Homogeneous-linewidth effects on radiative lifetimes of excitons in quantum wells

Abstract

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 ħΓ h . In the limits that ħΓ h is narrow compared with the exciton bandwidth E 1 below the crossing with the photon line or that k BT ⪢ ħΓ h ⪢ E 1, 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 1 s heavy-hole exciton peak is given by the fraction of the thermal exciton population lying within E 1 at the bottom of the band. For ħΓ h ⪢ k BT ⪢ E 1, we obtain the result of Feldmann et al. [Phys. Rev. Lett. 59, 2337 (1987)] which states that only those excitons lying within ħΓ h 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 rôle in the PL-decay time, not only at very low temperatures, but over the entire temperature range T < 150 K.