n‐type doping of mercury cadmium telluride was achieved using trimethylindium as the dopant source. The layers, grown by the alloy growth technique, were doped to ∼5×1018 cm−3. The donor concentration in these layers was found to exhibit a linear dependence on the dopant partial pressure over the carrier concentration range from 5×1016 to 3×1018 cm−3. Reasonably high electron mobility values were observed in these indium‐doped layers. Typically, layers with a Cd fraction x=0.23, doped to 3.5×1016 cm−3, exhibited a mobility value of 7.5×104 cm2/V s at 40 K. High electron mobility values, measured over the entire doping regime, suggest a high electrical activity of indium in these layers. The optically measured band edge in these indium‐doped layers was observed to shift to higher energy with increasing doping. The band‐edge energy values measured in 1×1017 and 3×1018 cm−3 doped layers correspond to x=0.23 and x=0.3, respectively. This increase can be due to an increase in the Cd fraction, or to a Burstein–Moss shift of the band edge with doping.