Dislocations In Si Research Articles

Energy level calculations of the reconstructed 90° partial dislocation in silicon

An LCAO scheme taking into account 10 atomic orbitals ( s-, p-, and d-type) applied to a supercell containing 256 atoms is used to calculate the bound states of the reconstructed 90° partial dislocation in Si. The results differ significantly from our earlier calculations on the unreconstructed 90° partial using the same method. We find two bands separate from each other in the entire Brillouin zone and the upper band penetrates deep into the indirect band gap which is in contradiction with the general opinion that core reconstruction clears the band gap of dislocation states.

Spatial distribution of dislocation-related centers in plastically deformed silicon

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Dynamical treatment of the splitting of HOLZ lines from dislocations in silicon

The splitting of higher-order Laue-zone (HOLZ) lines of convergent-beam electron diffraction (CBED) due to the presence of dislocations in Si was investigated experimentally and theoretically. The parameters affecting the separation and relative positions of the fringes of split HOLZ lines were examined with experiments and/or computations. According to the results obtained, a method for identification of Burgers vector is discussed.

Analysis of 2D and 3D defects associated with precipitation of Cu in silicon

Extrinsic gettering of Cu on near-surface dislocations in Si has been the topic of recent investigation. It was shown that the Cu precipitated hetergeneously on dislocations as Cu silicide along with voids, and also with a secondary planar precipitate of unknown composition. Here we report the results of investigations of the sense of the strain fields about the large (~100 nm) silicide precipitates, and further analysis of the small (~10-20 nm) planar precipitates.Numerous dark field images were analyzed in accordance with Ashby and Brown's criteria for determining the sense of the strain fields about precipitates. While the situation is complicated by the presence of dislocations and secondary precipitates, micrographs like those shown in Fig. 1(a) and 1(b) tend to show anomalously wide strain fields with the dark side on the side of negative g, indicating the strain fields about the silicide precipitates are vacancy in nature. This is in conflict with information reported on the η'' phase (the Cu silicide phase presumed to precipitate within the bulk) whose interstitial strain field is considered responsible for the interstitial Si atoms which cause the bounding dislocation to expand during star colony growth.

Interaction of impurities with dislocation cores in silicon

The interaction of P with 90° partial dislocations in Si is examined using a cluster method with local-density-functional pseudopotential theory. This method is capable of predicting structural properties such as bond lengths and angles to within a few per cent. We describe several states of P at dislocation cores which are normally reconstructed and which contain solitonic reconstructed bonding patterns. Our overall conclusion is that there is a clear tendency for P to migrate towards the dislocation core, and assume threefold coordination, thus firstly breaking reconstructed bonds across the core and secondly passivating the solitonic dangling bonds. These different states can explain the segregation of P to a dislocation, its locking effect and its effect upon the dislocation velocity. The passivation of P also contributes to the effect of plastic deformation on the carrier densities. © 1991 Taylor & Francis Group, LLC.

NEW POSSIBILITIES OF EBIC FOR DISLOCATION STUDY

The recent results of the EBIC investigations of dislocations in Si demonstrating the influence of point defect atmospheres on the characteristics of the EBIC contrast of the both charged and uncharged dislocations are discussed. It is shown that from such investigations characteristics of these atmospheres can be obtained.

EBIC Investigastion of the Electrical Activity of Dislocations with Different Impurity Atmospheres in Si

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Imaging of dislocations using backscattered electrons in a scanning electron microscope

Abstract A field-emission-gun scanning electron microscope (FEG SEM) has been fitted with a back-scattered electron detector in order to image dislocations by the electron channelling contrast mechanism. By using an efficient detector, optimizing its orientation with respect to the specimen and the incident beam, and applying an image-enhancement technique, it has been possible to image and characterize dislocations near the surface of bulk samples of a number of materials without the need of an electron-energy filter in front of the detector. Examples are presented of preliminary studies of dislocations in Si and Ni, Ga; the image widths are typically 20 nm, and the normal g·b = 0 invisibility criterion for screw dislocations applies. By dispensing with the electron-energy filter used by Morin et al., the design and operation of the system become very simple, and the technique should become available in commercial FEG SEMs. This non-destructive technique is likely to have wide applications to situations where conventional ‘thin-film’ microscopy is impractical or undesirable.

Copper precipitation on extrinsic defects in silicon

The gettering of impurity copper in silicon has been investigated for over a decade because of its technological importance in electronic device fabrication.it is known that Cu can be extrinsically gettered in silicon at deliberately introduced nucleation sites. However, its reaction mechanism and the nature of the reaction product are not well understood. Here we report the interaction of Cu with dislocations in Si created by mechanical abrasion.A damaged region was introduced into CZ{001} silicon wafers on one side by abrasion. A Cu layer 200nm thick was deposited onto the abraded surface in a UHV chamber at room temperature. After Cu deposition the wafers were sealed immediately into quartz ampules under vacuum and annealed at 1000 C for 24 hrs, followed by quenching. Cross section specimens were prepared by mechanical dimpling and Ar beam ion milling. Diffraction contrast imaging and microdiffraction experiments were done in a JEM-2000FX at 200kV, and a Philips 400TEM/STEM/FEG at 100kV.

Simulation and application of the distorted ZOLZ patterns from dislocations in Si

The previously reported distorted zeroth-order fringes in a bright-field Tanaka pattern from a dislocated region in silicon have been computer simulated and the experimental and the many-beam calculated patterns agree well. Calculations are carried out for nine distinct cases of edge, screw and 60° dislocations in a silicon crystal. The general usefulness of the distortion of the ZOLZ pattern in determining geometrical properties of a dislocation is discussed.

LCAO Recursion Approach for the Bound Electron States at the 90°‐Partial Dislocation in Silicon

AbstractThe evaluation of bound electron states at extended lattice defects in Si is studied within an LCAO scheme under full inclusion of s‐, p‐, and d‐states and their mutual non‐orthogonality. The levels are determined from a continuous‐fraction recursion treatment. Application to a supercell model of the unreconstructed 90°‐partial dislocation demonstrates that the method works well for basis sets of 2560 complex basis functions. The present results for the bound electron states at the 90°‐partial dislocation in Si appreciably differ from the earlier tight binding estimates due to the here included dangling bond interactions. Two one‐dimensional bands of bound states are found showing large band splitting inside the Brillouin zone and degeneracy of the bands at the zone boundary with an occupation limit between empty and full states 0.12 eV above the valence band edge.

Molecular Dynamics studies of Dislocations in SI

AbstractThe mobility of dislocations in a model Silicon lattice is examined at an atomistic level using molecular dynamics. Straight and double-kinked 30° and 90° partial dislocation glide-set dipoles are modelled in a strain-free environment: reconstruction and antiphase defects are found to be present for 30° partial dislocations. The effects of applied shear strains and of temperatures up to the melting point are considered.

Impurity gettering by misfit dislocations in Si (2% Ge) epitaxy: nickel

The microstructure associated with nickel gettering by an epitaxial misfit dislocation network generated in Si(2% Ge) chemical vapor deposition films has been determined using transmission electron microscopy. The configuration of misfit dislocations is a well-characterized network of b=a/2〈011〉 60° dislocations that all lie in the (001) interfacial plane. Nickel was deliberately introduced by deposition onto the front surface of the wafer followed by diffusion at temperatures from 600 to 1000 °C. Nickel segregated on or in the immediate vicinity of the misfit dislocations to form individual or agglomerates of fine precipitates. The strong temperature dependence of Ni solubility in Si and the nucleation enhancement by the localized strain effects in the vicinity of dislocations are considered to be the dominant factors controlling gettering by the misfit dislocations. An annealing temperature of 600 °C is suggested which appears to uniformly decorate the misfit dislocations with Ni for possible buried microwire applications.

Three-bond scission and the structure of the cleaved Si(111) surface

It is proposed that cleavage of Si to form Si(111) (2×1) occurs by the scission of three bonds between the closely spaced double layers, rather than by the severing of the single bond that connects the double layers. It is shown that three‐bond scission occurs in the behavior of dislocations in Si. Models of the surface structure based on this cleavage process are presented and discussed in light of the current understanding of this surface.

Hydrogen passivation of dislocations in silicon

The I–V characteristics of metal-insulator-semiconductor (MIS) and photoelectrochemical (PEC) solar cells fabricated on passivated and unpassivated p-silicon samples are used to study the effects of atomic hydrogen passivation of dislocations in Si. Upon passivation, both types of cells show a dramatic decrease in the reverse dark current. In general, the open circuit voltage V oc , the fill factor FF, and the short circuit current I sc are also improved. Occasionally, anomalous I–V characteristics were observed in some passivated samples indicating the possibility of acceptor neutralization by atomic hydrogen. This effect may complicate the interpretation of the experimental results, in terms of a dislocation conductivity model. Identifying specific effects of hydrogenation of dangling bonds on the conductivity and the density of recombination centers in dislocations is, thus, hampered.

Deep electron level calculations for dislocations in Si and Ge recursion approach exploiting the translational symmetry

Abstract For crystals with dislocations, the tight-binding recursion method is reformulated to maintain the translational symmetry along the dislocation line. The method is applied to the deep electron levels at dislocations in Ge and Si. Because of the translation symmetry up to 110 pairs of significant recursion coefficients (an, bn ) could be evaluated, revealing an asymptotic oscillatory behaviour of the coefficients. For unreconstructed and reconstructed 30°, 60° and 90° partial dislocations in Ge and Si, the one-dimensional bands of deep electron levels are presented as deduced from the continued-fraction density of states. Including the changes in the chemical shift brings the calculated deep level structure of the unreconstructed 90° partial into rather close agreement with the experimental findings.

The electrical behaviour of individual dislocations, shockley partials and stacking fault ribbons in silicon

The EBIC mode of the SEM has been used to study the electronic properties of individual dislocations in silicon at high spatial resolution. A theory of EBIC, relating the contrast to the fundamental defect parameters, such as the carrier lifetime in the vicinity of the defect, is presented. A means for the determination of defect energy levels at high spatial resolution is proposed. First results of a project designed to yield information on the energy levels associated with dislocations in Si are described. The first direct electrical observation of the individual Shockley partials of dissociated dislocations is also reported.

Generation and Recombination Images of Dislocations in Si by Scanning Microscopy

In high purity Si generation images of dislocations, appearing as white lines, may be obtained in scanning microscopy by using an IR beam with suitable wavelength, with excitations involving prevalently the dislocation energy levels. Different contrasts are observed with broad area contacts or with point contacts localized in the dislocation etch-pit centre. Dans Silicium de haute purete on a obtenu des images de dislocations comme des lignes blanches par le moyen d'un microscope a balayage. On a utilise un faisceau IR de convenable longueur d'onde, par excitation concernant les niveaux des dislocations. On a remarque des differents con-trastes avec larges contacts ou avec contacts ponctuels places dans le centre du “etch-pit” des dislocations.

Dynamical Oscillations of X-Ray Integrated Intensity in Laue Diffraction and Their Temperature Dependences for Si Dislocation Crystals

Results of a study of thickness oscillations (Pendellosung beats) of the X-ray integrated intensity for the symmetrical Laue case of silicon dislocation single crystals are presented over the temperature range from 100 to 295 K. The oscillation period is found to increase with the dislocation density and the reflection order. It is shown that the Debye temperature θM can be precisely determined by the temperature shift of the oscillation patterns for dislocation crystals. The value of θM, obtained from the temperature dependence of Pendellosung intensity beats for a real crystal agrees well with that for a perfect one. [Russian Text Ignored].

Calculation of Core Structure and Core Energy of Screw and 60° Dislocations in Si: Tight-Binding Method

A tight-binding type electronic theory is used to calculate the core structure and core energy of both screw and 60° dislocations in Si. The repulsive interaction energies at short distances are simulated by a Born-Mayer potential. It is shown that the glide-set dissociated dislocations are more stable than the corresponding shuffle-set perfect dislocation. The calculated core structures and core energies are compared with those of previous theoretical calculations as well as with available experimental results.