Intersubband relaxation of photoexcited carriers in asymmetric coupled quantum wells

Intersubband relaxation of hot carriers in III-V compound quantum well systems depends explicitly on the form of the polar optical coupling. In the GaAs/AlGaAs system, it is well known that the electrical and mechanical boundary conditions imposed on the atomic displacement at the interface lead to the formation of GaAs-like and AlAs-like slab and surface phonon modes. Thus, a variety of possible intersubband relaxation channels exist rather than a single phonon mechanism, as is the case with bulk-like phonons. Here the authors study the effect of such modes on the intersubband scattering rate in asymmetric coupled quantum wells in which an ensemble Monte Carlo simulation of electrons and holes is used to compare with recent time-resolved photoexcitation experiments. Their results show that, when energetically permitted, the dominant contribution to the transfer time between wells is due to AlAs modes originating in the barrier rather than GaAs-like modes in the well.