Methods for improving the performance of type-II and type-I ICLs, particularly in the mid-IR wavelength range, are provided. The electron injector of a type-II or a type-I ICL can be heavily n-doped to increase the ratio of electrons to holes in the active quantum wells, thereby increasing the probability of radiative recombination in the active quantum wells and reducing the threshold current density Jth needed to achieve lasing. For both type-II and type-I ICLs, the doping should have a sheet density in the low-1012 range. In either the type-II or the type-I case, in some embodiments, heavy doping can be concentrated in the middle quantum wells of the electron injector, while in other embodiments, doping with silicon can be shifted towards the active quantum wells.