Electronic conduction processes in Pt-doped tin oxide thin films prepared by RF magnetron sputtering

Thin films of Pt-doped SnO₂ were prepared by RF magnetron sputtering onto glass substrates maintained at room temperature. Gold electrodes were provided by conventional vacuum evaporation to form sandwich structures. X-ray diffraction measurements confirmed the films to be of an amorphous structure. Room temperature d.c. measurements showed a dominant Poole-Frenkel conduction process at low applied voltages, both under vacuum and in ambient air, but the results of the latter exhibited localized field enhancement caused by various adsorbed oxygen species. At higher voltages space-charge-limited conductivity was observed, with the temperature parameter characterizing the exponential trap distribution decreasing from approximately 1500 to 1050 K as a result of the oxygen adsorption. A.c. conductivity was characterized by an angular frequency, , dependence of the form ^s with an indexs < 1, and was associated with a relaxation process due mainly to a charge-carrier hopping mechanism. Both capacitance and loss tangent decreased with increasing frequency, in accordance with existing theory for samples provided with ohmic contacts.