EXCITON SATURATION AND FIELD SCREENING IN INGAAS INGAASP MULTIPLE-QUANTUM WELLS/

We performed differential transmission spectroscopy and time resolved pump probe measurements on biased InGaAs/InGaAsP multiple quantum well structures. At low carrier excitation levels we observe a shift in th e energy of the excitonic absorption resonance caused by the photogene rated carriers screening the applied electric field within the quantum wells. Increasing the pump power the exciton transmission energy blue shifts until it reaches the zero internal field energy position. For our pump-probe measurements field screening dominates at pump powers l ower than 50 W/cm2 while at higher powers exciton saturation becomes d ominant. We deduce a saturation intensity of 250 W/cm2.