HOMOGENEOUS-LINEWIDTH EFFECTS ON RADIATIVE LIFETIMES OF EXCITONS IN QUANTUM-WELLS

The temperature Green's-function formalism is used to calculate spectrally- integrated photoluminescence-decay (PL) times for quantum-well excitons. The treatment includes the dephasing of the exciton through the homogeneous linewidth hGAMMA(h)BAR. In the limits that hGAMMA(h)BAR is narrow compared with the exciton bandwidth E1 below the crossing with the photon line or that k(B)T much greater than hGAMMA(h)BAR much greater than E1, we obtain the result of Andreani et al. [Solid State Comm. 77, 641 (1991)] which states that the PL-decay rate spectrally integrated over the ls heavy-hole exciton peak is given by the fraction of the thermal exciton population lying within E1 at the bottom of the band. For hGAMMA(h) much greater than k(B)T much greater than E1, we obtain the result of Feldmann et al. [Phys. Rev. Lett. 59, 2337 (1987)] which states that only those excitons lying within hGAMMA(h)BAR at the band bottom can decay radiatively. The apparently conflicting views of exciton decay are here shown to be limiting cases of a more general theory. We also show that excitons localized by interface defects play an important role in the PL-decay time, not only at very low temperatures, but over the entire temperature range T < 150K.