Formation of V-shaped pits in GaN thin films grown on high temperature GaN

Effects on structural characteristics of growth temperature and Si doping in GaN thin films grown on high temperature GaN was investigated. GaN/GaN homojunction structure was grown via metalorganic chemical vapour deposition at intermediate temperature (IT, 840°C) with various Si doping concentrations. V-shaped pits are observed on the surface of the undoped GaN grown at IT by atomic force microscopy analysis. Two beam images by transmission electron microscopy show that only screw- and mixed-type component of dislocations contributes to pit formation. Moderate Si doping reduces pit density but the over-doping of Si deteriorates the IT-GaN property by forming pits again. Not all pits are related with threading dislocations but some of them are observed in the dislocation free area of high Si-doped GaN.