Intensity dependent absorption bleaching of high subband excitons in GaAs/AlGaAs multiple quantum wells

We have investigated the influence of carrier generation on the absorption bleaching of the n = 2 and n = 3 excitons in GaAs/AlGaAs multiple quantum wells (MQWs). With the excitation near the resonance of the n = 1 exciton absorption, the long range coulomb screening and collision broadening had significant effects on the exciton bleaching. At low excitation intensity, the absorption bleaching of the n = 2 exciton in 75 A-thick MQWs and that of the n = 3 exciton in 150 A-thick MQWs were due to linewidth broadening by the collision broadening effect only. At high excitation intensity, however, the reduction of oscillator strength due to the long range coulomb screening contributed dominantly to absorption bleaching.