An investigation was made of the mechanisms giving rise to surface reconstruction for GaN grown by molecular beam epitaxy onto a range of substrates. The effects of surface contamination by oxygen or arsenic were studied and it was demonstrated that both could influence the surface reconstruction. It was shown that surface reconstruction measured by reflection high-energy electron diffraction was associated with excess Ga on the surface, which underwent an order–disorder transition at 400 to 500C. For molecular beam epitaxy, growth on hydride vapour phase epitaxy GaN/SiC composite substrates having the Ga polarity, the 2 x 2 reconstruction was intrinsic. This intrinsic reconstruction could be destroyed by heating to a high temperature or by oxidation. The intrinsic 2 x 2 reconstruction could also be destroyed by adding an additional monolayer of more weakly bound Ga, which could be removed by desorption at high temperatures. For growth by molecular beam epitaxy onto sapphire with nitridation, a 3 x 3 reconstruction was observed upon cooling the sample to below 400C, but the reconstruction could be changed to 4 x 4 by contamination with oxygen. For the growth of GaN with a N polarity by molecular beam epitaxy on GaAs(111)B, a 4 x 4 reconstruction was observed upon cooling to below 400C, which might be caused by arsenic.

Gallium-Induced Surface Reconstruction Patterns of GaN Grown by Molecular Beam Epitaxy. C.T.Foxon, T.S.Cheng, S.V.Novikov, N.J.Jeffs, O. H.Hughes, Y.V.Melnik, A.E.Nikolaev, V.A.Dmitriev: Surface Science, 1999, 421[3], 377-85