Radiative behavior of negatively charged excitons in CdTe-based quantum wells: A spectral and temporal analysis

Using reflectivity and picosecond time-resolved photoluminescence, we have studied the intrinsic optical properties of negatively charged excitons in modulation doped CdTe quantum wells. In emission, we observe simultaneously a low energy exponential tail in the charged exciton spectral line and a linear increase of its radiative lifetime with temperature. In absorption, we find a consistent decrease of the charged exciton oscillator strength with temperature. For low electron concentrations these observations are well reproduced by a model of delocalized and thermalized three-particle complexes. The model takes into account the recoil momentum of the electron during the charged exciton optical transition. It is further found to compare well with lifetime measurements up to high carrier concentrations. Small deviations from the theoretical predictions occur only below 7 K due to localization effects and for the highest carrier concentration of $n_e\sim 2\times {10}^{11}{\mathrm{}\mathrm{cm}}^{-2}.$