The effect of annealing and layer numbers on the optical and electrical properties of cobalt-doped TiO2 thin films

• Published in: Materials research express 2019-10, Vol.6 (11)
• Main Authors: Mozaffari, Niloofar, Elahi, S Hossein, Parhizgar, Sara Sadat, Mozaffari, Nastaran, Elahi, Seyed Mohammad
• Format: Article
• Language: English
• Subjects: cobalt-doped TiO; electrical properties; optical properties; sol-gel method; spin-coating technique; thin films
• ISSN: 2053-1591
• DOI: 10.1088/2053-1591/ab4662

In this research, cobalt-doped TiO2 thin films were synthesized by sol-gel method using spin-coating technique. Spin-coating process was repeated 4 times to fabricate 1-, 2-, 3-, and 4-layer films. The 2-layer films were annealed at 523 K and 723 K for 60 min with the rate of 298 K min−1. The influence of multilayer deposition and annealing temperatures on the optical and electrical properties of cobalt-doped TiO2 thin films were investigated. Although transmission of films decreased with increasing the number of coated layers or annealing temperatures, but the transparency was above 60% in the visible region. The optical band gap (Eg) exhibited a decreasing trend with increasing the number of coated layers and temperatures, due to cobalt defects and oxygen vacancies, or formation of a new structure, while urbach energy is increased. Optical density of as-deposited films was calculated. With increasing the thickness at room temperature, conductivity of as-deposited films decreased, but it increased at higher fixed temperatures (such as 363.3 K). The investigation of electrical properties as a function of temperature indicated that conductivity of as-deposited and annealed films increased with rising temperatures which could be attributed to grain growth and electron-mobility enhancement. Activation energy (Ea) of virgin cobalt-doped TiO2 thin films decreased with increasing number of layers. However, annealed thin films had an increase trend in activation energy versus annealing temperatures. These results suggested that the number of coating layers and annealing temperatures influence on transmittance, absorbance, reflectance, optical band gap, urbach energy, conductivity and activation energy.