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 o nto glass substrates maintained at room temperature. Gold electrodes w ere provided by conventional vacuum evaporation to form sandwich struc tures. X-ray diffraction measurements confirmed the films to be of an amorphous structure. Room temperature d.c. measurements showed a domin ant Poole-Frenkel conduction process at low applied voltages, both und er 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, wi th the temperature parameter characterizing the exponential trap distr ibution decreasing from approximately 1 500 to 1050 K as a result of t he oxygen adsorption. A.c. conductivity was characterized by an angula r frequency, omega, dependence of the form omega(s) with an index s < 1, and was associated with a relaxation process due mainly to a charge -carrier hopping mechanism. Both capacitance and loss tangent decrease d with increasing frequency, in accordance with existing theory for sa mples provided with ohmic contacts.