Strain-compensated InP-based quantum cascade lasers with and without injector regions

A comparison between structures with and without injector regions - realised with a minimum number of strongly coupled subbands - is presented. The advantages and the limitations of injectorless structures on the laser performance are discussed and compared with those of quantum cascade lasers with injector minibands. The main advantage of the former structures is that fewer layers and electron states are involved in the active volume allowing the realization of very compact gain regions with increased flexibility in waveguide design and a larger optical confinement factor. On the other side problems connected with thermal-backfilling, doping and negative differential resistance limit the performance of such devices. Especially the last effect presently limits the maximum operating temperature to only 200 K.