Growth of GaN on Nitriding TiN Buffer Layers

Abstract

The breakthrough of GaN epitaxial layer growth with mirror-like surface on the sapphire substrate using a MOCVD (metal organic chemical vapor deposition) technique was made by discovery of an AlN buffer layer prior to GaN deposition about 20 years ago. Since then, extensive efforts have been made to develop a conductive substrate for MOCVD grown GaN layers. In the present study, we explored a possibility of growing continuous, flat GaN layers on a metallic TiN buffer layer, and focused our experiments to investigate the effect of nitrogen contents of the TiN buffer layers on lateral growth of the GaN layers. It was concluded that nitrogen composition in the TiN buffer layers should be higher than that of stoichiometric TiN to grow smooth GaN layers. It was found that nitriding the TiN buffer layers after deposition enriched significantly the nitrogen content compared with increasing the ratio of N₂ to N₂+Ar (N₂⁄(N₂+Ar) ratio) during TiN deposition. Choice of the moderate N₂⁄(N₂+Ar) ratio during TiN deposition and nitriding the TiN buffer layers after TiN deposition were essential to grow continuous, flat GaN layers, since the reduction of the N₂⁄(N₂+Ar) ratio promoted few opening areas in the GaN layers.