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Four-wave mixing (FWM) in an InxGa1-xAs/AlAsySb1-y intersubband transition (ISBT) optical waveguide operating in the 1.55-μm wavelength region is discussed. The third-order optical nonlinear susceptibilities of InxGa1-xAs/AlAsySb1-y multiple quantum wells (MQWs) are estimated theoretically. ISBT excitation causes large third-order optical nonlinearity. χ(3) values of more than 1 × 1016 m2/V2 are obtained. The propagation of interacting waves for FWM in InxGa1-xAs/AlAsySb1-y ISBT optical waveguides is discussed. The interaction length is limited not only by phase matching but also by ISBT absorption. Sufficiently high FWM conversion efficiencies were obtained theoretically and experimentally for realizing coherent wavelength convertors. FWM in an InxGa1-xAs/AlAsySb1-y ISBT waveguide is a promising method for realizing compact and high-efficiency coherent wavelength conversion. [ABSTRACT FROM AUTHOR]

Nearly lattice-matched AlxGa1-xAsySb1-y alloys with Al composition x>0.7 were grown by molecular beam epitaxy. The indices of refraction for a series of alloy compositions were measured. The Al composition was determined by x-ray diffraction (XRD) measurements assuming that the AlxGa1-xAs film that was grown prior to the growth of the AlxGa1-xAsySb1-y layer has the same Al composition. The arsenic to antimony ratio was determined by (004) symmetrical and (115) asymmetric reflection XRD rocking curve measurements. The refractive index and thickness were obtained by prism coupler measurements. A symmetric 75° Si prism coupler was employed to excite the waveguide modes with wavelengths of 1319 and 1540 nm. The shift in the measured indices of refraction from that of the calculated values revealed a deviation from the interpolating scheme based on the binary or ternary alloy data. [ABSTRACT FROM AUTHOR]

Pd Schottky barrier diodes were fabricated on undoped AlxIn0.02Ga0.98-xN/GaN with x less than 20%. The material properties, which were characterized by photoluminescence, x-ray diffraction, and atomic force microscopy, indicated that the quaternary samples were coherently grown on GaN template with high crystalline quality. The flatband barrier height obtained by capacitance-voltage (C-V) measurement increased with increasing Al mole fraction (increasing the band gap of the quaternary) up to 2.06 eV, in agreement with the predictions of the Schottky-Mott theory. However, current-voltage (I-V) measurements revealed that the barrier height decreased from 1.32 to 1.12 eV, which was accompanied by an increase in ideality factor from 1.04 to 1.73. The large difference of barrier height between I-V and C-V measurements could not be quantitatively explained by the traditional electron transport mechanisms of Schottky diode, such as tunneling effect, image force effect, and barrier inhomogeneity theory. Strong polarization effect in strained AlxIn0.02Ga0.98-xN/GaN heterostructure was proposed to account for the experimental results, since similar phenomena had been observed extensively in strained AlyGa1-yN/GaN heterojunction structures. [ABSTRACT FROM AUTHOR]

The nonlinear optical phase shift in self-assembled InAs quantum dots (QDs) under resonant excitation in a ground-state transition was measured by a unique two-color pump/probe ellipsometric polarization analysis. This ellipsometric analysis makes use of the large optical birefringence of SK-QD [(SK) — Stranski-Krastanov] originating from the asymmetric structure. A phase shift of 0.5π rad was obtained at an input pump pulse energy density of 30 pJ/μm2, a detuning of 11 meV, and a time delay of 20 ps in a 1 mm long waveguide having QDs with a peak wavelength of 1290 nm, a volume density of 4×1015 cm-3, and inhomogeneous broadening of 35 meV. Analysis revealed that the phase shift is mainly attributed to the absorption saturation for TE-polarized light, though other mechanisms also could contribute at higher pumping. The calculation, based on the two-level approximation, revealed that the minimum energy density for π shift is 240 fJ/μm2, calculated under ideal conditions. [ABSTRACT FROM AUTHOR]

The normal-incidence reflectance measurement was employed to obtain the free exciton transition energy (E[sub FX]) of AlGaN alloys in Al[sub x]Ga[sub 1-x]N/GaN/sapphire heterostructure grown by metalorganic chemical vapor deposition. It was found that the thickness variation of the AlGaN layer may cause a noticeable change in the line shape of reflectance spectrum and impede the identification of the desired excitonic position. By using a reflection model of two absorbing layers with a transparent substrate, the experimental reflectance spectra were theoretically simulated and utilized to explain the reflection mechanism in Al[sub x]Ga[sub 1-x]N/GaN heterostructures. On the basis of the above analysis, the feasibility of the reflectance measurement for such heterostructures is confirmed. At room temperature, the E[sub FX]s obtained from the fitting showed an excellent agreement with the corresponding peak energies in the photoluminescence spectra. Furthermore, at the optical energy position about 100 meV above the E[sub FX], the spectral feature of exciton-LO phonon interaction was observed in the reflectance spectrum record for low Al composition (x≤0.16). Using the Al mole fraction derived from x-ray diffraction measurement, the bowing parameter of the epitaxial AlGaN layer was determined. In the range of 0≤x<0.3, the resulting bowing parameter shows a downward value of 0.53 eV. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The dependence of the properties of AlInGaN/GaN Schottky barrier diodes (SBDs) on Al mole fraction is analyzed. Strong polarization effect in strained [Al.sub.x][In.sub.0.02][Ga.sub.0.98-x]/GaN heterostructure is proposed to account for the results as similar phenomena is seen in strained [Al.sub.y][Ga.sub.1-y]N/GaN heterojunction structures.

The characteristics of InGaN multiple quantum-well (MOW) green light emitting diodes (LEDs) on Si substrates grown by metal organic chemical vapor deposition are reported. The LED also exhibited a stable operation over 500 h under automatic current control (20 mA) condition at 27 degrees C.

The Nd-Fe-B (tNFB=30 nm)/[Dy (tDy nm)/Nd (tNd nm)] (tDy/Nd=20 nm) (thickness tDy=0-10 nm) thin films were deposited on Al2O3(0001) substrate and subsequently in-situ annealed at 470°C. As-deposited Nd-Fe-B thin films with a highly perpendicular orientation of c-axis were deposited by introducing bcc-Mo(111) single crystal buffer layer. After post-annealing, the grain size of the Nd-Fe-B/Dy/Nd thin films with the tDy=10 nm and tNd=10 nm becomes large due to the Dy and the Nd atoms thermal diffusion, while DyFe2 and Dy oxide compounds are formed in Nd-Fe-B layers, which is confirmed by means of a combination of atomic force microscopy observation and X-ray diffraction measurement. The Hc of Nd-Fe-B/Dy/Nd thin films with the tDy=10 nm and tNd=10 nm was approximately the same value of the Nd-Fe-B thin films without Dy/Nd double layer annealed at 470°C. On the other hand, Hc is enhanced to be about 22.1 kOe in the annealed Nd-Fe-B/Dy/Nd films with the tDy=0.8 nm and tNd=19.2 nm. [ABSTRACT FROM AUTHOR]

A reflection model of two absorbing layers with a transparent substrate is used and the power reflectance of the AlGaN/GaN/sapphire heterostruture is numerically calculated. The analysis shows that reflectance measurement is undoubtedly feasible in determining the free exciton transition energy (E(Sub FX) of the AlGaN epilayer in the AlGaN/GaN heterostructure.

We report on a direct comparison of the depth and lateral resolution of the current state-of-the-art laser-assisted atom probe microscopy analysis of single-crystalline silicon. The isotopic heterostructures composed of 5-15 nm-thick 28Si- and 30Si-enriched layers were measured to reconstruct three-dimensional images of 28Si and 30Si stable isotope distributions in the surface perpendicular and parallel directions for the analysis of the depth and lateral resolution, respectively. The decay length experimentally obtained for the lateral direction is only about twice longer than in the direction, meaning that the lateral resolution is higher than obtained by secondary ion mass spectrometry. [ABSTRACT FROM AUTHOR]

We report the characteristics of InGaN multiple-quantum-well (MQW) green light-emitting diodes (LEDs) on Si (111) substrates. The MQW LEDs were grown on Si by metalorganic chemical vapor deposition using Al[sub 0.27]Ga[sub 0.73]N/AlN intermediate layers. The LED on Si showed an operating voltage of 7 V, a series resistance of 100 Ω, an optical output power of 20 μW, and a peak emission wavelength of 505 nm with a full width at half maximum of 33 nm at 20 mA drive current. The optical output power was half as compared to that of green LED on sapphire. The LED also exhibited a stable operation over 500 h under automatic current control (20 mA) condition at 27 °C. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Details a study which investigated the magneto-optical properties of (Yb, Tb, Bi)[sub3]Fe[sub5]O[sub12] thick garnet films. Experimental methods; Compositional dependence of the magneto-optical properties of the films; Temperature dependence of bismuth-substituted rare-earth garnet films on rotation coefficients.

Presents information on a study which described the effect of stress relaxation on the polarization of indium gallium arsenide phosphate buried heterostructure lasers by means of a repetitive temperature change. Examination of the effect of temperature on the polarization state for the lasers; Analysis of the change in the ratios of four samples under a repetitive temperature change; Discussion on the optical power for thermal efficiency and TM modes in all samples at room temperature.

Presents a study that proposed a high-efficiency flat-surface buried heterostructure (BH) distributed feedback laser. Description of an InGaAsP/indium phosphide flat-surface BH distributed feedback laser; Structural features of the laser; Fabrication of the laser using a three-step liquid phase epitaxy.

Presents an evaluation of the coupling coefficient of a distributed feedback laser with residual facet reflectivity. Details of the experimental techniques used; Analysis of the behavior of mode spacing under the influence of small facet reflectivities.