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, rho, of the samples has been found to decrease markedly with increasing thickness, but only for d < 100 nm. The behaviour of rho d versus d was found to fit properly with the Fuchs and Sondheimer relation with parameters rho(o) = 4.95 x 10(6) Omega cm and mean free path, l = 310 +/- 2 nm. The log rho 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. (c) 2005 Elsevier B.V. All rights reserved.