Effect of Sn-doping content on the electrical and optical properties of ITO films by colloid method

Transparent conductive ITO films (5 wt%similar to 20wt% Sn-doped) were fabricated on soda lime float glass substrate by a colloid technique. The colloidal solutions were prepared from indium metal ingots and hydrous tin (IV) chloride. The electrical and optical properties of the ITO films were investigated by using the four-probe instrument and UV-VIS spectrophotometer. The results indicate that the ITO thin films containing 10 wt% Sn showed a minimum sheet resistance of 153 Omega/square, and the high transparent ITO thin films have been obtained in visible region. X-ray diffraction measurements were performed to determine the crystallinity of the ITO films to be polycrystalline with a cubic bixbyite structure. The lattice distortion of ITO films has been discussed based on their own XRD data respectively with tin doping concentration. The results indicate that the free carriers of these ITO films are attributed to the oxygen vacancies mostly. Linear simulation on absorptance near optical absorption edge of the ITO films indicates that the transition from valance band to conduction band is a direct transition. It was found that the optical band gap of the ITO thin films is dependent on the tin doping concentration and increases with increasing Sn content up to 15 wt%. The optical band gap of 15 wt% Sri content ITO films showed the maximal value of 3.65 eV, and after that it started to decrease.