HfAlO_x/Al₂O₃ Bilayer Dielectrics for a Field Effect Transistor on a Hydrogen-Terminated Diamond

In this work, a hydrogen-terminated (H-terminated) diamond field effect transistor (FET) with HfAlO_x/Al₂O₃ bilayer dielectrics is fabricated and characterized. The HfAlO_x/Al₂O₃ bilayer dielectrics are deposited by the atomic layer deposition (ALD) technique, which can protect the H-terminated diamond two-dimensional hole gas (2DHG) channel. The device demonstrates normally-on characteristics, whose threshold voltage (V_TH) is 8.3 V. The maximum drain source current density (I_DSmax), transconductance (G_m), capacitance (C_OX) and carrier density (ρ) are -6.3 mA/mm, 0.73 mS/mm, 0.22 μF/cm² and 1.53 × 10¹³ cm^-2, respectively.