High-mobility rutile SnO₂ epitaxial films grown on (1−100) α-Al₂O₃

Abstract

Tin dioxide (SnO2) is a semiconductor with significant potential for use in the electronic industry, including sensors, transparent electrodes, and thin film transistors among other purposes. To realize these applications, the synthesis of high-quality thin films is a prerequisite. Here, we show the epitaxial growth of SnO2 films on (1100) α-Al2O3 (M-sapphire) by pulsed laser deposition method. The epitaxial relationship was clarified to be (001)[100]SnO2 || (1100)[0001] α-Al2O3 with 4-fold symmetry, consistent with that grown on (001) TiO2 single crystal. Orthorhombic distortion was absent, possibly owing to a combination of high strain relaxation due to a large lattice mismatch along [0001] α-Al2O3, coupled with a negligible mismatch-induced strain absence along [1120] α-Al2O3. The mobility increases up to ∼57 cm2 V−1 s−1 with increasing film thickness while the density of states (DOS) effective mass keeps a constant around the theoretical value of ∼0.3 m0. Furthermore, the trend of carrier concentration versus mobility is analogous to those of single crystal SnO2, thereby indicating the applicability of M-sapphire substrates in facilitating the epitaxial growth of high-quality SnO2 films.