CdTe-Cd: a new semiconductor with polytype structure

Cd-doped CdTe thin films were prepared by sputtering on unheated glass subs trates. Targets of stoichiometric CdTe with inclusions of elemental Cd were used to vary the Cd concentration of the films in the approximate range 47 -55 at.%. The amount of Cd in the films is directly related to the area of the Cd pieces on the CdTe target. The electrical and structural properties of the films were analysed using Hall measurements and X-ray diffraction. I t is found that both properties strongly depend on the Cd concentration. Fo r Cd concentrations below or equal to the stoichiometric value, the crystal line structure corresponds to the regular zincblende, and the electrical tr ansport is dominated by the extended states. For Cd concentrations above th e stoichiometric value, the X-ray data show an unusual 6H polytype structur e and the electrical conduction takes place by hopping along localized stat es. It is proposed that this latter behaviour in the conductivity occurs be cause the excess of ed atoms enter the CdTe lattice in interstitial sites, creating energy levels in the forbidden bandgap.