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

Metal-semiconductor (MES) field-effect transistors (FETs) and metal oxide-s emiconductor (MOS) FETs are fabricated using p-type conductive layers on hy drogen-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 chan ging the electronegativity of the gate metal. The MOSFETs, using evaporated SiOx as gate insulators, operate in depletion mode. The best transconducta nce of each type of FET exceeds 10 mS mm(-1) with a gate length of 3-7 mu m . The DC performance of the diamond FETs is evaluated by two-dimensional de vice simulations, varying the distribution depth of the acceptors. In the s imulations, a distribution depth of less than 1 nm or the two-dimensional a cceptor distribution on the surface reproduces well the actual DC character istics. In this case, the hole concentration at a depth of 10 nm is decreas ed by three orders of magnitude as compared to that at the surface. This th in 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 leng ths such as 50 nm. Microfabrication technology on hydrogen-terminated diamo nd surfaces may give rise to a new field of nanoscale devices. (C) 1999 Els evier Science S.A. All rights reserved.