Fabrication of metal-oxide-diamond field-effect transistors with submicron-sized gate length on boron-doped (111) H-terminated surfaces using electron beam evaporated SiO ₂ and Al ₂O ₃

A H-terminated surface conductive layer of B-doped diamond on a (111) surface was used to fabricate a metal-oxide-semiconductor field-effect transistor (MOSFET) using an electron beam evaporated SiO ₂ or Al ₂O ₃ gate insulator and a Cu-metal stacked gate. When the bulk carrier concentration was approximately 10 ¹⁵/cm ³ and the B-doped diamond layer was 1.5 μm thick, the surface carrier mobility of the H-terminated surface on the (111) diamond before FET processing was 35 cm ²/Vs and the surface carrier concentration was 1.5 × 10 ¹³/cm ². For the SiO ₂ gate (0.76 μm long and 50 μm wide), the maximum measured drain current at a gate voltage of -3.0 V was -75 mA/mm and the maximum transconductance was 24 mS/mm, and for the Al ₂O ₃ gate (0.64 μm long and 50 μm wide), these features were -86 mA/mm and 15 mS/mm, respectively. These values are among the highest reported direct-current (DC) characteristics for a diamond homoepitaxial (111) MOSFET.