Coupled 2D electron-exciton system under microwave irradiation

We develop a new experimental approach in order to study the dynamical properties of charged excitons in a wide range of a 2D-electron gas density, n_2D. We use undoped mixed type I - type II GaAs/AlAs QWs (MTQWs), tune n_2D by short-pulsed He-Ne-laser photoexcitation and measure the PL and its excitation (PLE) spectra obtained under a Ti-sapphire laser cw illumination, at various delays after the He-Ne-light pulses terminate. The effect of microwave (mw) irradiation on the PL and PLE spectrum is studied by applying pulse-modulated mw radiation of 36 GHz (8 mm) with variable delays relative to the He-Ne-light pulses. These experiments unambiguously showed that the excitons are captured by localized electrons and form localized charged exciton complexes at n_2D values as high as 5 × 10¹⁰ cm^-2.