Influence of non-stoichiometry on the recombination activity of dislocations in undoped semi-insulating GaAs crystals

The effect of non-stoichiometry of gallium arsenide melt composition on the recombination activity of dislocations in undoped semi-insulating GaAs crystals is studied and analyzed. It is shown that the deviation from the stoichiometric melt composition is one of the major factors affecting the recombination activity of dislocations in undoped semi-insulating GaAs crystals. namely: the recombination activity of dislocations is increased when the arsenic-rich melt is used, and, on the contrary, is decreased when the gallium-rich melt is used. The regularities observed are explained by the complex processes of interaction of dislocations with the non-stoichiometry-induced intrinsic point defects.     

Methods for measuring light scattering in germanium and paratellurite crystals

Methods for studying the scattered light in germanium and paratellurite (α-TeO₂) crystals are considered. Investigations of the light scattering in Ge crystals were performed in the infrared wavelength range by the photometric-sphere method (in the range 2–3 μm) and by measuring the line-scattering functions (at 10.6 μm). In the visible range, the paratellurite single crystals were investigated by recording and analyzing images of laser beams transmitted through the samples. It is shown that small-angle Mie scattering is characteristic of both materials. Some conclusions about the sizes and the physical nature of scattering inhomogeneities are drawn. The effect of high-temperature annealing on the scattering intensity is studied.     

Raman scattering study of dopant homogeneity in GaP and GaAs single crystals

Application of Raman scattering as a non-destructive method with high spatial resolution suitable for the determination of charge carrier profiles connected with dopant segregations in polar semiconductors is reported. Single crystals of GaP and GaAs are investigated. The results are in good agreement with electrical measurements.     

Stability of dislocations in MgO single crystals at high temperatures

The dislocation structures of MgO single crystals annealed at 1900 °C for 3 hrs and at 2000°C for 1 hr were observed electron microscopically, and it was found that the following reactions took place at high temperatures: a/2 〈11 0〉 + a/2 [110], = a [100], a/2 [110] + a/2 〈11 01〉 = a/2 [011]. The resultant dislocations were sessile. Their interaction with impurities would make the subgrain boundaries stable.     

On splitting of dislocations at a reverse motion in germanium single crystals

The dislocation dissociation after the reverse motion along a slip plane in Ge single crystals have been investigated. It has been established that the dissociation width as well as the constriction density were independent on the motion direction. The results obtained have been used to clarify the role of the dislocation splitting in the formation of the phenomenon of the dislocation mobility asymmetry.     

Growth dislocations in zonal isomorphously mixed crystals

The orientation, distribution, and density of dislocations in isomorphously mixed potassium-rubidium biphthalate crystals composed of two zones with different concentrations of isomorphous rubidium impurity are experimentally studied. A model for the formation of growth dislocations in the external zone, which compensate internal heterometry-induced stresses at the interface between the zones, is proposed.     

Studies of helical dislocations,polygonization and pile-ups of dislocations in magnesium orthosilicate single crystals

(010) cleavages of magnesium orthosilicate crystals have been etched in concentrated hydrochloric acid and in its vapour at room temperature and also in the melts of sodium and potassium hydroxides at 400 °. Evidences of helical dislocations with their axes along [100] and [001] directions as revealed by etching is reported. Observations of polygonizations and pile-ups of dislocations are described and the implications are discussed.     

Geometrical properties of dislocations in potassium bichromate crystals

The geometry of growth dislocations present in potassium bichromate crystals grown from aqueous solution has been studied by etching. Etch topographs composed of dislocation etch grooves and grooves representing sector boundaries and growth bands have been analysed. It was found that most of the dislocation lines are straight and have well-defined directions in each sector. Refractions of dislocations at growth sector boundaries and at other defects have been observed.     

Raman scattering in sillenite-type crystals

The Raman spectra of Bi₂₄AlPO₄₀ and Bi₃₈ZnO₅₈ crystals have been studied for the first time. The polarization Raman spectra of Bi₁₂GeO₂₀, Bi₁₂TiO₂₀, Bi₂₄AlPO₄₀, and Bi₃₈ZnO₅₈ crystals are also studied. The lines in the Raman spectra of Bi₁₂TiO₂₀, Bi₂₄AlPO₄₀, and Bi₃₈ZnO₅₈ are identified and compared with the lines of the Bi₁₂GeO₂₀ spectra studied earlier. It is shown that the differences in the Raman spectra of the crystals studied are associated with the specific features of their atomic structures.     

Tracing of dislocations in ammonium hydrogen tartrate single crystals

Sparingly soluble ammonium hydrogen tartrate (AHT) crystals are grown by the gel method, derived from the diffusion of ammonium chloride into the set gel containing tartaric acid. Crystals up to 23 × 5 × 3 mm³ in size are grown at room temperature. AHT crystals are cleaved along (010) planes and the cleavage surfaces are studied by using multiple beam interferometry. The interferograms have revealed that the cleavages are quite flat. An attempt is made to trace the trajectory of dislocations of isolated as well as matched pairs of (010) cleavages of AHT when etched in a mixture of formic acid and methyl alcohol (2:1) and 1.0 M SrCl₂ solutions. Optical and transmission electron micrographs of dislocations show oblique, parallel and continuous line characteristics. Rows of equally spaced dislocation pits are observed and the implications of this are discussed.     

Optical birefringence images of dislocations in large gallium phosphide crystals

The optical birefringence induced by the strain field of a dislocation has been used to follow dislocation lines through large gallium phosphide crystals. Dislocations could be seen whether their lines were parallel to the imaging light beam or were steeply inclined to it. The images obtained so far suggest that it would be possible to resolve individual dislocations in crystals that contain ?5 × 10⁵ dislocations per cm².     

Kinetics of etching of dislocations in magnesium orthosilicate single crystals

Cleavages of undoped, doped and natural magnesium orthosilicate crystals have been simultaneously etched in concentrated hydrochloric acid solution. The lateral and normal velocities of the growth of pits were then measured at different temperatures for the varieties of crystals. The time dependence of the growth of pit dimensions is found to be linear, while the temperature dependence of the growth of pits is found to be exponential, viz. V = A exp (− E/kT). The dissolution parameters, e. g. the activation energy (E) and the pre-exponential factor (A) for dissolution along the surface and along the dislocation lines have been computed. It is observed that: (1) the activation energy (E₁) of dissolution along [001] direction is found to be greater than the activation energy (E_b) along [100] direction, irrespective of whether the crystals are doped, undoped or natural, and (2) the doping of the crystal with manganese has lowered down the activation energy (E_d) to such an extent that it is less than E₁ and E_b. The implications are discussed.     

Electron microscopic investigations of the recombination activity of dislocations in silicon

By combined application of scanning electron microscopy (EBIC technique) and transmission electron microscopy conclusions on the electrical activity (recombination efficiency) of individual dislocations in silicon are drawn.     

TEM investigation of precipitates in VCz GaAs crystals

Bulk GaAs crystals were grown from various Ga‐rich melts by the vapour‐pressure controlled Czochralski method in order to reduce As precipitates. The correlation of the melt composition with both, structural perfection and solid composition was examined by various methods of transmission electron microscopy (TEM). From transmission electron diffraction and diffraction contrast imaging a direct correlation between melt composition and sample properties is missing. High‐resolution TEM imaging hints to inhomogeneities only for the sample grown from a melt with a mole fraction of y = 0.492. Strain analysis of a selected defect reveals a strained crystal lattice in the surrounding of the defect. For the same sample, high angle annular dark‐field imaging and energy dispersive X‐ray spectroscopy verify the formation of precipitates. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation of dislocations in Sb crystals grown by pulling from melts

Results of experimental investigations on regularities of the formation of dislocations in crystals of pure antimony during pulling from melts are reported. The mean density of dislocations is compared with the values calculated by different theories.     

Domain structure investigations in triglycine sulphate single crystals

The domain structure of pure and irradiated TGS crystals was investigated by electron microscope decoration technique. Changes in the decoration pictures due to irradiation are shown and the way in which small lenticular domains disappear in the spontaneous ageing process is presented. Moreover, the thickness of the domain wall was assessed to be for good TGS crystals, grown in the paraelectric phase, of about 120 Å.