A MICROSTRUCTURAL COMPARISON OF THE INITIAL GROWTH OF ALN AND GAN LAYERS ON BASAL-PLANE SAPPHIRE AND SIC SUBSTRATES BY LOW-PRESSURE METALORGANIC CHEMICAL-VAPOR-DEPOSITION

The initial growth by low pressure metalorganic chemical vapor deposit ion and subsequent thermal annealing of AlN and GaN epitaxial layers o n SiC and sapphire substrates is examined using high resolution transm ission electron microscopy and atomic force microscopy. Growth under l ow pressure conditions on sapphire substrates is significantly differe nt from that reported for conventional (atmospheric pressure) conditio ns. Smooth, single crystal AlN and GaN layers were deposited on sapphi re in the initial low temperature (600 degrees C) growth step. Interfa cial banding and not lattice mismatch was found to be the determining factor for obtaining good crystallinity for the epitaxial layers as in dicated by the growth results on SiC substrates.