Effect of interface manipulation for MBE growth of AlN on 6H-SiC

AlN layers were grown on 6H-SiC(0001) by molecular beam epitaxy using ammonia as the nitrogen source. Clean (√3x√3)R30° SiC surfaces was prepared by in-situ annealing alone and also by in situ annealing consisted of followed by Si deposition and subsequent annealing. The surface morphology of the AlN films observed by AFM was significantly changed by the nucleation procedure. When the AlN growth was initiated with Al flux exposure on a SiC surface prepared by thermal annealing, the surface roughness of the AlN was significantly reduced. Two-dimensional growth of AlN was observed with reflection high-energy electron diffraction from the very beginning. Atomically flat AlN surfaces with a RMS-roughness of ∼O.3 nm were obtained. On the other hand, when film growth was initiated with an ammonia flux exposure on a Si rich SiC surface, a high density of bumps was observed. The bumps seemed to originate from SiN _x formation at the heteroepitaxial interface. It was found that control of the Si composition and the V/III ratio at the growth interface is crucial for the AlN film quality.