Hiroki Gima

Electrical characteristics of nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite films prepared by coaxial arc plasma deposition

Nitrogen-incorporated ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were synthesized in nitrogen and hydrogen mixed gas atmospheres by coaxial arc plasma deposition. The temperature dependence of electrical resistivity implies that carriers are transported in hopping conduction. Heterojunctions comprising 3 at. % nitrogen-doped films and p-Si substrates exhibited a typical rectifying action. The expansion of a depletion region into the film side was confirmed from the capacitance–voltage characteristics, and the built-in potential and carrier concentration were estimated to be 0.51 eV and 7.5 × 1016 cm−3, respectively. It was experimentally demonstrated that nitrogen-doped UNCD/a-C:H is applicable as an n-type semiconductor.

Defect and field-enhancement characterization through electron-beam-induced current analysis

To investigate the effects of defects and field enhancement in diamond power devices, a biased Schottky barrier diode was characterized by electron-beam-induced current (EBIC) analysis. The nonuniform distribution of the electrical field was revealed by bright spots on the laterally expanded depletion layer of the EBIC intensity map when the applied electrical field exceeded 0.95 MV/cm. The nonuniformity is partly due to a structural effect: the roughness at the edge of the Schottky electrode, induced by lithography and lift-off processes. A second family of spots was shown to increase the leakage current of the device. The time constant associated with this second spot family was 0.98 ms, which is three orders of magnitude shorter than that for defects previously characterized by deep-level transient spectroscopy.

Effects of Hydrogen and Nitrogen Atmospheres on Growth of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films by Reactive Pulsed Laser Deposition

The growth of ultrananocrystalline diamond/nonhydrogenated amorphous carbon composite films was realized by pulsed laser deposition with a graphite target in a nitrogen atmosphere totally excluding hydrogen. The existence of 7 nm diamond grains was confirmed by X-ray diffraction. Nitrogen incorporation into the films was confirmed by X-ray photoemission and near-edge X-ray absorption structure spectroscopies, and the nitrogenation produced n-type conduction with an electrical conductivity of 0.2 Ω-1 cm-1 at 300 K. The results of study proved that nitrogen acts as a reactive gas for the formation of diamond grains, similarly to hydrogen.

Chemical bonding structural analysis of nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite films prepared by coaxial arc plasma deposition

Nitrogen-doped ultra-nanocrystalline diamond/hydrogenated amorphous carbon composite films prepared in hydrogen and nitrogen mixed-gas atmospheres by coaxial arc plasma deposition with graphite targets were studied electrically and chemical-bonding-structurally. The electrical conductivity was increased by nitrogen doping, accompanied by the production of n-type conduction. From X-ray photoemission, near-edge X-ray absorption fine-structure, hydrogen forward-scattering, and Fourier transform infrared spectral results, it is expected that hydrogen atoms that terminate diamond grain boundaries will be partially replaced by nitrogen atoms and, consequently, π C–N and C=N bonds that easily generate free electrons will be formed at grain boundaries.

A Comparative Study of Energy Security in Okinawa Prefecture and the State of Hawaii

The energy securities of Okinawa Prefecture and the State of Hawaii, both of which are isolated islands in the Pacific Ocean, were studied by comparison. While both islands depend on thermal power for more than 80% of their energy needs, power generation methods differ between them. The cost of energy supply in Okinawa is low because electrical energy is produced primarily by coal-fired power stations, whereas in Hawaii it is extremely high because oil, which is extensively used for various purposes such as airplanes and vehicles, is the energy source for most thermoelectric power stations. At present, Hawaii is installing renewable energy facilities as a test case for a next-generation energy-mix in the USA. On the other hand, Okinawa prefers energy security and low costs, similar to the strategy of Japan as a whole, since Japan is at high risk of natural disasters.

Characteristics of electron emission from cross-sectional surface of porous Si layer

Electrons are emitted from the cross-sectional surface of a porous Si layer. The measurement of electron emission from the cross-sectional surface of the porous Si layer on a glass substrate by applying positive and negative DC voltage and AC voltage is demonstrated. The electron emission device is formed of a layered structure composed of a Au electrode, a porous Si layer with a cross-sectional surface, and a glass substrate with an Al electrode. The threshold voltage of electron emission changed with the variation of the thickness of the porous Si layer, and also changed with the polarity of the applied voltage and the conductive type of Si in the original porous silicon layer. Measurement of the electron emission from the cross-sectional surface of the porous Si layer has been demonstrated with an applied AC voltage. Electron emission occurred at the positive or negative peak of the AC voltage higher than the threshold voltage.

UV detection of n-type Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films by Coaxial Arc Plasma Deposition

N-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were deposited in nitrogen and hydrogen mixed gas atmospheres by coaxial arc plasma deposition (CAPD) with graphite targets. The n-type conduction of the films was thermally confirmed. A heterojunction diode with p-type Si exhibited typical rectifying action. Under illumination, photocurrent is clearly detected at reverse voltages.