High Mobility Normally-OFF Hydrogenated Diamond Field Effect Transistors With BaF₂ Gate Insulator Formed by Electron Beam Evaporator

High performance normally-OFF hydrogenated diamond (C-H diamond) metal–insulator–semiconductor (MIS) field-effect transistors (FETs) have been achieved with Al/BaF₂ gate materials. The 15-nm BaF₂ film was formed by electron beam evaporation at room temperature. The flat-band voltage and hysteresis voltage extracted from the capacitance–voltage characteristics of the Al/BaF₂/ C-H diamond MIS diode indicate low positive fixed charges and trapped charges in the BaF₂ film. The 4- $\mu \text{m}$ FET device with a threshold voltage ( ${V}_{\text {TH}}$ ) of −0.90 V exhibits distinct pinch-off characteristics. The enhancement mode could be due to primarily the Schottky barrier depletion effect of the gate metal on the channel, and secondarily the positive fixed charges present in the BaF₂ layer. The maximum transconductance and maximum saturated drain current are 30 mS/mm and −96.5 mA/mm, respectively. The device performance benefits from the decent conductivity at the BaF₂/C-H diamond interface with an almost constant effective hole mobility of about 225.0 cm²/ $\text{V}\cdot \text{s}$ for −2.1 V $\le {V}_{\text {GS}}$ – ${V}_{\text {TH}} \le -4.1$ V.