Dislocations In Silicon Research Articles

Optical properties of shuffle dislocations in silicon

The radiative recombination processes in dislocated float zone silicon samples deformed under gigapascal stresses were studied by photoluminescence (PL) spectroscopy. The observed shuffle dislocations present a reconstructed core and their generation is accompanied by the introduction of point defects and point defect clusters, whose signature is evident in the PL spectra. A broad band around 1eV is the only PL feature which could be directly related to shuffle dislocations and it is explained conjecturing strain field induced gap changes, as confirmed by molecular dynamics simulations.

Kinetic Monte Carlo and density functional study of hydrogen enhanced dislocation glide in silicon

We investigate Hydrogen Enhanced Dislocation Glide [HEDG], using n-fold way Kinetic Monte Carlo simulations of the interaction between hydrogen and 90° partial dislocations in silicon, and a range of new density functional calculations. We examine two different hydrogen arrival species, as well as hydrogen recombination at the dislocation. The Monte Carlo simulations use a line-wise description of the dislocation line parameterized using density functional calculations of migration and formation energies of various dislocation line defects and their complexes with hydrogen. From this we suggest that the rate of H2 expulsion from the dislocation core increases as we approach HEDG, but that if the concentration of the hydrogen species goes beyond that required for HEDG it then slows dislocation motion by choking the line with defects comprised of two hydrogen atoms in a reconstruction bond. A `dislocation engine' model is proposed whereby hydrogen enters the dislocation line, catalyses motion, and is expelled along the core as H2.

First principles simulations of antiphase defects on the SP90° partial dislocation in silicon

We study the structure and energies of formation of antiphase defects on the single period (SP)90° partial dislocation in silicon using a first principles density functional method. Weconsider two types of antiphase defect, the type first proposed by Hirsch (1980 J.Microsc. 118 3) wholly inside the dislocation core, and another type that liespartly outside the core. Both types are stable and contain one atom which isthreefold coordinated. Each of these atoms has a dangling hybrid which lies in adirection perpendicular to the dislocation line on the slip plane. We obtain values of1.39 ± 0.03 eVand 1.41 ± 0.03 eV for the average formation energy of single antiphase defects of the inside and outsidetypes, respectively. We have obtained, using a tight binding scheme, bandstructurescorresponding to these two types of defect, and we find both of them to be associated withstates in the gap and each dangling hybrid to contain one electron.

Defect studies on silicon and silicon–germanium for PV and optoelectronic applications

Defect monitoring and engineering techniques were applied to multicrystalline silicon grown from electronic grade silicon scraps and strained silicon–germanium alloys to test their suitability for low-cost photovoltaics and high-speed electronics, respectively. The combination of lifetime, photoluminescence and electron beam induced current (EBIC) measurements was found a very effective practice for the analysis of the effect of impurities on the electrical activity of grain boundaries and dislocations in multicrystalline silicon. Room temperature photoluminescence has been also used to monitor the effect of various cell fabrication process steps on the local recombination activity of defects. The application of the EBIC technique was found as well a good tool for a quantitative determination of threading dislocation density in Si–Ge alloys, in view of the optimisation of the low energy plasma-enhanced chemical vapour deposition (LEPECVD) used for their growth.

Molecular Dynamics Analyze on Effects of Abrasive Size and Cut Depth on the Monocrystal Silicon Grinding

Molecular dynamics (MD) simulation is carried out to analyze the effects of abrasive ngrain size and cut depth on monocrystal silicon grinding process. Tersoff potential is used to describe the interactions of diamond and silicon atoms. Based on classical Newtonian mechanics law, the motion equations of atoms are established and the trajectory of each atom in phase space is obtained with the aid of Velocity Verlet algorithm. Debye model is introduced to convert between kinetic energy and temperature of an atom. The grinding processes of by single grain with different size and different cut depth are investigated in atomic space. Through comparing shearing force and potential energy in the single grain grinding process, the effects of cut depth and grain size on the grinding process are discussed. From the results of MD simulation, it is revealed that when the cut depth increases, both the shearing force in silicon crystal and potential energy between the silicon atoms rise, deformation and dislocations in the silicon lattices increase. As a result, all theses lead to^more severe surface and subsurface damage. With the decreasing of grain size in the same cut-depth nanometric grinding processes, the shearing force in silicon crystal and potential energy between the silicon atoms become larger, deformation and dislocations in the silicon lattices increase.

259 イオンインプランテーション起因のシリコン転位の発生・進展過程の転位動力学解析(欠陥,OSO7 電子・原子・マルチシミュレーションに基づく材料特性評価)

259 イオンインプランテーション起因のシリコン転位の発生・進展過程の転位動力学解析(欠陥,OSO7 電子・原子・マルチシミュレーションに基づく材料特性評価)

Impact of Low Temperature Hydrogenation on Recombination Activity of Dislocations in Silicon

Silicon samples doped with gallium and intentionally contaminated with iron have been studied by means of electron beam current (EBIC), capacitance voltage (CV) and deep level transient spectroscopy (DLTS) methods. Reverse bias anneal (RBA) treatments at temperatures of 390-420K were used to move hydrogen and dissolved iron atoms away from the surface. A new procedure was developed to find dislocations lying on desirable depth from the surface and to analyze the depth distribution of their recombination contrast. Iron contaminated dislocations do not noticeably change their recombination activity when kept in an electrical field as high as 104 V/cm at 420K for several hours. This implies a tight binding of iron atoms at dislocations. The binding energy of iron with dislocations seems to be much larger than for Fe-Ga and H-Ga pairs. Low temperature hydrogenation of iron contaminated dislocations does not produce any passivation effect. In opposite, the recombination activity of the dislocations significantly increases after RBA treatment.

The equilibrium structures of the90° partial dislocation in silicon

We consider the free energies of the single-period (SP) and double-period (DP) core reconstructions of thestraight 90° partial dislocation in silicon. The vibrational contributions are calculated with aharmonic model. It is found that it leads to a diminishing difference between thefree energies of the two core reconstructions with increasing temperature. Thequestion of the relative populations of SP and DP reconstructions in a single straight90° partial dislocation is solved by mapping the problem onto a one-dimensional Ising model ina magnetic field. The model contains only two parameters and is solved analytically. Itleads to the conclusion that for the majority of the published energy differences betweenthe SP and DP reconstructions the equilibrium core structure is dominated by the DPreconstruction at all temperatures up to the melting point. We review whether it is possibleto distinguish between the SP and DP reconstructions experimentally, both in principleand in practice. We conclude that aberration corrected transmission electronmicroscopy should be able to distinguish between these two core reconstructions, butpublished high resolution micrographs do not allow the distinction to be made.

Controlled nucleation of dislocations by a spatially localized stress field

We analyze the nucleation of dislocations in silicon at spatially localized stress fields generated by silicon nitride pads having a high intrinsic stress. The nucleation and final configuration of the dislocations were studied using hot-stage transmission electron microscopy and were compared with dislocation simulations based on calculations of the stress fields around the pads. We find that the simulated configurations match well with the experimental data, and we show that the dislocation configuration can be controlled by the pad size.

Nitrogen effects on generation and velocity of dislocations in Czochralski-grown silicon

The dynamic properties of individual dislocations in nitrogen (N)-doped Czochralski-grown Si crystals with concentrations up to 6×1015cm−3 were investigated at temperatures of 650–950°C using the etch pit technique and compared with such characteristics of N-free Si crystals. The velocity of dislocations in motion in N-doped crystals was revealed to be unaffected by N doping. It was found that the generation of dislocations from a surface scratch was suppressed in N-doped Si and that the critical stress for dislocation generation increased with N concentration, which is interpreted as being due to dislocation immobilization caused by impurity segregation. N doping is concluded to be effective in the promotion of precipitation of oxygen impurity resulting in immobilization of dislocations.

On the core structures of dislocations in semiconductors

Dislocations in silicon are nucleated under high stresses as perfect ones in the shuffle set. It is shown that the same nucleation mechanism operates in hexagonal 4H-polytype SiC but, in contrast to silicon, perfect-shuffle configurations are unstable and transform by cross-slip into glide set dislocations.

Three-dimensional structure of dislocations in silicon determined by synchrotron white x-ray topography combined with a topo-tomographic technique

We have studied the propagation and elimination of dislocations generated at the early stage of Czochralski silicon crystal growth using synchrotron white x-ray topography combined with a topo-tomographic technique. Two silicon crystals with [001] growth-axes were examined. One was intentionally grown without enlarging its diameter to easily observe the features of the dislocation propagation, and the other was grown with Dash necking, followed by a 2 inch enlargement of its diameter in order to observe the elimination of the dislocations. The three-dimensional structure of the individual dislocation, i.e. the direction of the dislocation line, its Burgers vector and the glide plane, were determined. These investigations revealed that dislocation half loops, which were generated from tangled dislocations, were expanded on their glide planes and were often deformed by their interaction, cross slip and collision with the crystal surface, followed by a gradual decrease in their density. The dislocation-elimination effect of the Dash necking was caused by the expansion of the dislocation half loops being terminated within the crystal and by their pinning on the crystal surface.

Electrical properties of gold at dislocations in silicon

Deep level transient spectrocsopy has been used to study deep levels in plastically deformed n-type silicon introduced by gold impurities at concentrations differing by about one order of magnitude. A DLTS-line is observed which shows the signatures of extended localized states and emission characteristics close to that of the gold acceptor level in dislocation-free silicon. It is attributed to gold accumulated in the strain-field of dislocations. The amplitude of the C-line typically found in plastically deformed silicon shows no correlation with the gold concentration. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Spin‐resonant change of unlocking stress for dislocations in silicon

In this work we have observed a significant increase of unlocking stress for dislocations in Cz-Si caused by the microwave magnetic field in a condition of spin resonance corresponding to g-factor value of about 2.0. The result can be interpreted in terms of spin-dependent reactions of oxygen accumulated at dislocations. However, the specific atomistic model for the effect is still missing. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanoscale Measurement of Stress and Strain by Quantitative High-Resolution Electron Microscopy

The geometric phase technique (GPA) for measuring the distortion of crystalline lattices from high-resolution electron microscopy (HRTEM) images will be described. The method is based on the calculation of the “local” Fourier components of the HRTEM image by filtering in Fourier space. The method will be illustrated with a study of an edge dislocation in silicon where displacements have been measured to an accuracy of 3 pm at nanometre resolution as compared with anisotropic elastic theory calculations. The different components of the strain tensor will be mapped out in the vicinity of the dislocation core and compared with theory. The accuracy is of the order of 0.5% for strain and 0.1° for rigid-body rotations. Using bulk elastic constants for silicon, the stress field is determined to 0.5 GPa at nanometre spatial resolution. Accuracy and the spatial resolution of the technique will be discussed.

Structural and electrical properties of metal impurities at dislocations in silicon

AbstractThe electrical properties of silicon materials containing dislocations are strongly affected by deep levels at or close to the dislocation core. Such deep levels are frequently thought to be due to metal impurities that are chemically bound to the dislocation core, segregated in the long‐range strain field or precipitated at the dislocation. This paper summarizes recent experimental studies of the interaction of metal impurities with dislocations in silicon. Transmission electron microscopy and deep level transient spectroscopy are the main techniques to study precipitation at dislocations and binding or segregation of metal impurity atoms, respectively. Focus is drawn to precipitation of fast diffusing 3d transition metals where dislocations not only serve as nucleation sites but also establish fast growth kinetics. In addition, gold impurities in the strain field of dislocations give rise to an acceptor level with the capture kinetics of extended localized defects while the emission characteristics are hardly distinguished from those of the acceptor level of gold atoms in the undisturbed bulk. The results will be discussed in terms of possible response of the deep impurity level and the silicon bands to the dislocation strain field. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

Electronic charge effects on dislocation cores in silicon

Using first-principles calculations, we investigate electronic charge effects on the structural stability of partial dislocations in silicon. For the 30° partial dislocation, we find that the unreconstructed core sustains all possible charge states associated with the dislocation-related electronic bands, as the Fermi level (μe) sweeps the electronic band gap, while the reconstructed core remains neutral for p-type doping and intrinsic regimes. Both core configurations become negatively charged for n-type doping. In the case of the 90° partial dislocation, the three known core configurations (namely, the single-period and double-period reconstructed cores and the unreconstructed one) remain neutral in the p-type and intrinsic regimes, but the negatively charged states become stable in the n-type region, for all three geometries. More important, we find that the relative stability between the three structures is strongly charge-state dependent, with the unreconstructed core becoming energetically favorable in the n-type regime. Our results provide elements for understanding the role of doping on dislocation mobility in semiconductors.

Migration Processes of the 30° Partial Dislocation in Silicon

The migration processes of the 30 degrees partial dislocation in silicon have been investigated using first-principles total-energy calculations. We have presented for the first time a reliable determination of the formation and migration energies of kinks, which are consistent with experiments. The obtained results indicate that the 30 degrees partial dominates the dislocation dynamics in Si and suggest the dislocation glide picture based on the no-collision model. We suggest that the interpretation of experimental studies on the dislocation dynamics should be reexamined in light of these results.

Plastic deformation by shuffle dislocations in silicon

Abstract The dislocation substructures of silicon deformed under hydrostatic pressure at room temperature in various deformation conditions have been characterized by transmission electron microscopy. This confirms the occurrence of deformation mechanisms by perfect dislocations for high-stress conditions. Dislocation line instabilities are found being consistent with a deep Peierls potential along 〈123〉 orientations. The nature of the core of those perfect dislocations is discussed in relation with these observations.