Microstructural evolution and electrical property of Ta-doped SnO₂ films grown on Al₂O₃(0001) by metalorganic chemical vapor deposition

Ta-doped tin oxide, SnO₂, films have been deposited using metalorganic chemical vapor deposition system on sapphire (0001) substrates in temperature range of 400-600°C. When Ta concentration is varied from 0 to 8.30 at.% in the films, the electrical resistivity is changed by three orders of magnitude where the minimum resistivity was observed at 1.35% of Ta. An increase in the carrier concentration is a dominant factor responsible for such a large decrease in the resistivity while improved crystalinity contributes to the improvement in the mobility among doped samples. Microstructural investigation revealed the Ta-doped film showed a clean epitaxial relationship of SnO₂(100)//Al₂O₃(0001) with SnO₂[100]//Al₂O₃〈12̄10〉 between the substrate and the film while undoped film had a weak epitaxial correlation with an extra epitaxial relationship of SnO₂(100)//Al₂O₃(0001) with SnO₂[010]//Al₂O₃〈11̄00〉.