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

This 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.     

Ätzuntersuchungen an Alaunen mit nichtwäßrigen Lösungsmitteln. Will Kleber zum Gedenken

This paper presents investigations on etching of KAl-, NH₄Al-, KCr- and K(Al, Cr)-alum crystals. The etchant was a solution of tartaric acid in ethyl alcohol which produces well-defined etch pits on {111} faces. The correspondence of etch pits with dislocations was investigated by KAl-alum crystals. Between microscopic holes in the crystals and dislocations are not stated.     

Studies on twin boundaries in calcite crystals

Natural single crystals of calcite have been cleaved along (100) planes and cleavage faces have been etched in 2% and 3% citric acid solutions. Etching produces twin boundaries oriented in 〈010〉 directions. The etch pits on the two sides of the twin boundary are oppositely oriented. It has been conjectured that the rows of pits might have been formed due to etching of dislocations on twin boundaries. One to one correspondence of twin boundaries has been established on matched cleavage faces. This is further confirmed by studying the induced twin regions produced on a (100) cleavage plane by indenting that plane itself. The implications are discussed.     

Structural Etching of {001} and {110} Faces of Various AIIIBV Compounds

The present paper discusses the use of selective photoetching with H₃PO₄:H₂O₂ for characterizing various A^IIIB^V compounds and detecting misfit dislocations in transition layers. For GaP, the results obtained are compared with those realized with the use of an AB etchant for which suitable conditions for the structural etching of {001} material and the characterization of cleavage faces are given. The direction of the dislocation line is inferred from the shape and orientation of etch pits. The etch figures of different types of misfit dislocations are discussed.     

Causes of the formation of etch pits of different size and morphology on {100} faces of CsI crystals

Causes of the formation of dislocation etch pits of different shape and size on {100} faces of cesium iodide crystals by an etchant composed from 25–35 mg/1 CuCl₂ · 2 H₂O in 96% ethanol are studied. It is shown that one of the reasons of the change in the morphology of etch pits is the segregation of excessive iodine at dislocations.     

The Morphology of Hydrothermally Grown Plagioclase

Plagioclase crystals Ab₂₀An₀₀ and nearly pure anorthite were grown on the surface of artificial melts by hydrothermal treatment at 2 kb. The average crystal size was 0.002 to 0.008 mm. In the temperature range of 400° to 600°C a pseudohexagonal habit was observed for anorthite while a lath-like habit due to the prevalence of {010} was found for the Ab₂₀An₈₀ composition. Dominating faces are {010} {130} {110} {100} {110} {130} in the zone [001] and {021} {111} {111} {021} {111} {111} together with {001}.     

Growth Mechanism and Crystal Form of Potassium Dichromate

The structure of potassium dichromate (P-1, Z = 4) consists of two layers parallel to (001), between which no crystallographic symmetry relation exists. These layers are nearly coincident with each other when rotated through 90° about c*. One question remained unanswered: do the crystals grow parallel to {001} with d(002) or d(001) layers? The pseudo-fourfold axis does not run parallel to a crystallographic direction and acts only between two layers. This means that crystal growth parallel to {001} occurs in d(001) layers, which corresponds to the occurrence of one-sided intergrowths on (00-1). The layers are also nearly coincident with each other through pseudo-twofold axes parallel to [110] and [-110]. These axes do not act in the (100) or (010) projections. In the projections along the [110] and [-110] directions, the lattice directions are then extended by a factor of approximately 1.414, and the formula units in the cell of the d(002) layer are doubled. This indicates a further possible growth mechanism. The theoretical growth forms of the crystals were calculated with the Fourier transform method of morphology.     

Dislocations of salol crystals grown by the Czochralski method

Crystals of salol were grown by the Czochralski method in three different pulling directions to examine the crystallographic orientation effect of the seed. They were characterized by the etch pit method and X-ray projection topography. It was found that the dislocation density was 2 × 10³−1 × 10⁴/cm² and that the configuration of dislocations was straight. The running directions of dislocations strongly depend on the pulling directions; i.e., [11 0] and [1 10] for the crystal grown in [100] axis, [11 0], [1 10] and [110] for the crystal pulled along [112] axis and [010] for [010] axis crystal.     

Surface structures of fluorite crystals

Optical studies have been made of the microstructures on the natural {100} and {111} faces of natural fluorite crystals. The protrudance of triangular elevations, growth pyramids, and natural etch pits have been observed on a large number of crystals. It is suggested that fluorite crystals grown by two-dimensional spreading and piling of growth layers parallel to {100} faces. The natural etch pits on {100} and {111} faces suggest that they have been produced as a result of a dissolution process in nature. The natural faces have been etched in the laboratory and it is established that the pits indicate the existence of linear defects in the crystals. The implications are discussed.     

硫镓银晶体(112)面蚀坑形貌研究

本文报道了一种能在室温下对硫镓银晶体(112)面进行择优腐蚀的新腐蚀液配方,采用新腐蚀液对改进的Bridgman法生长的AgGaS2晶体进行腐蚀,用扫描电镜对蚀坑进行了观察,得到了清晰的(112)面蚀坑形貌,形状为三角锥形.初步解释了蚀坑的形成原因.AgGaS2晶体低指数的{100}面的腐蚀速度较慢,在腐蚀过程中逐渐显露出来,最终使晶体(112)面呈现出三角锥形蚀坑形貌.     

Basal and Non-Basal Slip in Anthracene Single Crystals

The role of basal and non-basal slip in the deformation of anthracene single crystals is considered in the light of published evidence and further work to establish their relative importance is described. Compression and shear tests on suitably orientated crystals show that the critical resolved shear stress for non-basal slip is at least ten times greater than that for basal slip. It is concluded that at room temperature slip generally takes place on the (001) [010] and (001) [110] systems and that the non-basal (201) [010], (100) [010], (100) [001], (010) [100] and (010) [001] systems suggested previously are only activated to any other extent under deformation conditions which severely limit basal slip.     

Defect Structure of Strained Heteroepitaxial In(1—x)Al(x)P Layers Deposited by MOVPE on (001) GaAs Substrates

Weak-beam, large angle convergent beam electron diffraction and high resolution transmission electron microscope experiments have revealed, that after strain relaxation due to plastic deformation dislocation networks can be observed in In_(1—x)Al_(x)P heteroepitaxial layers grown on (001) GaAs substrates under compressive stress. The 60° slip dislocations are mostly dissociated into partials of Shockley type whereas in the particular case of layers grown under tension twins are predominantly formed by successive nucleation and slip of 90° Shockley partials on adjacent {111} glide planes lying inclined to the (001) surface. When a few 90° Shockley partials pile up during extension of twins, then planar incoherent twin boundaries with {112} coincidence planes have been formed during strain relaxation. Due to the space group symmetry ((InAl)P belongs to the space group F4-3m) there is a striking asymmetry in defect formation, i.e. defect nucleation and slip on the planes (111) and (1-1-1) slip of the [1-10] zone are preferred to nucleation and slip on the {111} planes of the [110] zone. Apparently, the occupacy of the atomic sites in the dislocation core with either group-III or group-V atoms is responsible for this behaviour. The nature of the defects implies that their spontaneous nucleation should have taken place at the growing surface. Under tensile strain the 90° Shockley partial is nucleated first and the 30° one trails. Under compressive strain this sequence is reversed. It is evident, for dissociated dislocations lying at the interface always the 30° partial, i.e. the partial with less mobility or with higher friction force, is detained near or directly in the interface. Thus, in layers grown under tension the stacking fault associated with the dissociated 60° dislocation lies inside the GaAs substrate. For layers grown under compression it is located inside the ternary layer.     

Wet KOH etching of freestanding AlN single crystals

We investigated defect-selective wet chemical etching of freestanding aluminum nitride (AlN) single crystals and polished cuts in a molten NaOH–KOH eutectic at temperatures ranging from 240 to 400 °C. Due to the strong anisotropy of the AlN wurtzite structure, different AlN faces get etched at very different etching rates. On as-grown rhombohedral and prismatic facets, defect-related etching features could not be traced, as etching these facets was found to mainly emphasize features present already on the un-etched surface. On nitrogen polar basal planes, hexagonal pyramids/hillocks exceeding 100 μm in diameter may form within seconds of etching at 240 °C. They sometimes are arranged in lines and clusters, thus we attribute them to defects on the surface, presumably originating in the bulk material. On aluminum polar basal planes, the etch pit density which saturates after approx. 2–3 min of total etching time at 350 °C equals the density of a certain type of dislocations (presumably screw dislocations) threading the surface. Smaller etch pits form around annealed indentations, in the vicinity of some bigger etch pits after repeated etching, and sometimes also isolated on the surface area. Although alternate explanations exist, we attribute these etch pits to threading mixed and edge dislocations. This paper features etching parameters optimized for different planes and models on the formation of etching features especially on the polar faces. Finally, the issue of reliability and reproducibility of defect detection and evaluation by wet chemical etching is addressed.     

Dislocation etching of tin iodide single crystals

Single crystals of tin-iodide (SnI₂) have been grown using the controlled reaction between SnCl₂ and KI by diffusion process in gel medium. As grown (010) surfaces of the crystals have been optically studied. Characteristic etch pits have been observed on them. This suggests that SnI₂ crystals might go into dissolution in the acid-set gel. By successively etching (010) surfaces in a mixture of ammonia, acetic acid, and CdCl₂ solution, it is established that the pits indicate the site of dislocations in the crystals. This is further confirmed by comparing the etch patterns before and after chemically polishing (010) surfaces. The average dislocation density in the crystals have been evaluated and found to be 3.2 × 10³ cm⁻² and the implications are discussed.     

Kinetics of Etching of Dislocations in Ferroelectric Ammonium Hydrogen Tartrate Single Crystals

Ferroelectric crystals of Ammonium Hydrogen Tartrate (AHT) have been synthesised using the controlled reaction between NH₄Cl and (CHOHCOOH)₂ by diffusion process in silica gel medium. (010) cleavages of AHT crystals have been etched in 1.0 M and 1.5 M solutions of SrCl₂ solution. The lateral and normal velocities of the growth of pits were measured at different temperatures. The time dependence of the growth of the pit dimensions is found to be linear, whereas the temperature dependence of the growth of pits is found to be exponential, viz. \documentclass{article}\pagestyle{empty}\begin{document}$ \[V = A\,\exp \left({\frac{E}{{kT}}} \right)\] $\end{document}. The dissolution parameters, e.g. the activation energies and the pre-exponential factors for dissolution along the surface and along the dislocation lines have been computed. It is observed that the activation energy (E₁) of dissolution along [001] direction is found to be greater than the activation energy (E_b) along [100] direction and the implications are discussed.     

Etching Figures in Neodymium Gallate and Yttrium Aluminate Crystals

The dislocations existing in single crystals of neodymium gallate and yttrium aluminate grown by the Czochralski technique have been studied by means of etch pits. The data concerning their solubility in cases of different directions of a face orientation, various treatment temperatures and several enchant types are reported. The investigation of etch pits in the twinned YAlO₃ and NdGaO₃ crystals showed that twins are formed during a growth process. In the [110]‐pulled NdGaO₃ crystals the discrepancy between the twin and matrix parts of a crystal is accommodated by the dislocation congestion and the dislocation low‐angle boundaries whereas in [010]‐pulled YAlO₃ crystals the microcracks perform this function.     

Effect of Impurities on the Etching of Sodium Chloride Crystals

The results of a study of the effect of HgCl₂, ZnCl₂, PbCl₂ and CaCl₂ on the surface micro-morphology and kinetics of etching of {100} planes of NaCl crystals in methanol and ethanol are described and discussed. It was found that addition of an impurity to the solvent leads to the formation of contrasting dislocation etch pits, and that the overall dissolution rate in a solvent decreases with an increase in additive concentration. In the case of HgCl₂ impurity added to methanol terraced etch pits are observed, but their terracing behaviour diminishes with the increasing impurity concentration.     

Nature and origin of V-defects present in metalorganic vapor phase epitaxy-grown (InxAl1−x)N layers as a function of InN content,layer thickness and growth parameters

Our study of samples grown in different metalorganic chemical vapor deposition reactors and with different growth conditions reveals that V-pits are always present in (In_xAl_1?x)N films whatever the layer thickness and the InN content. V-pits are empty inverted pyramids terminating threading dislocations. InN-rich triangular regions are present around the threading dislocations terminated by pits with a hexagonal 6-fold symmetry distribution in {11?20} planes. The nature of the facets of the V-pits depends on the growth conditions: pits with either {11?2l}, l being between 1 and 3, or {1?101} facets have been observed. Moreover, the nature of the threading dislocations terminated by pits also depends on the growth conditions. Our observations suggest that with a high V/III ratio only edge a+c-type dislocations are terminated by pits whereas with a low V/III ratio both edge a-type and mixed a+c-type dislocations are terminated by pits.     

Dislocation studies by chemical etching on solution-grown NaSbF4 and Na3Sb4F15 single crystals

An attempt has been made to study the etch pit dislocations of isolated as well as matched pairs of cleavage planes of solution grown NaSbF₄ and Na₃Sb₄F₁₅ single crystals when etched with analar grade methyl alcohol and ethyl alcohol. On etching of cleavage faces the pits nucleate at the intersection sites of dislocations with the cleavage face. On successive etching of a cleavage face, arrays of triangular shape etch pits are observed. After prolonged etching some of the etch pits disappear. These pits are curved and terminated indicating that they are crystallographically non-oriented. One-to-one correspondence with respect to number, shape, position and structure of the pits has been established by etching of a matched cleavage face. The etch pit densities of both NaSbF₄ and Na₃Sb₄F₁₅ crystals are found to be 10³ per cm².     

Stacking faults in deformed zinc and magnesium single crystals

Using the transmission electron microscopy dissociated dislocations containing stacking faults were observed in Mg single crystals, deformed in (0001) <1120> slip system, and in Zn single crystals deformed in {1122} <1123> slip system. The overlapping flat stacking faults lying in {1102} planes and dissociated triple nodes in (0001) planes are observed in Mg. In Zn flat stacking faults are found in {112 2} planes. The value of stacking fault energy γ has been determined in Mg crystals (γ ⋍ 10 erg/cm²). Such a low value of γ is attributed to the segregation of impurities on dislocations.