Sn-assisted epitaxial growth of high-crystallinity κ/ε-Ga2O3 on sapphire (0001) by low-pressure Mist-CVD

The ultrawide-bandgap gallium oxide (Ga2O3) polymorphs have opened frontiers in high-power electronics and multifunctional devices. Among these, the orthorhombic phase (commonly referred to as κ-Ga2O3 or ε-Ga2O3, hereafter denoted as ε-Ga2O3 in this work) stands out with its exceptional spontaneous polarization and large piezoelectric coefficients, positioning it as a prime candidate for next-generation high-electron mobility transistors and radio frequency resonators. However, the epitaxial growth of high-quality ε-Ga2O3 films remains challenging due to interfacial transition layers and limited crystallographic control. Herein, we demonstrate a pioneering Sn-assisted low-pressure mist chemical vapor deposition technique that enables the growth of single-phase ε-Ga2O3 films on c-plane sapphire substrates with unprecedented crystalline quality. The resulting films exhibit a remarkably narrow x-ray diffraction rocking curve (full width at half maximum, FWHM = 0.08°) while achieving atomically smooth surfaces (root mean square, RMS roughness = 1.51 nm). Key innovations include the complete suppression of interfacial transition layers through Sn-mediated nucleation and the realization of true layer-by-layer growth under optimized low-pressure conditions. This synergistic approach combines the inherent cost-effectiveness of Mist-CVD with enhanced crystallographic precision, establishing a viable pathway for industrial-scale production of ε-Ga2O3-based quantum well devices and polarization-engineered heterostructures.