【Member Papers】Xidian University --- 1.96 kV p-Cr₂O₃/β-Ga₂O₃ heterojunction diodes with an ideality factor of 1.07

      Researchers from the Xidian University have published a dissertation titled "1.96 kV p-Cr₂O₃/β-Ga₂O₃ heterojunction diodes with an ideality factor of 1.07" in Applied Physics Letters.

Project Support

      We would like to thank the National Natural Science Foundation of China (NSFC) for their support and funding (Grant No. 62222407). This work was also supported by the Guangdong Basic and Applied Basic Research Foundation (Grant No. 2023B1515040024).

Background

      Beta-gallium oxide (β-Ga₂O₃), with its ultra-wide bandgap (UWBG) of ~4.8 eV, high critical breakdown field (E_c) of 8 MV/cm, and significant Baliga’s figure of merit (BFOM) of 3200, along with controllable n-type doping concentrations, has emerged as a promising material for power semiconductor applications. It is theoretically poised to surpass silicon carbide (SiC) and gallium nitride (GaN) in performance. The ability to manufacture large-area native substrates using cost-effective crystal growth methods further enhances β-Ga₂O₃’s potential for future commercialization. However, the lack of p-type Ga₂O₃ has hindered the development of high-power bipolar devices, limiting the implementation of commercial deployment strategies. Devices based on p-type terminations generally rely on heterojunction (HJ) structures, with alternative p-type materials including Cu₂O, NiO, IrO_X, Cr₂O₃, and p-Si. Breakdown voltage (BVs) ranging from 1 kV to over 10 kV have been reported in Ga₂O₃ lateral and vertical diodes, as well as lateral MOSFETs. Among these, NiO has drawn considerable attention for its use in β-Ga₂O₃ diodes and MOSFETs due to its promising potential. However, its thermal stability remains a major challenge.

Abstract

      In this Letter, we report on a p-Cr₂O₃/n-Ga₂O₃ vertical heterojunction diode (HJD) with a kilovolt-level breakdown voltage (BV). The chromium oxide (Cr₂O₃) film was deposited via magnetron sputtering, with a controlled thickness of approximately 20 nm and a hole concentration of 1 × 10¹⁶ cm⁻³. High-resolution transmission electron microscopy of the p-Cr₂O₃ film reveals a polycrystalline lattice structure. At room temperature, the 40 μm radius HJD exhibits a turn-on voltage (V_on) of 1.7 V, a specific on-resistance (R_{on, sp}) of 4.6 mΩ·cm², and a BV of 1.96 kV. Notably, the ideality factor (η) of the HJD is 1.07, the closest to 1 among all reported Ga₂O₃ HJDs, indicating a high-quality interface at the p-Cr₂O₃/n-Ga₂O₃ HJ. Additionally, the BVs at 75 and 150 °C are 1.63 and 1.4 kV, respectively, demonstrating the promising potential of p-Cr₂O₃/n-Ga₂O₃ HJDs for high-temperature and high-power applications.

Conclusion

      In summary, we have fabricated p-Cr₂O₃/n-Ga₂O₃ HJDs with kilovolt-level BVs and an exceptionally low η\neth of 1.07. The 40μm radius diode achieved a P-FOM of 835 MW/cm², with a R_on,sp of 4.6 mΩ·cm², a BV of 1.96 kV, and a low I_R < 10 μA/cm². At 75 and 150 °C, the BV values were 1.63 and 1.40 kV, respectively. Outstanding HJ contact interface, crystalline material quality, and high-temperature reliability make p-Cr₂O₃ a promising material for Ga₂O₃-based medium-voltage and high-voltage devices.