Special quasiordered structures: Role of short-range order in the semiconductor alloy (GaN)1-x(ZnO)x

This paper studies short-range order (SRO) in the semiconductor alloy (GaN)(1-x)(ZnO)(x). Monte Carlo simulations performed on a density functional theory (DFT)-based cluster expansion model show that the heterovalent alloys exhibit strong SRO because of the energetic preference for the valence-matched nearest-neighbor Ga-N and Zn-O pairs. To represent the SRO-related structural correlations, we introduce the concept of special quasiordered structure (SQoS). Subsequent DFT calculations reveal the dramatic influence of SRO on the atomic, electronic, and vibrational properties of the (GaN)(1-x)(ZnO)(x) alloy. Due to the enhanced statistical presence of the energetically unfavored Zn-N bonds with the strong Zn3d-N2p repulsion, the disordered alloys exhibit much larger lattice bowing and band-gap reduction than those of the short-range ordered alloys. Lattice vibrational entropy tilts the alloy toward less SRO.