Band gap and mobility of epitaxial perovskite BaSn1−xHfxO3 thin films

A wide band-gap perovskite oxide $\mathrm{BaSn}{\mathrm{O}}_{3}$ is attracting much attention due to its high electron mobility and oxygen stability. On the other hand, $\mathrm{BaHf}{\mathrm{O}}_{3}$ was recently reported to be an effective high-$k$ gate oxide. Here, we investigate the band gap and mobility of solid solutions of $\mathrm{BaS}{\mathrm{n}}_{1\ensuremath{-}x}\mathrm{H}{\mathrm{f}}_{x}{\mathrm{O}}_{3}$ ($x=0\ensuremath{-}1$) (BSHO) as a basis to build advanced perovskite oxide heterostructures. All the films were epitaxially grown on MgO substrates using pulsed laser deposition. Density functional theory calculations confirmed that Hf substitution does not create midgap states while increasing the band gap. From x-ray diffraction and optical transmittance measurements, the lattice constants and the band-gap values are significantly modified by Hf substitution. We also measured the transport properties of $n$-type La-doped BSHO films $[(\mathrm{Ba},\mathrm{La})(\mathrm{Sn},\mathrm{Hf}){\mathrm{O}}_{3}]$, investigating the feasibility of modulation doping in the $\mathrm{BaSn}{\mathrm{O}}_{3}/\mathrm{BSHO}$ heterostructures. The Hall measurement data revealed that, as the Hf content increases, the activation rate of the La dopant decreases and the scattering rate of the electrons sharply increases. These properties of BSHO films may be useful for applications in various heterostructures based on the $\mathrm{BaSn}{\mathrm{O}}_{3}$ system.