Fabrication of diamond MISFET with micron-sized gate length on boron-doped (111) surface

A hydrogenated surface conductive layer of B-doped diamond on (111) was employed to fabricate a metal insulator semiconductor field effect transistor (MISFET) using a CaF2 and Cu stacked gate. The carrier mobility and concentration of the hydrogenated surface on (111) before FET processing were 35 cm2/V s and 1013/cm2, respectively, when bulk carrier concentration and film thickness of the B-doped underlaying diamond was 3 × 1015/cm3 and 1.5 μm, respectively. The DC characteristics of the gate with 1.1 μm length and 50 μm width showed that the maximum measured drain current was 240 mA/mm at − 3.0 V gate voltage, and the maximum transconductance (gm) was 70 mS/mm. The cut-off frequency of 4 GHz was obtained, which is one of the best values for the RF characteristics of a diamond homoepitaxial (111) MISFET.