Extreme Enhancement-Mode Operation Accumulation Channel Hydrogen-Terminated Diamond FETs with Vₜₕ < -6V and High On-Current

In this work we demonstrate a new Field Effect Transistor device concept based on hydrogen-terminated diamond (H-diamond) that operates in an Accumulation Channel rather than Transfer Doping regime. Our FET devices demonstrate both extreme enhancement-mode operation and high on-current with improved channel charge mobility compared to Transfer-Doped equivalents. Electron-beam evaporated Al₂O₃ is used on H-diamond to suppress the Transfer Doping mechanism and produce an extremely high ungated channel resistance. A high-quality H-diamond surface with an unpinned Fermi level is crucially achieved, allowing for formation of a high-density hole accumulation layer by gating the entire device channel which is encapsulated in dual-stacks of Al₂O₃. Completed devices with gate/channel length of 1 μ m demonstrate record threshold voltage $< -6 V$ with on-current $> 80 mA/mm$. Carrier density and mobility figures extracted by CV analysis indicate high 2D charge density of ~ 2 × 10¹² cm⁻² and increased hole mobility of 110 cm² /V · s in comparison with more traditional Transfer-Doped H-diamond FETs. These results demonstrate the most negative threshold voltage yet reported for H-diamond FETs and highlight a new strategy for the development of high-performance power devices that better exploit diamond's intrinsic dielectric properties and high hole mobility.