Semiconducting tin oxide thin films on glass
Stannic oxide films on glass, deposited by th ·spray technique, are found to be n-type semiconductors. The large carrier concentration (~10¹⁹/cm³) of these films causes the donor level to blend into an impurity band. Annealing the stannic oxide film results in a diffusion of glass components on the film surface which is also accompanied by the increase in the sheet resistance. Donors such as antimony, phosphorus and tellurium raise the infrared absorption and carrier concentration and lower the sheet resistance and extrinsic activation energy. At higher concentrations (≥ 5-10 mole%) the impurities do not act like dopants, instead they become the bulk part of the film which causes an increase in the sheet resistance, infrared transmittance and the extrinsic gap energy. Addition of acceptors like indium and thallium shows an increase in the sheet resistance resulting from the neutralization of the conduction electrons. This also causes the impurity band to shrink and show an increase in the extrinsic activation energy and near infrared transmission.