Nitridation of sapphire substrate and its effect on the growth of GaN layer at low temperature

Abstract

A remote plasma enhanced-ultrahigh vacuum chemical vapor deposition system equipped with a radio frequency (RF) – inductively coupled plasma which produces the reactive nitrogen species was employed to grow GaN layers at low temperature. The X-ray photoelectron spectroscopy analysis of nitrogen composition on the nitridated substrate surface indicated that the nitridation process on the substrate surface is largely affected by RF power at low temperature. However, the atomic force microscope images indicated that the protrusion density on the nitridated sapphire surface is critically dependent on the nitridation temperature. It was possible to nitridate the sapphire surface without the production of protrusions by controlling the RF power and nitridation temperature even at low temperatures. The crystallinity of the GaN grown at 450°C was found to be much improved when the sapphire substrate was nitridated at low temperature prior to the GaN layer growth. Moreover, lateral growth of the GaN layer was enhanced not only by an increase in growth temperature but also by the nitridation of sapphire substrate prior to the GaN layer growth.