Effects of lattice‐mismatch induced built‐in strain on the valence band properties of wurtzite ZnO/Zn 1–x Mg x O quantum well heterostructures

Abstract

We present a theoretical study of the effects of lattice-mismatch induced built-in strain on the electronic properties of valence band states in wurtzite ZnO/Zn1–xMgxO Quantum Well (QW) heterostructures. In this purpose, a 6x6 k·p method has been used to incorporate the effects of strain and nonparabolicity. The energies corresponding to the transitions between conduction band (C), heavy hole (HH), light hole (LH) and crystal-field split-off hole (CH) bands have been calculated as a function of Mg composition and strain. We have also calculated the energy dispersions and wave functions of strained wurtzite ZnO. It is found that ZnO is always under a biaxial tensile strain, in the whole Mg composition range investigated (x < 40%). As a consequence, the light hole valence subband is shifted upwards with respect to the corresponding heavy hole valence subband, resulting in a reduction of ZnO direct band gap by almost 6% when x = 35%. This is found to result in turn in a significantly reduced in-plane hole effective mass at the top of the valence band which is always LH-like. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)