Optical properties of vapour chopped and nonchopped tin oxide thin films

The optical properties of vapour chopped and nonchopped undoped tin oxide thin films (1000 Å) have been studied. The films were prepared by thermal oxidation (in air) of vacuum evaporated vapour chopped and nonchopped tin thin films. Effect of varied oxidation temperature and duration was also studied. As revealed by X ray diffraction studies, polycrystalline (both tetragonal and orthorhombic) films were obtained. The refractive indices ranged from 1.575 to 1.667 and 1.600 to 1.810 for nonchopped and vapour chopped tin oxide films respectively. Refractive index was found to increase after ageing. The effect was found lower in vapour chopped films. The direct band gap values ranged from 2.18 to 2.51 and 2.95 to 3.08 for nonchopped and vapour chopped tin oxide films respectively. The films showed high optical transmittance in the visible range of the spectrum. It was observed that the heat treatment process strongly affects the properties of the films. The vapour chopped tin oxide thin films showed higher packing density, optical band gap and refractive index with lower ageing effect.