Thermal quenching processes in the low temperature photoluminescence of excitons bound to nitrogen pairs in GaP

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Abstract
We have measured the photoluminescent efficiency of excitons bound to isolated nitrogen, and to nitrogen pairs of different separations, in GaP. Excitons bound to a particular center were excited selectively with a tunable dye laser, and the temperature dependence of the emission intensity measured between 10 and 100 K. Detailed balance considerations show that the efficiency at 10 K is near 100%. Luminescence from excitons bound by less than 40 meV is found to be thermally quenched by the escape of a free exciton. For excitons bound by 40 meV or more, we find that luminescence is quenched by the escape of the hole. In the case of excitons bound to nearest-neighbor pairs (binding energy 143 meV) the electron remains attached to the pair, forming a charged acceptorlike center with a lifetime long enough for quasiequilibrium to be established with the valence band. This leads to a superlinear dependence of emission intensity on exciting power.