Dislocation Etch Research Articles

Tailoring the defects and resistivity in CdZnTe single crystal via one-step annealing with CdTe compound

Defects deteriorate the optical and electronic properties of the cadmium zinc telluride (CZT) single crystal. However, the growth of defects, such as vacancies and precipitation, could not be avoided in the industrial-grade preparation of CZT single crystal. Therefore, it is crucial to explore ways to eliminate defects after growth. This paper employs one-step heat treatment with the CdTe compound as an annealing atmosphere source. After annealing, some large-size Te inclusions are eliminated in CZT crystal, but nano Te precipitates still exist. At the same time, the crystal surface becomes rougher, caused by the thermal migration of Te droplets, dislocation proliferation, and aggregation. Increasing annealing time, dislocations migrate, decompose, and interact with each other to form dislocation walls, stacking faults or terminating at the surface, reducing dislocation etch pit density. In addition, a large number of ordered phases are still found in the crystal. Single annealing with CdTe significantly improved the crystal's optical and electrical properties. After 180 h annealing, the infrared (IR) transmittance of the as-grown wafer increased from 40% to 65%, and resistivity increased from 2.2 × 109 Ω cm to 1.7 × 1011 Ω cm. Compared to reducing the Te precipitation phase, these increasements were mainly dominated by replacing point defects, like Cd vacancies.

Characterization of dislocation etch pits by molten KOH etching in n- and p-type 4H–SiC epilayers doped by ion implantation

Dislocation etch pits by molten KOH etching in 4H–SiC epilayers doped by ion implantation have been characterized in this work. The sizes and shapes of dislocation etch pits are studied in an implanted nitrogen concentration range from 2 × 1019 cm−3 to 4 × 1019 cm−3 and an implanted aluminum concentration range from 1 × 1018 cm−3 to 1 × 1019 cm−3. It has been found that the etch rates at dislocations follow a trend of n+ < n− < p− ≈ p + while in all samples the threading dislocation etch pits show the anisotropic etching characteristic of hexagonal shape. Characteristics of dislocation etch pits in n + -4H–SiC samples are analyzed based on the effect of preferential N occupation at dislocations.

Luminescence Characteristics of the MOCVD GaN Structures with Chemically Etched Surfaces.

Gallium nitride is a wide-direct-bandgap semiconductor suitable for the creation of modern optoelectronic devices and radiation tolerant detectors. However, formation of dislocations is inevitable in MOCVD GaN materials. Dislocations serve as accumulators of point defects within space charge regions covering cores of dislocations. Space charge regions also may act as local volumes of enhanced non-radiative recombination, deteriorating the photoluminescence efficiency. Surface etching has appeared to be an efficient means to increase the photoluminescence yield from MOCVD GaN materials. This work aimed to improve the scintillation characteristics of MOCVD GaN by a wet etching method. An additional blue photo-luminescence (B-PL) band peaking at 2.7-2.9 eV and related to dislocations was discovered. This B-PL band intensity appeared to be dependent on wet etching exposure. The intensity of the B-PL was considerably enhanced when recorded at rather low temperatures. This finding resembles PL thermal quenching of B-PL centers. The mechanisms of scintillation intensity and spectrum variations were examined by coordinating the complementary photo-ionization and PL spectroscopy techniques. Analysis of dislocation etch pits was additionally performed by scanning techniques, such as confocal and atomic force microscopy. It was proved that this blue luminescence band, which peaked at 2.7-2.9 eV, is related to point defects those decorate dislocation cores. It was shown that the intensity of this blue PL band was increased due to enhancement of light extraction efficiency, dependent on the surface area of either single etch-pit or total etched crystal surface.

Electrostructural and morphological features of etch pits in boron-doped HPHT-diamond single crystals and multisectoral plates

Morphological, structural, and nano-electrical features of the growth defects and sectoral boundaries revealed by selective etching in synthetic boron-doped single crystals of diamond (BDD) and multisectoral plates are characterized by a set of scanning probe microscopy (SPM) methods, confocal micro-Raman, and micro-FTIR spectroscopy. Diamond single crystals were grown under high pressure and high temperature conditions (HPHT) in the FeAlBC system. Morphology of dislocation etch pits and micro-defect related pits/protrusions compared both on the growth facets and multisectoral plates cut parallel to the {110} facet of BDD single crystals. Ex situ AFM observation of the etched surface revealed non-homogeneously distributed pits and protrusions over the growth facets correlated with irregular macroscopic growth defects. There is a center-to-periphery gradient of dislocation density in multisectoral plates. The protrusions are homogeneously distributed over plates; some often decorate dislocation pits. Micro-Raman mapping on dislocation pits (boron-rich regions) decorated by low-boron content regions revealed crystalline imperfections in three dimensions, with apparent compressive/tensile strain. The defects were mainly electrically neutral under surface potential mapping by Kelvin probe force microscopy, opposite to the inter-sectoral boundaries having pronounced surface potential steps. The scanning spreading resistance microscopy shows resistivity variations at etching-reviled surface defects and sectoral boundaries if the appropriate DC bias is applied to the SPM tip.

Investigation on dislocation and deflection morphology of PVT-grown on-axis 4H-SiC crystals

The morphologies of dislocation etch pits and dislocation deflections of on-axis 4H-SiC substrate etched by molten KOH were observed with the help of a microscope. Based on experimental observation and etch mechanism, a method for the identification of threading edge dislocations, threading screw dislocations (TSDs) and threading mixed dislocations was proposed. The details about the inner micro-structure of threading edge dislocations and TSDs were observed by laser scanning confocal microscope and scanning electron microscopy. The morphologies and the cross-sectional views of the basal plane dislocation formed by threading edge dislocation were observed and two models were formed to explain it.

Effect of Cr co-doping on the optical absorption and emission characteristics of Yb:YVO4 single crystals grown by OFZ technique

Cr co-doped Yb:YVO4 (Cr:Yb:YVO4) single crystals with concentrations of 1.0 and 1.5 at.% of Cr and 3.0 at.% of Yb were grown by the optical floating zone technique. X-ray diffraction analysis on the grown crystals revealed that the lattice parameters of Cr:Yb:YVO4 crystals do not depend on the Cr doping concentration. The dislocation etch pit density estimated from the etching study was found to be 103/cm2. The observed fringes of nearly uniform thickness and spacing in birefringence interferometry for [100] plate and conoscopy pattern for [001] plate indicate the compositional and optical homogeneity of the crystal. Further, the influence of the Cr doping concentration on the 2A1→2B2 transition (at ∼1100 nm) and 2A1→2E transition (at ∼640 nm) due to Cr5+ ion were analysed using two orthogonal polarized light with electric field perpendicular (π-polarization) and parallel (σ-polarization) to [001] axis. These absorption peaks of Cr ion were found to be sensitive to the polarization of incident light. The absorption transition 2A1→2B2 around 1100 nm are permitted for π-polarization and on the other hand, the absorption transition 2A1→2E at 640 nm are permitted only for σ-polarization. The characteristic broader absorption band around ∼1100 nm is of importance as it is useful for self-Q-switching in a laser gain medium. The absorption coefficient corresponding to Cr5+ ions at 1100 nm increases with the increase in Cr doping concentration. The band-gap for σ-polarized light is slightly higher than π-polarized light and decreases with Cr doping. The increase in the estimated Urbach energy (50–122 meV) with the increase in the Cr doping concentration confirms that the defect states close to the band edge increase thus decrease the band gap. Further the photoluminescence intensity is in-line with the absorption data and decreases with increase in the Cr concentration from 0 to 1.5 at.%.

Dislocation Etching Morphology on the A Plane of Sapphire Crystal

AbstractIn this work, the dislocation etching pit morphology and etching kinetics on the A‐{110} plane of sapphire crystal (α‐Al2O3) are studied experimentally. The results show that the etch pit exhibits a subrhombic 3D morphology, which is consistent with the atom arrangement symmetry of the A plane. Further analysis shows that the two adjacent sides of the rhombic etch pits correspond to the directions [30] and [302], respectively; both of them are in the atomic close‐packing direction of A plane. The etch pits are controlled by a chemical reaction between Al2O3 and potassium hydroxide (KOH) with the reaction activation energy of 51.7 kJ mol−1, which is developed in a manner of kinematic wave by the step moving with a constant speed.

Dislocation evolution along the growth direction of 2-inch GaN crystal grown by Na-flux LPE

2-inch GaN crystals with 1170 μm thickness were successfully grown on MOCVD-GaN thin film seed by Na flux liquid phase epitaxy (Na-flux LPE) technique. X-ray diffraction analysis confirmed that the structure of as-grown GaN crystals was wurtzite. The dislocation etching pit morphologies of GaN crystals at different growth thicknesses were observed by SEM using chemical etching and the dislocation densities were measured. The dislocation density decreased as the growth thickness increased, which could decrease to 105 cm−2 order at the thickness of 870 μm, comparing to about 108 cm−2 of original MOCVD-GaN thin film seed. The mechanism of dislocation density reduction was discussed.

Growth and optical investigation of Nd co-doped Yb:YVO4 crystal: A promising material for laser gain medium

Abstract Nd co-doped Yb:YVO4 single crystals were grown for the first time by using optical floating zone method to the best of our knowledge. The dimension of grown crystals were ~4–5 mm in diameter and 10–15 mm in length. Powder crystal XRD shows that there is a small shift of diffraction peaks towards the lower angle with Nd doping in the crystal, signifying the expansion of the lattice volume. The quality of the crystal was estimated by Rocking curve measurement. The observed nearly straight fringes in birefringence interferogram ensured the good optical homogeneity of grown crystals. The variation in birefringence was found to be less than 5.64 × 10−4. The dislocation etch pit density was estimated by chemical etching and found to be ~12 × 103/cm2. The measured fluorescence life-time of Yb (0.8 at.%) and Nd (0.8 at.%) co-doped YVO4 crystal is around 581 and 66 μs respectively. The polarized absorption spectra depicted an overall higher absorption for π-polarization (E||c) than the σ-polarization (E┴c). The absorption coefficient at 808 nm & 985 nm corresponding to Nd (0.8 at.%) & Yb (0.8 at.%) ions are ~ 28 & 9.2 cm−1 for π-polarization and ~13.7 & 4.6 cm−1 for σ-polarization, respectively, which is found to be better than the crystals grown by conventional Cz technique. However, the fluorescence lifetime of the crystal grown by OFZ and Cz technique is similar. The present findings revealed that π-polarized absorption of Nd ion at 808 nm can be effectively utilized for pumping Yb:YVO4 gain medium for developing an efficient laser system.

Informative Aspects of Molten KOH Etch Pits Formed at Basal Plane Dislocations on the Surface of 4H‐SiC

Despite being a destructive technique, molten KOH etch pits at basal plane dislocations are found to have informative aspects, as revealed by photoluminescence imaging and optical microscopy, on the 4° off‐cut (0001) surface of 4H‐SiC p–i–n diode chips, where single Shockley‐type stacking faults have expanded during electroluminescence experiments. Smaller etch pits are observed aligning on single lines along ±[100] that are the shallowest sides of stacking faults. Through closer observation of the pits, the facing directions are found to agree well with a model explaining the two types of partial dislocations constituting the line. Other basal plane dislocation pits are observed by scanning electron microscopy on the sublimation‐grown wafer surface before epitaxial growth. The distances between the partial dislocation cores are measured at each pit. No basal plane dislocation etch pit facing toward ±[100] is found, but a weak correlation is noted between the partial dislocation distance at the cores and the direction that the basal plane dislocations face. The corresponding results are discussed in terms of the image force and the force exerted on steps perpendicular to the (0001) plane, to understand the mechanisms of basal plane dislocation propagation and/or conversion to threading edge dislocations.

Investigation of defect structure in homoepitaxial (2¯01) β-Ga2O3 layers prepared by plasma-assisted molecular beam epitaxy

Abstract We report growth and comprehensive study on structural properties of homoepitaxial ( 2 ¯ 01 ) β-Ga2O3 layers grown by plasma-assisted molecular epitaxy. Effects of growth temperature on surface morphology, crystal quality of homoepitaxial β-Ga2O3 layers were investigated in detail. Characterization indicates that the growth temperature plays an important role on both of surface morphology and the crystal quality of the homoepitaxial β-Ga2O3 layers. Characteristic of defects in homoepitaxial ( 2 ¯ 01 ) β-Ga2O3 layers was investigated comprehensively. Two types of defects were found out including threading dislocation and twin boundary. Origin and formation mechanism of these defects were clarified. The densities of the twin boundary and dislocation based on growth temperature are investigated and discussed. As the growth temperatures changed from 750 to 850 °C, the densities of the threading dislocation etch pit changed from 1.1 × 106–6.6 × 105 cm−2, while those of the twin boundary defect changed from 7.5 × 103–2.1 × 102 cm−1. It is clear that while the densities of the twin boundary were dramatically reduced by 35 times, the densities of the threading dislocation were reduced by 1.7 times.

A Comparison of Defects Between InAs Single Crystals Grown by LEC and VGF Methods

InAs single crystals grown by the liquid-encapsulated Czochralski (LEC) method and vertical gradient freezing (VGF) are studied by low-temperature photoluminescence spectroscopy, infrared transmission and reflectance spectroscopy, double-crystal x-ray diffraction and Hall effect measurement, respectively. A properly controlled etching solution is used to reveal beautiful square dislocation etch pits in the crystals. In addition to extremely low dislocation density, the concentration of native defects in the VGF-InAs single crystals is much lower than that in LEC-InAs, giving VGF-InAs better electrical and optical properties. The nature of the defects in InAs single crystals is discussed by considering the variation in stoichiometry and environment during the crystal growth processes.

Origin and evolution of threading dislocation in CdZnTe(0 0 1)/GaAs(0 0 1) epilayer grown by close spaced sublimation

The origin and evolution of threading dislocations (TDs) in CdZnTe(0 0 1)/GaAs(0 0 1) epilayer grown by close spaced sublimation (CSS) were experimentally investigated. The dislocation formed at the initial growth stage was observed and analyzed by the plan-view (scanning) transmission electron microscopy (STEM). The thickness-dependent migration and recombination of TDs along the growth direction were revealed by the dislocation etch pit. The origin of TDs is mainly related to the mismatch of growth domains. Strong lateral migration of dislocation in film can be explained by epitaxial lateral overgrowth (ELO) process. The blocking effect on TD movement by growth pit which is related to antiphase boundary (APB) is the primary cause of epilayer quality deterioration.

Wet etching generation of dislocation pits with clear facets in LEC-InAs single crystals

Dislocation etch pits with clear rectangular and elongated hexagonal shapes on indium arsenide (1 0 0) wafer surface have been obtained by carefully controlling the etch condition of HCl-based etchant with the addition of a surfactant. Etching activation energies of (1 0 0), (1 1 1)A and (1 1 1)B faces have been obtained by etching at different temperatures. The results suggest a chemically-controlled reaction restricted by the surfactant. Indices of the facet surfaces in the pits were analyzed with the aid of optical microscopy as well as pit side wall cross section observation by cleavage. It is similar to the etch pit facets of an In-doped GaAs wafer. Mechanism of the etching behavior of InAs has been discussed based on the results.

The mechanism of pitting initiation and propagation at deformation bands intersection of cold-rolled metastable stainless steel in acidic ferric chloride solution

Pitting initiation and propagation at the deformation bands intersection of cold-rolled 14Cr10Mn stainless steel in acidic ferric chloride solution with a pH of 1.3 were investigated by a scanning electron microscope equipped with electron back scatter diffraction and a high-resolution transmission electron microscopy. The experimental results show that the pits with regular morphology are a sort of dislocation etch pit with strict triggering conditions. The pitting corrosion resistance of the etch pits is closely related to the orientations in the increasing order of {100}〈001〉 < {110}〈112〉 < {111}〈110〉. The pit wall will expand to the periphery along the trend of retaining the close-packed plane, leading to an increase in pit depth after the pitting initiation is triggered. We believe that hydrogen ions compete with chloride ions and preferentially adsorbed on the dislocation outcrops in the austenite around α′-martensite and form hydrogen atoms occupying vacancies to prevent chloride ions from eroding the metal matrix. The results also reveal that the vacancy bands formed by the slip of edge dislocations, and the vacancy groups formed by the dissolve of partial dislocation outcrops are patterns for triggering dislocation etch pits.

Dependence of the Shape of the Dislocation Etch Pits of an Epitaxial GeSi (001)-Si Film on the Film’s Thickness

The crystallography of a quadrangular contour confining dislocation etch pits in the plane of the surface of a film is investigated via the structural-sensitive etching of GeSi epitaxial films on Si(001) in combination with atomic force microscopy. Depending on such characteristics of a film as its thickness and the presence of dislocation slip stripes, the sides of the contour can be parallel to direction 〈110〉 or 〈010〉. Etch pits are confined by {111} and {110} low-index facets. According to the electrochemical hypothesis, their formation is associated with the stress distribution near the slip stripes.

Synthesis, structural, dielectric and domain properties of Al-doped KNbO3 single crystal

Single-crystal samples of Al-doped potassium niobate (KNbO3) [KN] were synthesized by a high-temperature flux technique. X-ray diffraction analysis of the crystal suggests that a single phase with an orthorhombic structure was formed. The dielectric studies of the KN single crystal as a function of temperature (from 30 to 500 °C) show that the compounds underwent a phase transition, which was confirmed by thermal analysis of the DTA curve. The measured loss tangent of the crystal, which is in good agreement with the dielectric studies. The ferroelectric property of the crystal was confirmed by studying the hysteresis loop. In this study, several parameters, like the coercive field and spontaneous polarization, were measured and calculated. The domain study was carried out using a trinocular microscope, which reported the formation of the 60° domain line and dislocation etch pits. The effects of the electric field on the domain of the Al-doped KN single crystal were discussed.

The possibility to obtain ZnSe crystals with high structural perfection for cryogenic bolometric technics

In this work the samples of ZnSe zinc selenide crystal grown from the melt by Bridgman method from high-purity (chemical and radio) raw materials were studied for further use in experiments on the search for neutrinoless double beta decay. The microstructure of the test samples was studied. Chemical selective etching, first of all, has allowed to determine the nature of distribution and sizes of area twinning, as well as the etch pits along twins boundaries. It is shown the figures found by chemical etching are the dislocation exits to the studied crystal surface. The dislocation density was estimated by counting the dislocation etch pits on the plane perpendicular to the growth direction and was 104 cm-2. As a rule, thermophysical conditions of ZnSe crystal growth, as well as high concentration of foreign inclusions and impurities in the crystal significantly affect the formation of twins and growth dislocations and are the cause of the optical, electrical, and mechanical heterogeneity of the material. The optical and electrical characteristics of the samples were measured. The absorption bands observed in the optical transmission spectra of the visible and IR ranges gave important information about the presence of local defects and impurities in the crystal, namely in 470÷550 nm and 580÷650 nm regions – absorption by point defects and in 3÷15 μm region – Fe2+, CSe and CSe2 absorption. The total transmission level in the visible range reached 60 %, which is lower than the theoretical one and due to scattering by defects. The phonon thermal conductivity of ZnSe sample was measured in the temperature range 5÷298 K. Based on the approximation of obtained temperature dependences of the thermal conductivity, it was shown that the phonon mean free path at low temperatures is comparable with the distance between twins’ boundaries in the sample.

Approaches to identification of fragments of a dislocation etch pit on a semiconductor monocrystal waffer

Approaches to identification of fragments of a dislocation etch pit on a semiconductor monocrystal waffer

Formation of extended thermal etch pits on annealed Ge wafers

An extended formation of faceted pit-like defects on Ge(0 0 1) and Ge(1 1 1) wafers was obtained by thermal cycles to T > 750 °C. This temperature range is relevant in many surface-preparation recipes of the Ge surface. The density of the defects depends on the temperature reached, the number of annealing cycles performed and correlates to the surface-energy stability of the specific crystal orientation. We propose that the pits were formed by preferential desorption from the strained regions around dislocation pile-ups. Indeed, the morphology of the pits was the same as that observed for preferential chemical etching of dislocations while the spatial distribution of the pits was clearly non-Poissonian in line with mutual interactions between the core dislocations.