  Transparent conducting oxides (TCOs) and transparent oxide semiconductors
(TOSs) have become necessary materials for a variety of applications in the
information and energy technologies, ranging from transparent electrodes to
active electronics components. Perovskite barium stannate (BaSnO3), a new TCO
or TOS system, is a potential platform for realizing optoelectronic devices and
observing novel electronic quantum states due to its high electron mobility,
excellent thermal stability, high transparency, structural versatility, and
flexible doping controllability at room temperature. This article reviews
recent progress in the doped BaSnO3 system, discussing the wide physical
properties, electron-scattering mechanism, and demonstration of key
semiconducting devices such as pn diodes and field-effect transistors.
Moreover, we discuss the pathways to achieving two-dimensional electron gases
at the interface between BaSnO3 and other perovskite oxides and describe
remaining challenges for observing novel quantum phenomena at the
heterointerface.
