Toshihiro Ando

Surface vibrational studies of CVD diamond

Abstract Using high-resolution electron energy loss spectroscopy (HREELS), the surface vibrations of adsorbed hydrogen were investigated on homoepitaxially grown boron-doped single-crystal (001) and (111) films. As-grown surfaces are terminated by hydrogen and the surface carbon atoms are in the sp3 hybridized state. Hydrogen desorption by heating affects the long-range and/or shortrange ordering of the surface. On hydrogen readsorption the long-range ordering on the (001) surface is not recovered, and even the short-range structure remains disturbed in the (111) case. In contrast, heating the sample in D2 (H2) gas results in H-D exchange of the adsorbate without largely disturbing the surface structure. Off-specular HREELS shows two C-H stretching modes and two C-H bending modes on the as-grown (111) surface, which is consistent with CH3 termination. The dispersionless C-H modes indicate weak direct interaction between each adsorbed species. An acoustic surface phonon is observed and shows a small isotope shift, which can be explained by either a CH3 termination or H (monohydride) termination model.

Sulfur-doped homoepitaxial (001) diamond with n-type semiconductive properties

Abstract We have investigated the growth of sulfur-doped (S-doped) diamond crystals via microwave plasma assisted chemical vapor deposition by introducing hydrogen sulfide (H 2 S) into the gas phase. Adding a small amount of H 2 S effectively improved the crystal quality, and the sulfur was successfully incorporated into the crystal. No evidence of hydrogen incorporation was observed in the crystal. The S-doped homoepitaxial (001) diamond showed n-type conduction by Hall effect measurements in the temperature range 250–550xa0K. The mobility of electrons at room temperature was 597xa0cm 2 xa0V −1 s −1 ; this value suggests that there could be many practical uses. The crystallinity of the S-doped n-type diamond films were characterized by various techniques which demonstrated the high quality of the films.

Homoepitaxial diamond growth with sulfur-doping by microwave plasma-assisted chemical vapor deposition

Abstract We have investigated sulfur incorporation and the effects of H 2 S addition on the crystal quality and electrical properties of sulfur-doped homoepitaxial (100) and (111) diamond grown by microwave plasma-assisted chemical vapor deposition. In the case of (100) homoepitaxial growth, adding a small amount of H 2 S effectively improved the crystal quality, whereas adding an excess of H 2 S degraded the crystal quality. The amount of incorporated sulfur increased with increasing amounts of H 2 S. At the same time, the amount of undesirable silicon impurities decreased. Adding H 2 S in the range of 50–100 ppm yielded a high-quality S-doped diamond. In a temperature range of 250–550 K, the high-quality S-doped homoepitaxial (100) diamond showed n -type conduction by Hall-effect measurements. The electrical properties of S-doped (100) diamond were sensitive to the quality of the crystal. The crystal quality of the S-doped (111) homoepitaxial diamond was poorer than that of the (100) diamond. The quality of the S-doped (111) diamond was insensitive to the amount of additional H 2 S. The resistivity of the (111) diamond was very high compared to that of the (100) diamond. The resistivity of the undoped (111) diamond was lower than that of the S-doped (111) diamond. The Hall effect measurement could not be performed on the (111) homoepitaxial diamonds.

Surface oxygenation studies on (100)-oriented diamond using an atom beam source and local anodic oxidation

Surface oxidation studies on pre-deuterated (1 0 0)-oriented single crystal diamond have been performed by oxidizing the diamond surfaces macroscopically using an oxygen atomic beam source as well as microscopically using local anodic oxidation by atomic force microscope (AFM). Oxygen-deuterium exchange on diamond (1 0 0) was investigated by X-ray photoelectron spectroscopy, elastic recoil detection and time-of-flight SIMS. Exchange of pre-adsorbed D by atomic O is thermally activated, with almost complete exchange of surface D by atomic O at 300 °C. At higher oxidation temperatures, oxidation states which are chemically shifted from the C 1s bulk peak by 3.2 eV was observed together with a disordering of the diamond surface. Micron-scale, localized oxygenation of the diamond surface at room temperature could be achieved with a biased AFM tip where we confirmed that the modified areas show a lower secondary electron yield and higher oxygen content. In addition, the electronic structure of the oxygenated diamond surface (on-top (OT) and bridging model) has been investigated by calculating the layered-resolved partial density of states using first principles plane wave ab initio pseudopotential method within the local density functional theory. For the oxygen OT model, sharp features due to occupied surface states in the valence band and unoccupied surface states in the gap exist. The increase in emission intensity near the valence band edge for oxygenated diamond (1 0 0) was verified by ultraviolet photoelectron spectroscopy study.

Effect of oxygen addition on boron incorporation on semiconductive diamond CVD

Abstract The suppression effect of oxygen on elemental incorporation in homoepitaxial diamond films grown by microwave assisted CVD is investigated by secondary ion mass spectrometry. In the H2–CH4–B2H6–O2 gas system, boron incorporation into CVD diamond decreases with increasing oxygen addition, and boron concentration can be controlled by oxygen addition. In the H2–CH4–B2H6 gas system, a linear relationship between diborane in the gas and boron incorporation is observed. The growth rate of diamond is reduced by small amount of diborane.

Effects of UV irradiation on the growth of diamond at lower temperatures

Abstract The effects of irradiation of UV light on the growth of diamond from the gas phase were studied in the range of substrate temperatures from 300 to 500 °C, using microwave plasma-assisted chemical vapor deposition. The increase in the growth rate due to UV irradiation was observed at all the temperatures studied. At 300 and 400 °C, the change in morphology and crystal quality has been noted.

Cubic boron nitride thin film synthesis on silica substrates by low-pressure inductively-coupled r.f. plasma chemical vapor deposition

Cubic boron nitride (cBN) thin films were successfully deposited on fused silica substrates by low pressure inductively coupled radio frequency plasma chemical vapor deposition from B2H6+N2+Ar gas mixtures. Ion bombardment was a necessary condition for the cubic phase growth. Glancing angle X-ray diffraction showed reflections of cBN up to 311 and confirmed the growth of the cubic phase. Lattice distortion in the films estimated from the X-ray diffraction data was about a half of that of films on silicon substrates. Adhesion to the silica substrates was better than to the silicon substrates. Auger and electron energy loss spectroscopy also confirmed the formation of cBN phase. Ultraviolet and visible spectra showed the films are transparent with an optical bandgap of ∼5.4 eV.