Growth of GaN by gas-source molecular beam epitaxy by ammonia and by plasma generated nitrogen radicals

Abstract

We will present a comparison between GaN grown on c- and r-plane sapphire by gas-source molecular beam epitaxy (GSMBE) using solid source elemental Ga with uncracked ammonia (NH 3). Improved GaN film quality was found for samples grown at substrate temperatures above 700°C with optimized temperatures at 780°C. GaN deposited on a low-temperature (∼ 350°C) GaN buffer layer grown using an rf-plasma radical beam source exhibited poor photoluminescence (PL) intensity and carrier mobility while SEM analysis showed smooth GaN surface morphologies. GaN deposited on an ammonia-grown low-temperature (∼ 550°C) GaN or AlN buffer were found to have improved PL intensity and line widths, GaN surface morphology and carrier mobility. X-ray rocking curve (XRC) data showed that the GaN crystal quality improved as a function of increasing substrate growth temperature independent of buffer layer implementation.