Dislocations In Germanium Research Articles

Impact of nanosecond UV laser pulses on the surface of germanium single crystals

For the first time, a detailed comprehensive study of the "dry" etching of dislocation and dislocation-free germanium samples on the {111}, {110} and {100} planes has been carried out. Etching was carried out by exposure to pulses of nanosecond UV laser radiation of subthreshold intensity (wavelength 355 nm, duration ~ 10 ns, energy density ~ 0.5–1.3 J/cm2, pulse repetition rate 100 Hz, divergence 1–2 mrad). Before and after laser heat treatment of the surface, the samples were examined using a Zygo optical profilometer and a scanning electron microscope. Features of the nature of damage to surfaces corresponding to different crystallographic planes of single crystals of industrial dislocation germanium are revealed. They are compared with data on subthreshold damages of typical dislocation-free crystals.It is shown that in dislocation samples of germanium on the {111} plane, it is possible to create a regime of exposure to radiation, leading to the formation of etch pits that are outwardly identical to dislocation pits detected during selective chemical etching. Their concentration corresponds in order of magnitude to the density of dislocations.On the {100} plane of dislocation samples, etching results were also found, which clearly have a crystallographic nature. At an energy density of the acting radiation ≥ 0.4 J/cm2, on the surfaces of dislocation ({100} plane) and dislocation-free germanium ({111}, {100}, {110} planes), only individual spots ~ 50 μm in size were registered, as well as individual microcraters ~ 0.1–1 μm in size, which do not have crystallographic features. The possibility of environmentally friendly detection of dislocations in germanium without the use of chemical reagents is shown.

The Third-Order Elastic Constants and Mechanical Properties of 30° Partial Dislocation in Germanium: A Study from the First-Principles Calculations and the Improved Peierls–Nabarro Model

The elastic constants, core width and Peierls stress of 30° partial dislocation in germanium has been investigated based on the first-principles calculations and the improved Peierls–Nabarro model. Our results suggest that the predictions of lattice constant and elastic constants given by LDA are in better agreement with experiment results. While the lattice constant is overestimated at about 2.4% and most elastic constants are underestimated at about 20% by the GGA method. Furthermore, when the applied deformation is larger than 2%, the nonlinear elastic effects should be considered. And with the Lagrangian strains up to 8%, taking into account the third-order terms in the energy expansion is sufficient. Except the original γ—surface generally used before (given by the first-principles calculations directly), the effective γ—surface proposed by Kamimura et al. derived from the original one is also used to study the Peierls stress. The research results show that when the intrinsic−stacking−fault energy (ISFE) is very low relative to the unstable−stacking−fault energy (USFE), the difference between the original γ—surface and the effective γ—surface is inapparent and there is nearly no difference between the results of Peierls stresses calculated from these two kinds of γ—surfaces. As a result, the original γ—surface can be directly used to study the core width and Peierls stress when the ratio of ISFE to the USFE is small. Since the negligence of the discrete effect and the contribution of strain energy to the dislocation energy, the Peierls stress given by the classical Peierls–Nabarro model is about one order of magnitude larger than that given by the improved Peierls–Nabarro model. The result of Peierls stress estimated by the improved Peierls–Nabarro model agrees well with the 2~3 GPa reported in the book of Solid State Physics edited by F. Seitz and D. Turnbull.

Four pioneers: Jany Thibault-Pénisson–Pierre Delavignette–Claude Goux–Jacques Lévy

In memory of four pioneers in the field of grain boundaries (GBs) and Interfaces, who recently expired: Jany Thibault-Penisson († 2011), Pierre Delavignette († 2011), Claude Goux († 2012) and Jacques Levy († 2012), I recall some of their major achievements. Jany Thibault-Penisson was a pioneer in the use of High Resolution Transmission Electron Microscopy. She studied dislocations in Germanium with Alain Bourret in Grenoble, then GBs in Ge and Si, their structures and their interactions with extrinsic dislocations under plastic deformation, and finally interfaces in metallic multilayers. Pierre Delavignette also was a marvellous electron microscopist who worked on dislocations in non-metallic multilayered structures with Severin Amelinckx in Mol (Belgium), and on GBs in hexagonal metals, for which he contributed to the extension of Ranganathan’s approach, together with George Bleris, Theodoros Karakostas, Gerard Nouet, Serge Hagege and others, in parallel with Hans Grimmer, David Warrington, Walter Bollmann, and Roland Bonnet. Claude Goux developed a school of processing, observation, and atomistic simulation of GBs in very pure metals, bringing to the Ecole des Mines of Saint-Etienne what he had learnt in Vitry under Georges Chaudron in the late 1950s. He also had a strong taste for modelling, and his impulse culminated with the 1975 Conference on GBs in Metals held in Saint-Etienne. Jacques Levy has been one of Goux’s first Ph.D. students. They probably made the first electron microscopic observations of high-angle GBs around 1966. Jacques Levy rapidly exerted to assume important positions and became, for instance, the Director of the Ecole des Mines of Paris. Despite all his responsibilities, he still attended IIB conferences many times.

Characterization of Threading Dislocations in Thin Germanium Layers by Defect Etching: Toward Chromium and HF-Free Solution

Defect etching is a fast and simple technique for the revelation of defects in single-crystalline materials. We propose here three different chemistries that allow accurate monitoring of the density of threading dislocations in germanium. This work especially focuses on solutions that have low etch rates and high selectivity in order to work on thin layers. Moreover, solutions that do not contain any carcinogenic nor HF acid are proposed in order to reduce the impact on environment and the risks for the user. A comparison of the etch rate and the selectivity toward defects is given as a function of the composition of the etching solutions (components and concentrations). A complete procedure for the proper determination of threading dislocation densities is also presented.

Stress and strain around grain-boundary dislocations measured by high-resolution electron microscopy

Stresses and strains around a dislocation at a grain boundary in germanium are measured by a combination of high-resolution electron microscopy and geometric phase analysis. The method is established by first measuring the strains around a matrix dislocation in silicon. Stresses are determined using linear elastic theory and bulk elastic constants. Strain measurements are shown to agree with theoretical calculations based on linear anisotropic elastic theory to 0.2% at a spatial resolution of 2–3 nm. A dislocation constricted at a coherent twin boundary in germanium is subsequently analyzed. The method is adapted to cope with the problem that the reference lattice is not identical for the whole field of view, due to the grain boundary. Strains are compared with theoretical calculations of a matrix dislocation in germanium. Whereas strains in the grains on either side of the twin boundary agree closely with the isolated dislocation case, significant additional strains are localized at the boundary plane. By comparing the stresses and strains across the boundary plane, values for the elastic modulus of the twin boundary are proposed. The significant reduction in elastic modulus for the boundary, when compared to bulk elastic constants, is interpreted in terms of the non-equilibrium configuration of the boundary. An extension of the method is proposed to measure more generally the elastic properties of grain boundaries and interfaces.

Photoconductivity at dislocations in germanium

The spectral photoresponse of a group of parallel 60°-dislocations in a thin plate of germanium is investigated by measurements of the photoccurrent along the dislocations and from the dislocations to the bulk. The experimental data are interpreted, using the results of a theoretical calculation of the dislocation core states and adding some important modifications to take care of our specific experimental conditions. A new model calculation of the potential around the dislocation is presented which, for the first time, takes into account the deformation potential of its strain field. This has significant consequences for electron transitions between the dislocation and the bulk and is essential for the understanding of the experimental results.

Charged Dislocations in Germanium

Charged Dislocations in Germanium

EBIC Experiments at Dislocations in Germanium

A new kind of EBIC contrast is observed at 60°-dislocations in thin slabs of germanium. Minority carriers are collected near one surface by the electrostatic potential of the dislocation and are carried along its conducting core to a contact on the opposite side. This experiment nicely demonstrates the existence of the dislocation potential as well as the conductivity of the dislocation core. A theoretical model of the effect which includes also enhanced recombination at the dislocation is developed and evaluated in a first-order approximation. The results reflect important features of the experimental contrast profiles. Further experimental and theoretical work is expected to provide better insight into the mechanisms of capture and recombination at dislocations. Ein neuartiger EBIC-Kontrast an 60°-Versetzungen wird in dünnen Germaniumscheiben beobachtet. Minoritätsträger werden in der Nähe der einen Oberfläche von der Versetzung gesammelt und durch den leitfähigen Versetzungskern zu einem Kontakt auf der gegenüberliegenden Seite transportiert. Das Experiment demonstriert gleichzeitig sowohl die Existenz eines Versetzungspotentials als auch die Leitfähigkeit des Versetzungskerns. Ein theoretisches Modell des Effektes wird entwickelt und in erster Näherung durchgerechnet. Die Ergebnisse geben wichtige Eigenschaften der gemessenen Kontrastprofile wieder. Von weiteren experimentellen und theoretischen Untersuchungen darf man ein besseres Verständnis der Einfang- und Rekombinationsmechanismen erwarten.

Photoluminescence and splitting of dislocations in germanium

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Electron states associated with 90°partial dislocations in germanium

The unreconstructed 90\ifmmode^\circ\else\textdegree\fi{} partial dislocations in germanium are examined by means of a linear combination of atomic orbitals electron Hamiltonian with ten Gaussian-type atomic orbitals for every atom, which for a perfect crystal yields accurate results for both the valence- and conduction-band states. A pair of alternate unreconstructed 90\ifmmode^\circ\else\textdegree\fi{} partial dislocations with corresponding stacking faults are incorporated via a supercell containing 256 atoms. When the bound electron states were evaluated, the translation symmetry both along the dislocation line and in the plane perpendicular to the dislocation line was exploited. A powerful mathematical approach for large sparse matrices makes it possible to treat this supercell, its size being large enough to decouple the interactions between neighboring dislocations. The deep energy levels in the gap and the resonant states were extracted with use of the Lanczos algorithm and a continued-fraction representation of the local density of states. Two defect bands for the 90\ifmmode^\circ\else\textdegree\fi{} partial dislocation in germanium were obtained. In the center of the one-dimensional Brillouin zone the two bands are widely split and are joined together at the zone boundary. The upper band is a resonant state near the center of the zone and becomes a bound state at the zone boundary. The lower band is a bound state over the entire zone.

The effect of high pressure gaseous He, Ar and N 2 on the photoconductivity of deformed Ge

In order to examine the effect of the penetration process of compressed gases on the electrical activity of dislocations, photoconductivity (PC) measurements were carried out on deformed and undeformed germanium samples at 200 K and at high pressures of helium, argon and nitrogen. The results show that dislocations allow the gases to diffuse into the crystal interior more easily. Argon atoms and nitrogen molecules penetrate into dislocations in germanium much less (if at all) than helium atoms. He atoms can be built into the dislocation core, thus changing the electrical activity of the dislocations and causing the reconstruction of some dislocation partials.

Dislocations in germanium: Effects of plasma hydrogenation

Dislocations in germanium: Effects of plasma hydrogenation

Core structure of the Lomer dislocation in germanium and silicon

Abstract The core structure of the Lomer dislocation has been determined by high-resolution transmission electron microscopy at the 2.5 A level. In addition to the Hornstra model without dangling bonds, a new core model containing one pair of atoms in a stacking-fault position is proposed. This form is stabilized either by a small amount of impurity in the core or by core reconstruction. It. is inferred from these observations that the Lomer-Cottrell lock is not the lowest energy state of a Lomer dislocation. From a comparison between experimentally deduced atomic positions around the core, and those calculated by elasticity theory, a 6 A core radius is determined.

On the correlation of constrictions with jogs in dissociated dislocations in germanium

Abstract By means of TEM-tilting experiments on foils of deformed Ge it is shown that in edge dislocations constrictions of the stacking fault are closely correlated with jogs. In particular, each jog higher than 5 A is connected with a constriction. Jogs are generally shorter than 25 A and have different signs. Plus/minus jog pairs appear twice as often as those of equal sign.

Elastic moduli, drag coefficients, and Keating's parameters in germanium

It is well known that phonon-phonon interactions produce a drag on moving dislocations in a solid. In the present work, the temperature dependence of the drag coefficients for edge and screw dislocations in germanium has been estimated at 800 and 1000 K. The Keating's-theory parameters have been evaluated as functions of temperature so as to explain the temperature dependence of third-order elastic moduli. The four parameters $\ensuremath{\gamma}$, $\ensuremath{\delta}$, $\ensuremath{\epsilon}$, and $\ensuremath{\zeta}$ have been estimated from the elastic constants ${c}_{11}$, ${c}_{12}$, ${c}_{111}$, ${c}_{112}$, and ${c}_{123}$ and the rest of the third-order elastic moduli have been predicted using the calculated temperature dependence of $\ensuremath{\gamma}$, $\ensuremath{\delta}$, $\ensuremath{\epsilon}$, and $\ensuremath{\zeta}$. Agreement with experimental results is satisfactory.

Electron states below the conduction band in Germanium originating from dissociated 60°‐dislocations

AbstractElectron states due to the strain field from dissociated 60°‐dislocations in Germanium are calculated using effective mass methods. The strain field is found to give rise to states with energies down to (Ec − 0.08) eV.

Quergleiten einzelner aufgespaltener versetzungen in germanium

Abstract Cross slip of single extended dislocations in germanium Isolated dislocation loops with a screw segment intersecting a (111) or a (541) surface have been introduced in dislocation-free germanium single crystals. The behaviour of the loops during annealing in the temperature range of 673-823 K and at low stresses of 0-4 N/mm2 were investigated both by the double-etch-pit method, and by X-ray topography with a double X-ray spectrometer. Two competing processes were observed : the shrinkage of the loops and the cross slip of the screw segments intersecting the surface. The velocity of shrinkage and the frequency of the cross slip were measured and the activation energies of both processes determined. The activation energy of cross slip is compared with theoretical calculations. Zusammenfass In versetzungsfreien Germaniumeinkristallen werden isolierte Versetzungsringe eingeführt, bei denen jeweils ein Schraubensegment eine (111) oder eine (541)-Oberfläche durchstösst. Das Verhalten dieser Ringe während einer Glühbehandlung im Temperaturbereich von 673-823 K und bei kleinen Spannungen 0-4 N/mm2 wird sowohl mit der Doppelätzmethode wie röntgentopographisch mit einem Doppel-kristallspektrometer untersucht. Zwei konkurrierende Prozesse werden dabei beobachtet: das Zusammenziehen der Versetzungsringe und ein Quergleiten der die Oberfläche durchstossenden Schraubensegmente. Die Geschwindigkeit des Schrumpfens und die Häufigkeit der Quergleitprozesse werden in Abhängigkeit von Temperatur und Spannung gemessen und die Aktivierungsenergien bestimmt. Die Aktivierungsenergie für das Quergleiten wird mit theoretischen Berechnungen verglichen.

On the mobility of dislocations in germanium and silicon

Abstract The motion of single dissociated dislocations in germanium and silicon has been studied directly in the electron microscope by moans of the weak-beam technique and utilizing a heating stage. The observations indicate that the dislocations glide in the dissociated configuration. Screws whose images appear as single peaks in 220 reflections with g220 parallel to the screw direction, have been shown to have cross-slipped from the (111) plane parallel to the plane of the specimen, to the steeply inclined (111) plane, on which they are dissociated. Contrast experiments and calculations show that the two partials can be resolved as sharp peaks with g202 at 60° to the screw direction.

Constrictions in the stacking faults of dislocations in germanium

Abstract Under suitable imaging conditions using the weak-beam method of electron microscopy, constrictions in the stacking faults of dislocations in Ge become clearly visible. After deformation at relatively low temperatures they occur at an average separation of 950 Å. In short segments they reduce the width of the stacking fault.

The optical absorption of 60° dislocations in germanium

Measurements of optical absorption suggest a two level model for the dislocation states. One of them is 0.1 eV below the conduction band edge, the other one 0.1 eV above the valence band edge. A dangling bond level does not appear directly in optical measurements. The reason is probably the poor overlapping of the dangling bond state with band states. The maximum electrostatic charging in the environment of the dislocation line is found to be much smaller than it is commonly assumed. Messungen der optischen Absorption lassen auf ein Zwei-Niveau-Modell der Versetzungs-zustande schliesen. Ein Zustand liegt 0,1 eV unterhalb der Leitungsbandkante, der andere 0,1 eV oberhalb der Valenzbandkante. Ein dangling-bond-Zustand wird bei optischen Meassungen direkt nicht gefunden, vermutlich, weil der dangling-bond-Zustand schlecht mit Bandzustanden uberlappt. Die grostmogliche elektrostatische Aufladung der Umgebung der Versetzungslinie ist nach diesen Messungen viel geringer als bisher angenommen wurde.