Electronic structure and band parameters for ZnX (X = O, S, Se, Te)

TL;DR

This study uses first-principles calculations to analyze the electronic structure of zinc monochalcogenides, revealing the effects of spin-orbit coupling and Coulomb correlations on band parameters and effective masses.

Contribution

It demonstrates the importance of including spin-orbit coupling and Coulomb correlations, specifically using LDA+U, to accurately predict band structures and parameters of ZnX compounds.

Findings

LDA underestimates band gaps and misplaces Zn-3d levels.

Spin-orbit coupling causes anomalous state order in ZnO phases.

LDA+U improves agreement with experimental Zn-3d level positions.

Abstract

First-principles density-functional calculations have been performed for zinc monochalcogenides with zinc-blende- and wurtzite-type structures. It is shown that the local-density approximation underestimates the band gap, misplaces the energy levels of the Zn-3d states, and overestimates the crystal-field splitting energy. Without spinorbit coupling, the order of the states at the top of VB is found to be normal for all the ZnX phases considered. Upon inclusion of the spinorbit coupling in calculations, ZnO in zinc-blende- and wurtzite-type phases become anomalous. It is shown that the Zn-3d electrons are responsible for the anomalous order. The effective masses of electrons and holes have been calculated and found that holes are much anisotropic and heavier than the electrons in agreement with experimental findings. The typical errors in calculated band gaps and related parameters originate from strong Coulomb correlations, which are found to be highly significant in ZnO. The LDA+U approach is found to correct the strong correlation of the Zn-3d electrons, and thus improves the agreement with the experimentally established location of the Zn-3d levels. Consequently, it increases significantly the parameters underestimated in the pure LDA calculations.