Exciton spin relaxation time in quantum dots measured by continuous-wave photoluminescence spectroscopy

We demonstrate a method of measuring the exciton spin relaxation time in semiconductor nanostructures by continuous-wave photoluminescence. We find that for self-assembled CdTe quantum dots (QDs) the degree of circular polarization of emission is larger when exciting polarized excitons into the lower energy spin state (σ−-polarized) than in the case when the excitons are excited into the higher energy spin state (σ+-polarized). A simple rate equation model gives the exciton spin relaxation time in CdTe QDs equal to τS=4.8±0.3 ns, significantly longer than the QD exciton recombination time τR=300 ps.