Effect of the nucleation conditions on the polarity of AlN and GaN films grown on C-face 6H-SiC

The metalorganic chemical vapor deposition of AlN and GaN on C-face 6H-SiC was investigated. Similar to the procedure on Si-face SiC, GaN films were fabricated in it two-step process, where first a thin AlN base layer was deposited prior to the growth of the main GaN layer. Polarity conversion from the expected N-polar AlN and GaN to Al-polar AlN and Ga-polar GaN films was observed when the AlN base layers were deposited using a low ammonia to trimethylaluminum ratio of 250 during growth. The properties of' the resulting Ga-face GaN-films were similar to those grown on Si-face SiC. Hexagonal surface features were seen on the N-polar AlN and GaN films obtained with it high V/III-ratio during AlN growth.