High-resolution electron microscopy was used to characterize the structure of β-phase epilayers which had been grown onto (001)GaAs substrates by means of plasma-assisted molecular-beam epitaxy. A radio-frequency plasma source was used to produce chemically active N. Exposure of the layer surface to the As flux during growth of the first few monolayers was shown to result in a markedly flat GaN/GaAs interface. The best-quality GaN layers were achieved by ensuring near-stoichiometric nucleation, using an optimum Ga/N ratio. Deviation from these nucleation conditions led to interface roughening and to the formation of a wurtzite within the GaN layer. All of the layers contained a high density of stacking faults, near to the interface, but this density sharply decreased towards the surface. The stacking faults were anisotropically distributed within the GaN layer; probably due to the differing behavior of α, as compared with β, dislocations in cubic GaN. Most of the stacking faults intersected the interface along lines that were parallel to the major flat of the GaAs wafer. The stacking faults were often associated with atomic steps at the GaN/GaAs interface.

S.Ruvimov, Z.Liliental-Weber, J.Washburn, T.J.Drummond, M.Hafich, S.R.Lee: Applied Physics Letters, 1997, 71[20], 2931-3