The distribution profiles of Ga and Al near to the interface of the n-GaN/sapphire system were measured by means of X-ray energy dispersive spectroscopy. It was found that the diffusion of Ga into the sapphire substrate obeyed the complementary error function. The Ga diffusion coefficient, 2.30 x 10-13cm2/s, was calculated by fitting these results. The diffusion was associated with GaN growth at high temperatures. When compared with the diffusion of Ga into the sapphire, much less Al anti-diffusion from the substrate to the GaN film was observed; yielding an Al diffusion coefficient of about 4.8 x 10-15cm2/s.

Gallium/aluminium interdiffusion between n-GaN and sapphire S.Fung, X.Xu, Y.Zhao, W.Sun, X.Chen, N.Sun, T.Sun, C.Jiang: Journal of Applied Physics, 1998, 84[4], 2355-7