Correlation between structural and electrical properties of InN thin films prepared by molecular beam epitaxy

The strain-relaxation phenomena and the formation of a dislocation network in 2H-InN epilayers during molecular beam epitaxy are reported. The proposed growth model emphasizes the dominant role of the coalescence process in the formation of a dislocation network in 2H-InN. Edge type threading dislocations and dislocations of mixed character have been found to be the dominating defects in wurtzite InN layers. It is demonstrated that these dislocations are active suppliers of electrons and an exponential decay of their density with the thickness implies a corresponding decay in the carrier density. Room temperature mobility in excess of 1500 cm² V ⁻¹ s⁻¹ was obtained for 800 nm thick InN layers with dislocation densities of 3×10⁹ cm⁻².     

Kinetics of the motion and multiplication of dislocations in potassium chloride

The kinetic characteristics of the motion and multiplication of dislocations in KCl are analyzed. The assumption to the effect that the two processes act in parallel is discussed and given a sound basis. Accepting this assumption, certain physico-mechanical characteristics of the crystals in question may be calculated. It may in particular be shown that the mean distance between the centers of dislocation multiplication in the shear stress range 100–160 g/mm² is independent of the applied stress and approximately equals 75.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 91–95, February, 1973.     

Dislocation mobility in C<Subscript>60</Subscript> fullerite crystals

The dependences of the path of leading dislocations in indentation rosette rays on the load, the loading time, and the indentation temperature in the range 260 < T ≤ 373 K were studied for C₆₀ fullerite crystals. The dislocation mobility parameters are estimated: the exponent m characterizing the stress dependence of the dislocation velocity depends on the structural perfection of the crystal and ranges from 2.3 to 24.5, the activation energy for dislocation motion ΔH ₀ ? (0.4–0.5) eV, and the velocity of leading dislocations in indentation rosette rays v _l ? 10^?5?10^?4 cm/s. The data from micro-and macromechanical experiments are shown to agree with each other. The dislocation mobility is assumed to be controlled by the dislocation interaction with local barriers.     

Analysis of Similarity of Dislocation Interactions in Single Crystal Ni3Ge

Using the methods of diffraction electron microscopy and mechanical testing, the evolution of dislocation structure accompanied by deformation of single-crystal Ni₃Ge with different orientation of the axis of straining is studied at a range of temperatures. A linear relationship between shear stress and dislocation density ^0.5 is established. An analysis of the similarity of dislocation interactions is conducted in Ni₃Ge over a range of temperatures with developed octahedral and cubic slips, i.e. up to the anomaly peak temperature and higher, respectively. It is found out that under the octahedral slip, the dislocation interactions up to fracture deformations are similar at different temperatures in question. The similarity is also observed within the temperature range with developed cubic slip.     

Effect of electron irradiation on creep and dislocation structure of aluminium

The effect of electron irradiation and strain on structure of technical-purity aluminium subjected to constant-load tensile creep tests was investigated. The dislocation structure was statistically analyzed. The effect of electron irradiation appears in the creep rate reduction and generation of radiation defect clusters, the density of which is approximately proportional to the dose. The effect on the dislocation distribution is dependent on the dose as well. Doses1·2×10¹⁷ cm^–2 speed up the formation of a polygonal structure characterizing the steady-state creep.     

Effect of positive muon trapping by dislocations

Aluminum was deformed at room temperature so that vacancies are annealed out and only dislocations are remained. The muon spin depolarization rate was found to be decreased as the temperature is raised. This indicates that some trapping-detrapping occur. Fitting the spin relaxation to the calculated spin relaxation function for the trapping-detrapping model, the values of the activation energy for the trapping rate and detrapping rate and of the depolarization rate at the trapping are found to be 25 meV, 66 meV, and 0.24 sec^–1, respectively for the best fit. This indicates that positive muons diffuse to dislocations and diffuse along dislocation lines and are trapped at a jog of the dislocation, and detrap from the jog.     

Peculiarities of the low-temperature conductivity of radiation-treated p-Ge

It is shown that nonconservation of the transverse component of momentum when the electron-phonon interaction takes place around a dislocation leads to the dependence of the relaxation time of the momentum given by (p) p^–7/2 in the case of the hole energy being much less than thermal energy and by (p) p^–7 in the case of hole energy being much greater than thermal energy. Results are compared with experimental data on dislocation conductivity of radiationtreated p-Ge.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 61–64, May, 1984.Authors are grateful to V. P. Dobrego for bringing this subject to their attention and for fruitful discussions.     

Zur plastischen Verformung von Germanium und InSb

The lower yield stress of Germanium and InSb is shown to be proportional to the cube root of the strain rate and to a Boltzmann temperature factor with one third of the activation energy of the dislocation velocity. The stationary creep rate then depends on the applied stressτ asτ ³ and has the same activation energy as the dislocation velocity. These results follow from the “core diffusion” model of dislocation motion in the diamond structure when one considers elastic dislocation interaction.     

Viscous and solid friction in the motion of crystal defects

The motion of crystal defects can exhibit a variety of possible frictions. Examples are taken from point defects, dislocation lines and grain boundaries to illustrate this point.Dedicated to Dr. Frantiek Kroupa in honour of his 70^th birthday.     

The role of dislocations in radiation strenghtening of alkali halide crystals

The dependence of activation volume and dislocation start stress in sodium and calcium chloride crystals on-radiation dosage (in the range 10⁴–10⁹rad) is studied. It is established that these functions indicate that the hardening of crystals subjected to radiation is of a dislocation nature. Analysis of data from the literature leads to the conclusion that in the medium and high radiation dose region planar precipitates and surrounding dislocations formed by halogen molecules are responsible for hardening.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 99–103, June, 1976.     

The Peierls model for dislocation rings

The energy of a shear dislocation ring is calculated in the framework of the Peierls model in which the displacement is represented by a density of infinitesimal dislocations in the glide plane. This avoids the introduction of an uncertain core cut-off radiusr ₀ to prevent divergence in the usual treatment. The atomic misfit energy in the glide plane is accounted for explicitly and the influence of the interplanar potential on the ring energy and the core structure is studied. Whereas spontaneous formation of shear rings in a homogenous stress field can be ruled out, the emission of dislocation rings from crack tips in glide planes not containing the crack front is feasible.The paper is dedicated to Dr. Frantiek Kroupa in honour of his 70^th birthday.Stimulating discussions with miss Petra Fiala are gratefully acknowledged.     

Electrically stimulated motion of dislocations in a constant magnetic field

This paper reports on the results of investigations into the dislocation mobility in n-Si single crystals (N _d =5×10²⁴ m^?3) upon simultaneous exposure to electric (j=3×10⁵ A/m²) and magnetic (B≤1 T) fields. It is found that the introduction of dislocations (≈10⁹ m^?2) into dislocation-free silicon doped with phosphorus leads to the appearance of the paramagnetic component of the magnetic susceptibility. The paramagnetic component increases with an increase in the dopant concentration. Similar transformations in silicon account for the formation of magnetically sensitive impurity stoppers that respond to external magnetic perturbations. An analysis of the behavior of dislocations in electric and magnetic fields has revealed a parabolic dependence of the dislocation path length on the magnetic induction B. The effective charges and mobilities of dislocations are numerically calculated from the results obtained. A model is proposed according to which the observed increase in the dislocation mobility is associated with the decrease in the retarding power of magnetically sensitive stoppers due to a local change in the magnetic characteristics of the material and the spin-dependent reactions stimulated by a magnetic field.     

Role of fractal dimension in internal stress fields of Ni3Fe single crystals

In this paper, using the similarity method we have determined the fractal dimension of the dislocation structure of Ni₃Fe single crystals in chaos and in the stage of cell wall formation. We have established that in chaos D=1.04, and at the walls D=1.08. For a linear dependence =_f+·G·b·^1/2, the internal stresses increase by a factor of 1.1 in chaos and 1.22 in the cells, while the internal energy increases by a factor of 1.22 and 1.48 respectively. We discuss the mechanisms for roughening the dislocation structure.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 34–37, January, 1995.     

Calculation of shuffle 60° dislocation width and Peierls barrier and stress for semiconductors silicon and germanium

The dislocation width for shuffle 60° dislocation in semiconductors Si and Ge have been calculated by the improved P-N theory in which the discrete effect has been taken into account. Peierls barrier and stress have been evaluated with considering the contribution of strain energy. The discrete effect make dislocation width wider, and Peierls barrier and stress lower. The dislocation width of 60° dislocation in Si and Ge is respectively about 3.84 Å and 4.00 Å (～1b, b is the Burgers vector). In the case of 60° dislocation, after considering the contribution of strain energy, Peierls barrier and stress are increased. The Peierls barrier for 60° dislocation in Si and Ge is respectively about 15 meV/Å and 12–14 meV/Å, Peierls stress is about 3.8 meV/ų (0.6 GPa) and 2.7–3.3 meV/ų (0.4–0.5 GPa). The Peierls stress for Si agrees well with the numerical results and the critical stress at 0 K extrapolated from experimental data. Ge behaves similarly to Si.     

Influence of impurities and electric fields on the kinetic characteristics of the expansion of dislocation half-loops in NaCl:2236; Ca2+ crystals

The effect of the concentration (C) of Ca²⁺ impurity ions and electric fields up to 50 kV/cm on the kinetic characteristics of the expansion of edge and screw dislocation half-loops in annealed and quenched NaCl crystals is studied. It is confirmed that 1) the concentration dependence of the rate v of expansion of screw half-loops takes the form v = v^* exp (-AC^1/2); 2) with increasing field strength E the velocity v increases linearly in pure NaCl crystals'; in impure crystals for E>5 kV/cm the rate of expansion of the edge half-loops increases and that of the screw half-loops diminishes as exp (E). The extent of the latter effect depends on the concentration of Ca²⁺ impurity ions in the crystals and also on their heat treatment. The exponential change in v with field E is apparently a consequence of the reorientation of the Ca²⁺ ion-cation vacancy dipoles in the electric field. The activation energy for the reorientation of the dipoles is estimated. The linear increase in the rate of expansion of the half-loops is explained as being due to the reduction in the number of steps in the dislocation under the influence of the electric field.Translated from Izvestlya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 35–40, April, 1976.