Tomohiro Onda

Theoretical analysis of Cerenkov-type optical second-harmonic generation in slab waveguides

Optical second-harmonic generation in the Cerenkov-radiation scheme in slab waveguides has been theoretically investigated for all the possible type I configurations. By solving the nonlinear wave equations analytically, a simple general expression for the second-harmonic power has been obtained. Characteristics of the Cerenkov-type second-harmonic generation and optimum conditions for attaining high conversion efficiencies are discussed on the basis of the theoretical analysis. It is shown that, in order to attain high conversion efficiencies, off-diagonal elements of the nonlinear optical coefficient tensor should be utilized taking advantage of birefringence. >

An Extended X-Ray-Absorption Fine-Structure Study of Bond Lengths in GaAs1-xPx

Extended X-ray-absorption fine-structure measurements were performed on GaAs1-xPx, a typical III-V-V type semiconductor alloy, with the composition x as a parameter. The results reveal that the Ga-As and Ga-P nearest-neighbor bond lengths differ, showing a tendency to retain their respective bond lengths in the binary compounds. This feature is similar to that found earlier in Ga1-xInxAs, a III-III-V type alloy.

Thermodynamic Theory of III-V Semiconductor Quaternary Solid Solutions

A thermodynamic theory is proposed for two types of quaternary solid solutions of III-V semiconductors, AxByC1-x-y and AxB1-xCyD1-y. The free-energy xpression for the solid solutions is obtained on the basis of the bond picture of crystalline semiconductors. A concept of composition-dependent bond energies, which is consistent with the experimental results of recent EXAFS measurements, is introduced instead of the conventional pairwise-interaction energies. For solid solutions of the type AxByC1-x-yD, on the free-energy expression obtained coincides with the conventional expression. For solid solutions of the type AxB1-xCyD1-y, the other hand, a different type of behavior is predicted from the free-energy expression obtained, which is expected to agree better with experimental phase diagrams.

Theory of Optical Second-Harmonic Generation in Slab Waveguides

A theory of optical second-harmonic generation in a slab waveguide with a nonlinear dielectric core is presented; two types of second-harmonic generation, the guided-mode and the Cerenkov-radiation types, are systematically treated on an equal basis. We have obtained exact analytical solutions for the field distribution and the power of TE-mode second-harmonic waves, neglecting the depletion of the fundamental waves and assuming isotropic and nondissipative mediums. Conditions for attaining high conversion efficiency are discussed on the basis of the results of numerical calculations.

Theory of Long-Range Order in III–V Semiconductor Ternary Alloys. I. Thermodynamic Model

A thermodynamic model which describes the coexistence of immiscibility and long-range order is presented for III-V semiconductor ternary alloys. This model is an extension of the previously proposed bond model, combined with the Bragg-Williams approximation, and yields a description of long-range order basically different from the current theories based on five types of tetrahedral cells. Immiscibility is attributed to the composition dependence of the bond energies, and long-range order to the order dependence of them. It is also pointed out that order-disorder transitions observed in III-V semiconductor alloys should be of the first kind.

Theory of Optical Second-Harmonic Generation in Slab Waveguides with Dissipative Nonlinear Dielectric Cores

A theory of optical second-harmonic generation (SHG) in a dissipative slab waveguide is presented, where Cerenkov-radiation-type SHG and guided-mode-type SHG are treated on an equal basis. Analytical solutions of the field distribution are obtained for TE-mode second-harmonic waves generated in a slab waveguide consisting of a dissipative nonlinear-dielectric core and nondissipative linear-dielectric claddings. We then study the effects of absorption on the conversion efficiency, providing typical examples of numerical calculation for Cerenkov-radiation-type SHG.

Liquid Phase Epitaxy of Miscible and Immiscible GaInPAs Alloys on (100)-Oriented GaPxAs1-x (x=0, 0.2, 0.4) Substrates

A comprehensive study on miscible and immiscible GaInPAs LPE layers grown on (100)-oriented GaAs, GaP0.2As0.8 and GaP0.4As0.6 substrates is presented, including the studies by photoluminescence, X-ray diffraction, cathodoluminescence, Auger electron spectroscopy and transmission electron microscopy. Using three types of substrates with different lattice constants, we have obtained some new insights into the miscibility gap of GaInPAs alloys. It has been demonstrated that GaInPAs LPE layers inside the miscibility gap exhibit composition modulations and show peculiarities in luminescent spectra and X-ray rocking curves, the degree of which varies with layer thickness.

Behavior of miscibility gaps in the phase diagrams of III–V semiconductor: I. Ternary systems solid solutions

Abstract The behavior of miscibility gaps in solid-liquid/ gas phase diagrams has been studied for III-V semiconductor ternary solutions. The results are presented for the two types of immiscible system: (1) systems such as GaInAs where a miscibility gap appears only at low temperatures and (2) quite immiscible systems such as GaPSb where a miscibility gap extends to the melting temperatures of constituent binary semiconductors. The solid immiscibility brings about an extraordinary fold of the liquidus surface. The liquid on the folded portion, being supersaturated, is in quasi-equilibrium with the unstable or metastable solid inside the miscibility gap.

Extended X-Ray-Absorption Fine-Structure Beats: Application to III-V Semiconductors

The extended X-ray-absorption fine-structure beat method is applied to cases in which two scattering shells are composed of different atomic species. Though a knowledge of phase shift difference is required, the separation of the closely-lying shells can be obtained without any adjustable parameter. The method was tested on GaAs, InAs and In0.53Ga0.47As, and an accuracy of 0.02 A was obtained.

Behavior of Miscibility Gaps in the Phase Diagrams of III-V Semiconductor Solid Solutions: Quaternary Systems of the Type AxB1-xCyD1-y

The behavior of miscibility gaps in liquid-solid phase diagrams has been studied schematically for III-V semiconductor quaternary solutions of the type AxB1-xCyD1-y such as GaInPAs and AlInPAs. The topological features of the liquidus surface affected by solid immiscibility have been the focus of our examination. Liquidus surfaces below the melting temperatures of the constituent binary semiconductors are presented for typical geometric patterns of a miscibility gap. Liquidus surfaces around the melting temperatures are presented for two typical cases realized in systems such as GaInPAs and AlInAsSb.