Interband cascade lasers with engineered carrier densities

A type-II interband cascade gain medium, comprising:

• an active gain region having a plurality of cascading stages, each of the cascading stages including type-II active gain quantum wells;
• a hole injector region adjacent the active gain quantum wells on a first side thereof, the hole injector region comprising at least one hole quantum well and being configured to inject holes into the active gain quantum wells;
• and
• an electron injector region adjacent the active gain quantum wells on a second side thereof opposite the first side, the electron injector region comprising a plurality of electron quantum wells and being configured to inject electrons into the active gain quantum wells, a hole injector of a first stage being adjacent to an electron injector of a second stage, with a semimetallic interface being present therebetween;
• wherein at least some of the plurality of the electron quantum wells in the electron injector region are n-doped to a net sheet doping density of about 1.5 to about 7×1012 cm−2;
• and
• wherein a ratio of electrons to holes in the active quantum wells is increased as a result of the n-doping in the electron injector region.