Types Of Etch Pits Research Articles

Spatial correlation of defect-selective etching and dark luminescence spots in Al x Ga1−x N

Defect-selective etching with molten Ba(OH)2/MgO etch drops was performed on c-plane AlGaN layers covering the entire composition range between GaN and AlN. Regardless of the aluminum content, the etchant produced shallow, hexagonal etch pits with depth-to-diameter ratios of 1/10–1/100. Two predominant types of etch pits were observed, which differed in size. In addition, the etch rate decreased from the center to the edge of the area exposed to the etch drops, providing a radially symmetric variation in etch pit size. For all AlGaN compositions, the positions of the etch pits correlate perfectly with the positions of the dark luminescence spots in cathodoluminescence measurements. Areas on the AlGaN samples that were not exposed to the etching procedure showed identical dark spots with the same size and density as those in the etched regions. Additionally, the density of etch pits and dark spots corresponded to the density of threading dislocations in the AlGaN layers. These observations demonstrate that the density of threading dislocations in c-plane AlGaN layers can be determined by destructive defect-selective etching with Ba(OH)2/MgO and etch pit counting, as well as by nondestructive counting of the dark spots in cathodoluminescence images.

Study of Defects and Nano-patterned Substrate Regulation Mechanism in AlN Epilayers.

The high crystal quality and low dislocation densities of aluminum nitride (AlN) grown on flat and nano-patterned sapphire substrate that are synthesized by the metal-organic chemical vapor deposition (MOCVD) method are essential for the realization of high-efficiency deep ultraviolet light-emitting diodes. The micro-strains of 0.18 × 10-3 cm-2 for flat substrate AlN and 0.11 × 10-3 cm-2 for nano-patterned substrate AlN are obtained by X-ray diffractometer (XRD). The screw and edge dislocation densities of samples are determined by XRD and transmission electron microscope (TEM), and the results indicate that the nano-patterned substrates are effective in reducing the threading dislocation density. The mechanism of the variation of the threading dislocation in AlN films grown on flat and nano-patterned substrates is investigated comparatively. The etch pit density (EPD) determined by preferential chemical etching is about 1.04 × 108 cm-2 for AlN grown on a nano-patterned substrate, which is slightly smaller than the results obtained by XRD and TEM investigation. Three types of etch pits with different sizes are all revealed on the AlN surface using the hot KOH etching method.

Origin of Large Bumps Abnormally Grown on 4H-SiC Epitaxial Film by Adding HCl Gas with High Cl/Si Ratio in CVD Process

4H-SiC homo-epitaxial film was grown by adding HCl gas with a high Cl/Si ratio in CVD process, and defect formation and origin of the defect were investigated by confocal differential interference contrast (CDIC) microscope, PL imaging and normal differential interference contrast (DIC) microscope. It was found that a large number of large bumps are formed on the film grown at a high Cl/Si ratio of 30, and a large number of PL defects on bare substrate before the film growth are also observed. Coordinates where the bumps on the film are observed were good agreement with those where the PL defects on the bare substrate are observed. An etch pit sample on reproduced substrate from which epitaxial film was removed was fabricated by etching process using molten KOH+Na2O2, and some types of etch pits which might be originated from threading edge dislocations (TEDs), threading screw dislocations (TSDs) and basal plane dislocations (BPDs) in the substrate were observed. The coordinates where the etch pits on the reproduced substrate are observed were also good agreement with those where the bumps on the epitaxial film are observed. Therefore, it was clarified that a large number of the bumps abnormally grown on the epitaxial film are originated from the dislocations in the substrate.

HCl-H2SO4-H2O solution etching behavior of InAs (1 0 0) surface

Etch pits formed on (100)-oriented InAs surface by HCl-H2SO4-H2O solutions have been investigated by optical microscopy and atomic force microscopy (AFM) images. Depending on the composition of etchant, four types of etch pits are observed, which is attributed to different reaction rate of (111)A and (111)B planes by HCl and H2SO4. Excessive HCl results in long hexagonal shaped pits, whereas the addition of H2SO4 results in tetragonal pits. The direction of the composed pit sidewalls has been determined combining with the results of depth profiles on (110) and (11¯0) planes. The role of the HCl and H2SO4 in the over-all etching behavior of InAs and details about the geometrical relation between the sidewalls of the etch pits are discussed.

Direct evidence of Mg diffusion through threading mixed dislocations in GaN p–n diodes and its effect on reverse leakage current

Mg diffusion is a common problem in GaN devices with p–n junctions. Although this impurity diffusion is reported to occur through threading dislocations (TDs), no direct evidence has yet been obtained. Therefore, we tried the direct observation of Mg diffusion by atom probe tomography (APT) analysis. The n-type drift layer of the fabricated p–n diode was exposed, and etch pits were formed on the drift layer to identify the TD position. The APT analysis around TDs was carried out by lifting out the drift layer around specific etch pits using a focused ion beam to include TDs. The relationship between the etch pit shape and the TD type was confirmed by cross-sectional scanning transmission electron microscopy observation. The APT analysis of two types of etch pits formed on the mixed dislocations was performed, and Mg diffusion was clearly observed through the mixed dislocations. In this work, we show direct evidence of Mg diffusion via mixed dislocations in GaN p–n diodes and its effect on reverse leakage current.

Crystal defects observed by the etch-pit method and their effects on Schottky-barrier-diode characteristics on β-Ga2O3

A pixel array of vertical Schottky-barrier diodes (SBDs) was fabricated and measured on the surface of a β-Ga2O3 single crystal. Subsequently, etch pits and patterns were observed on the same surface. Three types of etch pits were discovered: (1) a line-shaped etch pattern originating from a void and extending toward the [010] direction, (2) an arrow-shaped etch pit whose arrow’s head faces toward the [102] direction and, (3) a gourd-shaped etch pit whose point head faces toward the [102] direction. Their average densities were estimated to be 5 × 102, 7 × 104, and 9 × 104 cm−2, respectively. We confirmed no clear relationship between the leakage current in SBDs and these crystalline defects. Such results are obtained because threading dislocations run mainly in the [010] growth direction and do not go through the sample plate.

Correlation of Etch Pits and Dislocations in As-grown and Thermal-Cycle-Annealed HgCdTe(211) Films

This paper reports observations of the different types of etch pits and dislocations present in thick HgCdTe (211) layers grown by molecular beam epitaxy on CdTe/Si (211) composite substrates. Dislocation analysis for as-grown and thermal cycle-annealed samples has been carried out using bright-field transmission electron microscopy. Triangular pits present in as-grown material are associated with a mixture of Frank partials and perfect dislocations, while pits with fish-eye shapes have perfect dislocations with $$ \frac{1}{2}[0\bar{1}1] $$ Burgers vector. The dislocations beneath skew pits are more complex as they have two different crystallographic directions, and are associated with a mixture of Shockley partials and perfect dislocations. Dislocation analysis of samples after thermal cycle annealing (TCA) shows that the majority of dislocations under the etch pits are short segments of perfect dislocations with $$ \frac{1}{2}[0\bar{1}1] $$ Burgers vector while the remainder are Shockley partials. The absence of fish-eye shape pits in TCA samples suggests that they are associated with mobile dislocations that have reacted during annealing, causing the overall etch pit density to be reduced. Very large pits with a density ∼2×103 cm−2 are observed in as-grown and TCA samples. These defects thread from within the CdTe buffer layer into the upper regions of the HgCdTe layers. Their depth in as-grown material is so large that it is not possible to locate and identify the underlying defects.

Correlation of Etch Pits and Dislocations in As-grown and Thermal Cycle-Annealed HgCdTe(211) Films

This paper reports observations of the different types of etch pits and dislocations present in thick HgCdTe (211) layers grown by molecular beam epitaxy on CdTe/Si (211) composite substrates. Dislocation analysis for as-grown and thermal cycle-annealed samples has been carried out using bright-field transmission electron microscopy. Triangular pits present in as-grown material are associated with a mixture of Frank partials and perfect dislocations, while pits with fish-eye shapes have perfect dislocations with $$ \frac{1}{2}[0\bar{1}1] $$ Burgers vector. The dislocations beneath skew pits are more complex as they have two different crystallographic directions, and are associated with a mixture of Shockley partials and perfect dislocations. Dislocation analysis of samples after thermal cycle annealing (TCA) shows that the majority of dislocations under the etch pits are short segments of perfect dislocations with $$ \frac{1}{2}[0\bar{1}1] $$ Burgers vector while the remainder are Shockley partials. The absence of fish-eye shape pits in TCA samples suggests that they are associated with mobile dislocations that have reacted during annealing, causing the overall etch pit density to be reduced. Very large pits with a density ∼2×103 cm−2 are observed in as-grown and TCA samples. These defects thread from within the CdTe buffer layer into the upper regions of the HgCdTe layers. Their depth in as-grown material is so large that it is not possible to locate and identify the underlying defects.

The dislocation structure of diamond crystals grown on seeds in the Mg-C system

The dislocation structure of diamond crystals grown in the Mg-C system at a pressure of 7GPa and temperatures of 1800–1900°C is studied by X-ray topography and selective etching. According to the selective etching data, diamond crystals have two types of dislocations whose outputs on the {100} faces of crystal are associated with two types of etch pits. It has been demonstrated that the etch pits with the side wall inclination angle of about 7° are formed at the outcrop points of full edge dislocations, while the etch pits with the inclination angle of about 4° are associated with 45° mixed dislocations. It has been found that the dislocation structure of diamonds grown at 1900°C is completely determined by the seed crystals structure and the dislocation density is 105cm−2. The dislocation density in the diamond crystals grown at 1800°C increases by two or three orders of magnitude due to nucleation of dislocations at the seed-overgrown layer interface and in the overgrown layer. The high dislocation density leads to the mosaic structure of crystals and misorientation of single blocks, up to 1°. Local ring clusters of edge dislocations were found to be the dominant source of growth layers on the {100} faces of diamond.

Revelation of dislocations in HVPE GaN single crystal by KOH etching with Na2O2 additive and cathodoluminescence mapping

Threading dislocations have been studied by means of etch pit method using molten KOH + Na2O2 solution, cathodoluminescence and transmission electron microscopy. We focus on the geometrical features of etch pits and their correlation with the recombination behavior at the dislocations. Four types of etch pits can be recognized after etching according to their sizes and depths, among which the middle-sized etch pits correspond to dislocations with the strongest non-radiative recombination. TEM observation has confirmed that dislocation beneath the large-sized etch pit is a mixed-type dislocation having both c- and a-component.

Study of dislocations in HgCdTe epilayers at (1 1 1)B and (1 1 0) surfaces using modified defect etchant

A new etchant, based on the modification of standard Chen etchant has been developed for revealing etch pits in HgCdTe epilayer at (111)B and (110) planes. We have optimized the oxidizing and dissolving agents in the solution by systematic experimentation to obtain the new etchant. By using this etchant we revealed the etch pits reliably and consistently in several HgCdTe epilayers grown on (111)B face CdZnTe substrates using LPE (liquid phase epitaxy) technique, The new etchant is not sensitive to the sample orientation and works equally well for both (111) and (110) planes. The dislocations revealed by the modified etchant were investigated by the study of etch pits at (111)B surface and at the cleaved plane, i.e., (110) face. Different types of etch pits have been observed and investigated. The etch pits were found to be dependent on the CdZnTe substrate and the stress induced during the growth itself.

Growth and dislocation studies of β-HMX

BackgroundThe defect structure of organic materials is important as it plays a major role in their crystal growth properties. It also can play a subcritical role in “hot-spot” detonation processes of energetics and one such energetic is cyclotetramethylene-tetranitramine, in the commonly used beta form (β-HMX).ResultsThe as-grown crystals grown by evaporation from acetone show prismatic, tabular and columnar habits, all with {011}, {110}, (010) and (101) faces. Etching on (010) surfaces revealed three different types of etch pits, two of which could be identified with either pure screw or pure edge dislocations, the third is shown to be an artifact of the twinning process that this material undergoes. Examination of the {011} and {110} surfaces show only one type of etch pit on each surface; however their natural asymmetry precludes the easy identification of their Burgers vector or dislocation type. Etching of cleaved {011} surfaces demonstrates that the etch pits can be associated with line dislocations. All dislocations appear randomly on the crystal surfaces and do not form alignments characteristic of mechanical deformation by dislocation slip.ConclusionsCrystals of β-HMX grown from acetone show good morphological agreement with that predicted by modelling, with three distinct crystal habits observed depending upon the supersaturation of the growth solution. Prismatic habit was favoured at low supersaturation, while tabular and columnar crystals were predominant at higher super saturations. The twin plane in β-HMX was identified as a (101) reflection plane. The low plasticity of β-HMX is shown by the lack of etch pit alignments corresponding to mechanically induced dislocation arrays. On untwinned {010} faces, two types of dislocations exist, pure edge dislocations with b = [010] and pure screw dislocations with b = [010]. On twinned (010) faces, a third dislocation type exists and it is proposed that these pits are associated with pure screw dislocations with b = [010].Graphical abstractEtch pits on the twinned (010) face of β-HMX.

Studies on dislocation and surface morphology of AlxGa1−xN/GaN heterostructures grown by MOCVD

In this work, AlxGa1−xN epilayers have been grown on sapphire substrate with GaN template by the metal organic chemical vapor deposition (MOCVD) method. The structural and morphological properties of these samples have been investigated and compared. The growth rate of AlGaN has been found to decrease with increasing Al composition. By increasing Al composition of AlGaN epilayer, tilt and twist angle has been found to increase, indicating higher threading dislocation density. Surface morphology and dislocation density (DD) have been investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Different types of dislocation etch pits have been observed in AlxGa1−xN/GaN epilayers, using orthophosphoric acid (85% H3PO4) as defect selective etchant. Three types of etch pits like screw type (α), edge type (β) and mixed type (α+β) dislocations have been observed. The mechanism of etch pits formation has been explained using Cabrera’s thermodynamic model. The etch pit density (EPDs) has been correlated with threading dislocation density (TDs) estimated using HRXRD measurements. Photoluminescence (PL) studies have revealed an increase in intensity of near band edge emission due to etching.

Single Etch-Pit Shape on Off-Angled 4H-SiC(0001) Si-Face Formed by Chlorine Trifluoride

The etch pit shape of an off-angled 4H-SiC Si-face formed by chlorine trifluoride (ClF3) in nitrogen (N2) ambient has been studied. One type of etch pit with a crooked hexagonal shape was formed at an etching temperature below 500 °C. The angle of the etch pit measured from a cross-sectional atomic force microscopy image was about 10° from the [112̄0] view. The dislocation type of the etch pit was discussed in relation to the etch pit shape and an electron-beam-induced current image.

Characterization of dislocation etch pits in HVPE-grown GaN using different wet chemical etching methods

The hydride vapor phase epitaxy (HVPE) grown GaN samples were etched by H 3PO 4, mixed solution of H 2SO 4 and H 3PO 4 (HH) and molten eutectic of KOH–NaOH ( E), respectively. The etching characteristics and surface morphologies were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The density of etch pits obtained by E etching under optimum etching condition was around 3.0 × 10 8 cm −2, which was consistent with the results obtained by the cathodoluminescence (CL) investigation. Two types of etch pits with different sizes were all revealed on the GaN surface using different etching methods. The large etch pits were formed on screw or mixed dislocations, while small etch pits were formed on edge dislocations. The difference in the size of etch pits was interpreted by Cabrera's thermodynamic theory. Prolonging etching time, the morphology changes of etch pits were different by using H 3PO 4, HH and E. The etching rate by H 3PO 4 etching was the fastest and that by E etching was the slowest. According to these etching results, it could be concluded that E etching was a better method for evaluation of dislocations.

Characterization of Surface Defects of Highly N-Doped 4H-SiC Substrates that Produce Dislocations in the Epitaxial Layer

The structures of defects that form different types of etch pits on highly N-doped 4H-SiC substrates, that were produced by a sublimation method, after molten KOH etching were characterized. It was found that most of the dislocations in the epitaxial layer originated from defects at the surface of substrate whose etch pit structures were clearly different from the conventional structures. The etch pits were classified into drop, oval, round and caterpillar pits. The drop and oval pits were concluded to be formed by the deformation of conventional etch pits. Round pits were concluded to originate from half loop dislocations and were transformed to complex dislocations by epitaxial growth. Analysis by transmission electron microscopy measurement indicates that slipped edge dislocations (or screw dislocations) on the basal plane form caterpillar pits.

Microstructure and origin of dislocation etch pits in GaN epilayers grown by metal organic chemical vapor deposition

Morphology and microstructure of dislocation etch pits in GaN epilayers etched by molten KOH have been investigated by atomic force microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). Three types of etch pits (α, β, and γ) are observed. The α type etch pit shows an inversed trapezoidal shape, the β one has a triangular shape, and the γ type one has a combination of triangular and trapezoidal shapes. TEM observation shows that α, β, and γ types etch pits originate from screw, edge, and mixed-type threading dislocations (TDs), respectively. For the screw-type TD, it is easily etched along the steps that the dislocation terminates, and consequently, a small Ga-polar plane is formed to prevent further vertical etching. For the edge-type TD, it is easily etched along the dislocation line. Since the mixed-type TDs have both screw and edge components, the γ type etch pit has a combination of α and β type shapes. It is also found that the chemical stabilization of Ga-polar surface plays an important role in the formation of various types of dislocation etch pits.

Low-temperature epitaxy of silicon by electron beam evaporation

In this paper we report on homoepitaxial growth of thin Si films at substrate temperatures T s = 500–650 °C under non-ultra-high vacuum conditions by using electron beam evaporation. Si films were grown at high deposition rates on monocrystalline Si wafers with (100), (110) and (111) orientations. The ultra-violet visible reflectance spectra of the films show a dependence on T s and on the substrate orientation. To determine the structural quality of the films in more detail Secco etch experiments were carried out. No etch pits were found on the films grown on (100) oriented wafers. However, on films grown on (110) and (111) oriented wafers different types of etch pits could be detected. Films were also grown on polycrystalline silicon (poly-Si) seed layers prepared by an Aluminum-Induced Crystallisation (AIC) process on glass substrates. Electron Backscattering Diffraction (EBSD) shows that the film growth proceeds epitaxially on the grains of the seed layer. But a considerably higher density of extended defects is revealed by Secco etch experiments.

Line defects in epitaxial silicon films grown at [formula omitted

We present an investigation of line defects in epitaxially grown silicon layers using Secco defect etching and transmission electron microscopy (TEM). 1 μ m thick layers were deposited onto Si (1 0 0) wafers at a substrate temperature of 560 ∘ C using electron cyclotron resonance chemical vapour deposition (ECRCVD). Defect etching reveals a variety of etch pits related to extended defects. A detailed analysis of the orientations and shapes of etch pits related to line defects is carried out. Using this information it is then possible to assign different types of etch pits to line defects observed by TEM. The investigations show, that one type of defect are extended dislocations parallel to 〈 1 1 2 〉 , while the direction of two other types are 〈 1 1 0 〉 as well as 〈 3 1 4 〉 , a direction uncommon for line defects in silicon.

Observation of Etch Figures on Protein Crystals by Atomic Force Microscopy

Etch figures on the (110) face of hen egg white lysozyme crystals in aqueous solution were investigated by atomic force microscopy. Three types of etch pits with flat, “deep” flat and point bottoms were observed. All etch pits are elongated to the [-110] direction, similar to the growth of 2D islands. The etch pit density of contaminated crystals, fabricated from a widely used commercial sample, was approximately ten times greater than that of pure crystals. Moreover, the density of “deep” flat bottom pits on contaminated crystals increased with supersaturation, while their density on pure crystals remained almost constant. These results suggest that the impurity molecules incorporated during growth and the line defects, such as edge dislocations, induced by the molecules are the dominant defects in lysozyme crystals grown from commercially available samples.