Thermalization of Photoexcited Carriers in Bulk and Quantum Wire Semiconductors

A theoretical study of the internal thermalization of high-energy carriers created by laser excitation in bulk and quantum wire semiconductors is presented. For the bulk case the results of our Monte Carlo simulation are compared to luminescence up-conversion experiments used to monitor the spectral and temporal evolution of the photoexcited carrier distributions with a time resolution of about 100 fs. The agreement between theory and experiment is very good and shows that the Coulomb interaction among carriers is responsible for the initial ultrafast thermalization. On the contrary, a much slower thermalization is found theoretically in quantum wires, which can be mainly attributed to the reduced efficiency of intersubband processes and to the reduced effect of electron-electron intrasubband scattering. Available experiments seem to confirm such findings.