A model was presented, for the microscopic structure of Mg-H complexes in GaN, which explained the unusual bond angle observed in recent vibrational spectroscopy studies. The structure was not the lowest-energy configuration at T = 0, but it was stabilized at elevated temperatures due to the large entropy associated with a set of low-energy rotational excitations. The rotational excitation spectrum was calculated by using a quantum-mechanical model in which the H atom moves in a weak corrugation potential.

Entropy-Driven Stabilization of a Novel Configuration for Acceptor-Hydrogen Complexes in GaN. S.Limpijumnong, J.E.Northrup, C.G.Van de Walle: Physical Review Letters, 2001, 87[20], 205505 (4pp)