Hiromu Shiomi

Electrical Characteristics of Metal Contacts to Boron-Doped Diamond Epitaxial Film

Current-voltage characteristics have been obtained for various metal contacts formed on boron-doped diamond epitaxial film prepared on synthesized Ib diamond by the microwave plasma-assisted chemical vapor deposition method. Ti contacts and W contacts have exhibited good ohmic and Schottky properties, respectively. For the first time, we have fabricated Schottky diodes on boron-doped diamond epitaxial films using these contacts and investigated their properties.

Epitaxial Growth of High Quality Diamond Film by the Microwave Plasma-Assisted Chemical-Vapor-Deposition Method

High-quality diamond epitaxial films were obtained on Ib diamond (100) substrates by means of the microwave plasma-assisted chemical-vapor-deposition (CVD) method. For the source gas, CH4 and H2 gases were used in different CH4 concentrations (CH4/H2), from 1 vol% to 8 vol%. At CH4/H2=6%, the surfaces of the films were smooth and streaks were observed by reflection high-energy electron diffraction (RHEED). Raman spectra showed that they had no graphitic components. In contrast, Raman spectra showed that both the (110) epitaxial films and the polycrystalline films grown at CH4=6% had graphitic components.

Field-Effect Transistors using Boron-Doped Diamond Epitaxial Films

Metal-semiconductor field-effect transistors (MESFETs) have been fabricated on a boron-doped diamond epitaxial film. This is the first report of a planar type transistor using a diamond film.

Extremely Low On-Resistance and High Breakdown Voltage Observed in Vertical GaN Schottky Barrier Diodes with High-Mobility Drift Layers on Low-Dislocation-Density GaN Substrates

Vertical GaN Schottky barrier diodes (SBDs) were fabricated on freestanding GaN substrates with low dislocation density. High quality n-GaN drift-layer with an electron mobility of 930 cm2 V-1 s-1 was obtained by optimizing the growth conditions by reducing the intensity of yellow luminescence using conventional photoluminescence measurements. The specific on-resistance (RonA) and the breakdown voltage (VB) of the SBDs were 0.71 mΩ cm2 and over 1100 V, respectively. The figure of merit (VB2/RonA) was 1.7 GW/cm2, which is the highest value among previously reported SBDs for both GaN and SiC.

Pulse-doped diamond p-channel metal semiconductor field-effect transistor

A p-type diamond metal semiconductor field-effect transistor (MESFET) structure, utilizing a boron pulse-doped layer as the conducting channel, has been successfully fabricated. The pulse-doped structure consists of an undoped diamond buffer layer, a highly doped thin diamond active layer, and an undoped diamond cap layer grown by the microwave plasma assisted chemical vapor deposition method. It is shown that this field-effect transistor with a gate length of 4 /spl mu/m and the gate width of 39 /spl mu/m exhibits an extrinsic transconductance of 116 /spl mu/S/mm with both pinch-off characteristics and current saturation.<<ETX>>

Characterization of Boron-Doped Diamond Epitaxial Films

Boron-doped diamond epitaxial films were characterized on the dependence of boron concentration by an optical microscope, reflection high-energy electron diffraction, secondary ion mass spectrometry, Hall effect measurement and metal contacts. These films were grown on synthesized single-crystal diamonds(100) by microwave plasma chemical vapor deposition (CVD) using H2, CH4 and B2H6 at a CH4 concentration of CH4/H2=6% and at doping gas ratios of B2H6/CH4=0.83 ppm, 8.3 ppm, and 167 ppm. They were all epitaxially grown and had smooth surfaces. Hall effect measurements were performed in the temperature range of 300 K to 773 K. They indicated that there existed acceptorlike centers other than boron in the films synthesized in the vapor phase. Fermi degeneracy was found to occur at a boron concentration of 3×1020 cm-3. Schottky diodes were fabricated using Al for Schottky contacts and Ti for ohmic contacts. Rectifying properties were degraded at high boron concentration.

High-Efficiency Nitride-Based Light-Emitting Diodes with Moth-Eye Structure

Nitride-based blue light-emitting diodes (LEDs) with a moth-eye structure on the back of a 6H–SiC substrate have been developed. The moth-eye LED has a roughness less than the optical wavelength at the back surface of the SiC substrate fabricated by reactive ion etching (RIE) with CF4 gas. The light extraction efficiency and corresponding output power have been increased to 3.8 times those of a LED with a conventional structure. The experimental findings agree with the results of a theoretical analysis of the effect of the moth-eye structure.

Atomic layer epitaxy of cubic SiC by gas source MBE using surface superstructure

Abstract Cubic SiC was eptiaxially grown by gas source MBE for the first time utilizing the change in surface superstructures when the source gases of Si 2 H 6 and C 2 H 2 were introduced alternately. The number of Si atoms forming the surface superstructure determines the growth rate of the layer, which gives atomic layer control in SiC growth.

Atomic level control in gas source MBE growth of cubic SiC

Abstract Single crystalline cubic SiC was homoepitaxially grown at a substrate temperature of 1000°C by supplying Si 2 H 6 and C 2 H 2 beams alternately to a substrate placed in a high vacuum. The growth mechanism is discussed based on RHEED observations of the transitions in the surface superstructures.

High-Voltage Schottky Diodes on Boron-Doped Diamond Epitaxial Films

High-voltage Schottky diodes have been fabricated on diamond epitaxial films with the structure: metal/undoped diamond/p+-type diamond. The films were epitaxially grown on synthesized single-crystal diamonds (100) by microwave plasma-assisted chemical vapor deposition (CVD) using H2 and CH4. B2H6 was used at B2H6/CH4=167 ppm for p+ diamond. Al Schottky electrodes and Ti ohmic electrodes were formed by an e-beam evaporation method and a thermal evaporation method, respectively. The forward current was independent of temperature because of the Fermi degeneracy in p+-type diamond. These diodes had a breakdown voltage of 520 V.