<100>, <110> ZnTe single crystals were grown by the liquid encapsulated Kyropoulos method. 80mm diameter single crystals with the both orientations were obtained. The EPD of the crystals was around 5000cm^<-2> , which was almost the same as that of crystals grown by the vertical gradient freeze method.
<111> oriented BaF_2 single crystals, as the optical material for F_2 laser, are grown by the vertical Bridgman-Stockbarger method. After ArF excimer laser irradiation, absorption spectra of these crystals are measured. The origin of absorptions are discussed.
We have developed a method of non-equilibrium molecular dynamics simulation of the crystal-melt interface [J. Jpn. Assoc. Cryst. Growth 29 (2002) 69], where the heat balance equation, k_sG_s-k_LG_L=LρV, holds. Here, the subscripts S and L represent the crystal and the melt, k denotes the thermal conductivity. G_s the temperature gradient, and L, ρ, and V are the latent heat of fusion, the density, and the pulling velocity, respectively.
By applying the point defect trapping model proposed by Webb to the Czochralski crystal growth from melted silicon with a assumption that the crystal-melt interface is diffuse, the growth rate fluctuations enable to incorporate nonequilibrium concentrations of the point defects into the crystal just below the crystal-melt interface. The change of predominat spicies of the point defects trapped in the crystal with variation of the magnitude of the growth rate fluctuations is possible.
Numerical analysis was carried out to clarify LiNbO_3 melt convection in the DCCZ process. The inner crucible and the outer crucible were rotated by using ACRT method. The effect of the inner crucible on the LiNbO_3 melt convection was investigated.
A three-dimensional numerical simulation study was carried out to have a better understanding for the role of Marangoni convection in the Floating-zone growth of bulk semiconductor single crystals. In the numerical model, a three dimensional Full-zone (FZ) growth configuration was considered under axisymmetric thermal boundary conditions. Numerical results showed that the flow and temperature fields in the none remained axisymmetric (two-dimensional) in early stages of the simulation. However. as time proceeded, the flow and temperature field patterns became three dimensional. The concentration field exhibited a three-dimensional behaviour even the flow and temperature fields were still axisymmetric. It was also shown that the rotation of the growth system is beneficial in growing axisymetrically uniform crystals .
The growth of CdZnTe crystals by the Vertical Gradient Freezing method was simulated numerically in order to optimize the growth process for high quality crystals_ In the simulation. the solid/liquid interface position was determined by the heat and mass balance equations along with the phase diagram. It was found that the zinc segregation in the crystal could be controlled by the convection control due to the steady crucible rotation and ACRT.
The self-adjusting reaction in the initial stage of YIG growth by the thermal image floating zone method was analyzed on the basis of phase equilibrium and the result demonstrated the usefulness of the present method.
To understand the environment of the early solar system, we have investigated the relation between the growth condition and dust morphology. The aggregation behaviors of SiO_2 glass indicate that high oxygen fugacity increases the interfacial free energy of the dust particles. The forsterite morphology indicates that the dust condensation condition in the early solar system was about 200 K below from its equilibrium temperature.
In order to understand the condition for the formation of typical radial pyroxene and barred olivine chondrules, the crystallization process of Enstatite (MgSiO_3) and Forsterite (Mg_2SiO_4) melt droplets (2〜3 mm, diameter) were observed in-situ. Experiments were performed under microgravity condition, which was realized by the parabolic flight of airplane and under containerless condition which was levitated by supersonic. In the results, both chondrules were crystallized from very large supercooling such as over hypercooling limit ( = AH_f/C_p). It is indicated that chondrules were formed in a very rapid process rather than it was thought previously.
In spite of the increasing interest on the carbide grain formation by the identification as the pre-solar grain, the laboratory experiments on the carbide were hardly achieved. A new attempt has been made for carbide core (SiC, TiC, ZrC etc.)-carbon mantle grains. Using the noble gas evaporation method, we succeeded in producing carbide core-carbon mantle grains with the same size as carbide core of pre-solar grains.
With the increasing interest of crystalline silicate grains, smoke experiment on the formation of FeSiO_3 grains have been done by the coalescence growth between Fe and SiO particles. In addition to FeSiO_3 crystal grains, FeSi_2 grains were produced even in the present method. FeSi_2 and FeSiO_3 growth have been discussed as the problem of Si and O rich conditions.
In the present study, the crystal morphology of small particles of Cu-Au, binary alkali halide and Si-Ge system prepared by gas-evaporation technique was investigated. It was found that the formation of solid solution causes the reduction of the anisotropy of surface energy and the non-uniformity of growth rate.
We examined the value of an annealing for crystallization of Cu-Phthalocyanine (CuPc) deposited on KCl substrate. Crystallites of CuPc were observed on the surface of annealed samples. We also discussed an annealing temperature and period to crystallize.
Chlorapatite [Ca_5Cl(PO_4)_3] crystals were grown using a sodium chloride (NaCl) flux. The grown crystals were transparent and colorless. The crystals had the forms of prism (up to 2.3 mm×0.35 mm) and needle (up to 2.1 mm×80μm). The forms of grown crystals were affected by the cooling rate. The occurrence proportion of the needle-like crystals increased with cooling rate.
Black crystals of LiMn_2O_4 (up t. 10μm) were grown from LiCl and Li_2MoO_4 fluxes. The form of grown crystals was octahedral. Plate-like Li_2MnO_3 crystals (up to 0.8 mm) were also obtained in these fluxes.
Calcium molybdate crystals were grown from a sodium chloride flux. Effect of cooling conditions on the crystal growth was investigated. The crystals obtained were colorless and transparent The crystal forms were bulk, needle, and powder. The number and size of crystals obtained was considered.
ZnS crystals were grown by a flux method using PbCl_2 as a flux. The crystals were grown into the shape of plate or bulk depending on growth conditions. X ray analysis showed that these crystal systems were cubic irrespective of the shape.
ZnO crystals doped with Al_2O_3, Ga_2O_3, In_2O_3 were hydrothermally grown in order to be used as homo-epitaxial growth substrates. Growth behavior and electrical and optical properties of these are reported.
The sol-gel method has a potential increasing the limit quantity of a doped luminous element and the synthesis of a new laser material. Codoping of neodymium and chromium to YAG ceramics upto 10 mol% was tested and reported at first an efficient energy transfer from Cr^<3+> to Nd^<3+> optimally doped at 3-4 mol% Cr ions with 1 mol% of Nd ions.
(Y_<1-x>La_x)Ba_2Cu_3O_y single crystals have been successfully grown by the pseudo-binary YBa_2Cu_3O_y - (7BaCuO_2+11CuO) phase diagram The structure and composition of the grown crystals were investigated using XRD and XPS.
(Nd_<1/3>Eu_<1/3>Gd_<1/3>)Ba_2Cu_3O_x (NEG123) materials have high critical current density(77K, 5.0× 10^4A/cm^2 in 2T) in high magnetic field. Pseudo-binaly phase diagrams between (Nd_<1/3>Eu_<1/3>Gd_<1/3>)Ba_2Cu_3O_x (referred as NED123) and Ba_3Cu_<10>O_<13> were constrcted in air and 0.1% O_2 in Argon by in-situ high temperature optical microscopic observation, and NEG123 single crystals were grown by freezing method.
Oxide superconductor YBa_2Cu_3O_6 has two dimensional structure and is interesting in crystal habit and surface morphology. The α-factors of (001) and (100) were 20 and 15-18, attributing to the difference of the surface morphology. Assumption that step advancing velocity_ is proportional to the summation of attachment energies of faces consisting the step conclude isometric shape of the crystal.
Calcium mixed metal-sodium flux was applied to high temperature solution growth of GaN single crystals. Semitransparent GaN single crystals could be grown in this method. Furthermore, critical pressure needed to grow GaN crystal was reduced by addition of calcium.
We have developed new solution stirring technique to grow high-quality CsLiB_6O_<10> crystals. The crystals have higher bulk laser-induced damage threshold than that of the conventional crystals and possess adequate optical uniformity.
We have grown high-quality nonlinear optical crystal CsB_3O_5 (CBO) by using a new solution stirring method. The crystal enables to generate the third harmonic of 1064・nm light with high conversion efficiency.
High quality 4-demethylamino-N-methyl-4-stilbazolium Tosylate (DAST) crystals have been obtained by the slope nucleation method (SNM) developed by our group. DAST crystals with thinner shapes could be grew with the growth conditions of lower solubility point. The aspect ratio (length/thickness) of 14 was obtained for the 0.15g/l solution , whereas it was 5 for the conventional condition (0.35g/l).
Uniform textures of colloidal crystals tailored in a flat capillary by strong shear flow were optically characterized. Results of angular dependent transmission spectroscopy, Kossel analysis and imaging spectroscopy will be reported.
Crystallization of charged colloids were examined for dispersion of polystyrene particles having diameters of 91 to 136 nm and various charge densities. Phase diagrams were determined as a function of particle and salt concentrations. The observed phase boundaries were compared with a numerical simulation results by Robbins et al.
Morphology change of the anthracene microcrystal in the suspension was observed by the weak pulsed laser irradiation. Several new crystals appeared on the top plane of the original crystal, and grew with irradiation, whereas original crystal disappeared. We discuss the mechanism of the morphology change.
Light induced crystal depodition and growth in the presence of benzophenone in ethanol/water (1:1) mixed solvent. The crystal was determined to be benzopinacol from NMR experimental results. Benzopinacol is produced from benzophenone ketyl radical.which is formed by excited benzophenone.
Utilizing synchrotron radiation from SPring-8, an X-ray microbeam with a narrow energy bandwidth and a small angular divergence has been developed. Using the X-ray microbeam, we have demonstrated to measure very local and minute lattice strain in various semiconducting materials after some wafer preparation processes or device fabrication processes. Local strain in a Si crystal around the SiO_2/Si film edges and that in top Si layers of silicon-on-insulator (SOI) crystals are discussed as sample materials.
Potential, present status and future prospect of nitride semiconductors are presented. Latest development on UV LED, InN and high-power, high-frequency electronic devices are especially focused in this paper.
We fabricated the GaN-based laser diodes (LDs) and evaluated these characteristics. Regarding the 400nm-LDs for digital versatile disks, we reported the new structure of LDS that was optimized for the mass production while meeting all other requirements. We fabricated the ultraviolet and blue LDS in order to broaden the emission wavelength. As the results, we were able to broaden the emission wavelength of the LDS ranging from 365nm to 480nm.
We report on the growth and optical properties of quaternary InAlGaN for the application of 300-350nm-band ultraviolet (UV) emitting devices. We demonstrated that the 300-nm-band UV emission is considerably enhanced by the In-segregation effect upon introducing 1-5% of In into AlGaN. We fabricated In_<x1>Al_<y1>Ga_<1-x1-y1>N/In_<x2>Al_<y2>Ga_<1-x2-y2>N multi-quantum wells (MQWs) with various compositions, and obtained room temperature intense emission in the wavelength of 290-380 nm. The emission from the InAlGaN-based MQWs was as strong as that of blue emission from InGaN-based QWs. We also fabricated UV-LEDS using a quatemary InAIGaN active region and achieved high-efficiency 330 nrn emission under R.T. CW operation.
A high-quality AlGaN with crack-free and low dislocation density is realized using low-temperature-deposited AlN interlayer and lateral seeding epitaxial technologies. UV light-emitting diode (LED) fabricated on the AlGaN layer exhibited high output power of 2.6 mW, operating voltage of 5.7 V and peak wavelength of 363 nm at a forward current of 100 mA (DC). These characteristics are the best in UV LEDs on sapphire substrate.
The formation of the GaN/AlGaN heterointerfaces, the internal polarization field of GaN/AlGaN quantum well, polarization controls in the LED device design, and the successful fabrication of a highly efficient AlGaN-based UV-LED are described. Further, the application of this UV-LED is demonstrated.
III-Vnitride semiconductors are useful for LED with colors covering ultraviolet, blue through green. Luminescence of these LEDs has high luminosity and high purity of color, and, therefore, many applications such as full color display and backlight of LCD module were realized by using these LEDs. Short wavelength LED is used for an exciter of phosphors that can generate any color including white. The air purifier is also developed by combining short wavelength LED and the photo-catalyst such as TiOx.
We present the design and fabrication of highly reflective and low loss multilayer dielectric mirrors (SiO,/Zr02) for GaN based vertical cavity surface emitting lasers (VCSELs). We consider two types of VCSEL structures; one consists of AlN/GaN DBR and SiO_2/ZrO_2 DBR on a sapphire substrate. A resonant emission from a photo-pumped GalnN/ GaN vertical cavity structure with a cavity length of 1.9 um has been demonstrated. The other consists of two dielectric mirrors (SiO_2/ZrO_2) with a polished thin sapphire substrate. A resonant emission from a photo-pumped GalnN/GalnN vertical cavity with a spectral linewidth of 3.8 nm has been demonstrated. Also, we propose a new structure using lateral growth on dielectric mirrors as a bottom reflector. We have demonstrated and characteried the thin GalnN/GaN Qws fabricated by removing a sapphire substrate with UV light irradiation for making a micro-cavity structure.
Although isotopic composition of silicon materials has been rarely determined, recent SIMS microanalysis revealed 0.4‰ of silicon isotopic heterogeneity in a single FZ crystal. We have carried out experiments of crystal growth and evaporation from silicon melt to evaluate the partitioning across the crystal/melt and vapor/melt interfaces. It is inferred that the silicon isotopic ratios in the FZ Silicon crystals vary according to the growth conditions such as the growth and rotation rates, and the extent of supercooling of the melt as well as the equilibrium fractionation between the crystal and its melt.
Behaviors of stable oxygen isotopes in crystallizing melts at high temperature have been poorly understood. Due to complicated behaviors of isotopes, it remained difficult to synthesis of isotopically homogeneous crystal Possible effects for cause of isotopic heterogeneity: (1) melt evaporation, (2) supercooling before crystallization, and (3) gravity were examined experimentally and theoretically Melt evaporations evaluated by vacuum heating experiment on some silicon melts always suggest negative isotope fractionation between vapor and melt (α_<v-m><1.0). Supercooling produces positive isotope fractionation between crystal and melt (α_<x-m>. 1.0). For the melt, gravity decreases vapor loss from melts and minimize the isotope fractionation (α_<v-m>.1.0). These fractionations simultaneously affect the FZ crystallization system. Consideration of over-all fractionation factor is necessary for prediction of isotope heterogeneity in the products.
Strain in crystals lowers the melting point. On a basis of this fact, we newly explained the strain induced poly-crystallization during met growth. According to our model, strain free crystal nucleates heterogenerously on the strained crystal from the supercooled melt in the vicinity of liquid-solid interface. Moreover, we successfully reproduced the poly-crystallization due to this model by the Monte Carlo simulation.
Growth conditions to obtain stable CuAlS_2 polycrystal as a feed material have been investigated. Single crystals of CuAlS_2 have been successfully grown by traveling heater method (THM) using In solvent.
Actual growth rate in a Bridgman growth of tin crystal is surmised to increase with the progress of solidification in the seeded growth. For the unseeded growth, however, the growth in initial stage proceeds with a high speed independently of the translation rate of the furnace.