Dislocation Etch Pits Research Articles

Penetration of Surface Damage Resulting from Abrasion and Heating of MgO Crystals

Chemical polishing and dislocation etch pit observations have been applied to the study of the depth of penetration of dislocations produced by abrading (100) surfaces of MgO. From the results it has been concluded that such dislocations penetrate from 100 to 700 μm depending on the source of the material. Heating of the abraded samples for short times up to 1300°C has little influence on the depth of penetration.

Eccentricity of hexagonal dislocation etch pits

Dislocation etch pits with hexagonal outlines are revealed on calcite cleavages which have been etched with glacial acetic acid. The pits are symmetric with respect to the [110] direction, but their depth points do not coincide with the geometrical centres of planar etch pits and thus they are eccentric. For hexagonal etch pits the shifts and eccentricities lie along the [110] direction, unlike rhombic etch pits where the eccentricity lies along the [ 110 ] direction. The eccentricity in the hexagonal etch pits is explained on the basis of lateral reaction rates which are dependent on the concentration of the etchant.

Cleavage Steps from Screw Dislocations of Inclusion-Growth Spiral Pairs in Stearic Acid Crystal

The existence and structure of screw dislocations along the long-chain axis were examined by a careful cleavage technique, in order to characterize the inclusion-growth spiral pairs in stearic acid crystals grown from solution. First, the correspondence between various kinds of dislocation etch pits and the originating centers of cleavage steps on the basal {001} planes was confirmed. Then the cleavage step structures were observed with a reflective Nomarski interference microscope on planes which were created by cutting the crystal between the growth spiral steps and the inclusions. The features of the originating points and the geometrical step structures of the cleavage steps are discussed in relation to the morphological characteristics of the inclusion-growth spiral pairs. As a result, the existence of screw dislocations in the inclusion-growth spiral pairs was clearly confirmed.

Optical and X‐ray Topographic Studies of Barium Fluoride Single Crystals

AbstractSingle crystals of synthetic barium fluoride have been cleaved along {111} planes and the freshly cleaved faces have been etched in (1 : 250) concentration of nitric acid solution. One to one correspondence of dislocation etch pits have been observed on matched pairs. The same crystal has been investigated using X‐ray topographic technique. By selecting 0222 and 0222 reflections and MoKα1 radiation, stereopair projection topographs have been obtained and critically compared with the optical micrograph. One‐to‐one correspondence between dislocation out crop images and dislccation etch pits have been established. Due to dislocation contrast, the outcrop of dislocation images have been observed with the associated dislocation etch pits. The orientation of the Burgers vectors of the dislocation lines have been identified using AgKα1 radiation with 1111, 1111 and 1111 reflections and the implications have been discussed.

X‐ray topographic investigation of growth defects in natural calcium fluoride crystals

AbstractCalcium fluoride crystals have been cleaved along {111} faces and the freshly cleaved faces have been chemically etched in 2.6 N nitric acid solution. The etched faces have been optically studied. One‐to‐one correspondence of dislocation etch pits have been established on the matched cleavage faces and on the opposite sides of thin flakes. The same crystal has been studied using X‐ray topographic technique. By using 022‐ and 022 reflections, stereopair projection topographs were studied and compared with the optical micrographs. The close resemblance between dislocation etch pits and dislocation out‐crop images has been established. The orientation of the Burgers vectors of the dislocation lines has been identified using AgKα radiation with 111‐, 111‐ and 111 reflections. It has been confirmed that Burgers vectors of dislocation lines lie parallel to 〈110〉 directions. The implications are discussed.

急冷Cu結晶(111)面におけるエッチビークの形成について

The (111) surfaces of copper crystals rapidly-cooled from 1273 K in a purified Ar atmosphere were etched in three kinds of dislocation etchants, and the etch patterns were studied by means of optical and electron microscopies. From the replica examinations with an optical microscope dark and deep etch pits with beaks were found in addition to the normal dislocation etch pits. Their densities amounted to 107–108 m−2, two orders of magnitude less than those of the normal ones. When the crystal was etched for a long period, the etch pits with beaks gradually changed from sharply-pointed and deep ones to flat-bottomed and shallow ones, and finally disappeared, while small ones newly appeared at some other places. It is noted that such etch pits cannot be observed in copper crystals slowly-cooled from the same temperature in Ar atmosphere. Detailed observations of the replicas with an electron microscope revealed that the beaks extended into the inside of the crystal from the apex of the etch pits along the oblique [110] (otherwise [101] or [011]) direction though details of their shapes varied with changing etching solution. Defect ribbons with a some-what complicated structure were observed in thin films obtained from the rapidly-cooled copper crystal, which might presumably be associated with the etch beaks.

Etch‐ and Transmission Electron Microscope Investigations of Microdefects in (001) LEC‐GaP Substrates

AbstractThe etch pattern of (001) and (110) LEC‐GaP doped with sulphur (NDNA in the range from 3–7 × 1017 cm−3) do not only show dislocation etch pits but fine pits, so‐called “saucer pits” (S‐pits). The distribution of S‐pits, their etching behaviour and transmission electron microscope observations of etched samples indicated a clear correlation between S‐pits and microdefects (fauted‐, prismatic dislocation loops and precipitates).

Eccentricity of rhombohedral dislocation etch pits

Rhombohedral dislocation etch pits were observed on calcite cleavages etched by glacial acetic acid under static and dynamic conditions. A lack of coincidence between the depth points and the geometrical centres of the planar etch pits results in eccentric etch pits. The eccentricities of the dislocation etch pits are not the same on matched faces etched with the same concentration of glacial acetic acid under static or dynamic conditions. This phenomenon is explained.

Dark current and breakdown characteristics of dislocation-free InP photodiodes

The reverse I-V characteristics of InP p-n junction mesa photodiodes carefully fabricated to contain only a small number of dislocation etch pits were studied and compared. The results show that I varies with V approximately as expected for defect-free junctions only when the mesas contain no visible etch pits.

STUDY OF DISLOCATION ETCH PITS ON PbFe<sub>12</sub>O<sub>19</sub> SINGLE CRYSTALS

Using 50% HCI as etchant, we studied the morphology of dislocation etch pits on cleavaged (0001) basal faces of PbFe12O19 single crystals grown by the fluxed method. Three kinds of etch pits are found and two of them correspond to {1010} and {1011} types of dislocations, respectively. The third kind of etch pits is related to the presence of screw dislocations which are responsible for growth mechanism. Dislocation etch pits arrays observed on (0001) faces are interpreted by applying the mechanism proposed by Matthews et al.

Shape of thermal etch pits and crystal structure in tellurium crystals

AbstractDuring the systematic study of thermal etching of tellurium crystals, various shaped thermal etch pits were observed on the {1010} cleavage faces of this crystal. An attempt has been made to explain the shape of non‐dislocation and dislocation etch pits. A simple model based on crystal structure and bonding of atoms has been suggested to explain the shape of etch pits.

Mechanism of dissolution of MgO crystals in acids

A simple model of dissolution of MgO crystals in acids involving chemical reactions and adsorption process on the crystal surface is used to derive expressions connecting rates of surface dissolution and selective etching with concentration, temperature and nature of an acid and with surface orientation. The experimental data of the dependence of etch rates of MgO on various etching parameters are then compared with the theory. The effect of acid viscosity and concentration are also briefly analysed and compared with the experimental observations. It is argued that the experimental results can be understood on the basis of the proposed mechanism if adsorption of the reactants and the complexes formed during dissolution on a perfect surface and at dislocation sites is taken into consideration. It is concluded that the adsorption processes play an important role in the formation of good, contrasting dislocation etch pits.

Etching of CaF2 single crystals in silica gels

AbstractEtching of {111} cleavage faces of CaF2 crystals in aqueous solution of 50% HCl is carried out in citric acid set silica gel, and the kinetics of growth of etch pits at the sites of dislocations is investigated as a function of temperature, time of etching and height of gel column above the crystal surface. It is observed that the transient period required to initiate etch pit at the sites of a dislocation decreases (1) at particular temperature, with a decrease in gel height, and (2) for a particular gel height, with an increase in the temperature of etching. It is also observed that the morphology of dislocation etch pits remains triangular irrespective of the gel height and the temperature of etching. The results are compared with those of solution etching and discussed.

Dislocation etch pits in LPE-grown Pb1−xSnxTe (LTT) heterostructures

Heterostructures of Pb1−xSnxTe grown by LPE were studied by an etch technique. A consistent pattern appeared in which the lattice-mismatched heterostructure exhibits a high etch-pit density (?1×107 cm−2) at the interface and in the heteroepitaxial layer. The greater the lattice mismatch, the higher is the defect density. A mismatch as small as ∼2×10−4 is already sufficient to generate defects at the interface. A low-etch-pit-density substrate does not moderate the defect performance in the interface and the epilayer. Homostructures show preservation of dislocation etch-pit density throughout the whole thickness of the epilayer without a substantial decrease, contrary to other reported results. Some differences were found with respect to the opposite heterostructures Pb1−xSnxTe/Pb1−ySnyTe and Pb1−ySnyTe/Pb1−xSnxTe. A high growth temperature (?600 °C) causes a decrease in etch-pit density and the disappearance of some defects. Enhanced nucleation, annealing of dislocations, and bulk diffusion are believed to take place at the high temperature. Some defects disappear and others diminish upon slow cooling, but the basic mismatch character remains.

ChemInform Abstract: DEFECT ETCH FOR <100> SILICON EVALUATION

AbstractZur Bestimmung der Versetzungs‐ dichte in (100)‐Si wird verbreitet das Ätzverfahren nach Secco mit 2 (HF) : 1 (0.1 5 M K2Cr2O7) unter Ultraschallverwirbelung angewendet.

Liquid phase epitaxial growth of InAs1-xSbx on GaSb

Reported here, for the first time, is the lattice matched growth of InAs1-xSbx on GaSb. The thermodynamic incompatibility of the system, i.e., the strong tendency for the In-As-Sb liquid to dissolve the GaSb substrate, was solved via a novel liquid phase epitaxial growth technique. Liquid compositions for lattice matching conditions have been determined in the 400-600°C range. Epitaxial growth has been examined for (100), (111)B and (111)A orientations. Dislocation etch pit densities for lattice matched, and near lattice matched conditions are shown to be less than 104-cm−2 and 105-cm−4, respectively. The composition of the epitaxial layers are determined by the Gandolfi X-ray diffraction technique and compositional homogeneity has been confirmed by SEM X-ray analysis. Some material related device properties which demonstrate the reproducibility of the growth technique are presented.

Defect Etch for Silicon Evaluation

The Secco etch, with ultrasonic agitation, is widely used to determine dislocation densities in <100> Si. Experiments have shown that under certain conditions, the cavitation of the ultrasonics can generate anomalous defect etch pits. A new defect etch formulation was developed for evaluating <100> Si ingot material which does not require ultrasonic agitation. It consists of . The etching time compared to Secco etch with ultrasonics is reduced by one‐half in developing etch pits of equivalent size. This composition is useful for revealing dislocations in 0.6–15 Ωcm n‐ and p‐type silicon. In addition, dislocation etch pits are readily developed in more heavily doped <100> Si crystals using a mixture of.

H3PO4 — etching of {001}‐faces of InP, (GaIn)P, GaP, and Ga(AsP)

AbstractThis paper shows that hot H3PO4 is a suitable etchant for the production of dislocation etch pits on {001}‐InP, (InGa)P, GaP, Ga(AsP), and {111}‐GaP. The effects upon etch pit morphology of the misorientation of samples and the type of dislocations are investigated in detail.

Etch pit morphology and calcium sulphate growth on {111} faces of calcium fluoride crystals etched in sulphuric acid

AbstractAn investigation of the etching behaviour of cleaved octahedral faces of calcium fluoride crystals in sulphuric acid of different concentrations and at various temperatures is carried out. It is observed that the morphology of dislocation etch pits depends on the temperature and concentration of the acid. With an increase in the acid concentration, growth of whiskers, elongated platelets, hexagonal and dice‐shaped elevations, spherulites and sheaves is observed. Temperature of the etchant also has an effect on their formation. By X‐ray diffraction techniques, the compounds forming the whiskers and elongated platelets, and hexagonal and dice‐shaped features are identified as CaSO4 · 2 H2O and CaSO4, respectively. The mechanism of the growth of CaSO4 · 2 H2O and CaSO4 and the change in the morphology of selective etch pit are discussed.

DETERMINATION OF SLIP PLANES IN CdxHg(1-x)Te BY ETCHING OF DISLOCATIONS INTRODUCED BY MICROHARDNESS INDENTATIONS

The importance of CdxHg(1-x)Te (CMT) for intra-red detector applications has stimulated interest in the mechanical and electrical properties of this material. Whereas considerable effort has been employed in the study of the electrical properties of this material, very little information has been published on the mechanical properties and, in particular, the slip system and dislocation properties. Most reported dislocation etches for CMT only reveal dislocation etch-pits within about 20° of the {111} orientation. A dislocation etchant which reveals dislocations on all orientations has been reported for HgTe, and it has been shown in our laboratories that this is effective also on most low index planes of CMT. Dislocation rosettes introduced at room temperature by Vickers microhardness indentation have been studied using the above etchant on two differently oriented faces. It is concluded that the operative slip planes are {111}. These studies are discussed and compared with reported work on CdTe.