Emission of mid-infrared radiation and intersubband population inversion in near-infrared laser QW structures

A new possibility to obtain the intersubband population inversion under current injection (or optical pumping) of the electrons into the structure with GaAs/AlGaAs quantum wells (QWs) is discussed. The QWs are embedded into the i-layer of a p+–i–n+ heterostructure. We consider QWs of funnel shape with three electron levels and find the conditions to realize mid-infrared (MIR)-stimulated emission due to intersubband electron transitions under simultaneous stimulated emission of near-infrared (NIR) radiation due to interband transitions. Experimental data on spontaneous MIR emission from InGaAs/GaAs QWs under simultaneous NIR lasing are presented.