Impact of carrier injector design on the threshold of interband cascade lasers

We theoretically investigate how the injector region design of interband cascade lasers (ICLs) impacts the threshold carrier and current densities. The model combines a polarization-sensitive 8-band k⋅p calculation, electrostatics, and a microscopic calculation of Auger recombination rates. The inelastic carrier–carrier scattering is included at the lowest order using quasi-equilibrium Green’s functions. Our approach captures the combined effects of charge-carrier redistribution, parasitic absorption, and bias voltage on the Auger recombination rate. We show that heavily doping the electron injector suppresses the dominant multi-hole Auger recombination by reducing the hole population of the recombination quantum wells. This agrees with the experimental observation that the heavy doping reduces threshold currents. Unlike the measurements, however, they do not increase at high doping concentrations in our model, which does not include scattering-mediated carrier escape and/or light absorption. Furthermore, by introducing indium to the conventional GaSb hole injector wells, we explain the rule of thumb from experiments that raising the hole injector levels does not outperform the doping strategy. Our model provides physical insights for optimizing ICL carrier injectors.