Yoshio Morita

Preparation and Properties of Single Crystal CuAlSe2 Film

Epitaxial CuAlSe2 film has been grown on the GaP(100) substrate by molecular beam epitaxy, and its optical and electrical properties have been characterized. The spectrum of optical reflectance suggests that the band gap of the film is about 2.7 eV, which agrees with that of the bulk material. The photoluminescence spectrum at 77 K showed no band edge emission, but only deep level-related emissions ranging from 520 nm to 870 nm. The CuAlSe2 sample exhibits n-type conductivity with the resistivity of 0.02 Ωcm, the carrier concentration of 4×1018 cm-3 and the mobility of 60 cm2V-1s-1.

Effects of nonmetal addition on hydriding properties for Ti–Mn Laves phase alloys

Abstract The effects of nonmetal addition such as B, C, O, S and Se, on hydriding properties were investigated for Ti 0.9 Zr 0.1 Mn 1.4 Cr 0.4 V 0.2 Laves phase alloys. It was found that for both as-cast and annealed samples, the addition of nonmetal elements such as S, Se and C greatly increases the plateau pressure, improves the plateau slope factor, and expands the hysteresis. The effect of increasing the plateau pressure was strongest for the S addition. These phenomena are possibly related to the appearance of manganese-rich minute particles as observed by scanning electron microscopy. The above effects pave the way for increasing the hydrogen storage capacity of the Ti–Mn Laves phase alloys.

Characterization of CuAlS2 Films Grown by Molecular Beam Epitaxy

Undoped and As-doped CuAlS2 films have been grown on GaAs(100) substrates by molecular beam epitaxy, and their optical and electrical properties have been characterized. X-ray diffraction patterns show that the films grow epitaxially with the c-axis perpendicular to the substrate surface. Both undoped and As-doped CuAlS2 films have exhibited a near-band-edge emission around 3.4 eV with accompanying deep-level-related emissions at 77 K. An As-doped CuAlS2 film exhibits p-type conductivity with the lowest resistivity of 1 Ωcm and the carrier concentration of 5×1017 cm-3.

Formation of a Cu-Al-Se Phase with a Long-Range Order by Molecular Beam Epitaxy

A new phase in the Cu-Al-Se system was found on GaP substrates under growth conditions of an excess Cu vapour pressure and a growth temperature of 1073 K by use of molecular beam epitaxy. The mean composition of this film is close to the formula Cu3AlSe5, and differs considerably from the chalcopyrite structure compound CuAlSe2. We provide the first evidence of the presence of a new Cu-Al-Se phase with a long-range order.

Powder X-ray diffraction under a high-pressure hydrogen atmosphere for Zr–Cr based Laves phase alloys

Abstract Zr–Cr based Laves phase alloys were investigated by powder X-ray diffraction under a high-pressure hydrogen atmosphere and/or high temperature in order to compare two crystal structures of the same composition. These alloys were synthesized in either the C14 or the C15 type and absorb hydrogen at room temperature. We observed the X-ray diffraction peaks of the C14 type in as-cast ingots and the C15 type in annealed ingots. Line broadening of the X-ray diffraction profile upon hydriding was not observed in either the C14 or C15 phase. The C14 H-free alloys had an axial ratio c/a slightly smaller than √(8/3), and the C14 hydrides had an axial ratio c/a slightly larger than √(8/3). Under a high-pressure hydrogen atmosphere, the cell volume of both the C14 and C15 hydrides decreases with an increase in temperature. These phenomena are explained by the change in hydrogen concentration. At constant hydrogen concentration, the cell volume expansion of the C15 phase upon hydrogenation was larger than that of the C14 phase.

Characterization of a new Cu-Al-Se phase grown by molecular beam epitaxy

We have confirmed the existence of a new Cu-Al-Se phase grown by molecular beam epitaxy. The phase possesses a crystal structure equivalent to the tetragonal structure compound Cu5FeS4 found in the Cu-Fe-S system, and has a direct band gap of around 3.1 eV at room temperature. The new Cu-Al-Se phase clearly differs from the chalcopyrite structure compound CuAlSe2, and is considered to be a Cu5AlSe4 compound.

Growth and characterization of Cu-Al-Se system by MBE

Undoped and Zn-doped Cu-Al-Se films have been grown on GaAs(100) substrates by molecular beam epitaxy, and their optical and electrical properties have been characterized. The compositions of the grown films are about 50 at% Cu, 10 at% Al and 40 at% Se, and single-crystal films are obtained. The photoluminescence spectrum of the undoped film exhibits blue emission at 77 K and room temperature. The undoped film annealed at 550°C for 16 h shows p-type conductivity with a resistivity of 6.9X10-3 Ω cm, a carrier concentration of 2.5X1018 cm-3 and a mobility of 370 cm2 V-1 s-1. On the other hand, Zn-doped as-grown film shows n-type conductivity with a resistivity of 2.1X10-3 Ω cm, a carrier concentration of 1.9X1019 cm-3 and a mobility of 150 cm2 V-1 s-1. These characteristics suggest the possibility of p-n junction optical devices fabricated with undoped and Zn-doped Cu-Al-Se films.

Characterization of Novel Cu-Al-Se Films Grown by Molecular Beam Epitaxy

Undoped and Zn-doped Cu-Al-Se films have been grown on GaAs(100) substrates by molecular beam epitaxy, and their optical and electrical properties have been characterized. The compositions of grown films are about 50 at%Cu, 10 at%Al and 40 at%Se, and single-crystal films are obtained. The photoluminescence spectrum of an undoped film exhibits a blue emission at 77 K and room temperature. The undoped film annealed at 550°C for 16 h shows p-type conductivity with the resistivity of 6.9×10-3 Ωcm, the carrier concentration of 2.5×1018 cm-3 and the mobility of 370 cm2V-1s-1. Zn-doped as-grown film shows n-type conductivity. These characteristics suggest the possibility of p-n junction optical devices fabricated with the novel Cu-Al-Se films. On the other hand, the current-voltage characteristic of Cl-doped ZnSe/undoped Cu-Al-Se/ p-GaAs exhibits a rectifying characteristic with the turn-on voltage of 2.7 V.