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We have investigated the spectroscopic properties of Bi2O3–B2O3 glasses doped with Nd3+ and Yb3+ separately, and doubly doped with the same ions, in order to search for appropriate phosphors for an optical coherence tomography (OCT) light source. The effects of Yb3+ and Nd3+ co-doping and varying Yb3+ concentration on the spectrum shape were studied to obtain an optimum line shape for OCT. We successfully obtained a Gaussian-like shape spectrum from 5.0Yb2O3–1.0Nd2O3–46.0Bi2O3–46.0B2O3 (in nominal molar composition) with a full-width-at-half-maximum (FWHM) of 101 nm in the wavelength region around 1000 nm. This FWHM corresponds to a depth resolution of 4.5 µm, which is about twice that of conventional light emitting diodes (LEDs) and super luminescent diodes (SLDs). The Gaussian-like line shape is very important to suppress ghost images in OCT. These results indicate that a Yb3+, Nd3+ co-doped Bi2O3–B2O3 glass phosphor can indeed be applied as a new type of OCT light source.

Structural and surface morphology studies of MnF2 epitaxial layers have been performed by x-ray diffraction and atomic force microscopy (AFM). MnF2 layers of different thicknesses (0.12–1.25 µm) were grown by MBE on Si(0 0 1) substrates with the deposited CaF2-buffer layer having a 1 1 0 orientation and a grooved and ridged surface. X-ray diffraction patterns in the 10°–60° angular range have been measured. Profiles of diffraction peaks in two directions—parallel and normal to the diffraction vector—as well as the intensity distribution around 2 2 0 reciprocal lattice points were obtained. It was found that the metastable orthorhombic phase of α-PbO2 type with [1 1 0] growth direction dominates in the films; a much smaller portion of the stable rutile type phase was also detected, though it increases with the film thickness. As follows from the x-ray diffraction data, the films have a mosaic block structure. Parameters of the crystallites were determined using the Williamson–Hall analysis of angular width of the diffraction peaks. It was obtained that the crystallites of the orthorhombic phase have an elongated shape oriented along the direction of the CaF2 ridges. The AFM study confirms a regular distribution of the orthorhombic crystallites and shows the appearance of some irregular shaped crystallites on the top of the thick MnF2 films.

Interfacial roughness of InxGa1-xAs/InP (x=0.53) multiple quantum wells (MQW) grown by metalorganic vapor phase epitaxy has been investigated by cross-sectional scanning tunneling microscopy (STM). The MQW structure is composed of 125 periods of 11-nm-wide well layers and 44-nm-wide barrier layers on an InP (001) substrate. The observed STM images have revealed that the InGaAs-on-InP interface is extremely sharp compared to the InP-on-InGaAs interface; the roughness and terrace size on the InGaAs-on-InP interface are 1–2 monolayers (ML) and 31 nm, respectively, while they are 3–4 ML and 9 nm on the InP-on-InGaAs interface. The large roughness observed for the InP-on-InGaAs interface is interpreted in terms of the incorporation of residual As atoms on the InGaAs surface.

Distribution of In in GaAs/InAs(1ML)/GaAs structure was investigated by X-ray crystal truncation rod scattering measurement. The InAs layer and the GaAs cap layer were grown at 480/spl deg/C on the GaAs buffer layer grown at 590/spl deg/C. After the growth, the samples were annealed at different temperatures, and the thermal stability of the GaAs/InAs/GaAs structure was investigated. In atoms were surely confirmed in 1ML when the sample was as grown. However, when the sample was annealed at 590/spl deg/C only for 10 min, the In atoms widely spreaded in the GaAs layers. The diffusion coefficient of In in the GaAs layer grown at 480/spl deg/C was greater than that in the GaAs layer grown at 590/spl deg/C. The difference is considered to be caused by the Ga vacancies generated in the GaAs layer grown at 480/spl deg/C.

We have grown InAs quantum structures by droplet hetero-epitaxy on InP nanopyramids and investigated their luminescence property. InP nanopyramids with improved size control were formed successfully by selective-area flow rate modulation epitaxy (FME). The standard deviation of the bottom size of the nanopyramids decreases by means of selective-area FME. Droplet hetero-epitaxy was carried out on InP nanopyramids to grow InAs quantum structures. The shape of the nanopyramids becomes sharper with longer TMIn supply time. In photoluminescence (PL) measurements at 4.2 K, characteristic luminescence is clearly observed. The mapping measurement of the PL intensities reveals that the luminescence originates from the patterned area with the nanopyramids. The PL peak positions shift slightly to a longer wavelength region with increasing supply time. These results suggest that InAs quantum structures are formed on InP nanopyramids.

GaAs active layers were successfully fabricated on ZnSe substrates using a metalorganic vapor phase epitaxy system. As a photocathode, a GaAs active layer shows a high quantum efficiency (QE) of 9% at 532 nm laser light illumination, which is comparable to a QE of 11% from GaAs bulk. In addition, a photoemission current of 10 µA was obtained from this photocathode. One more important point is that this photocathode could realize back-side illumination of 532 nm laser light, and thus its widespread applications are expected in microscopy and accelerator fields.

Aichi Synchrotron Radiation Center was designed for industrial use following five years of discussion among academia, industry and local government in the Aichi area. Among the six beam lines constructed, those that facilitated X-ray absorption fine structure (XAFS) analysis were given first priority. In addition to the hardware, attention was given to the development of operating procedures that were quick and user-friendly. The facility entered public service in March 2013. In the year 2013, 55% of the experiments involved XAFS analysis (hard X-ray, soft X-ray and vacuum ultraviolet regions) and in 2014 it was 57%. The range of research fields is very broad, emphasizing the importance of the XAFS beam lines.

A XAFS beamline, BL5S1, had been operated at Aichi Synchrotron Radiation Center, Japan since March 2013. The beamline was designed for the measurements in the energy range from 5 to 20 keV. The photon flux of 6 x 1010 at around 9 keV and beam spot size of 0.5 x 0.3 mm at sample position are as good as designed. For the standard transmission XAFS measurement, both of the step- and quick- scan modes are available. Energy resolution at around 9keV is good enough to discuss the energy shift of the order of 0.1 eV or higher even when the measurements are conducted in the quick-scan mode. With several kinds of detectors for fluorescence and/or CEY detection mode measurements, and various kinds of sample holders which are supported by the XAFS measurement software, users easily obtain spectra for their samples. Such a standard, well operated and easy to access XAFS beamline must be very important to broaden the base of the XAFS society further.

We report on room-temperature 1.54 µm electroluminescence, for the first time, of Er,O-codoped GaAs/GaInP double-heterostructure light emitting diodes grown by organometallic vapor phase epitaxy. The luminescence is due to intra-4f shell transition from the first excited state to the ground state of Er3+ ions. The erbium and oxygen were uniformly doped in the GaAs active layer with a concentration of 8 ×1018 cm-3. Emission lines in the spectrum indicated successful formation of the Er-2O center and a preferential excitation of the center by current injection. The intensity of the main line observed at 1.538 µm increased linearly with current density and exhibited a tendency to saturate at a current density higher than 20 A/cm2.

Spontaneous emission and optical gain are studied in MOCVD-grown epitaxial layers of GaAs co-doped with erbium and oxygen. Optimal growth conditions are used to obtain the high erbium concentrations up to 8 × 1018 cm-3. The measurements by the Shaklee — Leheny method revealed the optical gain ~45 cm-1 at rather low pump intensity ~0.1 kW cm-2 77 K.

Chemical and energetic interactions between broadband infrared intrinsic emission centers (IECs) of bismuthates and extrinsic emission centers (EECs) of Nd2O3 dopants were optically and electronically investigated. Although no visible absorption from the IEC was found in untreated Bi2O3-B2O3 glass, it was clearly observed after a moderate thermal treatment of

We calculated "density"/"molecular weight" ratio of glass former oxides and modifier oxides to increase a number density of rare-earth ions in glass phosphor. Based on the calculated results, GeO2 and ZnO were chosen for the glass former oxide and the modifier oxide, respectively. The effects of substituting GeO2 for B2O3, ZnO for Sb2O3, or ZnO for Bi2O3 on luminescence spectra in Sm3+-doped glass were not observed. On the other hand, a drastically luminescence spectrum changing of Pr3+-doped glass was observed by substituting GeO2 for B2O3. The output power of Sm3+ -doped glass and that of Pr3+ -doped glass increased with substituting ZnO for Bi2O3. We successfully achieved an ultra-wideband luminescence from 760 nm to 1100 nm with the output power of 2.5 mW by combining a blue LED with 0.15Sm2O3-0.12Pr6O11-10ZnO-45Sb2O3-45GeO2 glass in one package.

We have synthesized 0.3Sm2O3–0.12Pr2O3–10Bi2O3–45Sb2O3–45B2O3 glass as an ultrawide-band near-infrared phosphor for LED-based light sources. We have achieved an ultrawide-band luminescence from 760 to 1100 nm with an output power of over 1 mW by combining a blue LED with Sm3+,Pr3+-codoped borate glass in one package. Absorption bands corresponding to C–H and O–H stretchings in aqueous solutions of glucose have been observed using this light source and a multichannel spectrometer. These results indicate that the Sm3+,Pr3+-codoped borate glass combined with the blue LED is a useful novel light source for absorption spectrometry.

BaFe2(As, P)2 thin films were grown by molecular beam epitaxy. Single phase and c-axis oriented thin films were obtained on both LaAlO3 (LAO) and MgO substrates. The critical temperature (Tc) of the thin films grown on LAO substrates showed a P content dependence very similar to single crystals, while those grown on MgO showed a distinctly different dependence. Lattice parameter measurements showed that the thin films grown on MgO were under tensile strain, while no structural deformation was observed for the thin films grown on LAO substrates. The strain effect accounts well for the difference in the P content dependence of Tc. We also obtained the Poisson's ratio from the observed strain, which gave a reasonable value and a systematic change with the P content.

It is well known that a negative electron affinity GaAs photocathode shows a moderate temporal response when excited by a laser pulse of wavelength close to its band gap energy. We show here that the temporal response can be estimated using a diffusion model that describes the internal transport of the conduction electrons. Using a transverse deflection cavity system, we measured the temporal profile of the electron bunch generated by a DC photocathode gun illuminated by a ps pulsed laser. A systematic set of measurements of GaAs cathodes with various active layer thicknesses and boundary conditions confirmed that the observed temporal response is well understood by the diffusion model calculation.

The thermal decomposition of c-plane GaN/sapphire templates was studied in a metalorganic vapor phase epitaxy (MOVPE) system installed in a laboratory-level X-ray diffractometer by using in situ X-ray reflectivity (XRR). GaN remained thermally stable in pure N2 up to 900 °C, while a significant decomposition occurred at 950 °C. Then, thin In x Ga1-x N epilayers were grown on the annealed templates at 830 °C. In situ XRR measurements were conducted before and after InGaN growth. By theoretical and experimental analyses of the XRR spectra, the sample structure change upon thermal annealing was clarified. Photoluminecescence (PL) and atomic force microscopy (AFM) results demonstrated that thermal annealing affected the optical properties and microstructures of InGaN films. The PL peaks from InGaN slightly blue-shifted with thermal annealing.

By exposing a GaAs surface to Cs and O2, a surface which is called negative electron affinity (NEA) surface can be obtained where the vacuum level shifts lower than the bottom of GaAs conduction band. The Cs/GaAs NEA surface has been attracting great attention in recent years, because of its availability for a highly functional electron source which can be controlled by excitation light. In this work, XAFS and X-ray fluorescence measurements were conducted for Cs/GaAs NEA surface prepared on GaAs (001) and (110) substrates. As the result, As and O were considered as near neighbor atoms of center Cs for both of the samples. Most of Cs formed some kind of Cs-oxide and the Cs atoms at interface between Cs-oxide and GaAs were observed as forming Cs-As bond. Taking account of the ratios of coordination numbers and the fluorescence X-ray yield, the Cs-oxide on GaAs (001) surface forms island like structure in which the body/interface ratio is large, and the Cs-oxide on GaAs (110) surface forms layer like structure in which the body/interface ratio is small.

Optimized transmission-type photocathodes with a GaAs/GaAsP strain-compensated superlattice were developed. The strain-compensated superlattice structures were of high crystal quality, and electron beams from the photocathodes had a maximum spin polarization of 92% and a quantum efficiency of 0.4% without an antireflection coating. The strain-compensated superlattice structure effectively prevented strain relaxation, and the high spin polarization was maintained up to a superlattice layer thickness of 300 nm. Increasing the superlattice layer thickness effectively improved the quantum efficiency while keeping the super high-brightness.

We developed a new transmission-type GaAs/GaAsP strained superlattice photocathode with an AlGaAs transparent inter-layer and Si3N4 anti-reflection coating. The electrons emitted from this photocathode demonstrate a high spin-polarization of 90% with quantum efficiency as high as 0.4% that is a fourfold increase at room temperature compared with our previous photocathode.

Recent nanointegration of magnetic storage and spintronic devices is expected to lead to the development of systems that can analyze magnetic and spin states with a nanometer-order spatial resolution. Development of a polarized transmission electron microscope (SPTEM) that employs a spin-polarized electron source (PES) has commenced at Nagoya University. A spin-polarized electron beam is extracted from a photocathode that has a negative electron affinity surface. The temporal profile of the electron beam can be modulated by varying the temporal profile of the driving laser. The SPTEM can obtain temporal and spatial information about spin. The design and construction of the PES were optimized for the SPTEM. A beam energy of less than 40 keV (a low energy for a TEM) was used because the spin interaction with condensed matter is very small compared with the Coulomb interaction. A polarized electron gun was realized in an extreme high vacuum by applying a high field gradient of 4 MV/m to the photocathode surface. A 40-keV polarized electron beam with sub-millisecond pulses was generated using a backside-excited photocathode. The illumination system of the TEM was designed with the aim of producing a spin-polarized electron beam. The system contains two components that rotate spin: one performs azimuthal rotation and the other performs in-plane rotation in the condenser magnet system. The SPTEM has the potential to dynamically generate magnetic-field images with high contrast and high temporal resolution.

Composition profiles in and around GaInAs layers of InP/GaInAs/InP heterostructures grown by MOVPE were measured by the X-ray CTR scattering and the cross-sectional STM (XSTM) techniques. In the XSTM images, brightness fluctuations in GaInAs are clearly observed. It is discussed in terms of composition fluctuations in GaInAs and a possibility of clustering of GaAs-rich and InAs-rich regions is indicated. The compositions of Ga and As are calculated from the XSTM images and compared with those obtained by the X-ray CTR scattering measurements. Similarity and difference of both profiles are discussed.

To investigate the phenomena that occur at the growth temperatures, an MOVPE (metalorganic vapor phase epitaxy) growth system was installed in the X-ray diffractometer of the laboratory level. The present MOVPE system is capable of growing GaN and related materials that are advanced in the device applications but very little is known, especially experimentally, what is going on at the growth front and in the environment. Since MOVPE growth is conducted at an atmospheric pressure or at a low pressure, very limited tools can be used to probe the growing surface. It is demonstrated that the X-ray diffraction, X-ray CTR (crystal truncation rod) scattering, and X-ray reflectivity can be used even at 1000 o C that is a normal growth temperature for GaN and related materials.

For the X-ray crystal truncation rod (CTR) scattering measurement using laboratory level X-ray source, a new X-ray diffractometer equipped with a Johansson monochromator was developed. The ability of the new diffractometer was evaluated by measuring and analyzing the X-ray CTR scattering spectra of an InP/GaInAs/InP structure sample. By comparing the results with that obtained by conventional angular scan method using synchrotron radiation (SR) as an X-ray source, it was shown that the quality of the spectra measured by using the new diffractometer was comparable to that measured by using SR when the measurement time was 30min. When the measurement time was as sort as a few minutes, the quality of the spectra was worse. However, even when the measurement time was a few minutes, the spectra were still useful to discuss the layer structures qualitatively. Therefore, the new diffractometer must be very useful for the quick and in-situ measurements.

We have suggested using a superlattice semiconductor instead of a bulk semiconductor as an NEA-photocathode for small emittance and high quantum yield because the mini-band energy width and high joint density of states at the bottom of the conduction band can bring small photoelectron's momentum spread and high quantum yield at excitation energy of the band gap. We developed the test sample of the AlGaAs-GaAs superlattice semiconductor designed by using Klonig-Penny-Bastard model. The obtained quantum yield spectrum from the AlGaAs-GaAs superlattice semiconductor after NEA-surface activation was a step function of excitation photon energy most likely caused by the quantum confinement effect.

Although NEA (negative electron affinity) surface has been attracting great interest, atomic level structure of the NEA surface has not been elucidated. In this work, Cs/GaAs NEA surfaces were analyzed by fluorescence XAFS (x-ray adsorption fine structure) method. Cs-LIII XAFS measurement was conducted on the Cs/GaAs surfaces obtained by Yo-Yo method. By analyzing the local structure around Cs from the XAFS spectra, it was shown that Cs-O-As (or Ga) or O-Cs-As (or Ga) structure might be formed on Cs/GaAs surface. The results suggested that single atomic layer of Cs was adsorbed on GaAs surface intermediated by O on the Cs/GaAs NEA surface.

In order to study spin related phenomena in nano-size materials, spin-polarized electron source (PES) has been employed for the incident beam in transmission electron microscope (TEM). The PES has been designed and constructed with optimizing for spin-polarized TEM. The illuminating system of TEM is also designed to focus the spin-polarized electron beam emitted from a semiconductor photocathode with a negative electron affinity (NEA) surface. The beam energy is set to below 40 keV which is lower energy type as a TEM, because the spin interaction with condensed matters is very small corresponding with a Coulomb interaction. The polarized electron gun has realized in an extra high vacuum (XHV) condition and high field gradient of 4 MV/m on a surface of photocathode. Furthermore, it demonstrated that 40-keV polarized electron beam was operated with a sub-milli second pulse mode by using the backside excitation type photocathode. This high performance PES will make it possible to observe dynamically a magnetic field images with high contrast and highspeed temporal imaging in TEM.

The photoemission spectroscopy using synchrotron radiation has been carried out to study the electron affinity of cesium telluride thin films. We observed a formation of NEA surface on p-type gallium arsenide deposited with cesium telluride. An ultra thin film of cesium telluride is discussed as a possible candidate forming an NEA surface. The electron affinity of cesium telluride thin film was found to increase with time after fabrication. An increase of the affinity resulted in deterioration of a quantum efficiency under laser light exposure with constant wavelength. The surface of photocathode in RF gun can suffer enormous damage easily at the conditioning process of RF gun before electron extraction. A method to refresh the photocathode surface after RF conditioning has been required. A photodetachment process is a candidate to refresh aged/damaged photocathode with X-ray exposure. A recovery of quantum efficiency for the aged photocathode film by this refreshing process is shown.

Recently, we have developed a transmission-type polarized electron sources (PES)s for the generation of a high brightness beam. The developed PES can applied the extraction voltage of 20 kV at 4 mm electrode-gap and enables to realize the source beam radius of a few micro meter. As the results of prototype gun experiments, the brightness of ~2 ? 107 A.cm?2.sr?1 and a charge density lifetime of 1.8 ? 108 C.cm?2 were obtained. A maximum polarization of ~90 % and quantum efficiency of 0.09 % was achieved simultaneously using the transmission photocathode with GaAs-GaAsP strained superlattice layers. Up to now, another two electron gun was manufactured, and those mechanical designs are almost same as that of the prototype. The prototype gun and the second gun have been already operated for the photocathode R&D and for the Spin-LEEM application, respectively. In the near future, further experiments are prepared by using the third gun.

We successfully developed a transmission-type photocathode, and a high spin-polarization (90%) with a super-high brightness (1.3×107 Acm−2sr−1) of electron beam was achieved. In this research, the elimination of thickness modulation of GaAs/GaAsP superlattice by introduction of a GaAs inter-layer on a GaP substrate is the key point to realize the high spin-polarization. The thickness modulation of the superlattice is related with the surface roughness of the buffer layer. The compressive strain introduced in the GaAsP buffer layer on the GaP substrate causes hillock formation, where several degree off-angle surfaces are formed. The GaAs inter-layer deposited on the GaP substrate introduced a tensile strain in the GaAsP buffer layer instead of the compressive strain and relatively smooth GaAsP buffer layer was achieved. The smooth GaAsP buffer layer was attributed to the periodic GaAs/GaAsP superlattice layer growth.

We developed a spin-polarized low energy electron microscopy (SPLEEM) with a highly polarized and high brightness spin electron gun in the present study. Magnetic structures of Co/W(110) were observed with an acquisition time of 0.02 s with a field of view of 6 µm. We carried out a dynamic observation of magnetic structures with the SPLEEM during the growth of Co on W(110).

Solution growth method is a suitable growth technique to obtain a large-sized and good crystalline quality β-FeSi2 single crystal. However, during the solution growth method, solvent atoms are often automatically doped into the growing crystals and may affect properties of them. In this work, we investigated Ga atoms in β-FeSi2 grown from a Ga solvent by EXAFS and discussed the effect of the Ga atoms on electrical properties of β-FeSi2. The results of the EXAFS measurement indicated that 60% of Ga in β-FeSi2 substituted Si sites, and 40% of them substituted Fe sites. The ab-initio calculation of electron density of states indicated that when the concentration of Ga in β-FeSi2 is so high as 1.0at%, the residual Ga is not the origin of the p-type conductivity of the β-FeSi2 crystal grown from the Ga solvent. We should conduct further calculation to decide if the residual Ga is the origin of the p-type conductivity or not in the real β-FeSi2 crystal with only 0.1at% of Ga.

We developed AlGaAs photocathodes with low electron affinity for long negative electron affinity (NEA) lifetime. AlGaAs photocathodes achieved 10 times longer NEA lifetime than conventional NEA-GaAs photocathodes. We estimated the appropriate superlattice structure for small conduction mini band width, high density of state in the conduction band and high splitting energy between the heavy- and light-hole bands by theoretical energy band calculation. We conclude that the AlGaAs–GaAs superlattice semiconductor is a suitable NEA-GaAs photocathode that not only has acceptable NEA lifetime but also fulfills the requirements of small energy spread of photoelectrons, high quantum yield and highly spin-polarized electrons.

We have fabricated a novel near-infrared light source for optical coherence tomography (OCT) using a glass phosphor and a light emitting diode (LED) as the excitation source. We used 1.0Yb2O3–4.0Nd2O3–47.0Bi2O3–47.0B2O3–1.0Sb2O3 glass as the phosphor to obtain wideband light emission around 1000 nm. We observed a full-width at half-maximum (FWHM) as wide as 98 nm with an output power as high as 1 mW. The interference signal showed a coherence length of 4.6 µm. This value indicates that the depth resolution of the OCT is twice as high as that of conventional LEDs and super luminescent diodes (SLDs).

Using a newly developed transmission-type photocathode, an electron beam of super-high brightness [(1.3±0.5)×107 Acm-2sr-1] was achieved. Moreover, the spin-polarization was as high as 90%. We fabricated a transmission-type photocathode based on a GaAs–GaAsP strained superlattice on a GaP substrate in order to enhance the brightness and polarization greatly. In this system, a laser beam is introduced through the transparent GaP substrate. The beam is focused on the superlattice active layer with a short focal length lens. Excited electrons are generated in a small area and extracted from the surface. The shrinkage of the electron generation area improved the brightness. In addition, a GaAs layer was inserted between the GaP substrate and the GaAsP buffer layer to control the strain relaxation process in the GaAsP buffer layer. This design for strain control was key in achieving high polarization (90%) in the transmission-type photocathode.

It has been successfully shown that X-ray CTR scattering measurement is a good tool to study the formation process of the InP/GaInAs interfaces grown by OMVPE even when the measurement is conducted after the growth. Using the X-ray CTR scattering measurement, the contributions of effects, i.e., surface roughness, adsorption of atoms, and exchange of atoms, on the formation process of InP/GaInAs interface were able to be discussed. The adsorption of As atoms on the GaInAs surface was shown to have the largest contribution on the abruptness of the interface.

Even though several in-situ monitoring techniques exist and are quite useful to understand the growth processes in MBE or MOVPE, we also need a technique to reveal the buried interfaces along which carriers are transported and recombine to emit light. The interface is modified during the capping (overgrowth) and also during the device fabrication processes after growth. We need to correlate the interface structures in the devices and the device performances. The only technique we have at present is the X-ray CTR scattering measurements. We discuss the limits of the in-situ monitoring and the necessity to reveal the buried interfaces non-destructively, either in-situ or ex-situ.

Electron-spin-resonance (ESR) studies were performed on short-period MnF2–CaF2 superlattices on Si(111) grown by molecular beam epitaxy. In the case of one to three MnF2 monolayers in the repeated unit of samples, angular dependence of ESR linewidth revealed the behavior characteristic of a two-dimensional (2D) magnet, where the linewidth minimum was observed for the angle between the plane normal and the external field of 55° (magic angle). At the same time, the antiferromagnetic transition of the bulk crystal at around 67 K, observed for thick MnF2-layer films, is seen to have disappeared in films of a few monolayers. These results indicate the development of well-defined 2D magnetic layers in the present superlattice structures with a few MnF2 layers.

InGaAs epitaxial layers lattice-matched to InP substrates are studied by photoluminescence measurements modulated by far-infrared radiation under the condition of cyclotron resonance or impurity cyclotron resonance. Based on the experimental results, the ionization energy of shallow donors is estimated to be 2.3 meV, which is lower than the value of 3.0 meV obtained from the effective mass approximation. In order to explain the difference between the two values, we propose a model of the existence of a Ga-rich region in samples. In addition to electron cyclotron resonance, hole cyclotron resonance is observed. The effective masses of electron and light hole are estimated to be 0.041m0 and 0.051m0, respectively.

Thermal quenching of Er-related photoluminescence (PL) due to intra-4f shell transitions of Er3+ ions has been investigated in Ga x In1-x P (0≤x≤1) doped with Er by organometallic vapor phase epitaxy (OMVPE). In GaInP grown on GaP and InP, the 4.2 K PL intensity gradually increases with increasing Ga composition, while the spectral shape remains unchanged. In GaInP grown on GaAs, the 4.2 K PL spectrum is dominated by three emission lines whose relative intensity depends on the Ga composition. Thermal quenching of the Er-related luminescence gradually decreases with increasing Ga composition, i.e., increasing band gap. PL lifetimes and their temperature variations are discussed in relation to deep-level properties of Er in the excitation mechanism of the 4f shell.

Perfectly crystalline (InAs–GaAs) multilayer periodic structures on (001) GaAs, which contain InAs quantum dots (QDs), have been studied by high-resolution X-ray diffraction. It has been shown that the existence of such scattering objects as QDs strongly influences X-ray diffraction, changing the spatial distribution of scattered radiation. Additional long-range ordering in layers containing QDs results in unusual and significant elongation of superlattice and substrate reflections in the q x direction. A novel qualitative model of scattering layers consisting of perfect InAs and GaAs coherent clusters has been developed.

We have investigated nanoscale ErP islands formed on InP(001) during Er exposure in organometallic vapor-phase epitaxial growth by means of atomic force microscopy and scanning tunneling microscopy. Different features of surface morphologies are observed depending on the growth temperature and the ErP coverage. The generation of misfit dislocation arrays along the [1\bar0] direction leads to anisotropic strain relaxation that originates from the anisotropy of the atomic bonds at the interface. The residual strain of partially relaxed islands is ∼2% for growth at 530°C, which corresponds to the minimum of total areal energy of the strained film. Current imaging tunneling spectroscopy shows a high tunnel current at dislocations and ErP island edges suggesting the existence of high-density surface states near the Fermi level and the decrease in tunneling barrier height.

It has been found that there is a threshold growth temperature between 550°C and 580°C for the change of local structure around Er atoms in InP doped Er atoms grown by organometallic vapor phase epitaxy (OMVPE). To understand whether the structure change is induced at the growing surface or during the growth as an in situ annealing, the thermal stability of the local structures around the Er atoms doped in InP by the OMVPE at 530°C has been investigated by the extended X-ray absorption fine structure (EXAFS). The EXAFS analysis revealed that the local structure around the Er atoms, which existed substitutionally on In sites in the InP lattice, was stable against the post-growth annealing even for 1 h at 650°C. Therefore, it is concluded that the local structures are formed on the growth front, and not in the volume of InP by thermal annealing during or after the growth.

We have investigated local structures around Bi in metalorganic-vapor-phase epitaxy (MOVPE)-grown InAs1-xBix (x=0.007, 0.016 and 0.028) by fluorescence extended X-ray absorption fine structure (EXAFS). The EXAFS analysis revealed that even in higher-Bi-concentration InAs1-xBix (x=0.028) the majority of Bi atoms substituted the As sites in the zincblende-type InAs lattice. Obtained Bi-In bond length was 2.81-2.82Å, which was 7% longer than the In-As bond length (2.623Å) in the InAs bulk. Such a long Bi-In bond causes local distortion in the InAs lattice and hence disorder. The degree of the distortion and disorder was observed to increase with the Bi concentration.

Containing an array of vertically coupled InAs quantum dots (QDs) in GaAs matrix, multilayer periodic InAs-GaAs structures grown by molecular beam epitaxy, were investigated by SR-CTR (synchrotron radiation-crystal truncation rods) and double-crystal X-ray diffraction (DCXRD). X-ray diffraction is very sensitive to the formation of vertically coupled QDs array, which changes spatial distribution of the scattered radiation. The appreciable elongation of superstructural and substrate spots in lateral directions is explained by occurrence of an additional long-range lateral ordering of scattering objects and quasi-periodic deformation relief in the top GaAs layer. Perfect coherently-connected InAs and GaAs clusters are introduced as a novel qualitative structural model of scattering layers. Based on this model the main features of spatial distribution of diffracted intensity have been explained.

We have fabricated periodic arrays of InP pillars for two-dimensional (2D) photonic crystals by reactive ion etching (RIE) with SiCl4/Ar inductively coupled plasma (ICP) and Cl2 electron cyclotron resonance (ECR) plasma chemistry. Prior to the fabrication of the arrays, photonic band structures for electromagnetic waves are calculated theoretically, and photonic band gaps are predicted to appear in the optical wavelength region. Periodic arrays of InP micron pillars with fairly smooth etched surfaces are fabricated by ICP-RIE with SiCl4/Ar. The reflective properties of the arrays have been characterized in the optical wavelength region by Fourier-transformed infrared reflection absorption spectrometry (FTIR-RAS). FTIR-RAS spectra of the arrays exhibit characteristic features such as a blue shift with decreasing period of pillars. In ECR-RIE, we systematically investigate InP etch characteristics as functions of various etching parameters, and successfully fabricate periodic arrays of vertical submicron pillars with smooth surfaces.