Distribution of Al and in impurities along homogeneous Ge-Si crystals grown by the Czochralski method using Si feeding rod

A distribution of Al and In impurities in Ge_{1 ? x} Si _x crystals (0 ≤ x ≤ 0.3) grown by a modified Czochralski method (with continuous feeding of melt using a Si rod) have been studied experimentally and theoretically. Experimental Al and In concentrations along homogeneous crystals have been determined from Hall measurements. The problem of Al and In impurity distribution in homogeneous Ge-Si single crystals grown in the same way is solved within the Pfann approximation. A set of dependences of Al and In concentrations on the crystal length obtained within this approximation demonstrates a good correspondence between the experimental and theoretical data.     

The distribution of Ga and Sb impurities in Ge-Si crystals grown by the Bridgman method using a feeding rod

Gallium- and antimony-doped Ge_{1 ? x} Si _x crystals (0 ≤ x ≤ 0.25) have been grown by the improved Bridgman method using a silicon seed and a macrohomogeneous feeding Ge-Si rod of the corresponding composition. The impurity concentration profiles along the grown crystals were determined from Hall measurements. The mathematical problem of impurity distribution along two-component mixed crystals grown from a melt with uniform and graded composition is solved in the Pfann approximation and within the virtual-crystal model for the solid solution. It is shown that the experimental impurity distributions in Ge_{1 ? x} Si _x crystals are described well by the data calculated on the assumption of linear change in the impurity segregation coefficient with the crystal composition.     

Hybrid technique for growing homogeneous single crystals of semiconductor solid solutions from melt

A concept and fundamentals of a hybrid technique for growing homogeneous single crystals of semiconductor solid solutions (SSs) from melt are presented. The growth consists of two stages. In the first stage, a single crystal with a specified concentration of the more refractory component is grown by an innovative method of directional constitutional supercooling of a melt in the steady-state mode. In the second stage, the melt is fed with the second component. Using an example of the classical Ge-Si system, the concentration profiles of the components along the crystal axis are calculated and the SS growth dynamics ensuring single crystallinity over the entire ingot length is determined. An analysis of the results yields the optimal technological parameters and conditions for growing homogeneous single crystals of SSs of a specified composition and size.     

On the incorporation mechanism and distribution mode of impurities in potassium acid phthalate crystals grown from aqueous solutions

Mechanism of impurity structure formation in crystals grown from aqueous solutions has been studied on the example of potassium acid phtalate (abbreviated hereafter as KAP) single crystals. Gold decoration technique at an electronmicroscopic scale has been applied to the study of the distribution of uncontrolled impurities on KAP cleavage face (010) after 10, 20 and 30 days of growth, taking into consideration different growth rates in 〈001〉 and 〈001 〈 directions. A technique for visualization of impurities in water, based on the adsorption of these impurities by the surface of amorphous film of nitrocellulose (parlodion) and the vacuum decoration with gold of these impurities, has been developed. Differences in the impurity structure of KAP regions located in 〈001〉 and 〈001〉 directions from the seed have been established. In 〈001〉 direction after 20 days of growth impurity assemblies 0.1—0.4 μm in size are revealed, and in 〈001〉 direction heterogeneous impurity structure is revealed only after 30 days of growth. The real (impurity) structure of KAP outside impurity assemblies is quite homogeneous and is the same throughout the whole crystal volume, the impurities incorporating mainly into complex active centres. From comparison of the changes in time of the impurity structure of water used for crystallization solutions and the impurity structure of KAP crystals a conclusion is made that the impurity structure of crystals is “programmed” in the impurity structure of crystallization solutions which regularly changes with time, i. e. impurities from different kinds of assemblies which are selectively adsorbed by the growing crystal faces. The role of the adjacent to the growing face interfacial layers which control the growth rate and have a complex impurity structure is stressed.     

Structure perfection of some molecular crystals grown from the melt

Single crystals of anthracene, naphthalene, phenazine and anthracene sym. trinitrobenzene (TNB) were examined using X-ray topography. Low-angle boundaries were observed and misorientation vectors of adjacent mosaic blocks have been estimated. Using an X-ray camera with oscillating film dislocation density in crystals has been evaluated. Anthracene-TNB crystals showed a much higher structure perfection than the other crystals.     

Growth of KDP crystals from solutions with mechanical impurities

Growth of KDP crystals from aqueous solutions with SiO₂ particles whose size ranges from 10^–2 to 400 μm in the static and dynamic modes has been studied. The effect of mother-solution supersaturation and particle size and concentration on the process of particle capture by a growing crystal is considered as well as types of inhomogeneities formed in the crystal under the influence of these factors. It is shown that the larger the particle size, the higher the probability of particle capture by a crystal. The influence of supersaturation, growth rate, face morphology, and particle concentration on particle capture and defect formation in crystals is also discussed.     

Growth of single crystals of semiconductor solid solutions by double feeding of the melt method

Crystallography Reports - The problem of component distribution in solid solution crystals grown from a melt fed by rods made of the components of the system, with allowance for the dependence of...     

Striation in Ge single crystals grown from melt under vibrations and weak heat convection

The influence of vibrations on the formation of mictohomogeneities of the properties in Ga-doped Ge single crystals grown by the method of directional crystallization with the axisymmetric upper heat supply has been studied in earth experiments. It has been established that vibrations provide the formation of inhomogeneities in the dopant distribution in the grown crystals.     

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.     

Morphology and characterization of ammonium bichromate crystals grown from aqueous solutions

The morphology of ammonium bichromate single crystals grown from aqueous solutions by solvent evaporation method at temperatures between 22 and 56 °C is investigated. It is found that the crystal morphology changes monotonically with an increase in growth temperature. Chemical etching is used to characterize the as-grown crystals.     

Orientation dependence of electrical and optical properties of ZnSiP2 crystals grown from melt

Undoped and Ga-doped ZnSiP₂ crystals grown by spontaneous crystallization from nonstoichiometric melt show a pronounced dependence of electrical properties (conductivity, carrier concentration) and cathodoluminescence on the orientation of various crystal faces. Breakdown voltage measurements and Hall measurements yielded that the (112)B face is always low-resistivity n-type and the (112)A face is always semi-insulating. The spectral position of the broad luminescence band observed at 80 K differs in a characteristical manner for the various crystal faces. The luminescence behaviour correlates partly with the electrical properties. The results are explained by an orientation dependence of the impurity incorporation which is reflected also in the bulk properties of the crystals.     

Pyroelectric properties of real LiNbO3 single crystals grown from a congruent melt

The temperature dependences of the pyroelectric coefficient of lithium niobate single crystals grown from a congruent melt have been investigated in the range of 4.2–300 K. No anomalies were found at low temperatures, and the experimental dependence is described well by the Debye-Einstein model, with T _D = 357 K and two pyroactive frequencies of 692 and 869 cm^?1. Specific features of lithium niobate have been analyzed. Two sublattices, formed by two pairs of mesotetrahedra with (according to the symmetry conditions) dipole and octupole moments, were selected in the structure. Their contributions to the total polarization differ by an order of magnitude. Vacuum annealing of the samples leads to the occurrence of anomalies only at temperatures over 280 K; these anomalities are interpreted as a manifestation of superionic conductivity.     

On the scandium distribution in indium arsenide crystals grown by the Czochralski method

In this paper the behaviour of scandium in n-type monocrystalline indium arsenide grown by Czochralski method in sealed ampoule is studied. The crystals have been grown in [111] direction under different conditions: crystallization rate, As-partial pressure and scandium initial concentration in the melt. The effect of the above factors on the scandium distribution along the crystals have been investigated. Using these results and by means of the equation of normal freezing the effective Sc distribution coefficient (k) in InAs under different technological conditions has been determined. It has been found that k < 1 in all experiments. In order to find the equilibrium coefficient (k₀) at fixed growth conditions the Burton-Prim-Slichter model has been used. On the basis of Hall measurements and atomic absorption analysis of Sc-doped InAs it is concluded that connected with Sc electrically active centers behave as shallow donors, most probably monovalent ones.     

Study of inclusions and growth bands in potassium bichromate crystals grown from aqueous solutions

The nature of inclusions and growth bands in potassium bichromate crystals obtained from aqueous solutions and their formation in relation to growth temperature and supersaturation are investigated. It is observed that impurities present in solution, fluctuations in growth temperature and high growth rates are responsible for their formation.     

Effects of doping of Ca and Ba on the dislocation distribution in melt grown KCl crystals

The effects of doping of Ca and Ba (∼ 0.02 at %) upon the dislocation distribution in melt grown KCl crystals without cellular segregation were studied by an etch pit method in connection with the dispersion state of the dopants, which was examined by the dark field illumination. – (1) In the Ca-doped crystal, in which the dopants were distributed uniformly, the formation of subboundaries was completely suppressed and dislocations were distributed at random. (2) In the Ba-doped crystal, however, the dopants were non-uniformly distributed and the dislocations tended to form subboundaries. The dislocations within the subgrains were distributed in a non-uniform manner. (3) The dislocation density in the Ba doped crystal was higher than that of undoped or Ca-doped crystal. This was explained by the mechanism similar to the Tiller's prediction. – Finally, the stress distribution due to the concentration fluctuation was examined by the birefringence patterns.     

Impurity induced structural phase transformations in melt grown single crystals of lead iodide

Lead iodide is a wide‐band gap and highly resistive semiconductor considered to be a promising room temperature nuclear detector. The phenomenon of polytypism is posing interesting problems of phase transformations among its polytypic modifications and formation of polytypic admixture during growth due to native impurities. Transformations have also been observed even when the material is stored for few months that causes deterioration in functioning of the PbI₂ devices. Lead iodide has been purified and single crystals were grown using zone‐refining system. The observed phase transformations during growth and storage have been explained in the light of distortion of [PbI₆]^4‐ octahedron due to impurities present in the material and the known crystal structures of PbI₂. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Complex formation and background impurity of Oxygen in the PbTe:Eu doped crystals grown from melt by the Bridgman method

The magnetic field dependence of magnetization M(B) at the temperature 1.72 K in magnetic fields up to 5 T and the temperature dependence of magnetic susceptibility (M_S) χ(T) in the temperature range 1.7–400 K of six PbTe:Eu samples with the concentration of Eu impurity of the order of 1×10¹⁹–1×10²⁰ cm^?3, prepared from the doped crystals grown from the melt by the Bridgman method, have been investigated. It is shown that the dependence of M(B) and χ(T) can be quantitatively explained by the contribution of the single centers of Eu ions, their pairs, and the matrix of the doped crystals using the same set of parameters for each sample. This is true provided we use in our analysis the values of the exchange integrals between Eu ions in EuO normalized with the lattice constant of PbTe, i.e., J₁/k_B=0.056 K for the ferromagnetic interaction of the NN (nearest neighbor) pairs and J₂/k_B=?0.13 K for the antiferromagnetic interaction of the NNN (next nearest neighbor) pairs, as well as different values of the M_S of crystal χ_matrix. It is revealed that the probability of the formation of complexes based on the magnetic impurity pairs is higher in the incipient section of a doped ingot, and it decreases towards the ingot end where the single centers of Eu ions become the only centers of the impurity. We conclude that the pairs of Eu²⁺ ions, which are formed during the growth of the PbTe:Eu ingots from melt by the Bridgman method, are the constituents of the complexes of the magnetic impurities with the background Oxygen impurities in the crystal matrix of the doped lead telluride. It is shown that the formation of the complexes leads to an increase of the M_S of crystal matrix χ_matrix and can even cause the change of its sign from minus to plus, i.e., it can convert the crystal matrix from the diamagnetic to paramagnetic state. The possible causes of this effect are analyzed.     

Block (mosaic) structure as an indicator for cooling of crystals grown from a melt

The specific features of the formation of the block (mosaic) structure with low-angle misorientation of the block boundaries are investigated using fluorite and germanium crystals as an example. These structural features are considered an indicator of conditions under which plastic deformation and polygonization occur during cooling of the crystals grown from melts.     

Purity and doping possibilities of Al2O3 and YAG molten in Mo crucibles and crystals grown from this melt

Doping possibilities of Al₂O₃ and YAG crystals grown from the melt alternatively doped with alkali earth, silicon, iron group or molybdenum ions under 98% Ar – 2% H₂ or 98% He – 2% H₂ protective atmosphere are described. Alkali earth and particularly Si ions evaporate slowly from the melt. Reduction of iron group ions was observed. Mo may enter YAG phase using a wet protective atmosphere. Al₂O₃ phase contains Mo ions if grown from the electrolyzed melt.