Pump and probe measurement of intersubband relaxation time in short-wavelength intersubband transition

Population relaxation dynamics of the short-wavelength (2.5 mu m) intersubband transition (ISB-T) in narrow InGaAs/AlAs quantum wells is investigated. Femtosecond (similar to 100 fs) pump and probe measurement yields a relaxation time of similar to 2.7 ps, which is as fast as those observed for 10-5 mu m ISB-T (0.7-1.5 ps, respectively). The ISB relaxation time increases more rapidly than that predicted from the usual intersubband optical-phonon scattering model as the ISB-T energy increases. Our theoretical calculation, which takes into account the intrasubband energy relaxation process, agrees well with the experimental results. The intrasubband energy relaxation process is found to be important in the short-wavelength region. (C) 1999 American Institute of Physics. [S0003-6951(99)02110-5].