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

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 4.17 V, a breakdown voltage of 1310 V, a specific on-resistance of 19.1 mΩ cm2, 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.