Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session P37: Semiconductors III: Electronic and Optical Properties I |
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Sponsoring Units: FIAP Chair: Willes H. Weber, The Physical Review Room: Morial Convention Center 229 |
Wednesday, March 12, 2008 8:00AM - 8:12AM |
P37.00001: VLab: A Service Oriented Architecture for Distributed First Principles Materials Computations Cesar da SIlva, Pedro da Silveira, Renata Wentzcovitch, Marlon Pierce, Gordon Erlebacher We present an overview of VLab, a system developed to handle execution of extensive workflows generated by first principles computations of thermoelastic properties of minerals. The multiplicity ($10^{2-3}$) of tasks derives from sampling of parameter space with variables such as pressure, temperature, strain, composition, etc. We review the algorithms of physical importance that define the system's requirements, its underlying service oriented architecture (SOA), and metadata. The system architecture emerges naturally. The SOA is a collection of web-services providing access to distributed computing nodes, workflow control, and monitoring services, and providing data analysis tools, visualization services, data bases, and authentication services. A usage view diagram is described. We also show snapshots taken from the actual operational procedure in VLab. [Preview Abstract] |
Wednesday, March 12, 2008 8:12AM - 8:24AM |
P37.00002: Atomistic Treatment of Electronic Transport: The Effect of Bandstructure Neophytos Neophytou, Abhijeet Paul, Gerhard Klimeck The effect of bandstructrue on the electronic transport properties of nanowire devices is investigated using the sp3d5s*-SO 20-orbital nearest neighbor tight-binding model with spin-orbit interactions (LCAO), self consistently coupled to a Poisson solver for treatment of the electrostatics. Under strong spatial and electrostatic confinement at the nanoscale, atomistic effects become important. Non-parabolicity, anisotropy, band coupling, and valley splitting are evident in the electronic structure of these devices and strongly influence their transport properties. In addition to that, potential variations at the nanoscale also have strong influence on the device performance. It is shown that both the transport and quantization effective masses are a sensitive function of the device geometry and behave differently in different wire orientations. Under such conditions, traditional effective mass methods are inadequate and in general fail to describe device characteristics. [Preview Abstract] |
Wednesday, March 12, 2008 8:24AM - 8:36AM |
P37.00003: Analytical modelling of symmetry breaking in extraordinary optoconductance K.A. Wieland, S.A. Solin The EOC effect\footnote{ K. Wieland et al., Appl. Phys. Lett., 88 (2006) 52105} is due to the differential mobilities of the photogenerated electrons and holes. EOC devices with symmetric leads have a antisymmetric positional dependence which, when the device is uniformly illuminated, leads to a minimization of the output voltage. Using a previously employed point charge model, we address two ways to break the symmetry and recover the output signal. The first is to impose uniform illumination on half the sample. This method has practical limitations as the device is miniaturized to the nanoscale. The second is asymmetric placement of the voltage probes. The crucial effect of the surface charge density is modeled in two ways - with constant charge density and by fitting experimental data. Utilizing this approach, optimal lead positions are found. For a 10mm by 2mm thin sample of GaAs with a Au shunt, the EOC reaches a calculated maximum of $\sim $ 600{\%} for lead positions x$_{1 }$= 5 mm and x$_{2}\sim $5 mm using the fit surface charge density model. However, the voltage lead positions for maximum EOC were found to not correlate with the voltage lead positions for maximum output voltage, making EOC a poor indicator of the suitability of the device as a nanosacale sensor. [Preview Abstract] |
Wednesday, March 12, 2008 8:36AM - 8:48AM |
P37.00004: Micro-spectroscopy of Ga$_{1-x}$Mn$_{x}$As and Ga$_{1-x}$Be$_{x}$As films with gradient doping and compensation Brian Chapler, R.C. Myers, D.D. Awschalom, M.C. Martin, K.S. Burch, D.N. Basov A detailed study into the problem of carrier induced magnetism in ferromagnetic III-Mn-V semiconductors is being carried out using micro-infrared measurement techniques. Infrared micro-spectroscopy and broad-band micro-ellipsometry measurements have been performed on films of Ga$_{1-x}$Mn$_{x}$As, x = 0.03, 0.16, as well as Ga$_{1-x}$Be$_{x}$As, x = 0.018. The films were prepared using non-rotated molecular beam epitaxial growth. The results of this growth are films with a varying As:Ga ratio across the sample. Using the above experimental techniques, measurements can be taken at specific locations along the As:Ga gradient, which have shown to cause systematic changes in spectra as a function of As:Ga ratio. These experiments provide a unique opportunity to study the effects of disorder, compensation, and doping in these samples. In addition, comparing Mn doped and Be doped films allows for distinguishing the effects of doping with magnetic versus non-magnetic impurities. [Preview Abstract] |
Wednesday, March 12, 2008 8:48AM - 9:00AM |
P37.00005: Slow light and anomalous pulse breakup near an exciton resonance in GaAs quantum wells Timothy Sweeney, Yan Guo, Susanta Sarkar, Hailin Wang We report experimental studies of optical pulse propagation near an exciton resonance in GaAs quantum wells. The spectral dependence of the group velocity reveals a sharp decrease in the group delay when the spectral position of the optical pulse is varied from below to above the exciton absorption line center. The decrease in the group delay occurs in a spectral range that is small compared with the exciton absorption linewidth. Pulse breakups are also observed when input optical pulses with relatively low intensities are slightly below the exciton absorption line center. Detailed nonlinear optical studies suggest that these surprising behaviors arise from coherent population oscillation and especially a sharp increase of the exciton decoherence rate from below to above the exciton absorption line center. [Preview Abstract] |
Wednesday, March 12, 2008 9:00AM - 9:12AM |
P37.00006: ABSTRACT WITHDRAWN |
Wednesday, March 12, 2008 9:12AM - 9:24AM |
P37.00007: Electronic properties of dilute Bismide alloys Rajeev Kini, Denis Karaiskaj, Ryan France, Aaron Ptak, Angelo Mascarenhas, Tom Tiedje The alloying of GaAs with small amounts of N or Bi results in a large reduction of the fundamental band gap, leading to the so called ``giant band gap bowing''. GaAs$_{1-x}$N$_{x }$has been the subject of intense investigation in recent years; however the lower mobility of the dilute nitride alloys limits its use for device applications. Bi incorporation is predicted to mainly perturb the valence band and does not significantly affect the electron mobility, thus promising better device performance. We report photoluminescence (PL) measurements of GaAs$_{1-x}$Bi$_{x}$ epilayers grown by MBE, carried about at different temperatures (4 - 300K), with above-band gap and selective excitation. Time-resolved PL measurements were also carried out to study the carrier lifetimes of the Bi-related states in these samples. [Preview Abstract] |
Wednesday, March 12, 2008 9:24AM - 9:36AM |
P37.00008: Effect of spin-orbit coupling on excitonic levels in layered chalcogenide-fluorides Andriy Zakutayev, Robert Kykyneshi, Joseph Kinney, David H. McIntyre, Guenter Schneider, Janet Tate BaCuChF (Ch=S,Se,Te) comprise a family of wide-bandgap p-type semiconductors. Due to their high transparency and conductivity, they have potential applications as components of transparent thin-film transistors, solar cells and light-emitting devices. Thin films of BaCuChF have been deposited on MgO by pulsed laser deposition (PLD). Solid solutions BaCuS$_{1-x}$Se$_{x}$TeF and BaCuSe$_{1-x}$Te$_{x}$ have been prepared by PLD of alternating thin BaCuChF layers. All films were deposited at elevated substrate temperatures. They are preferentially c-axis oriented, conductive and transparent in the visible part of the spectrum. Double excitonic peaks have been observed in the absorption spectrum of these films in the temperature range from 80 to 300K. The separation between the peaks in the doublet increases with the increase of atomic mass of the chalcogen. It also increases with the increase of the heavy chalcogen component $x$ in the solid solutions. This separation most likely is caused by the effect of spin-orbit coupling in the chalcogen atoms on excitonic levels in BaCuChF. [Preview Abstract] |
Wednesday, March 12, 2008 9:36AM - 9:48AM |
P37.00009: Photocurrent-induced transport of exciton energy in a single heterojunction quantum well Patrick Folkes, Yingmei Liu Excitons which coexist with a degenerate two-dimensional electron gas (2DEG) in the same quantum well subband have been observed in the photoluminescence (PL) from the recombination of electrons with localized photoexcited holes. Under pulsed photoexcitation at a critical applied voltage, the screening response of the 2DEG/exciton system to the appearance of a remote photocurrent filament in the 2DEG results in the existence of spatially direct and red-shifted indirect excitons in the photoexcitation region and the anomalously fast formation of in-plane spatially indirect excitons which are localized around the filament. Our data suggests the occurrence of a fast long range transport of exciton energy. [Preview Abstract] |
Wednesday, March 12, 2008 9:48AM - 10:00AM |
P37.00010: Two-dimensional hole systems in InSb and In$_{x}$Ga$_{1-x}$As quantum wells Chomani Gaspe, Madhavie Edirisooriya, Tetsuya Mishima, Michael Santos CMOS circuits require $p-$type transistors with high hole mobility, in addition to \textit{n{\-}}type transistors with high electron mobility. In zinc-blende semiconductors, a narrower band gap leads to smaller effective masses for electrons and holes. We have achieved room-temperature electron mobilities of 10,000 and 40,000 cm$^{2}$/Vs in quantum wells made of In$_{0.53}$Ga$_{0.47}$As and InSb, respectively. To achieve high hole mobilities, strain and confinement must be maximized. Both parameters increase the energy splitting between holes with light in-plane mass and those with heavy in-plane mass. We have observed a room-temperature hole mobility of 600 cm$^{2}$/Vs in InSb quantum wells with remotely Be-doped Al$_{x}$In$_{1-x}$Sb barriers grown on GaAs substrates by molecular beam epitaxy. We will discuss the effects of strain, structural parameters, and defect density on hole mobility in InSb and In$_{x}$Ga$_{1-x}$As quantum wells. [Preview Abstract] |
Wednesday, March 12, 2008 10:00AM - 10:12AM |
P37.00011: ABSTRACT WITHDRAWN |
Wednesday, March 12, 2008 10:12AM - 10:24AM |
P37.00012: Non-Markovian damping of Rabi oscillations in semiconductor quantum dots Luiz E. Oliveira, Dmitri Mogilevtsev, A.P. Nisovtsev, S. Kilin, S.B. Cavalcanti, H.S. Brandi A systematic investigation is performed on the damping of Rabi oscillations induced by an external electromagnetic field interacting with a two-level semiconductor system. We have considered a coherently driven two-level system coupled to a dephasing reservoir, and shown that in order to explain the dependence of the dephasing rate on the driving intensity, it is essential to consider the non-Markovian character of the reservoir. Moreover, we have demonstrated that intensity- dependent damping may be induced by various dephasing mechanisms due to stationary as well non-stationary effects caused by the coupling with the environment. Finally, present results [1] are able to explain a variety of experimental measurements [2-4] available in the literature. \newline References: 1. D. Mogilevtsev, A. P. Nisovtsev, S. Kilin, S. B. Cavalcanti, H. S. Brandi and L. E. Oliveira, Phys. Rev. Lett. (in press); 2. A. Zrenner et al., Nature 418, 612 (2002); 3. Q. Q. Wang et al., Phys. Rev. B 72, 035306 (2005); 4. B. Patton, U. Woggon, and W. Langbein, Phys. Rev. Lett. 95, 266401 (2005). [Preview Abstract] |
Wednesday, March 12, 2008 10:24AM - 10:36AM |
P37.00013: Nonlinear Terahertz pump-Terahertz probe Measurements of Semiconductor Carrier Dynamics Haidan Wen, Aaron Lindenberg A table-top terahertz (THz) source has been employed to study the nonlinear response of semiconductors to near-half-cycle femtosecond pulses in the THz regime. We report nonlinear field-induced changes in the far infrared absorption coefficient induced by THz pulses. The transmittance as the function of THz peak field was measured using a z-scan technique and it is observed that the absorption coefficient dramatically increases above a threshold field. Temperature-dependent pump-probe measurements indicate that free carriers are generated by the intense fields, as a result of field-induced tunneling and impact ionization processes. [Preview Abstract] |
Wednesday, March 12, 2008 10:36AM - 10:48AM |
P37.00014: Effect of Spin-Orbit Interaction on the Lattice Properties of Solids: Sb and Bi M. Cardona, L. E. Diaz-Sanchez, X. Gonze, R. K. Kremer, A. H. Romero, J. Serrano We present measurements of the specific heat ($C)$ vs. $T $for Bi and Sb and vs. isotopic mass for Sb. The measurements are compared with \textit{ab-initio }calculations performed with the ABINIT code, including spin-orbit (S-O) interaction. It is shown that the S-O interaction softens the lattice and thus increases the value of $C $at the low $T $maximum ($T_{m}$ \textit{$\sim $}8K for Bi, $T_{m}$ \textit{$\sim $}14K for Sb), improving agreement between theory and experiment. The effect of S-O interaction on other thermodynamic properties, such as the lattice parameter, $a_{0}$, and the cohesive energy, $E_{c}$, is also calculated. It is shown that this interaction decreases $E_{c}$ and, correspondingly, increases $a_{0}$. These effects are proportional to $c_{2}$\textit{$\lambda $} $^{2}+c_{3}$\textit{$\lambda $}$^{3}$, where \textit{$\lambda $ }is the S-O coupling constant, about twice as large for Bi as for Sb. [Preview Abstract] |
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