Exciton Spin Relaxation Time in Quantum Dots Measured by Continuous-Wave Photoluminescence Spectroscopy

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