214 MW/cm2 vertical <i>β</i> -Ga2O3 UMOSFETs enabled by HF sidewall treatment

Vertical β-Ga2O3 U-shaped trench structures (UMOSFETs) incorporating current-blocking layers typically suffer from increased on-resistance, primarily caused by deep-level defect states in the trench sidewalls that trap free electrons. In this study, the hydrofluoric acid (HF) sidewall treatment was introduced prior to gate dielectric deposition to modify the trench surface. This process enables the effective incorporation of fluorine atoms into the sidewall region, increasing the electron concentration and mitigating the compensation associated with deep acceptor levels from heavy nitrogen implantation. As a result, the forward conduction is improved. In addition, the HF treatment partially passivates surface and interface traps and provides a mild polishing effect, which slightly reduces surface roughness. These changes help suppress interface scattering and further enhance carrier transport. The fabricated vertical β-Ga2O3 UMOSFETs achieved a specific on-resistance of 6.0 mΩ cm2, a channel mobility of 19.1 cm2/V s, and a breakdown voltage of 1132 V. These results demonstrate that HF sidewall treatment provides a simple and efficient surface engineering approach for significantly enhancing the conduction performance and overall electrical characteristics of β-Ga2O3 UMOSFETs.