Effect of substrate temperature on the electrical and optical properties of reactively evaporated tin oxide thin films.

Transparent conducting thin films of tin oxide have been prepared by reactively evaporating pure tin in oxygen atmosphere under controlled conditions. Variation in parameters such as sheet resistance, activation energy, optical band gap with variation in substrate temperature (100 to 275 degrees C) and annealing temperature (200 to 275 degrees C) were studied. The electrical, optical and structural properties of these films were measured to characterize the films. It is found that the activation energy of the film is decreased with increase in substrate temperature. The lowest activation energy of 0.268 eV was obtained for a film, deposited at a substrate temperature of 275 degrees C. The direct optical band gaps of the films at various substrate temperatures were determined and found to vary from 3.76 to 3.97eV. A conductivity of 1.8x10(-3) Omega m and a transmittance of more than 85% in visible region was obtained in the optimized conditions. It is observed from the XRD results that the films are polycrystalline. From SEM photograph, the grain size of tin oxide thin film annealed for 30 min at 275 degrees C is found to be 19.5 nm.