Reflection high-energy electron diffraction studies of wurtzite GaN grown by molecular beam epitaxy

We report a comprehensive reflection high-energy electron diffraction study of the surface structure of GaN as a function of substrate temperature and III–V ratio for growth using elemental gallium and active nitrogen derived from a rf plasma source. An emission spectroscopy analysis of the composition of the nitrogen plasma showed that the neutral atomic species dominated the growth process. The effect of substrate pretreatment is also discussed. It was found that good quality growth accompanied by a reconstructed surface are only obtainable during growth under a slightly Ga-rich regime and after pretreatment by nitridation and the growth of a low temperature buffer layer. Reconstruction mode diagrams are presented both for layers during growth and also for layers which have been cooled after growth. The implications of these plots are discussed in terms of surface vacancy densities.