Tight-binding branch-point energies and band offsets for cubic InN, GaN, AlN and AlGaN alloys

TL;DR

This paper calculates branch-point energies and band offsets for cubic III-nitrides and AlGaN alloys using tight-binding and CPA methods, providing data useful for heterostructure design.

Contribution

It introduces a method to compute band offsets for cubic III-nitrides and AlGaN alloys using tight-binding and CPA, extending previous approaches.

Findings

Good agreement with experimental and theoretical data

Directional dependence of BP energies discussed

Method applicable to arbitrary alloy compositions

Abstract

Starting with empirical tight-binding band structures, the branch-point (BP) energies and resulting valence band offsets (VBOs) for the zincblende phase of InN, GaN and AlN are calculated from their k-averaged midgap energy. Furthermore, the directional dependence of the BPs of GaN and AlN is discussed using the Green's function method of Tersoff. We then show how to obtain the BPs for binary semiconductor alloys within a band-diagonal representation of the coherent potential approximation (CPA) and apply this method to cubic AlGaN alloys. The resulting band offsets show good agreement to available experimental and theoretical data from the literature. Our results can be used to determine the band alignment in isovalent heterostructures involving pure cubic III-nitrides or AlGaN alloys for arbitrary concentrations.