Intersubband mid-infrared emission in optically pumped quantum wells

Optical emission between excited subbands of asymmetric coupled GaAs/AlGaAs quantum wells is investigated. The structures are designed to present an energy separation between the ground subband and the first excited subband close to the LO-phonon energy in order to enhance the non-radiative relaxation between those stales. Optical pumping at 10 mu m is used to excite electrons in the third subband. A mid-infrared emission at 1(Delta) mu m is shown to take place between the third and second subbands. The spontaneous emission is observed up to room temperature. The radiative efficiency is approximate to 60 nW/W in lightly doped samples. We also predict that this situation is very effective for achieving almost complete population inversion as well as large stimulated gains. The possibility of mid-infrared intersubband emission under band-to-band optical pumping is also discussed. (C) 1996 Academic Press Limited