We present a study of the e1-e2 intersubband absorption in modulation doped GaAs/Al0.3Ga0.7As MQW's that are photoexcited by interband radiation. A comprehensive study of the photoinduced absorption (PIA) strength as a function of exciting (laser) intensity and modulation frequency indicates that only a subgroup of the photoexcited electrons contribute to the PIA. These electrons are long lived in MQW's with a 2DEG density in the range of 1-×1010 cm-2. The existence of long lived electrons is explained by a model based on localized, photoexcited holes, that have a reduced radiative recombination rate with the 2DEG. We calculate this recombination rate and show that it is much longer than that of free electrons and holes.
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Acknowledgements--The work at the Technion was supported by the US-Israel Binational Science Foundation (BSF), Jerusalem, Israel, and was carried out in the Center for Advanced Opto-electronics. The work at UCSB was supported by the National Science Foundation Science and Technology Center, QUEST.