The effect of Hg partial pressure on arsenic doping of HgCdTe is studied. It is found that control of Hg partial pressure is very important in obtaining reproducible doping, and use of high Hg pressure is the key to obtain heavily doped layers. Typically, a factor of 4 increase in the partial pressure of Hg is found to increase the acceptor concentration by about this same magnitude. In addition, arsine doping results in almost uncompensated layers, even though high concentration of Hg vacancies are present. A mechanism is proposed by which As is incorporated as a Cd-As complex, so that it substitutes preferentially on Te sites. © 1991.