High mobility approaching the intrinsic limit in Ta-doped SnO₂ films epitaxially grown on TiO₂ (001) substrates

Achieving high mobility in SnO₂, which is a typical wide gap oxide semiconductor, has been pursued extensively for device applications such as field effect transistors, gas sensors, and transparent electrodes. In this study, we investigated the transport properties of lightly Ta-doped SnO₂ (Sn_1-xTa_xO₂, TTO) thin films epitaxially grown on TiO₂ (001) substrates by pulsed laser deposition. The carrier density (n_e) of the TTO films was systematically controlled by x. Optimized TTO (x = 3 × 10^-3) films with n_e ~ 1 × 10²⁰ cm^-3 exhibited a very high Hall mobility (μ_H) of 130 cm²V^-1s^-1 at room temperature, which is the highest among SnO₂ films thus far reported. The μ_H value coincided well with the intrinsic limit of μ_H calculated on the assumption that only phonon and ionized impurities contribute to the carrier scattering. The suppressed grain-boundary scattering might be explained by the reduced density of the {101} crystallographic shear planes.