Effects of Cd vacancies on the electrical properties of polycrystalline CdTe sputtered films

Polycrystalline CdTe films were grown on 7059 Coming glass substrates at room temperature by sputtering from a pure CdTe target and by co-sputtering from a composite CdTe-Cd target. The electrical, optical and structural properties of the films were analyzed as a function of their Cd concentration. It was found that the films grown from the pure CdTe target were Cd-deficient with electrical resistivity of about 10(7)-10(8) Omega cm and those grown from the CdTe-Cd target were Cd-rich with electrical resistivity of the order of 10(3) Omega cm. Dark electrical current vs 1/K(B)T measurements showed that the CdTe films with low cadmium content (< 50 at.%) exhibit an unusual current peak in the range of 1/K(B)T = 40-60 eV(-1). When the cadmium composition in the CdTe films approaches 50 at.%, this effect vanishes and the current has an exponential behavior for 1/K(B)T > 40 eV(-1). The current peak was associated with the presence of Cd vacancies in the CdTe lattice. (C) 2001 Elsevier Science Ltd. All rights reserved.