Yoshimi Momose

Formation of CaMgSi at Ca2Si/Mg2Si interface

Abstract The structural property and interfacial morphology have been investigated for the Ca 2 Si/Mg 2 Si interface. The Ca 2 Si layers were grown on Mg 2 Si layers by heat treatment of the Mg 2 Si/Si substrates in Ca vapor. It is found that the CaMgSi phase is formed at the Ca 2 Si/Mg 2 Si interface. The structural property of the resultant silicides was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The chemical composition of the layers was examined by energy dispersion spectroscopy (EDS). In addition, the chemical analysis by X-ray photoelectron spectroscopy (XPS) revealed the Mg segregation on the silicide surface. The growth mechanism of Ca 2 Si on Mg 2 Si/Si is also discussed.

Simple Fabrication of Mg2Si Thermoelectric Generator

Mg2Si polycrystals have been grown by heat treatment of bulk Si under Mg vapor. The structural property of the Mg 2Si has been investigated. The Mg 2Si shows n-type conduction. The impurity doping to obtain p-Mg 2Si was also demonstrated. In addition, simple fabrication procedure of Mg2Si thermoelectric generators has been developed.

Growth of ZnO on Sapphire (0001) by the Vapor Phase Epitaxy Using a Chloride Source

Zinc oxide (ZnO) films were deposited on sapphire (0001) substrates by vapor phase epitaxy using ZnCl2 as a chloride source. The X-ray diffractogram showed a typical pattern of epitaxially grown ZnO with a hexagonal structure, and a full width at half-maximum (FWHM) of 23.3 min was obtained in the X-ray diffraction profile. Growth rate of the ZnO film increased with increasing growth temperature, the growth rate varied from 0.5 to 3.0 µm/h. A strong band edge emission at 370.0 nm was observed at 20 K photoluminescence spectra.

Growth of InN pillar crystal films by means of atmospheric pressure halide chemical vapor deposition

Preparation of InN thin films has been examined using an atmospheric pressure halide chemical vapor deposition technique. It was found that the quality of the InN pillar crystal film grown on a Si(100) substrate is significantly dependent upon the ratio of NH3∶InCl3 used as source materials. Hall mobility decreases as the NH3∶InCl3 ratio is decreased, while the carrier concentration increases. This is explained in terms of the formation of nitrogen vacancies. A decrease of the NH3∶InCl3 ratio causes the increase of nitrogen defects in the InN film. This also increases the number of electrons being trapped by the defects, while their mobility is reduced because of the electrons being scattered at the vacancies.

Growth of In x Ga 1− x Sb alloy semiconductor at the International Space Station (ISS) and comparison with terrestrial experiments

Background:InxGa1−xSb is an important material that has tunable properties in the infrared (IR) region and is suitable for IR-device applications. Since the quality of crystals relies on growth conditions, the growth process of alloy semiconductors can be examined better under microgravity (μG) conditions where convection is suppressed.Aims:To investigate the dissolution and growth process of InxGa1−xSb alloy semiconductors via a sandwiched structure of GaSb(seed)/InSb/GaSb(feed) under normal and μG conditions.Methods:InxGa1−xSb crystals were grown at the International Space Station (ISS) under μG conditions, and a similar experiment was conducted under terrestrial conditions (1G) using the vertical gradient freezing (VGF) method. The grown crystals were cut along the growth direction and its growth properties were studied. The indium composition and growth rate of grown crystals were calculated.Results:The shape of the growth interface was nearly flat under μG, whereas under 1G, it was highly concave with the initial seed interface being nearly flat and having facets at the peripheries. The quality of the μG crystals was better than that of the 1G samples, as the etch pit density was low in the μG sample. The growth rate was higher under μG compared with 1G. Moreover, the growth started at the peripheries under 1G, whereas it started throughout the seed interface under μG.Conclusions:Kinetics played a dominant role under 1G. The suppressed convection under μG affected the dissolution and growth process of the InxGa1−xSb alloy semiconductor.

Investigation of directionally solidified InGaSb ternary alloys from Ga and Sb faces of GaSb(111) under prolonged microgravity at the International Space Station

InGaSb ternary alloys were grown from GaSb (111)A and B faces (Ga and Sb faces) under microgravity conditions on board the International Space Station by a vertical gradient freezing method. The dissolution process of the Ga and Sb faces of GaSb and orientation-dependent growth properties of InGaSb were analysed. The dissolution of GaSb(111)B was greater than that of (111)A, which was found from the remaining undissolved seed and feed crystals. The higher dissolution of the Sb face was explained based on the number of atoms at that face, and its bonding with the next atomic layer. The growth interface shape was almost flat in both cases. The indium composition in both InGaSb samples was uniform in the radial direction and it gradually decreased along the growth direction because of segregation. The growth rate of InGaSb from GaSb (111)B was found to be higher than that of GaSb (111)A because of the higher dissolution of GaSb (111)B.

Effect of gravity on InGaSb crystal growth

The effect of gravity on dissolution of GaSb in InSb melt and growth of InGaSb was experimentally investigated. Experiments were carried out in a GaSb(seed)/InSb/GaSb(feed) sandwich system under an imposed temperature gradient. In the experiments, the GaSb feed crystal dissolved into the InSb melt to supply the required GaSb component for the growth of In0.1Ga0.9Sb crystal. Two parameters were considered: (1) the inclination angle (θ) of the sample for gravity as 0° and 53°, and (2) the sample diameter (D) as 9 mm and 5mm. When θ was 0°, the interface was almost flat, indicating that convection was axisymmetric and stable. Whereas the interface was distorted towards gravitational direction when θ was 53°, indicating that solutal convection was dominant. The decrease of growth temperature and sample diameter reduced the distortion of interface and the dissolution amount of GaSb feed. The homogeneous crystals were grown at the initial growth stage by supplying the GaSb component during growth.

An experimental study for the role of natural convection in the dissolution of GaSb into InSb melt, and the growth of InxGa1-xSb crystals

The article presents an experimental study for the role of convection occurring during the dissolution of GaSb into InSb melt, and the growth of InxGa1-xSb crystals. Experiments were carried out in a GaSb(seed)/InSb/GaSb(feed) sandwich system under an imposed temperature gradient. In the experiments, the GaSb feed crystal dissolved into the InSb melt to supply the required GaSb component for the growth of InxGa1-xSb crystal. Experiments were carried out for two different reference temperatures and two sample diameters. It was observed that the shape of the GaSb(seed)/InGaSb interface became flatter when the reference temperature was lower and the sample diameter was smaller. The growth length of uniform composition section was larger in the case of higher reference temperature. Experiments show that by varying the reference temperature and the sample diameter, the growth interface and the composition of the grown crystal can be controlled by controlling the natural convection in the melt.