  La-doped SrSnO3 (LSSO) is known as one of deep-ultraviolet (DUV)-transparent
conducting oxides with an energy bandgap of ~4.6 eV. Since LSSO can be grown
heteroepitaxially on more wide bandgap substrates such as MgO (Eg ~7.8 eV),
LSSO is considered to be a good candidate as a DUV-transparent electrode.
However, the electrical conductivity of LSSO films are below 1000 S cm^-1, most
likely due to the low solubility of La ion in the LSSO lattice. Here we report
that high electrically conducting (>3000 S cm^-1) LSSO thin films with an
energy bandgap of ~4.6 eV can be fabricated by pulsed laser deposition on MgO
substrate followed by a simple annealing in vacuum. From the X-ray diffraction
and the scanning transmission electron microscopy analyses, we found that
lateral grain growth occurred during the annealing, which improved the
activation rate of La ion, leading to a significant improvement of carrier
concentration (3.26 x 10^20 cm^-3) and Hall mobility (55.8 cm^2 V^-1 s^-1). The
present DUV-transparent oxide semiconductor would be useful as a transparent
electrode for developing optoelectronic devices, which transmit and/or emit
DUV-light.
