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Bright flashes of exciton emission are observed in photoexcited, undoped GaAs/AlGaAs quantum wells under pulsed microwave (36 GHz) irradiation. The flash intensity is in the range of 10--100 times the steady-state photoluminescence intensity with a decay time of (1--10)×10^-8 s (depending on the applied microwave power and photoexcitation). These observations indicate a reservoir of long-lived carriers that is formed at low temperature due to localization of photogenerated electrons and holes at spatially separated shallow traps. Microwave-heated electrons activate the localized carriers into free states by means of avalanche impact ionization. This gives rise to rapid exciton formation with subsequent luminescence flash. A detailed model based on the coupled rate equations for free electrons, excitons and localized electrons (holes) is presented.
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Baskin et al. (2009) studied this question.
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