Conductivity behaviour of Cr implanted TiO2

In its pure state rutile is an insulator with a 3 eV band gap. Its electrical conductivity, less than 10(-13) Omega(-1) cm(-1), can be enhanced up to more than 12 orders of magnitude by reduction or doping. In this work we study the doping of [0 0 1] TiO2 single crystals with chromium ions implanted with 140 keV at room temperature and fluences of the order of 10(17)-10(18) ions/cm(2). Implantation damage and damage recovery were accessed using the Rutherford backscattering technique in the channeling mode. Electrical resistivity measurements were performed as a function of temperature between 5 and 300 K. Upon implantation the implanted region becomes completely disordered and displays an enhanced electrical conductivity with a variable range hopping behaviour. After annealings at temperatures up to 1300 K, the lattice recovers and the implanted Cr moves out of the implanted region. The electrical conductivity behaviour changes from variable to fixed range hopping and after the 1300 K annealing becomes typical of a thermally activated semiconductor with 0.36 eV activation energy. (C) 2002 Elsevier Science B.V. All rights reserved.