【Member Papers】Ultrathin Interlayer Engineered β-Ga₂O₃ Hybrid Schottky-Junction Rectifiers for High-Power Hard-Switching Conversion

      Researchers from the Xidian University and China Resources Microelectronics Limited have published a dissertation titled "Ultrathin Interlayer Engineered β-Ga₂O₃ Hybrid Schottky-Junction Rectifiers for High-Power Hard-Switching Conversion" in IEEE Transactions on Power Electronics.

Background

      Power diodes are indispensable components in power electronic converters, where they are used for rectification, freewheeling, clamping, and protection. For high-voltage and high-power applications, a power diode must not only block high voltages and conduct large currents under static conditions, but also turn off safely and efficiently during hard commutation. Therefore, modern converters demand multiple simultaneous requirements, including low V_F, low R_on,sp, high BV, surge-current ruggedness, low Q_rr, soft recovery behavior, and converter-level high efficiency. The ultrawide-bandgap semiconductor β-Ga₂O₃ has emerged as a promising material platform for next-generation power rectifiers owing to its wide bandgap of approximately 4.8 eV, high predicted critical electric field, and availability of melt-grown substrates. Considerable progresses have been made in β-Ga₂O₃ diodes, ranging from high-voltage small-area devices for approaching material limits to large-area devices for practical current handling. Large-area Schottky barrier diodes (SBDs) offer low V_on and majority-carrier switching, whereas heterojunction (HJ) PN diodes provide stronger electrostatic blocking capability and improved high-voltage margins. However, these device categories generally emphasize different aspects of power conversion: SBDs favor fast recovery and low conduction loss, while junction-based diodes favor high blocking capability but may introduce additional stored charge and recovery loss. A device concept that can bridge these two operating regimes is therefore needed for high-voltage hard-switching converters.

Abstract

      Large-area β-Ga₂O₃ rectifiers have made substantial progress in static voltage blocking and current handling; however, converter applications also require controlled reverse recovery, surge-current ruggedness, and low-loss hard commutation. This paper investigates an ultrathin p-Cr₂O₃ interlayer design for vertical β-Ga₂O₃ rectifiers, in which the interlayer thickness tunes the anode transport from Schottky-dominated conduction toward junction-influenced operation. A series of devices with 0-, 5-, 10-, 15-, and 20-nm p-Cr₂O₃ interlayers shows that the 5-nm device operates in a hybrid Schottky–junction (HSJ) regime, improving reverse blocking while preserving low-voltage conduction. A 9 mm² and 5-nm p-Cr₂O₃/β-Ga₂O₃ diode with ion-implanted edge termination (ET) exhibits a turn-on voltage (V_on) near 1 V, a specific on-resistance (R_on,sp) of 8-9 mΩ·cm², and a breakdown voltage (BV) of approximately 1.8 kV. After packaging, the diode conducts 60 A at a forward voltage (V_F) of 10 V and withstands a 40 A surge current with 1.60-J absorbed energy. Under 30 A/400 V hard commutation, it shows a peak reverse-recovery current (IRRM) of 1.48 A, reverse-recovery time (t_rr) of 31.3 ns, reverse recovery charge (Q_rr) of 30.1 nC, and a softness factor of 3.44. Implemented in a boost converter, the diode delivers approximately 1.45 kW output power (P_out) with 98.6% efficiency.

Highlights

      The introduction of a 5 nm p-Cr₂O₃intermediate layer on the β-Ga₂O₃anode side forms a hybrid Schottky junction (HSJ) rectifier, achieving a balance between a low forward conduction voltage and a high reverse blocking capability.

      Following ion implantation of the edge terminals, the 9 mm² device exhibits an on-voltage of approximately 1 V, a specific on-resistance of 8–9 mΩ·cm², and a breakdown voltage of approximately 1.8 kV.

      The packaged device can conduct 60 A at a forward voltage of 10 V and withstand a surge current of 40 A, absorbing 1.60 J of energy.

      Under hard-switching conditions of 30 A/400 V, the reverse recovery time is 31.3 ns, the reverse recovery charge is 30.1 nC, the peak reverse recovery current is 1.48 A, and the softness factor is 3.44.

      In a boost converter, an output power of approximately 1.45 kW and a conversion efficiency of 98.6 per cent were achieved, demonstrating the device’s potential for application in high-power hard-switching power electronic systems.

Conclusion

      This paper demonstrates an ultrathin p-Cr₂O₃ interlayer approach for large-area β-Ga₂O₃ hybrid rectifiers. By comparing devices with 0-, 5-, 10-, 15-, and 20-nm p-Cr₂O₃ interlayers, the static characteristics reveal a thickness-dependent transition from Schottky-dominated behavior toward more junction-influenced operation. Among these designs, the 5-nm interlayer provides a balanced hybrid operating point that preserves low-voltage forward conduction while improving reverse-blocking capability. The large-area 9-mm² 5-nm p-Cr₂O₃/β-Ga₂O₃ HSJ diode with ion-implanted ET achieves a V_on of approximately 1 V, a R_on,sp of 8-9 mΩ·cm², and a BV of approximately 1.8 kV. After packaging, the device conducts up to 60 A and sustains a 40-A surge-current pulse with an extracted surge energy of 1.60 J. Under 30 A/400 V hard commutation, the packaged diode maintains a low I_RRM of 1.48 A, a t_rr of 31.3 ns, a Q_rr of 30.1 nC, and a softness factor S of 3.44. In boost-converter operation, the diode enables a P_out of approximately 1.45 kW with a calculated efficiency of 98.6%. These results indicate that ultrathin-interlayer engineering provides an effective route for balancing static blocking, high-current capability, and hard-commutation recovery behavior in large-area β-Ga₂O₃ rectifiers. The key design implication is that the interlayer should be sufficiently effective in enhancing blocking capability while remaining thin enough to avoid excessive V_F penalty and charge-storage effects associated with strongly junction-dominated operation.