Density dependence of the structural and electronic properties of amorphous GaN

Abstract

We have performed quantum molecular-dynamics to simulate amorphous GaN. The network models at different densities are generated in such a way that the charge transfer between ions is included self-consistently throughout the simulation. The pair distribution function indicates that the network models are topologically disordered, and the detailed structural analysis implies the existence of a certain chemical short-range order. An important property is that the network models (64 atoms in a supercell) have no wrong pairs (homopolar bonds) or odd-membered rings in all the densities studied, indicating the strong ionicity in amorphous GaN. The valence band tail states are mostly localized on the threefold coordinated N sites and the conduction band tail states are mostly localized on the threefold coordinated Ga sites. There are no midgap states at any density, and the band gap is 2.6–3.6 eV depending on the density. The possible existence of amorphous GaN is suggested in a small range of density near 90 % of experimental value of wurtzite GaN.