Ideal threshold current densities of 2.1–4.1 &mgr;m IR lasers are calculated for active layers composed of InAs/InGaSb superlattices, InGaAsSb quantum well quaternaries, InAsSb bulk ternaries, and HgCdTe superlattices. The fullyK‐dependent band structure and momentum matrix elements, obtained from a superlatticeK⋅pcalculation, are used to calculate the limiting Auger and radiative recombination rates and the threshold current density. InGaAsSb quantum wells and InAs/InGaSb superlattices are found to be more promising laser candidates than HgCdTe superlattices and InAsSb bulk ternaries. The calculated threshold current densities of InAs/InGaSb superlattices are similar to those of InGaAsSb active layers at 2.1 &mgr;m, but are significantly lower at longer wavelengths. Comparison with experiment indicates that the threshold current densities of InGaAsSb‐based devices are about three times greater than those calculated for 25 cm−1gain. The threshold current densities of present InAs/InGaSb superlattices are about 100 times above their theoretical limit. ©1995 American Institute of Physics.