Phonon-assisted subband depopulation in semiconductor quantum well laser heterostructures

We study the rate of intersubband electron transitions assisted by LO-phonon emission in type-II InAs/GaSb DQW heterostructure, which models the active region of antimonide-based intersubband cascade laser. We show that in type-II heterostructures with broken-gap band alignment the phonon-assisted process is the most favorable for the fast depopulation of the lower lasing states. The main peak of the electron-phonon resonance corresponds to electron transitions from the lowest electron-like subband to the top of the highest heavy-hole subband, which is spin-split and displaced from the center of the Brillouin zone due to the asymmetry of type-II InAs/GaSb DQW. We show that phonon-assisted depopulation can be conveniently employed even when the lower lasing level is designed near the upper edge of the heterostructure leaky window, where direct interband tunneling depopulation becomes, inefficient.