Dislocations In Silicon Research Articles

Paramagnetic Structure of the Soliton of the 30° Partial Dislocation in Silicon

Based on ab initio calculation, we propose a new structure for the fundamental excitation of the reconstructed 30$^\circ$ partial dislocation in silicon. This soliton has a rare structure involving a five-fold coordinated atom near the dislocation core. The unique electronic structure of this defect is consistent with the electron spin resonance signature of the hitherto enigmatic thermally stable R center of plastically deformed silicon. This identification suggests the possibility of an experimental determination of the density of solitons, a key defect in understanding the plastic flow of the material.

Atomic structure of dislocation kinks in silicon

We investigate the physics of the core reconstruction and associated structural excitations (reconstruction defects and kinks) of dislocations in silicon, using a linear-scaling density-matrix technique. The two predominant dislocations (the $90\ifmmode^\circ\else\textdegree\fi{}$ and $30\ifmmode^\circ\else\textdegree\fi{}$ partials) are examined, focusing for the $90\ifmmode^\circ\else\textdegree\fi{}$ case on the single-period core reconstruction. In both cases, we observe strongly reconstructed bonds at the dislocation cores, as suggested in previous studies. As a consequence, relatively low formation energies and high migration barriers are generally associated with reconstructed (dangling-bond-free) kinks. Complexes formed of a kink plus a reconstruction defect are found to be strongly bound in the $30\ifmmode^\circ\else\textdegree\fi{}$ partial, while the opposite is true in the case of $90\ifmmode^\circ\else\textdegree\fi{}$ partial, where such complexes are found to be only marginally stable at zero temperature with very low dissociation barriers. For the $30\ifmmode^\circ\else\textdegree\fi{}$ partial, our calculated formation energies and migration barriers of kinks are seen to compare favorably with experiment. Our results for the kink energies on the $90\ifmmode^\circ\else\textdegree\fi{}$ partial are consistent with a recently proposed alternative double-period structure for the core of this dislocation.

Luminescence from Erbium‐Doped Silicon Epi Layers Grown by Liquid‐Phase Epitaxy

Dislocation‐related photoluminescence at 0.806 and 0.873 eV is observed in erbium‐doped silicon epi layers grown by liquid‐phase epitaxy on (100) Si wafers. These signals are detected at T = 2 K only on epi layers deposited on Czochralski grown silicon substrates. No luminescence is observed when float zone‐grown substrates are used. The peak intensity shows temperature quenching, but the signal remains detectable up to 195 K.The luminescence apparently is due to dislocations in silicon in the simultaneous presence of high oxygen concentration and erbium impurities. A comparison with the typical infrared emission from erbium‐implanted silicon samples is presented.

Integration of Multilayers in Er-Doped Porous Silicon Structures and Advances in 1.5 μm Optoelectronic Devices

AbstractInfrared photoluminescence (PL) and electroluminescence (EL) from erbium-doped porous silicon (PSi) structures are studied. The PL and EL from the Er-doped PSi structures and the absence of silicon band edge recombination, point defect, and dislocation luminescence bands suggest that the Er-complex centers are the most efficient recombination sites. PSi multilayers with very high reflectivity (R ≥ 90%) in the 1.5 gim range have been incorporated in the structures resulting in a PL enhancement of over 100%. Stable and intense EL is obtained from the Er-doped structures. The EL spectrum is similar to that of the PL, but shifted towards higher energy. The unexpected shift in emission opens up the possibility for erbium related luminescence to encompass a larger part of the optimal wavelength window for fiber optic communications.

TEM Imaging of Dislocation Kinks, their Motion and Pinning

HREM lattice images have been obtained using forbidden reflections generated by (111) stacking faults in silicon lying normal to the beam at temperatures up to 600 °C. Stationary and video images of 30°/90° partial dislocations relaxing toward equilibrium are studied. The lattice images formed from these forbidden reflections show directional fluctuations which are believed to be kinks, since, as expected from mobility measurements, a higher density is observed on 90° partials than on 30° partials, whereas artifacts contribute equally. Video difference images are used to obtain direct estimates of kink velocity. Observations of kink delay at obstacles, thought to be oxygen atoms at the dislocation core, yield unpinning energies and the parameters of the obstacle theory of kink motion. The kink formation energy is obtained from the distribution of kink pair separations in low-dose images. The kink migration rather than formation energy barrier is thus found to control the velocity of unobstructed dislocations in silicon under these experimental conditions.

Thermal Behaviour of Deep Levels at Dislocations in n-Type Silicon

The thermal behaviour of deformation-induced traps in plastically deformed n-type silicon has been investigated via Deep Level Transient Spectroscopy. Among the four traps usually detected in plastically deformed silicon only two have been found to survive upon annealing: trap A and trap C located at 0.18-0.23 eV and 0.38-0.43 eV from the conduction band edge, respectively. The last one has been related to dislocations.

Interaction of vacancies with partial dislocations in silicon

The interaction of vacancies with $30\ifmmode^\circ\else\textdegree\fi{}$ and $90\ifmmode^\circ\else\textdegree\fi{}$ partial dislocations in silicon is examined. In particular, the structures and binding energies are calculated using hydrogen-terminated clusters and local density-functional theory. Moreover the electronic structure is determined using supercells containing dislocation dipoles. Vacancies are found to have binding energies of approximately 2.0 eV and 0.9 eV to $90\ifmmode^\circ\else\textdegree\fi{}$ and $30\ifmmode^\circ\else\textdegree\fi{}$ partials, respectively. The elastic strain field of the partials makes the fourfold vacancy reconstruct, which essentially clears the fundamental gap.

Optical and electrical non-uniformity around dislocations in silicon doped GaAs

Optical and electrical non-uniformity around dislocations in silicon doped GaAs

Optical and electrical non-uniformity around dislocations in silicon doped GaAs

Highly spatially resolved mappings of photoluminescence (PL) and capacitance-voltage (C-V) measurements have been used to characterise the optical and electrical non-uniformity around dislocations in Si doped GaAs crystals. A broad emission band with a peak at 0.95 eV commonly appears in Si doped GaAs wafers with carrier concentrations ranging from 3 × 1017 to 4 × 1018 cm-3. The average intensity of the 0.95 eV band is lower in the dislocated area than in the dislocation free area. The microscopic intensity pattern of the band agrees with the dislocation pattern. The intensity increases in the core region of dislocations and decreases in the surrounding area. The band edge emission shows a complementary intensity pattern. The C-V mapping of a wafer indicates that the carrier concentration is higher in the dislocated area, correlating with the PL intensity pattern. These results suggest that the microdefects responsible for the 0.95 eV band act as acceptors compensating Si donors and that they are gettered by dislocations.

Multiscale Approach to Determination of Thermal Properties and Changes in Free Energy: Application to Reconstruction of Dislocations in Silicon

We introduce an approach to exploit the existence of multiple levels of description of a physical system to radically accelerate the determination of thermodynamic quantities. We first give a proof of principle of the method using two empirical interatomic potential functions. We then apply the technique to feed information from an interatomic potential into otherwise inaccessible quantum mechanical tight-binding calculations of the reconstruction of partial dislocations in silicon at finite temperature. With this approach, comprehensive ab initio studies at finite temperature will now be possible.

Modification of the Recombination Activity of Dislocations in Silicon by Hydrogenation, Phosphorous Diffusion and Heat Treatments

Modification of the Recombination Activity of Dislocations in Silicon by Hydrogenation, Phosphorous Diffusion and Heat Treatments

Interaction of Impurities and Dislocations in Silicon before and after External Gettering

Interaction of Impurities and Dislocations in Silicon before and after External Gettering

Simulation of dislocation source dynamics in silicon for a 60° dislocation

A new approach for the simulation of a Frank-Read source in directionally bonded, e.g. covalent, cubic materials based on an f.c.c. lattice is presented [1] (Geipel, Ph.D. Thesis, Case Western Reserve University, 1993). In this algorithm, a segment of a perfect dislocation, initially lying along a 〈11̄0〉 Peierls valley, is pinned at its two ends on a {111} glide plane. Under the application of a shear stress, this dislocation first develops into a semi-hexagonal half-loop and then swings around the pinning centers to form a full dislocation loop surrounding a reformed dislocation source. In the present study the temperature has explicitly been included through the thermal activation of kink pairs and their influence on dislocation velocity. One of the conclusions drawn from this work is that the critical stress for a 60 source dislocation in silicon appears to be highly temperature sensitive.

Kinetic properties of dislocations in semiconductors revealed by X-ray topography

In situ X-ray topography (in situ X-TOP) gives the most reliable and quantitative information on kinetic processes of dislocations in semiconductors among all experimental techniques available now. This paper gives a review on generation, motion and impurity pinning of dislocations in silicon which were investigated by means ofin situ X-TOP. It is emphasized how effectivelyin situ X-TOP has been applied to clarify impurity-related dislocation processes.

Temperature-dependence of the Frank-Read source in Si

In order to check a recently proposed model for deformation twinning in Si a new algorithm for the simulation of a Frank-Read source in materials with directional bonding — in this paper in (diamond) cubic semiconductors — is presented. In this algorithm a segment of a perfect dislocation pinned at its two ends (i.e. the source dislocation) lies along a 〈110〉 Peierls valley which develops into a semi-hexagonal loop under the application of a resolved shear stress. Previous simulations have not taken the temperature-dependence of the operation of the Frank-Read source into account. In covalent materials with directional bondings thermal activation plays the predominant role in dislocation motion, therefore temperature was taken into account via the thermal activation of kink pairs and its influence on dislocation velocity. The simulations for a 60 ° source dislocation in silicon suggest that the critical stress is highly temperature sensitive. It is shown that, in most cases, the back stress is much smaller than the line tension. As a result, for the continuous operation of the Frank-Read source, under an applied stress slightly larger than the critical stress, the back stress due to a small number of previously emitted loops upon a nascent dislocation brings the operation of the Frank-Read source to a (temporal) stop. Thus, the number of loops which stop the operation of the Frank-Read source is highly stress- and temperature-sensitive. The results of the simulations are compared with experimental TEM observations of Frank-Read sources in silicon for low and high temperatures.

Observation of Moving Dislocation Kinks and Unpinning.

Atomic resolution electron microscopy has been used to obtain images of moving dislocation kinks on partial dislocations at 600 \ifmmode^\circ\else\textdegree\fi{}C in silicon. Video difference images are used to obtain direct estimates of kink velocity. Observations of kink delay at obstacles, thought to be oxygen atoms at the dislocation core, yield unpinning energies and parameters of the obstacle theory of kink motion. The kink formation energy is obtained from the distribution of kink pair separations in low-dose images and is compared to the kink migration energy. Unlike metals, kink migration rather than formation controls the velocity of unobstructed dislocations in silicon under these experimental conditions.

Observation of twins formed by gliding of successive surface-nucleated partial dislocations in silicon

A new twin formation mechanism is proposed based on a transmission electron microscopy study of indentation-deformed silicon. It is found that the twins are formed by successive surface nucleation of half-loops and subsequent glide of Shockley partial dislocations on the neighbouring {111} planes. All the partial dislocations in the twin band have the same Burgers vector which points toward the bulk.

Structure, Barriers, and Relaxation Mechanisms of Kinks in the 90 degrees Partial Dislocation in Silicon.

Kink defects in the 90-degree partial dislocation in silicon are studied using a linear-scaling density-matrix technique. The asymmetric core reconstruction plays a crucial role, generating at least four distinct kink species as well as soliton defects. The energies and migration barriers of these entities are calculated and compared with experiment. As a result of certain low-energy kinks, a peculiar alternation of the core reconstruction is predicted. We find the solitons to be remarkably mobile even at very low temperature, and propose that they mediate the kink relaxation dynamics.

Precipitation of Cu, Ni, and Fe on Frank-Type Partial Dislocations in Czochralski-Grown Silicon

The segregation behavior of metallic impurities, Cu, Ni, and Fe on Frank-type partial dislocations in Czochalski-grown silicon depends not only on the species of impurities, but also significantly on the cooling rate of the specimen after contamination. In slowly cooled specimens, Cu develops precipitate colonies in the region away from Frank partials and does not decorate them even on an atomic scale, while Ni decorates Frank partials weakly. A high density of Cu or Ni precipitates is observed on Frank partials when specimens are cooled fast. Fe decorates Frank partials both in fast and slowly cooled specimens. The amount of precipitated Fe on Frank partials is larger in a slowly cooled specimen than in a fast cooled one. The difference in segregation behavior on Frank partials among Cu, Ni, and Fe is reasonably interpreted in terms of three parameters: precipitate nuclei as influenced by the dislocation-core structure, crystal structure of precipitates, and diffusivity of impurities in Si.

Annihilation of Self-Interstitials by Dislocations in Silicon as Studied by Gold Diffusion

Annihilation of Self-Interstitials by Dislocations in Silicon as Studied by Gold Diffusion