Dynamics of exciton relaxation and excitation transfer to donor-bound excitons in CdTe/CdMnTe quantum wells

Using time-resolved photoluminescence spectroscopy we investigate the dynamics of exciton relaxation in CdTe/Cd_1-xMn_xTe multiple quantum wells. Unbound excitons are photoexcited and the timescale of formation of the donor-bound excitons varies with excitation intensity from 73 ps to <8 ps and depends on movement of the unbound exciton in the well and the capture process at the donor site. Estimates of the capture cross-section of excitons by neutral donors and of the radiative recombination time of the donor-bound exciton are made. The rate of kinetic energy relaxation of a photocreated exciton from K=0 of the electron-light hole band to K=0 of the electron-heavy hole band is found to be (2.2±0.8)× 10⁸ eV s^-1.