Effects of polar and nonpolar on band structures in ultrathin ZnO/GaN type-II superlattices

The electronic structures of polar and nonpolar wurtzite (WZ) ZnO/GaN ultrathin superlattices (USLs) are investigated by using first-principles methods. The built-in electric fields and band gap become insensitive to GaN barrier layer in the polar WZ ZnO/GaN USLs when GaN layer is larger than 10 monolayers. However, the band gaps show less dependence on GaN layer in the nonpolar case. Moreover, the polar and nonpolar WZ ZnO/GaN USLs possesses the characteristics of the direct band structures and type-II heterostructures.