Interstitial Cd doping CdTe films by co-sputtering

A series of CdTe thin films were grown in a Cd enriched ambient by co-sputt ering a Cd-CdTe target. Different concentrations were obtained by changing the relative area occupied by the metallic Cd pieces placed onto the CdTe t arget. It was observed that the process of electrical conduction is not the same for all the samples. For samples with Cd < 50 at% the electrical cond uctivity is due to the direct activation of charge carriers from the valenc e band or from impurity states to the conduction band. For samples with Cd > 50 at% electrical conduction is due to the hopping of carriers from state to state by optimizing the distance of tunneling. Conductivity to) vs temp erature (T) measurements indicate that electrical conductivity behaves as l n sigma alpha (T-o/T)(1/4), the Mott law for variable range hopping (VRH) i n disordered systems. We think that this change in conductivity occurs beca use Cd atoms place in interstitial sites, doping the CdTe lattice, after th e Cd vacancy(V-cd) are filled. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.