Enhancement-Mode m-plane AlGaN/GaN Heterojunction Field-Effect Transistors with +3 V of Threshold Voltage Using Al₂O₃ Deposited by Atomic Layer Deposition

Enhancement-mode m-plane AlGaN/GaN heterojunction field-effect transistors were fabricated with an Al₂O₃ gate dielectric deposited by atomic layer deposition (ALD). A threshold voltage of +3 V and an on/off ratio of 4×10⁶ were obtained, demonstrating excellent subthreshold region characteristics. These results were achieved using non-polar m-plane GaN, Al₂O₃ as a gate dielectric, and a recessed-gate structure. The devices exhibited 138 mA/mm of maximum drain–source current at a gate–source voltage (V_gs) of +7 V and 45 mS/mm of maximum transconductance at V_gs=+5 V. The interface state density (D_it) of Al₂O₃ and m-plane GaN was measured using the photo assisted capacitance–voltage method, showing a D_it of (1–2)×10¹² cm^-2 eV^-1. These results indicate the potential of Al₂O₃ deposited by ALD on m-plane GaN for power switching devices.