Yukio Akiba

Formation Mechanism of p-Type Surface Conductive Layer on Deposited Diamond Films

A model of the formation of a p-type surface conductive layer on deposited diamond films is proposed. According to the model, the ionization of acid in water produces oxonium ion ( H3O+) which reacts with hydrogen on diamond films and causes the creation of holes in diamond films. The model also explains the disappearance of the p-type surface conductive layer by the action of alkaline substances. The experimental results concerning the change in electrical resistance at the surface of diamond films can be explained using the proposed model.

Characterization of Boron-Doped Diamond Film

Diamond films doped with boron were fabricated by the thermal filament CVD method. Powdered B2O3 was used as the doping source. The films were identified as diamond by means of several methods including Raman spectroscopy. The resistivity of the films was inversely proportional to the B/C ratio over four orders. The temperature dependence of current was measured and to fit this result to the theoretical calculation, the activation energy was evaluated.

Synthesis of n-type semiconducting diamond film using diphosphorus pentaoxide as the doping source

An n-type semiconducting diamond film has been synthesized by the hot filament CVD method using diphosphorus pentaoxide as the doping source. The obtained film was identified as polycrystalline diamond containing few sp2 components by means of several methods including Raman spectroscopy. From measurements of the Hall effect and the Seebeck effect, the film was found to be an n-type semiconductor.

Synthesis of Diamond Thin Films Having Semiconductive Properties

Semiconductive diamond films were fabricated by the thermal filament CVD method. A saturated solution of B2O3 powder in CH3OH mixed with acetone was used. The films deposited were identified as diamond by several methods including Raman spectroscopy. By the measurement of electrical properties, the obtained films were found to show p-type conduction.

Possibility of Realizing a Gas Sensor Using Surface Conductive Layer on Diamond Films.

The electrical surface resistance of diamond films deposited by the hot-filament chemical vapor deposition (CVD) method is measured in oxidizing and reducing atmospheres. The electrical surface resistance decreases in NO2, HCl and O3 gases. On the other hand, it increases in NH3 gas. The mechanism of change in electrical resistance is explained by the formation mechanism of a p-type surface conductive layer. The realization of a gas sensor will be discussed considering the experimentally obtained results.

Synthesis of B-doped diamond film

Abstract Boron-doped diamond films have been synthesized by the thermal filament CVD method. As the doping source, boron trioxide powder was used instead of diborane. The films obtained were identified as diamond by several methods including Raman spectroscopy. The resistivity of the films was inversely proportional to the doping concentration over four order. p-Type electrical conduction was also confirmed by measuring the Seebeck effect.

Fabrication of Metal-Insulator-Semiconductor Devices Using Polycrystalline Diamond Film

Metal-insulator-semiconductor (MIS) devices have been fabricated using a polycrystalline diamond film doped with boron. The diamond film has been deposited on Si substrate by a hot-filament chemical vapor deposition method. The SiO2 film has been deposited on the diamond by a plasma-assisted CVD method and aluminum has been evaporated as a gate on the SiO2 film. The MIS capacitance was varied as a function of voltage applied between the gate and substrate. Further, the metal-insulater-semiconductor field-effect transistor has indicated transistor operation capabilities at room temperature. These results suggest a possibility that the polycrystalline diamond film can be used as an electronics material.

Fabrication of a diamond p-n junction diode using the chemical vapour deposition technique☆

Abstract A diamond p − n junction diode has been fabricated by the chemical vapour deposition technique. Diphosphorus pentaoxide and boron trioxide were used for the doping sources for the n - and p -type layers, respectively. The diode shows distinct rectification characteristics at 300 K room temperature. This diode shows rectification even at 370 K and this result implies the possible use of diamond as a semiconductor in high temperature conditions.

Electrolysis by Using Diamond Thin Film Electrodes

Thin diamond films formed on Si substrates were electrolyzed in terms of the characteristics of their electrolysis in acidic solution for testing of the possibility of their use in industrial electrochemistry. It was found that boron doped diamond anodes (100, 1000 ppm) can be operated under conditions of severe polarization, with a current density of 10 A/cm2 in a sulfuric acid solution. It was also found that ozone gas is stably generated from boron doped diamond anodes at high current densities of over 1 A/cm2. This reveals that diamond electrodes can be used in various types of industrial electrolysis.

Isothermal capacitance transient spectroscopy measurements on polycrystalline diamond/hydrogenated amorphous silicon heterojunctions

A deep level in boron‐doped polycrystalline diamond films located approximately 0.6 eV above the valence‐band edge has been found using isothermal capacitance transient spectroscopy (ICTS) measurements. p‐n heterojunctions between polycrystalline diamond and hydrogenated amorphous silicon were used in the study. The density and the hole‐capture cross section of the deep level traps were determined from the temperature dependence of ICTS spectra and found to be 2×1016 cm−3 and 1×10−17 cm2, respectively.