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This letter reports a high drain current density and normally-off operation metal-oxide-semiconductor field-effect transistors (MOSFETs) with a gate insulator of 100 nm-Al2O3. A heavily boron-doped layer as the source/drain region was deposited on a (110) polycrystalline diamond substrate to achieve a low ohmic contact resistance. The MOSFETs demonstrate a maximum current density of −400 mA mm $^{-{1}}$ normalized by gate width and a maximum current density of $- 2000\,\,\mu \text{m}$ mA mm−1 normalized by gate length and gate width, which are the highest values for normally-off diamond FETs. The Grain boundaries (GBs) and the nitrogen impurities ($\sim {3}\,\,\times \,\,{10}^{{17}}$ cm $^{-{3}}$) as ionized donors in the channel region caused the threshold voltage (${V}_{\text {th}}$) to shift in the negative direction, exhibiting normally-off characteristics. This technique provides a promising method to achieve high-performance diamond devices, and help improve safety and save energy in switching systems. [ABSTRACT FROM AUTHOR]

Here, thermal stabilities for Ohmic contact properties of Pt, Au, and Pd on the same hydrogen-terminated diamond (H-diamond) epitaxial layer are investigated. A long-term annealing process is performed with an annealing temperature and time of 400 °C and 8 h, respectively. Before annealing, good Ohmic contact properties are observed for only two contacts of the Pt/H-diamond and Pd/H-diamond with specific contact resistivity (ρC) values of 2.7 × 10−3 Ω cm2 and 2.6 × 10−4 Ω cm2, respectively. After long-term annealing, all three contacts on the H-diamond show good Ohmic contact properties. The ρC values for the Pt/H-diamond and Au/H-diamond are 3.1 × 10−2 Ω cm2 and 4.2 × 10−4 Ω cm2, respectively. They are higher than that of the Pd/H-diamond (1.1 × 10−4 Ω cm2). Therefore, low ρC and good thermal stability for the Pd/H-diamond are achieved. This is meaningful for pushing forward the development of H-diamond-based electronic devices for high-temperature applications. [ABSTRACT FROM AUTHOR]