MBE growth of different hexagonal GaN crystal structures on vicinal (100) GaAs substrates

GaN thin films of different hexagonal crystal structures have been grown by radio-frequency nitrogen plasma source molecular beam epitaxy (RFMBE) on vicinal (100) GaAs substrates. Polycrystalline hexagonal material occurred for high temperature (630°C) nitridation of the GaAs surface or low temperatures of the initial GaN buffer layer deposition. On the contrary, initial GaN growth at 540°C gave hexagonal single crystals with [0001] axis either inclined at approximately 43° from the growth axis or aligned parallel to it. The GaN orientation depended on the annealing or not, respectively, of the initial low temperature buffer layer.