Study of the electrical and optical properties of CuO and CdS thin films prepared by spray method and formation of CuO/CdS heterojunction

Abstract

Cupric oxide (CuO) and Cadmium sulphide (CdS) thin films have been deposited on glass substrates by chemical spray pyrolysis technique and their structural, electrical and optical properties were studied. Film growth aspects have been reported in addition to optimization procedures. X-ray diffraction study· indicated that cupric oxide (CuO) deposit is crystalline and has monoclinic crystal structure with a=4.704A, b=3.414A and c=5.004A. For CdS films, X-ray diffraction pattern exhibit that the samples have hexagonal crystalline structure with a=4.136A and c=6.713A. Hall effect and thermoelectric power measurements show that CuO is p-type with carrier concentration about 1015-1016 cm-3 and CdS is n-type with low carrier concentration of order 1014 cm·3• In both the materials Fermi levels position changes with the thickness of the film. For CuO films, the resistivity is quite low and the value increases slightly with thickness but decreases on annealing. The conductivity behaviour show activation process to be present. In the case of CdS films substrate temperature has remarkable effect on resistivity and annealing the film reduces the resistivity. Thermoelectric power (TEP) measurements on CuO show a pinning character of the Fermi levels at high temperature. In the case of CdS TEP changes slightly with temperature near the room temperature range but almost remain constant at higher temperature. ------