Design and Simulation of a High-Performance GaN Vertical Merged P-i-N/Schottky (MPS) Diode with Multi-Drift-Layer and Field-Plate Termination

This paper presents the design, structural optimization, and two-dimensional (2D) technology computer-aided design (TCAD) simulation of a gallium nitride (GaN) vertical Merged P-i-N/Schottky (MPS) diode incorporating a multi-drift-layer doping profile, composite SiO2/Si3N4 passivation, and field-plate (FP) termination. The proposed device is constructed on an n+-GaN substrate with a three-sub-layer n-type drift region and a p-GaN/p+-GaN anode region. Systematic TCAD simulations are performed to investigate the dependences of key performance metrics—including knee voltage (Vknee), specific on-resistance (Ron), breakdown voltage (BV), reverse leakage current (Jleak), and Baliga’s figure of merit (BFOM)—on the Schottky metal work function, multi-drift-layer doping concentration, drift-layer thickness, Schottky-to-PN contact length ratio (γw), operating temperature, and reverse recovery switching transients. Results demonstrate that the MPS architecture effectively decouples forward conduction loss from reverse blocking capability, overcoming the conventional Ron–BV trade-off. The optimal doping profile (nmm = 2 × 1015, nm = 2 × 1015, n = 1 × 1016 cm−3) achieves a BFOM of ~31.97 GW·cm−2 with BV ≈ 5.98 kV and Ron ≈ 1.12 mΩ·cm2. Joint doping–thickness optimization further identifies a graded doping profile (nmm = 2 × 1015, nm = 5 × 1015, n = 1 × 1016 cm−3) combined with layer thicknesses (Tnmm, Tnm, Tn) = (4.49, 5, 20) μm as the overall optimum, achieving BFOM = 55.36 GW·cm−2 (BV = 6.61 kV, Ron = 0.79 mΩ·cm2)—a +73% improvement, governed by the punch-through/field-stop design principle. The optimal contact ratio of γw = 1.33 yields a BFOM of 38.71 GW·cm−2. Temperature analysis confirms a positive BV temperature coefficient due to drift-region-limited avalanche breakdown, and the BFOM improves monotonically from 33.31 to 37.82 GW·cm−2 between 200 K and 450 K. Mixed-mode switching simulations show that increasing γw substantially reduces reverse recovery charge (Qrr), demonstrating the strong potential of the proposed MPS diode for high-voltage, high-frequency, and high-temperature power electronic applications.