Experimental study of two-step growth of thin AlN film on 4H-SiC substrate by metalorganic chemical vapor deposition

We report growth optimizations of the thin AlN film on (0001) 4H-SiC substrates by metalorganic chemical vapor deposition. The influence of growth conditions, such as growth temperature and the V/III molar ratio, on the material quality of AlN film is studied. The surface morphology and crystalline quality of the epitaxial layers are investigated by atomic force microscope, X-ray diffraction, and transmission electronic microscope. A new approach is demonstrated to improve the crystalline quality of a 100 nm-thick AlN film by the use of a 5 nm-thick low temperature AlN nucleation layer. Compared to a conventional AlN layer directly grown on SiC substrate at high temperature, the surface morphology of two-step AlN film is remarkably improved along with a decreasing of defect density, leading to the improvement of crystalline quality for the subsequently grown GaN layer. The mechanisms of crystalline quality improvement by use of a low temperature AlN nucleation layer are also investigated and discussed.