Carrier-carrier contribution to intersubband scattering in wide quantum wells

Summary form only given. The importance of LO phonon emission for intersubband scattering (ISBS) processes is now well established. In very good agreement with theoretical expectations, such a process gives scattering times of 1 ps or less. The situation is different in wide quantum wells, when the energy separation /spl Delta/E/sub 12/ between the first two subbands is smaller than /spl planck//spl omega//sub LO/. It has often been proposed that ISBS should then be mediated mainly by acoustical phonons, and be quite slow. Such wells would then be promising for laser applications. However, the demonstration of such a laser failed to be obtained. An explanation was in fact proposed in 1989 by Goodnick and Lugli who computed carrier-carrier induced intersubband scattering. It is clear from their calculations that such ISBS could be as short as a few ps, 100 times faster than acoustic phonons. A number of results have nevertheless been published since then, with scattering times ranging from 1 ps to 1 ns. We have carefully studied ISBS by using femtosecond time-resolved luminescence with resonant excitation. The advantage of luminescence in addition to the very good time resolution is the ability to probe the whole distribution of electrons. This of course needs some assumptions on the behavior of holes, but we can show that their contribution to the observed dynamics is minimal.