Kensuke Akiyama

Growth of Epitaxial β-FeSi2 Thin Film on Si(001) by Metal-Organic Chemical Vapor Deposition

(100)-Oriented epitaxial β-FeSi2 films 200 nm in thickness were grown on Si(001) substrates using a 20-nm-thick template layer prepared by reactive deposition epitaxy (RDE). The films maintained a strong (100) orientation and the full width at half maximum (FWHM) of the rocking curve corresponding to the β-FeSi2800 diffraction peak decreased from 0.96° to 0.92° with post-annealing at 1173 K in Ar atmosphere for 300 min, suggesting a slight increase in orientation perfection. The films maintained a flat surface after the post-annealing up to 300 min. No photoluminescence (PL) spectrum was observed from the as-deposited film. However, a PL of 0.806 eV was observed at 10 K for the first time from the epitaxial β-FeSi2 film with a good surface flatness, when the film was post-annealed at 1173 K for 300 min.

Electrical Properties of (110)-Oriented Nondoped Mg 2 Si Films with p -Type Conduction Prepared by RF Magnetron Sputtering Method

Magnesium silicide (Mg2Si) thick films with (110) orientation were fabricated on (001) sapphire substrate using radiofrequency magnetron sputtering. Stoichiometric Mg2Si films with composition Si/(Mg + Si) = 0.33 were achieved over a range of vacuum from 10 mTorr to 140 mTorr and 300°C. On postannealing the film at 500°C, the out-of-plane lattice parameter shifted to lower values and the electrical conductivity increased by two orders of magnitude. A room-temperature Seebeck coefficient of 517 μV K−1 was observed and found to decrease with increasing temperature; the Seebeck coefficient remained at a constant positive value of 212 μV K−1 at 500°C. This can be related to the possibility of p-type conduction in this temperature range.

Photoluminescent iron disilicide on modified Si surface by using silver

Pronounced enhancement of photoluminescence (PL) intensity was observed from β-FeSi2 by using metal–organic chemical vapor deposition (MOCVD) on (100) Si substrates coated with a silver (Ag) layer. X-ray diffraction analysis revealed modifications to the crystal structure near the surface of Si, where the in-plane lattice parameter had been elongated, by Ag atomic diffusion from the surface to inside the Si during the heating process before deposition. This modified Si surface contributed to decreasing the non-radiative recombination centers at the β-FeSi2/Si interface and in the β-FeSi2 film, which led to the pronounced enhancement of PL intensity.

In-plane orientation and composition dependences of crystal structure and electrical properties of {100}-oriented Pb(Zr,Ti)O3 films grown on (100) Si substrates by metal organic chemical vapor deposition

In-plane orientation-controlled Pb(Zr x ,Ti1− x )O3 (PZT) films with a thickness of approximately 2 µm and a Zr/(Zr + Ti) ratio of 0.39–0.65 were grown on (100) Si substrates by pulsed metal–organic chemical vapor deposition (MOCVD). In-plane-oriented epitaxial PZT films and in-plane random fiber-textured PZT films with {100} out-of-plane orientation were grown on (100)c SrRuO3//(100)c LaNiO3//(100) CeO2//(100) YSZ//(100) Si and (100)c SrRuO3/(100)c LaNiO3/(111) Pt/TiO2/SiO2/(100) Si substrates, respectively. The effects of Zr/(Zr + Ti) ratio and in-plane orientation on the crystal structure, dielectric, ferroelectric, and piezoelectric properties of the films were systematically investigated. The X-ray diffraction measurement showed that the epitaxial PZT films had a higher volume fraction of (100) orientation than the fiber-textured PZT films in the tetragonal Zr/(Zr + Ti) ratio region. A large difference was not detected between the epitaxial films and the fiber-textured films for Zr/(Zr + Ti) ratio dependence of the dielectric constant, and remanent polarization. However, in the rhombohedral phase region [Zr/(Zr + Ti) = 0.65], coercive field was found to be 1.5-fold different between the epitaxial and fiber-textured PZT films. The maximum field-induced strains measured at 0–100 kV/cm by scanning atomic force microscopy were obtained at approximately Zr/(Zr + Ti) = 0.50 and were about 0.5 and 0.3% for the epitaxial and fiber-textured PZT films, respectively.

Epitaxial growth and photoluminescence properties of β-FeSi2 grains using liquid phase obtained by Au-Si eutectic reaction

Luminescent epitaxial β-FeSi2 grains were grown on the Si (111) substrates precoated with Au-layer. These epitaxial β- FeSi2 grains had (101)/(110)-preferred orientation and were constructed with two kinds of triple-domain structure. The Au-Si liquid phase obtained by the Au-Si eutectic reaction contributed to the formation of such β-FeSi2 grains on the Si (111) surface. Clear photoluminescence (PL) spectrum of β-FeSi2 were observed up to 240 K that indicated the formation of high-quality crystals with the low density of the non-radiative recombination center in the grains.

Preparation of Ca-Si Films on (001) Al2O3 Substrates by an RF Magnetron Sputtering Method and Their Electrical Properties

The constituent phases, electrical conductivity, and Seebeck coefficient of Ca-Si films deposited on (001) Al2O3 substrates by a radio frequency magnetron sputtering method using a Mg disk target with Ca and Si chips are investigated. X-ray diffraction analysis indicates that the films consist of a single phase of CaSi2, CaSi or Ca5Si3 that are deposited together with the films consisting of a mixture of CaSi2 and CaSi. Films with a CaSi2 or CaSi single phase exhibit a metallic behavior. In contrast, films with a Ca5Si3 single phase show p-type conduction and their Seebeck coefficient reaches 90xa0μV/K at 400°C.

Metal–organic chemical vapor deposition growth of β-FeSi2/Si composite powder via vapor–liquid–solid method and its photocatalytic properties

Semiconducting iron disilicide (β-FeSi2) island grains of a few hundred nanometers in diameter were formed on the surface of Si powder by metal–organic chemical vapor deposition. On Au-coated Si powder, the Au–Si liquidus phase was obtained by melting the Si surface via the Au–Si eutectic reaction, which contributed to the formation of island grains. The dramatic decrease in the defect density in β-FeSi2, which was due to this growth mechanism, was confirmed by the photoluminescence properties. The β-FeSi2/Si composite powder could evolve hydrogen from formaldehyde aqueous solution under irradiation of visible light with wavelengths of 420–650 nm.

Epitaxial growth of luminescent β-FeSi2 on modified Si(111) surface by silver

Luminescent epitaxial β-FeSi2 films were grown on the Ag-layer pre-coated Si(111) substrates. These epitaxial β-FeSi2 films had (101)/(110)-preferred orientation and were constructed with a triple-domain structure. The full width at half maximum of the rocking curve of β-FeSi2 202/220 was 0.19o for the films deposited at 760oC on the Si(111) substrates with 85 nm-thick silver layer. The transmission electron microscope analysis indicated the flat and steep β-FeSi2/Si interface. The photoluminescence intensity of this (101)/(110)-orientated epitaxial β-FeSi2 films was larger than that of the directly grown β-FeSi2 films on the Si(111) without silver layer, indicating the decreasing of the density of nonradiative recombination centers in β-FeSi2 film.

Structural characterization of epitaxial Mg2Si films grown on MgO and MgO-buffered Al2O3 substrates

(110)-oriented epitaxial Mg2Si films were grown on (100), (110), and (111) MgO single crystals by RF magnetron sputtering. Two, one, and three types of in-plane variants were observed for (100), (110), and (111) MgO single crystals, respectively. In addition, it was also demonstrated that epitaxial Mg2Si films can be grown on (001) Al2O3 substrates using an epitaxially grown (111) MgO buffer layer. Transmission electron microscopy studies revealed a clear interface between Mg2Si and the MgO buffer layer with an epitaxial relationship. This result indicates that Mg2Si films can be epitaxially grown on other substrates by using an epitaxial buffer layer of MgO.

Growth of (111)-oriented epitaxial magnesium silicide (Mg2Si) films on (001) Al2O3 substrates by RF magnetron sputtering and their properties

Epitaxial Mg2Si films with (111) orientation were successfully grown at 300xa0°C on (001) Al2O3 insulating substrates by RF magnetron sputtering method. The optimal conditions for the epitaxial growth were identified as a low deposition rate and high deposition pressure above 60xa0mTorr. X-ray diffraction and transmission electron microscopy analysis confirmed the growth of (111)-oriented epitaxial Mg2Si films with the following relationship: (111) Mg2Si//(001)Al2O3. The conduction type of the epitaxial films was p-type up to 450xa0°C, which is same conduction type of the (110)-one-axis oriented ones. The electrical conductivity of the epitaxial films was lower than that of (110)-one-axis oriented ones.