Dependence of GaN polarity on the parameters of the buffer layer grown by molecular beam epitaxy

The polarity of GaN films grown using GaN and AlN buffer layers on sapphire substrates by molecular beam epitaxy were investigated by atomic force microscopy, hot wet chemical etching, and reflection high-energy electron diffraction. We found that the GaN films grown on high temperature AlN (> 890 degreesC) and GaN (770-900 degreesC) buffer layers invariably show Ga and N polarity, respectively. However, the films grown using low temperature (similar to 500 degreesC) buffer layers, either GaN or AlN, could have either Ga or N polarity, depending on the growth rate of the buffer layer. (C) 2001 American Institute of Physics.