Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session S19: Bulk Semiconductors: Electronic and Optical Properties |
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Sponsoring Units: DCMP Chair: Stefan Zollner, Freescale Semiconductor Room: LACC 406B |
Wednesday, March 23, 2005 2:30PM - 2:42PM |
S19.00001: Reexamination of the Ab-Initio Calculation of the Electronic Structure of ZnSe, Ge, and GaAs G.L. Zhao, L. Franklin, D. Bagayoko We reexamined some of the mathematical and physical properties of the ab-initio LCAO calculations for the electronic structure of ZnSe, Ge, and GaAs. The utilization of non-strongly minimal systems in the self-consistent ab-initio calculations could lead to a non-uniformity in approaching the solution in the Ritz-process. We have proposed that an optimum basis set may be needed so that the calculated electron density is converged and the significant scattering of the Ritz-coefficients may be avoided. We have applied the new method to the calculations of the electronic structure of ZnSe, Ge, and GaAs. Our calculated results of the electronic properties agree well with experimental data. Work was funded in part by US NASA (NASA Award No. NCC 2-1344), ONR (Grant No: N00014-04-1-0587], and NSF and the Louisiana Board of Regents (NSF Award Nos. HRD-0000272 and LEQSF(2002-2003)-ENH-TR-57). [Preview Abstract] |
Wednesday, March 23, 2005 2:42PM - 2:54PM |
S19.00002: Local self-energy approach for electronic structure calculations Nikolay Zein, Serguei Savrasov, Gabriel Kotliar We implement method for electronic structure calculations which utilizes GW approximation combined with dynamical mean field theory (DMFT). To study the locality of electronic self-energy operator we compared all the relevant quantities as obtained in both R and k spaces. Convergence of the exchange diagram as well of the correlational part for the self-energy within GW and its first vertex correction are checked as functions of cutoff radius in the real space. Our approach permits calculations beyond GW in a controllable manner. Full self-consistency with respect to Green functions is implemented which erases information on the starting point given either by LDA or Hartree-Fock approximations. Results obtained for a number of covalent and ionic semiconductors will be discussed and compared with various existing calculations and experiments. Work supported by NSF, DOE and CMSN. [Preview Abstract] |
Wednesday, March 23, 2005 2:54PM - 3:06PM |
S19.00003: Ab-initio calculation of excitons in conventional and anorganic semiconductors Claudia Ambrosch-Draxl, Kerstin Hummer, Stephan Sagmeister, Robert Laskowsky, Niels Christensen The excitonic effects on the optical absorption properties of organic as well as inorganic semiconductors are studied from first-principles. The Coulomb interaction between the electron and the hole is accounted for by solving the two-particle Bethe-Salpeter equation. In the organic semiconductors the exciton binding energies strongly depend on the molecular size, the crystalline packing, as well as the polarization direction of the incoming light. We show that the electron-hole interaction can lead to strongly bound excitons with binding energies of the order of 1eV or to a mere redistribution of oscillator strength. In several cases, the screening is efficient enough such that free charge carriers govern the optical absorption process. In the inorganic counterparts the sensitivity of the exciton binding energy is tested against the structural parameters and the screening of the electron-hole Coulomb interaction. [Preview Abstract] |
Wednesday, March 23, 2005 3:06PM - 3:18PM |
S19.00004: Linear optical response of bulk GaAs from finite-temperature lattice dynamics A. Shkrebtii, M.J.G. Lee, K. Vynck, T. Teatro, D. Zekveld, W. Richter, T. Zettler, T. Trepk Measurements of the linear optical response of semiconductors are frequently carried out at and above room temperature, and linear optical probes are widely used to monitor various physical properties up to the melting point. We have found that Lorentzian broadening of the linear dielectric function, commonly used to model the effects of lattice vibrations, does not accurately describe the temperature dependence of the linear optical response. Instead, we determine the temperature dependence of the linear optical response of bulk GaAs in the temperature range 100 K to 1100 K from representative structural configurations extracted from finite-temperature molecular dynamics for an 8-atom supercell. The dielectric function corresponding to each structural configuration is calculated within the density functional theory (DFT) by the full-potential linearized augmented plane wave (FP-LAPW) method. The finite-temperature dielectric function is deduced by averaging the dielectric functions that correspond to the various structural configurations (about five structural configurations are sufficient for satisfactory convergence). The resulting finite-temperature dielectric functions are in good agreement with the experimental data over the whole temperature range. [Preview Abstract] |
Wednesday, March 23, 2005 3:18PM - 3:30PM |
S19.00005: Temperature-enhanced far-infrared absorption in GaAs and GaP Hadley M. Lawler, Eric L. Shirley, Simon G. Kaplan Our first-principles calculations and measurements of the far-infrared absorption in GaAs and GaP are presented and compared. Detailed frequency and temperature dependence are reported. Below the reststrahlen feature, a strong enhancement of the absorption is exhibited as the material is heated from 10 K to 300 K. The appearance of a phonon "gap" between acoustic and optical branches in GaP arises from the large ionic mass mismatch in that material, and causes a narrow infrared transmission band above the reststrahlen. Possible sources of discrepancy between experimental and theoretical spectra are addressed. These include the coexistence of two-phonon infrared channels independent of the anharmonic hybridization of two-phonon states with the infrared-active phonon, which is included in the calculation. Additional oscillator strength may be accounted for by considering direct two-phonon dipoles, or the higher-order charges. These additional channels account for the weak infrared absorption in diamond-type materials. [Preview Abstract] |
Wednesday, March 23, 2005 3:30PM - 3:42PM |
S19.00006: Deformation Electron-Phonon Coupling in Disordered Semiconductors and Nanostructures Andrei Sergeev, Michael Reizer, Vladimir Mitin We study the effective electron-phonon interaction, which is determined by the interference of electron scattering via the deformation potential and elastic electron scattering from impurities and defects. We have found that in contrast to the destructive interference in metals, which results in the Pippard ineffectiveness condition for the electron-phonon interaction, the interference in semiconducting structures substantially enhances the effective electron-phonon coupling. The interference also significantly changes temperature dependence of the electron-phonon relaxation (dephasing) rate in disordered semiconductors and low-dimensional structures. The obtained results provide an explanation of energy relaxation measurements in Si $\delta$-layers. [Preview Abstract] |
Wednesday, March 23, 2005 3:42PM - 3:54PM |
S19.00007: Bowing in the Compositional Dependence of Optical Transitions in GeSn alloys Vijay D' Costa, Andrew Chizmeshya, Candi Cook, John Kouvetakis, Jose Menendez Recent ellipsometric measurements provide a detailed picture of the band structure of GeSn alloys. In particular, the compositional dependence of the strongest interband optical transitions was determined in the compositional range x $<$ 0.2. The results show very strong deviations (bowing) from a linear interpolation between the band structures of pure Ge and $\alpha$-Sn. In this presentation we analyze the bowing parameters for GeSn alloys and compare them with similar parameters for the SiGe system. The possibility of a comparative study of bowing between these two systems is exciting due to their isoelectronic nature and the similarities in their structural relaxation parameters. Following the theory of Bernard and Zunger [J.E. Bernard and A. Zunger, PRB 36, 3199 (1987)], the bowing is described as the sum of three terms, involving volume deformation, charge redistribution, and internal relaxation. The first and third mechanisms are expected to scale with the lattice constant mismatch, which is much larger in the Ge-Sn system. The second mechanism is proportional to the electronegativity difference, which is also larger in Ge-Sn. The parameters needed for quantitative predictions are obtained from measured volume dependencies of optical transitions or from calculated band structures for Si, Ge, $\alpha$-Sn, SiGe, and GeSn as a function of volume. [Preview Abstract] |
Wednesday, March 23, 2005 3:54PM - 4:06PM |
S19.00008: Optical properties of InAsP alloys S.G. Choi, C.J. Palmstrom, T.J. Kim, Y.D. Kim, D.E. Aspnes Optical properties of InAs$_x$P$_{1-x}$ ternary alloys grown by chemical beam epitaxy (CBE) on S-doped InP(100) substrates are presented. Room-temperature pseudodielectric function spectra from 1.5 to 6.0 eV were measured by spectroscopic ellipsometry. The $E_0$, $E_1$, $E_1+\Delta_1$, $E'_0$, $E_2$, and $E_2+\delta$ interband critical point (CP) structures were observed in the spectra. By applying the parabolic-band critical point model to numerically calculated second-energy-derivatives of these spectra, accurate values of the CP parameters and their dependence on alloy composition $x$ were obtained. The experimentally determined variation of the $E_1$ and $E_2$ CP energies and the spin-orbit splitting $\Delta_1$ with alloy composition were in good agreement with the theoretical calculation based on the Van-Vechten-Berolo-Woolley (VV-B-C) model. [Preview Abstract] |
Wednesday, March 23, 2005 4:06PM - 4:18PM |
S19.00009: Optical Constants Determined by Genetic Algorithms David Y. Smith, William Karstens, Shaheen M. Malghani A recent determination$^{a}$ of the complex refractive index, $n$(\textit{$\lambda $}) + i \textit{$\kappa $}(\textit{$\lambda $}), of porous silicon employed a genetic$^{b}$ algorithm to fit the Fresnel equations to reflectance spectra. The procedure appeared to involve more unknowns than explicit equations available for fitting, an indeterminate problem. However, the index values obtained were reasonable, and predicted the properties of porous-silicon multilayes. We have traced this success to the interpolation formulas used for $n$ and \textit{$\kappa $} in the fitting algorithm. They amount to an implicit optical-constant model with the \textit{de facto }assumption of an analytic complex index that can be approximated by a cubic polynomial. Our analysis suggests the procedure can be improved by explicitly using a more appropriate model, e.g., one that uses wave number as the expansion variable and requires that $n$ and \textit{$\kappa $} be even and odd functions of \textit{$\lambda $}, respectively. $^{a}$ V. Torres-Costa, R. J. Mart\'{\i}n-Palma, and J. M. Mart\'{\i}nez-Duart, J. Appl. Phys. \textbf{96}, 4197 (2004). $^{b}$ D. E. Goldberg, \textit{Genetic Algorithms in Search, Optimization and Machine Learning} (Addison-Wesley, Reading, 1989). [Preview Abstract] |
Wednesday, March 23, 2005 4:18PM - 4:30PM |
S19.00010: Burstein-Moss effect in n-type MBE-grown ZnSe thin films Brian Karrer, Frank Peiris, Brenda VanMil, Ming Luo, Nancy Giles, Thomas Myers Using ellipsometry and prism coupling, we have measured the dielectric functions of a series of Cl-doped ZnSe epilayers grown on GaAs substrates. The carrier concentrations were determined using Hall measurements for samples between $6.30 \times 10^{16}~cm^{-3}$ and $9.50 \times 10^{18}~cm^{-3}$. Variable angle spectroscopic ellipsometry in the energy range between 0.7 and 6.5~eV was used in conjunction with prism coupling to obtain the complex dielectric functions of the specimens. Upon careful examination of the dielectric functions obtained for these thin films, we find that its fundamental band gap blue shifts with respect to the carrier concentration. As our theoretical calculations indicate, the origin of this blue shift is due to the Burstein-Moss effect. The characteristics of the higher order transitions are also determined for this doped system. [Preview Abstract] |
Wednesday, March 23, 2005 4:30PM - 4:42PM |
S19.00011: Sulfur isotope shift of the gap of PbS H. J. Lian, A. Yang, M. L. W. Thewalt, R. Lauk, M. Cardona PbS is one of the oldest known semiconductors, occurring naturally as the mineral galena. One of its interesting properties is a strong increase of the band gap energy with increasing temperature, opposite in sign to almost all other semiconductors. We report on the isotope shift of the band gap energy between natural PbS (containing mostly $^{32}$S) and PbS made with enriched $^{34}$S, measured using low temperature photoluminescence spectroscopy. The observed isotope shift is also opposite to the `normal' expectation of larger band gap for the heavier mass. In addition, we report on improved measurements of the temperature dependence of the band gap energy measured using absorption spectroscopy. [Preview Abstract] |
Wednesday, March 23, 2005 4:42PM - 4:54PM |
S19.00012: Microscopic Origin of Infrared Activity in Graphite Gun Sang Jeon, Gerald Mahan We investigate the phonon dispersion of the graphite within a generalized bond-charge model with emphasis on the microscopic origin of the infrared active mode. The resulting dispersion is in good agreement with those obtained by the experiments which include the full optical spectra obtained by the recent x-ray scattering. The computed strengths of the infrared peak are found to be comparable to the experimental values. We show that the dipole moment responsible for the infrared activity is induced by the interlayer Coulomb interaction between $\pi$- bond electrons. [Preview Abstract] |
Wednesday, March 23, 2005 4:54PM - 5:06PM |
S19.00013: High Resolution Studies of the Electronic Properties of Graphite and the Effect of Disorder S.Y. Zhou, G.-H. Gweon, C.D. Spataru, J. Graf, S.G. Louie, A. Lanzara We report a high resolution Angle Resolved Photoemission Spectroscopy (ARPES) study on the electronic properties of graphite. Data as a function of momentum, photon energy and temperature are presented. We report evidence of very sharp and well-defined quasiparticle peaks. A detailed analysis of the quasiparticle dispersion and scattering rate is presented. Coupling of quasiparticles to collective excitation as well as the effect of interlayer coupling on the quasiparticle is discussed. In addition we report evidence of orientational and potential disorder, coexisting with these sharp quasiparticle peaks and well-defined dispersions. We will give explanations for this paradox and discuss the implications of these results in line with similar effect observed in other correlated materials. [Preview Abstract] |
Wednesday, March 23, 2005 5:06PM - 5:18PM |
S19.00014: The electronic structure of boron doped diamond probed with XAS and XES P. -A. Glans, K. E. Smith, J. -H. Guo, M. Mattesini, R. Ahuja, S. Ferro, A. De Battisti Diamond is an interesting candidate for ultraviolet light-emitting devices. Device fabrication properly doped thin films of diamond. The valence and conduction band electronic of boron-doped diamond (BDD) has been measured using soft x-ray emission (XES) and x-ray absorption spectroscopy (XAS). Local density approximation of the electronic structure were also performed, and are in general agreement with XES and XAS data. However, XAS reveals the existence of three doped states in the band , only one of which is predicted by theory. Further improvements in terms of chemical and inertness can be obtained by modifying the surface by insertion of fluorine. The of XES and XAS measurements of BDD and fluorinated BDD will be presented. The Boston University program is supported in part by the NSF under DMR 0311792. [Preview Abstract] |
Wednesday, March 23, 2005 5:18PM - 5:30PM |
S19.00015: A New Photoluminescence Band in Hafnium-implanted Silicon Ravinder Sachdeeva, Andrei Istratov, P.N.K. Deenapanray, Eicke Weber A photoluminescence band in the energy range of 700 meV to 950 meV associated with hafnium implanted in silicon is reported for the first time. Activation of the Hf-optical centers requires a 1000\r{ }C anneal step. The intensity of the PL lines appear to depend on the cooling conditions. The spectrum consists of five peaks in the rapidly quench sample as opposed to twenty one in the slow cool sample. The peak with the highest intensity, occurred in the rapidly quench sample, is found at 943.8meV with two phonon replicas. Temperature and excitation power dependent PL are performed on this peak. It is also found that oxygen coimplantation enhances the PL intensity. A shift in the position of photoluminescence peaks observed on the samples implanted with two different isotopes of Hf confirms that Hfrelated origin of the observed photoluminescence band. [Preview Abstract] |
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S19.00016: Optical Matrix elements in empirical tight-binding with overlap Titus Sandu Calculations of optical and electronic properties of materials are mostly carried out making two assumptions: an orthogonal, atom-like basis and a diagonal coordinate operator in this basis. Thus the intra-atomic matrix elements of coordinate operator are neglected. We show that including the overlap between the orbitals, intra-atomic contributions between different orbitals on the same atom are considered. [Preview Abstract] |
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