Deep-Recessed β-Ga₂O₃ Delta-Doped Field-Effect Transistors With In Situ Epitaxial Passivation

We introduce a deep-recessed gate architecture in <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga₂O₃ delta-doped field-effect transistors (FETs) for improvement in dispersion and breakdown properties. The device design incorporates an unintentionally doped (UID) <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga₂O₃ layer as the passivation dielectric. To fabricate the device, the deep-recess geometry was developed using BCl₃ plasma-based etching at ~5 W reactive ion etching (RIE) power to ensure minimal plasma damage. Etch damage incurred with plasma etching was mitigated by annealing in vacuum at temperatures above 600 °C. A gate-connected field-plate edge termination was implemented for efficient field management. Negligible surface dispersion with lower knee walkout at high <inline-formula> <tex-math notation="LaTeX">${V}_{{\text {DS}}}$ </tex-math></inline-formula>, and better breakdown characteristics compared to their unpassivated counterparts were achieved. A three-terminal OFF-state breakdown voltage of 315 V, corresponding to an average breakdown field of 2.3 MV/cm was measured. The device breakdown was limited by the field-plate/passivation edge and presents scope for further improvement. This demonstration of epitaxially passivated FET is a significant step for <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga₂O₃ technology since the structure simultaneously provides control of surface-related dispersion and excellent field management.