Decay measurements of free- and bound-exciton recombination in doped GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells

In this study we present photoluminescence decay measurements of free-exciton (FE) and bound-exciton (BE) recombination in doped GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum wells (QW’s). It is found that the FE decay time is reduced in the doped QW’s compared with similar undoped samples. For a sample with a QW width of 80 Å, we obtain a capture rate of 0.12 ${\mathrm{cm}}^2$ ${\mathrm{s}}^{\mathrm{-}1}$ from the FE to the BE. The low-temperature decay time of the BE is slightly longer than for the FE, with BE decay times varying from 300 to 600 ps for well widths in the range of 50 to 150 Å, respectively. At temperatures above 10 K, we find a similar decay time for the FE and BE recombination. We conclude that the FE and BE are in thermal interaction and, based on the assumption of thermal equilibrium between the two states, we present a simple model to explain the temperature dependence of the photoluminescence data.