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 τs=0.65±0.15 ps for a 85 A GaAs quantum well and τs=0.8±0.2 ps for a 100 A 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 (≤100 K).

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