Unraveling\nthe Growth Dynamics of Rutile Sn<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub>O<sub>2</sub> Using\nTheory and Experiment

Rutile GeO<sub>2</sub> and related materials are attracting\ninterest\ndue to their ultrawide band gaps and potential for ambipolar doping\nin high-power electronic applications. This study examines the growth\nof rutile Sn<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub>O<sub>2</sub> films through oxygen-plasma-assisted hybrid molecular\nbeam epitaxy (hMBE). The film composition and thickness are evaluated\nacross a range of growth conditions, with the outcomes rationalized\nby using density functional theory calculations. We find that up to\n34% Ge can be successfully incorporated into Sn<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub>O<sub>2</sub>/r-Al<sub>2</sub>O<sub>3</sub> (<i>x</i> ≤ 0.34) at 600 °C.\nOur phase diagram calculations suggest that spinodal decomposition\noccurs at Ge concentrations exceeding 34%. However, the formation\nof a Ge-rich rutile phase is inhibited by amorphization of the Ge-rich\nfilm and volatility of GeO. We therefore speculate that maximizing\nthe Ge content requires higher Ge flux and more oxidizing environments,\nproviding insights into the growth mechanism of Sn<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub>O<sub>2</sub> and\npaving the way toward the synthesis of pure rutile GeO<sub>2</sub> films.