Abstract
Low-temperature (T≈2 K) photoluminescence (PL) and photoluminescence excitation (PLE) spectra of GaAs/AlGaAs(x = 0.05) structures with shallow quantum wells (QWs) wereinvestigated. It was found that the PLE spectra exhibit anumber of broad bands in the above-barrier energy region; thesebands alternate `in opposite phases' in the spectra of freeexcitons and excitonic complexes (trions) (i.e. an increase inthe exciton luminescence intensity is accompanied by a decreasein the luminescence intensity of the complexes). Effectsoriginating from simultaneous irradiation of the sample by twolaser beams of different wavelengths were studied. In the casewhere the photon energy of the Ti-sapphire laser is tuned toexcite only the QW states, additional pumping by a He-Ne or Ar-ionlaser results in the shift of the equilibrium in theexciton-trion system towards an increase in the concentration of the latter species. On the other hand, upon excitation into certainbarrier states with energies both below and above the barrierbandgap, additional pump shifts the equilibrium in theopposite direction.
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