Effect of annealing on properties of transparent conducting tin oxide films deposited by thermal evaporation

Abstract

The surface morphology, structural characteristics and optical properties of the transparent conducting SnO₂ films deposited by vapour deposition of SnCl₂.2H₂O on heated glass substrate have been evaluated by X-ray diffraction, scanning electron microscopy, EDAX analysis and spectro-photometric examination. The ‘as deposited’ films of tin oxide were found to be polycrystalline, adhesive and pin hole free. After annealing at a higher temperature, these films exhibited an improved crystalline surface morphology and also displayed random perforations having a dendrite structure. It is found that heat treatment of the ‘as deposited’ tin oxide films results in conversion of the SnO component into SnO₂ phase which resulted in a better transparency, larger crystallite size and reduced film thickness due to diffusion of tin into the matrix of the glass substrate thereby making the film more suitable for device applications. The increased porosity of ‘annealed’ films provides more surface area for use as sensors and also makes them less likely to fracture when used as high temperature electrodes.