Optical gain in homoepitaxial GaN

Optical gain in GaN epilayers, grown by metalorganic chemical-vapor deposition technique on bulk GaN substrates is studied by means of time-resolved luminescence spectroscopy at room temperature. Both stimulated emission and carrier recombination rate are analyzed under high photoexcitation conditions that are close to laser operation regime. Homoepitaxial GaN shows a high value of optical gain coefficient g=7200cm−1 estimated under intense pulsed excitation by a variable stripe method. For comparison, a GaN epilayer grown under identical conditions on sapphire shows a significantly lower value, g=2300cm−1. Larger values of the optical gain coefficient achieved in homoepitaxial GaN are due to the lower density of nonradiative traps. This is proved by the carrier capture time that is estimated right after exhaustion of the inverted population, and has values of τe=970 and 195ps for homo- and heterolayers, respectively.