Effect of heavy doping of ZnSe crystals with indium in creating compensating acceptors

Measurements of the Hall coefficient and the dc conductivity in ZnSe single crystals excessively doped with In are made in the temperature range 65 to 300 K in order to investigate the role of In in the ZnSe lattice at concentrations of In in the region 50 to 104 ppm. A very unusual effect of In-doping contrary to the normal donor behaviour is observed on the Hall coefficient and conductivity at these concentrations. This is explained in terms of the compensating effects arising due to the formation of acceptor complexes like In–Zn vacancy–Se and the triply ionized acceptor like ZnIn, in addition to the normal donor behaviour due to InSe. From the measurements, a compensation ratio varying from 79.4% (50 ppm In) up to 99.7% (104 ppm In) is obtained. The compensation effect is found to be so strong that the free-carrier concentration decreases with the increase of In-doping.