High-quality bulk β-Ga ₂ O ₃ single crystals have been grown by optimized edge-defined film-fed growth (EFG) method.

In this Letter, we report on establishing high performance hysteresis-free and μs-switching depletion/enhancement-mode (D/E-mode) β-Ga₂O₃ heterojunction (HJ) field effect transistors (FETs) with the state-of-art power figure-of-merit (P-FOM). By optimizing the p-NiO_x/n-Ga₂O₃ interface and n-Ga₂O₃ recess technology, a positive threshold voltage (V_T) as well as a low subthreshold slope can be substantially achieved. The trade-off between the on-resistance (R_on,sp) and breakdown voltage (BV) is improved by incorporation of T-shaped NiO_x, resulting in the R_on,sp of 6.24/13.75 mΩ cm² and the breakdown voltage (BV) of 2145/1977 V for D/E-mode devices and yielding the P-FOM = BV²/R_on,sp to be 0.74/0.28 GW/cm². To the best of all the authors' knowledge, those P-FOMs are the highest ones among all published lateral Ga₂O₃ FETs. Benefited from the high-quality interface, a negligible hysteresis of 4 mV and μs-switching can be essentially achieved, showing the great promise of Ga₂O₃ HJ-FETs for future high-power, high-efficiency, and high-speed power electronics.

In this letter, MOS capacitors with bilayer dielectrics consisted of large bandgap Al₂O₃ and high-k HfO₂ in different stacking order on n-type doped (100) β-Ga₂O₃ are investigated through C − V and J − V measurement. The C − V measurement results reveal that incoming HfO₂ makes both bilayer structures attain an increasing dielectric constant, which means a better gate control ability in transistors comparing with single Al₂O₃. Additionally, the interface state density extracted by high-low frequency capacitance method suggests that Al₂O₃/(100)β-Ga₂O₃ with no treatment shows a comparative D_it value (8.0 × 10¹² cm^-2eV^-1 to 2.2 × 10¹¹ cm^-2eV^-1) with HfO₂/(100)β-Ga₂O₃ (8.4 × 10¹² cm^-2eV^-1 to 1.0 × 10¹¹ cm^-2eV^-1) in energy range of 0.2 to 0.9 eV. Furthermore, HfO₂/Al₂O₃/Ga₂O₃ showing a bigger forward breakdown voltage of 11.0 V than 7.8 V of Al₂O₃/HfO₂/Ga₂O₃ demonstrates that inserted larger bandgap Al₂O₃ insulator between Ga₂O₃ semiconductor and high-k HfO₂ dielectric can prevent gate leakage current more effectively. Accordingly, the HfO₂/Al₂O₃/Ga₂O₃ can enhance gate control ability with an acceptable gate breakdown voltage and become an alternative choice in the design of the gate structure for Ga₂O₃ MOSFETs.