【Domestic Papers】Source-Field-Plated β-(AlₓGa₁₋ₓ)₂O₃ MOSFET with Breakdown Voltage Over 7kV

      Researchers from the Hebei Semiconductor Research Institute and University of Science and Technology of China have published a dissertation titled "Source-Field-Plated β-(Al_xGa_1-x)₂O₃ MOSFET with Breakdown Voltage Over 7kV" in Micro and Nanostructures.

Project Support

      This work was supported by the National Key Research and Development Program of China under Grant 2024YFE0205300.

Background

      Beta-Ga₂O₃, an ultra-wide bandgap (UWBG) semiconductor, has emerged as a promising candidate for next-generation power electronics due to its high critical electric field (∼8 MV/cm) and Baliga figure of merit (BFOM) surpassing conventional materials like SiC and GaN [1,2]. However, the relatively low thermal conductivity and limited bandgap tunability of pure β-Ga₂O₃ restrict its performance in high-power and high-frequency applications. To address these limitations, β-(Al_xGa_1-x)₂O₃/β-Ga₂O₃ heterostructures have been extensively explored, leveraging the alloying of Al₂O₃ with β-Ga₂O₃ to achieve tunable bandgaps (4.8–6.2 eV for Al content x = 0–0.71), enhanced BFOM [[3], [4], [5], [6]] and higer thermal conductivity (up to 30.4 W cm⁻¹ K⁻¹) [7]. These heterostructures enable superior electrostatic control and carrier confinement, making them ideal for high-electron-mobility transistors (HEMTs) and other power devices.

Abstract

      In this letter, β-(Al_xGa_1-x)₂O₃ MOSFET with high breakdown voltage are demonstrated. A 150-nm β-(Al_0.14Ga_0.86)₂O₃ epitaxial layer and a 30-nm Ga₂O₃ buffer were grown on Fe-doped semi-insulating β-Ga₂O₃ substrate by metal-organic chemical vapor deposition. The epitaxial thin film exhibits relatively high crystalline quality, with a FWHM of 54 arcsec in the XRD rocking curve and a surface roughness of 2.3 nm. A T-shaped gate and source-field-plated are fabricated to mitigate electric field crowding. The β-(Al_0.14Ga_0.86)₂O₃ MOSFET with source-drain length of 84 μm demonstrates breakdown voltage of 7.2 kV, combined with the specific on-resistance of 3534 mΩ cm², corresponding to power figures of merit of 14.7 MW/cm². The results highlight the potential of β-(Al_xGa_1-x)₂O₃ for high-voltage power electronics.

Highlights

      ● Addressed challenges in epitaxial growth, achieving 150 nm β-(Al_0.14Ga_0.86)₂O₃ layers.

      ● Implemented T-shaped gate and source-field-plated structures to enhance performance.

      ● Achieved 7.2 kV breakdown voltage in β-(Al_0.13Ga_0.87)₂O₃ MOSFETs.

      ● Demonstrated power figure of merit up to 14.7 MW/cm² for high-voltage applications.

Conclusion

      This study demonstrates the fabrication and characterization of the SFP β-(Al_0.14Ga_0.86)₂O₃ MOSFETs with a breakdown voltage exceeding 7 kV. The epitaxial growth of 150 nm β-(Al_0.14Ga_0.86)₂O₃ layers on Fe-doped β-Ga₂O₃ substrates via MOCVD enabled the realization of devices with enhanced breakdown characteristics. The introduction of T-shaped gate and SFP structures significantly suppressed the peak electric field, contributing to the high breakdown voltages of 5.1 and 7.2 kV for devices with L_GS of 44 and 84 μm, respectively. The devices exhibited relatively high on-resistance (1013 mΩ cm² and 3534 mΩ cm²) and non-ideal transfer characteristics, characterized by low on/off ratios and elevated off-state leakage currents. These issues can be attributed to the leakage path between epitaxial layer and substrate; besides, the high surface roughness could induce interface state formation at the channel/gate-dielectric interface, resulting in elevated leakage current. Future work will focus on optimizing the epitaxial growth process to reduce surface roughness and interface state density, as well as implementing advanced passivation techniques to mitigate parasitic conduction paths. Overall, this research highlights the potential of β-(Al_0.14Ga_0.86)₂O₃ for high-voltage power electronics, while identifying key areas for improvement to enhance device performance and reliability.