Transient characteristics of excitons bound at hole-attractive isoelectronic centers in GaP

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Abstract
In this paper we present detailed luminescence-decay-time measurements of excitons bound at hole-attractive isoelectronic centers in GaP. We have found that the measured luminescence decay time can generally be explained with a model assuming full thermalization between the two lowest, singlet (S=0) and triplet (S=1), electronic levels of the bound exciton (BE). The values for the decay time of the dipole-forbidden triplet transition vary between 100 μs and 1 ms for the different bound excitons, while the allowed singlet transitions have decay times of a few microseconds. For some centers the effect on the decay time of the thermal quenching of the BE is considered, and we obtain good agreement for the value of the thermal activation energy, when compared with previous photoluminescence measurements. Different mechanisms for the interaction causing thermalization between the singlet and triplet are discussed. Also, the effect on the measured decay time due to thermalized or unthermalized magnetic sublevels in the triplet is discussed, and we conclude that at least one of the centers, the 1.911-eV bound exciton, has an unthermalized triplet level.