Phase Competition and Rutile Phase Stabilization of Growing GeO ₂ Films by MOCVD

Rutile germanium dioxide (r-GeO2) is an ultrawide bandgap semiconductor with potential for ambipolar doping, making it a promising candidate for next-generation power electronics and optoelectronics. Growth of phase-pure r-GeO2 films by vapor phase techniques like metalorganic chemical vapor deposition (MOCVD) is challenging because of polymorphic competition from amorphous and quartz GeO2. Here, we introduce seed-driven stepwise crystallization (SDSC) as a segmented growth strategy for obtaining r-GeO2 films on r-TiO2 (001) substrate. SDSC divides the growth into repeated cycles of film deposition and cooling–heating ramps, which suppress the nonrutile phases. We demonstrate continuous, phase-pure, partially epitaxial r-GeO2 (001) films of thickness ∼2 μm exhibiting X-ray rocking curves with a full-width at half-maximum of ∼597 arcsec. We discuss the underlying mechanisms of phase selection during SDSC growth. SDSC-based growth provides a generalizable pathway for selective vapor-phase growth of metastable or unstable phases, offering opportunities for phase-selective thin-film engineering.