Enhanced breakdown voltage in GaN vertical trench MOSFETs through mesa-trench field balancing and mesa shielding ring structure

Abstract In this work, we report the design and optimization of GaN vertical trench metal–oxide–semiconductor field-effect transistors using technology computer-aided design simulation, focusing on the enhancement of off-state device breakdown voltage (BV). First, the impact of structural parameters including mesa depth ( D _mesa ), the distance between the mesa and source ( L _MS ), and the thickness of the SiO ₂ passivation layer, on the breakdown performance is investigated in detail. It is found that the BV exhibits a nonlinear dependence on these parameters due to electric field coupling effects. The optimal combination of parameters leads to a well-balanced electric field distribution between the trench and mesa corners, which effectively enhances the BV. Second, a p-GaN mesa shielding ring (MSR) structure is proposed to further enhance the breakdown performance. The doping concentration of the MSR plays a critical role in improving the BV by (1) suppressing the peak electric field at the trench corner and (2) creating a more uniform electric field distribution around the mesa corner. By properly optimizing the MSR doping concentration, the electric field can be effectively redistributed, mitigating premature breakdown. This design significantly enhances the reverse blocking capability of the device. As a result, with an MSR concentration of 7 × 10 ¹⁷ cm ⁻³ , the device with a 15 μ m-thick drift layer achieves a high BV of 2321 V, and a high Baliga’s figure of merit of 2.319 GW cm ⁻² . This optimized electric field engineering around the mesa and trench substantially improves breakdown performance, making the device more suitable for high-voltage power applications.