Fabrication and characterization of sputtered titanium dioxide films

TiO2 thin films were prepared under various conditions by using a reactive RF sputtering technique. The structural, optical and electrical characteristics of the films have been investigated. All as-deposited films were amorphous. After annealing at T > 673 K, the crystallinity of the observed tetragonal anatase phase appeared improved. The optical band gap, determined by using Tauc plot, has been found to amount to 3.38 0.03 and 3.21 0.03 eV for the direct and indirect transition, respectively. Also the complex optical constants for the wavelength range 300–2500 nm are reported. Using the two-point probe technique, the dark resistivity has been measured as a function of the film thickness, d. The resistivity, r, of the samples has been found to decrease markedly with increasing thickness, but only for d < 100 nm. The behaviour of rd versus d was found to fit properly with the Fuchs and Sondheimer relation with parameters ro = 4.95 106 V cm and mean free path, l = 310 2 nm. The log r versus 1/T curves show three distinct regions with values for the activation energy of 0.03 0.01, 0.17 0.01 and 0.50 0.02 eV, respectively.