Papers by Keyword: Single Crystal Growth

Abstract: The research and commercialization of SiC based power device have been burgeoning over the last decade worldwide, which is bringing about an increasing demand on lost-cost and low-defect SiC wafers. To meet this challenge, we have been continuously making efforts on improving the crystal growth and wafer processing techniques. Now, the mass-production of high quality 4-inch, 6-inch n-type and semi-insulating SiC wafers has been realized. Statistically, the micropipe density is lower than 0.5 cm^-2. The resistivity of the wafers is lower than 0.02 Ω·cm and up to 10⁸ Ω·cm for n-type and semi-insulating SiC single crystals, respectively. A state of the art processing technique has been developed to control wafer deformation and thickness within the desired values for subsequent epitaxy. The total defect number of the epitaxial layers grown on the "epi-ready" 4-inch SiC wafer is 63, and the usable area is 97.6%, indicating the high quality of our SiC substrates.

Abstract: The nonlinear optical properties of a novel AgGa_1-xIn_xSe₂ crystal were investigated. Its absorption coefficients and band gap were determined at wavelength 0.8-19 μm. The coefficients of its Sellmeier dispersion equations were calculated by using linear interpolation based on the Sellmeier equations of pure AgGaSe₂ and AgInSe₂. The corresponding phase matching curves for the second harmonic generation (SHG) of CO₂ laser radiation were calculated and plotted. The walk-off angle and accept angle curves were also determined and plotted. The measured phase matching angle θ_m and acceptance angle δθ·L are 68.5° and 3.66°·cm respectively for sample AgGa_1-xIn_xSe₂ (x=0.2).

Abstract: The class of R₂PdSi₃ single crystals (R= rare earth element) with hexagonal AlB₂-type crystallographic structure reveals the systematic dependence of anisotropic magnetic properties governed by the interplay of crystal-electric field effects and magnetic two-ion interactions. Here we compare the floating zone (FZ) crystal growth with radiation heating of compounds Pr₂PdSi₃ and Nd₂PdSi₃. The congruent melting behavior enabled moderate growth velocities of 3 to 5 mmh^-1. The preferred growth directions are close to the basal plane of the hexagonal unit cell. The composition of the crystals, is slightly Pd-depleted with respect to the nominal composition 16.7 at.% Pd. The Pr₂PdSi₃ compound exhibit antiferromagnetic order below the Néel temperatures T_N: 2.17 K and Nd₂PdSi₃ compound order ferromagnetically below the Curie temperature T_C = 15.1 K.

Abstract: Nonlinear optical materials 2-aminopyridinium trifluoroacetate and bis (2-aminopyridinium) sulfate, were synthesized and single crystals were grown from aqueous solution employing the technique of controlled evaporation. The solubility and metastable zone width were found. The crystal structure was analyzed to reveal the molecular arrangements and the formation of hydrogen bonds in the crystal. High-resolution X-ray diffraction rocking curve measurements were performed to analyze the structural perfection of the grown crystals. Functional groups were identified and thermal behaviour and stability were studied. Mechanical and dielectric properties of crystals were analyzed. Optical studies reveal that both crystals have good transparency window. The nonlinear optical parameters of crystals were derived.

Abstract: Optical quality 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystals have been grown by a novel technique. In conventional growth methods, it was difficult to control the position of spontaneous nucleation, number of nuclei, cluster formation and the nucleation period. Difficulty in the nucleation and growth positioning was effectively solved by the slope nucleation method (SNM) and sizable DAST crystal was grown by two zone growth technique (TZGT) using a seed. Furthermore removal and fixing of seed crystal was difficult in the two zone growth technique. In the present study, we could obtain optical quality bulk DAST crystals by combining SNM and TZGT. The growth rates, size are estimated with respect to temperature gradient and slope shape. The structural, functional and optical analyses were carried for the grown crystals and the results are discussed in detail.

Abstract: The crystal growth of electron-doped manganites Ca_1-xEu_xMnO₃ by the floating zone method is reported. The special features of the growth parameters are discussed. Results of x-ray analysis, magnetic and transport characteristics are shown.

Abstract: HfO₂ Has High Effective Atomic Number and No Radioactive-Isotope as the Background Source, and it Can Be the Candidate for the High-Stopping Scintillator Instead of Lu₂SiO₅:Ce Scintillator Used in Medical Imaging, Astronomy and etc. However, HfO₂ Has an Extremely High Melting Point of 2774 °C, and it Is Difficult to Grow the Crystal from the Melt Using Crucible, as there Is No Suitable Metals, which Can Survive around that Temperature. Thus, Czochralski, Bridgman, and Micro-Pulling down Method Cannot Be Applied. Therefore we Investigated Optical Properties of a 17-mol% b-Doped (Stabilized) HfO2 Crystal Grown by the Skull Melting Method, and this Crystal Had a High Refractive Index of 2.5 at 550 nm, and the Maximum Emission Peak at ~550 nm from ⁵D₄ Excited States of Tb³⁺. In Addition, we Found the Radiation Reaction of the Crystal Irradiated with Alpha and Gamma Rays Measuring with a Photomultiplier.

Abstract: Recent developments in producing large single crystal CVD diamond plates are reviewed. The developments consist of synthesis of large single crystal diamond and production of single crystal diamond plates from the bulk diamond by the lift-off process. Combining these developments, half-inch single crystal CVD diamond plates have been successfully produced.

Abstract: C-plane substrates with off-orientation to <1120 > may stabilize the grown polytype, but the stacking fault density (SFD) increases from zero in the on-axis sample to 4500 cm-1 (7.7° off). The SF form preferentially at the seed-crystal-interface by a kinetically induced rearrangement of surface ad-atoms on m-facets. Most SF start in bundles with an average distance of 100 .m, which are subdivided in smaller bundles with 8 .m distance. They start preferentially from the upper corner of the vertical non-polar plane of bunched steps, which may be composed of small pyramids with m-facet surfaces. The dislocation density could decrease with increasing SFD by a pinning mechanism.

Abstract: Superconducting single crystals of La1.85Sr0.15CuO4 have been grown at various temperatures without single crystal seeds by the traveling-solvent floating-zone method. In order to avoid the formation of bubbles during the crystal growth process, a flowing atmosphere of 2 atm oxygen or 1 atm air was applied in different temperature range. It was found that the crystal quality could be improved by raising the growth temperature in a certain range, and the orientation changed from (110) to (100) at higher temperature. X-ray diffraction results showed that the full-width at half-maximum of the best as-prepared crystal was 0.086°. The crystals grown in 2 atm oxygen showed a superconducting transition temperature (Tc) of 37.3 K, while the crystals grown in floating air showed a Tc of about 35 K and it could be improved to 36.5 K by annealing in flowing oxygen.