The effect of substrate preparation on the sublimation growth of AlN at about 1800 °C and 400 torr on (0001) 6H-SiC was investigated. The AlN grew in the step flow growth mode on an off-axis 6H-SiC substrate with a 6H-SiC epilayer, an island growth mode on as-received substrates, and a 2-D growth mode on substrates first coated with an AlN epitaxial layer by MOCVD. Cracks in the deposited AlN crystal due to the lattice and thermal expansion coefficient mismatches were always observed by SEM and optical microscopy.
