【Domestic News】Progress in the Research of Heteroepitaxy ε-Ga₂O₃ MOSFET Devices of Sun Yat-sen University

1、Heteroepitaxial ϵ−Ga₂O₃ MOSFETs on a 4-inch Sapphire Substrate with a Power Figure of Merit of 0.29 GW/cm²

      We have designed and fabricated a high-voltage metal-oxide-semiconductor field effect transistor (MOSFET) based on heteroepitaxial ε−Ga₂O₃. The high-quality unintentionally-doped (UID) ε−Ga₂O₃ film was grown by metalorganic chemical vapor deposition (MOCVD) on a 4-inch sapphire substrate. Through an optimized fluorine-plasma treatment process, we achieved high-density surface doping with a carrier sheet density (ns) exceeding 10¹⁴cm⁻² and mobility of 32 cm²/V⋅s. We proposed a dual-density channel design for the ε,Ga₂O₃ MOSFETs, which involved high-density doping in the access region to reduce the parasitic resistance and low-density doping under the gate to ensure device pitch-off. This concept was verified using TCAD simulation before device fabrication. The fabricated ε−Ga₂O₃ MOSFETs, with a gate-to-drain spacing (L_GD) of 10[ιm, exhibited a high breakdown voltage (V_br) of 2.85kV and a specific on-resistance (R_on,sp) of 27.6 mΩ⋅cm², yielding a power figure of merit (PFOM) of 0.29 GW/cm². This PFOM value is the highest reported value for heteroepitaxial Ga₂O₃ devices and among the best in homoepitaxial β−Ga₂O₃ lateral FETs.

2、Demonstration of High-Current E-Mode MOSFETs Using Heteroepitaxial ε-Ga₂O₃ on 4H-SiC Substrates

      High-current enhancement mode (E-mode) metal-oxide-semiconductor field effect transistors (MOSFETs) have been demonstrated using heteroepitaxial ε-Ga₂O₃ on 4H-SiC substrates. The devices featured an unintentionally-doped (UID) channel and ultra-highly conductive access regions, which were realized by a selective-area fluorine-plasma surface doping process. In the access regions, a high sheet carrier concentration ( ns) exceeding 3×10¹⁴ cm⁻² combined with a mobility of 47.1 cm²/V ⋅ s was achieved, significantly reducing the parasitic resistance. The fabricated E-mode MOSFET with a channel length (L_CH) of 2 μm exhibited a high maximum drain current density ( I_DS, max) of 209 mA/mm, a positive threshold voltage (V_th) of 2.7 V, a large peak transconductance ( G_{m, max}) of 42 mS/mm, and a high on/off current ratio ( I_on / I_off) exceeding 10⁷ . These competitive performance metrics are mainly attributed to the low parasitic resistance in the access regions and the high thermal conductivity of the 4H-SiC substrate, highlighting the great potential of heteroepitaxial ε-Ga₂O₃-on-4H-SiC MOSFETs for high-power and high-frequency applications.

3、Up to 3.7 A Operation of E-mode MOSFET based on Heteroepitaxial ε-Ga₂O₃

      Ultra-wide bandgap Gallium oxide (Ga₂O₃) has emerged as a promising candidate for next-generation
high-power electronic devices due to its exceptional material properties. Among its polymorphs, εGa₂O₃, the second most stable phase, exhibits unique advantages such as high-quality heteroepitaxial growth and strong polarization effects, making it particularly attractive for advanced device applications. In prior work, we demonstrated the successful fabrication of heteroepitaxial ε-Ga₂O₃ MOSFETs on sapphire substrates using metal-organic chemical vapor deposition (MOCVD) combined with a fluorine plasma surface doping technique. While recent research has predominantly focused on achieving high power figures of merit (PFOM) and exploring novel device architectures, the realization of large-area devices capable of sustaining high output currents remains critical for practical applications. However, the development of large-area Ga₂O₃ transistors is hindered by challenges such as non-uniform material growth and process variability. In this study, we present an enhancement-mode (E-mode) ε-Ga₂O₃ MOSFET achieving a record output current of 3.7 A, underscoring its potential for high-power applications.

4、Monolithic Integration of Enhancement- and Depletion-mode MOSFETs Based on Heteroepitaxial ε-Ga₂O₃ for Power ICs

      This work demonstrates the monolithic integration of enhancement-mode (E-mode) and depletion mode (D-mode) metal-oxide-semiconductor field effect transistors (MOSFETs) using a selective-area fluorine-plasma surface doping process on heteroepitaxial ε-Ga₂O₃ grown on sapphire substrates. The E-mode MOSFET achieves a maximum drain current density (IDS, max) of 105 mA/mm, a positive threshold voltage (V_th) of 4.28 V and an on/off current ratio (ION/IOFF) of ~10⁸. Direct coupled FET logic (DCFL) inverters were designed and fabricated, with the load/driver ratio (β) optimized by employing a wider gate design for the E-mode devices. This optimization enhances logic voltage swings and noise margins while reducing transition voltage regions. The optimized DCFL ε-Ga₂O₃ inverter exhibits logic low and logic high noise margins of 3.17 V and 3.96 V, respectively, a logic voltage swing of 8.96 V, a switching threshold of 4.31 V, and a voltage gain of 10.4 at a supply voltage of 9 V. These results validate the feasibility of monolithic integration of DCFL circuits based on heteroepitaxial ε-Ga₂O₃, presenting a promising solution for ultra-wide bandgap power integrated circuits (ICs).

 [1] Deke Zeng, Shengheng Zhu, Tiecheng Luo, Weiqu Chen, Zimin Chen, Yanli Pei, Gang Wang, and Xing Lu, “Heteroepitaxial epsilon-Ga2O3 MOSFETs on a 4-inch Sapphire Substrate with a Power Figure of Merit of 0.29 GW/cm2,” in 2024 36th International Symposium on Power Semiconductor Devices and ICs (ISPSD), Jun. 2024, pp. 192–195. doi: 10.1109/ISPSD59661.2024.10579602.

[2] Shengheng Zhu, Linxuan Li, Tiecheng Luo, Weiqu Chen, Chenhong Huang, Xifu Chen, Zhanyun Huang, Zimin Chen, Yanli Pei, Gang Wang, and Xing Lu, “Demonstration of High-Current E-Mode MOSFETs Using Heteroepitaxial ε-Ga2O3 on 4H-SiC Substrates,” IEEE Electron Device Lett., vol. 46, no. 5, pp. 721–724, May 2025, doi: 10.1109/LED.2025.3553520.

[3] DRC2025  (Not yet published)

[4] ISPSD2025（Not yet published）