Deformation-induced Dislocations Research Articles

Energy States of Deformation-Induced Dislocations in Silicon Crystals

Energy States of Deformation-Induced Dislocations in Silicon Crystals

Elevated-temperature mechanical behavior of plasma-sprayed MoSi 2SiC

The elevated-temperature mechanical behavior of a plasma-sprayed MoSi 2-9vol.%SiC particulate composite was investigated over the temperature range 1100–1500°C. At temperatures of 1200 °C or less the stress exponent of 2.3–2.5, grain size exponent of −2.2, activation energy for creep of about 300 kJ mol −1, equiaxed grains after deformation and no deformation-induced dislocations suggest grain boundary sliding controlled by lattice diffusion of either Mo or Si as the dominant deformation mechanism. At temperatures of above 1300 °C the stress exponent is 1.3–1.5 and the activation energy for creep is 190 kJ mol −1. It is believed that the dominant deformation mechanism in this temperature range is grain boundary sliding controlled by grain boundary diffusion. The decrease in the stress exponent and activation energy for creep is thought to be a result of melting or softening of an amorphous silica grain boundary phase. The creep resistance of the plasma-sprayed MoSi 2SiC composite is lower than that for MoSi 2SiC composites produced using powder metallurgy and in-situ techniques as a result of its finer grain size and/or lower volume fraction of SiC.

Scanning deep-level transient spectroscopy investigations on gallium arsenide

The present state of the art of the application of the scanning deep-level transient spectroscopy (SDLTS) technique is reported. Special attention is given to the theoretical modelling of the signal generation process, yielding important information on the factors influencing the spatial resolution to be attained. The experimental possibilities of the dedicated SDLTS equipment available now are described. This system was used to investigate point defects generated by plastic deformation in GaAs p+-n junctions induced by diamond indentations made at room temperature. A cloud of point defects (hole traps at Ev + 0.5 eV) up to a distance of approximately 20 μm from the indentations has been detected by SDLTS. Interestingly, the deformation-induced point defects are localized in regions outside the slip bands rather than within the slip bands of the deformation-induced dislocations. Annealing experiments seem to contradict their interpretation as the second charge state of the EL2 level.

Temperature Dependent Electron Beam Induced Current Study of Defects in Silicon

A new computer-aided electron beam induced current system was developed which makes it possible to obtain two-dimensional mapping of the absolute magnitudes of electron beam induced current signals over the temperature range 15 K-400 K. Electronic states of defects in cast silicon and deformation-induced dislocations in float-zone silicon were investigated from the analyses of temperature dependencies of electron beam induced current contrasts of the defects measured with the system. Electron beam induced current active defects in cast Si were identified to be Fe impurity atoms or Fe—B pairs incorporated at the dislocation core depending on the cooling rate of a crystal. Dislocations in float-zone silicon were shown to have an energy leve1 for carrier recombination in the lower half of the band gap. PACS numbers: 71.55.Fr, 72.80.Cw

DEVELOPMENTS OF IRBIC AND QIRBIC IN DEFECT STUDIES : A REVIEW

Optical injection, as well as the electronic one, is of great use for semiconductor material and component characterization, and in recent years several papers appeared dealing with the analysis of the depth response of scanning light microscopy, the distribution of the charge carriers generated by a focused light beam as well as the photoinduced current dependence on the measurement configuration and the consequent imaging of defects in semiconductors. In these works a laser source is always used because of its features of monochromaticity, focusing and high intensity. Actually the light microscopy has become a widely accepted wafer mapping technique for investigating inhomogeneities and, besides, a method to evaluate diffusion length and surface recombination velocity of minority carriers. We have applied the same principles of the scanning laser microscopy, but substituting filtered light corning from an halogen lamp to the laser source. This expedient, even though it involves some disadvantages about monochromaticity and focusing, allows, however, to easier handle light beam parameters as photon density and energy. We refer to this method as IRBIC (Infra-Red Beam Induced Current) since the photon energy of the scanning beam lies in the infrared portion of the spectrum. Object of our investigations is the current induced by the infrared light beam and, in more detail, the variations in defect imaging observed by changing penetration depth and intensity of the light. In addition, having a scanning light microswpe at our disposal, we have modified the basic experimental setup so as to irradiate the back surface of the sample by monochromatic sub-band gap light. When the photon energy of the back surface irradiation coincides with the distance E, of a deep level within the forbidden gap from one of the allowed energy bands, a level-band transition occurs and, as a consequence, the concentration of the efficient recombination traps at the level E, changes. This process, involving the defect recombination activity, produces strong variations in the current induced by the beam scanning the opposite surface. The above said phenomenon, known for long time in bulk material examinations and named photoconductivity quenching, has been applied by us to the scanning light microscopy and called that is Quenched Infra-Red Beam Induced Current. Both the methods, IRBIC and QIRBIC, very sensitive to the occupancy factor of the defects, have been used to investigate the electrical activity of extended defects, namely dislocations, and their interaction with impurities and point defects. Besides, investigations have been performed on lamellar structure precipitates and on deformation-induced dislocation loops.

Experimental evidence for creation of luminescence quenching localized defects by moving dislocations in gallium arsenide

The production of luminescence quenching localized defects by moving dislocations in GaAs plastically deformed at 350 °C has been established by low-temperature (80 K) band-edge cathodoluminescence (CL) and chemical etch-pit studies. Specimens were deformed to two levels, (1) measurable macroscopic plastic deformation, and (2) 20% of the stress applied in (1). It was established by CL and chemical etching that numerous dislocations were generated on the four {111} stressed slip planes of the macroscopically deformed specimen. Uniform bands of reduced CL signal were correlated to bands of enhanced etching in the lightly deformed samples. It was established from the etching and CL images that these bands are not produced by deformation-induced dislocations but must consist of numerous localized luminescence quenching (Refs. 1–3) defects (e.g., point defects and small dislocation loops) created by the passage of dislocations.

Interactions of deformation-induced dislocations with Σ = 9(122) grain boundaries in Si studied by HREM

Abstract The mechanisms of interaction between a twin boundary and dislocations created during the deformation of a bicrystal are analysed by means of HREM. It is shown, on an atomic scale, that intrinsic dislocations enter the grain boundary where they decompose into discrete grain-boundary dislocations with Burgers vectors belonging to the DSC lattice. These residues can migrate along the interface and interact, giving rise to new residues. It is shown that, when the strain remains low enough, the grain-boundary deformation history can be deduced from the HREM observations.

Secondary dislocations in [011] tilt boundaries in germanium

Abstract The structures of a series of tilt grain boundaries in germanium bicrystals and the interaction of deformation-induced lattice dislocations with these boundaries have been studied using transmission electron microscopy. High-resolution techniques were used to determine the Burgers vectors of the secondary dislocations. The bicrystals were grown from the melt using the Czochralski method to produce the low-Σ grain boundaries: Σ = 11, 33, 41 and 51. The Burgers vector of the secondary dislocations was usually not the primitive Burgers vector which might have been expected by applying O-lattice analysis. This interpretation is consistent with the Burgers vectors determined for secondary dislocations produced by lattice dislocations dissociating on entering the grain boundaries.

Observation of luminescence quenching dislocations in mercuric iodide by cathodoluminescence in a scanning electron microscope

Cathodoluminescence images of ingrown and deformation-induced dislocations were observed in single crystals of mercuric iodide that were vapor grown for the fabrication of radiation detectors. The imaging was done at 80 K in a scanning electron microscope.

Al-Li 2元合金の降伏応力の温度依存性と変形による転位配列

Yield stress of aged Al-11.1 mol%Li alloy was measured at temperatures between 77 and 523 K, and the deformation-induced dislocation structure was examined by transmission electron microscopy. Strength and dislocation arrangements depend largely both on the aging conditions and on the testing temperature. The peak positions in strength vs aging time curves shift to the side of shorter aging time with increasing testing temperature. The mode of interaction between dislocations and δ′-precipitates also varies with the testing temperature. For the specimens aged nearly to the peak strength, the positive temperature dependence of yield stress is observed in the temperature range where dislocations move in pairs cutting the δ′-precipitates. In the over-aged specimens, dislocations by-pass the precipitates leaving dislocation loops around the precipitates at the beginning of plastic deformation. The shift of peak positions in the aging curves and the variation of the interaction modes between dislocations and precipitates with testing temperature are explained in terms of the positive temperature dependence of cutting stress and the negative temperature dependence of by-passing stress.

Direct solid-state precipitation-processed A15 (Nb3A1) superconducting material

A ’’solid-state precipitation’’ process was used to prepare superconducting tapes containing Nb3Al in a niobium matrix. Small ingots of Nb–(17–19 at . %)Al were prepared by arc melting, homogenizing, quenching, warm rolling into tape, and aging at 750–900°C to precipitate the A15 phase. Transmission electron microscopy studies revealed Nb3Al precipitation in fine particles which formed a semicontinuous network over subgrain boundaries fromed by the recovery of deformation-induced dislocations. Promising high-field critical currents were obtained (Jc∼104 A/cm2 in a field of 14 T at 4.2 K).

Photoluminescence at lattice imperfections in gallium arsenide

We report about photoluminescence measurements on GaAs at low temperatures with high spatial resolution on the sample surfaces. Evidence for growth-induced dopant non-uniformities is presented. The influence of grown-in and deformation-induced dislocations on intensity and spectral distribution of the luminescence is measured.

Photoluminescence at Dislocations in GaAs

Photoluminescence measurements with high spatial and spectral resolution on $n$-type GaAs at helium temperatures show the reduction of radiative quantum efficiency immediately at individual deformation-induced dislocations to be orders of magnitude stronger than near grown-in dislocations.

Effect of Deformation-Induced Crystal Imperfections on Magnetocrystalline Anisotropy of Nickel Single Crystals

The first magnetocrystalline anisotropy constant of plastically deformed nickel single crystals was studied as a function of deformation. Contributions of specific types of imperfection, viz., interstitials, vacancies, and disclocations on the ``effective magnetic anisotropy constant'' K1′ were analyzed from the recovery characteristics of K1′. The dislocation structure of the deformed crystals was investigated by transmission electron microscopy at various stages of recovery. The absolute value of K1′ increased with deformation. The maximum change occurred at a strain ε≈0.17 with an increase of about 6.5% from the undeformed value of K1 = −5.52×104±0.02×104 erg/cc measured at 21.5°C and at a magnetic field of 8 kOe. Point defects were not found to have a measurable effect on the recovery of K1′. Deformation-induced dislocations were mainly responsible for the observed change. The recovery of K1′ was interpreted in terms of rearrangement and annihilation of disclocations.

Generation of Vacancies in MgO by Deformation

Electron spin resonance and x-ray line broadening were used to measure the deformation-induced vacancies and dislocation densities, respectively, in MgO. The vacancy concentration was found to increase with increasing deformation rate and dislocation density. The generation of vacancies is explained by the nonconservative motion of dislocation jogs created by dislocation intersections in regions where the dislocation density is high.