Normally-off polycrystalline C[sbnd]H diamond MISFETs with MgF2 gate insulator and passivation

Abstract

We report a normally-off CH diamond metal-insulator-semiconductor field effect transistor (MISFET) using a 15-nm-thick thermally evaporated MgF2 film as both the gate dielectric and the passivation layer. The normally-off channel is directly formed based on the Al/MgF2/C-H diamond MIS gate structure. The 4-μm device delivers a record high transconductance (gm) of 26.2 mS/mm among normally-off CH diamond FETs, and a threshold voltage of −0.60 V, a maximum μeff of 138.9 cm2/V·s, a maximum drain current (IDmax) of −49.7 mA/mm and an on-resistance (Ron) of 84.4 Ω·mm at the gate voltage of −5 V. The low Ron and high gm and large IDmax arise from the good conductivity at the MgF2/C-H diamond interface, and the normally-off operation could be attributed to the depletion effect of the gate on the channel with its 2DHG conductivity just slightly degraded after MgF2 deposition.