Monte Carlo simulation of ultrafast carrier relaxation in type-II MQW system

Hot carrier solar cells require an absorber layer, which inhibits the thermalization of photogenerated carriers. Although such absorbers have been experimentally demonstrated, the specific mechanics of carrier thermalization are not fully understood. AlAs_0.16Sb_0.84/InAs in particular is an interesting material system due to its type-II band alignment and the possibility of a phonon bottleneck. We calculate steady-state carrier distributions under laser excitation in AlAs_0.16Sb_0.84/InAs multi-quantum well structures. Carrier temperatures are extracted from these distributions and compared with experimental results. Due to the large depth of the wells, a more sophisticated Schrödinger solver that accounted for non-parabolic effects was implemented. Carrier recombination was modeled via an ABC model that used parameters obtained from experimental data. We achieved insight into how the non-equilibrium phonon interacts with the hot carriers and acts to inhibit thermalization as well as how Pauli blocking can affect this interaction. The picture is more complicated than previously described, with different ranges of the phonon wavenumber q interacting preferentially with different ranges of carrier energies. In addition, the effect of the electron-hole interaction on the carrier temperature over varying barrier widths was investigated. To match the experiment, larger longitudinal optical phonon lifetimes had to be used compared with bulk values used previously.