It is presented the effect of the reactive and non-reactive sputtering preparation, as well as, the atomic composition on the electrical properties and conduction mechanisms. Depending on the preparation conditions, samples present ohmic, Poole-Frenkel and space charge limited current conduction behaviours, as well as several orders of magnitude in resistivity values. As it is reported, impurities and non-stoichiometry play a very important role in the conduction mechanism and therefore on the thin film resistivity. (C) 2003 Elsevier B.V. All rights reserved.