Fumihiko Ohtani

Topmost surface analysis of SrTiO3 (001) by coaxial impact‐collision ion scattering spectroscopy

The terminating atomic plane of SrTiO3 (001) surface was investigated by means of coaxial impact‐collision ion scattering spectroscopy (CAICISS). CAICISS spectra proved that SrTiO3 (001) surfaces of as‐supplied substrates as well as of O2‐annealed substrates were predominantly terminated with TiO2 atomic plane, while the SrO atomic plane came at the topmost surface of SrTiO3 (001) homoepitaxial film. This indicates the structural conversion of the topmost atomic layer from TiO2 to SrO occurred during the SrTiO3 homoepitaxial growth. The azimuth rotational CAICISS spectra exhibited a fourfold symmetry in the surface atom alignments, showing the square lattice structure of a terminating plane.

Layer-by-layer growth of GaAs studied by glancing angle scattering of fast ions

Angular distribution of scattered ions at glancing angle incidence of 3 keV He ions on a (001) surface of GaAs is studied during its molecular beam epitaxial growth. We report observation of intensity oscillations of the scattered ions from the growing surface. The period of the oscillations corresponds to the growth time of one monomolecular layer. The oscillations of the intensity is due to the oscillatory change in surface step density during layer‐by‐layer growth of the surface. This observation is in agreement with the intensity oscillations of reflection high‐energy electron diffraction (RHEED) from epitaxially growing surface of GaAs.

Identification of the terminating structure of 6H–SiC(0001) by coaxial impact collision ion scattering spectroscopy

The terminating structure of 6H–SiC(0001) substrates fabricated by the Acheson method was directly identified by means of coaxial impact collision ion scattering spectroscopy (CAICISS). The CAICISS spectra showed that the topmost surfaces of the samples were Si-terminated planes for both the front and rear faces. It was also shown that the (0001)Si face was composed of Si-terminated flat terraces and steps, the height of which corresponded to one-half the unit cell length along the 6H–SiC c axis.

Cleaning of Si (100) surface by As ionized cluster beam prior to epitaxial growth of GaAs

It has been found that the exposure of a Si (100) surface to an As ionized cluster beam (ICB) is effective in the preparation of the surface prior to epitaxial growth of GaAs under conventional high vacuum conditions of 2×10−5 Pa. This process is achieved at a temperature as low as 600 °C. A clear 1×2 or 2×2 reflection high energy electron diffraction pattern observed after the procedure indicates good ordering of the sample surface. The cleaning process is attributed to chemical and physical sputtering by As ICB in the first stage and to the subsequent As termination of Si dangling bonds. It has been found that the optimum preparation conditions are an accelerating voltage of the As ionized cluster beam of 1.3 kV and a substrate temperature of 600 °C. GaAs films deposited on As ICB treated Si (100) substrates show good crystal quality with single domain structure.

ICB deposition and epitaxial growth of GaAs thin films

Abstract The hetero- and homoepitaxial deposition of GaAs films by the ionized cluster beam technique in connection with subsequent neutral beam deposition forming a double layer structure have been studied. It is found that ICB-deposited films have superior quality in comparison with conventional ion beam deposited films and comparable quality like MBE or MOCVD-deposited films. By the fabrication of device structures, it has been proved that the start of film growth from an interface formed by an ICB-deposited As layer is advantageous. Additionally, surface cleaning by low-energy ionized cluster beams has been studied. For the first time, defect-free surface cleaning by low-energy cluster ion beams has been realized.

Coaxial Impact Collision Ion Scattering Spectroscopy Measurements of As/Si(100) Structure Prepared by Ionized Cluster Beam Method

The surface structure of a Si (100) substrate exposed to an As ionized cluster beam (ICB) prior to epitaxial growth of GaAs was investigated by means of coaxial impact collision ion scattering spectroscopy (CAICISS). As a result of the measurement, first, it was proven that both As and Si dimers were formed after As ICB exposure. Second, both As and Si atoms form double domains of 2×1 and 1×2, and both As and Si areas of one domain are larger than those of the other domain in the case of a 3°-off Si substrate. Furthermore, it is likely that As atoms terminate Si atoms as if the As atoms replace the top Si layer. Third, the Si surface is not damaged by As ICB exposure, and the As ions seem to be implanted to the substitutional sites.

Observation of Ellipsometric Oscillations when Depositing SiOx Film on Si(100) Substrate Using an Electron Beam Deposition Method

We have observed ellipsometric oscillations when depositing SiOx film on Si(100) substrate using an electron beam deposition method. A period of these oscillations is calculated to be 5.3 A thick. From an investigation using a rough surface model in ellipsometry, it is considered that this SiOx film is deposited layer-by-layer. This ellipsometry oscillation, first reported in this letter, is applicable to noncrystalline films in which reflection high-energy electron diffraction (RHEED) oscillations are ineffective.

The determination of atomic plane on InP (001) surface by CAICISS

We have observed the sputtered and the annealed InP [001] surfaces to determine the species of the topmost atomic plane on these surfaces by coaxial impact collision ion scattering spectroscopy (CAICISS). We have identified that the indium top surface without serious roughness can be acquired by Ar/sup +/ sputtering even if the substrate temperature is as low as 300 /spl deg/C. In AFM observations, this surface exhibits textured structure, which is composed of double atomic height steps. Furthermore, the azimuthal dependence of CAICISS spectra show two-fold symmetry with respect to the <110> axis, which indicates that the crystalline quality of this surface is quite high. Therefore, we consider that this surface is applicable to the substrate for heteroepitaxial growth.

In Situ Determination of Terminating Atomic Plane of SrTiO3(001) by Coaxial Impact Collision Ion Scattering Spectroscopy

In situ characterization of the topmost surface of SrTiO3(001) was performed by means of coaxial impact collision ion scattering spectroscopy. As a result, it was proven that the displacement of Sr atoms occurred in the surface region at high temperatures around 500 °C in the case of the as-supplied SrTiO3 substrates terminated with TiO2 atomic plane. Sr atoms shifted by 0.012±0.002 nm toward [001] direction. On the other hand, no displacement was observed in the case of O2 annealed samples at 1000 °C for 10 hours. It indicated that the stable topmost surface structure was formed by the high temperature annealing in the SrTiO3 substrates.

In-Situ Study of Growing Surface by Glancing Angle Scattering of Fast Ions

At glancing angle incidence of fast ions on a clean single crystal surface, most of the ions are reflected from the topmost atomic layer without penetrating the crystal surface. This phenomenon is utilized for in-situ study of growing surface. Angular distribution of scattered ions at glancing angle incidence of 3 keV neutral He and He+ ions on the (001) surface of GaAs is studied during its molecular beam epitaxial growth (MBE). The intensity oscillations of the scattered ions are observed during the growth. The period of the oscillations corresponds to the growth time of one mono-molecular layer. The oscillations of the intensity are attributed to the oscillatory change in surface step density during layer-by-layer growth of the surface.