Gallium-induced surface reconstruction patterns of GaN grown by molecular beam epitaxy

We report on an investigation of the mechanisms giving rise to surface reconstruction for GaN grown by molecular beam epitaxy (MBE) on a range of different substrates. We have studied the effects of surface contamination by oxygen or arsenic and demonstrate that both can influence the surface reconstruction. We show that surface reconstruction measured by reflection high-energy electron diffraction (RHEED) is associated with excess Ga on the surface, which undergoes an order-disorder transition at about 400-500 degrees C. For MBE, growth on hydride vapour phase epitaxy (HVPE) GaN/SiC composite substrates having the Ga polarity the 2x2 reconstruction is intrinsic. This intrinsic reconstruction can be destroyed by heating to a high temperature or by oxidation. The intrinsic 2x2 reconstruction can also be destroyed by adding an additional monolayer of more weakly bound Ga, which can be removed by desorption at high temperature. For growth by MBE on sapphire with nitridation, a 3 x3 reconstruction is observed on cooling the sample to <400 degrees C, but the reconstruction can be changed to 4 x4 by contamination with oxygen. For growth of GaN with a N polarity by MBE on GaAs(111)B, a 4 x 4 reconstruction is observed on cooling to <400 degrees C, which may be caused by arsenic. (C) 1999 Elsevier Science B.V. All rights reserved.