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.

A universal trend in the binding energies of deep impurities in semiconductors

Abstract: Whereas the conventional practice of referring binding energies of deep donors and acceptors to the band edges of the host semiconductor does not produce transparent chemical trends when the same impurity is compared in different crystals, referring them to the vacuum level through the use of the photothreshold reveals a remarkable material invariance of the levels in III-V and II-VI semiconductors. It is shown that this is a consequence of the antibonding nature of the deep gap level with respect to the impurity atom-host orbital combinations.

Band Structure and Electronic Excitations in Cdl-xMnxTe

Abstract: We have performed spin-polarized, self-consistent local spin density total energy and band structure calculations for the prototype semimagnetic semiconductor alloy Cd1-xMnxTe. Based on the calculated band structures and taking into account the many body effects of localized states, we propose a schematic energy level diagram to interpret the d→d*, p→d, and photoemission transitions in Cd1-xMnxTe.

Symmetric Relaxation Around Interstitial 3d Impurities in Silicon

Abstract: EPR studies suggest that most transition atom impurities in silicon occupy the tetrahedral interstitial (TI) site, preserving the Td symmetry of the host (1). In this paper we will give, within the loca1-density approximation, a unified description of the electronic structure and “breathing-mode”. relaxation of tetrahedral interstitial Cr, Mn, Fe, Co and Ni impurities in bulk silicon.

The different shapes of spin textures as a journey through Brillouin zone chiral and polar symmetries

Abstract: Crystallographic space group symmetry (CPGS) such as polar and nonpolar crystal classes has long been known to classify compounds that have spin-orbit-induced spin splitting such as Rashba and Dresselhaus compounds, respectively. However, the enabling symmetries underlying the spin texture prototypes - the relationship between the expectation value of spin operator $S^{nk}$ in Bloch state $u(n,k)$ and the wavevector $\vec{k}$ - are instead specific rotations and reflection symmetries in the wavevector point group symmetry rather than the presence or absence of polar field in the global crystallographic space group. Relativistic band structures calculations demonstrate how compounds judged by their macroscopic CPGS to be typical Dresselhaus (GaAs) or Rashba (GeTe) or Wyle (Tellurium) compounds, manifest both Rashba and Dresselhaus spin textures, respectively at different wavevector chiralities and polarities.

Role of d Orbitals in Valence-Band Offsets of Common-Anion Semiconductors

Abstract: We show through all-electron first-principles electronic structure calculations of core levels that, contrary to previous expectations, the valence-band offsets in the common-anion semiconductors AlAs-GaAs and CdTe-HgTe are decided primarily by intrinsic bulk effects and that interface charge transfer has but a small effect on these quantities. The failure of previous models is shown to result primarily from their decision to omit cation d orbitals.

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. ...