Characterization of transparent semiconducting cobalt doped titanium dioxide thin films prepared by sol–gel process

Abstract

We report the synthesis of TiO2 and Cobalt doped TiO2 (CoT) thin films by sol–gel process and the influence of dopant incorporation onto the structural, optical and electrical properties of the host lattice is analysed. The XRD analysis shows the reduction of crystal size with increasing Co dopant concentration. FESEM analysis confirmed the agglomeration of particles in CoT films upon Co doping. Vibrational modes of the anatase phase of TiO2 along with the weak intensity peaks for cobalt doped samples have been identified in Raman spectroscopy. The average transmittance of the films decreases with an increase in the surface roughness and decrease in the crystallinity of the films. Red shift in the energy gap is observed with the increase in the cobalt dopant concentration due to the defect state formation in the band gap. Surface roughness of the samples increases from 0.646 to 6.486 nm. Room temperature photoluminescence (PL) measurements confirmed the increase of F+ colour centres in cobalt doped films. I–V measurements indicate the ohmic behaviour of TiO2 films with the increase of resistivity from 2.707 × 103 to 7.699 × 103 Ω-cm for the samples with cobalt content. The increase in resistivity due to dopant incorporation is significant from its application point of view and is evaluated using grain boundary model. It was observed that by increasing cobalt doping level in TiO2 the surface trap density increases and implicitly the conductivity decreases.