Tantalum incorporation in TiO2 based transparent conductive thin films

The growing number of applications of transparent electrodes in optoelectronic devices drives the need for novel cost-efficient transparent conductive materials. The epitaxial films of TiO2 doped with Nb or Ta show electrical resistivity values comparable to those of the best In2O3:Sn and ZnO:Al films. However, it is still challenging to achieve low electrical resistivity in polycrystalline TiO2-based films. In order to address this problem, we studied the films formed on glass substrates without heating by DC magnetron sputtering of reduced TiO2:Ta ceramic targets followed by vacuum annealing. It was crucial to use a plasma feedback system in order to enable a fine tuning of the oxygen supply into Ar and O2 gas mixture during the growth. This approach yielded the films with optical transittance above 85%, electrical resistivity in the range of 10-3  cm and free electron mobility of 8 cm²/Vs. The electrical activation of Ta dopant was above 60% that is substantially higher than that of Al in ZnO.