MORPHOLOGICAL AND STRUCTURAL TRANSITIONS IN GAN FILMS GROWN ON SAPPHIRE BY METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION

The structural and morphological evolution of GaN films grown by MOCVD at high temperature (1080 degrees C) on a low temperature grown GaN n ucleation layer (NL) on (0001) sapphire were studied using atomic forc e microscopy (AFM), transmission electron microscopy (TEM) and photolu minescence (PL) measurements. The high temperature (HT) GaN layers wer e found to grow by initially forming isolated truncated hexagonal isla nds having {10 (1) over bar 1} facet planes and a top (0001) plane. Th e non-wetting or partial wetting behavior of the HT GaN on the GaN NL is attributed to both the roughness and predominantly cubic nature of the NL.