Kazuaki Imai

Phase diagram of In-Se system and crystal growth of indium monoselenide

Abstract An equilibrium phase diagram of the In-Se system was investigated in detail by differential thermal analysis (DTA). It was confirmed experimentally that the maximum conversion rate of the InSe crystal as the primary crystal is obtained from an In 1.04 Se 0.96 melt. Composition analyses of ingots grown by the Bridgman method were performed using a He + ion Rutherford-backscattering technique (RBS). The results of the analyses were well consistent with the obtained phase diagram. To appreciate the quality of the InSe crystal, X-ray Laue and ion-blocking patterns, and energy dependance of channeled ions were investigated. These studies indicated that the InSe crystals had no mosaic structure. The values of electron mobility and decay time of photo-excited carriers also indicated the strong improvement of crystal perfection by the non-stoichiometric Bridgman method.

Optimal crystal growth condition of ZnSe grown by molecular beam epitaxy

Abstract The crystal quality of ZnSe grown on the (100) GaAs substrate by molecular beam epitaxy is characterized by ellipsometry and the Rutherford backscattering method. The growth rate and refractive index are measured as a function of the beam pressure ratio of Zn and Se molecules and the substrate temperature. It is discussed that the refractive index reflects the degree of packing of atoms in crystal films. The most close-packed ZnSe crystals are grown at the stronger Se beam pressure by several % than the Zn. The optimal crystal growth temperature around 270°C is confirmed by temperature dependence of growth rate and the refractive index. Substrate temperature dependence of the Rutherford backscattering spectra also shows that MBE ZnSe crystals of the best quality are grown near this temperature.

Photoluminescence of ZnSe-ZnTe strained layer superlattices

Abstract ZnSe-ZnTe strained layer superlattices of 500 periods have been grown on GaAs (001) surfaces by molecular beam epitaxy (MBE) without any buffer layer. The thickness ratio of ZnSe to ZnTe in one period is changed variously, keeping the thickness of one period to be 20 A constantly. The photoluminescence intensity of blue emission of a sample with thin ZnTe layers is 100 times stronger compared with I 2 (emission line due to the exciton-donor complexes) of a simple MBE-ZnSe at 9 K. The temperature dependence of this intensity predicts that the emission structure is due to the isoelectronic traps related to Te.

Anharmonic Properties of Ultrasounds in Diamond-Type Crystals and Quartz Plate under an Intense Exicitation

The harmonic generation due to the third-order elastic (TOE) constants in germanium and gallium arsenide, and the nonlinear current-jump effect due to the fourth-order elastic constants in a quartz plate have been investigated. The complete TOE constants were determined from the measurement using an optical interferometer and from the values derived from the valence-force field theory. They showed a good agreement with those obtained by other experimental techniques. A phenomenon analogous to the hybride optical bistability was observed in a thickness-shear mode quartz resonator, and this was analyzed in terms of an equivalent nonlinear network.

Characterization by ion-channeling of ZnSe grown by photo-assisted molecular beam epitaxy

Abstract Improvement in crystallinity of ZnSe crystals grown by molecular beam epitaxy (MBE) under UV light irradiation was assessed by ion channeling. The present study confirmed that UV irradiation during MBE improves the value of X min from 0.10 to 0.07 by reducing the density of lattice imperfections compared to unirradiated samples.

Phonon Folding in ZnSe–ZnTe Strained Layer Superlattices

Folding of longitudinal acoustic (LA) mode phonons in ZnSe–ZnTe strained layer superlattices, grown on the (001) GaAs without buffer layers by molecular beam epitaxy (MBE), was measured as a function of period and thickness of the layers by Raman scattenng. The dispersion relation between observed LA frequencies and wave number of the superlattices was analyzed by fitting the sound velocity as a parameter in the Rytov model. Two analytical solutions were obtained from the model. It is supported by consideration of calculation and experimental results that the sound velocity of the ZnSe and ZnTe layers in the superlattices is smaller and larger than their bulk values respectively, and this implies elongation of the ZnSe layers and compression of the ZnTe layers.

Interferometric Measurement of the Third-Order Elastic Constants in Germanium and Gallium Arsenide

New measuring technique of the third-order elastic (TOE) constants in solids by using an optical Fabri-Perot interferometer has been developed. The amplitudes of fundamental ultrasonic waves and of induced second harmonic by lattice anharmonicity were measured through a change of the reflected intensity of laser light which is introduced by ultrasonic displacement. The valiles of six independent TOE constants were derived with the aid of valence-force field theory show good agreement with the previously reported values. It is shown that the secondary piezoelectric effects on TOE constants in GaAs would be negligible small. We have developed a new measuring method for the TOE constants by using an optical Fabri-Perot interferometer with which one can measure a small ultrasonic displacement of less than 10-3 8. The detailed experimental method, and the experimental results in germaniums and semi-insulating gallium arsenides are decribed in the following sections.

Electroreflectance of γ-indium selenide above the fundamental edge

Abstract The electroreflectance of the layered semiconductor γ-InSe is measured between 2.3 and 3.0 eV at 78 K with the Schottky-barrier technique. It is found from the experiment that the structures are due to excitonic transition at nearly isotropic M 0 critical points. The transition energies, the binding energies of excitons in meV, and the reduced masses are those in the following parentheses: [2.547 ± 0.002, 14 ± 1, (0.12 ± 0.01) m 0 ] for the E′ 1 transition, and [2.883 ± 0.002, 10 ± 1, (0.090 ± 0.008) m 0 ] for the E 1 transition, respectively.