Femtosecond pump-probe experiments have been performed on asymmetric GaAs/AIGaAs quantum well structures, using a spectrally narrow excitation beam whose center wavelength could be tuned between 740 and 800 nm. The respective widths of the wells were chosen to exhibit n=1 and n=2 excitonic absorptions of the wide well clearly separated from the n'=l narrow well excitonic absorption line, which lies in between the two others. We monitor the time evolution of the photoexcited carrier population in both wells by measuring the variations of the sample transmission. This method is another approach to the study of the tunneling transfer between coupled quantum wells, mostly addressed by use of time-resolved photoluminescence techniques. The sample recovery after excitation shows drastic changes depending on the pump intensity. At high intensities, all three transitions are bleached and we observe an important band-filling. At low intensities we see a decrease with time of the carrier population in the narrow well, along with a simultaneous increase in the wide well. This shows that carriers tunnel through the barrier with a characteristic time much smaller than the recovery time measured at high intensities, and thus demonstrates that the presence of a large number of carriers dramatically reduces the tunneling efficiency between the two wells.

Date Published: 1 August 1990
PDF: 10 pages
Proc. SPIE 1268, Applications of Ultrashort Laser Pulses in Science and Technology, (1 August 1990); doi: 10.1117/12.20332

Published in SPIE Proceedings Vol. 1268:
Applications of Ultrashort Laser Pulses in Science and Technology
Andre Antonetti, Editor(s)