Hybrid molecular beam epitaxy of germanium-based oxides

Germanium-based oxides such as rutile GeO₂ are garnering attention owing to their wide band gaps and the prospects of ambipolar doping for application in high-power devices. Here, we present the use of germanium tetraisopropoxide (GTIP), a metal-organic chemical precursor, as a source of germanium for the demonstration of hybrid molecular beam epitaxy for germanium-containing compounds. We use Sn_1-xGe_xO₂ and SrSn_1-xGe_xO₃ as model systems to demonstrate our synthesis method. A combination of high-resolution X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy confirms the successful growth of epitaxial rutile Sn_1-xGe_xO₂ on TiO₂(001) substrates up to x = 0.54 and coherent perovskite SrSn_1-xGe_xO₃ on GdScO₃(110) substrates up to x = 0.16. Characterization and first-principles calculations corroborate that germanium occupies the tin site, as opposed to the strontium site. These findings confirm the viability of the GTIP precursor for the growth of germanium-containing oxides by hybrid molecular beam epitaxy, thus providing a promising route to high-quality perovskite germanate films.