787-V GaN-on-Si Quasi-Vertical Trench MOSFET with Thick Bottom SiO₂

Owing to the lack of high-quality thick oxides formed by in situ oxidation, gallium nitride (GaN) trench MOSFETs are subject to pronounced electric field crowding at the trench bottom corners, which limits their off-state blocking capability. In this work, based on a GaN-on-silicon (Si) epitaxy, a thick SiO2 deposition process was applied to the trench bottom. This approach effectively redistributes the electric field, shifting the field concentration from the dielectric/GaN corners into a 300-nm SiO2 layer. This terminal structure makes the device breakdown more dependent on the intrinsic blocking capability of GaN rather than on premature electric-field crowding at the trench bottom corners. As a result, a state-of-the-art breakdown voltage of 787 V was achieved for the quasi-vertical structure on a heterogeneous substrate. Furthermore, the device with the thick bottom oxide also exhibits a high threshold voltage (Vth) of 7.6 V, an on/off ratio exceeding 107 , a specific on-resistance (Ron,sp ) of 3.9 mΩ · cm2 , and a Baliga's figure of merit (BFOM) of 159 MW/cm2 , demonstrating the promise of this process for GaN-on-Si trench MOSFETs in future high-power electronics.