Polarity control of GaN/AlGaN/GaN heterostructure grown by molecular beam epitaxy

The importance of the polar orientation of the surface was not obvious in the case of GaN epilayer grown on a nonpolar substrate like sapphire. For rf-MBE growth the published results show that high temperature AlN buffer layers lead to Ga polar films, while GaN buffer layers lead to N polar films. There is a lack of general idea how the polarity is determined and how the polarity can be changed, both from N polarity to Ga polarity and from Ga to N polarity.