Photoinduced structures in the exciton luminescence spectrum of InGaAs/GaAs quantum well heterostructures

A large set of InGaAs/GaAs quantum well structures was investigated by means of continuous wave photoluminescence (PL) and photoluminescence excitation spectroscopy. Strong photomodulation effects are observed in PL, namely, a strong sensitivity to the excitation energy and strong changes in the line shape when resonant and nonresonant excitations are used together. Correspondingly, the exciton emission exhibits a doublet structure and the excitation spectra, as detected by monitoring the emission at the two peak energies of the PL doublet, show quite different profiles, with peaks and/or dips not directly related to absorption resonances. On the grounds of time-resolved experiments it is shown that band-bending modifications, due to trapping of free carriers at interface defects, account for the observed photomodulation.