Electrical and infrared optical properties of CdIn2S4 single crystals grown by chemical transport

Single crystals of CdIn₂S₄ were grown by chemical transport with iodine as transporting agent using different transporter concentrations and temperature gradients. It is found that the electron concentration increases with increasing transporter concentration and decreases after annealing in a sulphur atmosphere. Infrared reflectivity and absorption spectra are measured at room temperature in the wavenumber range from 180 to 4000 cm⁻¹ in order to determine the optical mode parameters of the compound and to evaluate the scattering mechanism of the electrons from the free carrier absorption. Lattice scattering is found to be predominant at room temperature for electron concentrations below about 4 · 10¹⁷ cm⁻³.     

Stoichiometric dependence of electrical characteristics in WSSe single crystals grown by direct and chemical vapour transport techniques

Single crystals of tungsten sulphoselenide (WSSe) have been grown by both direct and chemical vapour transport techniques. The crystals have been subjected to Hall effect and resistivity measurements for their electrical characterization. The observed differences in the electrical resistivity, type of conduction, and activation energy have been attributed to the stoichiometric differences between the crystals grown by the two techniques. The crystals grown by chemical vapour transport technique with iodine as the transport agent have been found to be more stoichiometric.     

Investigations on the structural perfection of bridgman-grown PbTe single crystals

It is reported on the possibility of improving the structural perfection by the Bridgman method, shown with the example of the influence on the low-angle grain boundary substructures in PbTe arranged in growth direction. In the employed crystal growth apparatus temperature gradients from 15 to 100°C/cm and solidification rates from 0.33 to 4.2 mm/hr could be achieved. The low-angle grain boundary substructure was characterized by X-ray-topographic and etch investigations on (100)-orientated ingots. The thermal conditions during the growth affect the structural perfection decisively. An axial spot dependence of etch pit density and substructure abundance was observed. By reducing the cooling rate during growth — expressed by the product of temperature gradient G and solidification rate V — it is possible to obtain more perfect PbTe-crystals. It seems that the diameter l of the substructure cells which was lying between 0.5 and 2 mm, is related to the cooling rate G · V by the functional coherency l ≈ 1/√G · V. The choice of different initial melt combinations up to 1 at.% Te-surplus exerted no influence on the abundance of the low-angle grain boundaries. The in literature suggested connection of low-angle grain boundary substructure with phenomena resulting from a constitutional supercooling could not be established.     

Investigations on the Nucleation Kinetics of L-Arginine Phosphate single crystals

The nucleation parameters, such as radius of the critical nucleus and critical free energy change have been evaluated for LAP single crystals. The interfacial tension determined by conducting the induction period measurements has been used for the evaluation of nucleation parameters. The determined interfacial tension is found to be comparable with theoretical literature values.     

Twins in CdMnTe single crystals grown by Bridgman method

Cd_1‐xMn_xTe (x =0.2, CdMnTe) crystal was grown by the vertical Bridgman method, which exhibits a pure zincblende structure in the whole ingot. The major defect, twins, which is fatal to CdMnTe crystal, was analyzed with scanning electron microscopy (SEM), X‐ray energy disperse spectroscopy (XEDS) and optic microscopy on the chemical etching surface. The twins observed in the as‐grown ingot are mainly lamellar ones, which lie on the {111} faces from the first‐to‐freeze region of the ingot and run parallel to the growth axis of the ingot. Coherent twins with {115}_t‐{111}_h orientations when indexed with respect to both the twin and host orientations, are often found to be terminated by {110}_t‐{114}_h lateral twins. Te inclusions with about 20 μm in width are observed to preferentially decorate the lamellar twin boundaries. The origin of the twins, relating to the growth twin and the phase transformation twin, is also discussed in this paper. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies on large uniaxially grown benzophenone single crystals

〈110〉, 〈010〉 and 〈100〉 oriented uniaxial benzophenone crystals were grown by uniaxially solution‐crystallization method of Sankaranarayanan ‐ Ramasamy (SR). The experimental parameters involved in the present study were investigated in detail and a constant growth rate was achieved by compensating the loss of growth units in the solution. A transparent uniaxial benzophenone crystal having dimension of 500 mm length and 55 mm diameter was grown at room temperature for the first time in the literature. In contrast to the conventional solution growth method, the growth rate along each direction was measured at ease during the respective growth experiment by monitoring the elevation of the solid‐liquid interface and found to be 2, 4 and 6 mm/day along the 〈110〉, 〈010〉 and 〈100〉 directions respectively for a chosen supersaturation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The twisting of LiNbO3 single crystals grown by the Czochralski method

As a result of our experimental work of mainly practical importance we established that for LiNbO₃ single crystals the Mg and Fe dopants promote spirality whereas decreasing of the pulling velocity strongly reduces the propensity of the system to produce spiralshaped crystals.     

Investigations for the improvement of the radial doping homogeneity of dislocation-free floating zone silicon crystals

In order to improve the doping inhomogeneities of dislocation free FZ Silicon crystals with diameters ≧ 75 mm investigations were carried out to influence the shape and curvature of the crystallization interface during the crucible-free floating zone crystal growth process. In this works shapes and geometries of the applied melting inductors and the relative positions of these inductors to the seed axis were examined concerning the values of radial macroscopic and microscopic doping inhomogeneities in dependence on other growth parameters, for instance crystal rotation rate. The application of eccentric inductor-seed positions effects a decreasing “bending value” of the crystallization interface, that means an improvement of the macroscopic radial doping inhomogeneity with crystal rotation rate in the range between 4 and 8 min⁻¹.     

Controlled growth of Ti4O7 crystals by chemical transport reactions

Ti₄O₇ is a striking example of the difficulties involved in the simultaneous control of crystal growth and composition. In this respect, the usual back-transport step must be avoided because it results to the formation of mixed phases. However, an appropriate H₂ heat treatment can reduce these mixed crystals into single phase single crystals. This result is ascertained by accurate and sensitive physical methods. Finally suitable pulling transport experiments lead to the growth of centimeter long crystals.     

Influence of chemical composition on dislocation structure and its change by plastic deformation of V3Si single crystals

The dislocation structure and its change by plastic deformation of V₃Si single crystals has been studied by an etch technique. The solution hardening effect established elsewhere is interpreted in terms of the observed dependence of the dislocation density ϱ(r) and its increment with the plastic deformation on the chemical composition within the range of homogeneity.     

Real structure investigations of LiNbO3 single crystals grown by the flux method

The real structure of flux grown LiNbO₃ crystals is investigated by etching technique, X-ray topography, and optical polariscopic method. The main defects are microdomains, dislocations and minor impurities of V³⁺−ions. The crystals do not contain growth striations. The mean dislocation density is in the order of 10³ cm⁻². The main origin of the defects seems to be post-growth mechanical stress. The results are discussed in comparison to the real structure typically found in the case of Czochralski crystals.     

On the growth mechanism of sodalite single crystals grown by the hydrothermal method on single crystal seeds coated with informative informative interfacial layers

The growth mechanism of the early formation stages of sodalite single crystals grown by the method of hydrothermal synthesis on single crystal seeds coated with interfacial layers of polycrystalline silver has been studied at an electronmicroscopic scale. Coating with interfacial layers leads to a very weak adhesion between the overgrown single crystal and the surface of the interfacial layer on top of the seed, thus providing a unique possibility of detaching the overgrown single crystals from seeds and investigating the very early crystallization stages by the morphology of the growth surface. In local microregions of seed surfaces coated with interfacial layers discrete particles arise differing from one another in morphology, this being primarily associated with the electrical heterogeneity of seed surfaces. During crystallization, the space between the discrete particles was filled with the hydrothermal solution which represented a liquid interfacial layer exhibiting informative properties occurred under the influence of electrically active elements of the seed surface. At the boundary separating the liquid interfacial layers with particular informative properties from the rest of the solution volume, at early crystallization stages, together with the formation of discrete particles directly on the coated seed surface, growth of a continuous sodalite single crystal took place. The informative properties of seed surfaces, which are regularly modified due to coating with interfacial silver layers, determine the occurrence on local regions of seed surfaces (under appropriate crystallization conditions) of one or the other polymorphous modification: either hexagonal – cancrinite, or cubic – sodalite.     

Electrical properties and deep levels spectra of bulk SiC crystals grown by hybrid physical–chemical vapor transport method

Concentrations of nitrogen shallow donors, boron shallow acceptors, charge carriers, and electron traps were measured as a function of position along the growth axis in a series of undoped 6H–SiC boules grown by sublimation method with and without addition of hydrogen to the growth atmosphere. Elemental analysis by secondary ion mass spectrometry and measurements of electrical properties indicate that the addition of hydrogen suppresses nitrogen incorporation and formation of all electron traps. Concentration of boron is not affected by hydrogen presence. The addition of hydrogen to the growth ambient improves the uniformity of nitrogen incorporation and deep trap distribution along the growth axis. The results are interpreted as due to increased carbon transport and corresponding shift of crystal stoichiometry toward carbon-rich side of the SiC existence range.     

Luminescent properties of CsI single crystals grown from the melt treated with EuI2

CsI single crystals treated with EuI₂ as a scavenger are grown and their radioluminescence spectra and scintillation light decay curves are obtained. Addition of the quantities of the scavenger comparable with the total concentration of the oxygen‐containing admixtures in the melt results in complete destruction of the latter. In its turn, this causes the disappearance of the band with a maximum at 2.8 eV in the radioluminescence spectrum and decreases the fraction of the slow 2 µs‐component to 0.01. The addition of larger quantities of EuI₂ leads to the appearance of a wide band with the maximum at 2.8 eV characterized by a decay constant of 2 µs; its intensity increases with the EuI₂ concentration. The maximum ratio of two faster components with the decay constants equal to 7 and 30 ns approaches 0.58:0.41 at EuI₂ concentration in CsI melt equal to 0.01 mol·kg⁻¹.     

Investigations on the defect depth of electroerosive-cut Te single crystals by reflection electron diffraction (RHEED)

Results of the experimentally determined defect depth due to electroerosive working of Te single crystals as a function of crystal orientation and electric cutting energy by RHEED are given. The abrasion of the disturbed surface layer was made by chemical etch polishing as well as by bombardment with Ar⁺ ions. The defect depths determined from the RHEED patterns depend on the crystal orientation and the applied cutting energy. In case of the lowest cutting energy, it has a value of about 3 μm for the (0001)-orientation and 6 μm for the (101 0)-orientation, the corresponding values for the highest cutting energy are about 8 μm and 20 μm, respectively. It is discussed in how far defect depths determined from the interpretation of RHEED patterns correspond to the “real defect depths” which can be determined by other measuring techniques.     

Growth of KDP single crystals by temperature reduction under diffusion transport

Growth rates of 37 μm/hour for {010} faces and 40 μm/hour for [001] directions have been found for KDP crystals growing in gelled media by temperature reduction. These values, higher than those recorded in alcohol-diffusing techniques are in the range of more classical methods. A device for obtaining larger crystal size is also described.     

On the variation of the impurity composition in LaF3 crystals grown by the Bridgman-Stockbarger method

Single crystals of the composition LaF₃ with CeF₃, YF₃, and SrF₂ impurities have been grown by the Bridgman-Stockbarger method in a graphite crucible with six cells. The CeF₃ concentration has been measured in the LaF₃ charge prior to the growth experiment and in the grown LaF₃ crystals upon it. It is shown that, depending on the growth conditions, the CeF₃ concentration can change during crystallization from 25% of its initial concentration in the charge up to 550%.     

Investigations of the growth mechanism and morphology of silver crystals grown electrolytically in gels

Gel medium has been used for the electrolytic growth of silver dendrites and single crystals of a variety of morphological features and forms. Microtopographic studies of the crystals have been carried out using optical and scanning electron microscopes. Some unusual growth surface morphologies have been observed. The surfaces of some of the crystals have a high degree of perfection. Sufficient experimental evidences are obtained for the striated growth of crystals and twin plane re-entrant edge (TPRE] mechanism of growth. The formation of tertiary three-dimensional (T3D) dendrites and dendrites with obliquely forward and backward branchings at different stages of growth have been investigated.