AlN growth on sapphire substrate by ammonia MBE

Kinetics of (0 0 0 1) Al2O3 surface nitridation and subsequent growth of AlN films on the sapphire substrate by ammonia molecular beam epitaxy (MBE) are investigated. Surface morphology evolution during AlN growth is studied in situ by reflection high energy electron diffraction and ex situ by atomic force microscopy. It is found that the surfaces of AlN layers thicker than 100 nm have two major features: a quite smooth background and noticeable amount of hillocks. The influence of growth conditions on the AlN surface morphology is studied in order to find a way for reducing of the hillocks density. A modification of nitridated sapphire surface by small amount of Al (1–2 monolayers) with subsequent treatment of the surface under ammonia flux is proposed. An improvement of AlN surface morphology of the layers grown on the modified surfaces is demonstrated.