Effects of Substrate Polarity and Pre-Growth Treatments on Plasma-Assisted Molecular-Beam Epitaxy of β-Ga2O3 on 4° Off-Axis 4H-SiC

This study reports the growth and structural analysis of β-Ga2O3 films on 4° off-axis (000±1) Si- and C-face 4H-SiC substrates by plasma-assisted molecular-beam epitaxy (PAMBE). Pre-growth treatments of 4H-SiC substrates were conducted by employing: (I) unintentional oxygen exposure, (II) intentional Ga pre-exposure, (III) a Ga flash-off process followed by Ga pre-exposure, and (IV) intentional oxygen-plasma pre-exposure prior to β-Ga2O3 growth, which led to different growth behaviors. The intentional Ga pre-exposure and Ga flash-off followed by Ga pre-exposure treatments modified the initial Si-face surface condition and were consistent with the mitigation of oxygen-induced surface degradation, including possible SiOx-related effects. In contrast, unintentional oxygen exposure and intentional oxygen-plasma pre-exposure produced RHEED evolution consistent with substantial surface disordering and possible amorphous SiOx formation on the Si-face 4H-SiC substrate, leading to disordered nucleation and degraded film growth. Growth on the C-face 4H-SiC substrate resulted in more ordered β-Ga2O3 films, suggesting that the C-face surface is less susceptible to SiOx-related degradation under the present oxygen-containing growth environment. The combined in situ RHEED, AFM, and HRXRD results indicate that substrate polarity and pre-growth surface treatments strongly influence the initial nucleation, morphology, and crystalline quality of β-Ga2O3 films on 4H-SiC. These findings provide a useful strategy for controlling oxide film growth on easily oxidized substrates under oxygen environments.