Chemical beam epitaxy of GaN on (0001) sapphire substrate

Gallium nitride films were grown on (0001) sapphire substrates by chemical beam epitaxy (CBE) using triethylgallium (TEGa) and ammonia (NH3) precursors. Prior to the GaN epilayer growth at 850°C, a thin GaN buffer layer was deposited at 560°C. Structural and optical properties of the epilayers were investigated as a function of the anneal treatment of the buffer layer. Annealing of the buffer in NH3 up to 900°C increases the roughness of the surface, resulting in a epilayer with higher crystallinity. Heating the buffer to 900°C results in partial desorption of the film leaving small grains on an exposed substrate. While the epitaxy on this thin buffer is two-dimensional the resulting surface consists of a hexagonal tile-structure. The level of unintentional carbon doping is high in all films, although the growth conditions need further optimization. CBE may become a promising candidate for the growth of nitride films only if the carbon incorporation is not an inherent problem of the technique.