Kenichi Ohtsuka

Surface reaction kinetics of gas‐phase diamond growth

Surface reaction kinetics for diamond growth by chemical vapor deposition (CVD) was investigated experimentally. The temperature dependence for the growth rate exhibited surface‐reaction controlled kinetics with the activation energy of about 23 kcal/mol below 900 °C. The dependence of the growth rate on the other CVD parameters and the corresponding calculated concentration of H and CH3 gave the growth rate (GR) expression GR= kX0HX1CH3, where k and Xi are a rate constant and the mole fraction of species i, respectively. A decrease in the activation energy for apparent diamond‐film growth with increasing nondiamond carbon content was also discussed in relation to the role of gaseous H atoms. A dramatic decrease of the activation energy occurred at high pressure (300 Torr) deposition, since the growth kinetics changed to the diffusion controlled growth.

Preparation of SnS Films by Sulfurization of Sn Sheet

Tin sulfide (SnS) films were grown by sulfurization using an inexpensive Sn sheet and S powder. The Sn sheet was sulfurized in a closed ampoule at a low temperature between 150 and 300 °C. The resulting sulfurized films had a flat surface and large grains, and exhibited adhered very well to the substrate. These samples exhibited X-ray diffraction peaks corresponding to SnS and contained no extra phases. These results represent the first step toward realizing an optical device such as a solar cell using a SnS film grown by a sulfurization method.

Effect of gas-phase composition on the surface morphology of polycrystalline diamond films

Abstract The film morphology of polycrystalline diamond was observed under a wide variety of conditions by an advanced hot-filament chemical vapor deposition (AHFCVD) method. The main advantage of AHFCVD is the independent and accurate controllability of the chemical vapor deposition (CVD) parameters, especially of the substrate temperature. Clear faceted planes were obtained under the conditions of higher filament temperature (2000–2100°C), pressures of 30–300 Torr, lower methane concentration (about 1.2% or less), lower gas flow rate (800 standard cm3 m−1 or less), shorter distance between the filament and substrate (10 mm or less), and lower substrate temperature (910°C or less). At higher pressures of 200–300 Torr, the facets became (100) dominant. The development of (111) and (100) crystal habits was examined with respect to the concentration of the chemical species in the gas phase as estimated by numerical simulation. A key parameter governing the crystal habit was found to be the concentration ratio of H to CH3; the (111) face developed at higher [H] [ CH 3 ] , while the (100) face could dominantly develop at lower [H] [ CH 3 ] . Both the (111) and (100) orientations of the films are then discussed in terms of the reconstruction of the growing surface and the contribution of this [H] [ CH 3 ] ratio.

Active-Nitrogen-Doped P-Type ZnSe Grown by Gas-Source Molecular Beam Epitaxy for Blue-Light-Emitting Devices

Active-nitrogen-doped p-type ZnSe epitaxial layers were grown by gas-source molecular beam epitaxy using H2Se. Electrical properties of the N-doped ZnSe layers changed drastically depending on the growth temperature and the VI/II ratio. With decreasing growth temperature, the net acceptor concentration increased. At the growth temperature of 300°C, the net acceptor concentration was as high as 1.02×1018 cm-3. Using this technique, p-n junction diodes with an active layer of ZnCdSe/ZnSe multiple quantum wells were fabricated. These diodes emitted clearly visible blue light (477 nm) at room temperature.

Gas Source Molecular Beam Epitaxial Growth of ZnSe Using Metal Zn and H2Se

ZnSe films were grown on GaAs substrates by gas source molecular beam epitaxy using metal Zn and H2Se as sources. H2Se was thermally cracked in a high pressure gas cell. The effects of growth temperature, VI/II ratio and H2Se cracking temperature on ZnSe growth were investigated. Under the condition where the cracked- H2Se flux controlled the growth rate, ZnSe films with smooth surface morphology were obtained at growth temperatures between 250 and 410° C. With increasing cracked- H2Se flux and/or H2Se cracking temperature, facets emerged on the growing surface and surface morphology was degraded.

Role of carbon and hydrogen in reactive ion etching of InP by gas mixture of ethane and hydrogen

InP crystals were etched by reactive ion etching (RIE) with ethane and hydrogen (C2H6/H2). Etched crystals and gas species were characterized by photoluminescence and mass spectroscopic measurements. Evaporation of phosphorus is induced by hydrogen, mainly originating from H2 gas. Incorporation of C increases with the gas species of hydrocarbon having multiple bonds. Near-bandgap emission with intensities greater than before RIE, which shows the hydrogen passivation, and defect-complex-related emission bands at 1.06-1.07 eV enhanced by RIE were observed. The role of gas species and the identification of defects are discussed on the basis of the experimental results.

Electrical characterization of Au/p-ZnSe structure

Au electrodes were deposited on p-ZnSe layers grown by molecular beam epitaxy (MBE) and gas source (GS) MBE. The influences of the chemical pretreatment before electrode formation and the following heat treatment on electrical characteristics were investigated. All of the samples showed nonohmic current flow. In MBE-grown samples before heat treatment, pretreatment lowers the voltage of current flow rise from 6 V to 4–5 V. On the other hand, GSMBE-grown samples with and without pretreatment showed current flow rise at 4–5 V. The increase of the voltage of current flow rise was observed after heat treatment, irrespective of pretreatment and the growth method. This is related to the difference in the as-grown surface between MBE and GSMBE. The resistivity of the p-ZnSe layer increased slightly after heat treatment below the growth temperature.

Blue Light Emitting Laser Diodes Based on ZnSe/ZnCdSe Structure Grown by Gas Source Molecular Beam Epitaxy

Diode structure with a (ZnSe/ZnCdSe)5 multiple quantum-well active layer sandwiched between n- and p-ZnSe layers was grown on a (100) GaAs substrate by gas source molecular beam epitaxy using H2Se. Stimulated emission from the diode structure was observed at a wavelength of 486 nm under a pulsed current injection at 77 K. The threshold current density was 1.16 kA/cm2.

Diffusion mechanism of Cd in InP and InGaAs

Cadmium was diffused into InP and InGaAs using Cd3P2 + P or Cd3P2 + Cd3As2 as the diffusion sources. Two diffusion fronts were observed. The diffusion characteristics for Cd3P2 + P sources are interpreted based on the interstitial-substitutional model, or its modification, the vacancy complex model. The charge state of the diffusing interstitial cadmium atom is a singly ionized donor. The chemical species of phosphorus which reacts with InP is P2 and gaseous Cd originates from solid-phase CdP2. For Cd3P2 + Cd3As2 diffusion sources, the effective diffusion coefficient and the surface acceptor concentration decrease with increasing the Cd3As2 weight fraction. The relative depth of the deeper diffusion front becomes more deep when the supply of vacancies is suppressed.

Nanometer-Scale Surface Modification Using Scanning Tunneling Microscope (STM)-Based Lithography with Conductive Layer on Resist

The resolution on electron-beam lithography is limited by the electron scattering to high-energy incident electron. The field emission of scanning tunneling microscope (STM)-tip is used for having a very-minute electron-beam. STM electron-beam lithography can do by the low energy of the tunnel current between STMTip and flat electrode, that is formed by three layers that are from an electric conductor, a resist and a semiconductor substrate. We obtain the line of width 82 nm and depth 11 nm by a creative method uses the conductive layer in STM-based lithography.