Dislocation internal friction and temperature dependence of yield stress in high-purity molybdenum single crystals

High purity molybdenum single crystals (residual resistivity ratio ≈ 6 · 10⁴) were studied by means of computer-controlled internal friction technique at frequencies of about 100 kHz in the temperature range 6 to 300 K. The amplitude dependences of decrement were measured within the vibrational strain amplitude 10⁻⁷ to 10⁻⁴. It was established that the temperature dependence of ultrasonic amplitude providing a constant level of reversible dislocation deformation coincides well in relative units with the temperature dependence of the critical resolved shear stress at 20 to 180 K.     

Plastische Verformung von Siliziumeinkristallen unterschiedlicher Ausgangsversetzungsdichte im Streckgrenzenbereich

Floating-zoned Silicon crystals orientated for single slip both dislocation-free and with grown-in dislocations (EPD₀ = 6,5 · 10⁴ cm⁻²) were dynamically deformed in compression in the temperature range 1120 … 1300 K up to the lower yield point. The dislocation structure of plastically deformed crystals (T = 1138 K; a₀ = 1,45 · 10⁻⁴ s⁻¹) was examined by etching and high-voltage electron microscopy. The crystals exhibit essential differences in deformation behaviour and in the resulting dislocation structure. Typical for the dislocation-free basic material are (i) an inhomogeneous deformation in the range of the upper yield point (ii) a greater portion of sessile lomer dislocations at the lower yield point in relation to the crystal with grown-in dislocations. The measured stresses were related to those values calculated from structure data by employing plasticity theory of diamond-like semiconductors.     

Dislocation etching in V3Si

Dislocations in as-grown and in plastically deformed V₃Si single crystals have been studied by chemical etching. In as-grown crystals dislocations are partly arranged in small-angle boundaries parallel to {001}, {011}, and {112} planes. The total dislocation density amounted to (10⁵−10⁶) cm⁻². After plastic deformation at elevated temperatures indications for slip and climb processes were observed. The dislocation density increased to 10⁷ cm⁻².     

Growth of Semiinsulating GaAs Crystals by Vertical Gradient Freeze Technique

GaAs crystals having dislocation densities of 1–2 10³ cm⁻² were grown using VGF technique. In the grown crystals Si_Ga is the dominant donor and C_As the dominant acceptor. Theoretical and experimental investigations have shown the possibilities to influence on the silicon and carbon content in GaAs. Based on these results, semiinsulating properties in the crystals could be achieved reproducibly.     

TSM-gewachsene Halbleiter-Einkristalle aus (Pb0,8Sn0,2)Te

By means of the Travelling Solvent Method (TSM) the authors succeeded in growing PbSnTe solid solution crystals using a simple working growing principle. Imperfections and constitution as well as electrical properties of the crystals have been investigated. The results lead to the conclusion that one can grow homogeneous, nearly perfect crystals having low carrier densities and high carrier mobilities in a relatively short time which seems to be the main advantage of the experimental techniques used. Representative values of electrical crystal parameters are p₇₇ ≦ 10¹⁷ cm⁻³, n₇₇ ≦ 10¹⁷ cm⁻³; pμ₇₇ ⋍ 1,6 × × 10⁴cm²/Vs; dimensions: 1 × 4 × 4 mm³.     

Influence of proton implantation on the properties of CuInSe2 single crystals (I). Ion channeling study of lattice damage

The lattice damage of p-type CuInSe₂ single crystals implanted with 10 keV protons in the fluence range from 2.5 · 10¹⁴ to 8 · 10¹⁵ cm⁻² was investigated using the Rutherford backscattering/channeling technique. At proton fluences up to about 2 · 10¹⁵ cm⁻² radiation annealing of the defects is observed which is ascribed to very high defect concentrations in the unimplanted samples. At higher fluences radiation damage occurs but the concentration of radiation induced defects ramains low. There are indications that selenium interstitials or defect complexes with selenium interstitials involved are stable defects at room temperature.     

IR-spannungsoptische Ermittlung züchtungsbedingter Eigenspannungen in Silizium

The growth conditions and the resultant defect structure are the cause of residual stresses in silicon single crystals. The field of residual stress is nearly axial symmetrically; tensile stresses are in the centre and compressive stresses are at the periphery. The field of residual stress adapts itself to crystal symmetry by plastic deformation during the growth or annealing processes. The tangential compressive stresses at the periphery are 25 kp/cm² for Czochralski-grown crystals (diameter 36 mm, etch-pit density 5 · 10³ cm⁻²) and about 70 kp/cm² for crystals grown by the floating zone technique (diameter 28 mm, etch-pit density 3 · 10⁴ cm⁻²). Dislocation free crystals are almost free of residual stresses.     

Zur Bestimmung der Mikrohärte von Baryt-Einkristallen bei hohem hydrostatischen Druck

An apparatus to generate high pressure up to 12000 kp · cm⁻² and a microhardness device to be put in it are described. The pyramid identations originate from the moving force of the falling indenter. To compare microhardnesses at normal and high pressure the viscosities of the pressure fluids are assimilated. For that purpose the microhardness device served as viscosimeter. With extrapolated falling height zero of the idennter and a load of 36 g the (001)-surface of Baryt single crystals have a microhardness of about 210 kp · mm⁻² at a hydrostatic pressure of 10000 kp · cm⁻². The corresponding microhardness at normal pressure is 90 kp · mm⁻²     

Impurity effects on low-angle boundary formation in silicon single crystals

The combined effects of crystal growth conditions and impurity (Sb, P, B, Ga) concentration on low-angle boundary (LAB) formation in silicon single crystals growing by Czochralski technique was investigated. The dependence of LAB formation frequency and LAB parameters on crystal growth conditions and impurity content was found. Impurity effects on LAB formation become apparent at concentrations of about 10¹⁸ cm⁻³. – All impurity investigated decreases the probability of LAB formation, the acceptor impurity influence is stronger. At B concentration exceeding 2 · 10¹⁹ cm⁻³ LAB formation does not occur. – Results are interpreted in terms of scheme of LAB formation in thermal stress field of growing crystal. To explain observed impurity effects assumptions about dislocation drag and about raising of critical stresses for dislocation generation with doping are made.     

EPR-spectrum of irradiated potassium dichromate single crystals

EPR-spectra of X-irradiated potassium dichromate crystals are studied at various temperatures from RT to LNT. The most intensive lines are interpreted as due to radicals CrO₄³⁻ (A-lines) and CrO₃⁻ (C-lines), resulting from Cr₂O₇ owing to X-irradiation. Hyperfine structure of C-line, due to interaction of unpaired electron with Cr⁵³ nucleus, occurs at low temperatures, and new unobserved earlier Q-lines appear near-by C-line. The spectrum may be described by usual spin Hamiltonian for S = 1/2 with following parameters: for A-line gz = 1.9841, gy = 1.9685, gx = 1.9592; for C-line gz = 1.9148, gy = 1.9671, gx = 1.9886, |Az| = 30.53 · 10⁻⁴ cm⁻¹, |Ax| = 10.62 · 10⁻⁴ cm⁻¹, |Ay| = 6.62 · 10⁻⁴ cm⁻¹.     

Zur Realstruktur von Ga1–xInxAs LPE-Schichten

Ga_1–xIn_xAs epitaxial layers (0.02 ≦ × ≦ 0.12) are grown on (111)-oriented GaAs substrates from nonstoichiometric melts. The etch pit densities – determined by chemical etching – yield values between 2 · 10⁵ cm⁻² and 3 · 10⁷ cm⁻² and were found to be dependent on composition, layer thickness and cooling rate. X-ray topography of cleaved {110}-planes gives information on layer quality and indicates the existence of stress in the substrate lattice near the heterojunction. The validity of Vegard's law in the investigated concentration range was confirmed by X-ray determination of the lattice constants. The half width of double crystal spectrometer rocking-curves, the epd and the relative intensity of photoluminescence show similar dependence on the composition of the mixed crystal layers.     

Crystal growth of PbTe and (Pb,Sn)Te by the bridgman method and by THM

Synthesis and growth of PbTe and (Pb, Sn)Te single crystals by the Bridgman method and by the Travelling Heater Method (THM) from Te-rich solutions are described. It is to be seen from comparative investigations that seeded THM growth reproducibly provides oriented single-crystalline ingots free of low-angle grain boundaries and with etch pit densities of 8–12 × 10⁴ cm⁻². All the materials were p-type with carrier concentrations from 1 to 2 × 10¹⁸ cm⁻³.     

Die Herstellung von einkristallinen Dünnschichten aus Halbleitern mit ausgeprägter Anisotropie durch gerichtete Kristallisation der Schmelze zwischen zwei Substraten

Investigation of monocrystalline thin layers (5 to 150 μm in thickness) of Te and CdSb orientedly grown between two substrates. The form of the solidifying front strongly influencing crystal perfection can be controlled. Thin layers grown with velocities < 0.25 cm · min⁻¹ are monocrystalline with etch pit densities of 6 · 10² cm⁻². The electrical quantities R_H, σ and α of the layers are nearly identical with those of bulk material. Doped monocrystalline CdSb layers had a minority carrier concentration of ∼ 10¹⁴ cm⁻³ at 77°K.     

Shaped crystal growth of PbTe by the open tube technique

The possibility of growing shaped A^IVB^VI crystals from the vapour phase by the open tube technique was investigated on PbTe. The thermodynamic conditions to reproducible prepare several habits of PbTe crystals — whiskers, tetrahedral prisms and cubes, platelets (a), dendrites, cubic and octahedral skeletons (b) as well as their properties were examined. The crystalline habits (a) are characterized by perfectly mirror-like (100) surfaces and low dislocation densities. The type and concentration of charge carriers are mainly determined by the vapour composition within the crystallization zone and very from n = 3 × 10¹⁷ to p = 1 × 10¹⁹cm⁻³. These properties are the reason of the interest in shaped PbTe crystals for the aim of IR optoelectronic devices.     

Effect of the defect structure character in calcite single crystals on X-ray diffraction

The paper presents experimental results for the dependence of the integral intensity of anomalous transmission T_i and Laue reflection R_i of X-rays on the structural quality of calcite single crystals as obtained by a two-crystal spectrometer. The relation between X-ray dynamic and kinetic scattering as a function of the sample thickness, densities of perfect dislocations in perfect CaCO₃ crystals and of atom-vacancy complexes in calcite crystals with „background”︁ has been found. Distortions due to perfect grown-in dislocations in calcite are shown to exceed those produced in crystals with „background”︁. The latter appear to be more X-ray transparent. A comparison with results of twin layer thickening experiments on CaCO₃ crystals of different qualities again points to the different nature of these distortions. In CaCO₃ crystals with the dislocation density of up to 2 × × 10³ cm⁻², the X-ray scattering, in our experiments, was consistent with the dynamic diffraction theory, while at higher dislocation densities, the X-ray scattering markedly differs from it.     

Optical defects in barium—strontium niobate single crystals

The distributions of edge dislocations and residual mechanical stresses in Ba_xSr_1-xNb₂O₆ (BSN) crystals are investigated and the explanation of the nature of the “growth column” is proposed. The “growth column” is a defect zone going through all of the crystal and usually repeating in its cross-section the contour of the seed crystal. The “growth column” boundary is the closed contour with extremely high edge dislocation density. These dislocations are connected with thermal stresses due to seed-melt contact or abrupt crystal widening. Under proper crystal seeding and widening conditions one can obtain the BSN crystals with dislocation densities less than 10 cm⁻² and without the “growth column”. The method of chemico-mechanical polishing of BSN crystals not forming a defect layer on the surface of the crystals have been developed. The high temperature diffusion annealing is shown to eliminate the growth striae in BSN crystals.     

Sub-boundaries on (002) cleavages of Li2CO3 single crystals

Linear arrays of dislocations (straight, terminating and curved) are observed on etching with 2% citric acid (002) cleavages of lithium carbonate (Li₂CO₃) single crystals, grown by zone melting technique. As the dislocations are non-uniformly spaced and disappear on successive etching, they may not be revealing low-angle grain boundary, nor slip traces as they are terminating and curved meaning crystallographically non-oriented. On the observation of experiments on successive etching and etching of matched pairs, it is concluded that the arrays of etch pits reveal dislocation walls (dislocation density 1.1 × 10⁶ — 1.5 × 10⁷ pits cm⁻²) probably created due to the localized thermal stresses released as a result of high temperature annealing of the crystal during growth. The implications are discussed.     

Study on the Growth of Triglycinsulphate Single Crystals

Crystallization of TGS at 52.0°C - above the transition point - has been studied in a wide range of supersaturation of the solution (σ = 0 to 10⁻²). The rates of growth of {110} and {001} faces were measured as a function of supersaturation at constant hydrodynamical conditions (Re = 3.4 · 10⁻³). Further, the influence of hydrodynamical conditions on the growth of {110} faces at constant supersaturation (σ = 4.2 · 10⁻³) was established. The parameters of the experimentally found dependences are determined on the basis of the surface-diffusion model of BURTON . CABRERA and FRANK . From these dependences follows that the growth rate of the {110} faces is already almost limited by the volume diffusion of TGS molecules towards the crystal surface, while in the case of {001} faces the surface diffusion mechanism of crystallization is clearly manifested. Dislocation densities in the crystals have been determined by means of etching technique. The number of dislocations increases with increasing supersaturation; hence, supersaturation of the solution together with the processes taking place in the regeneration zone surrounding the seed determine the number of dislocations in the crystal volume and thus the resulting structural perfection of single crystals. Investigation of the spontaneous redistribution of domains showed that the growth rate of TGS crystals influences the dielectric properties to much smaller extent than does chemical purity.     

A study of the Growth-Temperature-dependent Surface Morphology in InSb Liquid Phase Epitaxy

InSb LPE layers were grown on (111) InSb substrates, their phase diagram and growth rates studied. The InSb activity coefficient α(T), determined by fitting the experimental data, had a value of 2556–11.11 · T cal · mole⁻¹. The terraces on the surface were reduced by increasing the temperature to 350 °C. Hall measurements of InSb/CdTe heterostructure failed due to the high Te segregation. The carrier concentration of these InSb epilayers, however, was determined by C-V measurements with values between 7.5 · 10¹⁴ cm⁻³ and 5 · 10¹⁵ cm⁻³.