Density dependence of the structural and electronic properties of amorphous GaN

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. (C) 1998 Elsevier Science Ltd. All rights reserved.