Resistivity and Activation Energy of CdTe Electrodeposited at Various Cd(ll) Concentrations

Two methods have been investigated for incorporating excess cadmium into CdTe electrodeposited from tri-n-butyl-phosphine telluride. These were: (i) variation of the Cd(II):Te concentration ratio in situ from 0.009 to 0.30, and (it) the dif-fusion of metallic admium at high temperature. Resistivity and light response of various samples were studied after they had been removed from their substrates. Scanning electron microscopy was used to examine the morphology of some of the samples. For the series of films in which the Cd(II):Te concentration ratio was varied in situ the resistivity was found to increase moderately with increasing Cd(II) concentration. However, the activation energy was found to increase signif-icantly only at the highest Cd(II):Te ratio, otherwise it remained more or less constant. The light response was similarly unaffected. When cadmium was diffused into the film, the light response was increased markedly and the resistivity gen-erally decreased while the activation energy remained more or less the same. These results are discussed with reference to a model in which surface states at grain boundaries act as trapping centers for charge carriers, leading to the formation of a potential barrier to the transport of carriers across the grain boundaries. Various dopants have previously been found to change the electrical properties of p-type CdTe electrodeposited from tri-n-butylphosphine telluride (BPT) solution (1, 2)