Carrier conduction mechanisms of mesoporous titania thin films assessed by impedance spectroscopy

Abstract

The electrical characterization of porous titania thin films remain a subject of study due to the material interest in widespread device applications. Highly ordered mesoporous titania thin films prepared by sol-gel method under different post-synthesis annealing temperatures were prepared and characterized by impedance spectroscopy at different humidity conditions. Slow ionic and fast electronic processes have different responses to the humidity and are carefully studied by assessing their frequency dependence. Specific ionic conduction regimes are identified for different water content that strongly depend on the structural properties of the material such as porosity and pore size. Also, the analysis of the Warburg coefficient describes the response of the mass transport for the different materials characteristics. Highly porous materials obtained for elevated annealing temperatures do not saturate with water even at high humidities and present inferior ionic transport mechanism. By analyzing the impedance response at different bias voltage it was possible to discriminate the electronic conduction for the mesoporous layer and observe the electronic defects by reproducing a space charge limited current behavior.