Intersubband photoluminescence of GaAs quantum wells under selective interband excitation

We report on infrared spontaneous emission between subbands in GaAs quantum wells excited by an interband optical pumping. The active region consists of 15 periods of four coupled quantum wells which are embedded in a mid-infrared optical waveguide. Electrons are selectively injected from the valence band in the excited subbands of the quantum wells using interband optical pumping. Intersubband spontaneous emission is observed at low temperature between the E5 and E4 subbands of the quantum wells (E5−E4≈162 meV≈7.7 μm). The intersubband luminescence vanishes when the E5 subband is not selectively populated. The emission is polarized along the growth axis of the quantum wells as expected for intersubband transitions. The collected infrared power exhibits a linear dependence with the interband optical power with a slope ≈560 pW/W.