Suppression of phonon-mediated hot carrier relaxation in type-II InAs/AlAs_xSb_{1 - X} quantum wells: A practical route to hot carrier solar cells

InAs/AlAs_xSb_{1 - x} quantum wells are investigated for their potential as hot carrier solar cells. Continuous wave power and temperature-dependent photoluminescence indicate a transition in the dominant hot carrier relaxation process from conventional phonon-mediated carrier relaxation below 90 K to a regime where inhibited radiative recombination dominates the hot carrier relaxation at elevated temperatures. At temperatures below 90 K, photoluminescence measurements are consistent with type-I quantum wells that exhibit hole localization associated with alloy/interface fluctuations. At elevated temperatures, hole delocalization reveals the true type-II band alignment, where it is observed that inhibited radiative recombination due to the spatial separation of the charge carriers dominates hot carrier relaxation. This decoupling of phonon-mediated relaxation results in robust hot carriers at higher temperatures, even at lower excitation powers. These results indicate type-II quantum wells offer potential as practical hot carrier systems.