Substrate reactivity and "controlled contamination" in metalorganic chemical vapor deposition of GaN on sapphire

Atomic force microscopy (AFM) and lateral force microscopy (LFM) have been used to study the effect of common substrate surface pretreatments on the metalorganic chemical vapor deposition (MOCVD) of GaN on sapphire. It appears that contaminants play a major role in the surface chemistry and strongly influence the morphology of the treated surfaces. To investigate the role of these contaminants, we have introduced the concept of "controlled contamination" (CC), namely, exposure of the sapphire surfaces to controlled amounts of potential contaminants and investigation of the resulting sapphire morphology. The results showed that sapphire, considered to be a very stable oxide surface, is clearly reactive under typical conditions employed in the high-temperature MOCVD growth of GaN.