Femtosecond luminescence measurements of the intersubband scattering rate in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs quantum wells under selective excitation

We have investigated the intersubband scattering of electrons in GaAs quantum wells using luminescence up-conversion with 100-fs resolution. The decay time of the n=2 electron-to-heavy-hole transition (e,hh${)}_2$ depends both on the excess energy of the charge carriers and on the excitation density. A Monte Carlo simulation allows us to reproduce the experimental data with high accuracy. The intrinsic LO-phonon scattering rate is found to be 2.0×${10}^{12}$ ${\mathrm{s}}^{\mathrm{-}1}$ for 80-meV subband separation. We show the wave-vector dependence and explain the density and excess energy dependence. © 1996 The American Physical Society.