Dopant incorporation into TiO2 semiconductor materials for optical, electronic, and physical property enhancement: doping strategy and trend analysis

Doping of semiconductor materials can significantly alter the characteristics of the intrinsic semiconductors. The titanium dioxide (TiO2) has been doped with a variety of dopants to yield enhanced optical, electronic, and mechanical properties. Such dopants in the original lattice of TiO2 produce defect sites with segregation and accumulation of ions on the grain boundaries. The segregation of ions results in the decreased conductivity of the TiO2. Aside from the ion segregation, the diffusion of ions into the TiO2 may subsequently alter the grain boundaries arrangement by either increasing or reducing the barrier height. The ability to tailor the crystalline arrangement is highly dependent on the nature of the dopant employed. Therefore, it is important to understand the roll of the dopants and control the doping process in order to modify the grain boundary and thus band gap structure of the doped TiO2. This article provides a comprehensive review of the TiO2 doping with four different types of dopants in view of their impact on optical, electronic, and mechanical properties in order to obtain optimized characteristics. Significant application of doped TiO2 as a photocatalyst and surge protector is briefly discussed on the basis of optical, electronic and mechanical properties.