Top-seeded Solution Growth Method Research Articles

Top Seeded Solution Growth of 4H-SiC Bulk Crystal Using Graphite Block for Long-Term Growth

Solution growth method of SiC is assumed to be a promising technique to grow high quality SiC bulk crystal. Solution growth of SiC are based on the liquid phase growth from an incongruent melt composed of Si and C. Among various solution growth techniques, top seeded solution growth (TSSG) method for SiC has been widely studied for a next generation SiC growing technique. In TSSG method, the crystal growth on seed crystals is accomplished by the precipitation of solid SiC from C dissolved a Si melt on a seed crystal located at the top of the liquid. Because of the low solubility of C in liquid Si, SiC crystal growth on seed crystals using TSSG involves the use of a Si-rich Si-C solution. Therefore, in the TSSG method, high C solubility is required to increase the growth rate of SiC. Hence, there have been lots of studies how to increase the C solubility of Si melt. Eventually, several metallic solvents were proved to enhance the carbon solubility, so that the growth rate of SiC using TSSG were remarkably increased up to 2 mm/h. So, it is very optimistic to increase the thickness of grown crystal. However, TSSG has critical issue to increase crystal thickness because the C is supplied from the graphite crucible which is also the reservoir of Si melt. As growing time goes, therefore, the crucible will be dissolved to Si melt and the dissolved carbon will be consumed to grow single crystalline SiC crystal. Eventually, the thickness of SiC grown layer will be limited the volume size of graphite crucible. The reduction of graphite crucible will bring about the change of temperature distribution in the solid and liquid inside the reactor. Mechanical failure during crystal growth could be happened. Therefore, in this study, we applied a graphite block inside graphite crucible for elongate the growing time limit using graphite crucible for TSSG. Several graphite blocks with different design and materials properties were evaluated using finite element analysis using COMSOL multiphysics. The simulated results were then applied to the real experimental growth using small seed samples. Finally, the durability of graphite crucible and the crystal quality were comparatively evaluated with and without graphite blocks using several characterizations techniques.

Growth and characterization of Pb(Lu1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ternary piezo-/ferroelectric crystals

Piezo-/ferroelectric crystals of Pb(Lu1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ternary solid solution system with high Curie temperature, in the vicinity of morphotropic phase boundary (MPB) region, are grown by the top-seeded solution growth (TSSG) method for the first time. The compositions and structures of the crystals are analyzed, all the structures are found to have pure perovskite structure using X-ray diffraction analysis. Di-/piezo-/ferroelectric properties of the crystals are also characterized systematically. The Curie temperature Tc and coercive field Ec, increase gradually with increasing PbTiO3 content. In particular, the crystal with composition 0.34PLN-0.31PMN-0.35PT possesses excellent electric properties including the Curie temperature, the rhombohedral–tetragonal phase transition temperature, the piezoelectric coefficient, the remnant polarization and the coercive field, which are Tc = 228 °C, TRT = 156 °C, d33 = 2092 pC N−1, Pr = 35.5 μC cm−2 and Ec = 8.1 kV cm−1, respectively, making it a promising material for transducers or detectors in a wide temperature range.

Investigation of physical properties for nonlinear optical crystal MnTeMoO6: Hardness, density, specific heat and chemical stability

MnTeMoO6 crystals have been grown by the top-seeded solution growth method. The hardness, density, specific heat and chemical stability of MnTeMoO6 crystal were measured and analyzed. The actual density of MnTeMoO6 crystals are slightly larger than 5.0g/cm-3. An average Mohs hardness of about 4.5 is presented in MnTeMoO6 crystals, indicating the crystal is easy to cut and polish. The hardness and actual density of MnTeMoO6 crystals increase with the crystal quality, and the crystal with the smallest hardness and actual density has the poorest quality. The specific heat was measured to be 0.41-0.55 Jg-1K-1 over the temperature range of 20-300 \({}^{\circ}C\). The chemical stability measurements indicate that the MnTeMoO6 crystal has an excellent chemical stability and is resistant to diluted hydrochloric acid and diluted nitric acid.

Formation of Hybrid Perovskite Tin Iodide Single Crystals by Top-Seeded Solution Growth.

Hybrid perovskites have generated a great deal of interest because of their potential in photovoltaic applications. However, the toxicity of lead means that there is interest in finding a nontoxic substitute. Bulk single crystals of both cubic CH3NH3 SnI3 and CH(NH2)2 SnI3 were obtained by using the top-seeded solution growth method under an ambient atmosphere. Structural refinement, band gap, thermal properties, and XPS measurements of CH3NH3 SnI3 and CH(NH2)2 SnI3 single crystals are also reported in detail. These results should pave the way for further applications of CH3NH3 SnI3 and CH(NH2)2 SnI3.

Solution Growth on Concave Surface of 4H-SiC Crystal

A long-term growth of high-quality 4H-SiC single crystals by a top-seeded solution growth method using a Si–Cr-based melt was investigated. A new growth technique called “solution growth on concave surface” (SGCS) was developed to help prevent solvent inclusions. The concave shape of the growth surface was achieved by controlling the meniscus height, which enhances the step provision from the periphery to the center. In contrast, under the growth surface, the solution flows from the center to the periphery through convection by inductive heating. The opposite directions of the step flow and solution flow during solution growth create a smooth surface without solvent inclusions. SGCS was used to successfully grow a 1-in. diameter 4H-SiC crystal with a thickness of 30 mm, which is the thickest reported for a solution growth technique, and 1.7-in. diameter high-quality wafers without solvent inclusions were obtained. Schottky barrier diodes were fabricated on 4H-SiC substrates grown by SGCS, which demonstrat...

Large Birefringent Materials, Na6Te4W6O29 and Na2TeW2O9: Synthesis, Structure, Crystal Growth, and Characterization

A new d0 transition metal tellurite, Na6Te4W6O29, was synthesized by solid-state methods. The material crystallizes in monoclinic space group P21/c (No. 14) with the following values: a = 7.3297(3) A, b = 21.9057(9) A, c = 10.2871(3) A, β = 133.490(2)°, and Z = 2. Additionally, large crystals of Na6Te4W6O29 (13 mm × 11 mm × 10 mm) and Na2TeW2O9 (23 mm × 5 mm × 3 mm) were grown by the top seeded solution growth method. In addition to the crystal growth, refractive indices were measured, and the Sellmeier equations were fitted by using the minimum deviation technique. Interestingly, the two reported compounds exhibit relatively large birefringences: Δn3 = nz – nx = 0.0828–0.1248 from 1062.6 to 450.2 nm for Na6Te4W6O29, and Δn3 = nz – nx = 0.1471–0.2069 from 1062.6 to 450.2 nm for Na2TeW2O9. The results indicate that Na6Te4W6O29 and Na2TeW2O9 may have uses in applications involving birefrigent materials.

Giant strain and electric-field-induced phase transition in lead-free (Na0.5Bi0.5)TiO3-BaTiO3-(K0.5Na0.5)NbO3 single crystal

A lead-free single crystal 0.92(Na0.5Bi0.5)TiO3-0.06BaTiO3-0.02(K0.5Na0.5)NbO3 (NBT-6BT-2KNN) with dimension of Φ35 mm × 10 mm is grown by a precisely controlled top seeded solution growth method. The 〈001〉 oriented single crystals have excellent piezoelectric properties with a giant strain of 0.83% at 28 kV/cm. Application of an electric-field ≥14 kV/cm leads to a phase transition from pseudocubic to coexistence of tetragonal and pseudocubic. A strong ferroelectric domain texture occurs during the phase transition. Furthermore, the variation of tetragonal phase fraction agrees well with the macroscopic strain curve, demonstrating that the induced tetragonal phase plays a critical role in the high strain property.

Crystal growth, structure and optical properties of a new acentric crystal La2Al4.68B8O22 with a short UV absorption edge

A new acentric borate La2Al4.68B8O22 crystal, grown using the top seeded solution growth method, shows a short absorption edge at 193 nm.

Influence of Ta5+ content on the crystallographic structure and electrical properties of [001]PC-oriented (Li,Na,K)(Nb,Ta)O3 single crystals

A series of centimeter-sized lead-free piezoelectric Li+- and Ta5+-modified (Na,K)NbO3 single crystals with an ABO3 perovskite structure was successfully grown by the top-seeded solution growth method.

Origin of brown coloration in top-seeded solution grown SrTiO3crystals

SrTiO3 crystals grown by the top-seeded solution growth method in air show different shades of light brown coloration, depending on the growth conditions. In the optical transmission spectrum this is manifested as a broad absorption, tailing off from the fundamental absorption edge into the visible range. The investigation by transmission electron microscopy reveals that the light brown crystals contain voids of varying sizes in the nanometer range. Using the found size density distribution, the light scattering caused by such nano-voids in SrTiO3 is calculated on the basis of the Mie theory. A good agreement with the measured optical spectra is found. It is proposed that the formation of the nano-voids is due to vacancy clustering.

Optimized growth and electro-elastic properties of centimeter-sized piezoelectric crystals of Na2TeW2O9

Large sized crystals of Na2TeW2O9 with dimensions up to 75 × 35 × 25 mm3 were successfully grown using an optimized top-seeded solution growth method. The as-grown Na2TeW2O9 single crystal exhibits well-developed faces with the major forms {200}, {002}, {202}, and {220}, which are in superior accordance with the ideal morphology predicted by the Bravais–Friedel and Donnay–Harker methods. A complete set of room temperature elastic, dielectric, and piezoelectric constants of Na2TeW2O9 single crystals was determined using resonance techniques and impedance analysis. Our results show that Na2TeW2O9 exhibits excellent piezoelectric properties (d15 = −23.93 pC N−1, d24 = −20.34 pC N−1), making the crystal a promising candidate for piezoelectric applications. The relationship between the piezoelectric properties and the crystal structure is also discussed.

Growth and Nonlinear Optical Properties of GdAl3(BO3)4 in a Flux without Molybdate

Single crystals of the nonlinear optical (NLO) material GdAl3(BO3)4 (GdAB) were successfully grown by top-seeded solution growth method in the new flux Al2O3–B2O3–Li2O–NaF. The ultraviolet (UV) cutoff wavelength of GdAB grown from this new flux is approximately 175 nm, which is shorter than 266 nm. Measurement of second-harmonic generation powder suggested that the effect of the as-grown GdAB crystal is 3.5 times greater than that of KDP (KH2PO4), which was unchanged as the crystal grew from a molybdate-based flux. Therefore, the GdAB crystal obtained from the new flux is a promising candidate for NLO materials, which can be used to achieve fourth-harmonic generation in the UV region.

Effects of Growth Temperature on Crystal Morphology and Size Uniformity in KTa1–xNbxO3 and K1–yNayNbO3 Single Crystals

Solid-solution crystals play an increasing role in research and technology because their properties can be optimized by varying the concentration of their constituents for specific applications. Crystal morphology and size uniformity of cross-section are important factors to consider for obtaining high-quality crystals with excellent properties when crystals are grown by the top-seeded solution growth method. We propose effective energy models to explain the effects of growth temperature on the crystal morphology and size uniformity of KTa1–xNbxO3 and K1–yNayNbO3 single crystals, which are representative solid-solution crystals and have great application potential. Using the models, we could achieve the uniformity in size of cross-section by controlling the difference between growth temperature and equilibrium temperature. The as-grown KTa1–xNbxO3 and K1–yNayNbO3 single crystals with constant sizes of cross-section exhibited good crystallinities and had a large quadratic electro-optic coefficient s11 (s11 = 1.04 × 10–14 m2 V–2) and a large piezoelectric coefficient d33 (d33 = 110 pC/N), respectively, indicating their high quality and suitability for device applications.

Growth and Characterization of Lead-free Piezoelectric Single Crystals.

Lead-free piezoelectric materials attract more and more attention owing to the environmental toxicity of lead-containing materials. In this work, we review our first attempts of single crystal grown by the top-seeded solution growth method of BaTiO3 substituted with zirconium and calcium (BCTZ) and (K0.5Na0.5)NbO3 substituted with lithium, tantalum, and antimony (KNLSTN). The growth methodology is optimized in order to reach the best compositions where enhanced properties are expected. Chemical analysis and electrical characterizations are presented for both kinds of crystals. The compositionally-dependent electrical performance is investigated for a better understanding of the relationship between the composition and electrical properties. A cross-over from relaxor to ferroelectric state in BCTZ solid solution is evidenced similar to the one reported in ceramics. In KNLSTN single crystals, we observed a substantial evolution of the orthorhombic-to-tetragonal phase transition under minute composition changes.

Characterization of polarizer made of the deep-UV birefringent crystal Ba2Mg(B3O6)2.

In optical communications and the laser industry, modulating the polarization of light requires crystals with both large birefringence and a wide transparent range. A good candidate for a deep-UV birefringent crystal is Ba2Mg(B3O6) because it has a large birefringence and short UV cutoff edge. We grew Ba2Mg(B3O6)2 crystals with sizes up to 41 mm×40 mm×7 mm using the top-seeded solution growth method. We obtained the thermal-expansion coefficients in different directions and the thermo-optic coefficients and then designed and manufactured a Glan-Taylor type polarizer to fulfill the commercial requirements.

Controlled growth of large β-BaB2O4crystals based on theoretical guidelines

The diagram of phase equilibria in the BaB2O4–NaF system has been used to deduce the relationship between the cooling speed (ΔT), the pulling speed (v), the crystal radius (Rs), the slope of liquidus (m), the solution component (x) and the total quantity of melt, namely ΔT= 0.00159Rs2vmx2/G. The theoretical curves of the crystal thickness dependence on cooling rate and pulling rate have also been drawn. Under the guidance of the deduced formulas, the controlled growth of β-BaB2O4(BBO) crystals to a desired size has been achieved. A typical as-grown BBO crystal with dimensions of Ø76 × 33 mm (525.25 g) has been grown successfully by using the high-temperature top-seeded solution growth method. The measured optical homogeneity indicates that the as-grown BBO crystal has high optical quality (Δn≃ 6.9 × 10−6). The experimental curves of the crystal thicknessversusthe cooling rate and pulling rate were in line with the theoretical curves. The phenomenon of diameter shrinkage in the crystal growth has also been explained according to theory and practice. The theoretical derivation and experimental results provide the rationale for further growth of large BBO crystals with high optical quality.

Efficient orthogonally polarized dual-wavelength Nd:LaMgB_5O_10 laser

We reported an efficient, continuous-wave, diode-pumped, orthogonally polarized dual-wavelength laser working at 1051.8 and 1081.4 nm in a new neodymium-doped borate crystal, Nd:LaMgB5O10, which was grown by the top-seeded solution growth method. A maximum output power of 5.1 W was obtained with an absorbed pump power of 14.8 W, corresponding to an optical-to-optical conversion efficiency of 34.5% and a slope efficiency of 42.5%. By slightly tilting the laser cavity output mirror, the balanced dual-wavelength emissions were obtained with the total output power as high as 4.2 W. This new efficient dual-wavelength laser may be a promising light source for terahertz generation with a rarely large frequency difference of 7.8 THz through difference frequency generation.

Crystal growth and anisotropic thermal properties of the nonlinear and polar oxide Cs2TeW3O12

Large crystal of the nonlinear optical and polar oxide Cs2TeW3O12 with a size of 20×15×4mm3 has been grown by the top-seeded solution growth (TSSG) method. This crystal can be thermally stable up to 808°C and melts incongruently. It possesses a large transparent range of 0.415–5.250μm. Thermal properties, including thermal expansion, specific heat, thermal diffusivity and thermal conductivity were investigated. The average linear thermal expansion coefficients were calculated based on the measurement in the temperature range of 30–390°C. It exhibits strong anisotropic thermal expansion which was discussed according to the relationships between the structure and thermal properties. Furthermore, laser-induced damage threshold has been estimated to be 591.28MW/cm2 with a laser wavelength of 1064nm and pulse duration of 8ns.

Thermal and spectral characterization of Cr3+:MgWO4—a promising tunable laser material

This paper reports the growth, thermal and polarized spectral properties of Cr3+:MgWO4 crystal. Cr3+:MgWO4 crystal with dimensions of 20×18×13mm3 was grown successfully by a top-seeded solution growth method. The average thermal expansion coefficients are 10.47×10−6K−1, 15.68×10−6K−1 and 10.75×10−6K−1 along a-, b- and c-axis, respectively. The thermal conductivity is 8.69W/(mK) at room temperature. Both of the absorption and emission spectra show strong polarization characteristics. There is a broad and strong absorption band at around 790nm, which means that Cr3+:MgWO4 crystal is suitable for AlGaAs laser diode pumping. The crystal has a broad emission band at 961nm with a full width at half-maximum of 202nm; the emission cross-section is about 1.8×10−19cm2. The results show that Cr3+:MgMoO4 crystal can be regarded as a potential tunable laser gain medium.

Growth, spectral property and crystal field analysis of Cr3+-doped Na2Mg5(MoO4)6 crystal

This paper reports the growth and spectral properties of Cr3+:Na2Mg5(MoO4)6 crystals. The Na2Mg5(MoO4)6 crystal was grown from a flux of Na2Mo2O7 by the top seeded solution growth method. The absorption cross-sections are 0.692×10−19cm2 at 507nm and 1.151×10−19cm2 at 736nm, respectively. The emission cross-section is 1.62×10−19cm2 at 914nm with FWHM of 192nm. Based on the absorption and emission spectra, the crystal field strength Dq, the Racah parameters B and C, effective phonon energy ℏω and the Huang–Rhys factor S were calculated. The spectral properties of Cr3+:Na2Mg5(MoO4)6 crystal demonstrate a good potential for tunable laser material.