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The detailed crystalline structure of molecular beam epitaxially grown MnAs thin films on InP(001) substrate has been investigated using high resolution X-ray diffraction techniques. Reciprocal space mapping of the MnAs/InP(001) samples indicates that the MnAs has a cubic zinc-blende (zb) structure with the epitaxial relationship zb-MnAs[110]|InP[110]. The lattice constant of zb-MnAs is ∼6.06 A. The MnAs lattice is relaxed and is mosaic-like likely due to large lattice mismatch between the film and InP substrate. The isotropic nature of the magnetic properties supported our conjecture that the MnAs epitaxial film under study has indeed a cubic structure.

One approach to improve the efficiency of electricity generation of solar cells is to use a luminescent/fluorescent dye that absorbs a part of the spectrum of incident light and then simultaneously emits down-shifted light that matches the spectral response of the solar cells. In this study, the authors numerically simulated the escaping energy losses of isotropic diffuse down-shifted light emitted by luminescent dyes doped in micro/nanostructured solar cell systems. The simulation was accomplished by using the two-dimensional total-field finite-difference time-domain (FDTD) method, which simulates not only reflection and refraction but also diffraction. Two simulation models—one based on a V-grooved luminescent down-shifting (LDS) layer and the other based on a planar luminescent solar concentrator (LSC)—were used, and the size effects of the LDS layer and LSC, effect of doping position on the escaping energy loss, and angle dependency of the escaping energy loss were clarified. For the V-grooved LDS layer, the escaping loss was found to be less than 10% in the wavelength range of 400–1170 nm when the height and width of the V-groove were 360 and 424 nm, respectively. This value of the escaping loss is less than half of that calculated from ray optics, which simulates only reflection and refraction. A planar LSC with a thickness of 300 nm and a length in the submicron range also exhibited smaller escaping loss than a conventional-sized one. Furthermore, the authors confirmed that the reflectance of the micro/nanostructured solar cell systems is lower than the theoretical ray optical reflectance of an air–PMMA–Flat Si layer. This indicates that doping luminescent dyes in such micro/nanostructured solar cell systems potentially improves the light trapping efficiency of down-shifted diffuse light emitted by the luminescent dyes.

We investigated the growth of GaAs 1− x Sb x ( x =1.0, 0.82, 0.69, 0.44, 0.0) layers on Si (0 0 1) substrates using AlSb as a buffer layer. Epilayers were grown as a function of As beam equivalent pressure (BEP) under a constant Sb BEP, and they were then characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), and micro-Raman scattering analysis. We confirmed that GaAs 1− x Sb x layers have been successfully grown on Si substrates by introducing AlSb layers.

We report the magnetic and electrical properties in Mn-doped and undoped (Zn,Sn)As2 epilayers, that were annealed at slightly higher temperatures than the growth temperature. (Zn,Sn)As2 :Mn were epitaxially grown on InP (001) substrates at 300°C, and showed room-temperature ferromagnetism. The hole concentration, saturation magnetization and Curie temperature were measured and evaluated as a function of annealing temperature. The Curie temperature had a tendency to slightly increase at annealing temperatures up to 340°C, and completely disappeared at 400°C. The ferromagnetism could be attributed to hole-mediated ferromagnetism resulting from Mn ion substitutions at both the II-group Zn and IV-group Sn sites, especially from the large solubility of Mn2+ substitution at Zn sites. The disappearance of ferromagnetism may be explained by several types of mechanisms : migration of mobile interstitial Mn atoms, diffusion of substitutional Mn ions to the surface, substitution of interstitial Mn atoms on Zn vacancies, and formation of MnAs clusters. It is noteworthy that the growth of magnetic semiconductor thin films from substrate lattice matching is essential for avoiding magnetic secondary phases such as MnAs clusters.

A novel intersection waveguide-type polarization splitter based on total reflection using the birefringence of the GaInAsP/InP superlattice waveguide is proposed and analyzed in this paper. The semivectorial finite difference beam propagation method (FD-BPM) (which handles both TE and TM modes) is used in the analysis. The waveguide structure including the GaInAsP/InP superlattice is designed; and it is shown that, although with a superlattice core the refractive index for the TM mode is reduced by approximately 0.4 percent, there is no change for the TE mode. Based on this result, the optimal structural parameters such as superlattice layer number, rib height (h), intersecting angle (θ), and port separation length (Lsp) are investigated using a 1.55μm wavelength. It is found that the TE and TM modes can be separated with an insertion loss of less than 0.4 dB for both modes and a crosstalk of less than −35 dB using an intersecting angle of 5° and a device length of approximately 0.9 mm. It is shown that compared to conventional devices, the device length in the proposed device structure can be reduced by using total reflection. The wavelength dependence of the device is also analyzed.

In this paper, the aims of our study are to analyze the gain of semiconductor optical amplifiers with tensile strained multiple quantum wells and to examine the structure for polarization-insensitive characteristics for the purpose of showing the design guidelines. Since lasers with conventional lattice-matched multiple quantum wells have large optical confinement coefficient and large gain coefficient for TE mode, they are not polarization insensitive. Since the modal gain is the product of the optical confinement coefficient and the gain coefficient, the elimination of polarization sensitivity requires increasing the gain coefficient for the TM mode by applying the tensile strain to the well layer in order to compensate for the difference in the optical confinement factor. Assuming a multiple quantum well structure, the analysis obtains the strain distribution over the structure and an envelope function of the wave function and calculates the gain using a density matrix method by electron relaxation effect. It includes the band mixing effect of valence bands. As a result, a structure with little modal gain difference over a wide range at 1.55-μm wavelength has been designed. Also, as a result of examining the effect of deviation from the designed values, it has been found that the variation in the material composition (amount of strain) has a larger effect on the modal gain difference than the variation in the quantum well thickness.

Three-dimensional (3-D) analysis of an intersec-tional optical switch is performed using the finite difference beam propagation method (FD-BPM), and design guidelines are obtained from this analysis. The operating characteristics of the switch are evaluated by extinction ratio and power attenuation in two output ports. The optimal structure parameters, such as normalized frequency (V), waveguide relative refractive index difference (Δω), and intersecting angle (θ), are obtained for 1.55 μm wavelength operation. Wideband operation in the 1.3 to 1.6 μm wavelength range is discussed taking into account the wavelength dispersion of materials. It is found that to achieve an extinction ratio that is better than 20 dB, a refractive index variation of 0.5 percent is enough for single-wavelength operation; however, a refractive index variation larger than 0.7 percent is required at the longer-wavelength side for wideband operation. Finally, the results of 2-D and 3-D analyses are compared and good agreement is obtained with an error of about 1 dB.

This paper proposes an optical filter consisting of GaInAsP/InP waveguides whose performance is examined analytically. This filter is composed of a vertical three- or four-waveguide directional coupler. Based on an eigenmode analytical method, a compact and demultiplexing device is realized. The propagation characteristics of such devices are calculated as being expressed in terms of the superposition of the eigenmodes. A design criterion for both a demultiplexer and bandpass filter is presented. The demultiplexing of the two wavelengths of 1.545 and 1.585 μm with a crosstalk level better than -23 dB at a coupling length 265 μm is demonstrated. Also, with a multiple quantum well waveguide, a value of 6.9 nm for the -15 dB bandwidth at a coupling length 972 μm is obtained. Furthermore, the demultiplexing of the three wavelengths of 1.51, 1.545, and 1.60 μm is found to be possible in a four-guide coupler structure (coupling length 942 μm) with MQW waveguides.

This paper reports a gain analysis of a quantum well laser with multiple quantum well with different well thickness. Since quantum energy levels corresponding to each well appear in a quantum well with different well thickness, it is possible to control to a certain extent the energy distribution of the electrons. This characteristic is used advantageously to control the gain profile of a quantum well laser. In this case, the individual quantum well structures are different and are mutually coupled. Also, since the quantum levels of the second- and higher-order are used, the analysis must be carried out rigorously taking into account the wave nature of the electrons. The laser theory based on the electron relaxation phenomenon has been developed with the wave nature of the electrons considered so that the gain equation is derived. As an example, a structural design has been carried out for low current operation of the oscillation wavelength switch and for flattening the gain profile. Excellent numerical results were obtained. A possibility for new applications of the quantum effect devices is expected.

We prepared boron-doped Si/Si0.8Ge0.2 (Si:B/SiGe) multilayers sputter-deposited on quartz glass substrates, and investigated their structural and thermoelectric properties. These samples were processed by using conventional whole-layer annealing and layer-by-layer annealing methods. Si:B/SiGe multilayer samples annealed layer-by-layer showed good periodicity with well-defined interfaces as compared with conventionally annealed samples (whole-layer annealing). However, Ge diffusion was observed at the interfaces near substrates since the SiGe layer near the substrates suffered a longer integrated annealing time during the layer-by-layer annealing process. It was found that the Si:B/SiGe multilayer annealed layer-by-layer showed thermally stable thermoelectric properties in a wide temperature range from 50 to 800 °C. The present experiment proved that the layer-by-layer-annealing method is an effective way of achieving stable and reliable thermoelectric properties in Si:B/SiGe multilayer micro-thermoelectric devices.