Hiroshi Kawarada 교수

By forming a highly stable Al2O3 gate oxide on a C-H bonded channel of diamond, high-temperature, and high-voltage metal-oxide-semiconductor field-effect transistor (MOSFET) has been realized. From room temperature to 400 °C (673 K), the variation of maximum drain-current is within 30% at a given gate bias. The maximum breakdown voltage (VB) of the MOSFET without a field plate is 600 V at a gate-drain distance (LGD) of 7 μm. We fabricated some MOSFETs for which VB/LGD > 100 V/μm. These va

Enhancement mode-type metal-semiconductor field effect transistors using diamond have been fabricated. The transistor operation is based on the control of surface p-type conduction of a hydrogen terminated homoepitaxial layer. Boron doping was not used for the conduction. An aluminum contact is used for the Schottky gate and gold ohmic contacts are used for the source and drain. The obtained transconductance is 20–200 μs/mm using aluminum gates of 10–40 μm in length. The active region on the hom

The 2\ifmmode\times\else\texttimes\fi{}1/1\ifmmode\times\else\texttimes\fi{}2 surface reconstruction of a homoepitaxial diamond (001) surface has been examined using a scanning tunneling microscope at an atomic scale and reflection electron microscopy at a macroscopic scale. The monohydride dimer, which is a unit of the surface reconstruction, has a symmetric structure. These monohydride structures contribute to the surface p-type conduction in undoped films. The surface is composed of elongated

Diamond field effect transistors have operated in electrolyte solution for the first time. Since the hydrogen-terminated diamond surfaces are stable enough for the use as an electrochemical electrode, the diamond surface channels are exposed to the electrolyte in the transistor structure. A perfect pinch-off and saturated current–voltage characteristics have been obtained for bias voltages within the potential window. The threshold voltages are almost constant in electrolytes with different pH v

Large area chemical vapour deposition of diamond has been obtained using magneto-microwave plasma. The important point of the developed system is to set the electron cyclotron resonance condition (875 G), where the highest plasma density is expected, at the deposition area by controlling the distribution of an applied magnetic field. Even in 10 Torr where complete electron gyrations cannot be expected, the size of the discharge area controlled by the magnetic field is 70-80 mm in diameter. This

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 b

The correlation between free-exciton and bound-exciton recombination has been investigated by cathodoluminescence in high-quality and impurity-controlled chemical-vapor-deposited (CVD) diamond films. The films are formed by [CO(5%)]/[${\mathrm{H}}_{2}$] using microwave-plasma CVD and are doped with ${\mathrm{B}}_{2}$${\mathrm{H}}_{6}$ during deposition. In moderately doped (below 3\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$) semiconducting diamonds, t

Visible luminescence between 2.0–3.5 eV of undoped and boron-doped diamond formed by plasma-assisted chemical vapor deposition has been investigated by cathodoluminescence. Electroluminescence from Schottky diode of boron-doped semiconducting diamond has been observed for the first time and found to be due to the same luminescent center as that of cathodoluminescence. In the particles or films where the content of nitrogen and boron was greatly reduced, the cathodoluminescence peaks occurred at

Smooth and continuous diamond films have been heteroepitaxially grown on β-type silicon carbide (β-SiC) (001) surfaces. The smooth films can be obtained in the thickness of less than 6 μm which is the smallest in heteroepitaxial diamonds. The epitaxial growth is composed of three steps; (i) Bias enhanced nucleation on β-SiC (001) grown on silicon (001), (ii) 〈001〉 fast growth mode for the selection of epitaxially oriented particles, and (iii) 〈111〉 fast growth mode for the smoothing of (001) sur

Metal semiconductor field-effect transistors (MESFETs) or metal oxide semiconductor FETs (MOSFETs) can be fabricated on hydrogen-terminated diamond without losing the surface hydrogen–carbon bonds and the surface adsorbates responsible for the surface carrier generation. Those FETs show their best performance in diamond transistors. The maximum drain current density is above 1 A/mm and the highest transconductance is 400 mS/mm. These values are comparable to those of modern FETs made of Si or II

The controlled design of biosensors based on the photo-electrochemical technique with high selectivity, sensitivity, and rapid response for monitoring of mono-bioactive molecules, particularly dopamine (DA) levels in neuronal cells is highly necessary for clinical diagnosis. Hierarchical carbon-, nitrogen-doped (CN) nickel oxide spear thistle (ST) flowers associated in single-heads (S), and symmetric and asymmetric-double heads (D and A, respectively) that are tightly connected through a microme

We have deposited epitaxial diamond films with very low angular spread on epitaxial β-phase silicon carbide layers on silicon (001) substrates. From x-ray rocking curve measurements, half-widths of the angular spread of the crystal orientation as low as 0.6° have been determined, which is the smallest value ever reported in heteroepitaxial diamond films and appears to be smaller than those of the β-phase silicon carbide underlayers. The film surface exhibits a roughness of about 100 nm with very

The nitrogen-vacancy (NV) center in diamond is the most promising candidate for quantum sensing because of its beneficial properties. For quantum-sensing applications, a shallow NV center is critical for approximating the sensing target on a diamond surface. Such shallow NV centers are strongly affected by the diamond surface termination. The properties of shallow NV centers in hydrogen-, oxygen-, and fluorine-terminated diamond have been well studied. In recent years, silicon-terminated diamond