Kinetic Process of Polarity Selection in GaN Growth by RF-MBE

Extensively nitridated and non-nitridated sapphire substrate, At insertion layer and AlN intermediate layer were used as the platforms to investigate polarity selection processes of GaN grown by rf-MBE, aimed at giving a comprehensive understanding to the issues of GaN polarity. GaN growth was started on these platforms with different surface stoichiometry by controlling the order of source supplies. The results showed that GaN tended to grow with Ga polarity which was kinetically favorable on thermally cleaned sapphire substrate and At covered surfaces. N polarity could be reversed to Ga polarity by At insertion layers or AlN intermediate layer. It is suggested that the polarity conversion of GaN by AlN or At insertion layers relies on the fact that they provide an At platform on which the subsequent epilayer prefers to grow with Ga polarity.