【Member Papers】1.75-kV Vertical β-Ga₂O₃ Schottky Barrier Diodes with Room-Temperature Ohmic Contact Formation by a Thin ITO Interlayer

      Researchers from the Ningbo Institute of Materials Technology and Engineering have published a dissertation titled " 1.75-kV Vertical β-Ga₂O₃ Schottky Barrier Diodes with Room-Temperature Ohmic Contact Formation by a Thin ITO Interlayer" in Applied Surface Science.

Background

      β-Ga₂O₃ (Beta-gallium oxide) has attracted considerable research interest for high-voltage and high-frequency power electronic applications, owing to its ultra-wide bandgap of 4.8 eV and a large breakdown strength of 8 MV/cm. The theoretical Baliga's figure of merit (BFOM) for β-Ga₂O₃ is approximately 3400, which is much larger than SiC and GaN. This superior BFOM indicates its strong potential for power devices, since it enables a favorable trade-off between higher breakdown voltage (V_br) and lower specific on-resistance (R_on,sp). Furthermore, the availability of commercially viable melt-grown bulk substrates, combined with well-established n-type doping techniques, positions β-Ga₂O₃ as a competitive candidate for high-quality homoepitaxial growth and large-scale device fabrication.

Abstract

      Developing cost-effective Ohmic contacts with ultralow contact resistance and minimal degradation on the drift layer is highly desired for high-performance β-Ga₂O₃ power devices. In this letter, we demonstrate a 1.75-kV vertical Schottky barrier diode (SBD) based on a lightly doped β-Ga₂O₃  single-crystal substrate with Ohmic contacts sputtered at room temperature. The construction of β-Ga₂O₃ SBDs with a SiO₂ field-plate structure achieves a Schottky barrier height of 0.93 eV and a breakdown voltage of 1.75 kV, but suffers from large contact resistance on the cathode side with a direct Ti/Au bilayer electrode. The incorporation of a 20-nm-thick ITO interlayer between the β-Ga₂O₃  drift layer and Ti/Au electrodes facilitates Ohmic contact formation that exhibits a specific contact resistivity of 2.6 ×10^-5 Ω·cm² and an ideality factor of 1.10. This substantially reduces the specific on-resistance (R_on,sp) of the β-Ga₂O₃  SBDs by nearly two orders of magnitude from 1580 mΩ·cm² to 26 mΩ·cm². The use of a thin and degenerately doped ITO interlayer is critical to induce abrupt band bending and construct a narrow depletion region for field-emission-dominated tunneling, thus forming a more ideal Ohmic contact. The room-temperature Ohmic contact strategy is expected to facilitate industry-level device application of β-Ga₂O₃ power devices.

Highlights

      A low-resistance Ohmic contact is realized on lightly doped β-Ga₂O₃ substrate by room-temperature sputtered ITO interlayer.

      The 20 nm ITO interlayer reduces the specific on-resistance by nearly two orders of magnitude while maintaining a high breakdown voltage of 1.75 kV.

      The ITO interlayer enables efficient field-emission-dominated carrier tunneling by inducing abrupt band bending and narrow depletion region.

Conclusion

      We have demonstrated a 1.75-kV vertical β-Ga₂O₃ substrate-based Schottky barrier diode with low Ohmic contact resistivity enabled by introducing a 20-nm degenerately doped ITO interlayer sputtered at room temperature. The thin and degenerately doped ITO interlayer induces strong band bending and a narrow depletion region, enabling field-emission-dominated tunneling and more efficient carrier transport. This approach effectively overcomes the large contact resistance with lightly doped β-Ga₂O₃ and Ti/Au, leading to a low Ohmic contact resistivity of 2.6 ×10^-5 Ω·cm² at the cathode. The R_on,sp of the vertical β-Ga₂O₃ SBD with 20-nm ITO interlayer is substantially reduced by nearly two orders of magnitude from 1580 mΩ·cm² to 26 mΩ·cm², while a Schottky barrier height of 0.93 eV is simultaneously maintained. This room-temperature Ohmic contact strategy provides a practical and scalable route toward high-performance and industry-relevant β-Ga₂O₃ power device applications.

Project Support

      This work was supported by the National Natural Science Foundation of China (Grant No. 62204244) and the Zhejiang Provincial Natural Science Foundation of China (Grant No. LQ23F040003). Part of the research was supported by Ningbo Yongjiang Talent Introduction Programme (Grant No. 2021A-046-C).