Journal of Crystal Growth最新文献

The phase formation of terbium chromoborate TbCr₃(BO₃)₄ in the bismuth trimolybdate and lithium tungstate melt–solutions has been studied. The absence of the terbium chromoborate trigonal phase in the bismuth trimolybdate-based system at all component ratios has been shown. The component ratio in the lithium tungstate-based system has been found at which the TbCr₃(BO₃)₄ trigonal crystals are formed at temperatures above 1100 °C; below this temperature, the monoclinic phase dominates. The structural and magnetic properties of the grown crystals have been studied. It has been established that the trigonal and monoclinic TbCr₃(BO₃)₄ crystals synthesized from the lithium tungstate-based solvent exhibit identical magnetic properties. At the same time, a significant difference of the magnetic properties of the single crystals synthesized from the bismuth molybdate melt–solution has been observed. This difference has been attributed to the effect of Bi³⁺ ions that partially replace Tb³⁺ ions.

In this paper, we have examined the formation of the imidazole glutarate adduct by protonation-deprotonation between imidazole and glutaric acid using a direct precipitation method within a short period. Following that, we have succeeded in growing imidazolium glutarate (IMGA) single crystal directly from synthesized material and we have also grown IMGA single crystal from the melt method using the vertical Bridgman technique for the first time in literature. A special Bridgman furnace was constructed with a slight modification in the winding section for this crystal growth. Crystal structure, phase purity, and growth plane were analyzed for the grown crystal from both single and powder XRD analysis. Functional groups were verified after the growth using FTIR transmittance analysis. The optical homogeneity and growth mechanism were scrutinized by birefringence interferogram and chemical etching studies, respectively. The grown IMGA has 80 % transparency in the entire visible region. The cut-off wavelength of the grown crystal is 235 nm, and the optical band gap energy of IMGA was found to be 5.26 eV. The photocurrent study reveals that IMGA has a negative photoconductivity nature. Third-order nonlinear parameters were found by the Z-scan technique. IMGA has a self-defocusing nature, negative non-linearity, and saturated absorption properties. The calculated χ⁽³⁾ value is 2.045 x 10^-8 esu.

In the article Part 1, experimental relation of a temperature distribution and a poly-silicon size in a melting process of silicon Czochralski (CZ) method is investigated. In this work, numerical simulations are performed to obtain temperature distributions in a crucible of a silicon CZ melting process. And applicability of International Atomic Energy Agency (IAEA) formula of effective thermal conductivity to poly-silicon chunks is examined. Calculations are done with a two-dimensional symmetric axis system and an explicit finite difference method. Samples are poly-silicon chunks of two sizes and small cylindrical graphite pellets of three sizes. Temperatures at 6 points in a crucible have been simulated. Simulations using IAEA formula give a good agreement with measured temperatures in the article Part 1. The experimental relation of temperature and a sample size is reproduced by simulations. Though IAEA formula is constructed for sphere particles, it serves in predicting an effective thermal conductivity of poly-silicon chunks. When applying the formula to chunks, a measured value of the porosity and an average size are used as parameters. The method of estimating an effective thermal conductivity is hoped to be applied to a large diameter silicon CZ growth.

Relation between temperature distribution in a crucible and size of poly-silicon chunks is investigated in a melting process of silicon Czochralski (CZ) method. Five kinds of feedstocks with a different size are heated up to about 1,000 °C in a crucible and the temperature distributions and thermal gradients are measured with six thermocouples. Two sizes of commercial poly-silicon chunks and three sizes of cylindrical graphite pellets are tested. The result is that the lager the particle size is, the lager the thermal conductivity is for both poly-silicon chunks and graphite pellets. Averaged sizes of clashed poly-silicon are defined and measured, and also void porosities in various samples are measured. The results of these measurements are to be used in comparisons with numerical simulations in the article Part 2.

The “facet effect” had an important impact on the growth and quality of III-V semiconductor crystals. Herein, Te-doped 〈1 1 1〉 and 〈1 0 0〉 GaSb single crystals were grown by the liquid-encapsulated Czochralski (LEC) method. The theoretical causes of the central facets of 〈1 1 1〉 GaSb and the edge facets of 〈1 0 0〉 GaSb were studied in detail. The Te component segregation, electrical parameter changes, infrared transmittance differences, and epitaxial film defects caused by the “facet effect” were comprehensively analyzed. The influence of the shoulder angle on the edge facets of 〈1 0 0〉 GaSb and the size differences of edge facets between the Ga-face and Sb-face were studied.

We present an in situ experimental study of decoupled- and coupled-growth patterns in a binary faceted/ nonfaceted (f/nf) eutectic alloy. Real-time optical observation is carried out at low growth velocity $V$ ($<0.3\mu {\mathrm{ms}}^{-1}$) during directional solidification of the transparent AminoMethylPropaneDiol-Succinonitrile (AMPD-SCN) eutectic in thin samples. On a large scale, the two-phase growth front mostly exhibits irregularly spaced decoupled-growth patterns involving faceted fiber-like AMPD crystals that protrude in the liquid ahead of, and in weak diffusive interaction with the nonfaceted SCN solid. The morphological stability of low-velocity, steady-state decoupled-growth patterns is evidenced. In addition, three types of (f/nf) coupled-growth patterns with fiber-like, tubular (or “hollow”) and C-shaped morphologies, respectively, are identified. New light is cast on the pinning/depinning dynamics of trijunctions at which the two solid phases and the liquid meet in equilibrium. A discussion is initiated on the interplay between the interfacial kinetics of the more or less mobile facets and the solute diffusion field, and on the stability of triple junctions with strongly anisotropic interfaces.

Metamorphic In_xAl_1-xAs (x_max > 0.75) buffer layer (MBL) grown on GaAs with an optimized non-linear graded composition profile along the growth direction is proposed for enhanced reduction of misfit dislocation (MD) density in highly mismatched III-V/GaAs metamorphic heterostructures. The equilibrium distributions of MD density throughout such In_xAl_1-xAs/GaAs MBLs are calculated. The influence of the initial composition (x_min) of MBL and the elastically strained thin GaAs layer embedded into the In_xAl_1-xAs MBL on the MD density distribution was studied. An optimum value of the inverse step (Δ), representing the difference between the top In content of the In_xAl_1-xAs MBL and that of a In_0.75Al_0.25As virtual substrate (VS) grown atop is determined. It was theoretically shown that Δ above 0.04 results in relaxation of the elastic stresses in VS via formation of the MDs, while the lower Δ values allow growing the VS completely free of MDs. Finally, the metamorphic In_0.75Al_0.25As/graded-InAlAs/GaAs heterostructures differing from each other by only the composition profile of the graded-InAlAs MBL were grown by MBE on GaAs (0 0 1) and studied by atomic force microscopy. The structure with proposed optimized non-linear graded (x = 0.05–0.77) MBL demonstrated the ∼ 1.5 times less MD density as compared to that with the convex-graded (x = 0.05–0.81) MBL, which was estimated to be at the level of ∼ 2·10⁷ cm⁻².

The temperature homogeneity at polysilicon rods significantly affects the uniformity growth of the polysilicon rod and the product quality in reduction furnace. The heat transfer phenomena on the rod surface includes electric heating, radiation heat transfer, convection heat transfer, heat conduction and reaction heat. In this paper, a representative configuration (RC) of heat transfer model was selected from a “honeycomb” industrial furnace. The flow patterns with different outlets have been numerically investigated and the dependency of surface temperature distribution on the inlet velocity as well as the geometric parameters has been investigated. $\mathrm{Gr}/{\mathrm{Re}}_d^2$ = 100 is set as the transition point determining the natural convection and mixed convection heat transfer. The results indicated that the axial temperature difference at the rod surface has close relationship with the complicated convection heat transfer. With rods growth, the main difference of local heat loss is caused by radiation rather than convection heat transfer.

Bulk GaN samples were characterized by both photothermal deflection spectroscopy (PDS) and steady-state photocapacitance (SSPC) methods. The PDS signal intensity in the bandgap was found to correlate quantitatively with the defect density estimated by the SSPC method. The defect density of GaN bulks fabricated by hydride vapor phase epitaxy (HVPE) was decreased by controlling the incorporation of carbon and silicon impurities. Differences in the reciprocal of the slope near the valence band maximum and the signal intensity in the bandgap among HVPE GaN bulks could be detected by PDS, although they had the same crystalline quality. PDS can be used to evaluate the GaN bulks that have been improved with a highly insulative property caused by Fe- doping or low carbon incorporation.

This paper discusses crystal growth and characterization of 1.0-inch ⁶LiI:Ag scintillators for thermal and epithermal neutron detection on the lunar surface as part of the Lunar Vehicle Radiation Dosimeter project. Zone purification method was employed to purify the raw material of ⁶LiI, and the crystals were grown using the Bridgman method. X-ray luminescence spectrum was measured to confirm the presence of Ag⁺ in the crystal lattice of ⁶LiI. The feasibility of neutron detection under ²⁵²Cf fast neutron irradiation was investigated. A hydrogen-rich paraffin wax moderator was used to slow down fast neutrons to obtain thermal and epithermal neutrons. The charge comparison method was used to perform pulse shape discrimination. The maximum value of the Figure of Merit was obtained to be 1.3, which demonstrates the capability of using ⁶LiI:Ag crystal scintillators in high neutron and gamma mixed fields. The energy resolution of the thermal neutron peak varied with the thickness of scintillators, achieving 12.0 % for the 0.5 cm thick samples. The potential for further improvement of the scintillation performance of ⁶LiI:Ag crystal relies on reducing impurities and color centers.