Structure-property relationships and mobility optimization in sputtered La-doped BaSnO3 films: Toward 100cm2V−1s−1 mobility

Abstract

The wide band gap semiconducting perovskite $\mathrm{BaSn}{\mathrm{O}}_{3}$ is of high current interest due to outstanding room temperature mobility at high electron density, fueled by potential applications in oxide, transparent, and power electronics. Due in part to a lack of lattice-matched substrates, $\mathrm{BaSn}{\mathrm{O}}_{3}$ thin films suffer from high defect densities, however, limiting electron mobility. Additionally, the vast majority of $\mathrm{BaSn}{\mathrm{O}}_{3}$ thin film research has focused on pulsed laser deposition or molecular beam epitaxy. Here, we present an exhaustive optimization of the mobility of ${\mathrm{Ba}}_{0.98}{\mathrm{La}}_{0.02}\mathrm{Sn}{\mathrm{O}}_{3}$ films grown by a scalable, high-throughput method: high-pressure-oxygen sputter deposition. Considering target synthesis conditions, substrate selection, buffer layer structure, deposition temperature, deposition rate, thickness, and postdeposition annealing conditions, and by combining high-resolution x-ray diffraction, reciprocal space mapping, rocking curve analysis, scanning transmission electron microscopy, atomic force microscopy, and temperature-dependent electronic transport measurements, detailed understanding of synthesis-structure-property relationships is attained. Optimized room temperature mobility of $96\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\text{--}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\text{--}1}$ is achieved in vacuum-annealed $\mathrm{GdSc}{\mathrm{O}}_{3}$(110)/$\mathrm{BaSn}{\mathrm{O}}_{3}$(120 nm)/${\mathrm{Ba}}_{0.98}{\mathrm{La}}_{0.02}\mathrm{Sn}{\mathrm{O}}_{3}$(200 nm) heterostructures, as well as $92\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\text{--}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\text{--}1}$ on unbuffered substrates and $87\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\text{--}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\text{--}1}$ without postdeposition annealing. These results, including important trends in defect densities and a surprising dependence of mobility on lattice mismatch, substantially expand the understanding of the interplay between deposition conditions, microstructure, and transport in doped $\mathrm{BaSn}{\mathrm{O}}_{3}$ films, establishing competitive mobilities in films fabricated via a scalable, high-throughput, industry-standard technique.