【Member Papers】First Demonstration of CuCrO₂/β-Ga₂O₃ p-n Heterojunction Diode With High Breakdown Voltage and Low Leakage Current

      Researchers from the Xiamen University have published a dissertation titled "First Demonstration of CuCrO₂/β-Ga₂O₃ p-n Heterojunction Diode With High Breakdown Voltage and Low Leakage Current" in IEEE Transactions on Electron Devices.

Project Support

      This work was supported in part by the National Natural Science Foundation of China under Grant 62171396 and in part by Shenzhen Science and Technology Program under Grant JCYJ20240813145617023.

Background

      Ultrawide bandgap (UWB) semiconductors are capable of sustaining higher critical fields, allowing for higher blocking voltages at lower resistances, and therefore, they hold great promise of better conversion efficiency and maintaining higher voltages for modern industrial and electronics products. β-gallium oxide (β-Ga₂O₃) has a bandgap of 4.8 eV, a high critical field of 8 MV/cm, and a high Baliga’s figure of merit (3400), making β-Ga₂O₃ power devices enjoy predominant strength in UWB semiconductor devices. The past five years have seen great efforts made to improve device performance and push the limits in such power devices as Schottky barrier diodes (SBDs) and metal–oxide–semiconductor field-effect transistors (MOSFETs). Theoretically, β-Ga₂O₃ SBDs can achieve an ultrahigh breakdown voltage (V_br) up to 8.32 kV while maintaining a low specific ON-resistance (R_on,sp) of 5.24 mΩ· cm². However, the current performance of the device, especially the representative device parameter power figure of merit (PFOM), remains significantly below the expected material limits.

Abstract

      We demonstrate for the first time a high-performance CuCrO₂/β-gallium oxide (β-Ga₂O₃) p-n heterojunction diode (HJD) with high breakdown voltage and low leakage current. Without any composite termination structure, the CuCrO₂/β-Ga₂O₃ HJD reached a high breakdown voltage of 1.46 kV with low leakage current of 10 μA/cm², which is almost four times improvement over the traditional β-Ga₂O₃ Schottky barrier diodes (SBDs). Simultaneously, the HJD exhibited a turn-on voltage of 1.62 V and a relatively low specific on-resistance of 5.36 mΩ⋅cm², yielding a power figure of merit (PFOM) of 0.4 GW/cm². The measurements of temperature-dependent current density–voltage (J–V) showed that the HJD exhibited good thermal reliability and carrier transport got increasingly dominated by interface recombination at higher temperatures. Furthermore, a type-II band alignment was identified in the CuCrO₂/ β-Ga₂O₃ heterojunction with a valence band offset of 2.22 eV and a conduction band offset of 0.45 eV, respectively, as determined by the X-ray photoelectron spectroscopy (XPS) characterizations. Technology computer aided design (TCAD) simulations indicated that the depletion region primarily extended into the Ga₂O₃ epitaxial region due to the full depletion of the p-CuCrO₂ layer, which contributes to a more uniform distribution of electric field and higher breakdown voltages. Evidently, these results indicate that the formation of heterojunction by introducing a p-CuCrO₂ layer is feasible and effective for achieving high-performance and improving manufacturing of β-Ga₂O₃ bipolar power diodes.

Conclusion

      In summary, employing 40-nm p-type CuCrO₂ layer with high hole concentration via the sputtering process, the vertical CuCrO₂/β-Ga₂O₃ p-n HJD has been demonstrated with high V_br of 1455 V. Compared to the SBD of the same size, R_on,sp only saw slight increase to 5.36 m·cm² , yielding a high PFOM of 0.4 GW/cm² . In addition, the temperature dependence of J–V characteristics indicated that the HJD has shown good thermal stability and interface recombination mechanism was enhanced in forward conduction. A type-II band alignment was identified in the CuCrO₂/β-Ga₂O₃ heterojunction with a valence band offset of 2.22 eV and a conduction band offset of 0.45 eV, benefiting designing future optical and electronic devices. The high breakdown voltage of the HJD was primarily due to the depletion region extended into the β-Ga₂O₃ epitaxial layer, which then contributes to a more uniform distribution of electric field and higher breakdown voltages. This work provides an ideal design strategy based on β-Ga₂O₃ bipolar devices to enhance the performance of all β-Ga₂O₃-based p-n diodes. Hopefully, by employing field plates or other termination technologies, a higher V_br is possible in the future.