High-preformance diamond surface-channel field-effect transistors and their operation mechanism

Metal-semiconductor (MES) field-effect transistors (FETs) and metal oxide-semiconductor (MOS) FETs are fabricated using p-type conductive layers on hydrogen-terminated diamond surfaces. The FETs exhibit complete channel pinch-off and drain-current saturation. Both enhancement-mode and depletion-mode MESFETs are realized, the threshold voltage of which is controlled by changing the electronegativity of the gate metal. The MOSFETs, using evaporated SiO_x as gate insulators, operate in depletion mode. The best transconductance of each type of FET exceeds 10 mS mm^-1 with a gate length of 3-7 μm. The DC performance of the diamond FETs is evaluated by two-dimensional device simulations, varying the distribution depth of the acceptors. In the simulations, a distribution depth of less than 1 nm or the two-dimensional acceptor distribution on the surface reproduces well the actual DC characteristics. In this case, the hole concentration at a depth of 10 nm is decreased by three orders of magnitude as compared to that at the surface. This thin surface channel realizes enhancement-mode operation in MESFETs. Hydrogen-terminated diamond surfaces can already be equipped with FETs with shallow junction depths of less than 10 nm, which is necessary for short gate lengths such as 50 nm. Microfabrication technology on hydrogen-terminated diamond surfaces may give rise to a new field of nanoscale devices.