Ferroelectric lithium niobate (LiNbO3) is widely used in integrated and guided-wave optics because of its favorable optical, piezoelectric, electro-optic, elastic, photoelastic, and photorefractive properties. However, detailed summaries of its pertinent physical properties and crystal structure are not readily available. In this tutorial paper, the important tensor physical properties and their mathematical descriptions are compiled and presented. The essential features of the structure of lithium niobate, including its hexagonal and rhombohedral unit cells, are illustrated and the principal (Cartesian) axes used in the description of the anisotropic properties are specified relative to the crystal structure. Errors in property coefficient values and structure information that have been propagated in the literature are corrected.

Lithium niobate: Summary of physical properties and crystal structure

Transparent conductors as solar energy materials: A panoramic review

The electronic density of states (DOS) and magnetic moments of rare-earth antimonides (NdVSb3) has been studied by the first principles full-potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). For the exchange-correlation potential, the GGA+U method is used. The effective moments of NdVSb 3 B was found to be 4.50 . The exchange-splittings of V-3d state electrons and 4f-states of Nd atoms were analyzed to explain the magnetic nature of these systems. The V atom plays a significant role on the magnetic properties due to the hybridization between V-3d and Sb-5p state orbitals. The results obtained are compared and found to be in qualitative agreement with the available results.

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A First Principles Study

During the last few years the interest in the indium nitride (InN) semiconductor has been remarkable. There have been significant improvements in the growth of InN films. High quality single crystalline InN film with two-dimensional growth and high growth rate are now routinely obtained. The background carrier concentration and Hall mobility have also improved. Observation of strong photoluminescence near the band edge is reported very recently, leading to conflicts concerning the exact band gap of InN. Attempts have also been made on the deposition of InN based heterostructures for the fabrication of InN based electronic devices. Preliminary evidence of two-dimensional electron gas accumulation in the InN and studies on InN-based field-effect transistor structure are reported. In this article, the work accomplished in the InN research, from its evolution to till now, is reviewed. The In containing alloys or other nitrides (AlGaInN, GaN,AlN) are not discussed here. We mainly concentrate on the growth, characterization, and recent developments in InN research. The most popular growth techniques, metalorganic vapor phase epitaxy and molecular beam epitaxy, are discussed in detail with their recent progress. Important phenomena in the epitaxialgrowth of InN as well as the problems remaining for future study are also discussed.

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Indium nitride (InN): A review on growth, characterization, and properties

In this review, the structural, mechanical, thermal, and chemical properties of substrates used for gallium nitride (GaN) epitaxy are compiled, and the properties of GaN films deposited on these substrates are reviewed. Among semiconductors, GaN is unique; most of its applications uses thin GaN films deposited on foreign substrates (materials other than GaN); that is, heteroepitaxial thin films. As a consequence of heteroepitaxy, the quality of the GaN films is very dependent on the properties of the substrate—both the inherent properties such as lattice constants and thermal expansion coefficients, and process induced properties such as surface roughness, step height and terrace width, and wetting behavior. The consequences of heteroepitaxy are discussed, including the crystallographic orientation and polarity, surface morphology, and inherent and thermally induced stress in the GaN films. Defects such as threading dislocations, inversion domains, and the unintentional incorporation of impurities into the epitaxial GaN layer resulting from heteroepitaxy are presented along with their effect on device processing and performance. A summary of the structure and lattice constants for many semiconductors, metals, metal nitrides, and oxides used or considered for GaN epitaxy is presented. The properties, synthesis, advantages and disadvantages of the six most commonly employed substrates (sapphire, 6H-SiC, Si, GaAs, LiGaO 2 , and AlN) are presented. Useful substrate properties such as lattice constants, defect densities, elastic moduli, thermal expansion coefficients, thermal conductivities, etching characteristics, and reactivities under deposition conditions are presented. Efforts to reduce the defect densities and to optimize the electrical and optical properties of the GaN epitaxial film by substrate etching, nitridation, and slight misorientation from the (0 0 0 1) crystal plane are reviewed. The requirements, the obstacles, and the results to date to produce zincblende GaN on 3C-SiC/Si(0 0 1) and GaAs are discussed. Tables summarizing measures of the GaN quality such as XRD rocking curve FWHM, photoluminescence peak position and FWHM, and electron mobilities for GaN epitaxial layers produced by MOCVD, MBE, and HVPE for each substrate are given. The initial results using GaN substrates, prepared as bulk crystals and as free-standing epitaxial films, are reviewed. Finally, the promise and the directions of research on new potential substrates, such as compliant and porous substrates are described.

Substrates for gallium nitride epitaxy

The ferroelectric domain in Ti‐diffused c‐plate LiNbO3 optical waveguides were examined by chemical etching. In the Ti‐diffused +c layer, a domain‐inversion layer was formed where the spontaneous polarization is opposite to that of the substrate. The formation is dependent upon diffusion conditions. On the other hand, no domain inversion appeared in the diffused −c layer. It is concluded that the −c face is quite favorable for fabricating Ti‐diffused c‐plate optical waveguide for application in electro‐optic devices. A plausible explanation for the domain inversion is considered.

Ferroelectric domain inversion in Ti‐diffused LiNbO3 optical waveguide

The temperature characteristics of dielectric constants, spontaneous polarization, thermal‐expansion coefficients, indices of refraction, and optical rotatory power of Pb5Ge3O11 single crystals have been investigated in detail from room temperature up to above the Curie temperature, 177°C. From the results of these measurements, the following constants were obtained: linear thermal‐expansion coefficients (αa)F=7.75×10−6/deg°C and (αc)F=7.79×10−6/deg°C (ferroelectric phase), (αa)P=13.8×10−6/deg°C and (αc)P=13.4×10−6/deg°C (paraelectric phase); quadratic electro‐optic constants g33T=0.47×108 cm4 /C2, g13T=0.37×108 cm4 /C2; and electrogyration coefficient γ33 =8.7 cm2/C. An isomorphous compound Pb5(Ge2O7)(SiO4) was synthesized and was found to be ferroelectric with T c=60°C and Ps=1.7 μC/cm2 at room temperature. Ferroelectric properties and electrogyration coefficient were studied in the solid‐solution system Pb5(Ge2O7)(GeO4)1−x (SiO4)x.

Ferroelectric and optical properties of Pb5Ge3O11 and its isomorphous compound Pb5Ge2SiO11

A new method for determining refractive‐index changes in Ti‐diffused LiNbO3 optical waveguides is reported. The measurement process was as follows: (1) Diffusion profiles and Ti concentrations in LiNbO3 optical waveguides were measured by an x‐ray microanalyzer. (2) Ti concentrations in the samples were converted into refractive‐index changes using calibration curves which gave the relation between Ti concentrations and refractive‐index changes. The calibration curves were obtained from highly Ti‐diffused LiNbO3 samples, as well as Ti‐doped LiNbO3 single crystals. As an example, the maximum refractive‐index changes of a Ti‐diffused LiNbO3 optical waveguide made at 1000 °C for 10 h were determined to be Δne=1.05×10−2 and Δno=7.7×10−3.

Precise determination of refractive‐index changes in Ti‐diffused LiNbO3 optical waveguides

The threshold voltage of a GaAs metal‐semiconductor field‐effect transistor (MESFET) fabricated on a liquid encapsulated Czochralski grown, semi‐insulating substrate was found to be influenced by growth‐induced dislocations. Field‐effect transistors located at less than 20–30 μm from a dislocation exhibited a threshold voltage lower than that of FET’s located far from a dislocation. The maximum difference in threshold voltage of FET’s located at less than and more than this critical distance was obtained to be about 300 mV. The first definitive correlation between dislocations and FET threshold voltage is reported.

Direct observation of dislocation effects on threshold voltage of a GaAs field‐effect transistor

Ferroelectric LiNbO3 single‐crystal film was successfully grown onto a LiTaO3 substrate by a new method, epitaxial‐growth‐by‐melting (EGM) method. The propagation of a He–Ne laser beam fed into the film was demonstrated. Some preliminary results of this new technique for fabricating optical waveguides are reported.

Shintaro Miyazawa

Papers

Ferroelectric domain inversion in Ti‐diffused LiNbO3 optical waveguide

Ferroelectric and optical properties of Pb5Ge3O11 and its isomorphous compound Pb5Ge2SiO11

Precise determination of refractive‐index changes in Ti‐diffused LiNbO3 optical waveguides

Direct observation of dislocation effects on threshold voltage of a GaAs field‐effect transistor

Growth of LiNbO3 single‐crystal film for optical waveguides