Radiative lifetime of negative trions in GaAs and CdTe quantum wells

We have studied experimentally the radiative lifetimes of negatively charged excitons (X-) and neutral excitons (X) in GaAs and CdTe quantum wells. Despite the different optical properties (e.g. trion binding energies) and the different quantum well structures of the studied samples, we find quite similar X- lifetimes in the range of 45 to 60 ps. On the other side, the X lifetimes are very different and influenced by the material. For relatively low electron concentrations, the X- lifetime is found to be constant with increasing temperature in a given range. This time behaviour of X- suggests that X- is localised for low electron concentrations in the CdTe QW.