Role of heteroepitaxial misfit strains on the band offsets of Zn1−xBexO/ZnO quantum wells: A first-principles analysis

Abstract

There is a growing interest in Zn1−xBexO (ZBO)/ZnO heterostructures and quantum wells since the band gap energy of ZBO solid solutions can be tuned over a very large range (3.37–10.6 eV) as a function of the Be composition. Due to its extremely large exciton binding energy (263 meV for Zn0.8Be0.2O/ZnO), ZBO/ZnO has been utilized in ultraviolet light emission diodes and lasers, and may find applications as active elements of various other electronic and optoelectronic devices. In this study, we report the results of an ab initio study on valence and conduction band offsets (ΔEC and ΔEV) of strain-free and epitaxial ZBO/ZnO heterostructures. These offsets determine the degree of the localization of charges at the interfaces of semiconductor multilayers and thus their electronic/optoelectronic properties. We show that while ΔEV of strain-free ZBO/ZnO varies almost linearly from 0 eV to −1.29 eV as Be composition increases from 0 to 1, there is a large nonlinear increase in ΔEC from 0 eV for x = 0 to 5.94 eV for x = 1 with a bowing parameter of 5.11 eV. To understand the role of misfit strains, we analyze epitaxial c-plane and m-plane Zn0.75Be0.25O/ZnO heterostructures. Due to the differences in the atomic displacements for the two growth orientations, ΔEC and ΔEV of c-plane Zn0.75Be0.25O/ZnO are significantly larger than those of m-plane Zn0.75Be0.25O/ZnO heterostructures.