Opto-electronic characteristics of chemically deposited cadmium sulphide thin films

Cadmium sulphide thin films showing photo-to-dark conductivity ratio up to 10⁹ and photoconductivity up to 3 Omega ^-1 cm^-1 for white illumination approximately 300 W m^-2 can be prepared from chemical baths containing thiourea and triethanolamine complex of cadmium ions. The photocurrent decay time depends on the bath temperature and the duration of storage and it ranges from a few seconds to 10⁴ s per decade. The optical transmission of the films also varies significantly: from about 10% to 70-80% (above the band-gap absorption), depending on the deposition conditions. The high activation energy approximately=1 eV for dark conductivity as well as the high photosensitivity suggest the nearly stoichiometric nature of the films. The implications of these characteristics in various opto-electronic applications are discussed.