Diamond has unique physical properties, which show great promise for applications in the next generation power devices. Hydrogen-terminated (C-H) diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) often have normally-on operation in devices, because the C-H channel features a p-type inversion layer; however, normally-off devices are preferable in power MOSFETs from the viewpoint of fail safety. We fabricated hydrogen-terminated (C-H) diamond MOSFETs using a partially oxidized (partial C-O) channel. The fabricated MOSFETs showed a high breakdown voltage of over 2 kV at room temperature and normally-off characteristics with a gate threshold voltage V _th of -2.5--4 V.

Complementary power field effect transistors (FETs) based on wide bandgap materials not only provide high-voltage switching capability with the reduction of on-resistance and switching losses, but also enable a smart inverter system by the dramatic simplification of external circuits. However, p-channel power FETs with equivalent performance to those of n-channel FETs are not obtained in any wide bandgap material other than diamond. Here we show that a breakdown voltage of more than 1600 V has been obtained in a diamond metal-oxide-semiconductor (MOS) FET with a p-channel based on a two-dimensional hole gas (2DHG). Atomic layer deposited (ALD) Al₂O₃ induces the 2DHG ubiquitously on a hydrogen-terminated (C-H) diamond surface and also acts as both gate insulator and passivation layer. The high voltage performance is equivalent to that of state-of-the-art SiC planar n-channel FETs and AlGaN/GaN FETs. The drain current density in the on-state is also comparable to that of these two FETs with similar device size and V_B.

We investigated the charge state stability and coherence properties of near-surface single nitrogen vacancy (NV) centers in ¹² C-enriched diamond for potential use in nanoscale magnetic field sensing applications. The stability of charge states in negatively charged NV centers (NV ⁻ ) was evaluated using one of the pulsed optically detected magnetic resonance measurements, Rabi oscillation measurements. During the accumulation of Rabi oscillations, an unstable shallow NV ⁻ was converted to a neutral state. As a result, the contrast of Rabi oscillations degraded, depending on charge state stability. We stabilized the NV ⁻ state of very shallow NV centers (∼2.6 ± 1.1 nm from the surface) created by 1.2 keV nitrogen ion implantation by diamond surface modification, UV/ozone exposure, and oxygen annealing. This improvement indicates that we can suppress the upward surface band bending and surface potential fluctuations through Fermi level pinning originating from oxygen-terminated diamond surfaces.

Power semiconductor devices require low on-resistivity and high breakdown voltages simultaneously. Vertical-type metal-oxide-semiconductor field-effect transistors (MOSFETs) meet these requirements, but have been incompleteness in diamond. Here we show vertical-type p-channel diamond MOSFETs with trench structures and drain current densities equivalent to those of n-channel wide bandgap devices for complementary inverters. We use two-dimensional hole gases induced by atomic layer deposited Al₂O₃ for the channel and drift layers, irrespective of their crystal orientations. The source and gate are on the planar surface, the drift layer is mainly on the sidewall and the drain is the p⁺ substrate. The maximum drain current density exceeds 200 mA mm⁻¹ at a 12 µm source-drain distance. On/off ratios of over eight orders of magnitude are demonstrated and the drain current reaches the lower measurement limit in the off-state at room temperature using a nitrogen-doped n-type blocking layer formed using ion implantation and epitaxial growth.

Diamond is a promising material for power applications owing to its excellent physical properties. Two-dimensional hole gas (2DHG) diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) with hydrogen terminated (C-H) channel have high current densities and high breakdown fields, but often show normally-on operation. From the viewpoint of safety, normally-off operation is required for power applications. In this paper, we used ion implantation to form a shallow and thin nitrogen-doped layer below the C-H channel region, which realized normally-off operation. Nitrogen-ion implanted length is fixed at 5 or 10 lm. Nitrogen is a deep donor (1.7 eV) and the nitrogen-doped layer prevents hole accumulation near surface. The threshold voltage was as high as.2.5 V and no obvious dependence on the threshold voltage of nitrogen-ion implanted length is observed. The breakdown field was 2.7 MV/cm at room temperature. Of 64 devices with a common gate length, 75.