Dynamics of surface dislocation ensembles in silicon under conditions of mechanical and magnetic perturbations

This paper reports on the results of investigations into the dynamics of surface dislocation ensembles in silicon under conditions of mechanical and magnetic perturbations. The motion of defects is described with due regard for barriers of three types, including magnetically sensitive point defects and dislocations. Within the concept of spin-dependent reactions between structural defects, a kinetic model is proposed for the magnetic-field-stimulated changes observed in the dislocation mobility due to the formation of long-lived complexes involving paramagnetic impurities. It is experimentally proved that the preliminary treatment of dislocation-containing crystals in a magnetic field (B=1 T) for 5–45 min leads to an increase in the velocity of dislocations in n-Si and p-Si samples by factors of two and three, respectively. The magnetic memory effect is observed in dislocation-containing silicon crystals. Consideration is given to the decay kinetics of the magnetic memory during storage of the silicon samples under natural conditions after magnetic treatment. The basic quantitative characteristics of the motion of linear defects in a magnetic field (for example, the partial velocities of dislocations, the dynamics of dislocation segments at stoppers of different types, and the expectation times for the appearance of the appropriate stoppers) are determined by fitting the experimental data to the theoretical results.     

On the influence of a constant magnetic field on the electroplastic effect in silicon crystals

The influence of a constant magnetic field on the electroplastic effect induced by an electric current in silicon crystals is investigated. It is found that the preliminary magnetic field treatment of silicon crystals leads to a weakening of the electroplastic effect. A possible mechanism of the phenomena observed is discussed.     

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.     

Magnetically stimulated hardening of NaCl(Pb) crystals

Dislocation motion in NaCl(Pb) crystals under a pulsed mechanical load with and without a magnetic field is investigated. It is found that the dislocation mobility decreases when these crystals are deformed in a magnetic field. It is inferred that the observed magnetically stimulated hardening of NaCl(Pb) is due to a characteristic feature of spin-dependent electronic transitions in the dislocation-lead impurity system which increase the barrier for dislocation motion. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 3, 226–228 (10 August 1999)     

Magnetoplasticity and diffusion in silicon single crystals

The effect of static magnetic fields on the dynamics of surface dislocation segments, as well as the diffusion mobility of a dopant in silicon single crystals, has been analyzed. It has been experimentally found that the preliminary treatment of p-type silicon plates (the dopant is boron with a concentration of 10¹⁶ cm⁻³) in the static magnetic field (B = 1 T, a treatment time of 30 min) leads to an increase in the mobility of surface dislocation segments. The characteristic times of observed changes (about 80 h) and the threshold dopant concentration (10₁₅ cm⁻³) below which the magneto-optical effect in silicon is not fixed have been determined. It has been found that diffusion processes in dislocation-free silicon are magnetically sensitive: the phosphorus diffusion depth in p-type silicon that is preliminarily aged in the static magnetic field increases (by approximately 20%) compared to the reference samples.     

Influence of electron saturation of Tamm levels on the field-emission properties of silicon crystals

It has been shown that the plasma-chemical modification of the morphology and composition of the surface phase influences the emissivity of silicon crystals. It has been found that the saturation of Tamm states with electrons during the preparation of atomically clean silicon surfaces, along with stabilizing passivation of surface atoms in a highly ionized microwave plasma using Halon 14, decreases a threshold electric field at which field emission begins more than twofold and increases the maximal density of the field emission current by more than an order of magnitude compared with wafers covered by native oxide or subjected to ion physical etching in argon. Physicochemical mechanisms responsible for the modification of the silicon surface and the field-emission properties of silicon have been considered.     

Spin-dependent photoconductivity in n-type and p-type amorphous silicon

It is found that, as in crystalline silicon, the photoconductivity in amorphous silicon prepared by glow discharge is strongly spin-dependent. In this material, the position of the Fermi level can be smoothly varied by phosphorous or boron doping and the magnitude of the spin-dependent recombination has been measured as a function of the doping: it is found to have a large maximum when the material is intrinsic. The similarities with the spin-dependent effects in crystalline and dislocation silicon suggest that the recombination process in amorphous silicon is the same as in the crystalline material and that dislocation-like centres are responsible for the spin-dependent recombination properties in both materials.     

EPR investigation of a-Si:H aerosol particles formed under silane thermal decomposition

The dangling bond defects were investigated in a-Si:H particles formed under silane thermal decomposition in flow reactor. EPR together with hydrogen evolution method were used. The experimental results allowed us to conclude that there are two kinds of dangling bond defects in a-Si:H aerosol particles. The defects of the first kind are localized on the surface of interconnected microvoids and microchannels (surface dangling bonds) and those of the second kind are embedded in amorphous silicon network (volume dangling bonds). The thermal equilibration of dangling bonds and temperature dependence of equilibrium dangling bond concentration were investigated. It was found that at temperatures > 400 K the dangling bond concentrationNApplied Magnetic Resonance _s reversibly depends on sample temperature. The volume dangling bond concentration increases with temperature increasing (the effective activation energy of dangling bond formationU > 0), and the surface dangling bond concentration decreases with temperature increasing (U < 0). It has been found that EPR line is considerably asymmetric for samples with high hydrogen content and for low hydrogen content the EPR line is weakly asymmetric. A conclusion was drawn that the asymmetry degree depends on amorphous silicon lattice distortions. This conclusion has been confirmed by EPR spectra simulations.     

Modulation of Spin Distribution and Spin Transport by a Magnetic Field in a Quasi-One-Dimensional System with Spin--Orbit Coupling

The distributions of spin and currents modulated by magnetic field in a transverse parabolic confined two-dimensional electronic system with a Rashba spin--orbit coupling have been studied numerically. It is shown that the spin accumulation and the spin related current are generated by magnetic field if the spin--orbit coupling is presented. The distributions of charge and spin currents are antisymmetrical along the cross-section of confined system. A transversely applied electric field does not influence the characteristic behaviour of charge- and spin-dependent properties.     

Direct role of hydrogen in the Staebler-Wronski effect in hydrogenated amorphous silicon

We report a hydrogen-related defect that establishes the direct role of hydrogen in stabilizing the silicon dangling bonds created in the Staebler-Wronski effect in hydrogenated amorphous silicon. A specific NMR signal due to paired hydrogen atoms occurs only after optical excitation, exists at an intensity that is consistent with the density of optically induced silicon dangling bonds, and anneals at temperatures that are consistent with the annealing of the optically induced silicon dangling bonds. At this defect the hydrogen atoms are 2.3+/-0.2 A apart.     

Magnetically simulated variation of dislocation mobility in plastically deformed n-silicon

The acoustic emission method is employed for an experimental investigation of the effect of a magnetic field on the mobility of edge dislocations in a plastically deformed n-silicon sample carrying a current. It is found that the preliminary treatment of a dislocated crystal in a constant magnetic field (B<1 T) changes the intensity of its acoustic response depending on the magnetic induction. The observed effect is associated with spin-dependent magnetosensitive reactions of defects occurring in the vicinity of the dislocation core, which facilitate the detachment of the dislocations from the stoppers and, hence, increase the mobility of dislocations and the acoustic response of the dislocation structure.     

Magnetoplastic effects in solids

This paper is an overview of the studies into the effect of weak magnetic fields on the structure and mechanical properties of nonmagnetic solids of various nature (ionic, covalent, molecular, and metallic crystals, polymers, etc.). The various effects and aftereffects initiated by static, pulsed, and microwave magnetic fields that have been discovered over the past 15 years are classified and critically analyzed. The thermodynamic and kinetic aspects of the magnetic-field sensitivity of real solids with structural defects containing paramagnetic centers (electrons, holes, radicals, excitons, etc.) are discussed. Possible mechanisms for the effect of a weak magnetic field on the defect structure of crystals are considered. Special attention is given to the most developed chemical-physical theory of spin-dependent reactions between mobile particles and unpaired electrons. Interpretation of magnetoplastic effects is proposed in terms of the spin, electron, molecular, and dislocation dynamics of the complex multistage processes initiated by a magnetic field in a system of metastable structural defects.     

Electric stimulation of magnetoplasticity and magnetic hardening in crystals

The effect of electric field E on the magnetoplastic effect (MPE) has been investigated in NaCl crystals with different impurities, which provide either the plasticization of the samples in the magnetic field (positive MPE) or their magnetic hardening (negative MPE). The mobility of individual dislocations under the joint action of the magnetic and electric fields and the mechanical load on the crystals has been studied. The sharp electric stimulation of the MPE of both signs has been revealed, i.e., an increase or a decrease in the mean free path of dislocations that is roughly proportional to exp(±E/E ₀) at E ? E ₀ ～ 1–10 kV/m. In particular, in the negative-MPE NaCl(Pb) crystals, the accompanying electric field enhances the magnetic suppression of plasticity. The results are attributed to the electrically induced transformation of the additional part of the pinning impurity ions Me⁺⁺ to the magnetically active state of Me⁺ on the dislocations. The subsequent magnetic transformation of the structure of these pinning centers should lead to a sharper variation of the dislocation pinning force (either an increase or a decrease, depending on the MPE sign).     

On the nature of the influence of an electric current on the magnetically stimulated microplasticity of Al single crystals

A large increase in dislocation mobility in Al single crystals in a static magnetic field in the absence of mechanical loading of the samples is observed when a dc electric current of low density (10⁵–10⁶ A/m²)is additionally passed through the samples. Apparently, the role of the current reduces to depinning of dislocations from strong pinning centers on the surface of the crystal as a result of surface electromigration of defects. This interpretation is supported by the fact that in samples whose surface is insulated by a layer of lacquer the passage of a current through the volume of the crystal does not change the ordinary dislocation mobility level in a magnetic field. It is hypothesized that surface electromigration of defects, which frees dislocations and unblocks dislocation sources, also plays a key role in the physical mechanism of the long-ago discovered macroplastification of metals upon the passage of an electric current through them. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 788–793 (25 May 1998)     

Simplified model of dislocations as a SRH recombination channel in the HgCdTe heterostructures

A simple model of dislocation band formed by the dangling bonds of atoms of a dislocation core has been presented and discussed. The parameters of this model, which could be verified experimentally, are the average energy of the dislocation band states and the average length of the dislocation as well as electron and hole emission coefficients. The formulas for statistical functions of distribution of electrons in these bands have been derived. Next, we have developed a model of the SRH recombination channel connected with dislocation band states and we have adopted it to determine an effective lifetime of electron-hole pairs including effect of dislocations. In addition, influence of the tunnelling current from and into dislocation band has been considered, which seems to be a serious issue in reverse biased heterostructue HgCdTe photodiodes. Exemplary results of calculations for HgCdTe structures show that the number of the ionized atoms of the dislocation cores is of the order of a few percent. Moreover, the electric potential distributions in the area of the dislocation core has been calculated. Some experimental I-V characteristics of near room temperature HgCdTe devices are presented and compared with numerical simulations, what indicate on contribution of dislocations as a SRH recombination channel.     

Electrostimulation of the magnetoplastic effect in LiF crystals by an “internal” electric field induced during indentation

Indented LiF crystals demonstrate a change in the length of the dislocation rosette rays during their exposure to jointly acting dc magnetic and electric fields. It is shown that magnetic field with induction B = 1 T causes the electrostimulation or electrosuppression depending on the magnitude and direction of the external electric field with respect to the “internal” electric field induced by the charge transfer due to dislocations moving during the indentation.     

Kinetics of transformation of Eu<Superscript>2+</Superscript> dimers in NaCl crystals in a static magnetic field of 15 T

A static magnetic field of up to 15 T is found to affect the photoluminescence excitation spectra of NaCl: Eu crystals. The magnetic field has an effect on the excitation spectra starting at the stage at which dimers are formed through diffusion in the crystals. At earlier stages of impurity aggregation, the magnetic field affects the kinetics of dimer accumulation. It is revealed that the dimer transformation stimulated by the magnetic field involves stages that last for 10–15 min at room temperature in a static magnetic field of 15 T and, hence, are shorter than the aggregation time. Luminescence studies of dimers, which are the main dislocation stoppers in NaCl: Eu crystals, make it possible to explain the specific features of the magnetoplastic effect observed previously in these crystals.     

Features of X-ray diffraction at elastic deformations near the dislocation axis in section topography techniques

Features of the formation of an x-ray diffraction image by x-ray section topography are considered for a strongly distorted region near the dislocation axis in silicon single crystals. The results of experimental investigations and numerical calculations of the diffraction contrast and section topographs of rectilinear dislocations are presented for their different orientations and positions in the scattering triangle in silicon single crystals. A comparison and an analysis of the experimental topographs and the simulated images lead to the conclusion that the structure of the image of a dislocation strongly depends on its position and orientation in the scattering triangle. It has been found that each point of the strongly distorted region of the elastic field of a dislocation becomes a source of a new wave field propagating under the dislocation in a new scattering triangle. This new field interferes with the primary wave field forming the observed diffraction image of a dislocation. The addition of these waves with regard to their amplitudes and phases results in a large variety of images of defects. A comparison of different dislocation orientations in the Borrmann triangle allowed us to evaluate the role of different effects determined by the interference of the initial and newly formed wave fields, to determine on this basis the main dislocation parameters, and to optimize the diffraction conditions of the topographic measurement for the investigation of elastic-field characteristics.     

Deformation of Si under conditions of the combined influence of an electric current and a magnetic field

Changes in the physical and mechanical properties of single crystals of n- and p-type silicon are investigated under the combined influence of a constant electric current and a magnetic field and an electric current separately. There is a slight increase in the resistivity of Si as pressure is applied. Increased resistance to compressive deformation is observed under the combined influence of a magnetic field and an electric cur- rent during compression, while increased plasticity is seen under the sole influence of an electric current for p-Si samples. There is an opposite effect for samples of n-Si. Increased plasticity is observed under the combined influence of a magnetic field and an electric current during compression, while increased strength is seen under the sole influence of an electric current. Surface microstructures of deformed samples are studied. A possible physical explanation for the observed phenomena is proposed.     

Electric-field-induced changes in magnetization in PZT/Insulator/CoFe nanometer multilayer

The PZT/Insulator/CoFe nanometer multilayer has been proposed for applications of the spin-dependent devices in this paper. With the strains as a response of PZT layer to an applied electric field in the structure, the magnetization in CoFe layer can be significantly altered, leading to a significance change in magnetoresistance. Our numerical results have demonstrated that the magnetization states in CoFe layer can be tuned by an electric field without a magnetic field being present.