High Mobility Normally-OFF Hydrogenated Diamond Field Effect Transistors With BaF₂ Gate Insulator Formed by Electron Beam Evaporator
Qi He, Kai Su, Jinfeng Zhang, Zeyang Ren, Yufei Xing, Jincheng Zhang, Yingyi Lei, Yue Hao
Abstract
High performance normally-OFF hydrogenated diamond (C-H diamond) metal–insulator–semiconductor (MIS) field-effect transistors (FETs) have been achieved with Al/BaF<sub>2</sub> gate materials. The 15-nm BaF<sub>2</sub> 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/BaF<sub>2</sub>/ C-H diamond MIS diode indicate low positive fixed charges and trapped charges in the BaF<sub>2</sub> film. The 4-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> FET device with a threshold voltage (<inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula>) 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 BaF<sub>2</sub> 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 BaF<sub>2</sub>/C-H diamond interface with an almost constant effective hole mobility of about 225.0 cm<sup>2</sup>/<inline-formula> <tex-math notation="LaTeX">$\text{V}\cdot \text{s}$ </tex-math></inline-formula> for −2.1 V <inline-formula> <tex-math notation="LaTeX">$\le {V}_{\text {GS}}$ </tex-math></inline-formula>–<inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}} \le -4.1$ </tex-math></inline-formula> V.