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

We report on an investigation of the mechanisms giving rise to surface reco nstruction for GaN grown by molecular beam epitaxy (MBE) on a range of diff erent substrates. We have studied the effects of surface contamination by o xygen or arsenic and demonstrate that both can influence the surface recons truction. We show that surface reconstruction measured by reflection high-e nergy electron diffraction (RHEED) is associated with excess Ga on the surf ace, 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. Thi s intrinsic reconstruction can be destroyed by heating to a high temperatur e or by oxidation. The intrinsic 2x2 reconstruction can also be destroyed b y adding an additional monolayer of more weakly bound Ga, which can be remo ved by desorption at high temperature. For growth by MBE on sapphire with n itridation, 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 c aused by arsenic. (C) 1999 Elsevier Science B.V. All rights reserved.