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 of 1 T -V Se 2

Abstract: A first-principles self-consistent (non-muffin-tin) band-structure calculations on $1T$-V${\mathrm{Se}}_{2}$ is used to analyze some of the transport and optical properties. The material appears to be metallic with characteristic overlaps between the metal $d$-based and nonmetal $p$-based bands. These overlaps are found to be sensitively modulated both by the change of the (anomalously high) $\frac{c}{a}$ ratio and by the sandwich height parameter $z$ (determining the V-Se bond length). This leads to a number of interesting predictions regarding the electronic structural changes associated with the charge-density-wave instability.

Antidoping in Insulators and Semiconductors Having Intermediate Bands with Trapped Carriers.

Abstract: Ordinary doping by electrons (holes) generally means that the Fermi level shifts towards the conduction band (valence band) and that the conductivity of free carriers increases. Recently, however, some peculiar doping characteristics were sporadically recorded in different materials without noting the mechanism: electron doping was observed to cause a portion of the lowest unoccupied band to merge into the valance band, leading to a decrease in conductivity. This behavior, that we dub as ``antidoping,'' was seen in rare-earth nickel oxides ${\mathrm{SmNiO}}_{3}$, cobalt oxides ${\mathrm{SrCoO}}_{2.5}$, Li-ion battery materials, and even MgO with metal vacancies. We describe the physical origin of antidoping as well as its inverse problem---the ``design principles'' that would enable an intelligent search of materials. We find that electron antidoping is expected in materials having preexisting trapped holes and is caused by the annihilation of such ``hole polarons'' via electron doping. This may offer an unconventional way of controlling conductivity.

Instability of the high-pressure cscl structure in most iii-v semiconductors

Abstract: Using the density-functional linear response method, we study dynamical instabilities of the high-pressure CsCl phase in III-V semiconductors. For InSb, we find no phonon instability that could prevent the CsCl phase from forming, consistent with the experimental observation. In contrast, for the more ionic GaP, GaAs, InP, and InAs, we find that, while statically stable, the CsCl phase is dynamically unstable at high pressures with respect to transverse-acoustic [{xi}{xi}0] phonons. Analysis of the soft normal modes via {open_quotes}isotropy subgroup{close_quotes} suggests two candidate structures that will replace CsCl structure at high pressure: the tP4 (B10) InBi type and the oP4 (B19) AuCd type. Experimental examination of these predictions is called for. {copyright} {ital 1999} {ital The American Physical Society}

Design principles and coupling mechanisms in the 2D quantum well topological insulator HgTe/CdTe.

Abstract: We present atomistic band structure calculations revealing a different mechanism than recently surmised via k · p calculations about the evolution of the topological state (TS) in HgTe/CdTe. We show that 2D interface (not 1D edge) TSs are possible. We find that the transitions from a topological insulator at critical HgTe thickness of n = 23 ML (6.453 [corrected] A) to a normal insulator at smaller n is due to the crossing between two interface-localized states: one derived from the S-like Γ₆(c) and one derived from the P-like Γ₈(v) light hole, not because of the crossing of an interface state and an extended quantum well state. These atomistic calculations suggest that a 2D TS can exist in a 2D system, even without truncating its symmetry to 1D, thus explaining the otherwise surprising similarity between the 2D dispersion curves of the TS in HgTe/CdTe with those of the TS in 3D bulk materials such as Bi₂Se₃.

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. ...