The distribution of dislocations in slip bands of Fe-3% Si alloy single crystals deformed by bending

The distribution of dislocations at the ends of slip bands was studied by etching on surfaces parallel to the slip plane. In these places the slip band is formed by groups of asymmetric dislocation loops several hundred microns wide. The long mixed-type parts of these loops running nearly equidistantly and lying in near planes, are the equilibrium arrangement of dislocations of the same sign in the shear stress gradient. From the results we can judge that the dislocation sources are at larger distances from the ends of the slip bands and that the dislocation groups at the ends of the slip bands are sources of large stress fields.     

Hydrogen interaction with dislocations in Si

An H plasma has a remarkable effect on dislocation mobility in silicon, reducing its activation energy to 1.2 eV. Applying density functional theory to the interactions of H and H2 with the core of the 90 degrees partial dislocation in Si, we have identified a path for motion involving kink formation and migration at hydrogenated core bonds which conforms exactly to the experimentally measured activation energy.     

The starting stress for dislocations in a superlattice

The forces on superdislocations due to the state of the antiphase boundaries (APB) are examined as functions of temperature and concentration on the basis of a previously expounded theory of component concentrations and degree of order at APB in superlattices of CsCl type. Forces due to loss of position correlation in the glide plane are also examined. It is considered that the yield points of superlattices as functions of concentration may be explained by these mechanisms.     

Solid-phase crystallization of amorphous Si films on glass and Si wafer

When amorphous silicon films deposited on glass by physical or chemical vapor deposition are annealed, they undergo crystallization by nucleation and growth. The growth rate of Si crystallites is the highest in their 〈111〉 directions along or nearly along the film surface. The directed crystallization is likely to develop the 〈110〉//ND or 〈111〉//ND oriented Si crystallites. As the annealing temperature increases, the equiaxed crystallization increases, which in turn increases the random orientation. When amorphous Si is under a stress of the order of 0.1 GPa at about 540 °C, the tensile stress increases the growth rate of Si grains, whereas the compressive stress decreases the growth rate. However, the crystal growth rate increases with the increasing hydrostatic pressure, when the pressure is of the order of GPa at 530–540 °C. These phenomena have been discussed based on the directed crystallization model advanced before, which has been further elaborated.     

Interferometric optical isolator with Si guiding layer fabricated by wafer bonding

An interferometric optical isolator, with a Si guiding layer, employing a nonreciprocal phase shift was studied. The optical isolator was comprised of a magneto-optic waveguide with a magnetic garnet/Si/SiO₂ structure, which was fabricated by wafer bonding technique. The nonreciprocal phase shift in the magneto-optic waveguide with the Si guiding layer was calculated at a wavelength of 1.55 μm. Several kinds of layer structures in the magneto-optic waveguide were discussed.     

Two groups of misfit dislocations in GaAs on Si

High-resolution cross-sectional and conventional plan-view transmission electron microscope observations have been carried out for molecular beam epitaxially grown GaAs films on vicinal Si (001) before and after annealing as a function of film thicknesses and observation directions between two orthogonal 110 directions. Two groups of misfit dislocations are characterized at the interface regions between GaAs and Si by analyzing whether their extra half planes exist in the film or the substrate side. Group I misfit dislocations due to stress caused by a lattice misfit between GaAs and Si consist of partial dislocations and 60° and 90° complete dislocations in an as-grown state. With an increase in the film thickness, partial dislocations decrease and complete dislocations increase. After annealing, partial dislocations almost completely disappear and 90° perfect dislocations are predominantly observed. Group II misfit dislocations due to thermal-expansion misfit-induced stress are all 60°-type complete dislocations regardless of film thicknesses and annealing treatment.On leave from Central Research Laboratory, Hitachi, Ltd., Tokyo 185, Japan     

Large negative magnetoresistance introduced by line dislocations in a modulation doped Ga0.25In0.75As/InP quantum well

A large negative magnetoresistance at low magnetic fields of a high mobility two dimensional electron gas in a modulation-doped Ga_0.25In_0.75As/InP quantum well containing dislocations is reported. The effect is attributed to electrons on open orbits caused by scattering against the potential created by line dislocations formed in the Ga_0.25In_0.75As layer when the critical thickness for growth on InP was exceeded. By comparing the magnetoresistance for the structures containing dislocations with those without, but with etched trenches with a similar distribution as the line dislocations, we conclude that the dislocations introduce a strong potential in the two dimensional electron gas.     

Electronic properties of dislocations introduced mechanically at room temperature on a single crystal silicon surface

This paper focuses on the effects of temperature and environment on the electronic properties of dislocations in n-type single crystal silicon near the surface. Deep level transient spectroscopy (DLTS) analyses were carried out with Schottky electrodes and p⁺–n junctions. The trap level, originally found at E_C−0.50 eV (as commonly reported), shifted to a shallower level at E_C−0.23 eV after a heat treatment at 350 K in an inert environment. The same heat treatment in lab air, however, did not cause any shift. The trap level shifted by the heat treatment in an inert environment was found to revert back to the original level when the specimens were exposed to lab air again. Therefore, the intrinsic trap level is expected to occur at E_C−0.23 eV and shift sensitively with gas adsorption in air.     

Residual stress and strain in CdZnTe wafer examined by X-ray diffraction methods

A non-destructive method based on X-ray diffraction was developed to measure the stress and strain in CdZnTe single crystal near the surface. From the experimental results and calculations, the residual stresses in CdZnTe single crystal were determined to be σ₁=30 MPa, σ₂=14 MPa, and τ₁₂=-4 MPa, respectively. The residual stress derived from the measurement strain in CdZnTe was thought to be composed of the thermal stress, the misfit stress, and the mechanical stress. The distributions of non-uniform strain in a CdZnTe wafer are about 3.9%, while the distributions of uniform strain in the CdZnTe wafer are 0.5%, much smaller than those of the non-uniform strain. PACS 02.10.Xm; 71.55.Gs; 61.10.Nz; 68.35.Gy; 81.40.Jj     

Impact of misfit dislocations on wavefront distortion in Si/SiGe/Si optical waveguides

Silicon-rich SiGe alloys represent a promising platform for the development of large-area single-mode optical waveguides to be integrated in silicon-based optical circuits. We find that SiGe layers epitaxially grown on Si successfully guide radiation with a 1.55 μm wavelength, but, beyond a critical core thickness, their optical properties are strongly affected by the clustering of misfit dislocations at the interface between Si and SiGe, leading to a significant perturbation of the local refractive index. Transmission electron microscopy and micro-Raman spectroscopy, together with finite-element simulations, provide a complete analysis of the impact of dislocations on optical propagation.     

Redistribution of dislocations in silicon near stress concentrators

The distribution of defects in dislocation tracks in silicon plates was studied for various indentation angles. The regularities of variations in the linear density and maximum path of dislocations in slip bands are established. A model is proposed to describe the distribution of dislocations in the dislocation tracks. By fitting the theory to the experimental data, the dependence of this distribution on the energy relaxation time is determined.     

Elastic stress of moving dislocations in finite crystals

The elastic stress of a single crystal with finite dimensions is investigated by means of the linear continuum theory; external forces and dislocation motion are assumed to be known. A formal solution is derived with a Green's dyadic. The dyadic is expanded in a series, the first term of which delivers the well-known solution for infinite crystals, the following terms describe successive reflections of sound at the surface of the finite crystal. They can be computed by iteration. This expansion corresponds to the physical situation of pulse-echo-experiments. Fourier transforms lead to analogous expressions describing the influence of the surface on time-periodic dislocation experiments.     

Tensile crack patterns in Mo/Si multilayers on Si substrates under high-temperature bending

Mo/Si multilayers with a single-layer thickness in the nanometre range (60 Mo/Si layers in total) were deposited on Si(100) substrates by dc magnetron sputtering. Upon uniaxial bending at elevated temperatures between 300 and 440 °C in vacuum, unconventional crack patterns formed in the multilayers. Tensile stress within the multilayer stack and Si substrate due to bending during thermal treatment was estimated to be on the order of 100 MPa. A combination of external bending, residual and thermal stresses is considered to be the reason for this phenomenon. Cracks had either a sinusoidal or a spiral shape. The surface frequency of the spirals observed was 10 cm^-2, with a track width of 30 m and a spiral diameter of 300 m. In general, cracking was accompanied by complete local de-bonding of the whole Mo/Si multilayer stack from the substrate. Fracture patterns were studied by optical microscopy. In addition, the morphological parameters of the remaining non-delaminated multilayers were determined by means of X-ray reflectometry supported by investigation of phase content by wide-angle X-ray scattering . PACS 68.35.-p; 68.35.Bs; 68.90.+g; 81.05.Zx     

Theory of bending of polycrystalline beams by creep at low stress

Attempts to extend diffusion creep theory from simple grain geometries to more complex polycrystalline structures generally make the assumptions that the vacancy creation (or annihilation) rate is constant over each grain face and that the volume of each grain is conserved. These assumptions do not permit grain rotation, a common feature of polycrystalline creep, nor is diffusion allowed to occur between individual grains. These two aspects are investigated theoretically in this paper, for the specific case of the grain boundary diffusion controlled bending of a polycrystalline beam consisting of a set of orthorhombic grains of dimensions X, Y and Z, with the Z dimension, parallel to the axis of bending, assumed large such that two-dimensional diffusion predominates. The grains are aligned with continuous boundaries across the beam height. For grains highly elongated along the beam length (X???Y), the derived rotation rate is identical to that for a bicrystal having the same height as the beam. For smaller X, diffusion in boundaries along the beam length make increasing contributions and the rotation rate increases. The novel prediction is made that the non-conservation of grain volume is an inevitable consequence of the grain boundary diffusion controlled deformation of this particular polycrystalline configuration.     

Microstructural and compositional characteristics of GaN films grown on a ZnO-buffered Si (111) wafer

Polycrystalline GaN thin films have been deposited epitaxially on a ZnO-buffered (111)-oriented Si substrate by molecular beam epitaxy. The microstructural and compositional characteristics of the films were studied by analytical transmission electron microscopy (TEM). A SiO(2) amorphous layer about 3.5 nm in thickness between the Si/ZnO interface has been identified by means of spatially resolved electron energy loss spectroscopy. Cross-sectional and plan-view TEM investigations reveal (GaN/ZnO/SiO(2)/Si) layers exhibiting definite a crystallographic relationship: [111](Si)//[111](ZnO)//[0001](GaN) along the epitaxy direction. GaN films are polycrystalline with nanoscale grains ( approximately 100 nm in size) grown along [0001] direction with about 20 degrees between the (1l00) planes of adjacent grains. A three-dimensional growth mode for the buffer layer and the film is proposed to explain the formation of the as-grown polycrystalline GaN films and the functionality of the buffer layer.     

Effect of ultrasonic treatment on the mobility of short dislocations in Si crystals

The effect of ultrasonic treatment on the mobility of short surface dislocations in Si crystals is investigated. It is found that ultrasonic treatment of Si crystals changes the velocity of dislocations under a permanent mechanical load. The nature of variation of dislocation velocity is determined by the sign of external stresses acting on the sample: compressive forces decrease while tensile forces increase the velocity of dislocations. After ultrasonic treatment of the samples, a decrease in the activation energy for dislocation motion and the enhancement of the electroplastic effect are observed. A possible mechanism of the observed effects is considered.     

Limits on passivating defects in semiconductors: the case of Si edge dislocations

By minimizing the free energy while constraining dopant density, we derive a universal curve that relates the formation energy (E(form)) of doping and the efficiency of defect passivation in terms of segregation of dopants at defect sites. The universal curve takes the simple form of a Fermi-Dirac distribution. Our imposed constraint defines a chemical potential that assumes the role of "Fermi energy," which sets the thermodynamic limit on the E(form) required to overcome the effect of entropy such that dopant segregation at defects in semiconductors can occur. Using Si edge dislocation as an example, we show by first-principles calculations how to map the experimentally measurable passivation efficiency to our calculated E(form) by using the universal curve for typical n- and p-type substitutional dopants. We show that n-type dopants are ineffective. Among p-type dopants, B can satisfy the thermodynamic limit while improving electronic properties.