AFM measurement of initially grown GaN layer on GaAs substrate

We measured the surface roughness of initially grown GaN layers on GaAs sub strates in different precursor supply conditions. The surface morphology ch anged dramatically at low precursor flow even though the V/III ratio was co nstant. At low supersaturation, the number of grains decreased and the grai n size enlarged. Therefore the surface was too rough to cover the GaAs subs trate. A stepping-stone-like morphology occurred in extreme cases. A few co res grew abnormally large grains. Only nitridation occurred when supersatur ation was too low to grow a GaN core. To cover the GaAs surface with a thin GaN layer, a fairly large precursor supply was necessary. (C) 2000 Elsevie r Science B.V. All rights reserved.