Decay of stimulated and spontaneous emission in highly excited homoepitaxial GaN

The high-density effects in the recombination of electron-hole plasma in ph otoexcited homoepitaxial GaN epilayers were studied by means of transient p hotoluminescence at I aom temperature. Owing to the "backward" and "lateral " photoluminescence measurement geometries employed, the influence of stimu lated transitions on the decay of degenerate nonthermalized plasma was reve aled. The lateral stimulated emission was demonstrated to cause a remarkabl e increase in the recombination rate on the early stage of the luminescence transient. A delayed enhancement of the stimulated emission due to the coo ling of plasma from the initial temperature of 1100 K was observed. After c ompletion of the thermalization process and exhaustion of the stimulated em ission, the spontaneous-luminescence decay exhibited an exponential slope t hat relates to the nonradiative recombination of the carriers. The homoepit axially grown GaN layer featured a luminescence decay time of 445 ps that i mplies a room-temperature fret-carrier lifetime of 890 ps (considered to be extremely high for undoped hexagonal GaN). (C) 2001 American Institute of Physics.