Alex Zunger

Bio: Alex Zunger is an academic researcher from University of Colorado Boulder. The author has contributed to research in topics: Band gap & Quantum dot. The author has an hindex of 128, co-authored 826 publications receiving 78798 citations. Previous affiliations of Alex Zunger include Tel Aviv University & University of Wisconsin-Madison.

Electronic structure and phase stability of LiZnAs: A half ionic and half covalent tetrahedral semiconductor.

Abstract: The first electronic structure calculation of the ordered \ensuremath{\alpha}, \ensuremath{\beta}, and \ensuremath{\gamma} cubic phases of an ``interstitially filled tetrahedral compound'' ${\mathrm{A}}^{\mathrm{I}{\mathrm{B}}^{\mathrm{II}{\mathrm{C}}^{\mathrm{V}}}}$ (where the ${\mathrm{B}}^{\mathrm{II}}$ and ${\mathrm{C}}^{\mathrm{V}}$ atoms occupy the normal zincblende sites and ${\mathrm{A}}^{\mathrm{I}}$ occupies one of the empty zincblende tetrahedral interstitial sites) reveals strongly covalent (${\mathrm{B}}^{\mathrm{II}\mathit{\ensuremath{-}}{\mathrm{C}}^{\mathrm{V}}}$) and strongly ionic (${\mathrm{A}}^{\mathrm{I}\mathit{\ensuremath{-}}{\mathrm{C}}^{\mathrm{V}}}$) bonds in the same structure, uperior cohesion relative to the III-V analog (GaAs), and semiconducting (\ensuremath{\alpha} and \ensuremath{\beta} forms) as well as metallic (\ensuremath{\gamma}-form) behavior.

Inverse design approach to hole doping in ternary oxides: Enhancing p-type conductivity in cobalt oxide spinels

Abstract: Holes can be readily doped into small-gap semiconductors such as Si or GaAs, but corresponding $p$-type doping in wide-gap insulators, while maintaining transparency, has proven difficult. Here, by utilizing design principles distilled from theory with systematic measurements in the prototype ${A}_{2}B$O${}_{4}$ spinel Co${}_{2}$ZnO${}_{4}$, we formulate and test practical design rules for effective hole doping. Using these, we demonstrate a 20-fold increase in the hole density in Co${}_{2}$ZnO${}_{4}$ due to extrinsic (Mg) doping and, ultimately, a factor of 10${}^{4}$ increase for the inverse spinel Co${}_{2}$NiO${}_{4}$, the $x$ $=$ 1 end point of Ni-doped Co${}_{2}$Zn${}_{1\ensuremath{-}x}$Ni${}_{x}$O${}_{4}$.

Predicted bond length variation in wurtzite and zinc-blende ingan and algan alloys

Abstract: Valence force field simulations utilizing large supercells are used to investigate the bond lengths in wurtzite and zinc-blende InxGa1−xN and AlxGa1−xN random alloys. We find that (i) while the first-neighbor cation–anion shell is split into two distinct values in both wurtzite and zinc-blende alloys (RGa−N1≠RIn−N1), the second-neighbor cation–anion bonds are equal (RGa−N2=RIn−N2). (ii) The second-neighbor cation–anion bonds exhibit a crucial difference between wurtzite and zinc-blende binary structures: in wurtzite we find two bond distances which differ in length by 13% while in the zinc-blende structure there is only one bond length. This splitting is preserved in the alloy, and acts as a fingerprint, distinguishing the wurtzite from the zinc-blende structure. (iii) The small splitting of the first-neighbor cation–anion bonds in the wurtzite structure due to nonideal c/a ratio is preserved in the alloy, but is obscured by the bond length broadening. (iv) The cation–cation bond lengths exhibit three dis...

Surface-reconstruction-enhanced solubility of N, P, As, and Sb in III-V semiconductors

Abstract: We show that surface reconstructions may play an essential role in determining the equilibrium solubilities of N, P, As, and Sb in various III-V compounds. In particular, anion–anion dimerization of the (001)-β2(2×4) surface can enhance the solubility of N near the surface in GaAs, GaP, and InP by five, three, and two orders of magnitudes, respectively, at 1000 K. With certain assumptions on the growth kinetics, this high concentration of N may be frozen in as the crystal grows.

Effects of atomic short-range order on the electronic and optical properties of gaasn, gainn, and gainas alloys

Abstract: Using large ({approx}500{endash}1000atoms) pseudopotential supercell calculations, we have investigated the effects of atomic short-range order (SRO) on the electronic and optical properties of dilute and concentrated GaAsN, GaInN, and GaInAs alloys. We find that in concentrated alloys the clustering of like atoms in the first neighbor fcc shell (e.g., N-N in GaAsN alloys) leads to a large decrease of both the band-gap and the valence-to-conduction dipole transition-matrix element in GaAsN and in GaInN. On the other hand, the optical properties of GaInAs depend only weakly on the atomic SRO. The reason that the nitride alloys are affected strongly by SRO while GaInAs is affected to a much lesser extent is that in the former case there are band-edge wave-function localizations around specific atoms in the concentrated random alloys. The property for such localization is already evident at the (dilute) isolated impurity and impurity-pair limits. {copyright} {ital 1998} {ital The American Physical Society}

Ab initio molecular-dynamics simulation of the liquid-metal-amorphous-semiconductor transition in germanium.

Abstract: We present ab initio quantum-mechanical molecular-dynamics simulations of the liquid-metal--amorphous-semiconductor transition in Ge. Our simulations are based on (a) finite-temperature density-functional theory of the one-electron states, (b) exact energy minimization and hence calculation of the exact Hellmann-Feynman forces after each molecular-dynamics step using preconditioned conjugate-gradient techniques, (c) accurate nonlocal pseudopotentials, and (d) Nos\'e dynamics for generating a canonical ensemble. This method gives perfect control of the adiabaticity of the electron-ion ensemble and allows us to perform simulations over more than 30 ps. The computer-generated ensemble describes the structural, dynamic, and electronic properties of liquid and amorphous Ge in very good agreement with experiment. The simulation allows us to study in detail the changes in the structure-property relationship through the metal-semiconductor transition. We report a detailed analysis of the local structural properties and their changes induced by an annealing process. The geometrical, bonding, and spectral properties of defects in the disordered tetrahedral network are investigated and compared with experiment.

Self-interaction correction to density-functional approximations for many-electron systems

Abstract: The exact density functional for the ground-state energy is strictly self-interaction-free (i.e., orbitals demonstrably do not self-interact), but many approximations to it, including the local-spin-density (LSD) approximation for exchange and correlation, are not. We present two related methods for the self-interaction correction (SIC) of any density functional for the energy; correction of the self-consistent one-electron potenial follows naturally from the variational principle. Both methods are sanctioned by the Hohenberg-Kohn theorem. Although the first method introduces an orbital-dependent single-particle potential, the second involves a local potential as in the Kohn-Sham scheme. We apply the first method to LSD and show that it properly conserves the number content of the exchange-correlation hole, while substantially improving the description of its shape. We apply this method to a number of physical problems, where the uncorrected LSD approach produces systematic errors. We find systematic improvements, qualitative as well as quantitative, from this simple correction. Benefits of SIC in atomic calculations include (i) improved values for the total energy and for the separate exchange and correlation pieces of it, (ii) accurate binding energies of negative ions, which are wrongly unstable in LSD, (iii) more accurate electron densities, (iv) orbital eigenvalues that closely approximate physical removal energies, including relaxation, and (v) correct longrange behavior of the potential and density. It appears that SIC can also remedy the LSD underestimate of the band gaps in insulators (as shown by numerical calculations for the rare-gas solids and CuCl), and the LSD overestimate of the cohesive energies of transition metals. The LSD spin splitting in atomic Ni and $s\ensuremath{-}d$ interconfigurational energies of transition elements are almost unchanged by SIC. We also discuss the admissibility of fractional occupation numbers, and present a parametrization of the electron-gas correlation energy at any density, based on the recent results of Ceperley and Alder.

A comprehensive review of zno materials and devices

Abstract: The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...