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 Al 2 O 3 gate dielectric deposited by atomic layer deposition (ALD). A threshold voltage of +3 V and an on/off ratio of 4 × 10 6 were obtained, demonstrating excellent subthreshold region characteristics. These results were achieved using non-polar m -plane GaN, Al 2 O 3 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 Al 2 O 3 and m -plane GaN was measured using the photo assisted capacitance–voltage method, showing a D it of (1–2) × 10 12 cm -2 eV -1 . These results indicate the potential of Al 2 O 3 deposited by ALD on m -plane GaN for power switching devices.