Ion assisted deposition (IAD) has been investigated for the growth of GaN, and the resulting films studied by x-ray diffraction and absorption spectroscopy and by transmission electron microscopy. IAD grown stoichiometric GaN consists of random-stacked quasicrystals of some 3 nm diameter. Amorphous material is formed only by incorporation of 15% or more oxygen, which we attribute to the presence of non-tetrahedral bonds centered on oxygen. The ionic favourability of heteropolar bonds and its strikingly simple constraint to even-membered rings is the likely cause of the instability of stoichiometric a-GaN.
@article{arxiv.cond-mat/0407659,
title = {Stabilization of amorphous GaN by oxygen},
author = {F. Budde and B. J. Ruck and A. Koo and S. Granville and H. J. Trodahl and A. Bittar and G. V. M. Williams and M. J. Ariza and B. Bonnet and D. J. Jones and J. B. Metson and S. Rubanov and P. Munroe},
journal= {arXiv preprint arXiv:cond-mat/0407659},
year = {2009}
}