Luminescence flashes induced by microwave radiation in undoped GaAs quantum wells

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.