Hybrid Molecular Beam Epitaxy of Epitaxial Rutile-(Ge,Sn)O₂ films

Ultra-Wide-Bandgap (UWBG) semiconductors have gained significant attention for high-power devices and ultraviolet applications. Among these materials, rutile germanium dioxide (r-GeO₂) has emerged as a promising UWBG semiconductor, showing ultra-wide bandgap ~ 4.7 eV and ambipolar dopability. Although various growth methods have been explored, molecular beam epitaxy (MBE) has proven effective for growing high structural quality thin films with low surface roughness. However, the volatility of GeO and comparable formation energies of the rutile and amorphous phases present challenges in achieving stoichiometric and phase-pure r-GeO₂ films. To address these issues, we have developed a hybrid MBE approach using a metal-organic chemical precursor for Ge. In this talk, we will present our results on growth of single crystalline, epitaxial (Ge, Sn)O₂ films on TiO₂ (110) with Ge content up to 73 at.%. Films show atomically smooth surface morphology as evidenced by RHEED and AFM images. The bandgap and dielectric properties of (Ge, Sn)O₂ films were investigated as a function of Ge composition. The role of surface energy, and epitaxial strain on r-GeO₂ will be also discussed.