Control of normally on/off characteristics in hydrogenated diamond metal-insulator-semiconductor field-effect transistors

Abstract

Normally on/off operation in hydrogenated diamond (H-diamond) metal–insulator–semiconductor field-effect transistors (MISFETs) is reproducibly controlled by annealing at 180 °C. The transfer characteristics of the MISFETs reveal that the threshold gate voltage changes from 0.8 ± 0.1 to −0.5 ± 0.1 V after annealing, which indicates the MISFETs switch from normally on to normally off operation. Annealing also shifts the flat-band voltage in the capacitance–voltage curve of MIS capacitors from zero to −0.47 V. The mechanism behind the switch of normally on/off characteristics induced by annealing is explained by a change of transfer doping as follows. Adsorbed acceptors at the insulator/H-diamond interface allow the holes to accumulate in the H-diamond channel layer, so the MISFETs before annealing show normally on characteristics. Annealing causes loss of the adsorbed acceptors or provides compensatory positive charge in the insulator oxide, so the hole density in the H-diamond channel layer decreases markedly, and the MISFETs show normally off characteristics.