【Mmeber Papers】Nitrogen-graded electrostatic compensation for normally-off β-Ga₂O₃ planar-gate current-aperture vertical electron transistors

      Researchers from Nanjing University、Suzhou Institute of Nano-Tech and Nano-Bionics and The University of Hong Kong have published a dissertation titled " Nitrogen-graded electrostatic compensation for normally-off β-Ga₂O₃ planar-gate current-aperture vertical electron transistors " in Applied Physics Letters.

Background

      Gallium oxide (Ga₂O₃) is an emerging ultra-wide bandgap semiconductor for next-generation high-voltage and high-power electronics. In particular, recent demonstrations of megawatt-class pulsed switching at 1kV and 1kA highlight its unique capability for pulse power applications. Nevertheless, the absence of reliable p-type Ga₂O₃ fundamentally limits the realization of bipolar device architectures, making normally-off operation in vertical β-Ga₂O₃ transistors primarily dependent on electrostatic channel engineering.

Abstract

     Gallium oxide (Ga₂O₃) vertical transistors are promising for next-generation high-voltage power electronics, yet achieving normally-off operation remains challenging due to insufficient electrostatic depletion of the surface channel and severe gate-edge electric-field crowding. Here, we demonstrate a controlled transition from depletion-mode to enhancement-mode operation in all-ion-implanted planar-gate β-Ga₂O₃ current-aperture vertical electron transistors, a gate region-damage-minimized architecture that avoids gate-trench etching. A multi-step nitrogen-graded current-blocking layer (CBL) simultaneously engineers channel electrostatics and high-voltage electric-field distributions by introducing vertically distributed charge compensation. This graded profile enhances subsurface channel depletion, suppresses parallel conduction, and redistributes the peak electric field from the gate edge toward the buried CBL. As a result, the enhancement-mode device achieves a threshold voltage of 4.17V, a breakdown voltage of 1310 V, a specific on-resistance of 19.1 mΩcm², and an ultralow threshold hysteresis of 52 mV. These results establish nitrogen-graded electrostatic compensation as an effective strategy for simultaneously realizing normally-off operation and enhanced voltage-blocking capability in vertical β-Ga₂O₃ transistors.

Conclusion

      In summary, a controlled transition from depletion-mode to enhancement-mode operation has been demonstrated in planar-gate β-Ga₂O₃ CAVETs through nitrogen-graded implantation engineering. The graded compensation profile establishes a partially depleted channel, suppresses deep parallel conduction, and enhances gate electrostatic control, thereby shifting the threshold voltage from −13.38 to 4.17 V. Simultaneously, the nitrogen-graded current-blocking layer redistributes the electric field away from the gate edge, mitigating field crowding and promoting a more favorable bulk-field distribution. As a result, the optimized device achieves a breakdown voltage of 1310 V, a specific on-resistance of 19.1mΩcm², and an ultralow threshold- voltage hysteresis of 52mV. These results highlight the dual role of nitrogen-graded implantation in simultaneously engineering channel electrostatics and high-voltage electric-field distributions, providing an effective pathway toward high-performance normally-off vertical β-Ga₂O₃ power transistors.

Project Support

      This work was supported by the National Natural Science Foundation of China (Nos. 62425403 and 62234007) and the Jiangsu Provincial Science and Technology Major Project (No. BG2024030).