Four-constituent Type-II quantum-well laser for wavelengths beyond 3 μm

We discuss an improved design for mid-wave infrared diode lasers based on Type-II multiple quantum wells having four constituent layers in each period. Advantages include strong optical coupling (despite the Type-II band alignment), 2D dispersion for both electrons and holes, a small hole mass for reduced thresholds, prospects for significant suppression of the Auger recombination rate, and excellent electrical and optical confinement. The band profiles, energy levels, and wavefunctions for an InAs-Ga_1-xIn_xSb-InAs-Ga_1-xAl_x Sb multiple-quantum well which is predicted to emit at 3.6 μm are reported. The Ga_1-xIn_xSb barrier in each period serves to assure that neither carrier type will display dispersion along the growth axis. As a consequence, the gain per injected carrier is predicted to be much larger than for the analogous two-constituent InAs-Ga_1-xIn_xSb superlattice, whose electrons exhibit a 3D density of states