Optically induced changes of excitonic transitions in GaAs/AlAs single quantum well structures

Optically induced changes in excitonic transitions of type-I GaAs/AlAs single QW structures have been investigated by photoluminescence (PL) and wavelength-modulated reflectance (WMR) spectroscopies, under various excitation photon energies and at various temperatures. The remarkable difference was observed in PL and WMR spectra taken by the excitation only the QW and by the excitation both the QW and the AlAs barrier layers. The photoinduced broadening and red shift of excitonic features in the optical spectra dominates under photoexcitation within the QW by He-Ne laser, and could be associated with hole accumulation effects in the QW. Double-beam excitation WMR experiment showed that the damped excitonic transitions could be restored simultaneously exciting AlAs barriers by Ar+-ion laser. As it follows from the analysis of photomodulated PL, this behaviour could be attributed to optical depletion of the QW from the excess holes via a competing recombination process related to the barrier electrons. It was found that a thermal quenching of the PL line is activated by an escape of less confined electrons from the QW while a thermal quenching of photoinduced changes in the WMR spectra is related to the depopulation of the QW hole states.