Mechanistic insights into the conversion of Ga2O3 to GaN using TGA experiments and DFT modeling

Abstract

TG experiments and DFT calculations were used to investigate the mechanism of gallium oxide nitridation to gallium nitride. The overall conversion of the gas-solid reaction can be best described by a modified integrated model that accounts for diffusion influence at high temperatures and conversions. For that model, an apparent activation energy of 154 kJ mol−1 and a reaction order for Ga2O3 of n = 0.36 were estimated.NH3 favorably adsorbed on Ga2O3 without any energy barrier in which the nitrogen is attracted towards gallium (Ga–N). The Ga2O3 surface was nitridated to GaN via adsorbed NH2*, NH* and H* intermediates, obtained through NH3* dissociation, increasingly stabilized by the surface, preventing their early desorption, and testifying of the positive nitrogen (N) atom insertion into the crystal. The N–H bond became harder to break, increasing the dissociation reaction and activation energies. The first NH2* dissociation to NH* was a limiting step, with a high activation energy of 2.81 eV. The second limiting step was the formation of the third H2O molecule with an activation energy of 3.07 eV. According to the observations, the first layer of GaN was organized towards the wurtzite crystal structure.