  Transparent oxide semiconductors (TOSs) showing both high visible
transparency and high electron mobility have attracted great attention towards
the realization of advanced optoelectronic devices. La-doped BaSnO3 (LBSO) is
one of the most promising TOSs because its single crystal exhibits a high
electron mobility. However, in the LBSO films, it is very hard to obtain high
mobility due to the threading dislocations, which are originated from the
lattice mismatch between the film and the substrate. Therefore, many
researchers have tried to improve the mobility by inserting a buffer layer.
While the buffer layers increased the electron mobilities, this approach leaves
much to be desired since it involves a two-step film fabrication process and
the enhanced mobility values are still significantly lower than single crystal
values. We show herein that the electron mobility of LBSO films can be improved
without inserting any buffer layers if the films are grown under highly
oxidative ozone (O3) atmospheres. The O3 environments relaxed the LBSO lattice
and reduced the formation of Sn2+ states, which are known to suppress the
electron mobility in LBSO. The resultant O3-LBSO films showed improved mobility
values up to 115 cm2 V-1 s-1, which is among the highest in LBSO films on
SrTiO3 substrates and comparable to LBSO films with buffer layers.
