Formation and properties of In-doped high-conductivity CdS film

Abstract

High dark-conductivity CdS films have been prepared by coevaporation of CdS and In and the physical properties of the films were investigated. The dark conductivity of the films prepared at room ranged from 10−1 to 103 S cm−1. Analyzing the film structure by x-ray analysis, it was found that the In atoms were doped substitutionally into the Cd site of a CdS crystallite at a low concentration In doping stage and then doped interstitially into the CdS crystallite at a high concentration In doping stage. In the carrier density versus the doped In concentration relation, the n-type characteristic was found. This was explained by the two In doping processes described above. Further, the negative temperature dependence of the carrier density was detected in the very high-concentration In-doped samples. We used an explanation similar to the one given by Hung and Gliessman [Phys. Rev. 96, 1226 (1954)], that is, by using a tentative model in which the substitutionally doped low concentration In atoms form a shallow discrete donor level and the interstitially doped high-concentration In atoms form an impurity band in the forbidden band.