【Member Papers】High-performance large-area β-Ga₂O₃ MIS trench Schottky barrier diodes with Al₂O₃/GaON interfacial insulators

      Researchers from Xiamen University have published a research article titled "High-performance large-area β-Ga₂O₃ MIS trench Schottky barrier diodes with Al₂O₃/GaON interfacial insulators" in Applied Physics Letters. By in-situ forming an ultrathin GaON layer on the trench sidewalls via an atomic nitrogen beam treatment, and combining 60°-tilted fins with an Al₂O₃/GaON interfacial double layer, the team achieved a low specific on-resistance of 7.3 mΩ·cm² with a high current/voltage capability of 10 A/670 V on a 1×2 mm² large-area device, while reducing the interface trap density by one order of magnitude.

Background

      β-Ga₂O₃ has emerged as a pivotal material for kilovolt-class power devices owing to its ultra-wide bandgap (~4.9 eV), high theoretical critical breakdown field (~8 MV/cm) and controllable n-type doping. Among β-Ga₂O₃ devices, vertical Schottky barrier diodes (SBDs) are highly competitive for high-power applications because of low conduction losses, high breakdown voltages and fast switching. However, conventional vertical SBDs suffer from localized breakdown caused by electric-field crowding at edges/corners and increased reverse leakage due to thermionic field emission at the Schottky contact. Trench MIS SBDs divert the peak field into the bulk semiconductor via a dielectric layer, yet local electric-field crowding still occurs at trench bottom corners, and sub-surface defects introduced during fin etching exacerbate dielectric leakage. For switch devices requiring both high current and high voltage, scaling up the active area inevitably introduces more defects. Therefore, suppressing dielectric leakage at trench sidewalls and reducing interface defect density in large-area devices remain critical challenges.

Abstract

      In this work, the team fabricated a 1×2 mm² large-area Ni/Al₂O₃/GaON/β-Ga₂O₃ MIS trench SBD on a HVPE-grown β-Ga₂O₃ epitaxial wafer (550 μm (001) substrate with 5×10¹⁸ cm^-3 doping and a 10 μm drift layer with 2×10¹⁶ cm^-3 doping. An atomic nitrogen beam (OXFORD HD25; 300 W, 4 sccm N₂, 10^-2 Pa) was then irradiated onto the exposed trench sidewalls at room temperature for 2 h, in-situ forming an ultrathin GaON layer confirmed by HRTEM. The device with the GaON layer delivered a maximum forward current of ~10 A at V_F=9.5 V with R_on,sp of 7.3 mΩ·cm² (comparable to 6.7 mΩ·cm² for the reference), an ideality factor of 1.02, and a slightly increased turn-on voltage (0.72 to 0.75 V). Its breakdown voltage was 612–670 V, versus 365–407 V for the reference, with an I_on/I_off ratio above 10⁶ and a power figure of merit (V_BR²/R_on,sp) of 61.5 MW/cm², outperforming reported large-area (≥1×10^-2 cm²) β-Ga₂O₃ SBDs. Bias-stress measurements at -100 V for 1000 s confirmed stable operation. Temperature-dependent J-V-T analysis revealed that the reference device followed the Poole-Frenkel (PF) emission model, whereas the GaON-capped device showed weak temperature dependence and agreed well with the Fowler-Nordheim tunneling (FNT) model, indicating a leakage-mechanism transition from trap-assisted emission to tunneling. C-V measurements showed a positive flat-band shift from -0.2 to +5.6 V (N_ox ≈ 2.9×10¹² cm^-2), and the interface trap density D_it was reduced from 2×10¹² to 1.5×10¹¹ eV^-1·cm^-2，about one order of magnitude lower.

Highlights

      An in-situ trench-sidewall nitridation strategy using an atomic nitrogen beam: with the photoresist mask retained, only the trench inner walls are nitrided at room temperature to form an ultrathin GaON layer, without affecting the fin-top Schottky contact; the process is compatible with existing ICP etching and ALD.

      An Al₂O₃/GaON double-layer interfacial insulator: inserted between Al₂O₃ and β-Ga₂O₃, the GaON layer broadens the depletion region, suppresses trap-related charging, and reduces D_it from 2×10¹² to 1.5×10¹¹ eV^-1·cm^-2 (one order of magnitude).

      Co-optimized low conduction loss and high breakdown on a large area: a 1×2 mm² device achieves R_on,sp of 7.3 mΩ·cm², 10 A/670 V, an ideality factor of 1.02, and a PFOM of 61.5 MW/cm², outperforming reported large-area β-Ga₂O₃ SBDs.

      A reverse-leakage mechanism transition: the dominant leakage switches from temperature-sensitive Poole-Frenkel emission to weakly temperature-dependent Fowler-Nordheim tunneling, explaining the suppressed dielectric leakage and elevated breakdown voltage.

Conclusion

      In summary, large-area (1×2 mm²) high-performance β-Ga₂O₃ trench SBDs featuring 60°-tilted fins and an ultrathin GaON interlayer have been demonstrated. The devices exhibit an ideality factor of 1.02, a low R_on,sp of 7.3 mΩ·cm², and a high current/voltage of 10 A/670 V. The GaON interlayer optimizes the trench MIS interface by passivating oxygen vacancies, introducing favorable fixed charge, and modifying the dominant leakage mechanism-collectively reducing dielectric leakage under reverse bias and raising the breakdown voltage. These results demonstrate that the GaON layer is an effective approach for realizing next-generation β-Ga₂O₃ SBDs toward high-voltage power rectification.

Project Support

      This work was supported by the Shenzhen Science and Technology Program (Grant No. JCJYJ20240813145617023) and the National Natural Science Foundation of China (Grant No. 62171396).