Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P21: Computational Study of Semiconductor Band Structures |
Hide Abstracts |
Sponsoring Units: FIAP DCMP Chair: Chris Van de Walle, University of California, Santa Barbara Room: 323 |
Wednesday, March 18, 2009 8:00AM - 8:12AM |
P21.00001: First-Principles determination of deformation potentials in nitrides Qimin Yan, Patrick Rinke, Matthias Scheffler, Chris G. Van de Walle Group-III nitrides and their alloys are now commonly used in optoelectronic devices such as light emitting diodes (LEDs) and laser diodes (LDs). In these devices strain plays a crucial role since it affects the band structure near the valence- and conduction-band edge and thus the optical properties and the device characteristics. The deformation potentials that describe the change in band structure under strain have not yet been reliably determined, either experimentally and theoretically. Here we present a systematic study of the strain effects in AlN, GaN and InN in the zinc-blende and wurtzite phase. Besides density functional theory (DFT) in the most commonly applied local- and gradient corrected density approximation (LDA/GGA) we also apply the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional [1] and $G_{0}W_{0}$ quasiparticle corrections to address the band gap problem. We present a complete set of deformation potentials that allows us to predict the band positions under realistic strain conditions. For the wurtzite phase we observe non-linearities in the strain dependence that may, in parts, explain the appreciable scatter in previous theoretical work on deformation potentials of group- III-nitrides. [1] J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003) Work supported by the UCSB Solid State Lighting and Energy Center. [Preview Abstract] |
Wednesday, March 18, 2009 8:12AM - 8:24AM |
P21.00002: Band-gap bowing, band offsets, and electron affinity for InGaN alloys: A DFT study. Poul Moses, Chris Van de Walle InGaN alloys are successfully being used in optical, electronic, and photovoltaic devices; a novel application is for photochemical water splitting. In order to further improve InGaN-based devices a detailed understanding of the materials properties as a function of alloy composition is needed. To obtain such insight we have investigated the band bowing and absolute band positions of InGaN alloys using density functional theory. The HSE exchange correlation functional has been used in order to accurately calculate the electronic band structure [1]. Detailed surface calculations have been performed that, combined with bulk calculations for alloys, yield information about the positions of valence and conduction bands on an absolute energy scale. We will discuss bowing effects, band offsets, and electron affinities in light of the application of InGaN alloys for photochemical hydrogen production. [1] J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003) [Preview Abstract] |
Wednesday, March 18, 2009 8:24AM - 8:36AM |
P21.00003: A Hybrid Look at Band Offsets in AlN/GaN Heterostructures Jeremy Nicklas, John Wilkins Hybrid functionals have been gaining traction for their better estimation of band gaps in semiconductors. Recently, a screened hybrid functional, HSE, has been introduced that improves upon the hybrid functionals by essentially screening out the Fock exchange after a given radius. This study compares how well the HSE functional does with the technologically important band offsets in the AlN and GaN wide bandgap heterostructures compared to experiment and other previous theoretical calcuations. Both the strained polar hexagonal and the nonpolar cubic phases of these III-V semiconductors are taken into consideration. Due to the large induced electric field in the polar hexagonal strucuture, a multipole decomposition will be discussed as well. [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 8:48AM |
P21.00004: Reassessing the Description of the Electronic Structure of a Semiconductor Alloy Yong Zhang, A. Mascarenhas, L.-W. Wang Although an electronic state in an alloy like Ga$_{x}$In$_{1-x}$P is not a Bloch state, it is generally considered to be reasonably close to a Bloch state in the sense of a virtual crystal approximation (VCA), and it is often referred to as $\Gamma $-like, L-like, or X-like. We have find that within certain context one could call a band edge state as $\Gamma $-like, if the dominant component of its wavefunction is indeed the $\Gamma $ state of the VCA, but globally the alloy states are in general very different from those of the VCA in two important aspects: (1) a $\Gamma $-like state, for instance, could in fact have a very small $\Gamma $ component of the VCA state, and (2) if the corresponding VCA states are degenerate, for instance, a X-like band edge alloy state, there will be strong coupling among the degenerate valleys. These new insights have major impacts on our understanding of the optical and electronic properties[1], and the ordering effects [2] in a semiconductor alloy.\\[0pt] [1] Y. Zhang, A. Mascarenhas, and L.-W. Wang, Phys. Rev. Lett. 101, 036403 (2008). \\[0pt] [2]Y. Zhang, A. Mascarenhas, and L.-W. Wang, Phys. Rev. B (in press). [Preview Abstract] |
Wednesday, March 18, 2009 8:48AM - 9:00AM |
P21.00005: \textit{Ab initio} study of the optical properties of Si-XII Brad Malone, Jay Sau, Marvin Cohen We present a first-principles calculation of the optical excitation spectrum of Si-XII, a high-pressure, metastable phase of silicon in the R8 structure. Recent calculations of the quasiparticle spectrum have shown Si-XII to be semiconducting with a small, indirect band gap. In this paper we solve the Bethe-Salpeter equation (BSE) to obtain the optical spectrum of this material. We then compare our calculated optical spectrum with experimental data for other forms of silicon commonly used in photovoltaic devices. These include cubic, polycrystalline, and amorphous forms of silicon. We find that the calculated values of the optical functions relevant to photovoltaic absorption in Si-XII show greater overlap with the incident solar spectrum than those found in these other silicon phases. [Preview Abstract] |
Wednesday, March 18, 2009 9:00AM - 9:12AM |
P21.00006: First-Principles Hartree-Fock Study of Locations and Hyperfine Interactions of Transition Metal Impurities in Silicon R.H. Pink, S.R. Badu, Archana Dubey, R.H. Scheicher, Lee Chow, M.B. Huang, T.P. Das The study of the magnetic properties of transition metal ions in silicon is currently of great interest because of their potential applications in spintronics. An understanding of the ferromagnetism associated with the interactions between these impurities requires a knowledge of their locations in the lattice. Three possible locations of Mn$^{2+}$, V$^{2+}$, and Cr$^{+}$ ions have been investigated, namely, the interstitial hexagonal (H$_{i})$ and tetrahedral (T$_{i})$ and substitutional (S) sites. Both binding energies and hyperfine interactions are being studied using the Hartree-Fock Cluster procedure with many-body effects included by the many-body perturbation theory (MBPT) procedure. For Mn$^{2+}$ ion, the Hi site is found to be unstable while the Ti and S sites have positive binding energies. Our calculated 55Mn hyperfine constant favors the Ti site\footnote{G.W. Ludwig and H.H. Woodbury, Phys. Rev. Lett. 5, 98 (1960).} which is also supported by channeling measurements.\footnote{J. LaRose and M.B. Huang (to be published).} [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:24AM |
P21.00007: Theoretical analysis on the effect of tip-induced band bending on scanning tunneling spectroscopy measurements on H-terminated Si(100) surface Hideomi Totsuka, Satoshi Watanabe Scanning tunneling spectroscopy (STS) is widely used experimental technique. However, theoretical study on STS is not sufficient yet, in the sense that the effects of important factors such as the tip-induced band bending (TIBB) in measurements on semiconductor surfaces have not been examined yet. In this study, we have analyzed the STS spectra on a H-terminated Si(100) surface theoretically using a method [1] which can calculate the electron states under applied bias voltages self-consistently. We found that the band gap in the STS spectra is larger than that in the density of states in our calculation. Furthermore, we found that this cannot be understood from TIBB, while the bias voltage dependence of TIBB in our calculation corresponds well with experimental result [2]. [1] Y. Gohda et al., Phys. Rev. Lett. 85, 1750 (2000). [2] M. McEllisterm, et al., Phys. Rev. Lett. 70, 2471 (1993) [Preview Abstract] |
Wednesday, March 18, 2009 9:24AM - 9:36AM |
P21.00008: Band gaps and band offsets in the SiO$_2$/Si interface calculated by including the self-energy of electrons and holes Luiz Ferreira, Leonardo Fonseca, Mauro Ribeiro, Jr. Density Functional theory, as formulated by Kohn and Sham (Phys. Rev. {\bf 140}, A1133 (1965)), is insufficient when it comes to the calculation of one-particle excitations (electrons and holes). In this case, one has to include the self-energy of the particle (see for instance R. G\'{o}mez- Abal. et al Phys. Rev. Lett. {\bf 101}, 106404 (2008)). This self-energy is mostly the classical electrostatic self-energy of the particle charge density but has an important contribution from exchange and correlation. In a recent paper (L. G. Ferreira et al, Phys. Rev. B {\bf 78}, 125116 (2008)), it is shown that the self-energy can be calculated with the help of a ``self-energy potential'', wholly derived from pure atomic calculations. The band gaps calculated with those self-energies are precise, in no way worse than the GW band gaps, and yet the calculation is very simple and fast. Next challenge we faced was the calculation of the band-offsets of the all important Si/SiO$_2$ system. Notice that the ``self-energy potential'' is centered between two covalent bonded atoms in the Si side and centered at the O in the SiO$_2$ side. Then the question is whether these self-energy potential perturbations create a wrong charge density at the interface. The answer is that both gaps and band offsets were calculated with outstanding quality. [Preview Abstract] |
Wednesday, March 18, 2009 9:36AM - 9:48AM |
P21.00009: The influence of pressure on defects in amorphous silicon Jeffrey Grossman, Lucas Wagner Amorphous silicon(a-Si) thin-film solar cells are promising materials for solar cells, but they suffer from the Staebler-Wronski effect (SWE), in which the efficiency degrades over the course of a few hours of light exposure. While there has been progress in mitigating this effect through sample preparation, there is still no clear microscopic explanation for the degradation. We have used first principles density functional theory and highly accurate quantum Monte Carlo calculations to investigate the effect of pressure on different types of defects present in a-Si. Our calculations show that the effect of pressure on a-Si is strongly dependent on the particular type of defect, and they further may provide new ways to experimentally determine the dominant defect type. We also report on the effect of pressure on the simplest reaction in a-Si: a bond switch between two neighboring Si atoms, which could be an important element in the understanding of the SWE [1]. [1] L.K. Wagner and J.C. Grossman. PRL (in press) [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P21.00010: Ab initio calculations of the dielectric functions of semiconductors and alloys including excitonic effect via LASTO method Hyejung Kim, Yia-Chung Chang We calculate dielectric functions of semiconductors and alloys including the electron-hole interactions within the ab initio framework. The Bethe-Salpeter equation is constructed using a full-potential linear augmented-Slater-type orbital (LASTO) method. The electron-hole interaction is computed with a sufficiently dense k-point mesh, which shows good convergence. Point group symmetry has been utilized to speed up the computation significantly. Dielectric functions of alloys are calculated by the configurational average of special quasirandom structures. The inclusion of the electron-hole interaction both shifts the peak positions and changes peak heights of the imaginary part of the dielectric functions, resulting in better agreement with ellipsometry data than the spectra obtained without including the electron-hole interactions. [Preview Abstract] |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P21.00011: The Electronic and Optical Properties of Manganese-doped Wurtzite ZnO Yiming Mi, Xinxin Zhao, Shuichi Iwata The electronic and optical properties of Manganese-doped Wurtzite ZnO were studied by the first principles pseudopotential plane wave method within density functional theory formalism. The electronic structures, density of states, and optical absorption spectra were investigated for different doping concentration. The acquired results reveal that the energy gap of the Mn-doped ZnO increases with the increase of Mn-doping concentration, and the UV absorption of the system gets stronger with the Mn-doping concentration augmented, which are consistent with others' calculational and experimental results fairly well. [Preview Abstract] |
Wednesday, March 18, 2009 10:12AM - 10:24AM |
P21.00012: Electronic Structures of Zn(Te,O) Byounghak Lee, Lin-Wang Wang It was recently observed that highly mismatched semiconductor alloys display multiple band gaps of solar spectra, opening a possibility of higher efficiency photovoltaic materials in bulk systems [1]. The highest solar radiation conversion efficiency in these materials is expected to reach 56{\%}, almost twice as high as the best existing single crystal material. The existing empirical model explains observed band structures [2], but it lacks details of atomic level information and cannot explain the constituent atomic composition dependence. We present a theoretical study of Zn(Te,O) using newly developed Linear Scaling 3-Dimensional Fragment method [3] to answer technologically important questions, such as existence of nonradiative recombination centers, charge transfer, and wavefunction localization. [1] K. M. Yu, W. Walukiewicz, J. Wu, W. Shan, J. W. Beeman, M. A. Scarpulla, O. D. Dubon, and P. Becla, Phys. Rev. Lett. 91, 246403 (2003). [2] W. Shan et al. Phys. Rev. Lett. 82, 1221 (1999). [3] L.-W. Wang, Z. Zhao, and J. Mexa, Phys. Rev. B 77, 165113 (2008). [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 10:36AM |
P21.00013: Dielectric Function and Critical Point of GeSbTe Pseudo-binary Compound Thin Films Hosun Lee, Jun-Woo Park, Youn-Seon Kang, Tae-Yon Lee, Dong-Seok Suh, Ki-Joon Kim, Cheol Kyu Kim, Yoon Ho Kang, Juarez L. F. Da Silva We measure the dielectric functions of GeSbTe pseudo-binary thin films by using spectroscopic ellipsometry. We anneal the thin films at various temperatures. According to x-ray diffraction, the as-grown thin films are amorphous and the annealed films have metastable and stable crystalline phases. By using standard critical point model, we obtain the accurate values of the energy gap of the amorphous phase as well as the critical point energies of the crystalline thin films. The critical point energies are compared to the band gap energies determined by the method of linear extrapolation of the optical absorption. As the Sb to Ge atomic ratio increases, the optical (band) gap energy of amorphous (crystalline) phase decreases. Standard critical point fitting show several higher band gaps. The electronic band structures and the dielectric functions of the thin films are calculated by using density functional theory and are compared to the measured ones. The band structure calculations show in stable phase that GeTe, Ge$_{2}$Sb$_{2}$Te$_{5}$, and Ge$_{1}$Sb$_{2}$Te$_{4}$ have indirect gap whereas Ge$_{1}$Sb$_{4}$Te$_{7}$ and Sb$_{2}$Te$_{3}$ have direct gap. The measured indirect band gap energies match well with the electronic band structure calculations. [Preview Abstract] |
Wednesday, March 18, 2009 10:36AM - 10:48AM |
P21.00014: Origin of the unusually large band gap bowing and the breakdown of the band-edge distribution rule in the SnxGe1-x alloys Wan-Jian Yin, Xin-Gao Gong, Su-Huai Wei Most semiconductor alloy AxB1-x has a non-linear dependence of its band gap Eg(x) as a function of the alloy composition x, and the variation is usually described by a parabolic function Eg(x) = xEg$^{A }$+ (1-x)Eg$^{B}$ - bgx(1-x), where Eg$^{A }$and Eg$^{B}$ are the band gaps of A and B at their respective equilibrium lattice constants and bg is the so-called bowing parameter. The conventional band-edge distribution of bg is usually described by the equation bVBM(CBM) = $\Delta $EVBM(CBM)/$\Delta $Egbg , where $\Delta $EVBM(CBM) and $\Delta $EVBM(CBM) are VBM and CBM natural band offsets. Using first-principles calculations, we investigate the unusual nonlinear behaviors of the band gaps in SnxGe1-x alloys. We show that the large bowing of the direct band gap is induced by the disordering effect. Moreover, we calculated individual contribution of the band edge states and find that the bowing of the conduction band edge is much larger than the bowing of the valence band edge, although the natural valence band offset between Ge and Sn is larger than the natural conduction band offset. The breakdown of the band-edge distribution rule is explained by the large lattice mismatch between Ge and Sn and the large deformation potential of the band edge states. [Preview Abstract] |
Wednesday, March 18, 2009 10:48AM - 11:00AM |
P21.00015: Accurate electronic structure calculations of lead chalcogenides by QSGW method Sergey Faleev, Oleg Mryasov Enhancement of the energy conversion efficiency of thermoelectric materials has been a long goal of materials physics. Recent experiments show that distortion of the electronic structure of PbTe by adding small amount of impurities results in enhancement of the Seebeck coefficient and doubling of the ZT factor [Heremans et al., Science 321, 554 (2008)]. This enhancement is thought to be due to the impurity-induced increase of the energy dependence of density of states near the Fermi level. The reliable theoretical prediction of the energy states of impurities in host matrix (which often very difficult to measure experimentally) are required in order to explain the experiments and predict and optimize properties of new materials. Accurate calculations for bulk system is a first necessary step required for further study of systems with impurities. Here we report results for bulk lead chalcogenides obtained with recently developed QSGW method [Faleev et al., PRL 93, 126406 (2004)]. We found that electronic structure of lead chalcogenides and, in particular, the band gaps and effective masses are predicted with much higher accuracy within the QSGW approach than within most commonly used DFT theory. This result opens way for predictive search of novel thermoelectric materials. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2025 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700