Electric properties of chemically deposited lithium doped cadmium sulphide films

Electrical properties of chemically deposited CdS and lithium doped CdS films have been investigated by using techniques of Photo-thermoelectric and Photo-Hall effects. Dark electron densities are independent of temperature between 100 and 330°K because of shallow donors and quasi-intrinsic behaviour is apparent above 330°K. Electron density and mobility in these films have been measured as a function of temperature under strong photoexcitation. The electron mobility is found to be thermally activated with energies 0.2 and 0.22 eV for CdS:Li and CdS films respectively. The Hall mobility and electron density in these films have also been measured as a function of temperature under strong photoexcitation and found that both the free carrier density and mobility are reduced by the adsorption of oxygen, former by larger factor than the latter. The resulting very high electron density and very low electron mobility in the temperature region studied also indicate that most of the photoconductivity in chemically deposited films is caused by an increase in electron density due to photoexcitation.