Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Y21: Semiconductors: Thermodynamic & Transport Properties (Theory) |
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Sponsoring Units: FIAP Chair: Chris Palmstrom, University of California, Santa Barbara Room: 323 |
Friday, March 22, 2013 8:00AM - 8:12AM |
Y21.00001: Thermal transport in the two-dimensional disordered electron gas Georg Schwiete, Alexander Finkelstein We develop a theory of thermal transport in the two-dimensional disordered electron gas at low temperatures. Our approach is based on the calculation of the heat density correlation function. To this end we subject the Keldysh nonlinear sigma model in the presence of source fields to a renormalization group analysis. Special care is taken to additionally account for scattering processes with a very small frequency transfer. [Preview Abstract] |
Friday, March 22, 2013 8:12AM - 8:24AM |
Y21.00002: Electronic properties of near-surface InAs heterostructures Borzoyeh Shojaei, Javad Shabani, Brian Schultz, Chris Palmstrom The interest in low-dimensional narrow gap semiconductors with large spin orbit and high electron mobility has recently surged because of novel proposals on the realization of Majorana modes in such materials. To induce the proximity effect in the semiconductor by coupling to a superconductor, and to tune parameters of the system to realize Majorana excitations the electron channel has to form at or near the interface with the superconductor. In this work we have systematically studied near surface InAs heterostructures grown by molecular beam epitaxy (MBE). We have measured magnetotransport properties in these structures and compared them to theoretical values. We also discuss the in-situ growth of s-wave superconductors on InAs heterostructures and the proximity effect. [Preview Abstract] |
Friday, March 22, 2013 8:24AM - 8:36AM |
Y21.00003: Impact of Silicon Nitride Passivation Thickness on AlGaN $\backslash $GaN Transport Properties and Device Performance Helen Jackson, James Petrosky, Robert Hengehold, Zhaoqiang Fang Silicon nitride passivation (Si$_{3}$N$_{4}$) on AlGaN$\backslash $GaN heterojunction devices can improve performance by reducing electron traps at the surface. In this study, the effects of passivation layer thickness were investigated at various thicknesses (0, 20, 50 and 120 nanometers) on bare epilayer AlGaN$\backslash $GaN structures with either an AlN nucleation layer or a GaN cap. Hall system measurements were used to observe changes in carrier concentration and mobility as a function silicon nitride thickness. Mobility changes were measured and carrier scattering mechanisms are analyzed both with and without Si$_{3}$ N$_{4}$. Capacitance voltage measurements were done to give information about the surface donor states and the Si$_{3}$N$_{4}$ charge at the interface. A monatomic decrease in saturation capacitance with increasing Si$_{3}$N$_{4}$ thickness was observed. Gate current measurements were done to examine the effect of Si$_{3}$N$_{4}$ on the gate leakage current and thus device performance. [Preview Abstract] |
Friday, March 22, 2013 8:36AM - 8:48AM |
Y21.00004: Anomalous Mobility Enhancement via PPC of a GaAs/AlGaAs 2DEG Yun Suk Eo, Steven Wolgast, \c{C}a\u{g}liyan Kurdak, Loren Pfeiffer, Ken West We report the unusual transport behavior of a two-dimensional electron gas (2DEG) in a $\delta$-doped $GaAs/Al_{x}Ga_{1-x}As$ heterostructure. Typically, the carrier density can be varied with a gate voltage or via the persistent photoconductivity (PPC) effect. The relationship between carrier density and mobility has often been expressed with the empirical relation $\mu\sim n^{\alpha}$, where $\alpha$ contains scattering mechanism information and typically ranges between 1 and 2. Here, we study the carrier density and mobility using gating techniques and the PPC effect with infrared and white light in small incremental exposures. At 4.2K, we find that the addition of a gate structure greatly reduces the achievable mobility. For PPC, we find that after white exposures, $\alpha$ can become unusually large. At 0.3 K, we observe an unusual decrease in carrier density, accompanied by an enhancement in mobility ($\alpha < 0$) after repeated exposures of light. When the mobility is further enhanced by PPC, the 2DEG exhibits parallel conduction in its doping layer, and the transport becomes no longer controllable. However, the drifting mobility and carrier density eventually settle to reproducible values that are independent of the light increment history or other initial conditions. [Preview Abstract] |
Friday, March 22, 2013 8:48AM - 9:00AM |
Y21.00005: Parallel Magnetic Field Effect in the Insulating Phase of 2D Metal-Insulator Transition in p-GaAs with High r$_{\mathrm{s}}$ Richard L.J. Qiu, Xuan P.A. Gao, Loren N. Pfeiffer, Ken W. West We present magnetotransport measurements on the insulating side of the 2D metal-insulator transition in p-type GaAs quantum wells with 10 nm width (critical density p$_{\mathrm{c}}\sim $ 0.8*10$^{10}$/cm$^{\mathrm{2}}$, r$_{\mathrm{s}}\sim $ 36). Before entering the disorder dominated regime (p* \textless\ p \textless\ p$_{\mathrm{c}})$ (p* $\sim $ 0.5*10$^{10}$/cm$^{2})$, the conductance of the insulating phase follows a power-law like temperature dependence that is different from the well known thermally activated or variable range hopping behavior for insulators. In this unconventional insulating regime, a strong in-plane magnetic field (B$_{\mathrm{\vert \vert}}$ \textgreater\ B$_{\mathrm{c}} \sim $ 1-2 Tesla) drives the insulating phase into a ``normal'' insulating state which shows the variable range hopping behavior with Coulomb gap. Moreover, with the presence of a strong in-plane magnetic field in the hopping transport regime, large negative magnetoresistance ($\rho $ can decrease by a factor of 5) is observed when increasing the B$_{\mathrm{\bot}}$ component. The authors thank the NSF (DMR-0906415, DMR-0819860) and the Gordon and Betty Moore Foundation for funding support. [Preview Abstract] |
Friday, March 22, 2013 9:00AM - 9:12AM |
Y21.00006: Temperature dependence of TCR and 1/f Noise in p-type a-Si:H Vince Lopes, Eric Hanson, Kiran Shrestha, Chris Littler, Athanasios Syllaios The amorphous semiconductor a-Si:H is used for infrared detection applications. Key figures of merit are the temperature coefficient of resistance (TCR) and 1/f noise. We report on the temperature dependence of the electrical resistivity and noise of devices fabricated on as grown boron-doped p-type a-Si:H. The 1/f noise was found to be proportional to the bias voltage and inversely proportional to the square root of the device area. As a result, it can be described by Hooge's empirical expression. However, the 1/f noise was found to be constant in the temperature range investigated, even though the resistance changes by a factor of 2.5. We conclude that the carrier concentration is nearly constant in the temperature range studied; thus, the resistance change is due to the temperature dependence of the hole mobility. This interpretation is consistent with temperature dependent hole mobility measurements of others and suggest that the TCR for p-type a-Si:H material near room temperature is determined by changes in the hole mobility. [Preview Abstract] |
Friday, March 22, 2013 9:12AM - 9:24AM |
Y21.00007: Fabrication, electrical characterization and scanning gate microscopy of Schottky silicon nanowire devices Sorin Melinte, Andra Iordanescu, Constantin Dutu, Denis Flandre, Sebastien Faniel, Frederico Martins, Benoit Hackens We report the fabrication and the electrical characterization of Schottky silicon nanowire field effect transistors. Our devices are built with a top down approach on silicon-on-insulator wafers with (100) crystallographic orientation and 10 - 25 $\Omega$.cm resistivity of the silicon top layer. The transistor's channel is assured by silicon nanowires patterned by electron beam lithography and wet etching. The nanowires have nominal cross sections down to $30 \times 30 \ \rm nm^2$. For example, platinum-silicon Schottky contacts are made by physical deposition of a platinum layer followed by an annealing at 500$^{\circ}$C for 2 minutes in a $\rm N_2$ atmosphere. The devices are characterized at various temperatures by current-voltage measurements and scanning gate microscopy techniques. Varying the dimensionality and geometry of the contacts, the nature of metal-semiconductor junctions and the substrate strain, we get new insights into the influence of trapped charges at the $ \rm Si- SiO_2$ interface on transport through $\rm SiO_2$-enclosed nanowires, at the nanometer scale. [Preview Abstract] |
Friday, March 22, 2013 9:24AM - 9:36AM |
Y21.00008: Investigation of two-dimensional electron systems at low density on hydrogen-terminated silicon (111) surface Binhui Hu, Tomasz M. Kott, B. E. Kane Two-dimensional electron systems (2DESs) on hydrogen-terminated Si(111) surfaces show very high quality. The peak electron mobility of 325,000 cm$^{\mathrm{2}}$/Vs can be reached at T$=$90 mK and 2D electron density $n_{2d} =4.15\times 10^{11}$ cm$^{\mathrm{-2}}$ , and the device shows the fractional quantum hall effect[1]. 2DESs on H-Si(111) at lower densities may exhibit new physics, because both valley degeneracy and effective mass lead to a large Wigner--Seitz radius $r_{s} $ at accessible densities. In these devices, phosphorus ion implantation is used to defined the contacts to the 2DESs[2]. The contacts themselves work at low temperature. However, at lower 2D electron density ($<2\times 10^{11}$ cm$^{\mathrm{-2}})$ and low temperature (\textless 1 K), the contact resistance to the 2DESs shows strong temperature dependence. This makes accurate Hall measurements difficult in this region. We have systematically investigated the contact resistance at different electron densities and temperatures. Different ion implantation annealing parameters are adjusted to mitigate the issue. Possible measurement technique is also explored to overcome the problem. [1] Tomasz M. Kott, Binhui Hu, S. H. Brown, and B. E. Kane, arXiv:1210.2386 (2012) [2] K. Eng, R. N. McFarland, and B. E. Kane, Appl. Phys. Lett. 87, 052106 (2005) [Preview Abstract] |
Friday, March 22, 2013 9:36AM - 9:48AM |
Y21.00009: Electrical Properties of p-Ge and p-GeSn materials grown on n-Si substrates Thomas R. Harris, Yung Kee Yeo, Mee-Yi Ryu, Richard Beeler, John Kouvetakis The electrical properties of {\em p\em}-Ge and {\em p\em}-Ge$_{1-y}$Sn$_{y}$ ($y$=0.06-0.1\%) grown on {\em n \em}-Si substrate were investigated through temperature-dependent Hall-effect measurements. It was found that there exists a degenerate parallel conducting layer in Ge$_{1-y}$Sn$_{y}$/Si as well as a second, deeper acceptor in addition to a shallow acceptor. Additionally, a conductivity type conversion from {\em p \em} to {\em n \em} was observed between 370 and 440 K for these samples. The parallel conducting layer dominates the electrical properties of the Ge$_{1-y}$Sn$_{y}$ layer below 50 K, and also significantly affects those properties at higher temperatures. The conductivity type conversion and causes of the degenerate conduction layer will be discussed. [Preview Abstract] |
Friday, March 22, 2013 9:48AM - 10:00AM |
Y21.00010: ABSTRACT HAS BEEN MOVED TO H1.00346 |
Friday, March 22, 2013 10:00AM - 10:12AM |
Y21.00011: Theoretical and experimental study of kinetics of photoexcited carriers in wide band gap semiconductors Sara Shishehchi, Sergey Rudin, Gregory Garrett, Michael Wraback, Enrico Bellotti We present a theoretical and experimental study of the subpicosecond kinetics of photo-excited carriers in the wide band gap semiconductors GaN and ZnO. In the theoretical model, interaction with a photo-excitation laser pulse is treated coherently and a generalized Monte Carlo simulation is used to account for scattering and dephasing. The scattering mechanisms included are carrier interactions with polar optical phonons and acoustic phonons, and carrier-carrier Coulomb interactions. For comparison, experimental time-resolved photoluminescence studies on GaN and ZnO samples are performed over a range of temperatures and excitation powers. [Preview Abstract] |
Friday, March 22, 2013 10:12AM - 10:24AM |
Y21.00012: Electrical Resisitivity in Metals and Metallic Alloys from First Principles Alexander Slepko, Sadasivan Shankar, Justin Weber, Alexander Demkov We have developed a method for estimation of resistivity of metals and their alloys based on ab initio methods. The formalism is based on quantifying electron phonon interactions using Boltzmann-based electronic transport and plane wave-based density functional theory for electronic structure and phonon frequencies. We explicitly take into account long wave length scattering, energy band dispersion and interaction between impurities, often omitted in previous approaches. Given the detailed nature of our formalism, we will explain deviations from the most-used Matthiessen's Rule. We have tested our technique on Al, Cu, and Al-doping in Copper. Our resisitivity values compare very well with experimental data at room temperature; Al 2.75 $\mu\Omega$ cm (experimental, 2.83 $\mu\Omega$ cm), Cu 1.81 $\mu\Omega$ cm (experimental, 1.66 $\mu\Omega$ cm). We were also able to estimate the drops in conductivity of Cu due to alloying with Al for a wide range of composition (from dilute to concentrated alloys) which are consistent with the experiments. Given the general nature of our formalism, we believe that it is extendable to nanostructures. [Preview Abstract] |
Friday, March 22, 2013 10:24AM - 10:36AM |
Y21.00013: Ab-initio calculations of the lattice thermal conductivity from an exact solution of the Boltzmann-Peierls equation Laurent Chaput In this work we present \emph{ab-initio} calculations of the lattice thermal conductivity and related quantities for several semiconductors of interest in energy transport and thermoelectricity. Excellent agreements with experiments are found. A new method is proposed to obtain a numerically exact and fast solution to the Boltzmann-Peierls equation. This is made possible using the symmetry of the systems and open the way to the theoretical design of new materials. The collision kernel of the equation is constructed using an efficient parallelization of the code over the irreducible triplets of phonon wavevectors involved in the different possible collisions. These irreducible triplets are the equivalent of the irreducible part of the Brillouin zone for single particle quantities. Therefore a formulation of the self energy and collision kernel based on their use drastically reduce the computational time. [Preview Abstract] |
Friday, March 22, 2013 10:36AM - 10:48AM |
Y21.00014: Nonlinear strain generation in ultrafast laser excited semiconductors Eric Landahl, SooHeyong Lee, G. Jackson Williams, Donald Walko We have investigated the laser fluence dependence of the lattice response of Indium Antimonide and Gallium Arsenide crystals to ultrafast laser absorption using time-resolved x-ray diffraction. In both materials, slow thermal cooling follows an initial acoustic strain impulse. For Indium Antimonide, where the laser photon energy is significantly above the band gap, we find that both acoustic and thermal lattice expansions increase linearly with increasing laser fluence. The band gap and photon energy are much closer in Gallium Arsenide, where we find that while the thermal response remains linear with laser fluence, the magnitude of the acoustic impulse is highly nonlinear, exhibiting an initial saturation and recovery far below the laser damage threshold limit. Several hypotheses have been put forward of different nonlinear processes that could lead to this behavior. To place additional constraints on these models, we have recorded high-resolution diffraction lineshapes which can be directly compared to semiconductor strain models incorporating the transport of sound, heat, and charge. [Preview Abstract] |
Friday, March 22, 2013 10:48AM - 11:00AM |
Y21.00015: Topological scattering of an electron gas by edge dislocations Koushik Viswanathan, Srinivasan Chandrasekar A theory of electron scattering by the strain field surrounding an edge dislocation in a linear isotropic medium is presented. When considered on a continuum scale, edge dislocations are topological defects --- the underlying elastic medium can no longer be described as a Euclidean manifold, but instead must be mapped to a Riemann--Cartan manifold with nontrivial torsion. An electron gas placed in such a background has additional covariant terms in the Hamiltonian. These act alongside the usual deformation potential arising from the shift in the conduction band minima due to the dislocation strain field. When considered as perturbations, these additional terms scatter electrons from one planewave state to another. For a group of parallel, randomly distributed edge dislocations, it is shown, through an iterative evaluation of the Boltzmann equation, that the contribution of these terms to the electrical resistivity of cold-worked Cu is larger than that of the deformation potential and the resulting specific dislocation resistivity is very close to the experimentally established value. The corresponding effect in the presence of grain boundaries (edge dislocation walls) is discussed and the application of these general results to transport in semiconductors is also presented. [Preview Abstract] |
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