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We have synthesized 0.5Tm2O3–45Sb2O3–10ZnO–(45−X)GeO2–XB2O3 (in nominal molar composition, X = 0, 5, 11.25, 22.5, 45) glasses as wideband near-infrared phosphors for LED-based light-sources. At the B2O3 composition of 5 mol%, luminescence intensity around 800 nm was higher than that around 1200 nm. On the other hand, beyond the B2O3 composition of 5 mol%, luminescence intensity around 800 nm was lower than that around 1200 nm. The maximum phonon energy increased with increasing the B2O3 composition. Changes in luminescence spectra indicated an enhancement of multi-phonon relaxations from 3H4 level to 3H5 level by substituting B2O3 for GeO2. Luminescence efficiency around 800 nm decreased with increasing the B2O3 composition. At the B2O3 composition of 11.25 mol%, luminescence efficiency around 1200 nm decreased with increasing the B2O3 composition. On the other hand, beyond the B2O3 composition of 11.25 mol%, luminescence efficiency around 1200 nm increased with increasing the B2O3 composition. These results indicated that the Tm2O3-doped borate glass is suitable for a practical NIR phosphor around 1200 nm.

100-W class power storage systems were developed, which comprised spherical Si solar cells, a maximum power point tracking charge control-ler, a lithium-ion battery, and one of two different types of direct current (DC)-alter- nating current (AC) converters. One inverter used SiC met-al-oxide-semicon-ductor field-effect transistors (MOSFETs) as switching devices while the other used Si MOSFETs. In these 100-W class inverters, the ON resistance was considered to have little influence on the efficiency. Nevertheless, the SiC-based inverter exhibited an approximately 3% higher DC-AC conversion efficiency than the Si-based inverter. Power loss analysis indicated that the higher efficiency resulted predominantly from lower switching and reverse recovery losses in the SiC MOSFETs compared with in the Si MOSFETs.

Spin Polarized Low Energy Electron Microscopy (SPLEEM) is a powerful tool to reveal the magnetic structure of ferromagnetic surfaces on the atomic depth scale level[1-3]. With aberration corrected LEEM and a high brightness spin polarized electron gun, high spatial resolution will provide more details for ultra-thin ferromagnetic film studies. This study reports the first realization of aberration corrected SPLEEM (AC-SPLEEM). The performance of the setup was tested on ferromagnetic Fe nanoscale islands on a W(110) single crystal, with spatial resolution of 3.3 nm in spin asymmetry images.

Continuous in situ X-ray reflectivity (XRR) measurements were used to investigate the growth process of an In 0.11 Ga 0.89 N epilayer and its single quantum well grown on c-plane GaN/sapphire templates using an in-house-designed metalorganic vapor phase epitaxy installed in a laboratory-grade X-ray diffractometer. The surface roughening of the epilayer as a function of growth time was calculated from the continuous in situ XRR curve. The growth rate, critical thickness h c(r) for surface roughening, and roughening rate were obtained. The experimental critical thickness h c(r) of the In 0.11 Ga 0.89 N epilayer analyzed from the continuous in situ XRR curve was 14.8±0.4 nm. Based on the calculated theoretical critical thickness h c and the experimental h c(r,2) , Fischer’s model seems to be appropriate for describing the critical thickness of the InGaN/GaN.

A set of GaN/GaInN single quantum wells (SQWs) were grown on c-plane GaN/sapphire templates using metal organic vapor phase epitaxy (MOVPE) and atomic layer epitaxy (ALE). The structural information on the interfaces and surfaces was obtained by fitting the experimental X-ray spectra and was compared between MOVPE and ALE mode. The X-ray crystal truncation rod (CTR) scattering measurement results showed that the samples grown by ALE had sharper interfaces than those grown by MOVPE. Both the X-ray reflectivity (XRR) curve-fitting results and atomic force microscope (AFM) results indicated that the surfaces of the ALE-grown SQWs were smoother than those of MOVPE-grown SQWs. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have investigated the critical current density ( J c ) and the grain boundary property of BaFe 2 (As,P) 2 thin films grown on MgO single crystal or bicrystal substrates by molecular beam epitaxy. We found a strong correlation between J c and the Fe/Ba composition ratio, and a very large self-field J c of 1.2 × 10 7 A/cm 2 at 4.2 K with a thin film for which the Fe/Ba ratio was 2.4. A grain boundary junction was fabricated by growing a thin film on a MgO bicrystal substrate having a misorientation angle of 24°. The inter-grain J c at 4.0 K recorded 10 6 A/cm 2 , which is higher than that of YBa 2 Cu 3 O y . These results demonstrate the high potential of BaFe 2 (As,P) 2 in practical applications and indicate that the necessary condition for in-plane alignment is less severe than YBa 2 Cu 3 O y .

Pulse-mode operation was realized in spin-polarized transmission electron microscopy (SP-TEM) using a laser-driven electron gun with a GaAs-GaAsP strained-layer-superlattice photocathode. TEM images were acquired with a pulsed electron beam with a 5-μs pulse duration. Phase locking of wobbling TEM images was demonstrated using a pulsed beam with a 1-kHz repetition frequency, which matched the image wobbling frequency. It was found that in composite images formed by superimposing 2 × 10(4) separate single-pulse exposures, the amount of image blurring due to wobbling was a linear function of the pulse duration. These results suggest the possibility of pump-probe measurements in SP-TEM using the pulsed electron beam as a probe, allowing nanometer-scale time-resolved spin mapping.

GaN/InxGa1−xN/GaN single quantum wells (SQWs) have been grown on c-plane GaN/sapphire substrates using MOVPE system. PL (photoluminescence) and AFM (atomic force microscope) measurements demonstrate good quality of after-growth thermal-annealed SQWs. In situ XRD (X-ray diffraction), XRR (X-ray reflectivity), and X-ray CTR (crystal truncation rod) scattering measurements were successfully conducted on the SQWs under the NH3+N2 ambient at 1103 K. The analysis results of the XRR and the X-ray CTR spectra at 1103 K and at 300 K on the same sample matched well. It demonstrated that In0.09Ga0.91N SQW structure with several ML (monolayer) InGaN thicknesses was successfully investigated using the XRR and CTR scattering measurements at 1103 K.

Surface morphology change of GaAs0.6P0.4 and GaAs layer grown on GaP substrate during growth was investigated by an Atomic Force Microscope. The compressive strain in the GaAsP layer was relaxed by {111} plane slips while that in the GaAs layer was relaxed by formation of island structures. During growth, the GaAs layer showed much flatter surface morphology. It was found that the mechanism of the strain relaxation largely affects the surface morphology. Finally, we compared the critical thickness for the {111} plane slip and the transition thickness in which the layer growth mode transits from a layer growth to an island growth to explain the different strain relaxation mechanisms.

We demonstrate a new method of cleaning superlattice (SL) photocathodes using atomic hydrogen that allows an increased number of repeat activations. GaAs/GaAsP SL photocathodes were activated with either conventional heat cleaning or atomic hydrogen cleaning. Repeated heat cleaning was found to gradually lower the quantum efficiency (QE) of the photocathodes, while a relatively constant QE was maintained over repeated atomic hydrogen cleaning. These results show that atomic hydrogen cleaning allows a greater number of photocathode cleanings without a loss of performance. Analyses of SL photocathodes indicated that the degradation resulting from heat cleaning can likely be attributed to the build-up of residual Cs compounds as well as damage to the GaAs cap layer. The present study also determined the 1/e lifetime for a GaAs/GaAsP SL photocathode to be 7 h at an initial current of 2.2 µA.

A power storage system using spherical silicon (Si) solar cells, maximum power point tracking charge controller, lithium-ion battery and a direct current-alternating current (DC-AC) inverter was constructed. Performance evaluation of the DC-AC inverter was carried out, and the DC-AC conversion efficiencies of the SiC field-effect transistor (FET) inverter was improved compared with those of the ordinary Si-FET based inverter.

A photovoltaic power generation system using spherical silicon (Si) solar cells and silicon carbide (SiC) field effect transistor (FET) inverter for photovoltaic applications was constructed and evaluated. The spherical Si solar cells were connected to the SiC-FET inverter and were used as a power source. Comparing the photovoltaic power generation system using an ordinary Si-FET inverter, direct current-alternating current conversion efficiencies of the SiC-FET inverter were improved due to reduction of power loss in the SiC-FET inverter.

We realized the polytype-selective growth of 3C–SiC and 6H–SiC on a 6H–SiC (0 0 0 1) seed crystal by controlling the supersaturation. Both 6H–SiC and 3C–SiC grew on the 6H–SiC seed crystal at low supersaturation, but 3C–SiC increased with increasing supersaturation. At high supersaturation, 3C–SiC grew so rapidly that it completely covered the 6H–SiC seed crystal. The growth rates of 3C–SiC and 6H–SiC have different dependences on supersaturation. In the present case, the growth rate of 3C–SiC in 2D nucleation mode is compared with that of 6H–SiC in spiral growth mode. The present kinetic polytype-control technique is based on polytypes having different growth rates and it differs considerably from the conventional technique that is based on “inheritance” of stacking sequence, which is well known as “step-controlled epitaxy”.

We synthesized the Pr3+-doped Bi2O3-Sb2O3-B2O3glass phosphor and the Sm3+-doped CaO-Sb2O3-B2O3glass phosphor in order to fabricate a wideband luminescence. The luminescence bands of the Pr3+-doped glass phosphor were from 760 nm to 910 nm and from 920 nm to 1100 nm. The luminescence bands of the Sm3+-doped glass phosphor were from 840 nm to 1060 nm. The excitation band of the Pr3+-doped glass phosphor coincided with that of the Sm3+-doped glass phosphor at around 475 nm. We achieved the wideband luminescence from 760 nm to 1100 nm by stacking the Pr3+-doped glass phosphor (0.1mol% Pr6O11, 10 mm) on the Sm3+-doped glass phosphor (0.5 mol% Sm2O3, 10 mm) excited by one LED (470 nm). This luminescence covered the wavelength region that is suitable for the absorption spectrometry of agricultural products (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have fabricated stacked InAs quantum dots (QDs)/GaAs LED for a wideband near-infrared light source. The 15-stacked InAs QDs/GaAs structure and the indium tin oxide (ITO) electrode were used for the LED. Good current-voltage characteristics were achieved. The built-in voltage was 1.0 V. Gaussian-shape luminescence with a central wavelength of 1144 nm and a full width at half maximum (FWHM) of 99 nm was observed. We achieved a maximum output power of 2.9 mW. These LED properties should be suitable for practical applications. The transmission image of a finger was taken by using the 15-stacked InAs QDs/GaAs LED and the InGaAs camera without special optical settings or the image processing. As a result, the blood vessel under the skin was observed. These results indicate that the 15-stacked InAs QDs/GaAs LED can be equipped with practical measuring instruments (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

GaAsP buffer layers grown on (001) just oriented GaP substrate show an undulated vicinal surface morphology and a thickness modulated GaAs/GaAsP strained superlattice layer grew on the vicinal GaAsP buffer layer. Structural characteristics of the thickness modulated superlattice have been carried out by transmission electron microscopy (TEM). In the thickness modulated structure, the first GaAs layer grown on the vicinal GaAsP buffer layer consisted of (001) and (117) facets, and thicker GaAsP grew on thinner GaAs and vice versa. Nano-beam electron diffraction revealed that an inhomogeneous residual strain distribution existed in the first GaAs layer. Therefore, the value of strain introduced in subsequent superlattice layers should be different from place to place and the strains in GaAs and GaAsP superlattice layers are also different from each other. The nucleus formation rate is inversely proportional to the value of the strain. So it is understood that the strain distribution in the first GaAs layer results in the successive thickness modulation of GaAs/GaAsP superlattice layers.

NdFeAs(O,F) superconducting thin films were grown on MgO, GaAs, CaF 2 , and LaAlO 3 single crystal substrates by molecular beam epitaxy. All thin films exhibited a clear superconducting transition, while the critical temperature T c showed a distinct substrate dependence, although the same growth condition was employed for all samples. The difference in T c can be attributed to the lattice strain effect and how susceptible the substrate is to fluorine. The thin film grown on CaF 2 substrate showed the highest T c with an onset T c of 56 K and zero resistance at 52 K. A correlation between T c and the lattice constant ratio c / a was observed similar to what was reported for other iron-based superconductors, suggesting an intimate relation between the crystal structure and the superconducting properties.

We have optimized Yb2O3 concentration, Nd2O3 concentration, and thickness of a Yb3+, Nd3+ co-doped Bi2O3–B2O3-based glass phosphor to achieve a higher output power with a Gaussian-like shaped luminescence for an optical coherence tomography (OCT) light source. A simple model that includes absorption of excitation light, absorption of luminescent light, and luminescence efficiency was used for estimation of the output power. We have estimated from the model that the highest output power was achieved at Yb2O3 concentration of 3%, Nd2O3 concentration of 0.5%, and the thickness of 1.8 mm. This estimation showed a good agreement with the experimental results. For the optimized glass phosphor, we have observed Gaussian-like shaped luminescence, which is important for the OCT light source.

We synthesized Sb2O3-B2O3-Bi2O3 glasses doped with Sm3+ in order to increase the spectral width of an Yb3+, Nd3+ co-doped glass phosphor. We successfully realized wideband luminescence from 850 nm to 1220 nm by stacking the Sm3+ doped glass phosphor (1.1Sm2O3-44.4Sb2O3-44.6B2O3-9.9Bi2O3, in nominal molar composition, thickness of 1mm) underneath the Yb3+, Nd3+ co-doped glass phosphor (1.2Yb2O3-1.1Nd2O3-43.9Sb2O3-44.1B2O3-9.7Bi2O3, thickness of 1mm). On the other hand, luminescence of the Sm3+, Yb3+, and Nd3+ tri-doped glass phosphor (1.1Sm2O3-1.2Yb2O3-1.1Nd2O3-44.4Sb2O3-44.6B2O3-9.9Bi2O3, thickness of 2 mm) was almost the same as that of the Yb3+, Nd3+ co-doped glass phosphor. These results indicate that stacking the Sm3+ doped glass phosphor underneath the Yb3+, Nd3+ co-doped glass phosphor is a good approach to realize the wideband near-infrared phosphor. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface X-ray diffraction was applied to study structure of the fluorite-silicon interface forming upon epitaxial growth of CaF2 on Si(001) surface kept at 750 degrees C. Samples with CaF2 coverage of 1.5-4 (110)-monolayers were grown and in-situ characterized using synchrotron radiation. The 3 x 1-like surface reconstruction was observed in agreement with the previous studies by electron diffraction. Interestingly, a well pronounced splitting of the fractional x 1/3 reflections was revealed. This splitting was ascribed to the effect of antiphase domain boundaries in the row-like structure of the interface layer. The in-plane integrated intensities were used to reconstruct two-dimensional atomic structure of the high-temperature CaF2/Si(001) interface.

Doubly stacked InAs quantum dots (QDs) /GaAs structures with different thicknesses of a GaAs spacer layer were grown by organometallic vapor phase epitaxy (OMVPE) and optical properties were investigated by photoluminescence (PL) measurements. A PL spectrum showed Gaussian-like shape with a central wavelength of 1144 nm and an FWHM of 102 nm from doubly stacked InAs QDs with the nominal GaAs spacer layer thickness of 87 nm. The central wavelength and the FWHM are almost the same as those from single layer InAs QDs. On the other hand, an asymmetrical PL spectrum was observed from doubly stacked InAs QDs with the nominal GaAs spacer layer thickness of 25 nm. The PL spectrum from doubly stacked InAs QDs with the nominal GaAs spacer layer thickness of 55 nm showed Gaussian-like shape with the central wavelength of 1276 nm and the FWHM of 232 nm. This PL spectrum consisted of two emission bands around 1170 and 1300 nm with almost the same intensity. These results indicate that the spectral width can be increased by controlling the spacer layer thickness in the stacked InAs QDs/GaAs structure.

The growth of In x Ga 1− x N layers on c -plane GaN (2 μm)/sapphire (0 0 0 1) substrates was carried out using the special growth system installed in an X-ray diffractometer using solely N 2 as the carrier gas. X-ray CTR scatterings on In x Ga 1− x N layer were measured at growth temperatures and after cooling down to room temperature. The differences in X-ray CTR scattering spectra at growth temperatures and at room temperature were discussed. The peak InN (0 0 0 2) or InGaN was observed at growth temperature. On the other hand, In (1 0 1) and In (0 0 2) peaks were observed with InN (0 0 2) or In x Ga 1− x N in the X-ray CTR spectra after cooling down to room temperature. These differences should be important to reveal the real growth processes of In x Ga 1− x N. Single diffraction peaks of In 0.16 Ga 0.84 N and In 0.38 Ga 0.62 N films were observed at 830 and 780 °C, respectively.

A novel system for in-situ X-ray CTR scattering measurement on in-situ observation of group-III nitride semiconductor growth was constructed by setting an OMVPE reactor at the sample position of the X-ray diffractometer which was developed for in-situ measurement of growing semiconductor crystals. For in-situ observation of the growth of semiconductor, firstly, it is necessary to investigate the capabilities of the new system. In this work, after the safety check of the OMVPE reactor with thin Be windows, the capability of the new system as an X-ray diffractometer and a growth reactor of group-III nitride semiconductors was tested. After the GaInN layer was deposited successfully, the X-ray CTR scattering measurement was conducted at the growth temperature. The different CTR spectra measured at the growth temperature and at room-temperature after the growth were obtained. It indicates that the status of the crystal at growth conditions can be analyzed by using the new system. Therefore, the new system can be developed for in-situ observation of the OMVPE growth of the group-III nitride semiconductors.

We investigated dislocation behavior in the crystal grown on 6H-SiC (0001) by solution method using synchrotron X-ray topography and thermal chlorine etching. It was confirmed that basal plane dislocation was not newly formed in the grown layer. In addition, the positions of threading screw dislocations (TSDs) were displaced and some of them disappeared in the grown layer. This displacement was caused by the bending of the TSDs during growth.

We have grown high-quality and large-area (18×18 mm 2 ) 3C–SiC crystals on 6H–SiC seed crystals heteroepitaxially using a top-seeded solution method. The key technique here is the intentional inducement of a stacking error just at the surface of the seed crystal and crystal growth under conditions where the 3C–SiC is thermodynamically stable. The solution method developed here can be used to grow larger-area 3C–SiC crystals using 6H–SiC seed crystals 2–4 in. in diameter grown by a sublimation method. In cross-sectional transmission electron microscopy images, a transition area composed of twinned 3C–SiC variants was observed just above the boundary where the polytype changed from 6H–SiC to 3C–SiC. This transition area can be explained by lateral growth and collision of different variant 3C–SiC crystals.

6H-SiC hetero-epitaxially grown on a (111) 3C-SiC was observed with TEM. High-density stacking faults were formed around the hetero-interface, and the density of stacking faults decreased with increasing distance from interface. On the other hand, when 3C-SiC was homo-epitaxially grown on a 3C-SiC, any stacking faults did not exist at the interface between the grown crystal and the seed crystal. Thus, the stacking faults formation started from the 6H/3C hetero-interface. Considering the lattice-mismatch strain between 3C-SiC and 6H-SiC, the strain energy is equivalent to the stacking fault energy of 6H-SiC. This similarity suggests that the stacking faults formation could be caused by the relaxation of the lattice-mismatch strain.

The strains in GaAs/GaAsP superlattices used in spin-polarized photocathodes grown on GaAs and GaP (001) substrates were determined by X-ray diffraction. The thicknesses of the GaAs wells and GaAsP barrier layers were also determined. The band structures of the superlattices were calculated on the basis of these experimentally determined strains and layer thicknesses. The thicknesses and band structures were in good agreement with those observed by transmission electron microscopy and photoluminescence, respectively. The strains induced in the GaAs well layers were approximately linearly dependent upon the phosphorous fraction in the GaAsP layer, and the splitting between the heavy hole band and the light hole band of the superlattices grown on GaP substrates was larger than that of superlattices grown on GaAs substrates. In photocathodes grown on GaP substrates, low polarizations were observed, not due to a lack of band splitting, but to depolarization scattering caused by crystal defects, which were different from that induced in superlattices grown on GaAs substrates. [DOI: 10.1380/ejssnt.2010.125]

The crystalline structure of GaAsP layers grown on GaAs and GaP (001) substrates, used for spin polarized photocathodes, has been investigated by X-ray diffraction. The layers on the GaAs substrate possess a mosaic structure observable by X-ray topography and consist of many large blocks. The mosaicity anisotropic and the distribution of the mosaic is restricted within the (110) plane, and the blocks zigzag around the [110] direction. The layer grown on the GaP substrate was uniform and no mosaic was observed in the topographs. The results indicate that different mechanisms of strain release occur in GaAsP layers for tensile and compressive strains.

Most of high performance III-V compound semiconductor devices are fabricated utilizing heterostructures. However, when the heterostructures are grown by OMVPE, a compositional grading arises at a hetero-interfaces. The compositional grading may deteriorate the performance of the compound semiconductor devices. We have investigated the degree of the compositional grading at the interfaces using X-ray crystal truncation rod (CTR) scattering measurement. The X-ray CTR scattering measurement is a powerful technique to investigate the buried interfaces and determine the distributions of atoms quantitatively at an atomic-scale. In this work, we studied on the distributions of group-III atoms at InP/GaInAs interfaces grown by OMVPE with different growth rates, focusing on the influence of the exchange reaction of the group-III atoms near the surface during the growing. The experimental results showed that the degree of distributions of Ga atoms increased with the decrease of the growth rate. It suggested that the distribution of Ga atoms at interfaces were influenced by the exchange reaction. In order to discuss the exchange reaction, a calculation to simulate the distribution of Ga atoms was conducted considering potential energy of Ga in InP layers. The results showed that Ga atoms should exchange during the growth in top-most 3 atomic layers.

Solution growth was performed using a free-standing (001) 3C-SiC epilayer as a seed crystal at a growth temperature of 1700°C. The seed crystal was prepared by a CVD method on the undulated Si substrate. 3C-SiC stably grew on the (001) seed crystal. However, dark stripes from the seed crystal to the grown crystal along {111} planes were clearly observed. The stripes were due to the high-density stacking faults extended from the stacking faults in the 3C-SiC epilayer that were induced during the CVD growth on Si substrate.

We successfully developed a transmission-type photocathode, and a high polarization (90%) with a super-high brightness (1.3×10 7 A cm −2 sr −1 ) of electron beam was achieved. In this research, we found that the polarization of electrons from the GaAs–GaAsP superlattice on the GaP substrate was lower than that from the same superlattice on the GaAs substrate, and that a GaAs inter-layer deposition on the GaP substrate recovered that from the GaAs–GaAsP superlattice. Mechanism of the polarization degradation was investigated from a viewpoint of strain-relaxation process in the GaAsP buffer layer that was adopted between the superlattice and the substrates. The buffer layer with in-plain tensile strain was relaxed by inducing cracks, but that with in-plain compressive strain was relaxed by inducing dislocations. The dislocations may disturb the spin-polarization of electrons more effectively than the cracks do.

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.

A solution growth of 3C-SiC was performed on (111)Si-face or )111(C-face of 3C-SiC seed crystal at around 1700 °C by dipping method. The polytype of the crystal grown on the Si-face immediately changed to 6H-SiC. On the other hand, 3C-SiC stably grew on the C-face except for a small number of 6H-SiC precipitates. The polytype transition phenomenon can be explained by the difference of the chemical potential and the solution-crystal interfacial energy between 3C-SiC and 6H-SiC. To grow a larger 3C-SiC crystal, we carried out a long-term growth for 30 hours on the C-face. In the first 10 hours, the polytype of the grown crystal was 3C-SiC. In the next 10 hours, however, the polytype changed from 3C-SiC to 6H-SiC. According to our studies, 6H-SiC tends to grow on 6H-SiC at around 1700 °C, while both of 3C-SiC and 6H-SiC can grow on 3C-SiC at around the same temperature. In this case, 6H-SiC grows on 6H-SiC precipitates and then the dominant polytype changes to 6H-SiC after several 6H-SiC precipitations. To grow 3C-SiC crystal stably, it is necessary to surpress completely the polytype transition by the growth on C-face at lower growth temperatures.

We investigated effects of Ti and Ge additions to Si solvent on the volume and the polytype of SiC precipitate in unseeded SiC solution growth. The Ti addition increased the amount of SiC precipitates. Compared to pure Si solvent, the amount of crystal grown in Si-30at%Ti at 1600 °C increased by 5 times. In addition, the Ti addition induced the precipitation of 6H-SiC. Further, the Ge addition to Si-Ti solvent promoted several polytype precipitations (4H and 6H). These results indicate the possibility of polytype control by solvent composition.

We fabricated InAsP quantum dots on GaInP lattice-matched to GaAs (0 0 1) using three types of growth sequences by the droplet hetero-epitaxy. By changing group-V ambient before In droplets formation, we investigated the effects of absorbed group-V atoms on the lateral size, height, density, and luminescence intensity of InAsP quantum dots. By supplying tertiarybutylphosphine and tertiarybutylarsine mixed gases before In droplets formation, the lateral size and height of dots decreased, and the luminescence intensity increased by 550 times. It was revealed that the group-V ambient before In droplets formation was very important for the lateral size, height, and the luminescence intensity.

3C (cubic)-silicon carbide (SiC) bulk crystals that are stable at relatively low temperatures are difficult to grow by the sublimation method, which requires relatively high growth temperatures. This study focused on growth from the solution, which has the advantage that low growth temperatures are applied and the resulting crystals are mostly of high crystalline quality. Firstly, a large number of 3C-SiC crystals were grown by solution growth via spontaneous nucleation in a large temperature gradient. A relatively high yield of 6.4% was achieved from the charged Si solvent. Transmission electron microscopy and X-ray topography observations indicated that the stacking fault density of these crystals was much lower than that of the substrates grown by chemical vapor deposition methods. A dipping solution technique was then applied for 3C-SiC growth, using 3C-SiC seed crystals grown via spontaneous nucleation. Growth was performed on the (1 1 1)Si or (1¯ 1¯ 1¯)C faces. As a result, 3C-SiC grew on the (1¯ 1¯ 1¯)C face, but 6H-SiC crystals grew on the (1 1 1)Si face. For the stable growth of 3C-SiC crystals without 6H-SiC precipitation, growth on the (1¯ 1¯ 1¯)C faces is necessary.