Dislocation Rosettes Research Articles

The Sensitivity of Dislocation Rosettes to the Shape of a Berkovich Indenter on LiF and MgO Crystals

The peculiar effect observed under the indentation of the (001) plane of LiF and MgO single crystals, namely, the sensitivity of the form of dislocation rosettes to the shape of the indenter, is considered. It is shown that the dislocation rosettes being formed around Vickers indentations are symmetrical, while the rosettes around Berkovich indentations are asymmetrical, the edge arms of the dislocation rosettes are different with respect to their length, and the screw arms do not demonstrate such asymmetry. Also, an orientational effect is found under the penetration of a Berkovich indenter, thus, the form of the dislocation rosettes and length of the edge arms change at varying the orientation of the indenter relative to the crystallographic directions of the sample. It is also shown that the asymmetry of the dislocation rosettes is more pronounced on harder crystals and increases with the growth in the load on the indenter. The factors responsible for the anomaly in the development of the dislocation rosettes under nano- and microindentation of the (001) plane of cubic crystals by a Berkovich indenter are found.

Чувствительность дислокационных розеток к форме индентора Берковича на кристаллах LiF и MgO

A peculiar effect, namely, the sensitivity of the shape of dislocation rosettes to the indenter type under indentation of the (001) face of LiF and MgO single crystals has been revealed. It was shown that the dislocation rosettes forming around the Vickers indenter are symmetrical, while the rosettes around the Berkovich one are asymmetric, the edge beams of the dislocation rosettes vary in length, and the screw ones do not show such asymmetry. An orientation effect was found during the penetration of the Berkovich indenter: the shape of the dislocation rosettes and the length of the edge beams change with a change in the orientation of the indenter relative to the crystallographic directions of the sample. It was also shown that the asymmetry of dislocation rosettes is more visible on harder crystals and increases with load growth on the indenter. The factors responsible for the anomaly in the development of dislocation rosettes under indentation in nano and micro scale by the Berkovich indenter of the (001) plane of cubic crystals are established

Estimations of Low Temperature Dislocation Mobility in GaN

The size of dislocation rosettes introduced by indentation in the temperature range from 300 to 773 K are studied. The dislocation velocity and its temperature dependence are estimated. It is shown that the activation energy of dislocation movement at temperatures lower than 773 K does not exceed 1 eV.

Study on the local stress induced dislocations on [formula omitted] Te face of CdTe-based crystals

The rosette-like dislocation clusters around Te inclusions in as-grown CdZnTe/CdTe crystals and those introduced by the micro-indentation on CdZnTe/CdTe surface are studied experimentally. The extended dislocation patterns are formed around Te inclusions in both CdZnTe and CdTe crystals, owing to the build-in stress. Two mutually orthogonal tetrahedrons are observed in CdZnTe crystal. However, the “double-arms” dislocation rosette pattern extended along 〈110〉 direction is observed in CdTe crystal. The Peierls kink pair mechanism and the Hirsch effects are used to explain the discrepancy of these two different rosette patterns. Similar dislocation rosette patterns are observed on indentation surface of CdZnTe crystal. The dislocation rosette patterns are found to be independent of the indenter orientation, but completely determined by the crystallographic properties of zinc-blende structure of the crystal. Furthermore, the Te(g) and Cd(g) dislocation arms are found to be mixed and bended with each other in CdTe crystal under high indentation stress, making it different from that generated around Te inclusions. A model concerning the comprehensive impact of stress field and electronic polarities dislocations is proposed to clarify the dislocation bending phenomenon.

Indentation-introduced dislocation rosettes and their effects on the carrier transport properties of CdZnTe crystal

Herein, we study the crystallographic configuration of rosette-like dislocation clusters introduced by indentation in CdZnTe (CZT) crystal and the effects of the dislocations on the carrier transport process. The Vickers hardness test was used to generate dislocations artificially on the () Te face of the CZT crystal at room temperature. Etch pit density (EPD) revealed by Everson etchant showed that the dislocation density increased from 4.9 × 104 cm−2 to a concentration too high to be evaluated after the indentation. A model was proposed to explain the rosette-like dislocation clusters. It was verified that the tetrahedron with small size and high EPD belonged to Te(g) dislocations on the () Te face. The hexagon-like distribution of pile-ups formed during the indentation was determined by the zinc-blende structure of CZT, rather than the direction of the indenter. The dislocation pile-up during propagation was observed and analyzed based on the rule proposed by Lomer and Cottrell. The ion beam induced charge (IBIC) measurements showed low carrier collection efficiency (CCE) in the dislocation generation areas, which confirms that the dislocations and related defects can significantly degrade the CCE of a CZT detector. Measurements of low temperature photo-luminescence (PL) showed that the emission peak located at 1.485 eV highly increased in the indentation area and was responsible for the performance degradation of the detectors.

Dislocation formation in seeds for quasi-monocrystalline silicon for solar cells

An investigation of two industrially cast quasi-monocrystalline silicon blocks revealed a high dislocation density originating at intersections between the seed crystals. This may be ascribed to three different generation mechanisms. Firstly, a dislocation cell structure was observed in the seed crystals, probably as an effect of poor surface preparation of the seeds. Furthermore, clusters of dislocations form around contact points in the interface between two neighbouring seeds. At contact points, the two monocrystalline silicon seeds plastically deform and sinter together. Dislocation rosettes form as a result of an indentation mechanism at high temperatures. A third mechanism acts at the bottom surface, where dislocation clusters also form by indentation of contact points between the seed and the crucible. Since dislocations forming in the seeds will continue into the growing ingot, it is crucial to depress the dislocation formation in the seeds.

Electrostimulation of the magnetoplastic effect in LiF crystals by an “internal” electric field induced during indentation

Indented LiF crystals demonstrate a change in the length of the dislocation rosette rays during their exposure to jointly acting dc magnetic and electric fields. It is shown that magnetic field with induction B = 1 T causes the electrostimulation or electrosuppression depending on the magnitude and direction of the external electric field with respect to the “internal” electric field induced by the charge transfer due to dislocations moving during the indentation.

Nanoindentation-Induced Pop-In Effects in GaN Thin Films

The nanoindentation-induced pop-in phenomena in GaN thin film are investigated using Berkovich indenters. The formation of dislocation rosettes revealed by cathodoluminescence (CL) spectroscopy is found to closely relate with the pop-in effect displayed in depth-sensitive measurements. Namely, the CL images of the indented spots show well-defined rosette structures consistent with the hexagonal symmetry of GaN, indicating that the distribution of deformation-induced extended defects/dislocations may dramatically affect the CL emission. The use of CL thus may provide an alternative means for studying the near-surface plasticity in other semiconductor thin films, as well.

The Nanometer Scaled Defects Induces with the Dislocation Motion in II-VI Insulated Semiconductors

Dislocation-related defects induced by dislocation motion in p-CdTe were studied. Generation of “fresh” dislocations from the indented point of the CdTe (100), (110), and (111) surfaces at room temperatures was visualized by the chemical etching and low temperature photoluminescence in a mapping regime. The crystallographic orientation of the dislocation rosettes of macroscopic plastic deformation lines was analyzed on the (100), (110), and (111) surfaces.

Dislocations and cracks at Vickers indentations in GaN and GaAs bulk crystals

AbstractThe (0001) surface of GaN single crystals and ($ \bar 1 \bar 1 \bar 1 $)‐oriented GaAs wafers have been deformed using a Vickers indenter with two different orientations at room temperature. Dislocations and cracks at the indentations were observed by means of scanning electron microscopy, cathodoluminescence, light microscopy and transmission electron microscopy. Between dislocations, cracks and the orientation of the indenter, geometrical relations could be found.The GaN and GaAs samples were indented with loads in the range of 0.02 N to 4.90 N and 0.02 N to 1.00 N, respectively. In both materials, the dislocation rosettes correspond to the symmetry of the indented surface. In (0001) GaN, the crack system is predominantly determined by the symmetry and orientation of the indenter. In contrast, the crack formation in ($ \bar 1 \bar 1 \bar 1 $) GaAs is determined by the symmetry of the crystal and consists of different types of radial cracks with different probabilities. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

10.1007/s11451-008-2006-z

The micromechanical properties of Te-doped GaAs single crystals with free carrier density n 0 = 1017−5 × 1018 cm−3 were studied. The obtained data are as follows: the nonmonotonic concentration dependences of the microhardness, the lengths of dislocation rosette rays, the densities of dislocations, and the position and half-width of the Raman line of a transverse optical phonon. The data are interpreted in terms of spatial correlation in the impurity defect distribution.

Anisotropy of crack and dislocation formation in GaAs

AbstractThe dependence of cracking at Vickers indentations in (100) GaAs was investigated for different dopings by electron microscopy. Depending on the load, the formation of cracks was studied. In semiinsulating carbon‐doped GaAs, a clear anisotropy in the cracking pattern exists with cracks running preferentially along the ± [011] directions. In contrast, in n‐type as well as in p‐type GaAs little or no anisotropic crack pattern can be recognized. The formation and propagation of cracks does not correlate with the formation of the dislocation rosette. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Anomalous dissolution of microindentation deformed zone of ITO/Si coated system

AbstractThe joint effect of a film and a substrate on the modification of the mechanical properties of an ITO/Si coated system (CS), a promising material for solar cells, and its response to an external load in comparison with the Si substrate were considered. An unusual combination of a pronounced crack formation and a plastic character of indenter–sample contact zone was revealed. This feature was accounted for a high brittleness of the Si substrate and the enhanced plasticity of the ITO film that improves the mechanical characteristics of the whole ITO/Si structure, which is useful for its operation. Another unexpected result, the anomalous etching (dissolution) of the ITO film near the indentations, was found out when the ITO/Si CS was subjected to an aggressive medium. A preferable dissolution of the ITO film was detected in the deformed zone near the indentation (Df), commensurable with the dimension of the substrate elastic/plastic dislocation free zone which was two or three times larger than the indentation diagonal (d) and approximately ten times larger than the dislocation rosette around indentation on the Si support. An assumption was made that the effect is basically determined by high internal stresses in this zone and, hence, by weaker atomic bonds as compared with the undeformed part of the material. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Study on the indentation size effect in CaF 2: Dislocation structure and hardness

In this study nanoindentations have been performed on a cleaved surface of a CaF 2 single crystal and the dislocation structure has been investigated by the etch pit technique using atomic force microscopy. The deformation during indentation is first purely elastic until dislocations are created observable in a pop-in in the load displacement data, as well as in a dislocation rosette around the indentation. After pop-in a relatively high hardness is observed, which gradually decreases, until at 3 μm a nearly constant hardness is found. By using sequential polishing, etching and imaging, the dislocation structure underneath indentations with indentation depths of 300 nm and 110 nm (load: 5 mN, 1 mN) is quantified. The dislocation density and radial distribution of dislocation density depend on the indentation depth, where a smaller indentation depth leads to a higher dislocation density, which is in qualitative agreement with the observed increase in hardness.

Swift-ion-induced hardening and reduction of dislocation mobility in LiF crystals

Ion-induced change in Vickers hardness and arm length of dislocation rosettes created by indentation on the (1 0 0) face of LiF crystals was studied. The irradiations were performed using swift U, Bi and Ni ions with a specific energy of 11 MeV per nucleon at fluences between 106 and 1013 ions cm−2. Remarkable effects of the ion-induced hardening and reduction of dislocation arm length were observed above the threshold fluences of about 109–1010 ions cm−2 and 106–107 ions cm−2, respectively. The products of track core damage and aggregates of single defects in the halo of overlapping tracks are responsible for the effects. The results are analysed using the Orowan's model of dislocation impeding by strong obstacles. The advantages of the dislocation mobility method for the diagnostics of track damage at low-fluence irradiations are demonstrated.

Effect of correlation in the impurity defect distribution on the micromechanical properties of GaAs: Te single crystals

The micromechanical properties of Te-doped GaAs single crystals with free carrier density n0 = 1017−5 × 1018 cm−3 were studied. The obtained data are as follows: the nonmonotonic concentration dependences of the microhardness, the lengths of dislocation rosette rays, the densities of dislocations, and the position and half-width of the Raman line of a transverse optical phonon. The data are interpreted in terms of spatial correlation in the impurity defect distribution.

Effect of the surface energy state on the dynamics of dislocations in ionic crystals

The effect of the surface state and boundary physicochemical conditions on the starting stresses and dynamics of near-surface dislocations in lithium fluoride and sodium chloride crystals has been investigated by the method of prick dislocation rosettes arising in alkali halide single crystals upon microindentation. It has been shown that crystals with ionic bonds are characterized by a surface energy (potential) barrier that hinders the movement of near-surface dislocations and influences their starting stresses in crystal lattices.

Mechanical properties of undoped GaAs. III: Indentation experiments

Two types of microindentation experiments, “conventional static” as well as “dynamic displacement-sensitive” tests, have been performed on the (0 0 1) surface of GaAs over a range of temperatures. The temperature dependence of hardness has been measured and, from the disappearance of indentation cracks and the measured energy density at different temperatures, the indentation brittle-to-ductile transition temperature T IBDT has been determined. Comparison of the latter with the conventional brittle-to-ductile transition temperature T BDT by the four-point bend technique indicates that T IBDT is nearly 100 °C lower than T BDT. It is argued that this lowering is because of the superimposed hydrostatic component in an indentation test. The microstructure of the plastic zone around the indentation sites has also been investigated by transmission electron microcopy. Based on the observations, the asymmetry of the dislocation rosettes and indentation cracks is discussed in terms of different mobilities of α and β dislocations in GaAs. Finally, the indentation results are compared with data from compression experiments and 4-point bend tests.

Microstructure studies of the grinding damage in monocrystalline silicon wafers

Abstract The depth and nature of the subsurface damage in a silicon wafer will limit the performance of IC components. Damage microstructures of the silicon wafers ground by the #325, #600, and #2000 grinding wheels was analyzed. The results show that many microcracks, fractures, and dislocation rosettes appear in the surface and subsurface of the wafer ground by the #325 grinding wheel. No obvious microstructure change exists. The amorphous layer with a thickness of about 100 nm, microcracks, high density dislocations, and polycrystalline silicon are observed in the subsurface of the wafer ground by the #600 grinding wheel. For the wafer ground by the #2000 grinding wheel, an amorphous layer of about 30 nm thickness, a polycrystalline silicon layer, a few dislocations, and an elastic deformation layer exist. In general, with the decrease in grit size, the material removal mode changes from micro-fracture mode to ductile mode gradually.

Mechanical properties of InAs/InP semiconductor alloys

The microindentation studies have been reported for undoped and doped InAs/InP semiconductor alloys grown by metal organic vapor phase epitaxy (MOVPE). It was found that the microhardness value increases with increase of applied load and attains a constant value for further increase in the load. The mechanical properties like, fracture toughness, brittleness index, fracture surface energy and indentation size effect coefficient were determined using the microhardness value. The indented samples were etched in H 2SO 4:H 2O 2:H 2O of the ratio of (1:1:1) for 30 s. This reveals the dislocation rosette patterns generated around the edges of the indentation on subsequent etching process.