Monocrystalline Cd0.2Zn0.8Te solid solution obtained by self‐selecting vapour growth

Cd_0.2Zn_0.8Te monocrystals with the sizes of about 15 mm have been produced by self‐selecting vapour growth (SSVG). High degree of structural perfection of monocrystalline Cd_0.2Zn_0.8Te was achieved. Excellent compositional uniformity was observed as well. To our knowledge, no comparable results are reported for this solid solution. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of CdSe single crystals by modified vertical vapor phase method

Good quality, large single crystals of CdSe were grown by the modified growth method (i.e., vertical unseeded vapor phase growth with multi-step purification of the starting material in the same quartz ampoule without any manual transfer between the steps). Lower temperature gradients (8–9°C/cm) at the growth interface were used for the crystal growth. As-grown CdSe crystals was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive analyzer of X-rays, high-resistance instrument measurement, and etch-pit observation. It is found that there are two cleavage faces of (1 0 0) and (1 1 0) orientations on the crystal, the resistivity is about 10⁸ Ω cm, and the density of etch pits is about 10^3–4/cm². The crystal was cut into wafers and was fabricated into detectors. The detectors were tested using an ²⁴¹Am radiation source. γ-ray spectra at 59.5 keV were obtained. The results demonstrated that the quality of the as-grown crystals was good. The crystals were useful for fabrication of room-temperature-operating nuclear radiation detectors. Therefore, the modified growth technique is a promising, convenient, new method for the growth of high-quality CdSe single crystals.     

Sphalerite-type Cd(Te,Se) crystallised by self-selecting vapour growth

Monocrystals of sphalerite-type CdTe_1-xSe_x were grown by self-selecting vapour growth SSVG in the horizontal configuration. As measured on a series of points of a (110) split plane, the “rocking curve” half-width was below 30 arcsec, while the lattice parameter measurements demonstrated the molar fraction x varying within 0.0024 (0.24 %). The values of x obtained from photoluminescence spectra taken from samples of different quality were in the ranges of 0.0034 (0.34 %) and 0.0047 (0.47 %). On the basis of the photoluminescence measurements, the maximum difference in x within the crystallised material was estimated to be 0.01 (1 %).     

Recycled Crystallisation of ZnTe by Evaporation-Condensation

ZnTe crystals have been grown by self-selecting vapour growth SSVG in a vertical, modified system, which reduces contact of the crystallised material with foreign materials to the minimum possible. Geometrical stability of the growth system is increased. The obtained crystals are of the sizes slightly below 10 mm and the “rocking curve” measurement results in the value of 36 arc sec. Distinct purification effect appears. The lattice constant of ZnTe is equal to 0.61036 nm.     

Charge transfer in CdTe at 200 and 300 K

Using a perfect single crystal sample of CdTe grown using PVT method, the electronic charge transfer in the II–VI compound semiconductor CdTe at 200 and 300 K has been evaluated using two different approaches: (1) by solving a quadratic equation involving the observed structure factors of h+k+l=4n+2 type reflections; and (2) by a graphical approach in which the observed and calculated atomic form factors are extrapolated to sinθ/λ=0, to determine the transferred charge. Precise X-ray structure factors collected using MoK radiation have been used for the analysis. The results obtained are reasonable and clearly indicate the ionicity by which charge is transferred from Cd to Te in CdTe.     

Compositional variation in Si-rich SiGe single crystals grown by multi-component zone melting method using Si seed and source crystals

The effect of the supply of depleted Si solute elements on the compositional variation in the Si-rich SiGe bulk crystals was studied using the method which was used to grow Ge-rich SiGe single crystals with a uniform composition. By selecting the proper pulling rate, we can obtain Si-rich Si_1−xGe_x bulk crystals with uniform composition of x=0.1 without using the supply mechanism of depleted Si solute elements. When the supply mechanism of Si solute elements was used, the initial composition in Si-rich SiGe crystals can be much more easily determined by controlling the growth temperature than that in Ge-rich crystals because the Si seed crystal is not melted down. The supply of Si solute elements is very effective to change the compositional variation even for Si-rich SiGe crystals.     

P–T–X phase equilibrium and vapor pressure scanning of non-stoichiometry in the Cd–Zn–Te system

Technical applications of artificial crystals strongly depend on tailoring the defect structure. In compound semiconductors, native defect concentration is closely related to non-stoichiometry. Vapor pressure scanning (VPS) is a direct high precision method of in situ investigation of the composition of non-stoichiometric crystals at high temperatures. It is based on experimental measurements of the vapor pressure, from which three-dimensional P–T–X (pressure–temperature–composition) range of existence of the crystalline phase is outlined. In this communication VPS data on non-stoichiometry in the Cd–Zn–Te system are presented. Geometrical analysis of the phase equilibrium is performed, and composition of the crystal, melt and vapor is determined in the technologically most important melting region. It will be shown how to apply experimental P–T–X phase equilibrium data for preparation of the material with pre-determined composition, either stoichiometric or with a certain deviation from stoichiometry. Different technologies are analyzed: vapor-phase growth, vertical, horizontal and high-pressure Bridgman. VPS has proved to be a powerful analytical tool. For CdZnTe the accuracy of the VPS determination of non-stoichiometry was shown to be as high as 10⁻⁴ at.% for temperatures up to the melting point.     

Boron oxide encapsulated Bridgman growth of high-purity high-resistivity cadmium telluride crystals

High-purity semi-insulating CdTe crystals have been successfully grown by encapsulated (B₂O₃) Bridgman technique. The procedure strongly limits component losses allowing the achievement of stoichiometry control material and keeps a low level of impurity contamination as shown by mass spectroscopy analysis data. When strictly stoichiometry-controlled and high-purity polycrystalline source material has been used, high-resistivity crystals have been obtained without any intentional doping. EPD values in the range of 1–3×10⁴ cm⁻² have been observed in a wide region of the crystals. Luminescence spectroscopy confirms the purity and good structural quality of the material. The proposed method avoids the technical problems posed by the High Pressure Bridgman technique and fits the requirements for CdTe/CdZnTe crystals large-scale production.     

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.     

Compositional plane of a wide-gap semiconductor CaCdSeS lattice-matched to InP and GaAs

We have investigated compositional plane of a wide band gap solid solution semiconductor Ca_1−xCd_xSe_1−yS_y (x0.32) using powder synthesis under thermal equilibrium condition. The solubility limit at 1273 K varies with respect to the Se concentration y, taking a minimum Cd solubility limit of 0.12 at y=0.8 and a maximum limit of 0.32 at y=1.0. It is found that the system can be lattice-matched to GaAs and InP under covering the energy band gap of ultraviolet–visible region. These results allow to design optoelectronic devices adopting the Ca_1−xCd_xSe_1−yS_y system.     

Single crystal growth of copper phthalocyanine using exaltation–evaporation growth method

A new method of growing single crystal for β-form copper phthalocyanine (CuPc) is presented in this paper. Melted anthracene was used as solvent of CuPc. The method, vaporizing the solvent using an automatic exaltation machine, was employed to grow CuPc single crystals. The needle-like single crystals of CuPc up to 11.6 mm in length were obtained by applying this method. The influences of different temperatures, exaltation speeds and concentrations on the single crystals growth were also discussed. The method was called exaltation–evaporation growth method.     

Preparation and characterizations of bulk GaN crystals

The growth conditions and mechanism of hexagonal GaN platelet crystals by Li flux were studied. The experimental results confirmed that these crystals crystallized from Li–Ga–N liquid phase. Photoluminescence (PL) spectra and Raman scattering spectrum of the crystals were obtained, which show that GaN crystals obtained by this method possess good crystalline 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.     

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.     

Semiopen Physical Vapour Transport Growth of Urotropine Crystals

It is reported for the first time the growth of urotropine (HMT) crystals by a semiopen physical vapour transport (SOPVT) technique. HMT crystals, approximately 1 cm³ in volume, are grown on a glass pedestal from solution-grown seeds. The final habit of the crystals is limited by rhomboedrical {110} faces which develop on an otherwise hemispherical shape. Preliminary X-ray diffraction investigations (rocking curves and topographs) point to a still non-homogeneous crystal structure, which very likely originates at the seed-crystal interface. However, in comparison with solution-grown samples, the best structural quality was observed in a SOPVT-grown sample.     

Synthesis, growth of organic nonlinear optical crystal: Semicarbazone of 2-amino-5-chloro-benzophenone (S2A5CB) and its characterisation

A new organic crystal of semicarbazone of 2–amino–5–chloro–benzophenone has been grown as a single crystal by slow evaporation solution growth technique for the first time in the literature. The grown crystal has been characterised by proton nuclear magnetic resonance spectral analysis and single crystal and powder X-ray diffraction studies. Functional groups of the crystallised molecules were confirmed by FT-IR and FT-Raman analyses. Mechanical strength of the crystals was studied by microhardness test. Optical transparency of the grown crystals has been studied by UV-Visible spectra. The second harmonic generation property of the compound was analysed.     

The solid state controlled growth of sulphides and selenides of Ag and Cu using crystal rotation

An improved crystal growth method for ionic-electronic mixed conductors, such as the high temperature cubic modifications of Ag₂X and Cu₂X (where X = S or Se), is presented. Ag or Cu atoms are mobile in these compounds. If the respective sulphur or selenium vapour pressure was sufficiently high at the growth surface, the growth rate was limited by the solid state chemical diffusion of Ag or Cu atoms which was controlled by the rate of the injection of the metal atoms into the compounds. The crystals were grown in a silica ampoule, held in a vertical two zone furnace and rotated at 1 rpm about the vertical axis to achieve a uniform axial temperature distribution. Nearly cylindrical single crystals of size about 3–10 mm diameter, 10–35 mm long were grown by this method.     

Growth and properties of KTP crystals from a new flux

High-quality KTiOPO₄ (KTP) crystals were grown by a top seeded solution growth (TSSG) method using K₈P₆O₁₉–BaF₂ as a flux. The volatility of different solvents, such as K₈P₆O₁₉ (K₈), K₈–NaF, K₈–KF, and K₈–BaF₂, was measured. These fluoride additives in K₈ fluxes and their compositional effects on the growth of KTP crystals were studied and discussed. The transmissivity and optical homogeneity of KTP crystals were also measured.     

Defect characterization and composition distributions of mercury indium telluride single crystals

A mercury indium telluride (MIT) ingot was grown by the vertical Bridgman method. The defects in MIT crystals were characterized by the chemical etching method. A defect etchant for MIT crystals was developed. The etch pits of dislocations, microcracks and boundary was observed by scanning electron microscopy. It was elucidated that the etch pits density of dislocations of MIT wafers was about 4×10⁵ cm⁻². Te and In reduced at the grain boundaries, but were homogeneously distributed within the grains in the as-grown MIT crystals. The distribution of In in MIT crystals along the growth direction and radial direction was analyzed by electronic probe microscopy. It was found that In concentration was higher in the initial part and lower in the final part of the MIT ingot, which indicated that the segregation coefficient of In in MIT crystals was 1.15. The radial In concentration increased from the center to edge of the wafers and homogeneous in the middle part.     

Investigation of the growth rate of β-cyclodextrin in water during both flow-cell and batch experiments

Growth rate measurements of β-cyclodextrin in water were performed both ways. Firstly, experiments were conducted with single monocrystals located in a supersaturation-controlled flow cell. Diffusional limitations and perturbations due to a competition between surface secondary nucleation and growth at high level of supersaturation have been put in evidence. The evolution of the growth rate with supersaturation has been modelled with a BCF law, assuming a screw dislocation mechanism. Secondly seeded cooling batch trials have been carried on in a well-mixed suspension crystallizer in order to assess the growth rate of the seeds. Refractometry was used as an in situ sensor for measuring the evolution of the concentration of the solute. Measurements of the crystals size distribution of the seeds and of the final crystals are performed off line with laser diffraction technique. A kinetic law with three parameters allows a consistent assessment of the growth of the seeds. The comparison of the two sets of data shows that overall growth rate of the seed is partially limited by diffusion. Nevertheless, the estimation of a surface integration growth kinetic coefficient from batch trials is rather difficult. The theoretical framework of nucleation models developed by Mersmann et al. (Crystallization Technology Handbook, second ed., Marcel Dekker, New York, 2001, pp. 45–80 and 81–144) coupled with the estimated growth kinetics can therefore be used to better monitor the seeding process during batch crystallization operations so as to favor the growth of the seed crystals.