Yoshiki Nishibayashi

Epitaxially Grown Diamond (001) 2×1/1×2 Surface Investigated by Scanning Tunneling Microscopy in Air

Scanning tunneling microscopy (STM) observation was performed for the surface of diamond epitaxial film which was grown on a diamond (001) substrate by microwave plasma-assisted chemical vapor deposition (CVD). The surface was stable even in air, and it showed a reflection high-energy electron diffraction (RHEED) pattern of the 2×1/1×2 structure. Images of the atomic level corresponding to the RHEED pattern were obtained by STM in air. Significant extension of dimer rows was observed over the entire surface. Strong similarity between Si(001) grown by molecular beam epitaxy (MBE) and diamond (001) grown by CVD was shown.

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.

Smooth and high-rate reactive ion etching of diamond

Diamond surfaces with patterned Al masks were etched by a reactive ion etching (RIE) system under conditions that the RF power was 100-280 W, the CF 4 /O 2 ratio was 0-12.5% and the gas pressure 2-40 Pa. It was found that the roughness of the etched diamond surface decreased with an increase in the CF 4 /O 2 ratio, although this reduced the selective etching ratio of diamond against Al. The gas pressure also affected the surface roughness and the etching anisotropy. The etching rate of diamond considerably increased upon a small addition of CF 4 in O 2 . Based on these results, we were successful in an anisotropic etching of diamond at a very high rate (∼9.5 μm/h) with a smooth etched surface (R a < 0.4 nm), a high selective etching ratio of diamond vs. Al, and a high aspect ratio (the height/diameter was ∼8 for array structures and ∼25 for exceptional cases) by choosing appropriate etching conditions.

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-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.

Field emission mechanism of oxidized highly phosphorus-doped homoepitaxial diamond (111)

Spatially resolved electron field emission experiments on oxidized highly phosphorus-doped homoepitaxial diamond (111) were applied at room temperature. The diamond layer shows hopping conductivity. Field emission properties have three distinct regions. We attribute the variation in emission currents to: (a) Electron emission from conduction-band minimum (Region I), (b) Depletion of conduction-band electrons at the surface (Region II), and (c) emission from the phosphorus level (Region III). From these data, we calculate an effective positive electron affinity for the oxidized surface of 1–1.5eV.

R&D of diamond films in the Frontier Carbon Technology Project and related topics

R&D activities on diamond chemical vapor deposition (CVD) and field emission in the Frontier Carbon Technology Project are presented. The topics are (1) morphology control of diamond films grown by a 60-kW, 915-MHz microwave plasma CVD reactor, (2) growth technology of large single crystal diamond with a low density of defects, (3) heteroepitaxial growth technology of diamond films on Pt, (4) fabrication of sharp emitter tips on single crystal diamond, (5) field emission study from diamond particles, and (6) intense field emission from ion implanted homoepitaxial diamond layer. Research results of field emission obtained by Kyoto University and North Carolina State University are also described.