Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session R46: Electronic and Optical Properties of Semiconductors: First Principals |
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Sponsoring Units: FIAP Chair: Hai Ping Cheng, University of Florida Room: Baltimore Convention Center 349 |
Wednesday, March 15, 2006 2:30PM - 2:42PM |
R46.00001: Sequential Oxidation of Gallium Oxide Clusters - A First-Principles Study S. Gowtham, Aurora Costales, Ravindra Pandey The structural and electronic properties of gallium oxide lusters (Ga$_3$O$_n$; $n=4-8$) are studied under the framework of density functional theory, with respect to sequential oxidation. The focus is on changes induced by the addition or removal of an electron from the neutral species as well as similarities/differences between aluminum oxide clusters of the same size. Lowest energy isomers in case of neutral clusters were found in doublet electronic state, and except for Ga$_3$O$_4^-$, Ga$_3$O$_4^+$, and Ga$_3$O$_5^-$, all ionized clusters were found in triplet electronic state. We observed that both addition and removal of an electron from the neutral cluster leads to significant changes in the structure of the lowest energy isomer, apart from altering the sequence of other low-lying geometries. Structural resemblance to corresponding alumina clusters is limited to a few cases while we predict new results for others. Binding energy remains almost constant throughout the oxidation process, with values for ionized systems bracketing the neutral ones. All clusters considered in this study are found to be stable against fragmentation via O and O$_2$ channels. Analysis of vibrational frequencies confirms the tendency of Ga$_3$O$_6^+$, Ga$_3$O$_7$ and Ga$_3$O$_8$ to form O-O bonds. HOMO-LUMO gap values show an oscillatory trend while calculated values of electron affinity and ionization potential are in good agreement with the corresponding values for alumina clusters. [Preview Abstract] |
Wednesday, March 15, 2006 2:42PM - 2:54PM |
R46.00002: Density Functional Band Gaps of AlAs Hua Jin, Guanglin Zhao, Diola Bagayoko We present results of ab-initio, self-consistent calculations of electronic properties of AlAs in the zinc-blende structure. Our non-relativistic calculations employed the generalized gradient approximation (GGA) of density functional potential and Bagayoko, Zhao and Williams (BZW) implementation of the linear combination of atomic orbitals (LCAO) formalism. Our calculated indirect band gaps at the X ${\rm g}$and L points are 2.15 eV and 2.38 eV, respectively, in excellent agreement with experimental values. The calculated direct gap at $\Gamma $ is 25{\%} smaller than the experimental one. This discrepancy may be due to experimental difficulties in the determination of this gap and it is also possibly due to the fact that it is not the fundamental one and hence may not be described by a ground state calculation. We also present calculated total and partial density of states and the electron effective mass at the bottom of the conduction band at the $\Gamma \quad {\rm g}$point. This work was funded in part by the Department of the Navy, Office of Naval Research (ONR, Grant No. N00014-05-1-0009), NASA (Award Nos. NCC 2-1344 and NAG 5-10253), and by the National Science Foundation (Award No. HRD 0000272). The authors are indebted to Dr. S. Hasan for his excellent technical support with the computing facilities. [Preview Abstract] |
Wednesday, March 15, 2006 2:54PM - 3:06PM |
R46.00003: The band gap of InN and ScN: a quasiparticle energy study based on exact-exchange density-functional theory Patrick Rinke, Matthias Scheffler, Abdallah Qteish, J\"org Neugebauer The group-IIIA nitride InN and the group-IIIB nitride ScN have recently received increased attention in the field of opto-electronics and optical coatings. Due to the difficulty of growing clean samples, however, the size of their band gap has not been well established, yet. We have recently shown, that quasiparticle energy calculations in the $G_0W_0$ approximation based on density-functional theory (DFT) calculations in the exact-exchange (EXX) approach yield band gaps in very good agreement with experiment for GaN and II-VI compounds [1]. For wurtzite InN our approach predicts a gap of 0.7 eV, suggesting an intrinsic value at the lower end of the experimentally observed range [2]. For ScN there exists a longstanding controversy if the material is a semimetal or semiconductor, which has only very recently been resolved in favor of the latter. Our calculations for rocksalt ScN predict an indirect band gap of 0.9 eV in good agreement with recent experimental findings [3].\\ $[$1$]$ P. Rinke {\it et al.}, New J.\ Phys. {\bf 7}, 126 (2005)\\ $[$2$]$ W. Walukiewicz {\it et al.}, J.\ Crystal Growth {\bf 269}, 119 (2004)\\ $[$3$]$ A. A. Al-Brithen {\it et al.}, Phys.\ Rev.\ B {\bf 70}, 045303 (2004) [Preview Abstract] |
Wednesday, March 15, 2006 3:06PM - 3:18PM |
R46.00004: Calculated, Optical Proprieties of Wurtzite InN Diola Bagayoko, Hua Jin, Guanglin Zhao We report the results of ab-initio calculations of the dielectric function of wurtzite indium nitride (w-InN). These optical properties are derived from ab-initio energy bands obtained with a local density function approximation (LDA) potential in the Bagayoko, Zhao, and Williams (BZW) implementation of the linear combination of atomic orbital (LCAO) formalism. We practically reproduced the measured, dielectric function (Superlattices and Microstructures 36, 591-597, 2004) at energies up to 6 eV. This agreement is not limited to major peaks; it also includes the fine structures of the shoulders. Indubitably, these findings vindicate density functional theory, in general, and the local density approximation (LDA), in particular, for the correct description of properties of semiconductors -- provided the basis-set and variational effect, inherently associated with most calculations, is avoided with the first-principle BZW approach. This work was funded in part by the Department of the Navy, Office of Naval Research (ONR, Grant Nos. N00014-05-1-0009 and N00014-4-1-0587), NASA (Award Nos. NCC 2-1344, NAG 5-10253, and NNG 05G146G), and the National Science Foundation (Award No. HRD 0503362). [Preview Abstract] |
Wednesday, March 15, 2006 3:18PM - 3:30PM |
R46.00005: Predictions of Electronic and Optical Properties of Cubic InN Lashounda Franklin, Hua Jin, G. L. Zhao, Diola Bagayoko We present theoretical predictions of electronic, optical, and related properties of cubic indium nitride (c-InN). We utilized a local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO) in our ab-initio, self-consistent calculations that implemented the Bagayoko, Zhao, and Williams (BZW) method. The predicted band gap is 0.65 eV at a theoretical, equilibrium lattice constant of 5.017 {\AA} . We discuss other predictions for the structural and optical properties of c-InN, including the bulk modulus, electron effective masses, and the calculated dielectric function. This work was funded in part by the Department of the Navy, Office of Naval Research (ONR, Grant Nos. N00014-05-1-0009 and N00014-4-1-0587), NASA (Award Nos. NCC 2-1344, NAG 5-10253, and NNG 05G146G), and the National Science Foundation (Award No. HRD 0503362). [Preview Abstract] |
Wednesday, March 15, 2006 3:30PM - 3:42PM |
R46.00006: Band offsets of semiconductor heterostructures : dependence on density functionals Amita Wadehra, Richard G. Hennig, John W. Wilkins, Gustavo E. Scuseria There is an increasing interest in In-based heterostructures for HEMT. Predictions of band offsets could speed up the development process of these devices. We assess various exchange-correlation potentials including hybrid functionals such as HSE \footnote{J. Heyd, J.E. Peralta, G.E. Scuseria and R.L. Martin, {\it J. Chem. Phys.} {\bf 123}, 174101 (2005).} to analyze electronic properties and structural energetics of such systems. We calculate the band gaps and band offsets of InAs heterostructures such as InAs/InAlAs and InAs/InAsP. We also show a comparison of the structural energies for interfaces and site substitutions obtained by using different functionals. An accurate estimation of these properties is crucial for their application in the manufacture and performance of novel semiconductor devices. [Preview Abstract] |
Wednesday, March 15, 2006 3:42PM - 3:54PM |
R46.00007: All-Electron {\boldmath $GW$} Approximation in the Augmented-Plane-Wave Basis-Set Limit Christoph Friedrich, Arno Schindlmayr, Stefan Bl\"ugel, Takao Kotani The $GW$ approximation for the electronic self-energy is known to yield quasiparticle band structures in very good agreement with experiment, but almost all codes so far rely on the pseudopotential approach, which restricts the range of materials that can be treated efficiently. In addition, the adequacy of the pseudopotential approximation for quasiparticle calculations has recently come under debate. We have developed an alternative implementation within the full-potential linearized augmented-plane-wave (FLAPW) method. As possible errors resulting from the linearization of the basis set are frequently overlooked, we here investigate the influence on the $GW$ self-energy correction. A systematic improvement is achieved by including additional local orbitals defined as second and higher energy derivatives of solutions to the radial scalar-relativistic Dirac equation, which constitute a natural extension of the FLAPW basis set. Within this approach we can systematically reduce the linearization error and reach the exact augmented-plane-wave basis-set limit. While the electronic self-energy and the quasiparticle energies benefit from the better description of the unoccupied states, the resulting band gaps remain relatively unaffected. [Preview Abstract] |
Wednesday, March 15, 2006 3:54PM - 4:06PM |
R46.00008: Electronic transport in dilute GaAs:N Geoffrey Stenuit, Stephen Fahy Plane-wave pseudopotential-based DFT (density functional theory) are used to determine the electronic properties (band structure, effective mass and energy gap) of dilute GaAs:N with substitutional nitrogen concentration $x=1-3 \%$.Calculations are performed using LDA (local density approximation) for the exchange-correlation functional and applied to large supercells (more than 64 atoms) to achieve the dilute limit. Scattering cross-section, as well as the mobility are derived from the nitrogen concentration dependence of the band gap in GaAsN. The effects of an N$_2$ split interstitial substitution on the electronic properties are also discussed. Finally, the presence of a localized nitrogen state in such material is also studied within this ab initio framework. [Preview Abstract] |
Wednesday, March 15, 2006 4:06PM - 4:18PM |
R46.00009: Electronic band structure, crystal structure and phonons of ZnSiN$_2$ Tula R. Paudel, Walter R. L. Lambrecht ZnSiN$_2$ is an interesting alternative to GaN. Its crystal structure is derived from the wurtzite structure of GaN by a particular ordered subsitution of the Ga atoms by Zn and Si in such as way that each N is coordinated with two Si and two Zn atoms. Electronic structure calculations were performed with two different approaches, the plane-wave ultrasoft pseudopotential approach and the full-potential linearized muffin-tin orbital method both using the local density approaximation (LDA). The structure was fully optimized. The relaxation consists primarily of the N atom finding its optimum position inside its nearest neighbor tetrahedron by making a shorter Si-N and longer Zn-N bond. An indirect LDA band gap of about 3.4 eV is obtained. Thus a gap larger than for GaN is expected. Calculations of the phonons at the center of the Brillouin zone are in progress using the linear response approach. A comparison with ZnGeN2, which was studied earlier, [W. R. L. Lambrecht et al. Phys Rev. B 72, 155202 (2005)] will be presented. [Preview Abstract] |
Wednesday, March 15, 2006 4:18PM - 4:30PM |
R46.00010: Electronic and magnetic properties of Cu-doped ZnO Andreia Luisa da Rosa, Lunmei Huang, Rajeev Ahuja Diluted magnetic semiconductors have attracted attention in the past years, since they open the possibility for new devices with integrated magnetic, electronic and optical functionality. Among possible candidates ZnO is especially attractive, since it is a wide band gap material and is also piezoelectric. On the other hand, Cu and its oxides are non-magnetic, so magnetism coming from Cu clusters or precipitates can be ruled out. Although some experimental results confirm room temperature ferromagnetism in Cu-doped ZnO, other works have reported its absence. In this work we use first-principles calculations to study Cu-doped ZnO for various Cu concentrations. The total energy differences were computed for parallel and antiparallel arrangements of the Cu spins to determine whether Cu-doped ZnO has a ferromagnetic or anti-ferromagnetic ground state. We found that Cu-doped ZnO has a ferromagnetic ground state for all calculated concentrations. We also found that the exchange coupling between the Cu atoms is short ranged. We suggest that the strong hybridization between the Cu-3$d$ and O-2$p$ states is responsible for mediating the ferromagnetic interaction between the Cu atoms. [Preview Abstract] |
Wednesday, March 15, 2006 4:30PM - 4:42PM |
R46.00011: Computational band-gap engineering in wide-gap MgO-ZnO alloys R. Matt Leone, Gus L. W. Hart Wide-gap semiconducting materials are extending critical applications in high temperature/power electronics and optoelectronics such as with the continued advancement of blue to ultraviolet LEDs and lasers. MgO-ZnO alloys have been increasingly investigated due to their UV luminescence from 150-400 nm, 3.3-7.8 eV. We have developed a first-principles model Hamiltonian that predicts band gaps of cubic MgO-ZnO alloys for any superlattice type or atomic configuration. First-principles band gap energies were used as input to construct an Ising-like cluster expansion, and the cluster types used were determined using a novel genetic algorithm. The \textit{design} of specific wide-gap MgO-ZnO alloy superlattices for desired target band gaps is now possible with this resultant model Hamiltonian. [Preview Abstract] |
Wednesday, March 15, 2006 4:42PM - 4:54PM |
R46.00012: Electronic Structure and Vibrational spectra of C$_2$B$_{10}$ Based Clusters and Films L. L. Boyer, Kyungwha Park, M. R. Pederson, W. N. Mei, X. C. Zeng, S. Bulusu, Ellen Day, Shireen Adenwalla, Seamus Curran, James Dewald Semiconducting boron carbide films can be used to detect neutrons and convert energy of associated nuclear reactions directly into electrical current. Such films were prepared by removing hydrogen from the three polytypes of C$_2$B$_{10}$H$_{12}$ (carborane) deposited on various surfaces. Results from Raman scattering measurements on these films will be presented and compared with results of calculations for clusters. The electronic structure, total energy and vibrational properties of carborane molecules and C$_2$B$_{10}$ clusters calculated using density functional theory are reported. Computed vibrational spectra for carborane molecules are found to be in close agreement with previously published measured spectra taken on carborane solids. Eleven vibrationally stable C$_2$B$_{10}$ clusters have been identified and their relative energies, HOMO-LUMO gaps and vibrational properties will be discussed. Good agreement with the experimental Raman spectra is achieved from theoretical spectra computed using a Boltzmann distribution of the six lowest energy free-clusters. [Preview Abstract] |
Wednesday, March 15, 2006 4:54PM - 5:06PM |
R46.00013: Electron Distributions in Hexagonal Selenium and Tellurium and Monoclinic Selenium with Dilute Impurities and Associated Nuclear Quadrupole Interactions*. N.B. Maharjan, D.D. Paudyal, D.R. Mishra, S. Byahut, M.M. Aryal, Hwa-Suck Cho, R.H. Scheicher, Lee Chow, Junho Jeong, T.P. Das** The electron structures of Selenium chains and rings with Te impurities in hexagonal and monoclinic structures respectively and Se impurities in Te chains in hexagonal lattice have been studied using Hartree-Fock cluster model including many-body effects, including lattice relaxation effects. The calculated electronic wave-functions are utilized to obtain $^{77}$Se and $^{125}$Te nuclear quadrupole coupling constants e$^{2}$qQ and asymmetry parameters $\eta $ and compared with available experimental data from Mossbauer and perturbed angular correlation measurements. From our results, the expected nature of nuclear quadrupole interactions associated with Sb impurities will be discussed. *Supported by NSF US-Nepal Program and UGC Nepal **Also at UCF, Orlando [Preview Abstract] |
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