Microwave modulation of exciton luminescence in GaAs/AlxGa1−xAs quantum wells

We present a study of the photoluminescence (PL) modulation by microwave irradiation in GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum wells. At low temperatures, we observe that the inhomogeneously broadened PL band of (e1:hh1) excitons is split into low-energy negative-modulation and high-energy positive-modulation components. We interpret this spectral shape and its dependence on photoexcitation (laser) energy and on microwave power in terms of the following model: Photoexcited free electrons are heated by the microwave radiation and they impact activate the excitons into states with higher energies (without dissociating the excitons). This model is based on two types of exciton states: localized in the low-energy tail of the PL band and delocalized in its high-energy part. A well-defined exciton temperature is deduced from the anti-Stokes part of the microwave-modulated PL spectrum. It depends on the absorbed microwave power but is independent of the photoexcitation energy.