We report two-dimensional hole gas (2DHG) diamond field-effect transistors (FETs) with microwave plasma chemical vapor deposition (MPCVD)-regrown p+-diamond (B concentration ∼ 1 × 1022 /cm3) ohmic contacts. The heavily doped p+-diamond shows low ohmic contact resistance of 1.1 Ω mm, which is the lowest value reported in diamond to date. In addition, the p+-diamond with a TiC also offers much stronger metal adhesion when compared with previous Au/hydrogen-terminated diamond surfaces and is suitable for industrial use. Benefiting from the low contact resistance of the p+-diamond layer, a maximum drain current density of 1170 mA/mm and an ON-resistance of 8.9 Ω mm were demonstrated in a 2DHG diamond metal-oxide-semiconductor FET with a 1 μm gate length. These results indicate that the regrown p+-diamond ohmic contacts will make it possible to realize further improvements in the maximum drain current density of 2DHG diamond FETs.
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