Hybrid Molecular Beam Epitaxy of Germanium-Containing Oxides

Wide bandgap and high carrier mobility are two important materials characteristics for transparent conducting oxides and power device applications. Germanium-containing oxides such as SrGeO₃ and rutile GeO₂ meet both these requirements according to ab initio calculations. Predicted room-temperature mobilities exceed those of the well-known alkaline earth stannates such as BaSnO₃ and SrSnO₃. In this talk, we present the first demonstration of hybrid molecular beam epitaxy (MBE) growth of Ge-based oxides including perovskite SrGe_1-xSn_xO₃ and rutile Ge_1-xSn_xO₂. By combining high-resolution X-ray diffraction, scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and first-principles calculations, we demonstrate the successful growth of phase-pure, epitaxial, and coherent SrSn_1-xGe_xO₃ films on GdScO₃ (110) substrates up to x = 0.16 and of coherent Ge_1-xSn_xO₂ films on TiO₂ (001) with x = 0.54. These findings confirm the viability of the hybrid MBE method for the growth of germanium-containing oxides and open the door to further research on high-quality germanate films.