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 mic roscopy, hot wet chemical etching, and reflection high-energy electron diff raction. We found that the GaN films grown on high temperature AlN (> 890 d egreesC) and GaN (770-900 degreesC) buffer layers invariably show Ga and N polarity, respectively. However, the films grown using low temperature (sim ilar to 500 degreesC) buffer layers, either GaN or AlN, could have either G a or N polarity, depending on the growth rate of the buffer layer. (C) 2001 American Institute of Physics.