Floating zone growth of high-quality SrTiO3 single crystals

Strontium titanate single crystals 15–20 mm in diameter and 40–80 mm in length were grown by a floating zone method with radiation heating. Additional crystal heating just below the molten zone by an in-growth annealing furnace was applied in order to lower the temperature gradients and to achieve slower cooling of the grown crystal. The crystal perfection was studied with X-ray topography and double-crystal diffractometry. The most perfect crystals were grown in [0 0 1] direction with single grain rocking curve widths of about 30″ and subgrain misorientations of 1′–3′ over 10×10 mm² areas of the boule cross-section for both (0 0 1)-, (1 1 0)- and (1 1 1)-oriented slices. Such high-quality crystal can be grown reproducibly with starting materials of 4N grade quality.     

Growth and spectroscopic properties of Er single doped and Er–Yb co-doped YAl3(BO3)4 crystals

Er³⁺-doped and Er³⁺–Yb³⁺ co-doped yttrium aluminum borate (YAB) single crystals have been grown by the top-seeded solution growth method using a new flux system, namely NaF–MoO₃–B₂O₃. The Er³⁺ concentrations were 1.3 mol% for both single doped and co-doped crystals and the Yb³⁺ concentration in the Er³⁺–Yb³⁺ co-doped crystal was 20.0 mol% in the raw materials. The distribution coefficients of Er³⁺ single doped and Er³⁺–Yb³⁺ co-doped crystals were measured. The polarized absorption and fluorescence spectra of Er³⁺–Yb³⁺ co-doped crystal were recorded and compared with those of Er³⁺ single doped crystal. The results demonstrate that Er³⁺–Yb³⁺ co-doped YAB crystal is a potential candidate for 1.55 μm laser materials.     

Improved growth of PbI2 single crystals

The phase equilibrium and the crystallization process of lead iodide (PbI₂) melt have been primarily investigated according to the lead–iodine phase diagram. It is found that the iodine evaporation and the segregated lead deposition are the two important factors that affect the PbI₂ crystal quality. The new method of Pulling U-type quartz growth ampoule has been made to impede the decomposition of PbI₂ and the vaporization and condensation of iodine. An orange and translucent PbI₂ single crystal of large size was obtained by the improved growth method, i.e. U-type ampoule pulling. Resistivity of the as-grown crystal is up to 4×10¹¹ Ω cm, and IR transmission is up to 45% in the region from 7800 to 450 cm⁻¹. Therefore, the improved growth method is a promising convenient new method for the growth of high quality PbI₂ crystals.     

Crystal growth of Ce: PrF3 by micro-pulling-down method

Micro-pulling-down (μ-PD) growth apparatus was modified for fluoride crystals. PrF₃ was grown with various concentrations of Ce³⁺ from 0–100%. The crystals were transparent and colorless (CeF₃) or greenish and 3 mm in diameter and 15–50 mm in length. Neither visible inclusions nor cracks were observed. Radioluminescence spectra and decay kinetics were measured for the sample set at room temperature. In comparison to the Czochralski or Bridgman method, the μ-PD method allows to produce single crystalline material in a faster thus more economic way. Once it is established for the fluoride crystals, it is an efficient tool for exploring the field of new functional fluorides.     

X-ray characterization of detached-grown germanium crystals

Germanium (1 1 1)-oriented crystals have been grown by the vertical Bridgman technique, in both detached and attached configurations. Microstructural characterization of these crystals has been performed using synchrotron white beam X-ray topography (SWBXT) and double axis X-ray diffraction. Dislocation densities were measured from X-ray topographs obtained using the reflection geometry. For detached-grown crystals, the dislocation density is on the order of 10⁴ cm⁻² in the seed region, and decreases in the direction of growth to less than 10³ cm⁻², and in some crystals reaches less than 10² cm⁻². For crystals grown in the attached configuration, dislocation densities were on the order of 10⁴ cm⁻² in the middle of the crystals, increasing to greater than 10⁵ cm⁻² near the edge. The measured dislocation densities are in excellent agreement with etch pit density (EPD) results. Broadening and splitting of the rocking curve linewidths was observed in the vicinity of subgrain boundaries identified by X-ray topography in some of the attached-grown crystal wafers. The spatial distribution of rocking curve linewidths across the wafers corresponds to the spatial distribution of defect densities measured in the X-ray topographs and EPD micrographs.     

Growth and morphology of ruby crystals with unusual chromium concentration

Single crystals of ruby have been obtained from fluxed melts based on the systems Li₂O–MoO₃, Li₂O–WO₃, Na₂O–WO₃, 2PbO–3V₂O₅, PbO–V₂O₅–WO₃, PbF₂–Bi₂O₃ and Na₃AlF₆ by both the TSSG method and spontaneous crystallization at the temperatures 1330–900 °C. Al₂O₃ solubility has been measured for the flux composition of 2Bi₂O₃–5PbF₂ in the temperature range 1200–1000 °C and dissolution enthalpy has been defined as 29.4 KJ/Mol. The composition of grown crystals was studied by electron microprobe analysis. The synthetic ruby contains from 0.51 to 6.38 at% of chromium admixture depending on the crystal growth conditions. Experimental results on growth conditions, composition and morphology of grown crystals are presented for each flux and temperature interval.     

Growth and properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals directly from melt

Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals were grown by a modified Bridgman method directly from melt using an allomeric Pb[(Mg_1/3Nb_2/3)_0.69Ti_0.31]O₃ (PMNT69/31) single crystal as a seed. X-ray diffraction (XRD) measurement confirmed that the as-grown PZNT91/9 single crystals are of pure perovskite structure. Electrical properties and thermal stabilization of PZNT91/9 crystals grown directly from melt exhibit different characters from those of PZNT91/9 crystals grown from flux, although segregation and the variation of chemical composition are not seriously confirmed by X-ray fluorescence analysis (XPS). The [0 0 1]-oriented PZNT91/9 crystals cut from the middle part of the as-grown crystal boules exhibit broad dielectric-response peaks at around 105 °C, accompanied by apparent frequency dispersion. The values of piezoelectric constant d₃₃, remnant polarization P_r, and induced strain are about 1800–2200 pC/N, 38.8 μC/cm², and 0.3%, respectively, indicating that the quality of PZNT crystals grown directly from melt can be comparable to those of PZNT91/9 single crystals grown from flux. However, further work deserves attention to improve the dielectric properties of PZNT crystals grown directly from melt. Such unusual characterizations of dielectric properties of PZNT crystals grown directly from melt are considered as correlating with defects, microinhomogeneities, and polar regions.     

Growth of nitrogen-doped p-type ZnO films by spray pyrolysis and their electrical and optical properties

Nitrogen-doped ZnO films were deposited on silicon (1 0 0) substrate using zinc acetate and ammonium acetate aqueous solution as precursors by ultrasonic spray pyrolysis. Successful p-type doping can be realized at optimized substrate temperature. The p-type ZnO films show excellent electrical properties such as hole concentration of 10¹⁸ cm⁻³, hole mobility of 10² cm² V⁻¹ s⁻¹ and resistivity of 10⁻² Ω cm. In the photoluminescence measurement, a strong near-band-edge emission was observed, while the deep-level emission was almost undetectable in both undoped and N-doped ZnO films. The growth and doping mechanism of N-doped ZnO films were discussed.     

Influence of cooling rate on the liquid-phase epitaxial growth of Zn3P2

We report the liquid-phase epitaxial growth of Zn₃P₂ on InP (1 0 0) substrates by conventional horizontal sliding boat system using 100% In solvent. Different cooling rates of 0.2–1.0 °C/min have been adopted and the influence of supercooling on the properties of the grown epilayers is analyzed. The crystal structure and quality of the grown epilayers have been studied by X-ray diffraction and high-resolution X-ray rocking measurements, which revealed a good lattice matching between the epilayers and the substrate. The supercooling-induced morphologies and composition of the epilayers were studied by scanning electron microscopy and energy dispersive X-ray analysis. The growth rate has been calculated and found that there exists a linear dependence between the growth rate and the cooling rate. Hall measurements showed that the grown layers are unintentionally doped p-type with a carrier mobility as high as 450 cm²/V s and a carrier concentration of 2.81×10¹⁸ cm⁻³ for the layers grown from 6 °C supercooled melt from the cooling rate of 0.4 °C/min.     

Structural, thermal and dielectric studies on a new solution grown 4-dimethylaminopyridinium dihydrogen phosphate crystal

Single crystals of 4-dimethylaminopyridinium dihydrogen phosphate (DMAPDP) (C₇H₁₃N₂PO₄) were grown by the solvent evaporation method. The three-dimensional structure was solved by the single-crystal X-ray diffraction method which belongs to triclinic crystal system and the molecular arrangements in the crystal were studied. The thermal behaviour was investigated using differential scanning calorimetry (DSC) and no phase transition was identified in the temperature region −150 to 230 °C. The thermal parameters—thermal diffusivity (), thermal effusivity (e), thermal conductivity (K) and heat capacity (C_p) of DMAPDP were measured by an improved photopyroelectric technique at room temperature. Dielectric constant and dielectric loss of the grown crystal were evaluated for the frequency range 1–200 KHz in the temperature region 28–135 °C. The Vicker's hardness was measured as 42.2 for a load of 98.07 mN. The laser induced surface damage threshold of DMAPDP crystal was found to be 4.8 GW/cm² with nanosecond Nd:YAG laser.     

Growth, dielectric, ferroelectric and optical properties of Ca0.28Ba0.72Nb2O6 single crystals

Calcium barium niobate Ca_0.28Ba_0.72Nb₂O₆ (CBN-28) crystals were grown by the Czochralski method. The effective segregation coefficients of Ca, Ba, Na elements in CBN-28 crystal growth were measured, and the rocking curve from 0 0 2 reflection of CBN-28 wafer was also measured by the high-resolution X-ray diffractometer D5005, and the full-width at half-maximum value was measured to be 70.6″. The measured dependence of dielectric constants on temperature showed the Curie temperature of the CBN-28 crystals is between 246.8 and 260 °C. Typical polarization–electric field (P–E) hysteresis loops were measured at room temperature. Ferroelectric 180° domains were observed by scanning electron microscopy (SEM) on the etched (0 0 1) surface of the CBN-28 crystals. The transmittance of [0 0 1]-oriented CBN-28 crystals was measured and the result shows that optical properties of CBN-28 crystal are almost the same as those of SBN for wavelengths between 2500 and 7500 nm.     

Ambient-condition growth of superconducting YBa2Cu4O8 single crystals using KOH flux

YBa₂Cu₄O₈ is a stoichiometric oxide superconductor of T_c80 K. Unlike YBa₂Cu₃O_7−δ, this compound is free from oxygen vacancy or twin formation and does not have any microscopic disorder in the crystal. Doping with Ca raises its T_c to 90 K. The compound is a promising superconductor for technological application. Up to now, single crystals have not been grown without using specialized apparatus with extremely high oxygen pressure up to 3000 bar and at over 1100 °C due to the limited range of reaction kinetics of the compound. This fact has delayed the progress in the study of its physical properties and potential applications. We present here a simple growth method using KOH as flux that acts effectively for obtaining high-quality single crystals in air/oxygen at the temperature as low as 550 °C. As-grown crystals can readily be separated from the flux and exhibit a perfect orthorhombic morphology with sizes up to 0.7×0.4×0.2 mm³. Our results are reproducible and suggest that the crystals can be grown using a conventional flux method under ambient condition.     

Oriented growth of large size calcium fluoride single crystals for optical lithography

We report (1 1 1), (1 1 0) and (1 0 0) growth of CaF₂ by the vertical Bridgman method. Crystals up to 250 mm diameter were grown and various growth parameters such as growth rate, temperature gradient and post-growth cooling rate were studied. It was found that the growth rate and the cooling rate are slower for the larger diameter crystals with a fixed temperature gradient. These growth parameters were optimized for growing the crystals along specific orientation after realizing that CaF₂ has a tendency to grow along an orientation close to 1 1 0. Degradation in optical transmittance was evaluated by irradiating the crystal to γ-rays up to a dose of 10⁵ rad. Optimized scavenger addition resulted in crystals with better radiation resistance and excellent VUV transmittance.     

Growth and spectral properties of Nd:LaVO4 crystal

This paper reports the growth and spectral properties of 3.5 at% Nd³⁺:LaVO₄ crystal with diameter of 20×15 mm² which has been grown by the Czochralski method. The spectral parameters were calculated based on Judd–Ofelt theory. The intensity parameters Ω_λ are: Ω₂=2.102×10⁻²⁰ cm², Ω₄=3.871×10⁻²⁰ cm², Ω₆=3.235×10⁻²⁰ cm². The radiative lifetime τ_r is 209 μs and calculated fluorescence branch ratios are: β₁(0.88μm)=45.2, β₂(1.06μm)=46.7, β₃(1.34μm)=8.1. The measured fluorescence lifetime τ_f is 137 μm and the quantum efficiency η is 65.6%. The absorption band at 808 nm wavelength has an FWHM of 20 nm. The absorption and emission cross sections are 3×10⁻²⁰ and 6.13×10⁻²⁰ cm², respectively.     

Investigations on the effect of InSb and InAsSb step-graded buffer layers in InAs0.5Sb0.5 epilayers grown on GaAs (0 0 1)

We report the structural and electrical properties of InAsSb epilayers grown on GaAs (0 0 1) substrates with mid-alloy composition of 0.5. InSb buffer layer and InAs_xSb_1−x step-graded (SG) buffer layer have been used to relax lattice mismatch between the epilayer and substrate. A decrease in the full-width at half-maximum (FWHM) of the epilayer is observed with increasing the thickness of the InSb buffer layer. The surface morphology of the epilayer is found to change from 3D island growth to 2D growth and the electron mobility of the sample is increased from 5.2×10³ to 1.1×10⁴ cm²/V s by increasing the thickness of the SG layers. These results suggest that high crystalline quality and electron mobility of the InAs_0.5Sb_0.5 alloy can be achieved by the growth of thick SG InAsSb buffer layer accompanied with a thick InSb buffer layer. We have confirmed the improvement in the structural and electrical properties of the InAs_0.5Sb_0.5 epilayer by quantitative analysis of the epilayer having a 2.09 μm thick InSb buffer layer and 0.6 μm thickness of each SG layers.     

Thermal and laser properties of Yb:YAl3(BO3)4 crystal

Large optical-quality Yb:YAl₃(BO₃)₄(Yb:YAB) crystals have been grown by the flux method. The thermal properties of Yb:YAB crystal were measured for the first time. The thermal properties of Yb:YAB crystal with different Yb³⁺ ion concentrations are also reported. The results show that the ytterbium concentration influences the properties of Yb:YAB crystal. The specific heat decreases with the increase of Yb³⁺ ion concentrations in the experiment range. Apparently, the thermal expansion coefficient increases along the c-direction with the increase of Yb³⁺ ion concentrations, while it changes slightly along the a-direction. The output laser in 1120–1140 nm ranges has been demonstrated pumped by InGaAs laser. The slope efficiency is 3.8%. The self-frequency-doubling output power of 1 mW is achieved.     

Growth and luminescence mechanisms of Ba2ErCl7: a new laser up-conversion crystal

A modified synthesis method for the preparation of Ba₂ErCl₇, a new laser up-conversion material using Er₂O₃, BaCl₂·2H₂O and NH₄Cl, is reported for the first time. Single crystals 5–8 mm in diameter and 10–20 mm in length were grown by both the Czochralski and Bridgman methods. The transmittance spectra for a Ba₂ErCl₇ single crystal was first measured using a HITACHI U-3500 spectrophotometer. There were three intense absorption peaks ⁴I_9/2, ⁴I_11/2 and ⁴I_13/2 in the infrared range which can be excited by 803 and 980 nm and 1.5 μm laser diode (LD), respectively. The cut-off wavelength of the crystal was 230 nm. Intense green luminescence was observed when the crystals were pumped by an 803 nm LD. Up-conversion mechanisms are discussed.     

Study on the Ce substitution effects of BiFeO3 films on ITO/glass substrates

Ce substituted Bi_1−xCe_xFeO₃ (BCFO) films with x=0–0.15 were deposited on indium tin oxide (ITO)/glass substrates by sol–gel process annealed at 500 °C. Rhombohedral phase was confirmed by XRD study and no impure phases were observed till x=0.15. Substantially enhanced ferroelectricity was observed at room temperature due to the substitution of Ce. In the films with x=0.05 and 0.10, the double remnant polarization are 75.5 and 57.7 μC/cm² at an applied field 860 kV/cm. Moreover, the breakdown field was enhanced in the films with Ce substitution.     

Crystal growth of Co46Ni27Ga27 ferromagnetic shape memory alloys with large single-variant set

The present work proposes a directional solidification method based on liquid melt cooling (LMC) technique to prepare large grain with single-variant set in Co–Ni–Ga alloys. The competitive growth from equaixed grains to steady columnar crystals with 1 1 0 orientation along the axis was observed. The directionally solidified rod has a uniform chemical composition. It can be also found that the unidirectional lamellar martensitic variants were well aligned in a whole grain, forming a single-variant state. Furthermore, the needle-like Ni₃Ga-type γ′ precipitates were formed in alloy with lower growth velocity, and it exhibited the complicated microstructural evolution. At the lowermost part of rod-like crystal, a large number of precipitates were dispersed both in grain interiors and at boundaries but its amount decreased when the columnar crystals were formed and gradually increased again from bottom up to top in the whole rod.     

Characteristic crystal growth from amorphous WO3 film by vacuum heating

Selective growth of WO₂, W and WO_3−x crystals from amorphous WO₃ film by vacuum heating at 400–900°C was clarified. The grown WO_3−x crystals were incommensurate structure based on crystallographic share structure. The growth process of WO₂ crystal in the amorphous film was directly observed at high temperature in the electron microscope. The growth front of the WO₂ crystal consumes WO₃ microcrystallites with various orientations. The growth speed of the WO₂ depended on WO₃ microcrystallites orientation. The origin of the wavy growth front of WO₂ was due to an orientation dependence of the WO₃ microcrystallites.