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

The polarity of GaNfilmsgrown using GaN and AlNbuffer 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 GaNfilmsgrown on high temperature AlN (\u3e890 °C) and GaN (770–900 °C) buffer layers invariably show Ga and N polarity, respectively. However, the filmsgrown using low temperature (∼500 °C) buffer layers, either GaN or AlN, could have either Ga or N polarity, depending on the growth rate of the buffer layer