Effect of the VI/III ratio on the growth of κ -Ga2O3 films via MOCVD

The intrinsic spontaneous polarization of orthorhombic κ-Ga2O3 offers unique functionalities for advanced devices, yet a processing window for growing the pure κ-phase remains elusive. Herein, the effect of the oxygen-to-gallium precursor molar ratio (VI/III ratio) on the quality of κ-Ga2O3 films was systematically investigated via metal-organic chemical vapor deposition. Increasing the VI/III ratio from 500 to 1000 induced a transformation from an amorphous film to a mixed-phase layer containing both β- and κ-Ga2O3. At an optimized VI/III ratio of 2000, the competing β-phase was effectively inhibited. Concurrently, the resulting κ-Ga2O3 film demonstrated superior quality, with a low rocking curve FWHM of 0.66°, fewer oxygen vacancy defects, and reduced residual carbon. A continuous increase in the VI/III ratio beyond 2000, however, led to the recurrence of the β-phase. Furthermore, this phase evolution behavior during Ga2O3 growth is consistent with predictions from heteroepitaxial growth dynamics and classical nucleation theory. The establishment and elucidation of these critical parameters enable a viable route toward growing high-quality, single-phase κ-Ga2O3.