MEASUREMENT OF THE INTERSUBBAND SCATTERING RATE IN SEMICONDUCTOR QUANTUM-WELLS BY EXCITED-STATE DIFFERENTIAL ABSORPTION-SPECTROSCOPY

A new technique for the measurement of the intersubband lifetime in semiconductor quantum wells is demonstrated. Electrons are optically excited from the ground state to the first excited state of a doped quantum well. From measurements of the absorption cross section between excited states, we find a lifetime equal to tau(s)=0.65 +/- 0. 5 ps for a 85 angstrom GaAs quantum well and tau(s)=0.8 +/- 0.2 ps for a 100 angstrom Ga0.47In0.53As quantum well, in good agreement with the theoretical predictions of Ferreira and Bastard [Phys. Rev. B 40, 1074 (1989)]. In addition, our experiments unambiguously show that the intersubband absorption line is homogeneously broadened at cryogenic temperatures (less-than-or-equal-to 1 00 K).