Seed-Driven Stepwise Crystallization (SDSC) for Growing Rutile GeO₂ Films via MOCVD

Germanium dioxide (r-GeO2) is an emerging ultrawide bandgap (UWBG) semiconductor with significant potential for power electronics, thanks to its ambipolar doping capability. However, phase segregation during metal–organic chemical vapor deposition (MOCVD) on substrates like r-TiO2 has posed a significant barrier to achieving high-quality films. Conventional optimization of growth parameters has been found so far not very insufficient in film coverage and film quality. To address this, a seed-driven stepwise crystallization (SDSC) growth approach was employed in this study, featuring multiple sequential deposition steps on a pretemplated substrate enriched with r-GeO2 seeds. The process began with an initial 180 min deposition to establish r-GeO2 nucleation seeds, followed by a sequence of shorter deposition steps (90, 60, 60, 60, 60, and 60 min). This stepwise growth strategy progressively increased the crystalline coverage to 57.4, 77.49, 79.73, 93.27, 99.17, and ultimately 100%. Concurrently, the crystalline quality improved substantially, evidenced by a ∼30% reduction in the Full Width at Half Maximum (FWHM) of X-ray diffraction rocking curves. These findings demonstrate the potential of the SDSC approach for overcoming phase segregation and achieving high-quality, large-area r-GeO2 films.