Effect of substrate pretreatment on growth of GaN on (0001) sapphire by low pressure metalorganic chemical vapor deposition

GaN films were grown on c‐plane sapphire substrates by low pressure metalorganic chemical vapor deposition using a GaN buffer layer grown at lower temperatures. The quality and surface morphology of the GaN films were strongly affected by the surface pretreatment of the sapphire substrate before the growth of the GaN buffer layer and the GaN epitaxial layer. The films grown on pre‐nitrided sapphire substrates exhibit improved electrical and optical properties over those of the films grown on unnitrided substrates even though the surface morphology became rougher. We have achieved a carrier concentration in the range of 2×1016–5×1017 cm−3 and electron mobility in the range of 250–300 cm2/V s at room temperature. The GaN films were evaluated by photoluminescence, Hall measurement, x‐ray rocking curve, and transmission electron and scanning electron microscopies.