Radiative lifetimes of negatively charged excitons in CdTe quantum wells

Summary form only given. Using picosecond photoluminescence (PL), we have investigated the temperature dependence of the radiative lifetime of the negatively charged exciton (X/sup -/) in CdTe quantum wells (QWs). The X/sup $/lifetime is found to increase from 70 ps at 2 K up to about 200 ps at 30 K. The increase is linear for temperatures bigger than 5 K and reveals that X/sup $/cannot be treated as a purely localised species. A linear increase is indeed predicted theoretically for delocalised X/sup -/. In addition, the observed temperature behaviour demonstrates that unlike the donor bound exciton to which X/sup -/ has been previously compared, X/sup -/ radiative recombination can take place with a specific strongly k dependent selection rule. The behaviour of X/sup -/ lifetime at the lower temperatures indicates the presence of a certain degree of localisation.