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

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High performance normally-OFF hydrogenated diamond (C-H diamond) metal–insulator–semiconductor (MIS) field-effect transistors (FETs) have been achieved with Al/BaF2gate materials. The 15-nm BaF2film 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 BaF2film. The 4-μ mFET device with a threshold voltage (VTH) 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 BaF2layer. 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/V· sfor −2.1 V≤ VGS–VTH ≤ -4.1V.