Lifetime of nonequilibrium carriers in high‐Al‐content AlGaN epilayers

Abstract

AbstractAlGaN epilayers with different aluminum molar fractions have been comparatively studied by photoluminescence (PL) and light‐induced transient grating (LITG) techniques. The carrier diffusion length determined by LITG is shown to be close to the average distance between two first‐neighbor dislocations, which was roughly estimated by using the dislocation density obtained by etch pit technique. For epilayers containing the same amount of Al, the carrier lifetime and PL intensity are inversely proportional to the density of the dislocations, which limit the carrier lifetime by serving as nonradiative recombination centers. For AlGaN epilayers with similar lifetimes but with different Al contents, the PL intensity decreases with increasing Al fraction, which is explained by the Al content dependence of the radiative recombination rate. It is demonstrated that introduction of AlN/AlGaN superlattices on sapphire substrates by using Migration Enhanced Metal Organic Chemical Vapor Deposition (MEMOCVDTM) enables growth of AlGaN with an increased nonequilibrium carrier lifetime and enhanced photoluminescence intensity. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)