Etch Pits Research Articles

Characterization of Prismatic Slip in SiC Crystals by Chemical Etching Method

In 4H-silicon carbide crystals, basal plane slip is the predominant deformation mechanism. However, prismatic slip is often observed in single crystals grown by the physical vapor transport method as the diameter expands to 6 inches or larger. Thermal modeling has shown that occurrence of prismatic slip is attributed to increased radial thermal gradients. While X-ray topography can be used to characterize the presence and extent of prismatic slip, the feasibility of using the chemical etching method to assess the extent of prismatic slip in an industrial setting is investigated. The distribution of scallop shaped etch pits oriented along the directions that correspond to prismatic dislocations, correlate well with the results of the thermal model that predicts the occurrence of prismatic slip dislocations. This capability of the etch pit method to characterize prismatic slip can be used to manage radial thermal gradients during PVT growth.

Micro-Raman analysis of HVPE grown etched GaN epilayer with porous formation

The GaN epilayer grown by hydride vapor phase epitaxy was wet etched by phosphoric acid as the etchant. X-ray diffraction confirms that the GaN has a wurtzite structure. Scanning electron microscopy shows various sizes of hexagonal pits for different times of etchant reactions. Atomic force microscopy shows increase in surface roughness with different etchant rate. The photoluminescence gives a 3.4 eV luminescence for the pristine GaN epilayer. In the etched films, the deep-level defect belonging to yellow and green luminescence was found. The deconvoluted Ga 3d peaks of etched samples show Ga-rich epilayers. Micro-Raman spectroscopy is a non-destructive method for measuring carrier concentration, phonon lifetime and strain using A 1 (LO) spectra of Raman vibration mode was utilized via the Lorentz fitting method. The carrier concentration increases while the phonon lifetime decreases with etching rate. Overall, in the 9 min reaction, the epilayer was etched heavily with a perfect hexagonal etch pit structure.

In Situ EC-AFM Study of the Initial Stages of Cathodic Corrosion of Pt(111) and Polycrystalline Pt in Acid Solution.

An atomic scale understanding of the surface degradation mechanism during cathodic corrosion of a platinum electrode is still lacking. Here, we present results of surface structural changes observed during cathodic polarization of a polycrystalline Pt electrode and single crystalline Pt(111) in acid electrolytes in the absence and presence of cations (Na+) by in situ electrochemical atomic force microscopy (EC-AFM) imaging. The electrolyte cation is proved to be a prerequisite to trigger cathodic etching of the polycrystalline Pt surface. Further examination of the evolution of electrochemical signals and distinct surface structural transformations of an atomically defined Pt(111) single-crystal electrode during cathodic corrosion reveals clearly that the roughening process commences at the under-coordinated sites of the Pt(111) surface. The created triangular-shape pattern, actually a 100-oriented pit in a 111-terrace, grows primarily laterally in the initial regime, while prolonged cathodic corrosion leads to the existing etching pits growing in depth until ultimately they coalesce with each other, generating a highly roughened surface.

Postannealing Temperature Effects on the Etching Behavior and Field Emission Properties of Cu‐Implanted Diamond

To investigate the postannealing temperature effects on the surface etching behavior and electron field emission (EFE) properties of the Cu‐implanted microcrystalline diamond (MCD) films, they are subjected to furnace annealing in a temperature range of 600–900 °C under N2 atmosphere at a rapid annealing rate. The etching behavior happens when the samples are annealed at 700 °C and above. The EFE performances enhance first and then decrease with the increasing annealing temperature. The optimum EFE property with a low turn‐on field of 6.42 V μm−1 is obtained after the Cu‐implanted MCD film is annealed at 700 °C. The enhancement in EFE properties originates from the presence of nanographitic phase and the formation of electron‐rich Cu nanoparticles, which encourage a higher efficient electron transport. In contrast, the structural studies reveal that when the samples annealed at 800 °C and above, Cu nanoparticles evaporate from the diamond surface and the sp2‐bonded carbon decomposes. Consequently, etch pits appear on the surface of the MCD sample. Moreover, it demonstrates that graphitization is the dominant mechanism of the diamond surface etching behavior and the enhancing of EFE properties.

Line-shaped defects in bulk β-Ga2O3 single crystals grown by the vertical Bridgman method

We conducted an investigation of line-shaped defects, extending in the 〈010〉 direction, in bulk β-Ga2O3 single crystals grown by the vertical Bridgman (VB) method. Parallelepiped cross-section samples with {010} polished surfaces and {100} cleavage planes were prepared and were then etched in phosphoric acid at 140 °C. Rhombic etch pits were observed on the (010) surface and they were similar in shape to those reported as nanometer-sized grooves or plate-like nanopipes in crystals grown by the edge-defined film-fed growth (EFG) method. Groove-like voids in the 〈010〉 direction were also observed on {100} cleavage planes below the etch pits observed on the {010} surface. Therefore, we concluded that line-shaped defects observed in VB-grown crystals are similar to defects observed in EFG-grown crystals. The size of these defects was considerably smaller than that observed in EFG-grown crystals, but with a density of 5 × 105 cm−2. Based on these results, possible formation mechanisms for such defects were discussed.

Structural properties of MBE-grown CdTe (133)B buffer layers on GaAs (211)B substrates with CdZnTe/CdTe superlattice-based dislocation filtering layers

The ever-present demand for high-performance HgCdTe infrared detectors with larger array size and lower cost than currently available technologies based on lattice-matched CdZnTe (211)B substrates has fuelled research into heteroepitaxial growth of HgCdTe and CdTe buffer layers on lattice-mismatched alternative substrates with a (211)B orientation. Driven by the large lattice mismatch, the heteroepitaxial growth of (Hg)CdTe can result in (133)B-orientated material, which, however, has been less explored in comparison to (211)B-oriented growth. Herein, we report on the structural properties of heteroepitaxially grown single-crystal II–VI CdTe (133)B-oriented buffer layers on III–V GaAs (211)B substrates. Azimuthal-dependent x-ray double-crystal rocking curve measurements for the CdTe buffer layers show that the full-width at half-maximum value obtained along the GaAs [1¯11] direction is narrower than that obtained along the GaAs [011¯] direction, which is presumably related to the in-plane anisotropic structural characteristics of the grown CdTe layers. By incorporating strained CdZnTe/CdTe superlattice-based dislocation filtering layers (DFLs), a significant improvement in material quality has been achieved in (133)B-orientated CdTe buffer layers, including a reduced etch pit density in the low-105 cm−2 range and improved surface roughness. These results indicate that the CdTe (133)B DFL buffer layer process is a feasible approach for growing high-quality CdTe and HgCdTe materials on large-area, low-cost alternative substrates.

Study on Stress Intensity Factor of the Pit-Crack Model for Portal Crane Girders

In shipbuilding gantry cranes in long-term service in the coastal humid salt-spray environment, the main beam is affected in many places by corrosion fatigue-formed corrosion pits, affecting the structural strength of the main beam. This paper focuses on the impact of corrosion-generated pits under the conditions of crack nucleation. Corrosion fatigue crack nucleation is a local damage evolution process and the stress intensity factor criterion is one of the critical conditions to discern whether a crack sprouts at the corrosion pit. This paper establishes a corrosion pit-crack model based on the overall finite element model of the portal crane, and uses ANSYS software to simulate the stress intensity factor under complex boundary conditions. The results show that the different sizes and depth-to-diameter ratio of the pits greatly affect the value of the stress intensity factor and the stress concentration phenomenon may be the main factor causing the emergence of cracks; the change in the size of the pits on the stress intensity factor is not obvious, but with the increase in the depth-to-diameter ratio of the pits, the stress intensity factor of the pit-crack model is significantly increased. According to the hypothesis of semi-ellipsoidal pitting, the relationship between the stress intensity factor and the stress concentration factor at the pit is proposed, and its calculation results are within 5% error compared with the finite element method, and it is found that the effect of the etch pit on the stress intensity factor is positively correlated with the stress concentration factor; with the increase in the etch pit depth–diameter ratio, the crack budding location changes with the change in the stress concentration location, and the crack is more likely to be generated from the shoulder of the etch pit when the depth–diameter ratio of etch pit exceeds 1.

Effect of sub-grain boundaries in CdZnTe on HgCdTe film grown by molecular beam epitaxy

HgCdTe films grown by molecular beam epitaxy (MBE) are essential for creating high-performance infrared focal plane arrays (IRFPAs) like dual band detectors, high operating temperature (HOT) detectors, and avalanche photodiode (APD) detectors. CdZnTe is recognized as the optimal substrates for growing high crystal quality HgCdTe due to its lattice matching, which is adjusted by selecting the Zn mole fraction. However, defects like grain boundaries, twins, inclusions, dislocations, and sub-grain boundaries that often occur in CdZnTe substrates can significantly reduce the crystal quality of HgCdTe. HgCdTe grown on CdZnTe with these defects usually no longer suit for high quality device fabrication. Although the impact from various defects have been extensively studied in HgCdTe grown on CdZnTe, but the sub-grain boundaries is still not yet involved. In our study, to better understand the effect of sub-grain boundaries in CdZnTe on HgCdTe films, CdZnTe substrates with and without sub-grain boundary were selected to growth MWIR HgCdTe films under optimized condition. Results indicated that etch pit density (EPD) of CdZnTe substrates with sub-grain boundary is approximately 3–5 times higher than boundary free areas. But HgCdTe grown on these substrates bears more than an order of magnitude increase in dislocation proliferation compared to the boundary free region. Dislocation generation resulting from dislocation penetration from substrates, mismatch between HgCdTe and CdZnTe, and sub-grain boundaries were investigated and compared. The intense dislocation proliferation in HgCdTe may be mainly due to twins formed during the initial growth stage of HgCdTe films, rather than dislocation penetration from substrates, as revealed by reflection high-energy electron diffraction (RHEED) pattern monitoring. Therefore, screening for sub-grain boundaries in CdZnTe before HgCdTe growth is necessary.

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.

Synthesis, crystal growth and characterization of piperazinium 5-nitrosalicylate (P5NS) single crystal for nonlinear optical (NLO) applications

A single crystal of Piperazinium 5-nitrosalicylate (P5NS) was grown by using slow evaporation solution technique (SEST). The structural analysis (crystal system & cell parameter) of the grown P5NS crystal was examined by single crystal XRD and it exposed that the P5NS crystal has a crystal triclinic system and space group (P-1). Using powder XRD analysis, miller index and (h k l) planes were identified. The P5NS crystal has a sharp cutoff wavelength around 380 nm and is transparent in UV region. The FTIR analysis was investigated on the P5NS crystal to find out the P5NS functional groups. The thermogravimetric and differential thermal analysis illustrate that the P5NS crystal is thermally stable upto 255 °C. Further increase in the temperature resulted in decomposition of P5NS. The etch pit density of P5NS crystal has been calculated by using the chemical etching analysis. The Photoconductivity study reveals that the grown PMC crystal has positive photoconductive nature. The electrical properties, dielectric constant and dielectric loss were determined. The laser damage threshold (LDT) analysis was investigated by Nd: YAG laser and the wavelength of laser is 1064 nm. Intermolecular interactions of P5NS is executed by the Hirshfeld surface analysis. The NLO susceptibility (χ(3)) was calculated by the Z-scan method using the source of He-Ne laser, whose wavelength is 632.8 nm.

Ultrafast GaAs MOVPE growth for power electronics

Schottky diodes designed with negative breakdown voltages of up to 400 V are used in applications like power supplies, motor drives, battery charging and server/data centers. GaAs is an ideal choice for such devices. Due to its high electron mobilities, lower series resistance and thus lower power consumptions in the “on” state than using Si, GaN or SiC can be achieved. Also GaAs wafers are available up to 8” with extremely high quality and low etch pit densities. To achieve breakdown voltages above 200 V in GaAs, typically doping levels below 1*1015 cm−3 and thicknesses in the range of tens of micrometers are needed. In order to achieve minimum turn-on losses, the thickness and doping has to be precisely controlled. For the epitaxy, the process time and group V precursor consumption due to typically high V/III ratios are the two largest cost factors. Recently, we have introduced MOVPE processes on a close coupled CRIUS showerhead reactor with growth rates up to 280 µm/h. Due to the extremely high growth rate, the loss of group-V material due to evaporation off the growth surface is minimized and even at V/III ratios below 15 a low C-background doping can be achieved. It is demonstrated that this low cost and ultrafast growth process is suitable for Schottky power diodes. 15 µm thick GaAs:Si Hall samples were grown at a growth rate of 100 µm/h. Controlled n-doping levels as low as 1.2*1014 cm−3 have been reached for a V/III ratio of 12. The room temperature mobilities were as high as 9*103 cm−3/Vs. Also, the electronic defect levels were analyzed by deep level transient spectroscopy. The EL2 (As anti-site) defect is found with a concentration 4.8*1014 cm−3. Nominally 20 µm and 30 µm thick layers were deposited on n-GaAs wafers for initial Schottky test diodes. The I-V curve in forward characteristics is characterized by an ideality factor of 1.2, a Schottky barrier height of 0.8 eV and a series resistance as low as 3.7 mΩcm2. Breakdown voltages above 370 V in reverse bias for doping levels of 2*1014 cm−3 were achieved proving the high potential of this approach.

Relationship Between Propagation Angle of Dislocations in β-Ga2O3 (001) Bulk Wafers and Their Etch Pit Shapes

Relationship Between Propagation Angle of Dislocations in β-Ga2O3 (001) Bulk Wafers and Their Etch Pit Shapes

Alteration of trioctahedral micas in the presence of inorganic and organic acids

The alteration of two trioctahedral micas, biotite and phlogopite, was investigated at the meso, micro, and nanoscale using three complementary microscopy techniques to better understand mica surface reactivity. In situ and ex situ experiments were performed to monitor the mineral interface during dissolution in acidic solutions (nitric and oxalic acid, pH ∼ 1–2), over a temperature range of 25–100°C. The inorganic acid was used as a benchmark condition to elucidate the effect of the organic acid on the dissolution behavior. The observed topographical changes that arose during mineral alteration revealed the simultaneous occurrence of different processes that heterogeneously shaped the mica surface: 1) the retreat of pre-existing and newly formed steps (edge surface reactivity). In the case of biotite, layer curling and peeling-off occurred in the presence of nitric acid whereas dendritic-shaped step edges resulted from the effect of oxalic acid; 2) the nucleation of etch pits and the formation of dissolution channels on the (001) surface. Oxalic acid promoted the growth of the pits to such an extent that they were discernible at each scale and resolution investigated; and 3) precipitation of secondary phases. Overall, a multi-scale approach offers new insights into the dissolution behavior of biotite versus phlogopite and provides and enhances understanding of the effect that oxalic acid has on the surface reactivity of mica.

A study of thermal etching of GaN by atmospheric argon inductively coupled plasma

GaN has a wide application in electronics and optoelectronics due to its excellent electrical properties. The thermal etching process is commonly used in the growth and subsequent process of GaN. As an easy-to-operate technique, atmospheric argon inductively coupled plasma (Ar-ICP) is first applied to the thermal etching of GaN in this study. Through the analysis of surface chemical composition and near-surface plasma spectroscopy, the etching principle and mechanism of the circular etching pit formation are revealed. The maximum material removal rate of Ar-ICP thermal etching can reach 18.72 μm/min. The optical properties of the sliced GaN after the Ar-ICP thermal etching and lapping process are evaluated by photoluminescence (PL), respectively. The PL intensity of the Ar-ICP thermally etched sample increases and the peak position of near-band emission shows a red shift compared to the lapped sample.

Influence of polyvinyl alcohol coated porous Al2O3 ceramic waste particles on cement properties in geothermal applications

To improve the low strength of the existing geothermal temporary sealing cement (GTSC) and figure out the influence of PACW on cement performances in geothermal applications, the hard porous Al2O3 ceramic waste (PACW) was introduced into oil well cement. The water-soluble PVA was coated on PACW particles to wrap the porous ceramic at relatively low temperature for geothermal drilling, and dissolve in water at ≥ 90 ℃ for hot water flow. The compressive strength, hydrates, pore structures and interface transition zone of cement with raw or modified PACW were tested. The results showed that 10% raw and modified PACW enhanced the compressive strength of oil well cement by 57.69% and 60.31% respectively, during the 90 ℃ water immersing. For the cement containing 10% raw and modified PACW, thermal weight loss related to degradation of hydrates and CH increased, meso pores fraction rose to 52.73% and 51.93 % respectively, and the deeper etch pits on surfaces of the mineral suggested the promoting effect of PACW on cement hydration. The promoted cement hydration and formed hydrates with their filling effect contributed to the cement strength enhancement. As the thermal weight loss attributed to AFm increased after immersion, the thermodynamic parameters of the possible transformation reaction of AFt to AFm were calculated. The standard molar Gibbs free energy change of the reactions are negative, and microstructure images showed that the PACW surface was covered by lots of flaky AFm crisscrossed with large hexagonal AFt crystals, proving that the alumina in PACW participated in and promoted the transformation of AFt to AFm. In addition to reservoir protection, simplifying construction procedures and reducing the time cost of geothermal development, the high-strength GTSC will further strengthen the hole wall and reduce the risk of borehole collapse.

Artifacts in metallography: etching pits

The article considers etch pits that appear in metals and alloys during metallographic etching as an artifact. The optical contrasting tools capabilities, such as dark field, polarized light, and differential interference contrast in detecting etch pits, are demonstrated.

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.

Two types of etching pits in (100) β-Ga2O3 single crystals grown by casting method

Two types of micron-sized etching pits were observed on (100) plane of β-Ga2O3 single crystals grown by casting method. Type A etching pits were elongated along [010] direction with a density of 105/cm2. Using FIB and HRTEM, the atomic structure under the pits bottom remained complete but exhibited continuous microscopic strain, which could be attributed to strain-related. On the other hand, type B etching pits represented different geometric parameters, with 2 times larger and 6 times deeper than type A. Edge dislocations with clearly dislocation lines which perpendicular to b = <100> were observed. The origins of etching pits were clarified, especially the co-exist strain-related pits. After annealing at 1200 °C for 3 h in air, we found varying degrees of reduction in the density of both etching pits, which could be owing to partial stress release and dislocations slip at the oxygen-containing ambient during elevated temperature.

Comprehensive analysis of current leakage at individual screw and mixed threading dislocations in freestanding GaN substrates

The electrical characteristics of Schottky contacts on individual threading dislocations (TDs) with a screw-component in GaN substrates and the structures of these TDs were investigated to assess the effects of such defects on reverse leakage currents. Micrometer-scale platinum/GaN Schottky contacts were selectively fabricated on screw- and mixed-TD-related etch pits classified based on the pit size. Current–voltage (I–V) data acquired using conductive atomic force microscopy showed that very few of the screw TDs generated anomalously large reverse leakage currents. An analysis of the temperature dependence of the I–V characteristics established that the leakage current conduction mechanisms for the leaky screw TDs differed from those for the other screw and mixed TDs. Specifically, anomalous current leakage was generated by Poole–Frenkel emission and trap-assisted tunneling via distinctive trap states together with Fowler–Nordheim tunneling, with the mechanism changing according to variations in temperature and applied voltage. The leaky TDs were identified as Burgers vector b = 1c closed-core screw TDs having a helical morphology similar to that of other screw TDs generating small leakage currents. Based on the results, we proposed that the atomic-scale modification of the dislocation core structure related to interactions with point defects via dislocation climbing caused different leakage characteristics of the TDs.

Growth and thermal properties of InSe crystal by using the ground simulation apparatus of China space station

Indium selenide (InSe) semiconductor crystal was grown by using the ground simulation apparatus of China space station in this work. The furnace was controlled at 715 °C and the temperature gradient for crystal growth was ∼30 °C/cm. The as-grown InSe crystalizes in γ-phase with space group of R3m. The average etching pits density (EPD) is estimated to be about 104/cm2. Thermal analysis indicates a positive thermal expansion at 30–500 °C and no volatilization occurred even as high as 1000 °C. This work not only establishes a reliable process for preparing large-sized InSe single crystal but also creates a foundation for further work in outer space in the future.