Carrier–carrier scattering: an experimental comparison of 5 and 3 nm AlxGa1−xAs/GaAs quantum wells

We have studied carrier dynamics among highly nonequilibrium carrier distributions generated with femtosecond laser pulses in Be:AlxGa1−xAs/GaAs quantum wells with different well width at hot carrier densities between 109 and 1011 cm−2. The spectra, at moderately high densities (≥1010 cm−2) indicate that the initially narrow electron distribution is altered in a time less than or equal to the LO-phonon emission time, as a result of rapid carrier–carrier scattering. At an excitation density of about 1010 cm−2, the carrier–carrier scattering rate is faster in narrower quantum wells. By measuring the intensity of the unrelaxed peak, it is possible to determine the relative rates of carrier–carrier scattering and LO-phonon emission. Our results indicate that carrier–carrier scattering becomes as significant as LO-phonon emission at a density of about 1×1010 cm−2 in the 5 nm quantum wells.