The effects of H-2/N-2 mixed gas-plasma pretreatment of sapphire(0001) surface on the characteristics of GaN epilayers

Abstract

The effects of plasma pretreatment on sapphire and the properties of the GaN overgrown epilayers were investigated. The sapphire surface was pretreated with H-2/N-2 mixed-plasma at 350degreesC for 30 min with fixed 50 W plasma power from which an about 2 mm thick oxygeti-deficient layer was obtained. GaN epilaver of about 4.5 mum thick were grown using a metal organic chemical vapor deposition (MOCVD) system, X-ray rocking curves and cathodoluminescence spectra of the GaN epilavers showed that the crystallinity was improved through the mixed gas-plasma pretreatment of sapphire substrate. It was found that the oxygen-deficient thin layer plays a major role in reducing crytallographic defects in the GaN epilayers.