High Performance Superlattice Quantum Cascade Lasers

Superlattice Quantum Cascade (QC) lasers based on optical transitions between conduction minibands are unipolar semiconductor lasers with high current carrying capability and attendant high optical power due to miniband transport in the active and in the injector regions. Other advantages include the intrinsic population inversion associated with the large interminiband-to-intraminiband relaxation time ratio and the high oscillator strength of the laser transition at the superlattice Brillouin zone boundary. This oscillator strength is significantly larger than that of intersubband transitions in double quantum well active regions of conventional cascade lasers, particularly at long infrared wavelengths (>= 10 microns). Following a brief review of results on conventional QC lasers, design considerations for superlattice cascade lasers are discussed along with recent advances in long-wavelength (11 microns) with doped active regions.