Simultaneous reduction of multi-dimensional defects in Sn-excess BaSnO3 epitaxial films induced by surface chemical reconstruction

Multi-dimensional defects created by thermodynamic and mechanical condition strongly limit electron mobility by the scattering of charged carriers in semiconducting ${\mathrm{BaSnO}}_{3}$ (BSO) epitaxial films. Here, we demonstrate that the density of both extended and point defects in heteroepitaxial BSO films can be decreased simultaneously by exploiting surface phase instability and a subsequent redistribution of cations at thermal treatment under different oxygen chemical potentials. By delicately controlling both cation ratio and ambient oxygen partial pressure $p$(${\mathrm{O}}_{2}$), distinct surface topography and cation redistribution (i.e., BaO segregation or SnO evaporation) were observed along with effective healing of extended defects. Simultaneous control of extended and point defects in La-doped ${\mathrm{BaSnO}}_{3}$ (LBSO) films during treatment under reducing atmosphere decreased their scattering of charged carriers and yielded an increase in room-temperature electron mobility ${\ensuremath{\mu}}_{\mathrm{e}}$ by $\ensuremath{\sim}104%\phantom{\rule{0.16em}{0ex}}(55--112\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1})$ in initially Sn-excess LBSO films as a result of a complex interplay with the removal of Sn-related species at the surface. Our finding suggests a versatile strategy to further enhance electron transport of perovskite-type stannate films by exploiting chemical heterogeneity on the surface interfacing with the $p$(${\mathrm{O}}_{2}$)-controlled ambient.