PROPERTIES OF CDS FILMS PREPARED BY THE CHEMICAL MIST DEPOSITION PROCESS

Abstract

Cadmium sulphide thin films were prepared by the chemical mist deposition process from solutions containing equimolar (0.1 M) cadmium chloride and thiourea ((NH2)2CS) on glass substrates of which the temperature was varied from 250 to 450-degrees-C. Pure CdS films with a hexagonal structure were formed above 300-degrees-C and the number of pinholes in the films decreased as the substrate temperature increased. The optical transmittance of the films deposited at 400-degrees-C was about 75% and the optical band gap of the films was 2.43 eV regardless of substrate temperature. The dark electrical resistivity of the films deposited at 400-degrees-C was of the order of 10(5) OMEGA cm and all the films exhibited high photoconductivity. B-doped CdS films were prepared by adding boric acid (H3BO3) to the starting solution. The grain size of the B-doped CdS films decreased as the molar ratio H3BO3:CdCl2 increased. The dark electrical resistivity of the B-doped CdS exhibited a minimum value of about 10(2) OMEGA cm at a molar ratio of 0.01 and then increased with further increase in the molar ratio.