CdTe-Cd: A new semiconductor with polytype structure

Abstract

Cd-doped CdTe thin films were prepared by sputtering on unheated glass substrates. Targets of stoichiometric CdTe with inclusions of elemental Cd were used to vary the Cd concentration of the films in the approximate range 47–55at.%. 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. It is found that both properties strongly depend on the Cd concentration. For Cd concentrations below or equal to the stoichiometric value, the crystalline structure corresponds to the regular zincblende, and the electrical transport is dominated by the extended states. For Cd concentrations above the stoichiometric value, the X-ray data show an unusual 6H polytype structure and the electrical conduction takes place by hopping along localized states. It is proposed that this latter behaviour in the conductivity occurs because the excess of Cd atoms enter the CdTe lattice in interstitial sites, creating energy levels in the forbidden bandgap.