Intersubband scattering in quantum wells via carrier-carrier interaction

Summary form only given.Intersubband scattering is a process of great importance, especially for the understanding of the possible performances of devices such as quantum cascade lasers. The involved time scales are relatively well understood in the case of intersubband separation larger than the energy of the optical phonons and correspond well to the computed interaction with LO phonons. In the case of intersubband separation smaller than the energy of the LO phonon, the results are quite widespread (from 1 ps to 1 ns). We have studied in great detail the case of intersubband relaxation in large wells (220 /spl Aring/) using luminescence with resonant excitation and femtosecond (upconversion) or picosecond resolution (streak camera). We can first show that the luminescence from the n=2 subband disappears very quickly in the case of an excitation density of the order of 10/sup 10/ cm/sup -2/ to 10/sup 11/ cm/sup -2/. This can only be explained by the contribution of carrier-carrier scattering, and the computation of such a process by standard Monte-Carlo procedures confirms the large efficiency of carrier-carrier scattering for intersubband processes. The two carrier-carrier interaction processes of importance may be labeled by their form factor.