Changes in the growth mode of low temperature GaN buffer layers with nitrogen plasma nitridation of sapphire substrates

Abstract

Low temperature GaN buffer layers were grown by remote plasma enhanced metalorganic chemical vapor deposition on various pretreated sapphire substrates. The effects of the initial nitridation of sapphire substrates by rf nitrogen plasma on the subsequent growth mode and the crystallinity of the GaN buffer layers were studied. GaN buffer layers on non-nitridated sapphire substrates showed a three-dimensional island growth mode with rough surfaces and misoriented islands. On the other hand, those grown on nitridated sapphire substrates showed an enhanced two-dimensional growth mode with near-equilibrium truncated hexagonal pyramids. The structural quality of the low temperature GaN buffer layer improved significantly with nitrogen plasma nitridation.