Characterization and Mobility Analysis of Normally off Hydrogen‐Terminated Diamond Metal–Oxide–Semiconductor Field‐Effect Transistors

Hydrogen‐terminated diamond (H‐diamond) metal–oxide–semiconductor field‐effect transistors (MOSFETs) are fabricated, and a partial C–O channel is formed by UV‐ozone treatment of the H‐diamond surface to help realize normally off devices. The first parameterization of the vertical‐field ( F eff )‐dependent effective hole mobility ( μ eff ) in a normally off diamond FET is conducted using the fabricated MOSFETs with a gate length of 40 μm fat field‐effect transistors (FATFET). The FATFET with a threshold voltage of −0.69 V shows a low on‐resistance of 475.1 Ω mm and a record high drain current of −3.8 mA mm −1 for normally off H‐diamond MOSFETs with gate lengths over 20 μm. The extracted μ eff ranges from 127 cm 2 (V s) −1 (at V GS  = −4.5 V) to 276 cm 2 (V s) −1 (at V GS  = −1.5 V). Both μ eff versus F eff and μ eff versus V GS relations can be well fitted by the semiempirical formulas used for silicon counterparts. The resulting low‐field mobility without vertical‐field degradation for the two relations is 376 cm 2 (V s) −1 and 418 cm 2 (V s) −1 , respectively. The origin of this difference is also given.