Bilayer architecture for high-quality β-Ga2O3 thin films on Si

The growth of high-quality Ga2O3 thin films on silicon (Si) substrates using radio frequency (RF) magnetron sputtering has emerged as a critical research focus for fabrication of high-performance photoelectric devices. Previous studies have extensively documented the influence of sputtering parameters and post-annealing techniques on film characteristics. This report reveals that post annealing at 1000 °C not only induced α-to-β phase transition for single-layer Ga2O3 thin films, but also effectively increased crystallite and reduced microstrain in the films. However, thermal treatment counterintuitively increased the oxygen-vacancy (VO) concentration from 27.5% to 32.0%, as quantified by XPS analysis. The surface-absorbed oxygen component in the XPS spectra completely disappeared after annealing, indicating film densification. The increase in VO is attributed to large thermal mismatch-driven oxygen scavenging by the Si substrate. To overcome this detrimental annealing effect, a bilayer architecture consisting of an oxygen-deficient Ga2O3 bottom layer and an active Ga2O3 top layer was proposed. Remarkably, under the same annealing conditions, the bilayer film exhibited a decrease in VO concentration from 31.6% to 25.3%, a complete reversal of the trend. The oxygen-deficient layer simultaneously relieved interfacial stress and suppressed oxygen diffusion toward Si, as confirmed by cross-sectional EDS elemental mapping. Consequently, the bilayer film showed larger crystallites, lower microstrain, smoother surface morphology, and suppressed VO-relative photoluminescence. This work demonstrates that a rational bilayer design can transform a deleterious annealing effect into a beneficial one, providing a practical route to high-quality β- Ga2O3 thin films on Si.