Control of wurzite GaN layer polarity on initial stages of growth during ammonia molecular beam epitaxy on (0001) Al2O3 substrate

The polarity is a key parameter for growth of high-quality GaN films affecting the impurities incorporation, morphology and crystalline perfection of growing layers. The polarity of epitaxial GaN films on (0001) sapphire substrates is assigned at the stage of nucleation. Therefore, information about the polarity of a nucleated GaN film can help in the choice of conditions of subsequent growth. During MBE the polarity of a GaN film can be determined by observation of surface structures, typical for Ga- and N-faces. In the present work, the sequence of operations for obtaining a smooth surface, appropriate for the observation of surface structures of GaN films, after growth of only 20-30 nm of a buffer layer is disclosed. The influence of nucleation stages on the polarity of a growing film is determined with use of this technique.