Hiroshi Kawarada

Properties of metal/diamond interfaces and effects of oxygen adsorbed onto diamond surface

The current‐voltage characteristics of Schottky diodes fabricated using as‐grown diamond films depend on the electronegativities of metals. However for diamond films oxidized by boiling in a saturated solution of CrO in H2SO4 or by exposure to an oxygen plasma, this dependence vanishes. This is because of the adsorption of oxygen onto the surfaces of diamond synthesized by chemical vapor deposition. It has been shown by x‐ray photoelectron spectroscopy that very little oxide is present on the as‐grown surfaces, but that at least submonolayer oxygen coverage is present on the oxidized surfaces.

LARGE AREA CHEMICAL VAPOUR DEPOSITION OF DIAMOND PARTICLES AND FILMS USING MAGNETO-MICROWAVE PLASMA.

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 value is the largest of all plasma deposition systems of diamond. The crystallinity obtained by the above-mentioned plasma compares favourably with those of the best ones by previous methods.

Selective nucleation and growth of diamond particles by plasma‐assisted chemical vapor deposition

Diamond particles have been selectively synthesized on a SiO2 dot‐patterned Si substrate using plasma‐assisted chemical vapor deposition (plasma CVD). Nucleation densities on both Si and SiO2 have been increased, first by pretreatment using abrasive powders; then, to eliminate the pretreatment effect from almost all of the substrate and to retain the effect only at designed sites, an Ar beam is used to obliquely irradiate the pretreated substrate. After deposition using plasma CVD, diamond particles have selectively formed on one edge of the SiO2 dots according to the pattern and have grown large to adjoin with adjacent particles. Polycrystals with equal grain sizes have been synthesized.

Cathodoluminescence and electroluminescence of undoped and boron‐doped diamond formed by plasma chemical vapor deposition

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 2.8–2.9 eV. The characteristics of these emission spectra are very similar to those obtained in type‐IIa diamond where dislocations are luminescent. The doping of boron during the deposition form another luminescent center at 2.3–2.4 eV. From the monochromatic cathodoluminescence imaging, the luminescent regions differ in the two peaks. {100} sectors are much more luminescent than {111} sectors at the signal of 2.8 eV. This phenomenon has been discussed based on the difference in defect or impurity concentration of...

Growth of diamond films at low pressure using magneto-microwave plasma CVD

Abstract Diamond films have been grown by magneto-microwave plasma CVD at a lower pressure (0.1 Torr) than in more conventional diamond growth systems. At this pressure, a plasma with a high enough density (above 1 x 10 11 cm -3 ) to form diamond can be obtained around the substrate which is set at the ECR condition. At low temperatures ( -580 °C), using a CH 4 /H 2 or CO 2 /H 2 mixture as a reaction gas, diamond films have not been obtained. However, with CH 4 + CO 2 /H 2 mixture, high quality and uniform diamond films have been obtained at low pressure (0.1 Torr) and a lower temperature (500°C). We speculate that the OH radical is important for the low temperature deposition of diamond.

The Synthesis of Diamond Films at Lower Pressure and Lower Temperature Using Magneto-Microwave Plasma CVD

Diamond films have been obtained using magneto-microwave plasma assisted CVD at 0.1 Torr. The reaction gas is a CO/H2 mixture. By setting the ECR condition at the deposition area, a high density plasma (1×1011 cm-3) is obtained around the substrate. The discharge area is quite uniform in the pressure. Diamond films are obtained on positively biased substrates. As the reaction pressure becomes lower, the substrate temperature for the diamond formation tends to decrease. The films were evaluated by SEM imaging, electron diffraction and Raman spectroscopy.

Intrinsic and extrinsic recombination radiation from undoped and boron‐doped diamonds formed by plasma chemical vapor deposition

In small particles of chemical vapor deposited (CVD) diamond and polycrystalline thin films composed of the particles, the recombination radiation of free excitons and bound excitons associated with multiple phonons has been observed using cathodoluminescence. The bound excitons are due to neutral acceptors of boron in the diamonds. The cathodoluminescence imaging reveals that the recombinations of free excitons are located at {100} sectors. The crystal perfection and purity is high in {100} sectors compared with {111} sectors formed in the CVD process.

Nucleation control and selective growth of diamond particles formed with plasma CVD

Abstract To obtain polycrystals with large and uniform grain size, diamond particles have been selectively formed on a SiO 2 dot-patterned Si substrate using plasma-assisted CVD. After pretreatment by abrasive powders to increase diamond nucleation densities on both Si and SiO 2 , an Ar beam is used to irradiate obliquely the pretreated surface. As a result, diamond can no longer nucleate on Si, it nucleates only on one edge of the SiO 2 dots and grows over the Si substrate to about 10 #m. Well defined polycrystals having equal grain sizes have been obtained. The role of the Ar beam irradiation on Si and on SiO 2 is also discussed.

CHARACTERIZATION OF DIAMOND PARTICLES AND FILMS FORMED BY PLASMA-ASSISTED CHEMICAL VAPOUR DEPOSITION USING HIGH-VOLTAGE ELECTRON MICROSCOPY.

The internal and interfacial structures of diamond particles and films on Si substrates formed by plasma-assisted chemical vapour deposition have been investigated by high-voltage transmission electron microscopy. The feature of line defects–micro-twin lamellae or stacking faults–in a diamond particle indicates the concentric crystal growth originated from one nucleus. The particles are observed to be in direct contact with the Si substrate around the nucleation site within the resolution limit. The particles are stacked up to form a diamond film.

Preparation and characterization of wide area, high quality diamond film using magnetoactive plasma chemical vapour deposition

Abstract A magnetomicrowave plasma was used for the low pressure deposition of diamond. The important point in the plasma deposition system is to set the electron cyclotron resonance (ECR) condition (875 G in the case of a 2.45 GHz microwave) at the deposition area. The high density plasma (above 1 × 10 11 cm -3 ) necessary for high quality diamond formation was obtained by effective microwave absorption near the magnetic field, satisfying the ECR condition. The plasma is uniform at the discharge area (160 mm in diameter) and uniform diamond films of a high quality are obtained. From an investigation of diamond formation in the range 10 -2 –50 Torr in the same deposition system, it is obvious that the lower pressure reduces the formation temperature of diamond to 500 °C and that the effective species for diamond formation are low energy radicals.