Band-gap bowing and p-type doping of (Zn, Mg, Be)O wide-gap semiconductor alloys: a first-principles study

TL;DR

This study uses first-principles calculations to analyze band-gap bowing and p-type doping in (Zn, Mg, Be)O alloys, revealing composition-dependent properties and potential for optoelectronic applications.

Contribution

It provides a systematic first-principles analysis of band-gap bowing and p-type doping in (Zn, Mg, Be)O alloys, highlighting the effects of composition and dopant placement.

Findings

Large, composition-dependent bowing parameters for ZnBeO and MgBeO.

Adding Be to MgO reduces the band gap, indicating significant bowing.

N doping creates shallower acceptor levels with more Be neighbors.

Abstract

Using a first-principles band-structure method and a special quasirandom structure (SQS) approach, we systematically calculate the band gap bowing parameters and \emph{p}-type doping properties of (Zn, Mg, Be)O related random ternary and quaternary alloys. We show that the bowing parameters for ZnBeO and MgBeO alloys are large and dependent on composition. This is due to the size difference and chemical mismatch between Be and Zn(Mg) atoms. We also demonstrate that adding a small amount of Be into MgO reduces the band gap indicating that the bowing parameter is larger than the band-gap difference. We select an ideal N atom with lower \emph{p} atomic energy level as dopant to perform \emph{p}-type doping of ZnBeO and ZnMgBeO alloys. For N doped in ZnBeO alloy, we show that the acceptor transition energies become shallower as the number of the nearest neighbor Be atoms increases. This is thought to be because of the reduction of \emph{p}-\emph{d} repulsion. The N$_{\rm{O}}$ acceptor transition energies are deep in the ZnMgBeO quaternary alloy lattice-matched to GaN substrate due to the lower valence band maximum. These decrease slightly as there are more nearest neighbor Mg atoms surrounding the N dopant. The important natural valence band alignment between ZnO, MgO, BeO, ZnBeO, and ZnMgBeO quaternary alloy is also investigated.