Effect of carrier emission and retrapping on luminescence time decays in InAs/GaAs quantum dots

We report time-resolved photoluminescence measurements as a function of temperature for InAs quantum dots grown by molecular-beam epitaxy on GaAs(100). As the temperature is increased, the decays on the high-energy side of the photoluminescence band speed up, while the decay times on the low-energy side of the band increase. This increase occurs up to a ''drop'' temperature, which increases with decreasing emission energy, beyond which the decay times decrease. We present a coupled rate-equation model which includes the effects of thermal emission from quantum dot states into the wetting layer followed by transport and recapture, which reproduces the dispersive temperature dependence observed. The activation energy for thermal emission from quantum dots emitting at a given frequency is found to be approximately one-half the effective band-gap difference between the quantum dot and the wetting layer. This result is consistent with detailed balance requirements under the assumption that, on average, electrons and holes are captured and emitted by quantum dots in pairs.