Observation of optically pumped midinfrared intersubband luminescence in a coupled quantum wells structure

We have observed midinfrared emission due to intersubband transitions in a coupled quantum wells structure. The excitation process involves optical pumping of the carriers from the ground subband into the third subband and a generation of a population in the third subband. The luminescence is produced by a radiative transition of the photoexcited carriers from the third to the second subband, followed by a fast relaxation into the ground subband due to a resonance LO-phonon assisted relaxation process. The emission signal persists from low temperatures up to room temperature with a maximum efficiency at 190 K.