RADIATIVE CARRIER LIFETIME, MOMENTUM MATRIX ELEMENT, AND HOLE EFFECTIVE-MASS IN GAN

By using picosecond time-resolved photoluminescence we have measured t he lifetime of excess charge carriers in GaN epitaxial layers grown on sapphire at temperatures up to 300 K. The decay time turns out to be dominated by trapping processes at low excitation levels. The radiativ e lifetime derived from our data is dominated by free excitons at temp eratures below 150 K, but also clearly shows the gradual thermal disso ciation of excitons at higher temperatures. From our data, we are able to determine the free exciton binding energy and the free carrier rad iative recombination coefficient. By combining these data with optical absorption data, we find the interband momentum matrix element and an estimate for the hole effective mass, which is much larger than previ ously thought. (C) 1997 American Institute of Physics.