The Polarity of GaN: a Critical Review

GaN, AlN and InGaN have a polar wurtzite structure and epitaxial films of these materials typically grow along the polar axis. Although the polarity of these nitrides has been studied by quite a number of techniques, many results in the literature are in conflict. In this paper an attempt is made to lay out a set of polarity assignments to provide a context for discussion of these results. A “standard framework” is proposed to correlate the disparate results, and the framework is used to draw general conclusions about the polarity of bulk crystals, VPE and MBE epitaxial films, and devices.