Abstract
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 (Sn1−xTaxO2, TTO) thin films epitaxially grown on TiO2 (001) substrates by pulsed laser deposition. The carrier density (ne) of the TTO films was systematically controlled by x. Optimized TTO (x = 3 × 10−3) films with ne ~ 1 × 1020 cm−3 exhibited a very high Hall mobility (μH) of 130 cm2V−1s−1 at room temperature, which is the highest among SnO2 films thus far reported. The μH value coincided well with the intrinsic limit of μH 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.
Highlights
Sintered pellets of transport properties of Sn1−xTaxO2 (TTO) with x = 3 × 10−4–1 × 10−2 were used as pulsed laser deposition (PLD) targets
Nominal x values were used to represent the chemical compositions of the films because stoichiometric transfer of Ta from the targets to the films has been reported for TTO films grown under a similar condition[23]
The base pressure of the PLD chamber was maintained at 3 × 10−9 Torr
Summary
TTO films with a thickness of 100–120 nm, with x = 3 × 10−5–1 × 10−2, were grown on TiO2 (001) substrates by pulsed laser deposition (PLD) with a KrF excimer laser. TTO films with x = 3 × 10−3 were grown (001)-, (101)-, and (110)-planes of TiO2, and m-, r-, and c-planes of Al2O3 substrates. The repetition rate and the fluence of the laser were set at 2 Hz and 1–2 J ∙ cm−2, respectively. The typical growth rate was 0.14–0.17 Å per shot.
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