System (ADS)

    Miller, Eric Alan

    Semiconductor photoelectrochemical cells offer a cheap, easily constructed alternative to all-solid-state solar cells. However, a persistent problem in their development has been photocorrosion of the semiconductor electrode. Photocorrosion degrades the electrode, reducing the device lifetime to unacceptably short times. Much effort has gone into developing passivation schemes to reduce or eliminate photocorrosion. None has yet provided permanent protection. A better understanding of the basic interfacial chemistry and physics is necessary to achieve this. Toward this end, the studies described in this manuscript have been performed. n-GaAs has been chosen as the electrode material in these studies due to its strong absorption near a maximum in the solar spectrum. Its photoelectrochemical behavior in Nasb2S has been examined because of the known ability of Nasb2S to passivate photocorrosion. Although the protection provided by Nasb2S is known to be temporary, the focus of these studies is to gain a more complete understanding of the interactions between Nasb2S and GaAs which lead to passivation and photocorrosion. Three separate studies are described in this manuscript. In the first, time-resolved photoluminescence experiments were employed to determine whether the minority carrier surface recombination velocity (SRV) is dependent upon electrolyte concentration. The results indicate that, within the concentration range studied, the SRV is independent of Nasb2S concentration, suggesting that there is no significant change in the degree of semiconductor/electrolyte bond formation. In the second study, the dependence of photocorrosion and passivation on crystallographic orientation was examined. Results show that the (100) and (110) surfaces of GaAs were passivated equally well by Nasb2S, although surface states which eventually formed at the two surfaces were separated in energy by 300 meV. The (111)B surface was not passivated by Nasb2S. In the third study, the

  19. 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. PMID:25463183

  20. 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

    2012-12-01

    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. PMID:22972420

  1. Amorphous Ge bipolar blocking contacts on Ge detectors

    SciTech Connect

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

    1991-10-01

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

  2. Laser induced photocurrent transients in semiconductor liquid-junction solar cells employing n-WSe/sub 2/ and n-MoSe/sub 2/ photoanodes

    SciTech Connect

    Prybyla, S.G.

    1984-01-01

    The effects of perturbing a semiconductor liquid-junction solar cell from dark equilibrium conditions with a nanosecond (5 nsec FWHM) laser pulse of greater than bandgap energy were studied. It was found that n-WSe/sub 2/ and n-MoSe/sub 2/ photoanodes in either I/sup -//I/sub 3//sup -/ or Fe/sup 2 +//Fe/sup 3 +/ redox couple containing electrolyte solutions exhibit biexponentially decaying photocurrent transients in response to photoexcitation. For a given redox couple, n-WSe/sub 2/ was found to yield slightly higher peak photocurrents than n-MoSe/sub 2/ due to be more favorable band bending under dark conditions. The redox couple I/sup -//I/sub 3//sup -/ was found to be superior to Fe/sup 2 +//Fe/sup 3 +/ in spite of more positive redox potential of the Fe/sup 2 +//Fe/sup 3 +/ couple. The I/sup -//I/sub 3//sup -/ apparently adsorbs onto the semiconductor surface, negating the effects of surface states which tend to limit the amount of equilibrium band bending present. Quantum yields of charge transfer were determined for both redox couples as a function of laser pulse energy and energy density. Quantum yields of charge transfer were also determined for variation of the I/sup -//I/sub 3//sup -/ couple concentration for a fixed excitation energy. The resultant nonlinear dependency appears to follow the adsorption isotherm for I/sup -//I/sub 3//sup -/. Decay time constants and quantum yields of charge transfer as a function of added load resistance were studied.

  3. 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. PMID:25182502

  4. Semiconductor nanorod self-assembly at the liquid/air interface studied by in situ GISAXS and ex situ TEM.

    PubMed

    Pietra, Francesca; Rabouw, Freddy T; Evers, Wiel H; Byelov, Dima V; Petukhov, Andrei V; de Mello Donegá, Celso; Vanmaekelbergh, Daniël

    2012-11-14

    We study the self-assembly of colloidal CdSe/CdS nanorods (NRs) at the liquid/air interface combining time-resolved in situ grazing-incidence small angle X-ray scattering (GISAXS) and ex situ transmission electron microscopy (TEM). Our study shows that NR superstructure formation occurs at the liquid/air interface. Short NRs self-assemble into micrometers long tracks of NRs lying side by side flat on the surface. In contrast, longer NRs align vertically into ordered superstructures. Systematic variation of the NR length and initial concentration of the NR dispersion allowed us to tune the orientation of the NRs in the final superstructure. With GISAXS, we were able to follow the dynamics of the self-assembly. We propose a model of hierarchical self-organization that provides a basis for the understanding of the length-dependent self-organization of NRs at the liquid/air interface. This opens the way to new materials based on NR membranes and anisotropic thin films. PMID:23038984

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  7. SEMICONDUCTOR DEVICES Prospects of a β-SiC based IMPATT oscillator for application in THz communication and growth of a β-SiC p—n junction on a Ge modified Si (100) substrate to realize THz IMPATTs

    NASA Astrophysics Data System (ADS)

    Mukherjee, Moumita; Mazumder, Nilratan

    2010-12-01

    The prospects of a p+nn+ cubic silicon carbide (3C-SiC/β-SiC) based IMPATT diode as a potential solid-state terahertz source is studied for the first time through a modified generalized simulation scheme. The simulation predicts that the device is capable of generating an RF power output of 63.0 W at 0.33 THz with an efficiency of 13%. The effects of parasitic series resistance on the device performance and exploitable RF power level are further simulated. The studies clearly establish the potential of 3C-SiC as a base semiconductor material for a high-power THz IMPATT device. Based on the simulation results, an attempt has been made to fabricate β-SiC based IMPATT devices in the THz region. Single crystalline, epitaxial 3C-SiC films are deposited on silicon (Si) (100) substrates by rapid thermal chemical vapour deposition (RTPCVD) at a temperature as low as 800 °C using a single precursor methylsilane, which contains Si and C atoms in the same molecule. No initial surface carbonization step is required in this method. A p—n junction with an n-type doping concentration of 4 × 1024 m-3 (which is similar to the simulated design data) has been grown successfully and the characterization of the grown 3C-SiC film is reported in this paper. It is found that the inclusion of Ge improves the crystal quality and reduces the surface roughness.

  8. High-contrast X-ray radiography using hybrid semiconductor pixel detectors with 1 mm thick Si sensor as a tool for monitoring liquids in natural building stones

    NASA Astrophysics Data System (ADS)

    Krejci, F.; Slavikova, M.; Zemlicka, J.; Jakubek, J.; Kotlik, P.

    2014-07-01

    For the preservation of buildings and other cultural heritage, the application of various conservation products such as consolidants or water repellents is often used. X-ray radiography utilizing semiconductor particle-counting detectors stands out as a promising tool in research of consolidants inside natural building stones. However, a clear visualization of consolidation products is often accomplished by doping with a contrast agent, which presents a limitation. This approach causes a higher attenuation for X-rays, but also alters the penetration ability of the original consolidation product. In this contribution, we focus on the application of Medipix type detectors newly equipped with a 1 mm thick Si sensor. This thicker sensor has enhanced detection efficiency leading to extraordinary sensitivity for monitoring consolidants and liquids in natural building stones even without any contrast agent. Consequently, methods for the direct monitoring of organosilicon consolidants and dynamic visualization of the water uptake in the Opuka stone using high-contrast X-ray radiography are demonstrated. The presented work demonstrates a significant improvement in the monitoring sensitivity of X-ray radiography in stone consolidation studies and also shows advantages of this detector configuration for X-ray radiography in general.

  9. Studies of the n-GaAs/KOH-Se sub 2 sup 2 minus -Se sup 2 minus semiconductor/liquid junction

    SciTech Connect

    Tufts, B.J.; Abrahams, I.L.; Casagrande, L.G.; Lewis, N.S. )

    1989-04-20

    The current-voltage characteristics of the n-GaAs/KOH-Se{sub 2}{sup 2{minus}}-Se{sup 2{minus}} semiconductor/liquid junction have been determined for a variety of conditions, including changes in the majority carrier density, the minority carrier diffusion length, and the incident light intensity. These data provide an experimental test of previous digital simulation calculations and provide necessary data for use in further mechanistic studies of this system. Spectral response measurements have been performed to elucidate the anomalous increase in short circuit photocurrent density when the n-GaAs photoanodes, and we have observed solar simulated efficiencies in excess of 16% for Os{sup 3+}-treated n-GaAs photoanodes. Chemisorption of metal ions that yielded beneficial effects of n-GaAs photoanode performance also yielded increased charge-transfer rates at p-GaAs, n{sup +}-GaAs, and Sn-doped In{sub 2}O{sub 3} surfaces.

  10. Facile fabrication of porous thin films of Bi2O3/Bi2S3 nanocomposite semiconductors at gas/liquid interface and their photoelectrochemical performances

    NASA Astrophysics Data System (ADS)

    Lu, Xiaoqing; Pu, Fang; Xia, Yue; Huang, Wei; Li, Zelin

    2014-04-01

    Porous thin films of Bi2O3/Bi2S3 nanocomposite semiconductors were prepared rapidly at gas/liquid interface for the first time by contacting an acidic Bi(NO3)3 solution with vapors from ammonia water and ammonium sulfide solution. Hydrolysis of Bi3+ into Bi2O3 nanoparticles (NPs) and their partial sulfurization into Bi2S3 occurred at/near the solution surface upon contacting the vapors of NH3 and H2S, respectively. Based on photoelectrochemical performances, the conditions were optimized for preparation of Bi2O3/Bi2S3 thin films by interfacial reactions and self-assembly of the in situ produced nanocomposites, including concentrations of Bi(NO3)3 and HNO3, vapor sources, contact manners and contact times. The porous thin film of Bi2O3/Bi2S3 prepared under optimized conditions showed better photoelectrochemical performance than the respective thin films of Bi2O3 and Bi2S3 and their some other composites.

  11. Intense pulsed light induced crystallization of a liquid-crystalline polymer semiconductor for efficient production of flexible thin-film transistors.

    PubMed

    Yang, Hee Yeon; Park, Han-Wool; Kim, Soo Jin; Hong, Jae-Min; Kim, Tae Whan; Kim, Do Hwan; Lim, Jung Ah

    2016-02-14

    Here we demonstrated the split-second crystallization of a liquid-crystalline conjugated polymer semiconductor induced by irradiation with intense pulsed white light (IPWL) for the efficient improvement of electrical properties of flexible thin film transistors. A few seconds of IPWL irradiation of poly(didodecylquaterthiophene-alt-didodecylbithiazole) (PQTBTz-C12) thin films generated heat energy through the photo-thermal effect, leading to the crystallization of PQTBTz-C12 and formation of nodule-like nanostructures. The IPWL-induced crystallization of PQTBTz-C12 resulted in a threefold improvement in the field-effect mobility of thin film transistors compared to as-prepared devices. The conformational change of the PQTBTz-C12 chains was found to be strongly related to the irradiation fluence. As a proof-of-concept, the IPWL treatment was successfully applied to the PQTBTz-C12 layer in flexible transistors based on plastic substrates. The performance of these flexible devices was significantly improved after only 0.6 s of IPWL treatment, without deformation of the plastic substrate. PMID:26795202

  12. Direct Observation of Transient Surface Species during Ge Nanowire Growth and Their Influence on Growth Stability.

    PubMed

    Sivaram, Saujan V; Shin, Naechul; Chou, Li-Wei; Filler, Michael A

    2015-08-12

    Surface adsorbates are well-established choreographers of material synthesis, but the presence and impact of these short-lived species on semiconductor nanowire growth are largely unknown. Here, we use infrared spectroscopy to directly observe surface adsorbates, hydrogen atoms and methyl groups, chemisorbed to the nanowire sidewall and show they are essential for the stable growth of Ge nanowires via the vapor-liquid-solid mechanism. We quantitatively determine the surface coverage of hydrogen atoms during nanowire growth by comparing ν(Ge-H) absorption bands from operando measurements (i.e., during growth) to those after saturating the nanowire sidewall with hydrogen atoms. This method provides sub-monolayer chemical information at relevant reaction conditions while accounting for the heterogeneity of sidewall surface sites and their evolution during elongation. Our findings demonstrate that changes to surface bonding are critical to understand Ge nanowire synthesis and provide new guidelines for rationally selecting catalysts, forming heterostructures, and controlling dopant profiles. PMID:26147949

  13. Mn segregation in Ge/Mn5Ge3 heterostructures: The role of surface carbon adsorption

    NASA Astrophysics Data System (ADS)

    Dau, Minh-Tuan; Thanh, Vinh Le; Le, Thi-Giang; Spiesser, Aurélie; Petit, Mathieu; Michez, Lisa A.; Daineche, Rachid

    2011-10-01

    Mn5Ge3 compound, with its room-temperature ferromagnetism and possibility to epitaxially grow on Ge, acts as a potential spin injector into group-IV semiconductors. However, the realization of Ge/Mn5Ge3 multilayers is highly hampered by Mn segregation toward the Ge growing surface. Here, we show that adsorption of some monolayers of carbon on top of the Mn5Ge3 surface prior to Ge deposition allows to greatly reduce Mn segregation. In addition, a fraction of deposited carbon can diffuse down to the underneath Mn5Ge3 layers, resulting in an enhancement of the Curie temperature up to ˜360 K. The obtained results will be discussed in terms of the formation of a diffusion barrier by filling interstitial sites of Mn5Ge3 by carbon.

  14. 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.

  15. 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.

  16. Semiconductor processing

    NASA Technical Reports Server (NTRS)

    1982-01-01

    The primary thrust of the semiconductor processing is outlined. The purpose is to (1) advance the theoretical basis for bulk growth of elemental and compound semiconductors in single crystal form, and (2) to develop a new experimental approaches by which semiconductor matrices with significantly improved crystalline and chemical perfection can be obtained. The most advanced approaches to silicon crystal growth is studied. The projected research expansion, directed toward the capability of growth of 4 inch diameter silicon crystals was implemented. Both intra and interdepartmental programs are established in the areas of process metallurgy, heat transfer, mass transfer, and systems control. Solutal convection in melt growth systems is also studied.

  17. Size, shape, and ordering of SiGe/Si(001) islands grown by means of liquid phase epitaxy under far-nonequilibrium growth conditions

    SciTech Connect

    Hanke, M.; Boeck, T.; Gerlitzke, A.-K.; Syrowatka, F.; Heyroth, F.; Koehler, R.

    2005-04-04

    Applying scanning electron microscopy, we have studied the evolution of shape and lateral positional correlation of Si{sub 1-x}Ge{sub x}/Si(001) Stranski-Krastanov islands grown by means of liquid phase epitaxy (LPE). However, in contrast to conventional near-equilibrium LPE, a distinctly higher cooling rate of 10 K/min ensures extremly nonequilibrium growth conditions. The facet inclination of subsequent island stages decreases from nearly vertical sidewalls toward {l_brace}111{r_brace}- and {l_brace}101{r_brace}-type facets. Energy dispersive x-ray microanalysis yields a size-independent germanium content of 8.9% within islands between 760 and 1700 nm base width which is--by more than a factor of 2--smaller than islands of the same concentration grown in a near-equilibrium LPE process. Square-like formations of subsequently smaller islands around a large central island indicate only next to island interactions during the lateral self-assembling.

  18. 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.

  19. Isotopically engineered semiconductors

    NASA Astrophysics Data System (ADS)

    Haller, E. E.

    1995-04-01

    Scientific interest, technological promise, and increased availability of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled semiconductor crystals. This review of mostly recent activities begins with an introduction to some past classical experiments which have been performed on isotopically controlled semiconductors. A review of the natural isotopic composition of the relevant elements follows. Some materials aspects resulting in part from the high costs of enriched isotopes are discussed next. Raman spectroscopy studies with a number of isotopically pure and deliberately mixed Ge bulk crystals show that the Brillouin-zone-center optical phonons are not localized. Their lifetime is almost independent of isotopic disorder, leading to homogeneous Raman line broadening. Studies with short period isotope superlattices consisting of alternating layers of n atomic planes of 70Ge and 74Ge reveal a host of zone-center phonons due to Brillouin-zone folding. At n≳40 one observes two phonon lines at frequencies corresponding to the bulk values of the two isotopes. In natural diamond, isotope scattering of the low-energy phonons, which are responsible for the thermal conductivity, is very strongly affected by small isotope disorder. Isotopically pure 12C diamond crystals exhibit thermal conductivities as high as 410 W cm-1 K-1 at 104 K, leading to projected values of over 2000 W cm-1 K-1 near 80 K. The changes in phonon properties with isotopic composition also weakly affect the electronic band structures and the lattice constants. The latter isotope dependence is most relevant for future standards of length based on crystal lattice constants. Capture of thermal neutrons by isotope nuclei followed by nuclear decay produces new elements, resulting in a very large number of possibilities for isotope selective doping of semiconductors. This neutron transmutation of isotope nuclei, already used

  20. 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

  1. Tracks and voids in amorphous Ge induced by swift heavy-ion irradiation.

    PubMed

    Ridgway, M C; Bierschenk, T; Giulian, R; Afra, B; Rodriguez, M D; Araujo, L L; Byrne, A P; Kirby, N; Pakarinen, O H; Djurabekova, F; Nordlund, K; Schleberger, M; Osmani, O; Medvedev, N; Rethfeld, B; Kluth, P

    2013-06-14

    Ion tracks formed in amorphous Ge by swift heavy-ion irradiation have been identified with experiment and modeling to yield unambiguous evidence of tracks in an amorphous semiconductor. Their underdense core and overdense shell result from quenched-in radially outward material flow. Following a solid-to-liquid phase transformation, the volume contraction necessary to accommodate the high-density molten phase produces voids, potentially the precursors to porosity, along the ion direction. Their bow-tie shape, reproduced by simulation, results from radially inward resolidification. PMID:25165936

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  4. 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)

  5. Nanochannel-Directed Growth of One-Dimensional Multi-Segment Heterojunctions of Metallic Au1-xGex and Semiconducting Ge

    SciTech Connect

    Li, Xiangdong; Meng, Guowen; Qin, Shengyong; Xu, Qiaoling; Chu, Zhaoqin; Zhu, Xiaoguang; Kong, Mingguang; Li, An-Ping

    2012-01-01

    We report on the synthesis of multi-segment nanowire (NW) junctions of Au{sub 1-x}Ge{sub x} and Ge inside the nanochannels of porous anodic aluminum oxide template. The one-dimensional heterostructures are grown with a low-temperature chemical vapor deposition process, assisted by electrodeposited Au nanowires (AuNWs). The Au-catalyzed vapor-liquid-solid growth process occurs simultaneously in multiple locations along the nanochannel, which leads to multi-segment Au{sub 1-x}Ge{sub x}/Ge heterojunctions. The structures of the as-grown hybrid NWs, analyzed by using transmission electron microscopy and energy-dispersive X-ray spectroscopy elemental mapping, show clear compositional modulation with variable modulation period and controllable junction numbers. Remarkably, both GeNW and Au{sub 1-x}Ge{sub x}NW segments are single crystalline with abrupt interfaces and good crystallographic coherences. The electronic and transport properties of individual NW junctions are measured by using a multi-probe scanning tunneling microscope, which confirms the semiconducting nature of Ge segments and the metallic behavior of Au{sub 1-x}Ge{sub x} segments, respectively. The high yield of multiple segment NW junctions of a metal-semiconductor can facilitate the applications in nanoelectronics and optoelectronics that harness multiple functionalities of heterointerfaces.

  6. 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.

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

    PubMed

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

    2015-09-23

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

  8. 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

  9. Creating semiconductor metafilms with designer absorption spectra

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    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.

  10. Creating semiconductor metafilms with designer absorption spectra.

    PubMed

    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

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    A study of the bandgap character of compressively strained GeSn0.060-0.091/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 Γ 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, bL = 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. %.

  13. 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. %.

  14. Hydrogen on semiconductor surfaces

    SciTech Connect

    Schaefer, J.A.; Balster, T.; Polyakov, V.; Rossow, U.; Sloboshanin, S.; Starke, U.; Tautz, F.S.

    1998-12-31

    The authors review structural and electronic aspects of the reaction of hydrogen with semiconductor surfaces. Among others, they address the Si(100), Ge{sub x}Si{sub 1{minus}x}(100), GaAs(100), InP(100), SiC(100), SiC(0001) and SiC(000{bar 1}) surfaces. It is demonstrated that high resolution electron energy loss spectroscopy (HREELS) in conjunction with a number of other surface sensitive techniques like low energy electron diffraction (LEED) and photoelectron spectroscopy (XPS/UPS) can yield important information about the surface atomic structure, the effects of hydrogen passivation and etching and on electronic properties of the surfaces. 67 refs., 7 figs., 3 tabs.

  15. Transport Phenomena in Liquid Phase Diffusion Growth of Silicon Germanium

    NASA Astrophysics Data System (ADS)

    Armour, Neil Alexander

    Silicon Germanium, SiGe, is an important emerging semiconductor material. In order to optimize growth techniques for SiGe production, such as Liquid Phase Diffusion, LPD, or Melt Replenishment Czochralski, a good understanding of the transport phenomena in the melt is required. In the context of the Liquid Phase Diffusion growth technique, the transport phenomena of silicon in a silicon-germanium melt has been explored. Experiments isolating the dissolution and transport of silicon into a germanium melt have been conducted under a variety of flow conditions. Preliminary modeling of these experiments has also been conducted and agreement with experiments has been shown. In addition, full LPD experiments have also been conducted under varying flow conditions. Altered flow conditions were achieved through the application of a variety of magnetic fields. Through the experimental and modeling work better understanding of the transport mechanisms at work in a silicon-germanium melt has been achieved.

  16. 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.

  17. 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.

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

    PubMed

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

    2016-01-01

    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. PMID:27095012

  19. 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.

  20. 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.

  1. Optimization and Design of 2d Honeycomb Lattice Photonic Crystal Modulated by Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Guo, Caihong; Zheng, Jihong; Gui, Kun; Zhang, Menghua; Zhuang, Songlin

    2013-12-01

    Photonic crystals (PCs) with infiltrating liquid crystals (LCs) have many potential applications because of their ability to continuously modulate the band-gaps. Using the plane-wave expansion method (PWM), we simulate the band-gap distribution of 2D honeycomb lattice PC with different pillar structures (circle, hexagonal and square pillar) and with different filling ratios, considering both when the LC is used as filling pillar material and semiconductors (Si, Ge) are used in the substrate, and when the semiconductors (Si, Ge) are pillar material and the LC is the substrate. Results show that unlike LC-based triangle lattice PC, optimized honeycomb lattice PC has the ability to generate absolute photonic band-gaps for fabricating optical switches. We provide optimization parameters for LC infiltrating honeycomb lattice PC structure based on simulation results and analysis.

  2. Semiconductor Cubing

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Through Goddard Space Flight Center and Jet Propulsion Laboratory Small Business Innovation Research contracts, Irvine Sensors developed a three-dimensional memory system for a spaceborne data recorder and other applications for NASA. From these contracts, the company created the Memory Short Stack product, a patented technology for stacking integrated circuits that offers higher processing speeds and levels of integration, and lower power requirements. The product is a three-dimensional semiconductor package in which dozens of integrated circuits are stacked upon each other to form a cube. The technology is being used in various computer and telecommunications applications.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  4. 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

  5. Hypersonic modes in nanophononic semiconductors.

    PubMed

    Hepplestone, S P; Srivastava, G P

    2008-09-01

    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. PMID:18851224

  6. 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.

  7. 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.

  8. Mechanistic aspects of photoconversion at semiconductor-liquid junctions and in facilitated transport membranes. Final report, March 15, 1994--March 14, 1998

    SciTech Connect

    Koval, C.A.

    1998-06-01

    A major portion of the research completed during this funding period involved the use of rotating ring-disk electrochemical techniques in conjunction with carefully chosen solution redox systems to investigate hot electron transfer reactions at the semiconductor electrolyte interface. This paper cover the following topics: photoreduction reactions at GaAs/AlGaAs superlattice electrodes; photoelectrochemistry at GaInP{sub 2} capped p-GaAs electrodes; further investigation of p-InP photocathodes; rotating ring disk photoelectrochemistry at TiO{sub 2} films; and photomodulation of interfacial mass transport rates.

  9. 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.

  10. 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.

  11. Thermal stability and radiation resistance of tin valent states in the structure of the (As{sub 2}Se{sub 3}){sub 1-z}(SnSe){sub z-x}(GeSe){sub x} semiconductor glasses

    SciTech Connect

    Bordovskii, G. A.; Kastro, R. A.; Marchenko, A. V.; Nemov, S. A.; Seregin, P. P.

    2007-12-15

    The ratio between the content of bivalent and tetravalent tin atoms in the (As{sub 2}Se{sub 3}){sub 1-z}(SnSe){sub z-x}(GeSe){sub x} glasses depends on the rate of quenching of the alloy and on its temperature. Irradiation of these glasses with {gamma}-ray photons brings about a partial oxidation of bivalent tin with formation of amorphous (finely divided) SnO{sub 2} phase blocked by the glass, so that the physicochemical properties of the glasses (density, microhardness, glassformation temperature, and the electrical-conductivity activation energy) are virtually unaffected by irradiation.

  12. 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.

  13. 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.

  14. Effect of imidazolium-based ionic liquids on the nanoscale morphology of CuTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) metal-organic semiconductors.

    PubMed

    Pearson, Andrew; O'Mullane, Anthony P; Bhargava, Suresh K; Bansal, Vipul

    2013-01-01

    We demonstrate for the first time the ionic-liquid-mediated synthesis of nanostructured CuTCNQ by the simple immersion of copper in a solution of TCNQ where the viscosity of the medium significantly impacts the corrosion-crystallization process and the final morphology of the material. PMID:23244737

  15. 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

  16. 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.

  17. Kesterite Cu2Zn(Sn,Ge)(S,Se)4 thin film with controlled Ge-doping for photovoltaic application.

    PubMed

    Zhao, Wangen; Pan, Daocheng; Liu, Shengzhong Frank

    2016-05-21

    Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm(2) without an anti-reflection layer. PMID:27121893

  18. Vibrational Properties of Ge Nanocrystals Determined by EXAFS

    SciTech Connect

    Araujo, L. L.; Kluth, P.; Ridgway, M. C.; Azevedo, G. de M.

    2007-02-02

    The vibrational properties of Ge nanocrystals (NCs) produced by ion implantation in SiO2 followed by thermal annealing were determined from temperature dependent Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopy measurements. Using a correlated anharmonic Einstein model and thermodynamic perturbation theory it was possible to extract information about thermal and static disorder, thermal expansion and anharmonicity effects for the Ge NCs. Comparison with results for bulk crystalline and amorphous Ge indicates that the Ge NCs bonds are stiffer than those of both bulk phases of Ge. Also, the values of the anharmonic linear thermal expansion and the thermal expansion coefficient obtained for the Ge NCs were considerably smaller those for bulk crystalline Ge. Similar trends are reported in the literature for other semiconductor NC systems. They suggest that the increased surface to volume ratio of nanocrystals and the presence of the surrounding SiO2 matrix might be responsible for the different vibrational properties of the nanocrystal phase.

  19. Band alignment at interfaces of amorphous Al{sub 2}O{sub 3} with Ge{sub 1−x}Sn{sub x}- and strained Ge-based channels

    SciTech Connect

    Chou, H.-Y.; Afanas'ev, V. V. Houssa, M.; Stesmans, A.; Vincent, B.; Gencarelli, F.; Shimura, Y.; Merckling, C.; Loo, R.; Nakatsuka, O.; Zaima, S.

    2014-05-19

    Spectroscopy of internal photoemission of electrons from Ge and Ge{sub 1−x}Sn{sub x} (x ≤ 0.08) alloys into amorphous Al{sub 2}O{sub 3} is used to evaluate the energy of the semiconductor valence band top. It is found that in Ge and Ge{sub 1−x}Sn{sub x} the valence bands are aligned within the measurement accuracy (±0.05 eV) irrespective of the strain imposed on the semiconductor or by the kind of passivating inter-layer applied between the semiconductor and alumina. This indicates that the Ge{sub 1−x}Sn{sub x}-stressor approach may be useful for strain engineering in p-channel Ge metal-oxide-semiconductor transistors.

  20. Reduction of Schottky barrier height at metal/n-Ge interface by introducing an ultra-high Sn content Ge1-xSnx interlayer

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    We investigated the impact of introducing an ultra-high Sn content Ge1-xSnx interlayer on the electrical properties at the metal/Ge interface. We achieved epitaxial growth of a Ge1-xSnx thin layer with an ultra-high substitutional Sn content of up to 46% on a Ge(001) substrate by considering the misfit strain between Ge1-xSnx and Ge. From the current-voltage characteristics of Al/Ge1-xSnx/n-Ge Schottky diodes, we found an increase in the forward current density of the thermionic emission current with increasing Sn content in the Ge1-xSnx interlayer. The Schottky barrier height estimated in Al/Ge1-xSnx/n-Ge diodes decreases to 0.49 eV with an increase in the Sn content up to 46% of the Ge1-xSnx interlayer. The reduction of the barrier height may be due to the shift of the Fermi level pinning position at the metal/Ge interface with a Ge1-xSnx interlayer whose valence band edge is higher than that of Ge. This result enables the effective reduction of the contact resistivity by introducing a group-IV semiconductor alloy interlayer of Ge1-xSnx into the metal/n-Ge interface.

  1. Interfacial effects on the optical behavior of Ge:ITO and Ge:ZnO nanocomposite films.

    PubMed

    Shih, Grace H; Allen, Cary G; Potter, B G

    2012-02-24

    Nanophase semiconductors are of interest for their unique, size-tunable solar spectral absorption characteristics as well as their potential to contribute to the improved energy conversion efficiency of photovoltaics (PV). Embedding these nanoparticles within electrically active transparent conductive oxides (TCO) can also provide an opportunity for enhanced, long-range carrier transport. However, differences in the atomic and electronic structure, dielectric behavior, and chemistry between the matrix and semiconductor phases highlight the influence of interfacial effects on the optical absorption properties of the composite. In this work, nanocomposites of Ge:indium tin oxide (Ge:ITO) and Ge:ZnO were fabricated with sequential RF-magnetron sputtering and annealed at temperatures from 310 to 550 °C to investigate the impact of matrix identity on this interface and its contribution to nanostructure-mediated optical absorption. Transmission electron microscopy showed a decrease in Ge nanocrystal size relative to the initial semiconductor domain size in both matrices that was correlated with an increase in absorption onset energy after annealing. The effect was particularly pronounced in Ge:ITO composites in which Raman spectroscopy indicated the presence of germanium oxide at the semiconductor-ITO interface. These results support the primary contribution of carrier confinement in the Ge nanophase to the shifts in absorption onset energies observed. PMID:22261039

  2. Epitaxial Electronic Oxides on Semiconductors Using Pulsed-Laser Deposition

    SciTech Connect

    Norton, D.P.; Budai, J.D.; Chisholm, M.F.

    1999-12-01

    We describe the growth and properties of epitaxial (OO1) CeO{sub 2} on a (001) Ge surface using a hydrogen-assisted pulsed-laser deposition method. Hydrogen gas is introduced during film growth to eliminate the presence of the GeOs from the semiconductor surface during the initial nucleation of the metal oxide film. The hydrogen partial pressure and substrate temperature are selected to be sufficiently high such that the germanium native oxides are thermodynamically unstable. The Gibbs free energy of CeO{sub 2} is larger in magnitude than that of the Ge native oxides, making it more favorable for the metal oxide to reside at the interface in comparison to the native Ge oxides. By satisfying these criteria. the metal oxide/semiconductor interface is shown to be atomically abrupt with no native oxide present. Preliminary structural and electrical properties are reported.

  3. Codoped direct-gap semiconductor scintillators

    DOEpatents

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

    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.

  4. 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.

  5. 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.

  6. Reexamination of Fermi level pinning for controlling Schottky barrier height at metal/Ge interface

    NASA Astrophysics Data System (ADS)

    Nishimura, Tomonori; Yajima, Takeaki; Toriumi, Akira

    2016-08-01

    The element metal/germanium (Ge) interface exhibits a strong Fermi level pinning (FLP), which is usually characterized on the basis of Ge side semiconductor properties. In this work, we demonstrate that metal properties significantly affect the Schottky barrier height (SBH) on Ge. Metallic germanides show both FLP alleviation and a clear substrate orientation dependence of SBH on Ge, despite the nearly perfect FLP and very slight orientation dependence in the element metal case. As a result, ohmic characteristics are observed at germanide/n-Ge (111) junctions. The metal properties required to alleviate the FLP on Ge are also discussed.

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

    SciTech Connect

    Walukiewicz, W.

    1988-07-01

    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.

  8. 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.

  9. Temperature dependences of the gapwidth of A/sup IV/Se and A/sub 2//sup V/Se/sub 3/ semiconductors

    SciTech Connect

    Rasulov, S.M.

    1988-03-01

    The gapwidth of semiconductors E/sub g/ is related with the change in the enthalpy H/sub T/ - H/sub o/. The authors obtained a dependence between the temperature coefficient of the gapwidth and the heat capacity c/sub p/. They determined (par. deltaE/sub g//par. deltaT)p and E/sub g/(T) for semiconductors of the type A/sup IV/Se(A - Ge, Sn, Pb) and A/sub 2//sup V/Se/sub 3/ (A - As, Sb, Bi) in the solid and liquid states. For c/sub p/(T) and (H/sub T/ - H/sub o/)(T) based on the experimental data, empirical equations which are obeyed for temperatures above 273 K were derived.

  10. 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.

  11. Nanowires and Nanobelts: Volume 1, Metal and Semiconductor Nanowires

    NASA Astrophysics Data System (ADS)

    Wang, Zhong Lin

    This two volume reference, Nanowires and Nanobelts: Materials, Properties and Devices, provides a comprehensive introduction to the field and reviews the current state of the research. Volume 1, Metal and Semiconductor Nanowires covers a wide range of materials systems, from noble metals (such as Au, Ag, Cu), single element semiconductors (such as Si and Ge), compound semiconductors (such as InP, CdS and GaAs as well as heterostructures), nitrides (such as GaN and Si3N4) to carbides (such as SiC).

  12. Float Zone Growth of Alloy Semiconductor Crystals: Influence of Solutocapillary Convection

    NASA Technical Reports Server (NTRS)

    Dold, P.; Schweizer, M.; Croell, A.; Campbell, T.; Boschert, S.; Benz, K. W.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    Growth techniques with large free melt surfaces are affected by convective flows induced by gradients of the surface tension. In the case of dilute semiconductor alloys (in our case: germanium-silicon), the impact of solutocapillary convection (due to the concentration dependence of the surface tension) has to be taken into account in addition to the "normal" thermocapillary convection (due to the temperature dependence of the surface tension). Theoretical considerations, based on experimental temperature profiles, growth geometry, segregation coefficient, and measured values for the temperature and concentration coefficients of the surface tension, lead to the conclusion that for the germanium rich side of the Ge(1-x)Si(x) system, the contribution of solutocapillary convection is, at least in front of the solid-liquid interface, the dominant factor. It results in an additional flow roll with a flow direction opposite to the thermocapillary flow, similar to the ones reported for metal alloys or high Prandtl-number fluids.

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

    DOE PAGESBeta

    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 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

  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. 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)

  16. Photorefractive Semiconductors and Applications

    NASA Technical Reports Server (NTRS)

    Chen, Li-Jen; Luke, Keung L.

    1993-01-01

    Photorefractive semiconductors are attractive for information processing, becuase of fast material response, compatibility with semiconductor lasers, and availability of cross polarization diffraction for enhancing signal-to-noise ration. This paper presents recent experimental results on information processing using photorefractive GaAs, InP and CdTe, including image processing with semiconductor lasers.

  17. 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.

  18. 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.

  19. Structure of two liquid semiconductors : Ag{sub 1-x}Se{sub x} and Ag{sub 0.67}Te{sub 0.33}.

    SciTech Connect

    Price, D. L.; Saboungi, M.-L.; Susman, S.; Volin, K. J.; Enderby, J. E.; Barnes, A. C.; Materials Science Division; Univ. of Bristol

    1993-01-01

    Neutron diffraction measurements have been carried out on Ag{sub 1-x}Se{sub x} and Ag{sub 0.67}Te{sub 0.33} alloys to investigate possible structural causes for the differences in electrical transport properties observed in the two alloys. Ag{sub 1-x}Se{sub x} was measured for the compositions, x=0.30, 0.33 and 0.36, at temperatures just above the liquidus (1045, 915 and 855 degrees C, respectively), and for x=0.33 at three temperatures (915, 985 and 1045 degrees C). The Ag{sub 1-x}Te{sub x} system was measured at only one composition x=0.33, just above the liquidus (985 degrees C). At the level of the average correlation function, the behavior of liquid Ag-Se shows no unusual dependence on either concentration or temperature, and the selenium and tellurium alloys show generally similar behavior. There is no obvious structural connection with the anomalous concentration dependence of the electrical conductivity in Ag{sub 1-x}Se{sub x} alloys or with the different behavior in both electronic and ionic conduction observed in the Ag-Se and Ag-Te systems.

  20. 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.

  1. Gate-stack engineering for self-organized Ge-dot/SiO2/SiGe-shell MOS capacitors

    NASA Astrophysics Data System (ADS)

    Lai, Wei-Ting; Yang, Kuo-Ching; Liao, Po-Hsiang; George, Tom; Li, Pei-Wen

    2016-02-01

    We report the first-of-its-kind, self-organized gate-stack heterostructure of Ge-dot/SiO2/SiGe-shell on Si fabricated in a single step through the selective oxidation of a SiGe nano-patterned pillar over a Si3N4 buffer layer on a Si substrate. Process-controlled tunability of the Ge-dot size (7.5‑90 nm), the SiO2 thickness (3‑4 nm), and as well the SiGe-shell thickness (2‑15 nm) has been demonstrated, enabling a practically-achievable core building block for Ge-based metal-oxide-semiconductor (MOS) devices. Detailed morphologies, structural, and electrical interfacial properties of the SiO2/Ge-dot and SiO2/SiGe interfaces were assessed using transmission electron microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Notably, NiGe/SiO2/SiGe and Al/SiO2/Ge-dot/SiO2/SiGe MOS capacitors exhibit low interface trap densities of as low as 3-5x10^11 cm^-2·eV^-1 and fixed charge densities of 1-5x10^11 cm^-2, suggesting good-quality SiO2/SiGe-shell and SiO2/Ge-dot interfaces. In addition, the advantage of having single-crystalline Si1-xGex shell (x > 0.5) in a compressive stress state in our self-aligned gate-stack heterostructure has great promise for possible SiGe (or Ge) MOS nanoelectronic and nanophotonic applications.

  2. 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.

  3. 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.

  4. 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.

  5. Ultrathin (5 nm) SiGe-On-Insulator with high compressive strain (-2 GPa): From fabrication (Ge enrichment process) to in-depth characterizations

    NASA Astrophysics Data System (ADS)

    Glowacki, F.; Le Royer, C.; Morand, Y.; Pédini, J.-M.; Denneulin, T.; Cooper, D.; Barnes, J.-P.; Nguyen, P.; Rouchon, D.; Hartmann, J.-M.; Gourhant, O.; Baylac, E.; Campidelli, Y.; Barge, D.; Bonnin, O.; Schwarzenbach, W.

    2014-07-01

    300 mm ultrathin Silicon-On-Insulator (SOI) wafers with SiGe/Si stacks on top were used as pre-structures for the fabrication of 5 nm thick SiGe-On-Insulator (SGOI) substrates obtained by the Ge enrichment technique. Those substrates will be used as the channel of advanced Fully Depleted (FD) p-type Metal Oxide Semiconductor Field Effect Transistors (pMOSFET). We present in the first part the successful fabrication of 5 nm SGOI wafers. Various characterization techniques are used to investigate the Ge profile and the final strain in the fabricated 5 nm Si0.7Ge0.3 film. Secondary Ions Mass Spectrometry (SIMS) and Scanning Transmission Electron Microscopy (STEM) clearly show that the Ge content is very homogeneous (xGe = 30 ± 1%) in the SiGe layer. Raman spectroscopy and High Angle Annular Dark Field (HAADF) STEM both confirm that the 5 nm thick SiGe film is compressively strained (-2 GPa). The second part is dedicated to the sensitivity of the Ge enrichment process (based on numerical modelling). We investigate the impact of single and combined fluctuations of the pre-structure parameters (TSi, TSiGe,0, xGe,0) on the final SiGe layer (TSiGe, xGe).

  6. Pseudomorphic GeSn/Ge (001) heterostructures

    SciTech Connect

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

    2013-11-15

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

  7. Resistive switching memory characteristics of Ge/GeOx nanowires and evidence of oxygen ion migration

    PubMed Central

    2013-01-01

    The resistive switching memory of Ge nanowires (NWs) in an IrOx/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/GeOx NWs is confirmed by both scanning electron microscopy and high-resolution transmission electron microscopy. Defects in the Ge/GeOx NWs are observed by X-ray photoelectron spectroscopy. Broad photoluminescence spectra from 10 to 300 K are observed because of defects in the Ge/GeOx NWs, which are also useful for nanoscale resistive switching memory. The resistive switching mechanism in an IrOx/GeOx/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 IrOx 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 GeOx film in the annealed device contains more oxygen vacancies. Under SET operation, Ge/GeOx nanofilaments (or NWs) form in the GeOx film. The diameter of the conducting nanofilament is approximately 40 nm, which is calculated using a new method. PMID:23657016

  8. Asymmetrically contacted germanium photodiode using a metal-interlayer-semiconductor-metal structure for extremely large dark current suppression.

    PubMed

    Zang, Hwan-Jun; Kim, Gwang-Sik; Park, Gil-Jae; Choi, Yong-Soo; Yu, Hyun-Yong

    2016-08-15

    In this study, we proposed germanium (Ge) metal-interlayer-semiconductor-metal (MISM) photodiodes (PD), with an anode of a metal-interlayer-semiconductor (MIS) contact and a cathode of a metal-semiconductor (MS) contact, to efficiently suppress the dark current of Ge PD. We selected titanium dioxide (TiO2) as an interlayer material for the MIS contact, due to its large valence band offset and negative conduction band offset to Ge. We significantly suppress the dark current of Ge PD by introducing the MISM structure with a TiO2 interlayer, as this enhances the hole Schottky barrier height, and thus acts as a large barrier for holes. In addition, it collects photo-generated carriers without degradation, due to its negative conduction band offset to Ge. This reduces the dark current of Ge MISM PDs by ×8000 for 7-nm-thick TiO2 interlayer, while its photo current is still comparable to that of Ge metal-semiconductor-metal (MSM) PDs. Furthermore, the proposed Ge PD shows ×6,600 improvement of the normalized photo-to-dark-current ratio (NPDR) at a wavelength of 1.55 μm. The proposed Ge MISM PD shows considerable promise for low power and high sensitivity Ge-based optoelectronic applications. PMID:27519063

  9. High density group IV semiconductor nanowire arrays fabricated in nanoporous alumina templates

    NASA Astrophysics Data System (ADS)

    Redwing, Joan M.; Dilts, Sarah M.; Lew, Kok-Keong; Cranmer, Alexana E.; Mohney, Suzanne E.

    2005-11-01

    The fabrication of high density arrays of semiconductor nanowires is of interest for nanoscale electronics, chemical and biological sensing and energy conversion applications. We have investigated the synthesis, intentional doping and electrical characterization of Si and Ge nanowires grown by the vapor-liquid-solid (VLS) method in nanoporous alumina membranes. Nanoporous membranes provide a convenient platform for nanowire growth and processing, enabling control of wire diameter via pore size and the integration of contact metals for electrical testing. For VLS growth in nanoporous materials, reduced pressures and temperatures are required in order to promote the diffusion of reactants into the pore without premature decomposition on the membrane surface or pore walls. The effect of growth conditions on the growth rate of Si and Ge nanowires from SiH 4 and GeH 4 sources, respectively, was investigated and compared. In both cases, the measured activation energies for nanowire growth were substantially lower than activation energies typically reported for Si and Ge thin film deposition under similar growth conditions, suggesting that gold plays a catalytic role in the VLS growth process. Intentionally doped SiNW arrays were also prepared using trimethylboron (TMB) and phosphine (PH 3) as p-type and n-type dopant sources, respectively. Nanowire resistivities were calculated from plots of the array resistance as a function of nanowire length. A decrease in resistivity was observed for both n-type and p-type doped SiNW arrays compared to those grown without the addition of a dopant source.

  10. The Physics of Semiconductors

    NASA Astrophysics Data System (ADS)

    Grundmann, Marius

    The historic development of semiconductor physics and technology began in the second half of the 19th century. Interesting discussions of the early history of the physics and chemistry of semiconductors can be found in treatises of G. Busch [2] and Handel [3]. The history of semiconductor industry can be followedin the text of Morris [4] and Holbrook et al. [5]. In 1947, the realization of the transistor was the impetus to a fast-paced development that created the electronics and photonics industries. Products founded on the basis of semiconductor devices such as computers (CPUs, memories), optical-storage media (lasers for CD, DVD), communication infrastructure (lasers and photodetectors for optical-fiber technology, high frequency electronics for mobile communication), displays (thin film transistors, LEDs), projection (laser diodes) and general lighting (LEDs) are commonplace. Thus, fundamental research on semiconductors and semiconductor physics and its offspring in the form of devices has contributed largely to the development of modern civilization and culture.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Spin injection into semiconductors

    NASA Astrophysics Data System (ADS)

    Oestreich, M.; Hübner, J.; Hägele, D.; Klar, P. J.; Heimbrodt, W.; Rühle, W. W.; Ashenford, D. E.; Lunn, B.

    1999-03-01

    The injection of spin-polarized electrons is presently one of the major challenges in semiconductor spin electronics. We propose and demonstrate a most efficient spin injection using diluted magnetic semiconductors as spin aligners. Time-resolved photoluminescence with a Cd0.98Mn0.02Te/CdTe structure proves the feasibility of the spin-alignment mechanism.

  18. 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.

  19. 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.

  20. Kesterite Cu2Zn(Sn,Ge)(S,Se)4 thin film with controlled Ge-doping for photovoltaic application

    NASA Astrophysics Data System (ADS)

    Zhao, Wangen; Pan, Daocheng; Liu, Shengzhong (Frank)

    2016-05-01

    Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm2 without an anti-reflection layer.Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm2 without an anti-reflection layer. Electronic supplementary information (ESI) available: The XRD patterns, chemical component analysis, top-view and cross-sectional images, and XPS of CZTGSSe thin films with different Ge content are exhibited. See DOI: 10.1039/c6nr00959j

  1. SiGe nanowire growth and characterization

    NASA Astrophysics Data System (ADS)

    Qi, Cheng; Goncher, Gary; Solanki, Raj; Jordan, Jay

    2007-02-01

    Single-crystal SiGe nanowires were synthesized via the vapour-liquid-solid (VLS) growth mechanism using disilane and germane as precursor gases. We have investigated the effect of temperature, pressure, and the inlet gas ratio on the growth and stoichiometry of SixGe1-x nanowires. The nanowires were characterized using scanning and transmission electron microscopies and energy dispersive x-ray analysis. It was found that nanowires with a Si:Ge ratio of about 1 had smooth surfaces, whereas departure from this ratio led to rough surfaces. Electrical properties were then investigated by fabricating back-gated field effect transistors (using a focused ion beam system) where single SiGe nanowires served as the conduction channels. Gated conduction was observed although resistance in the undoped devices was high.

  2. SiGe nanowire growth and characterization.

    PubMed

    Qi, Cheng; Goncher, Gary; Solanki, Raj; Jordan, Jay

    2007-02-21

    Single-crystal SiGe nanowires were synthesized via the vapour-liquid-solid (VLS) growth mechanism using disilane and germane as precursor gases. We have investigated the effect of temperature, pressure, and the inlet gas ratio on the growth and stoichiometry of Si(x)Ge(1-x) nanowires. The nanowires were characterized using scanning and transmission electron microscopies and energy dispersive x-ray analysis. It was found that nanowires with a Si:Ge ratio of about 1 had smooth surfaces, whereas departure from this ratio led to rough surfaces. Electrical properties were then investigated by fabricating back-gated field effect transistors (using a focused ion beam system) where single SiGe nanowires served as the conduction channels. Gated conduction was observed although resistance in the undoped devices was high. PMID:21730497

  3. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  5. Thin SiGe virtual substrates for Ge heterostructures integration on silicon

    SciTech Connect

    Cecchi, S. Chrastina, D.; Frigerio, J.; Isella, G.; Gatti, E.; Guzzi, M.; Müller Gubler, E.; Paul, D. J.

    2014-03-07

    The possibility to reduce the thickness of the SiGe virtual substrate, required for the integration of Ge heterostructures on Si, without heavily affecting the crystal quality is becoming fundamental in several applications. In this work, we present 1 μm thick Si{sub 1−x}Ge{sub x} buffers (with x > 0.7) having different designs which could be suitable for applications requiring a thin virtual substrate. The rationale is to reduce the lattice mismatch at the interface with the Si substrate by introducing composition steps and/or partial grading. The relatively low growth temperature (475 °C) makes this approach appealing for complementary metal-oxide-semiconductor integration. For all the investigated designs, a reduction of the threading dislocation density compared to constant composition Si{sub 1−x}Ge{sub x} layers was observed. The best buffer in terms of defects reduction was used as a virtual substrate for the deposition of a Ge/SiGe multiple quantum well structure. Room temperature optical absorption and photoluminescence analysis performed on nominally identical quantum wells grown on both a thick graded virtual substrate and the selected thin buffer demonstrates a comparable optical quality, confirming the effectiveness of the proposed approach.

  6. Semiconductor materials: From gemstone to semiconductor

    NASA Astrophysics Data System (ADS)

    Nebel, Christoph E.

    2003-07-01

    For diamond to be a viable semiconductor it must be possible to change its conductivity by adding impurities - known as dopants. With the discovery of a new dopant that generates electron conductivity at room temperature, diamond emerges as an electronic-grade material.

  7. 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

  8. Flexible germanium nanomembrane metal-semiconductor-metal photodiodes

    NASA Astrophysics Data System (ADS)

    Kim, Munho; Seo, Jung-Hun; Yu, Zongfu; Zhou, Weidong; Ma, Zhenqiang

    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/cm2 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. Density and Capture Cross-Section of Interface Traps in GeSnO2 and GeO2 Grown on Heteroepitaxial GeSn.

    PubMed

    Gupta, Somya; Simoen, Eddy; Loo, Roger; Madia, Oreste; Lin, Dennis; Merckling, Clement; Shimura, Yosuke; Conard, Thierry; Lauwaert, Johan; Vrielinck, Henk; Heyns, Marc

    2016-06-01

    An imperative factor in adapting GeSn as the channel material in CMOS technology, is the gate-oxide stack. The performance of GeSn transistors is degraded due to the high density of traps at the oxide-semiconductor interface. Several oxide-gate stacks have been pursued, and a midgap Dit obtained using the ac conductance method, is found in literature. However, a detailed signature of oxide traps like capture cross-section, donor/acceptor behavior and profile in the bandgap, is not yet available. We investigate the transition region between stoichiometric insulators and strained GeSn epitaxially grown on virtual Ge substrates. Al2O3 is used as high-κ oxide and either Ge1-xSnxO2 or GeO2 as interfacial layer oxide. The interface trap density (Dit) profile in the lower half of the bandgap is measured using deep level transient spectroscopy, and the importance of this technique for small bandgap materials like GeSn, is explained. Our results provide evidence for two conclusions. First, an interface traps density of 1.7 × 10(13) cm(-2)eV(-1) close to the valence band edge (Ev + 0.024 eV) and a capture cross-section (σp) of 1.7 × 10(-18) cm(2) is revealed for GeSnO2. These traps are associated with donor states. Second, it is shown that interfacial layer passivation of GeSn using GeO2 reduces the Dit by 1 order of magnitude (2.6 × 10(12) cm(-2)eV(-1)), in comparison to GeSnO2. The results are cross-verified using conductance method and saturation photovoltage technique. The Dit difference is associated with the presence of oxidized (Sn(4+)) and elemental Sn in the interfacial layer oxide. PMID:27172051

  10. 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.

  11. 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)

  12. Electrolysis of a molten semiconductor.

    PubMed

    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

  13. 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

  14. 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.

  15. 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.

  16. Growth kinetics of Si and Ge nanowires

    NASA Astrophysics Data System (ADS)

    Kodambaka, S.; Tersoff, J.; Reuter, M. C.; Ross, F. M.

    2009-02-01

    Si and Ge nanowires have potential applications in a wide variety of areas including thermoelectrics, optoelectronics, and sensors. Nanowires are most commonly grown via the vapor-liquid-solid (VLS) process. In this method, a vapor phase containing the material of interest preferentially dissociates at a liquid catalyst and is incorporated as a solid at the solid-liquid interface. However, despite 40 years of research in this area, several aspects of nanowire growth remain unclear, even for relatively simple elemental Si and Ge wires. Here, we will review our in situ transmission electron microscopy (TEM) investigations of Si and Ge nanowire growth kinetics. The observations are carried out in an ultra-high vacuum TEM (the IBM UHV-TEM) equipped with facilities for deposition during observation. Using Au as the catalyst, we study the VLS growth of Si and Ge nanowires as a function of disilane or digermane pressure and substrate temperature. We find surprisingly different growth mechanisms for the two materials. The insights gained from in situ results may help devise methods for large-scale fabrication of wires with controlled architecture.

  17. Investigation of the optical properties of ordered semiconductor materials

    NASA Astrophysics Data System (ADS)

    McCrae, Jack E., Jr.

    1997-11-01

    Optical Studies have been conducted upon CdGeAs2 and ZnGeP2, two of the most promising semiconductors being developed for mid-infrared non-linear optics applications. These experiments included photoluminescence (PL) studies of both compounds as well as photoreflectance (PR) measurements upon CdGeAs2. In addition, Hall effect measurements were carried out upon CdGeAs2, to aid in interpretation of the optical data. PL was measured as a function of laser power, sample temperature, and crystal orientation for CdGeAs2. One broad weak peak near 0.38 eV, and another somewhat narrower and often far brighter peak near 0.57 eV were found by low temperature (4 K) PL measurements. Strongly polarized PL was observed with the E field of the PL parallel to the material's c-axis. A polarization ratio as high as 6:1 was observed. PL on ZnGeP2 in the mid-IR revealed a previously unreported PL peak near 0.35 eV. PR measurements on CdCeAs2 allowed the estimation of the bandgap as a function of temperature. The low temperature bandgap proved to be lower than that reported for electroreflectance measurements on other samples of this compound. Hall effect measurements on CdGeAs2 reveals the dominant acceptor level lies about 120 meV above the valence band.

  18. 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

  19. 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.

  20. 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

  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. PMID:26291331

  2. 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.

  3. 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.

  4. Structural properties of Ge on SrTiO3 (001) surface and Ge/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Pu, Long; Wang, Jianli; Tang, Gang; Zhang, Junting

    2015-03-01

    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) SrTiO3 by first-principle calculations. The specific adsorption sites at the initial growth stage and the atomic structure of Ge on the SrTiO3 (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/SrTiO3 (001) interfaces. The atomic structure and electronic properties of the intrinsic point defects were calculated and analyzed for the Ge/SrTiO3 (001) interfaces.

  5. Thermionic evaporation of films of multicomponent chalcogenide semiconductors

    SciTech Connect

    Serigenko, T.I.; Gritsenko, K.P.; Kryuchin, A.A.; Petrov, V.V.; Yudin, G.Y.

    1985-08-01

    This paper describes a procedure for the preparation of thin films of multicomponent chalcogenide semiconductors of As-Te-Se and As-Te-Ge by thermionic evaporation, using a discrete evaporator. Films of thickness 20-60 nm evaporated onto a glass substrate had an adhesion of 35-40 kg/cm/sup 2/. The films have enhanced homogeneity and time stability as compared to thin films of the same composition prepared by thermal evaporation.

  6. Glasslike Heat Conduction in High-Mobility Crystalline Semiconductors

    NASA Astrophysics Data System (ADS)

    Cohn, J. L.; Nolas, G. S.; Fessatidis, V.; Metcalf, T. H.; Slack, G. A.

    1999-01-01

    The thermal conductivity of polycrystalline semiconductors with type-I clathrate hydrate crystal structure is reported. Ge clathrates (doped with Sr and/or Eu) exhibit lattice thermal conductivities typical of amorphous materials. Remarkably, this behavior occurs in spite of the well-defined crystalline structure and relatively high electron mobility ( ~100 cm2/V s). The dynamics of dopant ions and their interaction with the polyhedral cages of the structure are a likely source of the strong phonon scattering.

  7. 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.

  8. Using Organonitriles to Modify the Semiconductor Interface

    NASA Astrophysics Data System (ADS)

    Filler, Michael A.; Bent, Stacey F.

    2002-03-01

    The creation of an ordered array of covalently-bonded organic molecules at semiconductor interfaces has potential applications in molecular electronics, sensors, and nonlinear optics. The dimers on the Si(100) and Ge(100) surfaces exhibit some properties of alkenes and provide an ordered template of reactive sites for classical organic reactions. The present work focuses on organonitrile compounds as candidates for first and subsequent layer surface reactions. Bonding chemistry is investigated with infrared spectroscopy and DFT. We show that the conjugated molecule, 2-propenenitrile, bonds to Ge(100) through two distinct pathways: a [2+2] cycloaddition through the alkene and a [4+2] cycloaddition involving the conjugated pi system. Reaction on Si(100) resulted in one additional product: a [2+2] cycloaddition through the nitrile. A reaction only through the nitrile group is thermodynamically unfavorable on Ge(100) and this functional group remains available for second layer reactions. The use of photochemical techniques to induce further reactions will also be presented.

  9. Nanocavity effects on misfit accommodation in semiconductors

    SciTech Connect

    Myers, S.M.; Follstaedt, D.M.; Floro, J.A.; Lee, S.R.; Dawson, L.R.; Reno, J.L.

    1997-04-01

    The authors report an experimental and theoretical examination of the interaction of dislocations with microscopic cavities in semiconductors and the consequences for strain relaxation in heteroepitaxial structures. Dislocation-mediated relaxation and control of the resulting defect microstructure is central to the exploitation of such heterostructures in devices, and they demonstrate here that the introduction of nanometer-scale voids provides a means of strongly influencing this microstructural evolution. Methods for nanocavity formation using He ion implantation and annealing were developed for Si, SiGe on Si, GaAs, and InGaAs on GaAs. In detailed microstructural studies of SiGe on Si, cavities in the interfacial zone were shown to bind dislocations strongly. This effect reduced the excursion of dislocations into the nearby matrix, although threads into the SiGe overlayer were not eliminated. Interfacial cavities also increased the rate of stress relaxation by more than an order of magnitude as a result of enhanced nucleation of misfit dislocations. Further, in the presence of such cavities, the development of thickness variations in the overlayer during relaxation was suppressed. A theoretical model was developed to describe semiquantitatively the forces on dislocations arising from the combined influences of cavities, misfit strain, and the external surface. Predictions of this model are in accord with microstructural observations.

  10. 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

  11. 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.

  12. 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.

  13. Accurate strain measurements in highly strained Ge microbridges

    NASA Astrophysics Data System (ADS)

    Gassenq, A.; Tardif, S.; Guilloy, K.; Osvaldo Dias, G.; Pauc, N.; Duchemin, I.; Rouchon, D.; Hartmann, J.-M.; Widiez, J.; Escalante, J.; Niquet, Y.-M.; Geiger, R.; Zabel, T.; Sigg, H.; Faist, J.; Chelnokov, A.; Rieutord, F.; Reboud, V.; Calvo, V.

    2016-06-01

    Ge under high strain is predicted to become a direct bandgap semiconductor. Very large deformations can be introduced using microbridge devices. However, at the microscale, strain values are commonly deduced from Raman spectroscopy using empirical linear models only established up to ɛ100 = 1.2% for uniaxial stress. In this work, we calibrate the Raman-strain relation at higher strain using synchrotron based microdiffraction. The Ge microbridges show unprecedented high tensile strain up to 4.9% corresponding to an unexpected Δω = 9.9 cm-1 Raman shift. We demonstrate experimentally and theoretically that the Raman strain relation is not linear and we provide a more accurate expression.

  14. 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.

  15. Comet Ge-Wang

    NASA Astrophysics Data System (ADS)

    Ge, Yong-liang; Wang, Qi; Han, Tao

    1990-03-01

    Comet Ge-Wang (1988o) was discovered by GE Yong-liang and WANG Qi at Xinglong Station of Beijing Observatory on 1988 November 4. We collected 13 observations of this comet in China and abroad and calculated its orbit. It passed the perihelion on 1988 May 23. Ephemerides up to 1991 April are given.

  16. Comet Ge-Wang

    NASA Astrophysics Data System (ADS)

    Ge, Yong-Liang; Wang, Qi; Han, Tao

    1989-03-01

    Comet Ge-Wang (1988o) was discovered by GE Yong-liang and WANG Qi at Xinglong Station of Beijing Observatory on November 4, 1988. Thirteen observations of this comet were collected in China and abroad and calculated its orbit. It passed the perihelion on May 23, 1988. Ephemerides up to April 1991 are given.

  17. Synthesis and atomic and electronic structure of new Si-Ge-C alloys and compounds

    SciTech Connect

    Kouvetakis, J.; Nesting, D.; Smith, D.J.

    1998-10-01

    The synthesis and characterization of completely novel binary and ternary alloy semiconductors and ordered phases based on C, Si, and Ge are discussed in this review. Metastable compound semiconductors with ordered structures, which include stoichiometric SiGe, Si{sub 4}C, Si{sub 3}GeC{sub 4} (sphalerite), Ge{sub 4}C, (Si{sub 2}Ge)C{sub x}, and (Ge{sub 2}Si)C{sub x} (x = 5%), are described. Materials systems include diamond-structured silicon-germanium solid solutions with dissolved carbon (Si{sub 1{minus}x{minus}y}Ge{sub x}C{sub y}), monocrystalline Ge{sub 1{minus}x}C{sub x} hybrids of Ge, and C-diamond and related Si-containing random alloy systems. The Si{sub 4}C and Ge{sub 4}C materials incorporate the corresponding tetrahedra that are linked together to form a diamond-cubic structure related to Si. The Si{sub 3}GeC{sub 4} phase is related to sphalerite and (Si{sub 2}Ge)C{sub x} had a new P{anti 3}m1 structure formed by Ge-Si-Si ordering along the diamond {l_angle}111{r_angle} direction. These compounds offer the prospect of band gaps wider than that of Si; in some cases, the band gaps are expected to become direct. This report emphasizes an approach that combines novel precursor chemistries and modern deposition techniques (ultrahigh-vacuum chemical-vapor deposition) to develop heteroepitaxial, device-quality inorganic materials. Important highlights of recent research based on conventional deposition methods are also summarized.

  18. 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)

  19. Superconductivity in doped semiconductors

    NASA Astrophysics Data System (ADS)

    Bustarret, E.

    2015-07-01

    A historical survey of the main normal and superconducting state properties of several semiconductors doped into superconductivity is proposed. This class of materials includes selenides, tellurides, oxides and column-IV semiconductors. Most of the experimental data point to a weak coupling pairing mechanism, probably phonon-mediated in the case of diamond, but probably not in the case of strontium titanate, these being the most intensively studied materials over the last decade. Despite promising theoretical predictions based on a conventional mechanism, the occurrence of critical temperatures significantly higher than 10 K has not been yet verified. However, the class provides an enticing playground for testing theories and devices alike.

  20. 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

    2014-11-01

    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. PMID:24975009

  1. 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).

  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. 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.

  4. 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.

  5. 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…

  6. 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.

  7. Ge growth on porous silicon: The effect of buffer porosity on the epilayer crystalline quality

    NASA Astrophysics Data System (ADS)

    Calabrese, G.; Baricordi, S.; Bernardoni, P.; De Salvador, D.; Ferroni, M.; Guidi, V.; Morandi, V.; Vincenzi, D.

    2014-09-01

    We report on the epitaxial growth of Ge virtual substrates directly on Si (001) and on different porosity porous silicon (pSi) buffers. Obtained results indicate that Ge grown on low porosity (22%) pSi buffer has a better crystalline quality compared to Ge grown on bulk Si and on higher porosity buffers. This result is attributed to the compliant nature of pSi and to its reduced Young's modulus, which leads to plastic tensile deformation of the 22% porosity buffer under the in-plane tensile stress introduced by Ge lattice. The same result is not observed for higher porosity buffers, this effect being attributed to the higher buffer fragility. A low porosity pSi layer can hence be used as buffer for the growth of Ge on Si virtual substrates with reduced dislocation content and for the growth of Ge based devices or the successive integration of III-V semiconductors on Si.

  8. Strain relief and shape oscillations in site-controlled coherent SiGe islands.

    PubMed

    Hrauda, N; Zhang, J J; Groiss, H; Etzelstorfer, T; Holý, V; Bauer, G; Deiter, C; Seeck, O H; Stangl, J

    2013-08-23

    Strain engineering and the crystalline quality of semiconductor nanostructures are important issues for electronic and optoelectronic devices. We report on defect-free SiGe island arrays resulting from Ge coverages of up to 38 monolayers grown on prepatterned Si(001) substrates. This represents a significant expansion of the parameter space known for the growth of perfect island arrays. A cyclic development of the Ge content and island shape was observed while increasing the Ge coverage. Synchrotron-based x-ray diffraction experiments and finite element method calculations allow us to study the strain behavior of such islands in great detail. In contrast to the oscillatory changes of island shape and average Ge content, the overall strain behavior of these islands exhibits a clear monotonic trend of progressive strain relaxation with increasing Ge coverage. PMID:23892543

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  10. Photoluminescence study of high density Si quantum dots with Ge core

    NASA Astrophysics Data System (ADS)

    Kondo, K.; Makihara, K.; Ikeda, M.; Miyazaki, S.

    2016-01-01

    Si quantum dots (Si-QDs) with Ge core were self-assembled on thermally grown SiO2 from alternate thermal decomposition of pure SiH4 and GeH4 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.

  11. Phase formation during Mn thin film reaction with Ge: Self-aligned germanide process for spintronics

    NASA Astrophysics Data System (ADS)

    Abbes, O.; Portavoce, A.; Le Thanh, V.; Girardeaux, C.; Michez, L.

    2013-10-01

    Interesting results have been reported concerning the magnetic properties of the Mn5Ge3 compound, opening the road to possibly create spin injectors in Ge. However, a process compatible with the Complementary Metal Oxide Semiconductor technology, allowing to produce a Mn5Ge3 layer on the active regions of Ge-based transistors has not been well established yet. Here, we report on the solid state reaction between a 50 nm-thick Mn film and amorphous Ge, aiming to investigate a similar process than the one (Salicide) used for contact production in the standard Si technology. In situ X-ray diffraction combined with ex situ structural and magnetic characterizations were used to identify and study phase formation during the Mn/Ge reaction.

  12. Strain relief and shape oscillations in site-controlled coherent SiGe islands

    NASA Astrophysics Data System (ADS)

    Hrauda, N.; Zhang, J. J.; Groiss, H.; Etzelstorfer, T.; Holý, V.; Bauer, G.; Deiter, C.; Seeck, O. H.; Stangl, J.

    2013-08-01

    Strain engineering and the crystalline quality of semiconductor nanostructures are important issues for electronic and optoelectronic devices. We report on defect-free SiGe island arrays resulting from Ge coverages of up to 38 monolayers grown on prepatterned Si(001) substrates. This represents a significant expansion of the parameter space known for the growth of perfect island arrays. A cyclic development of the Ge content and island shape was observed while increasing the Ge coverage. Synchrotron-based x-ray diffraction experiments and finite element method calculations allow us to study the strain behavior of such islands in great detail. In contrast to the oscillatory changes of island shape and average Ge content, the overall strain behavior of these islands exhibits a clear monotonic trend of progressive strain relaxation with increasing Ge coverage.

  13. 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.

  14. Development of a ReaxFF reactive force field for Si/Ge/H systems and application to atomic hydrogen bombardment of Si, Ge, and SiGe (100) surfaces

    NASA Astrophysics Data System (ADS)

    Psofogiannakis, George; van Duin, Adri C. T.

    2016-04-01

    A new reactive force field was developed for use in molecular dynamics simulations of chemical systems composed of silicon (Si), germanium (Ge), and hydrogen (H) with the ReaxFF code. The development incorporated Ge into the ReaxFF family of reactive potentials by fitting against a diverse training set of DFT data that pertain to Si/Ge/H bonding environments. The predictive capacity of the force field was manifested in molecular dynamics simulations of the H atom bombardment of the (100) surface of c-Si, c-Ge, and c-SiGe crystalline solid slabs in order to simulate the effects of the H-plasma semiconductor cleaning process in the near-surface region. Phenomena related to surface and subsurface H adsorption, H2 generation, and surface etching were described and compared in relation to material composition and the kinetic energy of the impinging atoms.

  15. 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

  16. Origin of Fermi-level pinning and its control on the n -type Ge(100) surface

    NASA Astrophysics Data System (ADS)

    Kuzmin, Mikhail; Laukkanen, Pekka; Mäkelä, Jaakko; Tuominen, Marjukka; Yasir, Muhammad; Dahl, Johnny; Punkkinen, Marko P. J.; Kokko, Kalevi

    2016-07-01

    Strong Fermi-level pinning (FLP) near the valence-band maximum on n -type Ge surfaces has been a long-standing challenge in semiconductor physics, and the nature of this phenomenon has been heavily debated for years. Here, we report a systematic synchrotron-based photoemission study of atomically well-defined Ge(100) surfaces and interfaces to elucidate the origin of FLP in such systems. It is experimentally shown that the FLP on n -Ge is not due to the dangling-bond, back-bond, and defect states, but is strongly contributed by the evanescent state of the Ge bulk. The conditions required for alleviating the FLP and even the implementation of a flatband structure on Ge(100) are formulated. Such a structure is realized in the BaO/Ge(100) system where one can obtain control over the Fermi-level position in the Ge gap. These findings are not only important from a fundamental viewpoint, but also open a route to producing Ohmic metal-insulator-semiconductor contacts for n -type Ge-based technology.

  17. Phosphate-free synthesis, optical absorption and photoelectric properties of Cu2ZnGeS4 and Cu2ZnGeSe4 uniform nanocrystals.

    PubMed

    Shi, Liang; Yin, Peiqun

    2013-10-01

    Copper-based quaternary chalcogenide semiconductor Cu2ZnGeS4 and Cu2ZnGeSe4 nanocrystals have been synthesized successfully via a simple and convenient one-pot phosphine-free solution approach. Oleylamine was used as both the solvent and reductant for Se or S and benefited the formation of homogeneous quaternary nanocrystals. Scanning transmission electron microscopy-EDS elemental mapping confirms the uniform spatial distribution of four elements in nanocrystals. UV-Vis absorption spectra of Cu2ZnGeS4 and Cu2ZnGeSe4 nanocrystals show strong photon absorption in the entire visible range. The photoresponsive behavior indicates the potential application of Cu2ZnGeSe4 nanocrystals in solar energy conversion systems. PMID:23900582

  18. Carrier Density Modulation in Ge Heterostructure by Ferroelectric Switching

    DOE PAGESBeta

    Ponath, Patrick; Fredrickson, Kurt; Posadas, Agham B.; Ren, Yuan; Vasudevan, Rama K.; Okatan, Mahmut Baris; Jesse, Stephen; Aoki, Toshihiro; McCartney, Martha; Smith, David J.; et al

    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

  19. Thermal reliability of thin SiGe epilayers

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  20. 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.

  1. Doped semiconductor nanocrystal junctions

    NASA Astrophysics Data System (ADS)

    Borowik, Ł.; Nguyen-Tran, T.; Roca i Cabarrocas, P.; Mélin, T.

    2013-11-01

    Semiconductor junctions are the basis of electronic and photovoltaic devices. Here, we investigate junctions formed from highly doped (ND≈1020-1021cm-3) silicon nanocrystals (NCs) in the 2-50 nm size range, using Kelvin probe force microscopy experiments with single charge sensitivity. We show that the charge transfer from doped NCs towards a two-dimensional layer experimentally follows a simple phenomenological law, corresponding to formation of an interface dipole linearly increasing with the NC diameter. This feature leads to analytically predictable junction properties down to quantum size regimes: NC depletion width independent of the NC size and varying as ND-1/3, and depleted charge linearly increasing with the NC diameter and varying as ND1/3. We thus establish a "nanocrystal counterpart" of conventional semiconductor planar junctions, here however valid in regimes of strong electrostatic and quantum confinements.

  2. 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.

  3. X-ray studies of multilayer semiconductors using synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Huang, Shiwen

    X-ray scattering and absorption techniques utilizing synchrotron radiation have been used to study a variety of multilayer semiconductors. The angular-dependent x-ray scattering at grazing incidence angles (grazing incidence x-ray scattering, GIXS) provides structural information of interfaces in these materials, such as rms interfacial roughness, cross- and lateral-correlation lengths, etc. Long-range order structures in material are probed by large-angle scattering (x-ray diffraction), in which strain and lattice constant as well as crystallinity of the epilayers are measured. Local structural variations in materials including local bond length, coordination number, and local disorder are obtained quantitatively by examining the modulation in the x-ray absorption spectrum some 40 eV above the absorption edge (extended x-ray absorption fine structure, EXAFS). Materials studied in the present work are SiGe/Si heterostructures, MnAs/GaAs ferromagnetic-semiconductor films, solar cell films, ZnSe-based II-VI semiconductor thin films, InGaAs/GaAs and GaAs/AlAs superlattices. Results obtained have shown (i) evidence for strain-induced surface/interface morphology variations in SiGe/Si heterostructures, (ii) template-dependent microstructures in MnAs/GaAs, (iii) changes in interface structures for films of different formations in solar cell films, (iv) differences between samples prepared by different epitaxial growth methods in II-VI semiconductor films, (v) observation of lateral structural ordering in one of the InGaAs/GaAs superlattices, (vi) differences in interfacial microstructures between MBE-grown samples with different interrupts in GaAs/AlAs superlattices. Most of all, x- rays are found to be a very useful nondestructive tool for probing microscopic structures in various multilayer semiconductor materials.

  4. 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.

  5. 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.

  6. Ultrathin GeSn p-channel MOSFETs grown directly on Si(111) substrate using solid phase epitaxy

    NASA Astrophysics Data System (ADS)

    Maeda, Tatsuro; Jevasuwan, Wipakorn; Hattori, Hiroyuki; Uchida, Noriyuki; Miura, Shu; Tanaka, Masatoshi; Santos, Nuno D. M.; Vantomme, André; Locquet, Jean-Pierre; Lieten, Ruben R.

    2015-04-01

    Ultrathin GeSn layers with a thickness of 5.5 nm are fabricated on a Si(111) substrate by solid phase epitaxy (SPE) of amorphous GeSn layers with Sn concentrations up to 6.7%. We demonstrate well-behaved depletion-mode operation of GeSn p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) with an on/off ratio of more than 1000 owing to the ultrathin GeSn channel layer (5.5 nm). It is found that the on current increases significantly with increasing Sn concentration at the same gate overdrive, attributed to an increasing substitutional Sn incorporation in Ge. The GeSn (6.7%) layer sample shows approximately 90% enhancement in hole mobility in comparison with a pure Ge channel on Si.

  7. Strained Germanium-Tin pMOSFET Fabricated on a Silicon-on-Insulator Substrate with Relaxed Ge Buffer

    NASA Astrophysics Data System (ADS)

    Su, Shao-Jian; Han, Gen-Quan; Zhang, Dong-Liang; Zhang, Guang-Ze; Xue, Chun-Lai; Wang, Qi-Ming; Cheng, Bu-Wen

    2013-11-01

    Germanium-tin (Ge1-xSnx) p-type metal-oxide-semiconductor field effect transistors (pMOSFETs) were fabricated using a strained Ge0.985Sn0.015 thin film that was epitaxially grown on a silicon-on-insulator substrate with a relaxed Ge buffer layer. The Ge buffer was deposited using a two-step chemical vapor deposition growth technique. The high quality Ge0.985Sn0.015 layer was grown by solid source molecular beam epitaxy. Ge0.985Sn0.015 pMOSFETs with Si surface passivation, TaN/HfO2 gate stack, and nickel stanogermanide [Ni(Ge1-xSnx)] source/drain were fabricated on the grown substrate. The device achieves an effective hole mobility of 182 cm2/V·s at an inversion carrier density of 1 × 1013 cm-2.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. Properties of nanocones formed on a surface of semiconductors by laser radiation: quantum confinement effect of electrons, phonons, and excitons.

    PubMed

    Medvid, Artur; Onufrijevs, Pavels; Mychko, Alexander

    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

  15. 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. PMID:27433604

  16. Low energy positrons as probes of reconstructed semiconductor surfaces.

    NASA Astrophysics Data System (ADS)

    Fazleev, Nail G.; Weiss, Alex H.

    2007-03-01

    Positron probes of semiconductor surfaces that play a fundamental role in modern science and technology are capable to non-destructively provide information that is both unique to the probe and complimentary to that extracted using other more standard techniques. We discuss recent progress in studies of the reconstructed Si(100), Si(111), Ge(100), and Ge(111) surfaces, clean and exposed to hydrogen and oxygen, using a surface characterization technique, Positron-Annihilation-Induced Auger-Electron Spectroscopy (PAES). Experimental PAES results are analyzed by performing first-principles calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons for the reconstructed surfaces, taking into account discrete lattice effects, the electronic reorganization due to bonding, and charge redistribution effects at the surface. Effects of the hydrogen and oxygen adsorption on semiconductor surfaces on localization of positron surface state wave functions and annihilation characteristics are also analyzed. Theoretical calculations confirm that PAES intensities, which are proportional to annihilation probabilities of the surface trapped positrons that results in a core hole, are sensitive to the crystal face, surface structure and elemental content of the semiconductors.

  17. Fully and partially Li-stuffed diamond polytypes with Ag-Ge structures: Li2AgGe and Li2.53AgGe2.

    PubMed

    Henze, Alexander; Hlukhyy, Viktor; Fässler, Thomas F

    2015-02-01

    In view of the search for and understanding of new materials for energy storage, the Li-Ag-Ge phase diagram has been investigated. High-temperature syntheses of Li with reguli of premelted Ag and Ge led to the two new compounds Li(2)AgGe and Li(2.80-x)AgGe(2) (x = 0.27). The compounds were characterized by single-crystal X-ray diffraction. Both compounds show diamond-polytype-like polyanionic substructures with tetrahedrally coordinated Ag and Ge atoms. The Li ions are located in the channels provided by the network. The compound Li(2)AgGe crystallizes in the space group R3̅m (No. 166) with lattice parameters of a = 4.4424(6) Å and c = 42.7104(6) Å. All atomic positions are fully occupied and ordered. Li(2.80-x)AgGe(2) crystallizes in the space group I4(1)/a (No. 88) with lattice parameters of a = 9.7606(2) Å and c = 18.4399(8) Å. The Ge substructure consists of unique (1)(∞)[Ge(10)] chains that are interconnected by Ag atoms to build a three-dimensional network. In the channels of this diamond-like network, not all of the possible positions are occupied by Li ions. Li atoms in the neighborhood of the vacancies show considerably enlarged displacement vectors. The occurrence of the vacancy is traced back to short Li-Li distances in the case of the occupation of the vacancy with Li. Both compounds are not electron-precise Zintl phases. The density of states, band structure, and crystal orbital Hamilton population analyses of Li(2.80-x)AgGe(2 )reveal metallic properties, whereas a full occupation of all Li sites leads to an electron-precise Zintl compound within a rigid-band model. Li(2)AgGe reveals metallic character in the ab plane and is a semiconductor with a small band gap along the c direction. PMID:25521213

  18. Theory of hydrogen in semiconductors

    SciTech Connect

    Walle, C.G. van de

    1998-12-31

    This paper treats the subject of hydrogen in semiconductors from various perspectives. First, a brief historical overview is given. Then, some basic principles governing the interaction between hydrogen and semiconductors are outlined. Finally, specific examples will emphasize the impact of hydrogen on technological applications. While the general treatment applies to interactions of hydrogen with any semiconductor, the applications will focus mainly on hydrogen interacting with silicon.

  19. New developments in power semiconductors

    NASA Technical Reports Server (NTRS)

    Sundberg, G. R.

    1983-01-01

    This paper represents an overview of some recent power semiconductor developments and spotlights new technologies that may have significant impact for aircraft electric secondary power. Primary emphasis will be on NASA-Lewis-supported developments in transistors, diodes, a new family of semiconductors, and solid-state remote power controllers. Several semiconductor companies that are moving into the power arena with devices rated at 400 V and 50 A and above are listed, with a brief look at a few devices.

  20. Method of passivating semiconductor surfaces

    DOEpatents

    Wanlass, M.W.

    1990-06-19

    A method is described for passivating Group III-V or II-VI semiconductor compound surfaces. The method includes selecting a passivating material having a lattice constant substantially mismatched to the lattice constant of the semiconductor compound. The passivating material is then grown as an ultrathin layer of passivating material on the surface of the Group III-V or II-VI semiconductor compound. The passivating material is grown to a thickness sufficient to maintain a coherent interface between the ultrathin passivating material and the semiconductor compound. In addition, a device formed from such method is also disclosed.

  1. Method of passivating semiconductor surfaces

    DOEpatents

    Wanlass, Mark W.

    1990-01-01

    A method of passivating Group III-V or II-VI semiconductor compound surfaces. The method includes selecting a passivating material having a lattice constant substantially mismatched to the lattice constant of the semiconductor compound. The passivating material is then grown as an ultrathin layer of passivating material on the surface of the Group III-V or II-VI semiconductor compound. The passivating material is grown to a thickness sufficient to maintain a coherent interface between the ultrathin passivating material and the semiconductor compound. In addition, a device formed from such method is also disclosed.

  2. 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.

  3. Ohmic contact on n-type Ge using Yb-germanide

    NASA Astrophysics Data System (ADS)

    Zheng, Zhi-Wei; Ku, Teng-Chieh; Liu, Ming; Chin, Albert

    2012-11-01

    Poor ohmic contact by Fermi-level pinning to valence band (EV) 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 °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.

  4. Lattice Location Determination of Ge in SiC by ALCHEMI

    NASA Astrophysics Data System (ADS)

    Kups, T.; Voelskow, M.; Skorupa, W.; Soueidan, M.; Ferro, G.; Pezoldt, J.

    The incorporation of Ge into cubic and hexagonal silicon carbide is compared for three different doping methods: ion-implantation, molecular beam epitaxy and liquid phase epitaxy. The lattice location of Ge was determined by the transmission electron microscopy based method ALCHEMI (atomic location by channelling enhanced microanalysis). Depending on the method used for incorporation, Ge is able to occupy different silicon carbide lattice locations.

  5. Semiconductor cooling apparatus

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor); Gaier, James R. (Inventor)

    1993-01-01

    Gas derived graphite fibers generated by the decomposition of an organic gas are joined with a suitable binder. This produces a high thermal conductivity composite material which passively conducts heat from a source, such as a semiconductor, to a heat sink. The fibers may be intercalated. The intercalate can be halogen or halide salt, alkaline metal, or any other species which contributes to the electrical conductivity improvement of the graphite fiber. The fibers are bundled and joined with a suitable binder to form a high thermal conductivity composite material device. The heat transfer device may also be made of intercalated highly oriented pyrolytic graphite and machined, rather than made of fibers.

  6. Semiconductor superlattice photodetectors

    NASA Technical Reports Server (NTRS)

    Chuang, S. L.; Hess, K.; Coleman, J. J.; Leburton, J. P.

    1984-01-01

    A superlattice photomultiplier and a photodetector based on the real space transfer mechanism were studied. The wavelength for the first device is of the order of a micron or flexible corresponding to the bandgap absorption in a semiconductor. The wavelength for the second device is in the micron range (about 2 to 12 microns) corresponding to the energy of the conduction band edge discontinuity between an Al/(sub x)Ga(sub 1-x)As and GaAs interface. Both devices are described.

  7. Semiconductor structure and devices

    NASA Technical Reports Server (NTRS)

    Dinkel, Nancy A. (Inventor); Goldstein, Bernard (Inventor); Ettenberg, Michael (Inventor)

    1987-01-01

    Semiconductor devices such as lasers which include a substrate with a channel therein with a clad layer overlying the substrate and filling the channel exhibit irregularities such as terraces in the surface of the clad layer which are detrimental to device performance. These irregularities are substantially eliminated by forming the channel in a surface of a buffer layer greater than about 4 micrometers thick on the substrate and forming the clad layer over the buffer layer and the channel. CW lasers incorporating the principles of the invention exhibit the highest output power in a single spatial mode and maximum output power which have been observed to date.

  8. Isotopically controlled semiconductors

    SciTech Connect

    Haller, Eugene E.

    2001-12-21

    Semiconductor bulk crystals and multilayer structures with controlled isotopic composition have attracted much scientific and technical interest in the past few years. Isotopic composition affects a large number of physical properties, including phonon energies and lifetimes, bandgaps, the thermal conductivity and expansion coefficient and spin-related effects. Isotope superlattices are ideal media for self-diffusion studies. In combination with neutron transmutation doping, isotope control offers a novel approach to metal-insulator transition studies. Spintronics, quantum computing and nanoparticle science are emerging fields using isotope control.

  9. Layered semiconductor neutron detectors

    DOEpatents

    Mao, Samuel S; Perry, Dale L

    2013-12-10

    Room temperature operating solid state hand held neutron detectors integrate one or more relatively thin layers of a high neutron interaction cross-section element or materials with semiconductor detectors. The high neutron interaction cross-section element (e.g., Gd, B or Li) or materials comprising at least one high neutron interaction cross-section element can be in the form of unstructured layers or micro- or nano-structured arrays. Such architecture provides high efficiency neutron detector devices by capturing substantially more carriers produced from high energy .alpha.-particles or .gamma.-photons generated by neutron interaction.

  10. Composite Semiconductor Substrates

    NASA Technical Reports Server (NTRS)

    Nouhi, Akbar; Radhakrishnan, Gouri; Katz, Joseph; Koliwad, Kris

    1989-01-01

    Epitaxial structure of three semiconductor materials - silicon, gallium arsenide, and cadmium telluride - makes possible integrated monolithic focal-plane arrays of photodectors. Silicon layer contains charge-coupled devices, gallium arsenide layer contains other fast electronic circuitry, and cadmium telluride layer serves as base for array of mercury cadmium telluride infrared sensors. Technique effectively combines two well-established techniques; metalorganic chemical-vapor deposition (MOCVD) and molecular-beam epitaxy (MBE). Multilayer structure includes HgCdTe light sensors with Si readout devices and GaAs signal-processing circuits. CdTe layer provides base for building up HgCdTe layer.

  11. Fabrication of crystalline Ge thin films by co-deposition of Au and Ge at low substrate temperatures (<200 °C) without post annealing

    NASA Astrophysics Data System (ADS)

    Sugiyama, Takatoshi; Mishiba, Naoya; Kamiko, Masao; Kyuno, Kentaro

    2016-09-01

    Crystalline Ge thin films with (111) orientation are obtained by co-depositing Au and Ge on a substrate heated to ∼170 °C, with Au segregating at the film surface, which is desirable for selective etching. Although in the conventional metal-induced crystallization method using Au as a catalyst, a bilayer of Au and amorphous Ge layers have to be annealed for Ge to crystallize, the film in this study is already crystalline in the as-deposited state. The effective crystallization process implies the existence of a supercooled liquid alloy layer at the growth front.

  12. The Kingdom of Semiconductors

    NASA Astrophysics Data System (ADS)

    Bellac, Michel Le

    2014-11-01

    In this chapter, we move on to the case of fermions, and we shall find out that fermions are no less interesting than bosons! In practice, electrons are the most important example of fermions, because they are responsible for electrical conductivity in metals and semiconductors. It is impossible to understand a phenomenon as familiar as electrical conductivity without appealing to quantum physics. Two properties play a fundamental role: first the propagation of electron waves in crystal lattices, and second the Pauli exclusion principle, which is a consequence of the fermionic character of the electrons. In Section 6.1, we introduce electron wave propagation in crystals which gives rise to the phenomenon of energy bands, and we describe the filling of these bands according to the Pauli principle. These results will be used in Section 6.2 to describe the electronic properties of semiconductors, on which almost all our modern technology (laser diodes, optical fiber communication, computers, smartphones and so forth) is grounded. Finally, in Sections 6.3 and 6.4, we shall describe the principles of light emitting diodes (LEDs) and laser diodes.

  13. Doped semiconductor nanocrystal junctions

    SciTech Connect

    Borowik, Ł.; Mélin, T.; Nguyen-Tran, T.; Roca i Cabarrocas, P.

    2013-11-28

    Semiconductor junctions are the basis of electronic and photovoltaic devices. Here, we investigate junctions formed from highly doped (N{sub D}≈10{sup 20}−10{sup 21}cm{sup −3}) silicon nanocrystals (NCs) in the 2–50 nm size range, using Kelvin probe force microscopy experiments with single charge sensitivity. We show that the charge transfer from doped NCs towards a two-dimensional layer experimentally follows a simple phenomenological law, corresponding to formation of an interface dipole linearly increasing with the NC diameter. This feature leads to analytically predictable junction properties down to quantum size regimes: NC depletion width independent of the NC size and varying as N{sub D}{sup −1/3}, and depleted charge linearly increasing with the NC diameter and varying as N{sub D}{sup 1/3}. We thus establish a “nanocrystal counterpart” of conventional semiconductor planar junctions, here however valid in regimes of strong electrostatic and quantum confinements.

  14. Doping semiconductor nanocrystals.

    PubMed

    Erwin, Steven C; Zu, Lijun; Haftel, Michael I; Efros, Alexander L; Kennedy, Thomas A; Norris, David J

    2005-07-01

    Doping--the intentional introduction of impurities into a material--is fundamental to controlling the properties of bulk semiconductors. This has stimulated similar efforts to dope semiconductor nanocrystals. Despite some successes, many of these efforts have failed, for reasons that remain unclear. For example, Mn can be incorporated into nanocrystals of CdS and ZnSe (refs 7-9), but not into CdSe (ref. 12)--despite comparable bulk solubilities of near 50 per cent. These difficulties, which have hindered development of new nanocrystalline materials, are often attributed to 'self-purification', an allegedly intrinsic mechanism whereby impurities are expelled. Here we show instead that the underlying mechanism that controls doping is the initial adsorption of impurities on the nanocrystal surface during growth. We find that adsorption--and therefore doping efficiency--is determined by three main factors: surface morphology, nanocrystal shape, and surfactants in the growth solution. Calculated Mn adsorption energies and equilibrium shapes for several nanocrystals lead to specific doping predictions. These are confirmed by measuring how the Mn concentration in ZnSe varies with nanocrystal size and shape. Finally, we use our predictions to incorporate Mn into previously undopable CdSe nanocrystals. This success establishes that earlier difficulties with doping are not intrinsic, and suggests that a variety of doped nanocrystals--for applications from solar cells to spintronics--can be anticipated. PMID:16001066

  15. Semiconductor cylinder fiber laser

    NASA Astrophysics Data System (ADS)

    Sandupatla, Abhinay; Flattery, James; Kornreich, Philipp

    2015-12-01

    We fabricated a fiber laser that uses a thin semiconductor layer surrounding the glass core as the gain medium. This is a completely new type of laser. The In2Te3 semiconductor layer is about 15-nm thick. The fiber laser has a core diameter of 14.2 μm, an outside diameter of 126 μm, and it is 25-mm long. The laser mirrors consist of a thick vacuum-deposited aluminum layer at one end and a thin semitransparent aluminum layer deposited at the other end of the fiber. The laser is pumped from the side with either light from a halogen tungsten incandescent lamp or a blue light emitting diode flash light. Both the In2Te3 gain medium and the aluminum mirrors have a wide bandwidth. Therefore, the output spectrum consists of a pedestal from a wavelength of about 454 to 623 nm with several peaks. There is a main peak at 545 nm. The main peak has an amplitude of 16.5 dB above the noise level of -73 dB.

  16. 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.

  17. Synthetic Strategies for Semiconductor Nanocrystals Expressing Localized Surface Plasmon Resonance.

    PubMed

    Niezgoda, J Scott; Rosenthal, Sandra J

    2016-03-01

    The field of semiconductor plasmonics has grown rapidly since its outset, only roughly six years ago, and now includes many crystalline substances ranging from GeTe to wide-bandgap transition-metal oxides. One byproduct of this proliferation is the sea of differing synthetic methods to realize localized surface plasmon resonances (LSPRs) based on the studied material. Strategies vary widely from material to material, but all have the common goal of introducing extremely high carrier densities to the semiconductor system. This doping results in tunable, size-quantized, and on/off-switchable LSPR modes, which are a complete departure from traditional metal-nanoparticle-based plasmon resonances. This Minireview will provide an overview of the current state of nanocrystal and quantum-dot plasmonics and the physical basis thereof, however its main purpose is to summarize the methods for realizing LSPRs in the various syntheses and systems that have been reported to date. PMID:26530667

  18. The Dielectric Properties of Semiconductors

    NASA Astrophysics Data System (ADS)

    Harrison, Walter A.

    1999-06-01

    It is indeed remarkable that aspects of solids as diverse as the bonding and the dielectric properties should be described by the same elementary theory. Phillips (1973) noted such a connection and defined an ionicity of the bonds in semiconductors in terms of the dielectric constant, rather than in terms of the bond energy as had been done by Pauling (1960). They gave remarkably similar ionicity scales, but Phillips argued that the dielectric basis was better because of its more direct relation to the electronic structure. We would agree with this, noting that the bond energy (cf. Eq. (2-34)) contains a term Epro and a complicated dependence upon polarity, while we shall find a rather simple dependence ( proportionality to αc3 = (1- αP2)3/2) for the susceptibility and approximately the same for the dielectric constant. The defining of an ionicity to be used to scale properties from one system to another is of course a much less ambitious undertaking than a derivation of the properties in terms of the electronic structure. On the other hand, because of its empirical content it can be a more accurate predictor of experimental values. It can be used, for example, to accurately predict the elastic constant of GaAs by interpolating between Ge and ZnSe which are isoelectronic with it. The result will be much more accurate than our prediction of the value from Eq. (3-11). On the other hand, because our value does not depend on empirical values for similar systems we can make predictions for totally different systems and obtain the dependence upon other features, such as the bond length or metallicity. The goals are completely different. The fact that our polarity is a similar concept to ionicity (in fact related more closely to the square root of the ionicity of Pauling and Phillips than to the ionicity itself (Harrison(1980), p. 190, Christensen, Satpathy, and Pawlowska(1987)), should not be allowed to confuse the totally different goals and

  19. Abrupt Schottky Junctions in Al/Ge Nanowire Heterostructures

    PubMed Central

    2015-01-01

    In this Letter we report on the exploration of axial metal/semiconductor (Al/Ge) nanowire heterostructures with abrupt interfaces. The formation process is enabled by a thermal induced exchange reaction between the vapor–liquid–solid grown Ge nanowire and Al contact pads due to the substantially different diffusion behavior of Ge in Al and vice versa. Temperature-dependent I–V measurements revealed the metallic properties of the crystalline Al nanowire segments with a maximum current carrying capacity of about 0.8 MA/cm2. Transmission electron microscopy (TEM) characterization has confirmed both the composition and crystalline nature of the pure Al nanowire segments. A very sharp interface between the ⟨111⟩ oriented Ge nanowire and the reacted Al part was observed with a Schottky barrier height of 361 meV. To demonstrate the potential of this approach, a monolithic Al/Ge/Al heterostructure was used to fabricate a novel impact ionization device. PMID:26052733

  20. 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.

  1. 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.

  2. Semiconductor devices incorporating multilayer interference regions

    DOEpatents

    Biefeld, R.M.; Drummond, T.J.; Gourley, P.L.; Zipperian, T.E.

    1987-08-31

    A semiconductor high reflector comprising a number of thin alternating layers of semiconductor materials is electrically tunable and may be used as a temperature insensitive semiconductor laser in a Fabry-Perot configuration. 8 figs.

  3. Semiconductor devices incorporating multilayer interference regions

    DOEpatents

    Biefeld, Robert M.; Drummond, Timothy J.; Gourley, Paul L.; Zipperian, Thomas E.

    1990-01-01

    A semiconductor high reflector comprising a number of thin alternating layers of semiconductor materials is electrically tunable and may be used as a temperature insensitive semiconductor laser in a Fabry-Perot configuration.

  4. 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.

  5. Fibre ring cavity semiconductor laser

    SciTech Connect

    Duraev, V P; Medvedev, S V

    2013-10-31

    This paper presents a study of semiconductor lasers having a polarisation maintaining fibre ring cavity. We examine the operating principle and report main characteristics of a semiconductor ring laser, in particular in single- and multiple-frequency regimes, and discuss its application areas. (lasers)

  6. Process for producing chalcogenide semiconductors

    DOEpatents

    Noufi, R.; Chen, Y.W.

    1985-04-30

    A process for producing chalcogenide semiconductor material is disclosed. The process includes forming a base metal layer and then contacting this layer with a solution having a low pH and containing ions from at least one chalcogen to chalcogenize the layer and form the chalcogenide semiconductor material.

  7. Process for producing chalcogenide semiconductors

    DOEpatents

    Noufi, Rommel; Chen, Yih-Wen

    1987-01-01

    A process for producing chalcogenide semiconductor material is disclosed. The process includes forming a base metal layer and then contacting this layer with a solution having a low pH and containing ions from at least one chalcogen to chalcogenize the layer and form the chalcogenide semiconductor material.

  8. Variable temperature semiconductor film deposition

    DOEpatents

    Li, X.; Sheldon, P.

    1998-01-27

    A method of depositing a semiconductor material on a substrate is disclosed. The method sequentially comprises (a) providing the semiconductor material in a depositable state such as a vapor for deposition on the substrate; (b) depositing the semiconductor material on the substrate while heating the substrate to a first temperature sufficient to cause the semiconductor material to form a first film layer having a first grain size; (c) continually depositing the semiconductor material on the substrate while cooling the substrate to a second temperature sufficient to cause the semiconductor material to form a second film layer deposited on the first film layer and having a second grain size smaller than the first grain size; and (d) raising the substrate temperature, while either continuing or not continuing to deposit semiconductor material to form a third film layer, to thereby anneal the film layers into a single layer having favorable efficiency characteristics in photovoltaic applications. A preferred semiconductor material is cadmium telluride deposited on a glass/tin oxide substrate already having thereon a film layer of cadmium sulfide.

  9. Variable temperature semiconductor film deposition

    DOEpatents

    Li, Xiaonan; Sheldon, Peter

    1998-01-01

    A method of depositing a semiconductor material on a substrate. The method sequentially comprises (a) providing the semiconductor material in a depositable state such as a vapor for deposition on the substrate; (b) depositing the semiconductor material on the substrate while heating the substrate to a first temperature sufficient to cause the semiconductor material to form a first film layer having a first grain size; (c) continually depositing the semiconductor material on the substrate while cooling the substrate to a second temperature sufficient to cause the semiconductor material to form a second film layer deposited on the first film layer and having a second grain size smaller than the first grain size; and (d) raising the substrate temperature, while either continuing or not continuing to deposit semiconductor material to form a third film layer, to thereby anneal the film layers into a single layer having favorable efficiency characteristics in photovoltaic applications. A preferred semiconductor material is cadmium telluride deposited on a glass/tin oxide substrate already having thereon a film layer of cadmium sulfide.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2003-10-01

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

  12. Physics with isotopically controlled semiconductors

    SciTech Connect

    Haller, E. E.

    2010-07-15

    This paper is based on a tutorial presentation at the International Conference on Defects in Semiconductors (ICDS-25) held in Saint Petersburg, Russia in July 2009. The tutorial focused on a review of recent research involving isotopically controlled semiconductors. 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, is the most prominent effect for semiconductors. Experimental and theoretical research exploiting the differences in all the properties has been conducted and will be illustrated with selected examples.

  13. Comparison of radiation damage parameter values for the widely used semiconductor gamma detector materials in wide energy range

    NASA Astrophysics Data System (ADS)

    Korkut, Turgay; Korkut, Hatun

    2014-04-01

    Number of displaced atoms (NDA) values for 3 different semiconductor detector materials (Ge, Si, and GaAs) was reviewed at 26 different primary energies emitted from 9 radiation sources (241Am, 133Ba, 109Cd, 57Co, 60Co, 137Cs, 152Eu, 55Fe and 153Gd) widely used in the literature. FLUKA Monte Carlo code was used to simulate interactions between X-gamma rays and semiconductor detector materials. Germanium has the highest average NDA value in the studied three semiconductors.

  14. 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.

  15. 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.

  16. Thermoelectric properties and nonstoichiometry of GaGeTe

    SciTech Connect

    Drasar, C.; Kucek, V.; Benes, L.; Lostak, P.; Vlcek, M.

    2012-09-15

    Polycrystalline samples of composition Ga{sub 1+x}Ge{sub 1-x}Te (x=-0.03 Division-Sign 0.07) and GaGeTe{sub 1-y} (y=-0.02 Division-Sign 0.02) were synthesized from elements of 5 N purity using a solid state reaction. The products of synthesis were identified by X-ray diffraction; phase purity and microstructure were examined by EDX/SEM. Samples for measurement of transport properties were prepared using hot-pressing. They were characterized by measurement of electrical conductivity, the Hall coefficient, and the Seebeck coefficient over a temperature range 80-480 K and of thermal conductivity over a temperature range 300-580 K. All samples show p-type conductivity. We discuss the influence of stoichiometry on the phase purity of the samples and on free carrier concentration. The investigation of thermoelectric properties shows that the power factor of these samples is low compared to state-of-the-art materials at room temperature but increases distinctly with temperature. - Graphical abstract: Structure and preparation of GaGeTe. Electrical conductivity {sigma}, the Hall coefficient R{sub H}, the Seebeck coefficient S and thermal conductivity {kappa} as a function of temperature for the Ga{sub 1.01}Ge{sub 0.99}Te{sub 0.99} sample. Highlights: Black-Right-Pointing-Pointer We explore thermoelectric and transport properties of Ga{sub 1+x}Ge{sub 1-x}Te and GaGeTe{sub 1-y}. Black-Right-Pointing-Pointer GaGeTe is p-type degenerate semiconductor; the hole concentration increase with x and y. Black-Right-Pointing-Pointer Maximum power factor {sigma}S{sup 2}=3.6 Multiplication-Sign 10{sup -4} Wm{sup -1} K{sup -2} at 475 K.

  17. 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

  18. Growth and activation of group IV semiconductors for application in infrared detectors and photovoltaics

    NASA Astrophysics Data System (ADS)

    Xie, Junqi

    Bandgaps in group IV semiconductors such as Ge1-ySn y and Ge1-x-ySixSny are tunable by varying the material composition. The tunable bandgaps make these materials with potential applications in photodetectors, modulators, waveguiders, lasers and photovolatics. This dissertation reports significant improvements of the low-temperature chemical vapor deposition (CVD) process leading to growth of device quality Ge0.98Sn0.02 films with thickness over 500 nm. Highly controlled and efficient doping protocols were also developed to obtain facile substitution and complete activation of dopant atoms at levels 1017 -- 1019 cm-3 via both conventional and custom built molecules. Ge0.98Sn0.02-based PIN structures were subsequently fabricated and characterized. Results show that the incorporation of only 2% of Sn extends the infrared performance of Ge0.98Sn 0.02 based optoelectronic devices to the entire range of transmission windows for telecom applications. Higher Sn content (5% Sn) Ge1-ySny films were also studied to extend the device performance range even further into the infrared. The successful depositions of intrinsic, p- and n-type materials with doping levels 1018-1020/cm3 indicate all components were in place for the fabrication of Ge0.95Sn 0.02-based PIN structures. Meanwhile, a new approach to high quality Ge1-x-ySix Sny ternaries grown directly on both Ge(100) and Si (100) substrates was established based on commercially available sources such as trisilane, digermane and stannane. The soft chemistry process was extended to fabricated p- and n-type layers on Si, and their optical and electrical properties were determined. Characterizations indicate that the properties of GeSiSn are independent of the platform on which they are grown including Si, Ge or GeSn/Si. First-principles calculations show that mixing entropy thermodynamically stabilizes SiGeSn in contrast to GeSn analogs with the same Sn content, in good agreement with experimentally observation. In addition

  19. Liquid precursor for deposition of copper selenide and method of preparing the same

    SciTech Connect

    Curtis, Calvin J.; Miedaner, Alexander; Franciscus Antonius Maria Van Hest, Marinus; Ginley, David S.; Hersh, Peter A.; Eldada, Louay; Stanbery, Billy J.

    2015-09-08

    Liquid precursors containing copper and selenium suitable for deposition on a substrate to form thin films suitable for semiconductor applications are disclosed. Methods of preparing such liquid precursors and methods of depositing a precursor on a substrate are also disclosed.

  20. Functionalization of Semiconductor Nanoparticles

    NASA Astrophysics Data System (ADS)

    Baraton, M.-I.

    Functionalization of nanoparticles surface by attachment of organic entities is used to achieve and tailor many new properties, such as lubrication, optical response, chemical sensing, or biocompatibility. But because at the nanometer scale the surface properties significantly contribute to the overall properties, the consequences of the surface modifications have to be thoroughly evaluated. This paper demonstrates the relevance of Fourier transform infrared spectroscopy to the study of the surface reactions leading to the functionalization, and of the stability of the functionalized surface under the expected working conditions. In the case of semiconductor nanoparticles, this technique additionally allows the analysis of the impact of the functionalization on the electrical properties. This will be illustrated by the case study of tin oxide nanoparticles for chemical gas sensors. The correlation between surface chemistry and electrical properties is critical to optimize the nanoparticles functionalization for the targeted properties.

  1. Semiconductor nanowire lasers

    NASA Astrophysics Data System (ADS)

    Eaton, Samuel W.; Fu, Anthony; Wong, Andrew B.; Ning, Cun-Zheng; Yang, Peidong

    2016-06-01

    The discovery and continued development of the laser has revolutionized both science and industry. The advent of miniaturized, semiconductor lasers has made this technology an integral part of everyday life. Exciting research continues with a new focus on nanowire lasers because of their great potential in the field of optoelectronics. In this Review, we explore the latest advancements in the development of nanowire lasers and offer our perspective on future improvements and trends. We discuss fundamental material considerations and the latest, most effective materials for nanowire lasers. A discussion of novel cavity designs and amplification methods is followed by some of the latest work on surface plasmon polariton nanowire lasers. Finally, exciting new reports of electrically pumped nanowire lasers with the potential for integrated optoelectronic applications are described.

  2. Semiconductor radiation detector

    DOEpatents

    Bell, Zane W.; Burger, Arnold

    2010-03-30

    A semiconductor detector for ionizing electromagnetic radiation, neutrons, and energetic charged particles. The detecting element is comprised of a compound having the composition I-III-VI.sub.2 or II-IV-V.sub.2 where the "I" component is from column 1A or 1B of the periodic table, the "II" component is from column 2B, the "III" component is from column 3A, the "IV" component is from column 4A, the "V" component is from column 5A, and the "VI" component is from column 6A. The detecting element detects ionizing radiation by generating a signal proportional to the energy deposited in the element, and detects neutrons by virtue of the ionizing radiation emitted by one or more of the constituent materials subsequent to capture. The detector may contain more than one neutron-sensitive component.

  3. 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%.

  4. 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.

  5. Quantitative evaluation of slow traps near Ge MOS interfaces by using time response of MOS capacitance

    NASA Astrophysics Data System (ADS)

    Tanaka, Katsuhisa; Zhang, Rui; Takenaka, Mitsuru; Takagi, Shinichi

    2015-04-01

    Time-dependent changes in current and threshold voltage due to slow traps near Ge metal-oxide-semiconductor (MOS) interfaces is one of the most serious problems in Ge metal-oxide-semiconductor field-effect transistors (MOSFETs). In this study, we propose a new evaluation method of slow traps near MOS interfaces utilizing the time response of capacitance in MOS capacitors at a constant gate voltage, allowing us to evaluate the density and time constant of slow traps. We apply this method to Au/Al2O3/GeOx/Ge MOS capacitors and evaluate the density and average time constant of slow traps. The slow trap density of n-Ge MOS capacitors is found to be much larger than that of p-Ge MOS capacitors, indicating that a higher density of slow traps exists near the conduction band edge. We also examine the effects of post deposition annealing in a variety of ambient gases, including several hydrogen-based species, on the properties of slow traps.

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

    SciTech Connect

    Moghadam, Mohammadreza J.; Ahmadi-Majlan, K.; Shen, Xuan; Droubay, Timothy C.; Bowden, Mark E.; Chrysler, M.; Su, Dong; Chambers, Scott A.; Ngai, Joseph

    2015-02-09

    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, electrical and photoemission characterization of SrZrxTi1-xO33-Ge heterojunctions for x = 0.2 to 0.75 and demonstrate the band offset can be tuned from type-II to type-I. The type-I band offset provides a platform to integrate the dielectric, ferroelectric and ferromagnetic functionalities of oxides with semiconducting devices.

  7. Charged Pion Multiplicity Below 1.0 GeV/c from the MIPP Experiment

    NASA Astrophysics Data System (ADS)

    Hart, Andrew; MIPP Collaboration

    2011-04-01

    The MIPP experiment is designed to study particle production from several targets, using various beam species and momenta. Using beams of +/- 58 GeV / c pions, kaons, and protons, we present multiplicities of 0 . 1 - 1 . 0 GeV / c charged pions versus target atomic weight (A) for the following targets: liquid hydrogen, beryllium, carbon, aluminum, copper, bismuth, and uranium. We fit Aα to these results and present α for each case. In addition, for liquid hydrogen, we present charged pion multiplicities for +/- 20 and +/- 85 GeV / c pion, kaon, and proton beam particles, illustrating the dependence on beam momentum.

  8. Electron correlations in semiconductors: Bulk cohesive properties and magnetic-field-induced Wigner crystal at heterojunctions

    SciTech Connect

    Louie, S.G.; Zhu, X.

    1992-08-01

    A correlated wavefunction variational quantum Monte Carlo approach to the studies of electron exchange and correlation effects in semiconductors is presented. Applications discussed include the cohesive and structural properties of bulk semiconductors, and the magnetic-field-induced Wigner electron crystal in two dimensions. Landau level mixing is shown to be important in determining the transition between the quantum Hall liquid and the Wigner crystal states in the regime of relevant experimental parameters.

  9. Metal-inducd assembly of a semiconductor-island lattice: Getruncated pyramids on Au-patterned Si

    SciTech Connect

    Robinson, J.T.; Liddle, J.A.; Minor, A.; Radmilovic, V.; Yi,D.O.; Greaney, P.A.; Long, K.N.; Chrzan, D.C.; Dubon, O.D.

    2005-08-28

    We report the two-dimensional alignment of semiconductor islands using rudimentary metal patterning to control nucleation and growth. In the Ge on Si system, a square array of sub-micron Au dots on the Si (001) surface induces the assembly of deposited Ge adatoms into an extensive island lattice. Remarkably, these highly ordered Ge islands form between the patterned Au dots and are characterized by a unique truncated pyramidal shape. A model based on patterned diffusion barriers explains the observed ordering and establishes general criteria for the broader applicability of such a directed assembly process to quantum dot ordering.

  10. Semiconductor Nanocrystals for Biological Imaging

    SciTech Connect

    Fu, Aihua; Gu, Weiwei; Larabell, Carolyn; Alivisatos, A. Paul

    2005-06-28

    Conventional organic fluorophores suffer from poor photo stability, narrow absorption spectra and broad emission feature. Semiconductor nanocrystals, on the other hand, are highly photo-stable with broad absorption spectra and narrow size-tunable emission spectra. Recent advances in the synthesis of these materials have resulted in bright, sensitive, extremely photo-stable and biocompatible semiconductor fluorophores. Commercial availability facilitates their application in a variety of unprecedented biological experiments, including multiplexed cellular imaging, long-term in vitro and in vivo labeling, deep tissue structure mapping and single particle investigation of dynamic cellular processes. Semiconductor nanocrystals are one of the first examples of nanotechnology enabling a new class of biomedical applications.

  11. Study on the Ge1-xSnx/HfO2 interface and its impacts on Ge1-xSnx tunneling transistor

    NASA Astrophysics Data System (ADS)

    Qiu, Yingxin; Wang, Runsheng; Huang, Qianqian; Huang, Ru

    2014-06-01

    In this paper, we employ first-principle calculation to investigate the Ge1-xSnx/HfO2 interface, and then evaluate its impacts on Ge1-xSnx tunneling field-effect transistor (TFET). First-principle calculations of Ge1-xSnx/HfO2 interfaces in the oxygen-rich process atmosphere indicate that the interface states originate from the Ge and Sn dangling bond, rather than Hf-bond. The total density of state shows that there are more interface states in the semiconductor bandgap with increasing Sn fraction. By further incorporating the material and interface parameters from density functional theory calculation into advanced device simulation, the electrical characteristics of Ge1-xSnx TFET are investigated. Removing the Sn atom from the first atom layer of Ge1-xSnx in device processes is found to be beneficial to reduce the degradations. For the degradation mechanisms, the trap-assisted-tunneling is the dominant mechanism at the low Sn fraction, and enhanced Shockley-Read-Hall recombination induced by traps becomes the dominant mechanism with increasing Sn fraction. The results are helpful for the interface optimization of Ge1-xSnx TFET.

  12. New Source Heterojunction Structures with Relaxed/Strained Semiconductors for Quasi-Ballistic Complementary Metal-Oxide-Semiconductor Transistors: Relaxation Technique of Strained Substrates and Design of Sub-10 nm Devices

    NASA Astrophysics Data System (ADS)

    Tomohisa Mizuno,; Naoki Mizoguchi,; Kotaro Tanimoto,; Tomoaki Yamauchi,; Mitsuo Hasegawa,; Toshiyuki Sameshima,; Tsutomu Tezuka,

    2010-04-01

    We have studied new abrupt-source-relaxed/strained semiconductor-heterojunction structures for quasi-ballistic complementary metal-oxide-semiconductor (CMOS) devices, by locally controlling the strain of a single strained semiconductor. Appling O+ ion implantation recoil energy to the strained semiconductor/buried oxide interface, Raman analysis of the strained layers indicates that we have successfully relaxed both strained-Si-on-insulator (SSOI) substrates for n-MOS and SiGe-on-insulator (SGOI) substrates for p-MOS without polycrystallizing the semiconductor layers, by optimizing O+ ion implantation conditions. As a result, it is considered that the source conduction and valence band offsets Δ EC and Δ EV can be realized by the energy difference in the source Si/channel-strained Si and the source-relaxed SiGe/channel-strained SiGe layers, respectively. The device simulator, considering the tunneling effects at the source heterojunction, shows that the transconductance of sub-10 nm source heterojunction MOS transistors (SHOT) continues to increase with increasing Δ EC. Therefore, SHOT structures with the novel source heterojunction are very promising for future quasi-ballistic CMOS devices.

  13. Two-dimensional GeS with tunable electronic properties via external electric field and strain.

    PubMed

    Zhang, Shengli; Wang, Ning; Liu, Shangguo; Huang, Shiping; Zhou, Wenhan; Cai, Bo; Xie, Meiqiu; Yang, Qun; Chen, Xianping; Zeng, Haibo

    2016-07-01

    Experimentally, GeS nanosheets have been successfully synthesized using vapor deposition processes and the one-pot strategy. Quite recently, GeS monolayer, the isoelectronic counterpart of phosphorene, has attracted much attention due to promising properties. By means of comprehensive first-principles calculations, we studied the stability and electronic properties of GeS monolayer. Especially, electric field and in-plane strain were used to tailor its electronic band gap. Upon applying electric field, the band gap of GeS monolayer greatly reduces and a semiconductor-metal transition happens under the application of a certain external electric field. Our calculations reveal that the band gaps of GeS monolayer are rather sensitive to the external electric field. On the other hand, for GeS under external strain, quite interestingly, we found that the band gap presents an approximately linear increase not only under compression strain but also under tensile strain from -10% to 10%. For biaxial compressive and tensile strains, the band gap follows the same trend as that of the uniaxial in the zigzag x direction. The present results provide a simple and effective route to tune the electronic properties of GeS monolayer over a wide range and also facilitate the design of GeS-based two-dimensional devices. PMID:27232104

  14. Semiconductor device PN junction fabrication using optical processing of amorphous semiconductor material

    SciTech Connect

    Sopori, Bhushan; Rangappan, Anikara

    2014-11-25

    Systems and methods for semiconductor device PN junction fabrication are provided. In one embodiment, a method for fabricating an electrical device having a P-N junction comprises: depositing a layer of amorphous semiconductor material onto a crystalline semiconductor base, wherein the crystalline semiconductor base comprises a crystalline phase of a same semiconductor as the amorphous layer; and growing the layer of amorphous semiconductor material into a layer of crystalline semiconductor material that is epitaxially matched to the lattice structure of the crystalline semiconductor base by applying an optical energy that penetrates at least the amorphous semiconductor material.

  15. 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

  16. 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

    2016-01-01

    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

  17. 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.

  18. Characteristics of Sn segregation in Ge/GeSn heterostructures

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  19. Alloy Semiconductor Crystal Growth Under Microgravity

    NASA Astrophysics Data System (ADS)

    Hayakawa, Yasuhiro; Arivanandhan, Mukannan; Rajesh, Govindasamy; Tanaka, Akira; Ozawa, Tetsuo; Okano, Yasunori; Sankaranarayanan, Krishnasamy; Inatomi, Yuko

    2010-12-01

    Microgravity studies on the dissolution and crystallization of InxGa1-xSb have been done using a sandwich combination of InSb and GaSb as the starting material using the Chinese recoverable satellite. The same type of experiment was performed under 1G gravity condition for comparison. From these experiments and the numerical simulation, it is found that the shape of the solid/liquid interface and composition profile in the solution was found to be significantly affected by gravity. GaSb seed was dissolved faster than GaSb feed even though the GaSb feed temperature was higher than that of GaSb seed temperature. These results clearly indicate that solute transport due to gravity affects dissolution and growth processes of alloy semiconductor bulk crystals.

  20. Chemical aerosol flow synthesis of semiconductor nanoparticles.

    PubMed

    Didenko, Yuri T; Suslick, Kenneth S

    2005-09-01

    Nanometer-sized semiconductor particles (quantum dots) have been the subject of intense research during the past decade owing to their novel electronic, catalytic, and optical properties. Fundamental properties of these nanoparticles (1-20 nm diameter) can be systematically changed simply by controlling the size of the crystals while holding their chemical composition constant. We describe here a new methodology for the continuous production of fluorescent CdS, CdSe, and CdTe nanoparticles using ultrasonically generated aerosols of high boiling point solvents. Each submicron droplet serves as a separate nanoscale chemical reactor, with reactions proceeding as the liquid droplets (which hold both reactants and surface stabilizers) are heated in a gas stream. The method is inexpensive, scalable, and allows for the synthesis of high quality nanocrystals. This chemical aerosol flow synthesis (CAFS) can be extended to the synthesis of nanostructured metals, oxides, and other materials. PMID:16131177

  1. Leakage current in high-purity germanium detectors with amorphous semiconductor contacts

    NASA Astrophysics Data System (ADS)

    Looker, Q.; Amman, M.; Vetter, K.

    2015-03-01

    Amorphous semiconductor electrical contacts on high-purity Ge radiation detectors have become a valuable technology because they are simple to fabricate, result in thin dead layers, block both electron and hole injection, and can readily be finely segmented as needed for applications requiring imaging or particle tracking. Though significant numbers of detectors have been successfully produced for a variety of applications using the amorphous semiconductor contact technology, there remains a need to better understand the dependence of performance characteristics, particularly leakage current, on the fabrication process parameters so that the performance can be better optimized. To this end, we have performed a systematic study of leakage current on RF-sputter-deposited amorphous-Ge (a-Ge) and amorphous-Si (a-Si) contacts as a function of process and operational parameters including sputter gas pressure and composition, number of detector temperature cycles, and time spent at room temperature. The study focused primarily on the current resulting from electron injection at the contact. Significant findings from the study include that a-Si produces lower electron injection than a-Ge, the time the detector spends at room temperature rather than the number of temperature cycles experienced by the detector is the primary factor associated with leakage current change when the detector is warmed, and the time stability of the a-Ge contact depends on the sputter gas pressure with a higher pressure producing more stable characteristics.

  2. Ge Nanocluster Enhanced Er Photoluminescence

    NASA Astrophysics Data System (ADS)

    Guzman, Julian; Chrzan, Daryl C.; Haller, Eugene E.

    2010-03-01

    We investigated the enhancement of the Er^3+ photoluminescence (PL) at 1540 nm by the incorporation of Ge nanoclusters into Er-doped silica using ion beams. We found that the Er^3+ PL enhancement is due to the presence of Ge and not to the radiation damage from the ion-implantation process. We determined that the Er^3+ PL depends on the Ge content, postgrowth annealing, and crystallinity of the Ge nanoclusters. Furthermore, we observed that the Er^3+ PL signal is maximized after annealing at 685 C for 1 h. This is the temperature at which Ge nanoclusters begin to crystallize. Transmission electron microscopy studies were conducted to determine the size distribution of the Ge nanoclusters. Moreover, extended X-ray absorption fine structure measurements performed at the Ge-K and Er-LIII edges revealed that there is negligible Ge-Er bonding. This suggests that Er is either fully oxidized or that it is not located in the Ge nanoclusters. Therefore, we believe that the energy transfer process from the Ge nanoclusters to the Er ions occurs through a non-optical resonant dipole transfer (F"orster ProcessfootnotetextT. F"orster, Discuss. Faraday Soc. 27, 7 (1959). similar to what has been proposed for the Si nanocrystal case.footnotetextM. Fujii, M. Yoshida, S. Hayashi, and K. Yamamoto, J. Appl. Phys. 84, 4525 (1998).

  3. Semiconductor technology program. Progress briefs

    NASA Technical Reports Server (NTRS)

    Bullis, W. M.

    1980-01-01

    Measurement technology for semiconductor materials, process control, and devices is reviewed. Activities include: optical linewidth and thermal resistance measurements; device modeling; dopant density profiles; resonance ionization spectroscopy; and deep level measurements. Standardized oxide charge terminology is also described.

  4. Semiconductor crystal high resolution imager

    NASA Technical Reports Server (NTRS)

    Levin, Craig S. (Inventor); Matteson, James (Inventor)

    2011-01-01

    A radiation imaging device (10). The radiation image device (10) comprises a subject radiation station (12) producing photon emissions (14), and at least one semiconductor crystal detector (16) arranged in an edge-on orientation with respect to the emitted photons (14) to directly receive the emitted photons (14) and produce a signal. The semiconductor crystal detector (16) comprises at least one anode and at least one cathode that produces the signal in response to the emitted photons (14).

  5. Impurity gettering in semiconductors

    DOEpatents

    Sopori, B.L.

    1995-06-20

    A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device is disclosed. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500 C to about 700 C for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal. 1 fig.

  6. Impurity gettering in semiconductors

    DOEpatents

    Sopori, Bhushan L.

    1995-01-01

    A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500.degree. C. to about 700.degree. C. for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal.

  7. Semiconductor film Cherenkov lasers

    NASA Astrophysics Data System (ADS)

    Walsh, John E.

    1994-12-01

    The technical achievements for the project 'Semiconductor Film Cherenkov Lasers' are summarized. Described in the fourteen appendices are the operation of a sapphire Cherenkov laser and various grating-coupled oscillators. These coherent radiation sources were operated over the spectral range extending from 3 mm down to 400 micrometers. The utility of various types of open, multi-grating resonators and mode-locked operation were also demonstrated. In addition to these experiments, which were carried out with a 10-100 kV pulse generator, a low-energy (3-3.6 MeV) Van de Graaff generator and a low-energy RF linac (2.8 MeV) were used to investigate the properties of continuum incoherent Smith-Purcell radiation. It was shown that levels of intensity comparable to the infrared beam lines on a synchrotron could be obtained and thus that grating-coupled sources are potentially an important new source for Fourier transform spectroscopy. Finally, a scanning electron microscope was adapted for investigating mu-electron-beam-driven far-infrared sources. At the close of the project, spontaneous emission over the 288-800 micrometers band had been observed. Intensity levels were in accord with expectations based on theory. One or more of the Appendices address these topics in detail.

  8. The control of purity and stoichiometry of compound semiconductors by high vapor pressure transport

    NASA Technical Reports Server (NTRS)

    Bachmann, Klaus J.; Ito, Kazufumi; Scroggs, Jeffery S.; Tran, Hien T.

    1995-01-01

    In this report we summarize the results of a three year research program on high pressure vapor transport (HPVT) of compound semiconductors. Most of our work focused onto pnictides, in particular ZnGeP2, as a model system. Access to single crystals of well controlled composition of this material is desired for advancing the understanding and control of its point defect chemistry in the contest of remote, real-time sensing of trace impurities, e.g., greenhouse gases, in the atmosphere by ZnGeP2 optical parametric oscillators (OPO's).

  9. Experiments with phase transitions at very high pressure. [compressed solidifed gases, semiconductors, superconductors, and molecular crystals

    NASA Technical Reports Server (NTRS)

    Spain, I. L.

    1983-01-01

    Diamond cells were constructed for use to 1 Mbar. A refrigerator for cooling diamond cells was adapted for studies between 15 and 300 K. A cryostat for superconductivity studies between 1.5 to 300 K was constructed. Optical equipment was constructed for fluorescence, transmission, and reflectance studies. X-ray equipment was adapted for use with diamond cells. Experimental techniques were developed for X-ray diffraction studies using synchrotron radiation. AC susceptibility techniques were developed for detecting superconducting transitions. The following materials were studied: compressed solidified gases (Xe, Ar), semiconductors (Ge, Si, GaAs), superconductors (Nb3Ge, Nb3Si, Nb3As, CuCl), molecular crystals (I).

  10. Ba termination of Ge(001) studied with STM.

    PubMed

    Koczorowski, W; Grzela, T; Radny, M W; Schofield, S R; Capellini, G; Czajka, R; Schroeder, T; Curson, N J

    2015-04-17

    We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy. Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (∼0.15 ML) that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that the thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps to temperatures of 470, 570, 670 and 770 K although a gradual ordering of the Ba layer is observed at 570 K and above, accompanied by a decrease in Ba layer density. Annealing above 770 K produces the 2D surface alloy phase accompanied by strain relief through monolayer height trench formation. An annealing temperature of 1070 K sees a further change in surface morphology but retention of the 2D surface alloy characteristic. These results are discussed in view of their possible implications for future semiconductor integrated circuit technology. PMID:25797886

  11. Ba termination of Ge(001) studied with STM

    NASA Astrophysics Data System (ADS)

    Koczorowski, W.; Grzela, T.; Radny, M. W.; Schofield, S. R.; Capellini, G.; Czajka, R.; Schroeder, T.; Curson, N. J.

    2015-04-01

    We use controlled annealing to tune the interfacial properties of a sub-monolayer and monolayer coverages of Ba atoms deposited on Ge(001), enabling the generation of either of two fundamentally distinct interfacial phases, as revealed by scanning tunneling microscopy. Firstly we identify the two key structural phases associated with this adsorption system, namely on-top adsorption and surface alloy formation, by performing a deposition and annealing experiment at a coverage low enough (∼0.15 ML) that isolated Ba-related features can be individually resolved. Subsequently we investigate the monolayer coverage case, of interest for passivation schemes of future Ge based devices, for which we find that the thermal evaporation of Ba onto a Ge(001) surface at room temperature results in on-top adsorption. This separation (lack of intermixing) between Ba and Ge layers is retained through successive annealing steps to temperatures of 470, 570, 670 and 770 K although a gradual ordering of the Ba layer is observed at 570 K and above, accompanied by a decrease in Ba layer density. Annealing above 770 K produces the 2D surface alloy phase accompanied by strain relief through monolayer height trench formation. An annealing temperature of 1070 K sees a further change in surface morphology but retention of the 2D surface alloy characteristic. These results are discussed in view of their possible implications for future semiconductor integrated circuit technology.

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

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

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

  13. Enhanced electrical activation in In-implanted Ge by C co-doping

    SciTech Connect

    Feng, R. Kremer, F.; Mirzaei, S.; Medling, S. A.; Ridgway, M. C.; Sprouster, D. J.; Decoster, S.; Pereira, L. M. C.; Glover, C. J.; Russo, S. P.

    2015-11-23

    At high dopant concentrations in Ge, electrically activating all implanted dopants is a major obstacle in the fulfillment of high-performance Ge-channel complementary metal oxide semiconductor devices. In this letter, we demonstrate a significant increase in the electrically-active dopant fraction in In-implanted Ge by co-doping with the isovalent element C. Electrical measurements have been correlated with x-ray absorption spectroscopy and transmission electron microscopy results in addition to density functional theory simulations. With C + In co-doping, the electrically active fraction was doubled and tripled at In concentrations of 0.2 and 0.7 at. %, respectively. This marked improvement was the result of C-In pair formation such that In-induced strain in the Ge lattice was reduced while the precipitation of In and the formation of In-V clusters were both suppressed.

  14. Present Status and Future Directions of SiGe Hbt Technology

    NASA Astrophysics Data System (ADS)

    Khater, Marwan H.; Adam, Thomas N.; Krishnasamy, Rajendran; Dahlstrom, Mattias E.; Rieh, Jae-Sung; Schonenberg, Kathryn T.; Orner, Bradly A.; Pagette, Francois; Stein, Kenneth; Ahlgren, David C.

    2007-06-01

    The implementation of challenging novel materials and process techniques has led to remarkable device improvements in state-of-the-art high-performance SiGe HBTs, rivaling their III-V compound semiconductor counterparts. Vertical scaling, lateral scaling, and device structure innovations required to improve SiGe HBTs performance have benefited from advanced materials and process techniques developed for next generation CMOS technology. In this work, we present a review of recent process and materials development enabling operational speeds of SiGe HBTs approaching 400 GHz. In addition, we present device simulation results that show the extendibility of SiGe HBT technology performance towards half-terahertz and beyond with further scaling and device structure improvements.

  15. One-step chemical vapor growth of Ge/SiC(x)N(y) nanocables.

    PubMed

    Mathur, Sanjay; Shen, Hao; Donia, Nicole; Rügamer, Thomas; Sivakov, Vladimir; Werner, Ulf

    2007-08-01

    Single-step synthesis of one-dimensional Ge/SiCxNy core-shell nanocables was achieved by chemical vapor deposition of the molecular precursor [Ge{N(SiMe3)2}2]. Single crystalline Ge nanowires (diameter approximately 60 nm) embedded in uniform SiCxNy shells were obtained in high yields, whereby the growth process was not influenced by the nature of substrates. The shell material exhibited high oxidation and chemical resistance at elevated temperatures (up to 250 degrees C) resulting in the preservation of size-dependent semiconductor properties of germanium nanowires, such as intact transport of charge carriers and reduction of energy consumption, when compared to pure Ge nanowires. PMID:17629271

  16. Reconstruction of GeV Neutrino Events in LENA

    SciTech Connect

    Moellenberg, R.; Feilitzsch, F. von; Goeger-Neff, M.; Hellgartner, D.; Lewke, T.; Meindl, Q.; Oberauer, L.; Potzel, W.; Tippmann, M.; Winter, J.; Wurm, M.; Peltoniemi, J.

    2011-10-06

    LENA (Low Energy Neutrino Astronomy) is a proposed next generation liquid-scintillator detector with about 50 kt target mass. Besides the detection of solar neutrinos, geoneutrinos, supernova neutrinos and the search for the proton decay, LENA could also be used as the far detector of a next generation neutrino beam. The present contribution outlines the status of the Monte Carlo studies towards the reconstruction of GeV neutrinos in LENA. Both the tracking capabilities at a few hundred MeV, most interesting for a beta beam, and above 1 GeV for a superbeam experiment are presented.

  17. Atomically precise semiconductor—graphene and hBN interfaces by Ge intercalation

    NASA Astrophysics Data System (ADS)

    Verbitskiy, N. I.; Fedorov, A. V.; Profeta, G.; Stroppa, A.; Petaccia, L.; Senkovskiy, B.; Nefedov, A.; Wöll, C.; Usachov, D. Yu.; Vyalikh, D. V.; Yashina, L. V.; Eliseev, A. A.; Pichler, T.; Grüneis, A.

    2015-12-01

    The full exploration of the potential, which graphene offers to nanoelectronics requires its integration into semiconductor technology. So far the real-world applications are limited by the ability to concomitantly achieve large single-crystalline domains on dielectrics and semiconductors and to tailor the interfaces between them. Here we show a new direct bottom-up method for the fabrication of high-quality atomically precise interfaces between 2D materials, like graphene and hexagonal boron nitride (hBN), and classical semiconductor via Ge intercalation. Using angle-resolved photoemission spectroscopy and complementary DFT modelling we observed for the first time that epitaxially grown graphene with the Ge monolayer underneath demonstrates Dirac Fermions unaffected by the substrate as well as an unperturbed electronic band structure of hBN. This approach provides the intrinsic relativistic 2D electron gas towards integration in semiconductor technology. Hence, these new interfaces are a promising path for the integration of graphene and hBN into state-of-the-art semiconductor technology.

  18. Atomically precise semiconductor—graphene and hBN interfaces by Ge intercalation

    PubMed Central

    Verbitskiy, N. I.; Fedorov, A. V.; Profeta, G.; Stroppa, A.; Petaccia, L.; Senkovskiy, B.; Nefedov, A.; Wöll, C.; Usachov, D. Yu.; Vyalikh, D. V.; Yashina, L. V.; Eliseev, A. A.; Pichler, T.; Grüneis, A.

    2015-01-01

    The full exploration of the potential, which graphene offers to nanoelectronics requires its integration into semiconductor technology. So far the real-world applications are limited by the ability to concomitantly achieve large single-crystalline domains on dielectrics and semiconductors and to tailor the interfaces between them. Here we show a new direct bottom-up method for the fabrication of high-quality atomically precise interfaces between 2D materials, like graphene and hexagonal boron nitride (hBN), and classical semiconductor via Ge intercalation. Using angle-resolved photoemission spectroscopy and complementary DFT modelling we observed for the first time that epitaxially grown graphene with the Ge monolayer underneath demonstrates Dirac Fermions unaffected by the substrate as well as an unperturbed electronic band structure of hBN. This approach provides the intrinsic relativistic 2D electron gas towards integration in semiconductor technology. Hence, these new interfaces are a promising path for the integration of graphene and hBN into state-of-the-art semiconductor technology. PMID:26639608

  19. Ferromagnetism in ion implanted amorphous and nanocrystalline MnxGe1-x

    NASA Astrophysics Data System (ADS)

    Verna, A.; Ottaviano, L.; Passacantando, M.; Santucci, S.; Picozzi, P.; D'Orazio, F.; Lucari, F.; de Biase, M.; Gunnella, R.; Berti, M.; Gasparotto, A.; Impellizzeri, G.; Priolo, F.

    2006-08-01

    The structural, electronic, and magnetic properties of a MnxGe1-x alloy prepared through room-temperature ion implantation ( 100keV , 2×1016ions/cm2 ) and subsequent 400°C annealing have been investigated with several experimental techniques. The as-implanted sample shows a quasi-Gaussian Mn concentration depth profile with a projected range (peak Mn concentration x≃12at./% ) at 55nm and end of range at 140nm . The structural investigation shows that the overall implanted Ge layer is amorphous. In particular, up to a depth of 60nm , the implanted layer is also porous and oxidized, whereas the deepest implanted region (60-140nm) is purely composed of amorphous Ge with Mn atoms diluted in it. This sample manifests magnetic hysteresis up to 20K and a strong nonlinear S-shaped magnetic response up to 150K . Upon annealing at 400°C , the top porous layer remains essentially amorphous, whereas partial reconstruction into Ge nanocrystals ( ˜10nm in diameter) occurs in the 60-140-nm -deep implanted region. Part of the Mn atoms, mainly belonging to the top porous layer, further diffuses toward the surface and forms chemical bonds with O contaminants, becoming magnetically inactive. The other Mn atoms, mainly in the region between 60 and 140nm from the surface, remain trapped in the residual amorphous matrix or in the Ge nanocrystals, whereas formation of Mn-Ge extrinsic phases (like Mn11Ge8 and Mn5Ge3 ) is excluded. The magnetic response of the annealed sample originates from the existence of a soft and a harder magnetic component, assigned to the dilution of Mn atoms in residual amorphous Ge and Ge nanocrystals, respectively. The hard component, attributable to a MnxGe1-x diluted magnetic semiconductor in nanocrystalline form, manifests magnetic hysteresis up to above 250K .

  20. Wide-Bandgap Semiconductors

    SciTech Connect

    Chinthavali, M.S.

    2005-11-22

    With the increase in demand for more efficient, higher-power, and higher-temperature operation of power converters, design engineers face the challenge of increasing the efficiency and power density of converters [1, 2]. Development in power semiconductors is vital for achieving the design goals set by the industry. Silicon (Si) power devices have reached their theoretical limits in terms of higher-temperature and higher-power operation by virtue of the physical properties of the material. To overcome these limitations, research has focused on wide-bandgap materials such as silicon carbide (SiC), gallium nitride (GaN), and diamond because of their superior material advantages such as large bandgap, high thermal conductivity, and high critical breakdown field strength. Diamond is the ultimate material for power devices because of its greater than tenfold improvement in electrical properties compared with silicon; however, it is more suited for higher-voltage (grid level) higher-power applications based on the intrinsic properties of the material [3]. GaN and SiC power devices have similar performance improvements over Si power devices. GaN performs only slightly better than SiC. Both SiC and GaN have processing issues that need to be resolved before they can seriously challenge Si power devices; however, SiC is at a more technically advanced stage than GaN. SiC is considered to be the best transition material for future power devices before high-power diamond device technology matures. Since SiC power devices have lower losses than Si devices, SiC-based power converters are more efficient. With the high-temperature operation capability of SiC, thermal management requirements are reduced; therefore, a smaller heat sink would be sufficient. In addition, since SiC power devices can be switched at higher frequencies, smaller passive components are required in power converters. Smaller heat sinks and passive components result in higher-power-density power converters

  1. Optical pumping in semiconductors

    NASA Astrophysics Data System (ADS)

    Hermann, C.; Lampel, G.; Safarov, V. I.

    Optical Pumping in Semiconductors (OPS) arises from the transfer of angular momentum from light to the localized states of a semiconductor. Spin polarized electrons are thus excited in the conduction band; their polarization is convenient measured through the circular polarization of photoluminescence. This review gives an insight of the various studies based on OPS. After describing the first OPS experiment, we show that this technique allows the determination of band structure properties, and the optical detection of conduction electron spin resonance. The nuclei are polarized by hyperfine interaction, which permits the optical detection of nuclear resonance. A magnetic field transverse to the direction of light propagation produces an electronic depolarization analogous to the Hanle effect. The electron lifetime and spin relaxation time are measured under steady-state conditions by comparison to their Larmor frequency in this transverse field. By activation to Negative Electron Affinity of a GaAs surface, electrons oriented by OPS can be photoemitted into vacuum, leading to a highly spin-polarized beam : we describe a collision experiment in which such a beam transfers angular momentum to atoms. Le Pompage Optique dans les semiconducteurs (POS) provient du transfert de moment angulaire de la lumière vers les états délocalisés d'un semiconducteur. On excite ainsi dans la bande de conduction des électrons polarisés de spin, dont on mesure commodément la polarisation à partir de la polarisation circulaire de la photoluminescence. Cet article de revue présente un aperçu des différentes études fondées sur le POS. Après avoir décrit la première expérience de POS, nous montrons que par cette technique on peut déterminer des propriétés liées à la structure de bande, et détecter optiquement la résonance de spin des électrons de conduction. Les noyaux sont polarisés grâce au couplage hyperfin qui permet également la détection optique de la r

  2. Spinodal nanodecomposition in semiconductors doped with transition metals

    NASA Astrophysics Data System (ADS)

    Dietl, T.; Sato, K.; Fukushima, T.; Bonanni, A.; Jamet, M.; Barski, A.; Kuroda, S.; Tanaka, M.; Hai, Pham Nam; Katayama-Yoshida, H.

    2015-10-01

    This review presents the recent progress in computational materials design, experimental realization, and control methods of spinodal nanodecomposition under three- and two-dimensional crystal-growth conditions in spintronic materials, such as magnetically doped semiconductors. The computational description of nanodecomposition, performed by combining first-principles calculations with kinetic Monte Carlo simulations, is discussed together with extensive electron microscopy, synchrotron radiation, scanning probe, and ion beam methods that have been employed to visualize binodal and spinodal nanodecomposition (chemical phase separation) as well as nanoprecipitation (crystallographic phase separation) in a range of semiconductor compounds with a concentration of transition metal (TM) impurities beyond the solubility limit. The role of growth conditions, codoping by shallow impurities, kinetic barriers, and surface reactions in controlling the aggregation of magnetic cations is highlighted. According to theoretical simulations and experimental results the TM-rich regions appear in the form of either nanodots (the dairiseki phase) or nanocolumns (the konbu phase) buried in the host semiconductor. Particular attention is paid to Mn-doped group III arsenides and antimonides, TM-doped group III nitrides, Mn- and Fe-doped Ge, and Cr-doped group II chalcogenides, in which ferromagnetic features persisting up to above room temperature correlate with the presence of nanodecomposition and account for the application-relevant magneto-optical and magnetotransport properties of these compounds. Finally, it is pointed out that spinodal nanodecomposition can be viewed as a new class of bottom-up approach to nanofabrication.

  3. A first principles study of the lattice stability of diamond-structure semiconductors under intense laser irradiation

    SciTech Connect

    Feng Shiquan; Zhao Jianling; Cheng Xinlu

    2013-01-14

    Using density-functional linear-response theory, we calculated the phonon dispersion curves for the diamond structural elemental semiconductors of Ge, C and zinc-blende structure semiconductors of GaAs, InSb at different electronic temperatures. We found that the transverse-acoustic phonon frequencies of C and Ge become imaginary as the electron temperature is elevated, which means the lattices of C and Ge become unstable under intense laser irradiation. These results are very similar with previous theoretical and experimental results for Si. For GaAs and InSb, not only can be obtained the similar results for their transverse-acoustic modes, but also their LO-TO splitting gradually decreases as the electronic temperature is increased. It means that the electronic excitation weakens the strength of the ionicity of ionic crystal under intense laser irradiation.

  4. Sn-based Ge/Ge0.975Sn0.025/Ge p-i-n photodetector operated with back-side illumination

    NASA Astrophysics Data System (ADS)

    Chang, C.; Li, H.; Huang, S. H.; Cheng, H. H.; Sun, G.; Soref, R. A.

    2016-04-01

    We report an investigation of a GeSn-based p-i-n photodetector grown on a Ge wafer that collects light signal from the back of the wafer. Temperature dependent absorption measurements performed over a wide temperature range (300 K down to 25 K) show that (a) absorption starts at the indirect bandgap of the active GeSn layer and continues up to the direct bandgap of the Ge wafer, and (b) the peak responsivity increases rapidly at first with decreasing temperature, then increases more slowly, followed by a decrease at the lower temperatures. The maximum responsivity happens at 125 K, which can easily be achieved with the use of liquid nitrogen. The temperature dependence of the photocurrent is analyzed by taking into consideration of the temperature dependence of the electron and hole mobility in the active layer, and the analysis result is in reasonable agreement with the data in the temperature regime where the rapid increase occurs. This investigation demonstrates the feasibility of a GeSn-based photodiode that can be operated with back-side illumination for applications in image sensing systems.

  5. Structural and phonon transmission study of Ge-Au-Ge eutectically bonded interfaces

    SciTech Connect

    Knowlton, W.B. |

    1995-07-01

    This thesis presents a structural analysis and phonon transparency investigation of the Ge-Au-Ge eutectic bond interface. Interface development was intended to maximize the interfacial ballistic phonon transparency to enhance the detection of the dark matter candidate WIMPs. The process which was developed provides an interface which produces minimal stress, low amounts of impurities, and insures Ge lattice continuity through the interface. For initial Au thicknesses of greater than 1,000 {angstrom} Au per substrate side, eutectic epitaxial growth resulted in a Au dendritic structure with 95% cross sectional and 90% planar Au interfacial area coverages. In sections in which Ge bridged the interface, lattice continuity across the interface was apparent. Epitaxial solidification of the eutectic interface with initial Au thicknesses < 500 A per substrate side produced Au agglomerations thereby reducing the Au planar interfacial area coverage to as little as 30%. The mechanism for Au coalescence was attributed to lateral diffusion of Ge and Au in the liquid phase during solidification. Phonon transmission studies were performed on eutectic interfaces with initial Au thicknesses of 1,000 {angstrom}, 500 {angstrom}, and 300 {angstrom} per substrate side. Phonon imaging of eutectically bonded samples with initial Au thicknesses of 300 {angstrom}/side revealed reproducible interfacial percent phonon transmissions from 60% to 70%. Line scan phonon imaging verified the results. Phonon propagation TOF spectra distinctly showed the predominant phonon propagation mode was ballistic. This was substantiated by phonon focusing effects apparent in the phonon imaging data. The degree of interface transparency to phonons and resulting phonon propagation modes correlate with the structure of the interface following eutectic solidification. Structural studies of samples with initial Au thickness of 1,000 {angstrom}/side appear to correspond with the phonon transmission study.

  6. Vibrational dynamics and band structure of methyl-terminated Ge(111)

    NASA Astrophysics Data System (ADS)

    Hund, Zachary M.; Nihill, Kevin J.; Campi, Davide; Wong, Keith T.; Lewis, Nathan S.; Bernasconi, M.; Benedek, G.; Sibener, S. J.

    2015-09-01

    A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD3-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH3-Ge(111) and CH3-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers.

  7. Vibrational dynamics and band structure of methyl-terminated Ge(111).

    PubMed

    Hund, Zachary M; Nihill, Kevin J; Campi, Davide; Wong, Keith T; Lewis, Nathan S; Bernasconi, M; Benedek, G; Sibener, S J

    2015-09-28

    A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD3-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH3-Ge(111) and CH3-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers. PMID:26429030

  8. Vibrational dynamics and band structure of methyl-terminated Ge(111)

    SciTech Connect

    Hund, Zachary M.; Nihill, Kevin J.; Sibener, S. J.; Campi, Davide; Bernasconi, M.; Wong, Keith T.; Lewis, Nathan S.; Benedek, G.

    2015-09-28

    A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD{sub 3}-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH{sub 3}-Ge(111) and CH{sub 3}-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers.

  9. Thermodiffusion of high-density electron-hole plasmas in semiconductors

    SciTech Connect

    Mahler, G.; Maier, G.; Forchel, A.; Laurich, B.; Sanwald, H.; Schmid, W.

    1981-12-21

    The spatial distributions of temperature and density in electron-hole plasmas in surface-excited semiconductors are investigated with use of linear irreversible thermodynamics and a microscopic plasma theory. Above a certain threshold the density distribution is dominated by a characteristic density, which increases with temperature. Experimental results for Ge, unstressed Si, and Si under high uniaxial stress are in agreement with the theory.

  10. 75 FR 47318 - GE Asset Management Incorporated and GE Investment Distributors, Inc.; Notice of Application and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-05

    ... COMMISSION GE Asset Management Incorporated and GE Investment Distributors, Inc.; Notice of Application and.... Applicants: GE Asset Management Incorporated (``GEAM'') and GE Investment Distributors, Inc. (``GEID....\\3\\ The Commission alleged in the complaint (``Complaint'') that, from 2000 to 2003, four...

  11. Pressure-Induced Amorphization and a New High Density Amorphous Metallic Phase in Matrix-Free Ge Nanoparticles.

    PubMed

    Corsini, Niccolo R C; Zhang, Yuanpeng; Little, William R; Karatutlu, Ali; Ersoy, Osman; Haynes, Peter D; Molteni, Carla; Hine, Nicholas D M; Hernandez, Ignacio; Gonzalez, Jesus; Rodriguez, Fernando; Brazhkin, Vadim V; Sapelkin, Andrei

    2015-11-11

    Over the last two decades, it has been demonstrated that size effects have significant consequences for the atomic arrangements and phase behavior of matter under extreme pressure. Furthermore, it has been shown that an understanding of how size affects critical pressure-temperature conditions provides vital guidance in the search for materials with novel properties. Here, we report on the remarkable behavior of small (under ~5 nm) matrix-free Ge nanoparticles under hydrostatic compression that is drastically different from both larger nanoparticles and bulk Ge. We discover that the application of pressure drives surface-induced amorphization leading to Ge-Ge bond overcompression and eventually to a polyamorphic semiconductor-to-metal transformation. A combination of spectroscopic techniques together with ab initio simulations were employed to reveal the details of the transformation mechanism into a new high density phase-amorphous metallic Ge. PMID:26457875

  12. Strong electroluminescence from direct band and defects in Ge n+/p shallow junctions at room temperature

    NASA Astrophysics Data System (ADS)

    Lin, Guangyang; Wang, Chen; Li, Cheng; Chen, Chaowen; Huang, Zhiwei; Huang, Wei; Chen, Songyan; Lai, Hongkai; Jin, Chunyan; Sun, Jiaming

    2016-05-01

    Strong room temperature electroluminescence with two emission peaks at around 0.786 eV and 0.747 eV from Ge n+/p shallow junctions was reported. The peak at around 0.786 eV comes from direct band luminescence (DBL) in n + Ge regions, while the peak fixing at 0.747 eV is resulted from defects induced by ion implantation. Heavy n-type doping in Ge renders realization of strong defect-related luminescence (DRL) feasible. The peak intensity ratio of DRL/DBL decreases with increase of injection current since more electrons are filled in Γ valley. Above all, the Ge n+/p shallow junction is fully compatible with the source and drain in Ge metal-oxide-semiconductor field effect transistors.

  13. Multilayered Ge/SiGe Material in Microfabricated Thermoelectric Modules

    NASA Astrophysics Data System (ADS)

    Samarelli, A.; Llin, L. Ferre; Cecchi, S.; Chrastina, D.; Isella, G.; Etzelstorfer, T.; Stangl, J.; Gubler, E. Muller; Weaver, J. M. R.; Dobson, P.; Paul, D. J.

    2014-10-01

    Results for low dimensional p-type Ge/SiGe superlattices with Ge quantum wells of 3.43 nm are presented. A range of microfabricated test structures have been developed to characterise the cross-plane electrical and thermal properties of the Ge/SiGe heterostructures. These superlattices were directly grown on 100-mm-diameter silicon wafers by a chemical vapour deposition growth system with rates up to 6 nm/s. Quantum well and quantum mechanical tunnel barriers with dimensions down to nm have been designed, grown and tested; they demonstrate a ZT of 0.08 ± 0.011 and power factor of 1.34 ± 0.15 m W m-1 K-2 at 300 K. A complete microfabricated module using indium bump-bonding is reported together with preliminary results on unoptimised material and leg dimensions. Routes to optimise the material and modules are discussed.

  14. High hole mobility GeSn on insulator formed by self-organized seeding lateral growth

    NASA Astrophysics Data System (ADS)

    Liu, Zhi; Wen, Juanjuan; Zhang, Xu; Li, Chuanbo; Xue, Chunlai; Zuo, Yuhua; Cheng, Buwen; Wang, Qiming

    2014-11-01

    Tensile strained single-crystal GeSn on insulator (GSOI) was obtained using self-organized seeding lateral growth. Segregation of Sn atoms and Sn distribution occurred during the lateral growth of the GeSn stripe. At both edges of the GSOI, Sn concentration distribution was found in good agreement with calculation based on the Scheil equation. P-channel metal-oxide-semiconductor field effect transistors were fabricated using the GSOI materials. Good transistor performance with the low field peak hole mobility of 383 cm2 V-1 s-1 was obtained, which indicated the high quality of this GSOI structure.

  15. Ru{sub 2}Ge{sub 3}: Crystal growth and some properties

    SciTech Connect

    Borshchevsky, A.; Fleurial, J.P.

    1993-10-01

    Large samples of Ru{sub 2}Ge{sub 3} were grown from Ge-rich off-stoichiometric melts at a temperature close to 1,460 C by a vertical gradient freeze method in graphite and glassy carbon crucibles. Diffusionless transition from high temperature tetragonal structure to low temperature orthorhombic structure causes twinning and crack formation. Thermal expansion coefficients of both low and high temperature phases were measured. Some electrical transport properties in the 25--1,000 C temperature range in different crystallographic directions are also described for this high temperature semiconductor. Substantial anisotropy is observed.

  16. Ultrafast photoinduced charge separation in metal-semiconductor nanohybrids.

    PubMed

    Mongin, Denis; Shaviv, Ehud; Maioli, Paolo; Crut, Aurélien; Banin, Uri; Del Fatti, Natalia; Vallée, Fabrice

    2012-08-28

    Hybrid nano-objects formed by two or more disparate materials are among the most promising and versatile nanosystems. A key parameter in their properties is interaction between their components. In this context we have investigated ultrafast charge separation in semiconductor-metal nanohybrids using a model system of gold-tipped CdS nanorods in a matchstick architecture. Experiments are performed using an optical time-resolved pump-probe technique, exciting either the semiconductor or the metal component of the particles, and probing the light-induced change of their optical response. Electron-hole pairs photoexcited in the semiconductor part of the nanohybrids are shown to undergo rapid charge separation with the electron transferred to the metal part on a sub-20 fs time scale. This ultrafast gold charging leads to a transient red-shift and broadening of the metal surface plasmon resonance, in agreement with results for free clusters but in contrast to observation for static charging of gold nanoparticles in liquid environments. Quantitative comparison with a theoretical model is in excellent agreement with the experimental results, confirming photoexcitation of one electron-hole pair per nanohybrid followed by ultrafast charge separation. The results also point to the utilization of such metal-semiconductor nanohybrids in light-harvesting applications and in photocatalysis. PMID:22792998

  17. Thin-film transistors based on organic conjugated semiconductors

    NASA Astrophysics Data System (ADS)

    Garnier, Francis

    1998-02-01

    The use of organic semiconductors as active layers in thin-film transistors has raised in the recent years a large interest, both for the fundamental understanding of the charge transport processes in organic materials, and also for the potential applications of these devices in the new field of flexible electronics. Short conjugated oligomers have been shown to possess much higher field-effect mobilities than their parent conjugated polymers. The origin of such increase in the efficiency of charge transport is mainly attributed to the close-packing and long-range structural organization displayed in thin films of conjugated oligomers. The various routes for controlling this organization are described, which allow to realize liquid crystal-like two-dimensional structures for these semiconductors, whose carrier mobility has now become equivalent to that of amorphous silicon. It is also shown that the effect of conjugation length on carrier mobility is not as critical as previously thought, but the associated increase of the band gap energy effects the efficiency of charge injection at the metal/semiconductor interface. This problem can be answered by realizing a local doping of the semiconductor, which allows the injection of charge to operate through an efficient tunneling mechanism. Organic-based thin-film transistors have now become viable devices.

  18. Hydrogen in semiconductors and metals

    SciTech Connect

    Nickel, N.H.; Jackson, W.B.; Bowman, R.C.; Leisure, R.G.

    1998-12-31

    Major highlights of the conference include further understanding of the structure of extended hydrogen clusters in semiconductors, switchable optical properties of metal-hydride films, reversible changes in the magnetic coupling in metallic superlattices, and increased lifetime of integrated circuits due to deuterium device passivation. Continued progress has also been achieved in understanding hydrogenation of defects in compound semiconductors and on surfaces. Total energy calculations in semiconductors have progressed sufficiently to predict energetics and vibration frequencies as measured by experiment. Similarly, electronic structure calculations of hydrogen-metal systems provide a deeper understanding of stability, bonding, and phase changes. Various nuclear techniques have been refined to yield important information regarding the concentration and transport of hydrogen in condensed matter. Finally, the interaction of hydrogen to create thermal donors has been used to create deep p-n junctions without the need for deep diffusion of dopants. The volume has been organized along the order of presentation within the conference. Similar methods and subjects have been grouped together. The authors have attempted to keep similar metal and semiconductor papers together in order to further promote cross-fertilization between the fields. Major categories include hydrogen on surfaces, theory and thermodynamics, hydrogen transport phenomena, nuclear characterization techniques, compound semiconductors, metal bulk, devices and applications, bulk silicon, and carbon and carbon-like materials. Separate abstracts were prepared for most papers.

  19. Nonlinear optical interactions in semiconductors

    NASA Astrophysics Data System (ADS)

    Salour, M. M.

    1985-12-01

    The optical pumping technique in GaAs has led to the development of a novel and highly sensitive optical temperature sensor. Completed is the experiment on two photon optical pumping in ZnO. An external cavity semiconductor laser involving ZnO as a gain medium was demonstrated under two-photon excitation. This laser should have a major impact on the development of tunable blue-green radiation for submarine communication. Completed is a paper on heat buildup in semiconductor platelets. New lasers are used to explore elementary excitation in optical thin film layers of semiconductors. This has led to the first demonstration of the feasibility of room temperature operation of a tunable coherent source involving multiple quantum well material. Completed is the construction of a simple remote (non-contact) temperature sensor to directly measure heat buildup in semiconductor materials as a result of high power optical laser excitation. Finally, an experiment involving optical frequency mixing to probe electrodynamics in the GaAlAs multiple quantumwell and superlattice structures, utilizing two recently constructed tunabel laser systems,has been successful. Attempts were focused on observing a number of new optical effects including nonlinear absorption and transmission phenomena, enhanced spontaneous and stimulated light scattering processes, etc. The construction of an external cavity semiconductor HgCdTe has been successful.

  20. Production of High Value Fluorine Gases for the Semiconductor Industry

    SciTech Connect

    Bulko, J. B.

    2003-10-23

    The chemistry to manufacture high purity GeF{sub 4} and WF{sub 6} for use in the semiconductor industry using Starmet's new fluorine extraction technology has been developed. Production of GeF{sub 4} was established using a tube-style reactor system where conversion yields as high as 98.1% were attained for the reaction between and GeO{sub 2}. Collection of the fluoride gas improved to 97.7% when the reactor sweep gas contained a small fraction of dry air (10-12 vol%) along with helium. The lab-synthesized product was shown to contain the least amount of infrared active and elemental impurities when compared with a reference material certified at 99.99% purity. Analysis of the ''as-produced'' gas using ICP-MS showed that uranium could not be detected at a detection limit of 0.019ppm-wt. A process to make WF{sub 6} from WO{sub 2}, and UF{sub 4}, produced a WOF{sub 4} intermediate, which proved difficult to convert to tungsten hexafluoride using titanium fluoride as a fluorinating agent.

  1. Band-structure calculations for semiconductors within generalized-density-functional theory

    NASA Astrophysics Data System (ADS)

    Remediakis, I. N.; Kaxiras, Efthimios

    1999-02-01

    We present band-structure calculations of several semiconductors and insulators within the framework of density-functional theory in the local-density approximation (DFT/LDA), employing the correction for excited states proposed by Fritsche and co-workers. We applied the method to examine typical elemental (C,Si,Ge), compound group-IV (SiC, SiGe, GeC) and compound III-IV semiconductors (AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InP, InAs, InSb), and examined in detail the approximations involved in the conduction-band energy correction. This quite simple method (referred to as generalized density-functional theory), while not a substitute for more rigorous theoretical approaches such as the GW method, gives results in reasonable agreement with experiment. Thus, it makes possible the calculation of semiconductor band gaps with the computational effort of a DFT/LDA calculation, at least for systems where more elaborate methods are not readily applicable.

  2. Examination of the temperature dependent electronic behavior of GeTe for switching applications

    NASA Astrophysics Data System (ADS)

    Champlain, James G.; Ruppalt, Laura B.; Guyette, Andrew C.; El-Hinnawy, Nabil; Borodulin, Pavel; Jones, Evan; Young, Robert M.; Nichols, Doyle

    2016-06-01

    The DC and RF electronic behaviors of GeTe-based phase change material switches as a function of temperature, from 25 K to 375 K, have been examined. In its polycrystalline (ON) state, GeTe behaved as a degenerate p-type semiconductor, exhibiting metal-like temperature dependence in the DC regime. This was consistent with the polycrystalline (ON) state RF performance of the switch, which exhibited low resistance S-parameter characteristics. In its amorphous (OFF) state, the GeTe presented significantly greater DC resistance that varied considerably with bias and temperature. At low biases (<1 V) and temperatures (<200 K), the amorphous GeTe low-field resistance dramatically increased, resulting in exceptionally high amorphous-polycrystalline (OFF-ON) resistance ratios, exceeding 109 at cryogenic temperatures. At higher biases and temperatures, the amorphous GeTe exhibited nonlinear current-voltage characteristics that were best fit by a space-charge limited conduction model that incorporates the effect of a defect band. The observed conduction behavior suggests the presence of two regions of localized traps within the bandgap of the amorphous GeTe, located at approximately 0.26-0.27 eV and 0.56-0.57 eV from the valence band. Unlike the polycrystalline state, the high resistance DC behavior of amorphous GeTe does not translate to the RF switch performance; instead, a parasitic capacitance associated with the RF switch geometry dominates OFF state RF transmission.

  3. Boron diffusion mechanism and effect of interface Ge atoms in Si/SiO2 and SiGe/SiO2 interfaces

    NASA Astrophysics Data System (ADS)

    Kim, Geun-Myeong; Oh, Young Jun; Lee, Chang Hwi; Chang, K. J.

    2014-03-01

    In metal-oxide-semiconductor field effect transistors (MOSFETs) it is known that implanted B dopants easily segregate to the oxide during thermal annealing after ion implantation, causing threshold voltage shift and sheet resistance increase. On the other hand, SiGe alloys have been considered as a promising material for p-type MOSFETs due to reduced B diffusion and high hole mobility. However, there is a lack of studies for B diffusion in Si/SiO2 and SiGe/SiO2 interfaces. In this work, we perform first-principles density functional calculations to study the mechanism for the B diffusion in Si/SiO2 and SiGe/SiO2 interfaces. We investigate the diffusion pathways and migration barriers by using the climbing nudged elastic band and dimer methods. For Si/SiO2 interface, B in Si turns into an interstitial B and tends to intervene between the Si and bridge O atoms at the interface. The overall migration barrier is calculated to be about 2 eV, comparable to that in bulk SiO2. In SiGe/SiO2, interface Ge atoms enhance the stability of B-related defects in the interface region, resulting in the higher migration barrier of about 3.7 eV. Our results indicate that Si/SiO2 interface does not hinder the B diffusion, however, the B diffusion is suppressed in the presence of interface Ge atoms.

  4. Conductivity (ac and dc) in III-V amorphous semiconductors and chalcogenide glasses

    NASA Astrophysics Data System (ADS)

    Hauser, J. J.

    1985-02-01

    Variable-range hopping, as evidenced by a resistivity proportional to exp(T-1/4), has been induced in many III-V amorphous semiconductors (InSb, AlSb, and GaAs) and even in chalcogenide glasses (As2Te3, As2Te3-xSex, and GeTe) by depositing films at 77 K. It is therefore remarkable that the same procedure failed to generate variable-range hopping in GaSb, which is one of the less ionic III-V semiconductors. Besides differences in the dc conductivity, there are also different behaviors in the ac conductivity of amorphous semiconductors. The low-temperature ac conductivity of all amorphous semiconductors is proportional to ωsTn with s~=1 and n<1, which is consistent with a model of correlated barrier hopping of electron pairs between paired and random defects. However, in the case of a-SiO2 and a-GeSe2 one finds, in addition, that the capacitance obeys the scaling relation C=A ln(Tω-1), which would suggest a conduction mechanism by tunneling relaxation. Furthermore, this scaling relation cannot be fitted to the data for a-As2Te3, a-InSb, and a-GaSb although the functional dependence of C on T and ω are similar.

  5. Synthesis of Group IV Nanowires on Graphene: The Case of Ge Nanocrawlers.

    PubMed

    Mataev, Elnatan; Rastogi, Sahil Kumar; Madhusudan, Atul; Bone, Jennifer; Lamprinakos, Nicholas; Picard, Yoosuf; Cohen-Karni, Tzahi

    2016-08-10

    In recent years, there has been a growing interest in using graphene as a synthesis platform for polymers, zero-dimensional (0D) materials, one-dimensional materials (1D), and two-dimensional (2D) materials. Here, we report the investigation of the growth of germanium nanowires (GeNWs) and germanium nanocrawlers (GeNCs) on single-layer graphene surfaces. GeNWs and GeNCs are synthesized on graphene films by gold nanoparticles catalyzed vapor-liquid-solid growth mechanism. The addition of hydrogen chloride gas (HCl) at the nucleation step increased the propensity toward GeNCs growth on the surface. As the time lag before HCl introduction during the nucleation step increased, a significant change in the number of out-of-plane GeNWs versus in-plane GeNCs was observed. The nucleation temperature and time played a key role in the formation of GeNCs as well. The fraction of GeNCs (χNCs) decreased from 0.95 ± 0.01 to 0.66 ± 0.07 when the temperature was kept at 305 °C for 15 s versus maintained at 305 °C throughout the process, respectively. GeNCs exhibit ⟨112⟩ as the preferred growth direction whereas GeNWs exhibit both ⟨112⟩ and ⟨111⟩ as the preferred growth directions. Finally, our growth model suggests a possible mechanism for the preference of an in-plane GeNC growth on graphene versus GeNW on SiO2. These findings open up unique opportunities for fundamental studies of crystal growth on graphene, as well as enable exploration of new electronic interfaces between group IV materials and graphene, potentially toward designing new geometries for hybrid materials sensors. PMID:27400248

  6. Amphoteric behavior and precipitation of Ge dopants in InP

    SciTech Connect

    Yu, K.M.; Moll, A.J.; Walukiewicz, W.

    1996-11-01

    We have directly correlated the electrical behavior, the impurity lattice site location, ion damage, and the local bonding environments of Ge-dopant ions implanted into InP. We have found that after rapid thermal annealing the free electron concentration in the samples implanted at room temperature (RT) are always higher than those implanted at liquid nitrogen temperature (LNT). Although the macroscopic structure seems to be insensitive to the implantation temperature, significantly more local disorder is created in the LNT implanted amorphous layers. Moreover, the amphoteric bonding structure of the Ge atoms is found to be well established already in the as-implanted amorphous InP. After high temperature annealing ({approx_gt}800{degree}C), the Ge atoms rearrange locally with more of the Ge substituting the In site than the P site resulting in {ital n}-type conductivity. The solid solubility of Ge in the InP is measured to be {approximately}1.4{endash}1.6{times}10{sup 20}/cm{sup 3} while the free electron concentration is estimated to saturate at {approximately}3.4{times}10{sup 19}/cm{sup 3}. The relatively low electron concentration can be explained by Ge precipitation and the compensation of Ge{sub In} donors by Ge{sub P} acceptors in the RT implanted case. The further reduction in electron concentration in the LNT implanted samples is believed to be related to the high residual damage found in these samples. The high solubility of Ge in InP can be attributed to the availability of two possible sublattice sites for the dopant and the compensation of the local strains due to the amphoteric substitution of the Ge. The concentration ratio of the Ge{sub In} to Ge{sub P} determined in the heavily implanted material has been used to estimate the difference in the formation energy of Ge substituting those two different sites.

  7. High mobility emissive organic semiconductor.

    PubMed

    Liu, Jie; Zhang, Hantang; Dong, Huanli; Meng, Lingqiang; Jiang, Longfeng; Jiang, Lang; Wang, Ying; Yu, Junsheng; Sun, Yanming; Hu, Wenping; Heeger, Alan J

    2015-01-01

    The integration of high charge carrier mobility and high luminescence in an organic semiconductor is challenging. However, there is need of such materials for organic light-emitting transistors and organic electrically pumped lasers. Here we show a novel organic semiconductor, 2,6-diphenylanthracene (DPA), which exhibits not only high emission with single crystal absolute florescence quantum yield of 41.2% but also high charge carrier mobility with single crystal mobility of 34 cm(2) V(-1) s(-1). Organic light-emitting diodes (OLEDs) based on DPA give pure blue emission with brightness up to 6,627 cd m(-2) and turn-on voltage of 2.8 V. 2,6-Diphenylanthracene OLED arrays are successfully driven by DPA field-effect transistor arrays, demonstrating that DPA is a high mobility emissive organic semiconductor with potential in organic optoelectronics. PMID:26620323

  8. High mobility emissive organic semiconductor

    PubMed Central

    Liu, Jie; Zhang, Hantang; Dong, Huanli; Meng, Lingqiang; Jiang, Longfeng; Jiang, Lang; Wang, Ying; Yu, Junsheng; Sun, Yanming; Hu, Wenping; Heeger, Alan J.

    2015-01-01

    The integration of high charge carrier mobility and high luminescence in an organic semiconductor is challenging. However, there is need of such materials for organic light-emitting transistors and organic electrically pumped lasers. Here we show a novel organic semiconductor, 2,6-diphenylanthracene (DPA), which exhibits not only high emission with single crystal absolute florescence quantum yield of 41.2% but also high charge carrier mobility with single crystal mobility of 34 cm2 V−1 s−1. Organic light-emitting diodes (OLEDs) based on DPA give pure blue emission with brightness up to 6,627 cd m−2 and turn-on voltage of 2.8 V. 2,6-Diphenylanthracene OLED arrays are successfully driven by DPA field-effect transistor arrays, demonstrating that DPA is a high mobility emissive organic semiconductor with potential in organic optoelectronics. PMID:26620323

  9. High mobility emissive organic semiconductor

    NASA Astrophysics Data System (ADS)

    Liu, Jie; Zhang, Hantang; Dong, Huanli; Meng, Lingqiang; Jiang, Longfeng; Jiang, Lang; Wang, Ying; Yu, Junsheng; Sun, Yanming; Hu, Wenping; Heeger, Alan J.

    2015-12-01

    The integration of high charge carrier mobility and high luminescence in an organic semiconductor is challenging. However, there is need of such materials for organic light-emitting transistors and organic electrically pumped lasers. Here we show a novel organic semiconductor, 2,6-diphenylanthracene (DPA), which exhibits not only high emission with single crystal absolute florescence quantum yield of 41.2% but also high charge carrier mobility with single crystal mobility of 34 cm2 V-1 s-1. Organic light-emitting diodes (OLEDs) based on DPA give pure blue emission with brightness up to 6,627 cd m-2 and turn-on voltage of 2.8 V. 2,6-Diphenylanthracene OLED arrays are successfully driven by DPA field-effect transistor arrays, demonstrating that DPA is a high mobility emissive organic semiconductor with potential in organic optoelectronics.

  10. Selenium semiconductor core optical fibers

    SciTech Connect

    Tang, G. W.; Qian, Q. Peng, K. L.; Wen, X.; Zhou, G. X.; Sun, M.; Chen, X. D.; Yang, Z. M.

    2015-02-15

    Phosphate glass-clad optical fibers containing selenium (Se) semiconductor core were fabricated using a molten core method. The cores were found to be amorphous as evidenced by X-ray diffraction and corroborated by Micro-Raman spectrum. Elemental analysis across the core/clad interface suggests that there is some diffusion of about 3 wt % oxygen in the core region. Phosphate glass-clad crystalline selenium core optical fibers were obtained by a postdrawing annealing process. A two-cm-long crystalline selenium semiconductor core optical fibers, electrically contacted to external circuitry through the fiber end facets, exhibit a three times change in conductivity between dark and illuminated states. Such crystalline selenium semiconductor core optical fibers have promising utility in optical switch and photoconductivity of optical fiber array.

  11. Device Concepts in Semiconductor Spintronics

    NASA Astrophysics Data System (ADS)

    Molenkamp, Laurens W.

    Semiconductor spintronics has now reached a stage where the basic physical mechanisms controlling spin injection and detection are understood. Moreover, some critical technological issues involved in the growth and lithography of the magnetic semiconductors have been solved. This has allowed us to explore the physics of meanwhile quite complex spintronic devices. The lectures will start with an introduction to spin transport in metals and semiconductors. Building upon this, I will discuss various simple devices that demonstrate this basic physics in action. Subsequently, more advanced devices will be covered. For example, I will discuss resonant tunneling diodes (RTDs) fabricated from paramagnetic II-VI semiconductors that can be operated as a voltage controlled spin-switch. A quantum dot version of these RTDs exhibits, unexpectedly, remanent magnetism at zero external field, which we interpret as resulting from tunneling through a single magnetic polaron. In the ferromagnetic semiconductor (Ga, Mn)As we have observed a very large spin valve effect due to domain wall pinning at sub-10 nm sized constrictions. Furthermore, we have found a novel magnetoresistance effect in this material, dubbed tunnel anisotropic magnetoresistance (TAMR), which is due to the strongly (magneto-)anisotropic density of states in a ferromagnetic semiconductor. The effect leads to the observation of a spin valve-like behavior in tunnel structures containg a single ferromagnetic layer and also dominates the spin-valve signal obtained from structures containing two (Ga, Mn)As layers, where the effect may cause resistance changes of five orders of magnitude. Note from Publisher: This article contains the abstract only.

  12. Exciton Transport in Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Menke, Stephen Matthew

    Photovoltaic cells based on organic semiconductors are attractive for their use as a renewable energy source owing to their abundant feedstock and compatibility with low-cost coating techniques on flexible substrates. In contrast to photovoltaic cells based traditional inorganic semiconductors, photon absorption in an organic semiconductor results in the formation of a coulombically bound electron-hole pair, or exciton. The transport of excitons, consequently, is of critical importance as excitons mediate the interaction between charge and light in organic photovoltaic cells (OPVs). In this dissertation, a strong connection between the fundamental photophysical parameters that control nanoscopic exciton energy transfer and the mesoscopic exciton transport is established. With this connection in place, strategies for enhancing the typically short length scale for exciton diffusion (L D) can be developed. Dilution of the organic semiconductor boron subphthalocyanine chloride (SubPc) is found to increase the LD for SubPc by 50%. In turn, OPVs based on dilute layers of SubPc exhibit a 30% enhancement in power conversion efficiency. The enhancement in power conversion efficiency is realized via enhancements in LD, optimized optical spacing, and directed exciton transport at an exciton permeable interface. The role of spin, energetic disorder, and thermal activation on L D are also addressed. Organic semiconductors that exhibit thermally activated delayed fluorescence and efficient intersystem and reverse intersystem crossing highlight the balance between singlet and triplet exciton energy transfer and diffusion. Temperature dependent measurements for LD provide insight into the inhomogeneously broadened exciton density of states and the thermal nature of exciton energy transfer. Additional topics include energy-cascade OPV architectures and broadband, spectrally tunable photodetectors based on organic semiconductors.

  13. Synthesis, fabrication and characterization of Ge/Si axial nanowire heterostructure tunnel FETs

    SciTech Connect

    Picraux, Samuel T; Dayeh, Shadi A

    2010-01-01

    Axial Ge/Si heterostructure nanowires allow energy band-edge engineering along the axis of the nanowire, which is the charge transport direction, and the realization of asymmetric devices for novel device architectures. This work reports on two advances in the area of heterostructure nanowires and tunnel FETs: (i) the realization of 100% compositionally modulated Si/Ge axial heterostructure nanowires with lengths suitable for device fabrication and (ii) the design and implementation of Schottky barrier tunnel FETs on these nanowires for high-on currents and suppressed ambipolar behavior. Initial prototype devices resulted in a current drive in excess of 100 {micro}A/{micro}m (I/{pi}D) and 10{sup 5} I{sub on}/I{sub off} ratios. These results demonstrate the potential of such asymmetric heterostructures (both in the semiconductor channel and metal-semiconductor barrier heights) for low-power and high performance electronics.

  14. Ge-Au eutectic bonding of Ge {100} single crystals

    NASA Astrophysics Data System (ADS)

    Knowlton, W. B.; Itoh, K. M.; Beeman, J. W.; Emes, J. H.; Loretto, D.; Haller, E. E.

    1993-11-01

    We present preliminary results on the eutectic bonding between two {100} Ge single crystal surfaces using thin films of Au ranging from 900Å/surface to 300Å/surface and Pd (10% the thickness of Au). Following bonding, plan view optical microscopy (OM) of the cleaved interface of samples with Au thicknesses ≤ 500Å/surface show a eutectic morphology more conducive to phonon transmission through the bond interface. High resolution transmission electron microscopy (HRTEM) cross sectional interface studies of a 300Å/surface Au sample show <100> epitaxial growth of Ge. In sections of the bond, lattice continuity of the Ge is apparent through the interface. TEM studies also reveal <110> heteroepitaxial growth of Au with a Au-Ge lattice mismatch of less than 2%. Eutectic bonds with 200Å/surface Au have been attained with characterization pending. An optical polishing technique for Ge has been optimized to insure intimate contact between the Ge surfaces prior to bonding. Interferometry analysis of the optically polished Ge surface shows that surface height fluctuations lie within ±150Å across an interval of 1mm. Characterization of phonon transmission through the interface is discussed with respect to low temperature detection of ballistic phonons.

  15. A brief history of ... semiconductors

    NASA Astrophysics Data System (ADS)

    Jenkins, Tudor

    2005-09-01

    The development of studies in semiconductor materials is traced from its beginnings with Michael Faraday in 1833 to the production of the first silicon transistor in 1954, which heralded the age of silicon electronics and microelectronics. Prior to the advent of band theory, work was patchy and driven by needs of technology. However, the arrival of this successful quantum theory of solids, together with a concentration on the growth of pure silicon and germanium and an understanding of their properties, saw an explosion in activity in semiconductor studies that has continued to this day.

  16. Wide band gap semiconductor templates

    SciTech Connect

    Arendt, Paul N.; Stan, Liliana; Jia, Quanxi; DePaula, Raymond F.; Usov, Igor O.

    2010-12-14

    The present invention relates to a thin film structure based on an epitaxial (111)-oriented rare earth-Group IVB oxide on the cubic (001) MgO terminated surface and the ion-beam-assisted deposition ("IBAD") techniques that are amendable to be over coated by semiconductors with hexagonal crystal structures. The IBAD magnesium oxide ("MgO") technology, in conjunction with certain template materials, is used to fabricate the desired thin film array. Similarly, IBAD MgO with appropriate template layers can be used for semiconductors with cubic type crystal structures.

  17. Thermoelectric performance of granular semiconductors.

    SciTech Connect

    Glatz, A.; Beloborodov, I. S.; Materials Science Division; California State Univ.

    2009-01-01

    We study the effects of doping and confinement on the thermoelectric properties of nanocrystalline semiconductors. We calculate the thermopower and figure of merit for temperatures less than the charging energy. For weakly coupled semiconducting grains it is shown that the figure of merit is optimized for grain sizes of order 5 nm for typical materials, and that its value can be larger than one. Using the similarities between granular semiconductors and electron or Coulomb glasses allows for a quantitative description of inhomogeneous semiconducting thermoelectrics.

  18. Growth and Characterization of Bulk GeSi Solid Solutions

    NASA Technical Reports Server (NTRS)

    Ritter, Timothy M.

    1999-01-01

    In this work we have grown and characterized several GeSi samples in order to investigate the effects that Silicon concentration, applied magnetic field, and liquid encapsulation have on crystalline quality. Characterization techniques include NDIC microscopy and microprobe spectroscopy. Two samples were grown with a Silicon concentration of approximately 3% and are compared to previous growths having a Silicon fraction of approximately 5%. Growth conditions for one of these samples was varied with the presence of an external applied magnetic field to investigate the possibility of magnetic field damping. A comparison between these two ingots, and with previously grown material, revealed no clear improvement in sample crystalline quality. Three additional samples were grown using a CaCl2 liquid encapsulation technique that produced GeSi material with improved structural quality over previous samples. Comparisons to prior non-encapsulation grown material, details of our methodology, and suggestions for further improvements are discussed.

  19. Amorphous Semiconductor Nanowires Created by Site-Specific Heteroatom Substitution with Significantly Enhanced Photoelectrochemical Performance.

    PubMed

    He, Ting; Zu, Lianhai; Zhang, Yan; Mao, Chengliang; Xu, Xiaoxiang; Yang, Jinhu; Yang, Shihe

    2016-08-23

    Semiconductor nanowires that have been extensively studied are typically in a crystalline phase. Much less studied are amorphous semiconductor nanowires due to the difficulty for their synthesis, despite a set of characteristics desirable for photoelectric devices, such as higher surface area, higher surface activity, and higher light harvesting. In this work of combined experiment and computation, taking Zn2GeO4 (ZGO) as an example, we propose a site-specific heteroatom substitution strategy through a solution-phase ions-alternative-deposition route to prepare amorphous/crystalline Si-incorporated ZGO nanowires with tunable band structures. The substitution of Si atoms for the Zn or Ge atoms distorts the bonding network to a different extent, leading to the formation of amorphous Zn1.7Si0.3GeO4 (ZSGO) or crystalline Zn2(GeO4)0.88(SiO4)0.12 (ZGSO) nanowires, respectively, with different bandgaps. The amorphous ZSGO nanowire arrays exhibit significantly enhanced performance in photoelectrochemical water splitting, such as higher and more stable photocurrent, and faster photoresponse and recovery, relative to crystalline ZGSO and ZGO nanowires in this work, as well as ZGO photocatalysts reported previously. The remarkable performance highlights the advantages of the ZSGO amorphous nanowires for photoelectric devices, such as higher light harvesting capability, faster charge separation, lower charge recombination, and higher surface catalytic activity. PMID:27494205

  20. Nonlinear absorption and transmission properties of Ge, Te and InAs using tuneable IR FEL

    SciTech Connect

    Amirmadhi, F.; Becker, K.; Brau, C.A.

    1995-12-31

    Nonlinear absorption properties of Ge, Te and InAs are being investigated using the transmission of FEL optical pulses through these semiconductors (z-scan method). Wavelength, intensity and macropulse dependence are used to differentiate between two-photon and free-carrier absorption properties of these materials. Macropulse dependence is resolved by using a Pockles Cell to chop the 4-{mu}s macropulse down to 100 ns. Results of these experiments will be presented and discussed.

  1. GeSi strained nanostructure self-assembly for nano- and opto-electronics.

    SciTech Connect

    Means, Joel L.; Floro, Jerrold Anthony

    2001-07-01

    Strain-induced self-assembly during semiconductor heteroepitaxy offers a promising approach to produce quantum nanostructures for nanologic and optoelectronics applications. Our current research direction aims to move beyond self-assembly of the basic quantum dot towards the fabrication of more complex, potentially functional structures such as quantum dot molecules and quantum wires. This report summarizes the steps taken to improve the growth quality of our GeSi molecular beam epitaxy process, and then highlights the outcomes of this effort.

  2. Method of preparing nitrogen containing semiconductor material

    DOEpatents

    Barber, Greg D.; Kurtz, Sarah R.

    2004-09-07

    A method of combining group III elements with group V elements that incorporates at least nitrogen from a nitrogen halide for use in semiconductors and in particular semiconductors in photovoltaic cells.

  3. Semiconductor Reliability--Another Field for Physicists.

    ERIC Educational Resources Information Center

    Derman, Samuel; Anderson, Wallace T.

    1994-01-01

    Stresses that an important industrial area is product reliability, especially for semiconductors. Suggests that physics students would benefit from training in semiconductors: the many modes of failure, radiation effects, and electrical contact problems. (MVL)

  4. Spin-dependent transport phenomena in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Bergeson, Jeremy D.

    Thin-film organic semiconductors transport can have an anomalously high sensitivity to low magnetic fields. Such a response is unexpected considering that thermal fluctuation energies are greater than the energy associated with the intrinsic spin of charge carriers at a modest magnetic field of 100 Oe by a factor of more than 104 at room temperature and is still greater by 102 even at liquid helium temperatures. Nevertheless, we report experimental characterization of (1) spin-dependent injection, detection and transport of spin-polarized current through organic semiconductors and (2) the influence of a magnetic field on the spin dynamics of recombination-limited transport. The first focus of this work was accomplished by fabricating basic spin-valve devices consisting of two magnetic layers spatially separated by a nonmagnetic organic semiconductor. The spin-valve effect is a change in electrical resistance due to the magnetizations of the magnetic layers changing from parallel to antiparallel alignment, or vice versa. The conductivities of the metallic contacts and that of the semiconductor differed by many orders of magnitude, which inhibited the injection of a spin-polarized current from the magnet into the nonmagnet. We successfully overcame the problem of conductivity mismatch by inserting ultra-thin tunnel barriers at the metal/semiconductor interfaces which aided in yielding a ˜20% spin-valve effect at liquid helium temperatures and the effect persisted up to 150 K. We built on this achievement by constructing spin valves where one of the metallic contacts was replaced by the organic-based magnetic semiconductor vanadium tetracyanoethylene (V[TCNE]2). At 10 K these devices produced the switching behavior of the spin-valve effect. The second focus of this work was the bulk magnetoresistance (MR) of small molecule, oligomer and polymer organic semiconductors in thin-film structures. At room temperature the resistance can change up to 8% at 100 Oe and 15% at

  5. 6. Credit GE. Photographic copy of photograph, view looking east ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. Credit GE. Photographic copy of photograph, view looking east at Test Stand 'A' during test firing of a liquid-fueled Corporal engine. Structure in immediate left foreground of view appears to be a propellant tank enclosure (JPL negative no. 383-1225, July 1945); compare HAER CA-163-A-7 for enclosure. - Jet Propulsion Laboratory Edwards Facility, Test Stand A, Edwards Air Force Base, Boron, Kern County, CA

  6. Semiconductor electrode with improved photostability characteristics

    DOEpatents

    Frank, Arthur J.

    1987-01-01

    An electrode is disclosed for use in photoelectrochemical cells having an electrolyte which includes an aqueous constituent. The electrode includes a semiconductor and a hydrophobic film disposed between the semiconductor and the aqueous constituent. The hydrophobic film is adapted to permit charges to pass therethrough while substantially decreasing the activity of the aqueous constituent at the semiconductor surface thereby decreasing the photodegradation of the semiconductor electrode.

  7. Semiconductor nanocrystal-based phagokinetic tracking

    DOEpatents

    Alivisatos, A Paul; Larabell, Carolyn A; Parak, Wolfgang J; Le Gros, Mark; Boudreau, Rosanne

    2014-11-18

    Methods for determining metabolic properties of living cells through the uptake of semiconductor nanocrystals by cells. Generally the methods require a layer of neutral or hydrophilic semiconductor nanocrystals and a layer of cells seeded onto a culture surface and changes in the layer of semiconductor nanocrystals are detected. The observed changes made to the layer of semiconductor nanocrystals can be correlated to such metabolic properties as metastatic potential, cell motility or migration.

  8. Semiconductor electrode with improved photostability characteristics

    DOEpatents

    Frank, A.J.

    1985-02-19

    An electrode is described for use in photoelectrochemical cells having an electrolyte which includes an aqueous constituent. The electrode consists of a semiconductor and a hydrophobic film disposed between the semiconductor and the aqueous constituent. The hydrophobic film is adapted to permit charges to pass therethrough while substantially decreasing the activity of the aqueous constituent at the semiconductor surface thereby decreasing the photodegradation of the semiconductor electrode.

  9. Diode having trenches in a semiconductor region

    DOEpatents

    Palacios, Tomas Apostol; Lu, Bin; Matioli, Elison de Nazareth

    2016-03-22

    An electrode structure is described in which conductive regions are recessed into a semiconductor region. Trenches may be formed in a semiconductor region, such that conductive regions can be formed in the trenches. The electrode structure may be used in semiconductor devices such as field effect transistors or diodes. Nitride-based power semiconductor devices are described including such an electrode structure, which can reduce leakage current and otherwise improve performance.

  10. Semiconductor devices having a recessed electrode structure

    SciTech Connect

    Palacios, Tomas Apostol; Lu, Bin; Matioli, Elison de Nazareth

    2015-05-26

    An electrode structure is described in which conductive regions are recessed into a semiconductor region. Trenches may be formed in a semiconductor region, such that conductive regions can be formed in the trenches. The electrode structure may be used in semiconductor devices such as field effect transistors or diodes. Nitride-based power semiconductor devices are described including such an electrode structure, which can reduce leakage current and otherwise improve performance.

  11. Semiconductor assisted metal deposition for nanolithography applications

    DOEpatents

    Rajh, Tijana; Meshkov, Natalia; Nedelijkovic, Jovan M.; Skubal, Laura R.; Tiede, David M.; Thurnauer, Marion

    2002-01-01

    An article of manufacture and method of forming nanoparticle sized material components. A semiconductor oxide substrate includes nanoparticles of semiconductor oxide. A modifier is deposited onto the nanoparticles, and a source of metal ions are deposited in association with the semiconductor and the modifier, the modifier enabling electronic hole scavenging and chelation of the metal ions. The metal ions and modifier are illuminated to cause reduction of the metal ions to metal onto the semiconductor nanoparticles.

  12. Semiconductor assisted metal deposition for nanolithography applications

    DOEpatents

    Rajh, Tijana; Meshkov, Natalia; Nedelijkovic, Jovan M.; Skubal, Laura R.; Tiede, David M.; Thurnauer, Marion

    2001-01-01

    An article of manufacture and method of forming nanoparticle sized material components. A semiconductor oxide substrate includes nanoparticles of semiconductor oxide. A modifier is deposited onto the nanoparticles, and a source of metal ions are deposited in association with the semiconductor and the modifier, the modifier enabling electronic hole scavenging and chelation of the metal ions. The metal ions and modifier are illuminated to cause reduction of the metal ions to metal onto the semiconductor nanoparticles.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  14. (Magnetic properties of doped semiconductors)

    SciTech Connect

    Not Available

    1990-01-01

    Research continued on the transport behavior of doped semiconductors on both sides of the metal-insulator transition, and the approach to the transition from both the insulating and the metallic side. Work is described on magneto resistance of a series of metallic Si:B samples and CdSe. (CBS)

  15. Conductive Container for Semiconductor Devices

    NASA Technical Reports Server (NTRS)

    Rice, J. T.

    1986-01-01

    Container for semiconductor components not only protects them against mechanical damage but ensures they are not harmed by electrostatic discharges. Container holds components in fixed positions so they can be serialized and identified from their locations. Suitable for holding components during both storing and shipping. Originally developed for microwave diodes, container concept readily adaptable to transistors and integrated circuits.

  16. Semiconductor-based optical refrigerator

    DOEpatents

    Epstein, Richard I.; Edwards, Bradley C.; Sheik-Bahae, Mansoor

    2002-01-01

    Optical refrigerators using semiconductor material as a cooling medium, with layers of material in close proximity to the cooling medium that carries away heat from the cooling material and preventing radiation trapping. In addition to the use of semiconducting material, the invention can be used with ytterbium-doped glass optical refrigerators.

  17. Electronic spectra of semiconductor nanocrystals

    SciTech Connect

    Alivisatos, A.P.

    1993-12-31

    Semiconductor nanocrystals smaller than the bulk exciton show substantial quantum confinement effects. Recent experiments including Stark effect, resonance Raman, valence band photoemission, and near edge X-ray adsorption will be used to put together a picture of the nanocrystal electronic states.

  18. Semiconductor technology program: Progress briefs

    NASA Technical Reports Server (NTRS)

    Galloway, K. F.; Scace, R. I.; Walters, E. J.

    1981-01-01

    Measurement technology for semiconductor materials, process control, and devices, is discussed. Silicon and silicon based devices are emphasized. Highlighted activities include semiinsulating GaAs characterization, an automatic scanning spectroscopic ellipsometer, linewidth measurement and coherence, bandgap narrowing effects in silicon, the evaluation of electrical linewidth uniformity, and arsenicomplanted profiles in silicon.

  19. Mechanical scriber for semiconductor devices

    DOEpatents

    Lin, Peter T.

    1985-01-01

    A mechanical scriber using a scribing tip, such as a diamond, provides controlled scriber forces with a spring-loaded compound lever arrangement. The scribing force and range of scribing depth are adjusted by a pair of adjustable micrometer heads. A semiconductor device, such as a multilayer solar cell, can be formed into scribed strips at each layer.

  20. Mechanical scriber for semiconductor devices

    DOEpatents

    Lin, P.T.

    1985-03-05

    A mechanical scriber using a scribing tip, such as a diamond, provides controlled scriber forces with a spring-loaded compound lever arrangement. The scribing force and range of scribing depth are adjusted by a pair of adjustable micrometer heads. A semiconductor device, such as a multilayer solar cell, can be formed into scribed strips at each layer. 5 figs.

  1. A Brief History of ... Semiconductors

    ERIC Educational Resources Information Center

    Jenkins, Tudor

    2005-01-01

    The development of studies in semiconductor materials is traced from its beginnings with Michael Faraday in 1833 to the production of the first silicon transistor in 1954, which heralded the age of silicon electronics and microelectronics. Prior to the advent of band theory, work was patchy and driven by needs of technology. However, the arrival…

  2. 2010 Defects in Semiconductors GRC

    SciTech Connect

    Shengbai Zhang

    2011-01-06

    Continuing its tradition of excellence, this Gordon Conference will focus on research at the forefront of the field of defects in semiconductors. The conference will have a strong emphasis on the control of defects during growth and processing, as well as an emphasis on the development of novel defect detection methods and first-principles defect theories. Electronic, magnetic, and optical properties of bulk, thin film, and nanoscale semiconductors will be discussed in detail. In contrast to many conferences, which tend to focus on specific semiconductors, this conference will deal with point and extended defects in a broad range of electronic materials. This approach has proved to be extremely fruitful for advancing fundamental understanding in emerging materials such as wide-band-gap semiconductors, oxides, sp{sup 2} carbon based-materials, and photovoltaic/solar cell materials, and in understanding important defect phenomena such as doping bottleneck in nanostructures and the diffusion of defects and impurities. The program consists of about twenty invited talks and a number of contributed poster sessions. The emphasis should be on work which has yet to be published. The large amount of discussion time provides an ideal forum for dealing with topics that are new and/or controversial.

  3. Semiconductor ac static power switch

    NASA Technical Reports Server (NTRS)

    Vrancik, J.

    1968-01-01

    Semiconductor ac static power switch has long life and high reliability, contains no moving parts, and operates satisfactorily in severe environments, including high vibration and shock conditions. Due to their resistance to shock and vibration, static switches are used where accidental switching caused by mechanical vibration or shock cannot be tolerated.

  4. Electron beam pumped semiconductor laser

    NASA Technical Reports Server (NTRS)

    Hug, William F. (Inventor); Reid, Ray D. (Inventor)

    2009-01-01

    Electron-beam-pumped semiconductor ultra-violet optical sources (ESUVOSs) are disclosed that use ballistic electron pumped wide bandgap semiconductor materials. The sources may produce incoherent radiation and take the form of electron-beam-pumped light emitting triodes (ELETs). The sources may produce coherent radiation and take the form of electron-beam-pumped laser triodes (ELTs). The ELTs may take the form of electron-beam-pumped vertical cavity surface emitting lasers (EVCSEL) or edge emitting electron-beam-pumped lasers (EEELs). The semiconductor medium may take the form of an aluminum gallium nitride alloy that has a mole fraction of aluminum selected to give a desired emission wavelength, diamond, or diamond-like carbon (DLC). The sources may be produced from discrete components that are assembled after their individual formation or they may be produced using batch MEMS-type or semiconductor-type processing techniques to build them up in a whole or partial monolithic manner, or combination thereof.

  5. Optical bistability in semiconductor microcavities

    SciTech Connect

    Baas, A.; Karr, J.Ph.; Giacobino, E.; Eleuch, H.

    2004-02-01

    We report the observation of polaritonic bistability in semiconductor microcavities in the strong-coupling regime. The origin of bistability is the polariton-polariton interaction, which gives rise to a Kerr-like nonlinearity. The experimental results are in good agreement with a simple model taking transverse effects into account.

  6. Semiconductor alloys - Structural property engineering

    NASA Technical Reports Server (NTRS)

    Sher, A.; Van Schilfgaarde, M.; Berding, M.; Chen, A.-B.

    1987-01-01

    Semiconductor alloys have been used for years to tune band gaps and average bond lengths to specific applications. Other selection criteria for alloy composition, and a growth technique designed to modify their structural properties, are presently considered. The alloys Zn(1-y)Cd(y)Te and CdSe(y)Te(1-y) are treated as examples.

  7. Amphoteric native defects in semiconductors

    SciTech Connect

    Walukiewicz, W.

    1989-05-22

    We show that a new concept of amphoteric native defects with strongly Fermi level dependent defect formation energy provides the basis for a unified explanation of a large variety of phenomena in semiconductors. Formation of Schottky barriers, particle irradiation induced compensation, doping-induced superlattice intermixing, and limits of free-carrier concentration find for the first time a common simple explanation.

  8. Uniaxially stressed Ge:Ga and Ge:Be

    SciTech Connect

    Dubon, O.D. Jr.

    1992-12-01

    The application of a large uniaxial stress to p-type Ge single crystals changes the character of both the valence band and the energy levels associated with the acceptors. Changes include the splitting of the fourfold degeneracy of the valence band top and the reduction of the ionization energy of shallow acceptors. In order to study the effect of uniaxial stress on transport properties of photoexcited holes, a variable temperature photo-Hall effect system was built in which stressed Ge:Ga and Ge:Be could be characterized. Results indicate that stress increases the lifetime and Hall mobility of photoexcited holes. These observations may help further the understanding of fundamental physical processes that affect the performance of stressed Ge photoconductors including the capture of holes by shallow acceptors.

  9. Semiconductor films on flexible iridium substrates

    DOEpatents

    Goyal, Amit

    2005-03-29

    A laminate semiconductor article includes a flexible substrate, an optional biaxially textured oxide buffer system on the flexible substrate, a biaxially textured Ir-based buffer layer on the substrate or the buffer system, and an epitaxial layer of a semiconductor. Ir can serve as a substrate with an epitaxial layer of a semiconductor thereon.

  10. Effect of mixed Ge/Si cross-linking on the physical properties of amorphous Ge-Si-Te networks

    SciTech Connect

    Gunasekera, K.; Boolchand, P.; Micoulaut, M.

    2014-04-28

    Amorphous Ge{sub x}Si{sub x}Te{sub 1−2x} glasses are studied as a function of composition by a combination of experimental and theoretical methods, allowing for a full description of the network structure in relationship with physico-chemical properties. Calorimetric and thermal measurements reveal that such glasses display an anomalous behavior across a range of compositions x{sub c1}=7.5% and liquid fragility. These anomalies allow defining an intermediate phase, where network rigidity onsets as the content x of Group IV atoms (Ge, Si) are increased. The structural manifestation of these anomalies is understood from  {sup 119}Sn Mössbauer spectroscopy and First Principles Molecular Dynamics at selected compositions (Ge{sub 20}Te{sub 80}, Si{sub 20}Te{sub 80}, and Ge{sub 10}Si{sub 10}Te{sub 80}). The numerical models reveal the quite different roles played by the modifier or network cross-linker Ge or Si atoms, Si being more tetrahedral in sp{sup 3} geometry, whereas Mössbauer spectroscopy shows that the nature of chemical bonding is dramatically changed around x≃ 8%. The precise evolution of the local structure and chemical bonding ultimately allows understanding the origin of the intermediate phase in these complex tellurides.

  11. Development of a System for Measuring the Shape of β Spectra Using a Semiconductor Si Detector

    SciTech Connect

    Bisch, C.; Mougeot, X.; Bé, M.-M.; Nourreddine, A.-M.

    2014-06-15

    A system for the measurement of beta energy spectra has been developed. It is based on a silicon semi-conductor detector operating at liquid nitrogen temperatures, under ultra high-vacuum. Monte-Carlo simulations were made to optimize the detection chamber and the source holder. Descriptions of the electronic and mechanical systems are included, as well as the first measured spectra.

  12. Transfer-free synthesis of highly ordered Ge nanowire arrays on glass substrates

    SciTech Connect

    Nakata, M.; Toko, K. Suemasu, T.; Jevasuwan, W.; Fukata, N.; Saitoh, N.; Yoshizawa, N.

    2015-09-28

    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.

  13. Nanoscale templating and self-assembly of organic semiconductors

    NASA Astrophysics Data System (ADS)

    Hulvat, James Francis

    Improvements in organic electronic materials could lead to novel device applications, ranging from large-area, flexible displays to light weight, plastic electronics. Progress on these applications would benefit from development of low-cost, aqueous, solution-based fabrication techniques for organic semiconductors. Supramolecular self-assembly enables molecules to organize in complex structures through non-covalent interactions. The nanoscale structure and aggregation of organic semiconductors influence conductivity, charge mobility and luminescence. We developed three approaches to enhance the performance of organic semiconductors through molecular self-assembly. The first uses a liquid crystalline (LC) template to mediate electrochemical polymerization of poly(3,4-ethyldioxythiophene) (PEDOT), a conducting polymer used for hole injection in organic light emitting diodes (OLED). Monomers were polymerized in the cylindrical, hydrophobic cores of a hexagonal, lyotropic LC formed by a non-ionic amphiphile in water, The templated, conducting polymer films exhibited anisotropic optical properties and increased conductivity as a direct result of the nanoscale, self-organized structure of the template. Another approach was used to control molecular order by preparing organic semiconductors that are themselves liquid crystalline. We developed a novel series of triblock oligo(phenylene vinylene) (OPV) amphiphiles that form thermotropic and lyotropic LC mesophases. The self-organized, layered structure of these mesophases influences aggregation of OPV, enhancing fluorescence in the liquid crystalline state compared with disordered films. These OPV-amphiphiles are the first example of a water-soluble oligo(phenylene vinylene) that can self-organize into aligned, well-ordered, highly fluorescent films. In a third system, a triblock, dendron rod-coil (DRC) molecule containing a quaterthiophene segment was prepared and its self-assembly and electronic properties investigated

  14. Heavy-fermion semiconductor behavior of the SU({ital N}{sub {ital d}}) Anderson lattice model

    SciTech Connect

    Hu, L.; Yang, F.; Sun, J. |; Lin, T. |

    1995-08-15

    The heavy-fermion semiconductor behavior of the SU({ital N}{sub {ital d}}) Anderson lattice model is examined by using the slave-boson technique within the framework of mean-field theory. The results show that the slave-boson mean-field theory of this model can present a heavy Fermi liquid or a heavy-fermion semiconductor ground state for different {ital n} values ({ital n} is the total number of the conduction and the on-site {ital f} electrons per lattice site), thus providing a unified description of the heavy Fermi liquid and the heavy-fermion semiconductor. The basic features of this theory are in qualitative agreement with the experimentally observed heavy-fermion semiconductor behavior of some rare-earth compounds.

  15. Vertically grown Ge nanowire Schottky diodes on Si and Ge substrates

    NASA Astrophysics Data System (ADS)

    Chandra, Nishant; Tracy, Clarence J.; Cho, Jeong-Hyun; Picraux, S. T.; Hathwar, Raghuraj; Goodnick, Stephen M.

    2015-07-01

    The processing and performance of Schottky diodes formed from arrays of vertical Ge nanowires (NWs) grown on Ge and Si substrates are reported. The goal of this work is to investigate CMOS compatible processes for integrating NWs as components of vertically scaled integrated circuits, and elucidate transport in vertical Schottky NWs. Vertical phosphorus (P) doped Ge NWs were grown using vapor-liquid-solid epitaxy, and nickel (Ni)-Ge Schottky contacts were made to the tops of the NWs. Current-voltage (I-V) characteristics were measured for variable ranges of NW diameters and numbers of nanowires in the arrays, and the I-V characteristics were fit using modified thermionic emission theory to extract the barrier height and ideality factor. As grown NWs did not show rectifying behavior due to the presence of heavy P side-wall doping during growth, resulting in a tunnel contact. After sidewall etching using a dilute peroxide solution, rectifying behavior was obtained. Schottky barrier heights of 0.3-0.4 V and ideality factors close to 2 were extracted using thermionic emission theory, although the model does not give an accurate fit across the whole bias range. Attempts to account for enhanced side-wall conduction due to non-uniform P doping profile during growth through a simple shunt resistance improve the fit, but are still insufficient to provide a good fit. Full three-dimensional numerical modeling using Silvaco Atlas indicates that at least part of this effect is due to the presence of fixed charge and acceptor like traps on the NW surface, which leads to effectively high ideality factors.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  17. A Low-Leakage Epitaxial High-κ Gate Oxide for Germanium Metal-Oxide-Semiconductor Devices.

    PubMed

    Hu, Chengqing; McDaniel, Martin D; Jiang, Aiting; Posadas, Agham; Demkov, Alexander A; Ekerdt, John G; Yu, Edward T

    2016-03-01

    Germanium (Ge)-based metal-oxide-semiconductor field-effect transistors are a promising candidate for high performance, low power electronics at the 7 nm technology node and beyond. However, the availability of high quality gate oxide/Ge interfaces that provide low leakage current density and equivalent oxide thickness (EOT), robust scalability, and acceptable interface state density (Dit) has emerged as one of the most challenging hurdles in the development of such devices. Here we demonstrate and present detailed electrical characterization of a high-κ epitaxial oxide gate stack based on crystalline SrHfO3 grown on Ge (001) by atomic layer deposition. Metal-oxide-Ge capacitor structures show extremely low gate leakage, small and scalable EOT, and good and reducible Dit. Detailed growth strategies and postgrowth annealing schemes are demonstrated to reduce Dit. The physical mechanisms behind these phenomena are studied and suggest approaches for further reduction of Dit. PMID:26859048

  18. Investigation of Semiconductor Surface Structure by Transmission Ion Channeling.

    NASA Astrophysics Data System (ADS)

    Lyman, Paul Francis

    The primary thrust of this dissertation is the investigation of the composition and structure of two important surface systems on Si, and the study of how this structure evolves under the influence of ion bombardment or film growth. I have studied the initial stages of oxidation of Si immediately following removal of a surface oxide by an HF etch. I have also studied the structure of Ge deposited on clean Si(100) at low temperatures. These systems are of considerable technological interest, but were chosen because they naturally pose fundamental questions regarding physical and chemical processes at surfaces. In the study of the oxidation of Si, I have focused on the influence of the bombarding ion beam in altering the structure and composition of the surface layer. Thus, the system then provides a natural vehicle to study ion-induced chemistry. In the study of low-temperature growth of Ge, I have focused on the structure of the Ge layer and the evolution of that structure upon further deposition or upon heating. This simple system is a model one for observing strained semiconductor heteroepitaxial growth. The primary probe for these studies was transmission channeling of MeV ions. The sensitivity of this technique to correlations between the substrate and an overlayer allowed us to make the following observations. The O, Si and H bound in the thin oxide formed after an HF etch and H_2O rinse occupy preferred positions with respect to the Si matrix. Upon ion bombardment, the O further reacts with the Si (the reaction proceeds linearly with the ion fluence) and the portion of the H that is uncorrelated to the substrate is preferentially desorbed. For the case of Ge growth on Si(100)-(2 x 1) at room temperature, a substantial fraction of the Ge films is strained to occupy sites having the lattice constant of the Si substrate (pseudomorphic growth). A model for film growth is proposed in which pseudomorphic domains constitute roughly half of the Ge films up to a

  19. Oxygen and germanium migration at low temperature influenced by the thermodynamic nature of the materials used in germanium metal-insulator-semiconductor structures

    SciTech Connect

    Kato, Kimihiko; Taoka, Noriyuki; Sakashita, Mitsuo; Nakatsuka, Osamu Zaima, Shigeaki

    2015-09-07

    The influence of the reductive character of the metals used for the gate electrode on O migration in gate stacks and following reductive or oxidative reactions at an interface between a high permittivity (high-k) insulating layer and Ge or Si was investigated. The magnitude of the increase or decrease of Ge or Si oxides in the gate stacks caused by the metal layer deposition can be systematically correlated with the oxygen chemical potential (μ{sub O}) of gate metals for both Ge and Si systems. However, the influence of the gate metals on oxidative/reductive reactions of a semiconductor element is more significant for the Ge gate stacks than the Si system. Detailed investigations of Ge oxide as a function of depth were used to determine that the strong μ{sub O} dependence of the increase or decrease in the Ge oxide is because of the high diffusivity of Ge into the high-k oxide. In particular, migration of Ge into the high-k oxide occurs concurrently with O migration towards the reductive metal layer, and the strong reductive character of the metal significantly influences the decrease in the amount of Ge oxide. These results indicate the importance of the selection of gate metals based on μ{sub O} for controlling high-k/Ge interfacial structures.

  20. Preservation of surface features on semiconductor surfaces

    SciTech Connect

    Wilt, D.P.

    1989-02-14

    A semiconductor laser is described comprising a Group III-V compound semiconductor body having a major surface, p1 an optical grating on the major surface, a protective coating on the grating, the coating including a transition metal, a Group III-V compound semiconductor heterostructure formed on the coating, the heterostructure having the shape of a mesa and including a Group III-V compound semiconductor active layer, a current-blocking Group III-V compound semiconductor structure laterally adjacent the mesa and effective to direct the primary flow of current through the mesa during operation of the laser, and means forming electrical contact to the laser.