Etch Pit Density Research Articles

Thermally stimulated dislocation generation in silicon crystals grown by the Float-Zone method

Based on own previous studies on dislocation generation in FZ- silicon crystals and in order to verify the location and conditions of dislocation generation and spreading, in the current work we present results from a model experiment using a measurement set-up close to the FZ process. Here, an as-grown dislocation-free FZ crystal with a diameter of 20 mm was exposed to temperature-induced strains. No mechanical surface treatment or sample preparation were applied and no mechanical stress was induced during measurement. The crystal was stepwise heated up in the temperature range from 700 °C till 1180 °C controlled by a pyrometric system. The crystal was cut into several samples and analyzed by Lateral Photovoltage Scanning (LPS), photoluminescence (PL) and etch pit density (EPD) as well as the lifetime (MDP) were measured. Our experimental results show that there is an indication that the dislocation density and the lifetime show an inverse behavior depending on the temperature increase in the investigated range. Therefore, this basic correlation known from the literature was confirmed. The area of dislocations generation and its spreading behavior could be revealed. Possible origins and correlations are discussed.

Effectiveness of InGaAs/GaAs superlattice dislocation filter layers epitaxially grown on 200 mm Si wafers with and without Ge buffers

Low threading dislocation density (TDD) in GaAs epitaxial layers grown on silicon substrate (e.g. TDD < 106 cm−2) is critical for GaAs-based optoelectronic and high-performance electronic devices on silicon. Ge buffers and InxGa1-xAs/GaAs superlattice layers (SLs) are commonly used to reduce the TDD in GaAs epitaxial layers grown on Si wafers. In previous reports, TDD of ~107 cm−2 in GaAs and InGaP layers grown on 200 mm Si wafers was achieved by using Ge buffers only (e.g. Wang et al 2017 Semicond. Sci. Technol. 32 125013) and TDD of ~106 cm−2 in GaAs epi-layers for quantum dot lasers on Si was achieved by using SL insertion layers (e.g. Shang et al 2019 IEEE J. Sel. Top. Quantum Electron. 25 1502207). In this work, the effectiveness of the dislocation filtering effect of InxGa1-xAs/GaAs SLs combined with Ge buffers is investigated. The results are compared with wafers where InxGa1-xAs/GaAs SLs were directly grown on GaAs-on-Si buffers without Ge buffers. The InxGa1-xAs/GaAs dislocation filter layers (DFLs) consisted of 10 nm InxGa1-xAs/10 nm GaAs layers superlattice spaced by GaAs layer. Then, 1000 nm thick InGaP layers were grown on top of the DFLs to characterize the effect. Transmission electron microscopy, etch-pit density, x-ray diffraction, and photoluminescence were performed to characterize the quality of the materials. Our results indicate that for the growth with Ge buffers there was no significant difference in the final TDDs in the InGaP layers compared with a reference wafer that did not have DFL. For the growth without Ge buffers, the dislocation filtering effect was indeed observed, although it was not as significant as in other reports. For all wafers with DFLs, large wafer bow and dense film cracks appeared, which hinders the practical application of this method.

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.

Device quality templates of InxGa1−xN (x &amp;lt; 0.1) with defect densities comparable to GaN

InGaN/GaN multiple quantum well (MQW) structures currently used in optical devices are based on highly strained InGaN films. The presence of strain reduces quantum efficiency and indium incorporation, two critical parameters in addressing the green gap. We report on the growth of InGaN-relaxed templates on GaN as substrates to reduce the strain in the MQW structures. Relaxation in the InGaN templates, due to the lattice mismatch, is accommodated by the generation of V-pits rather than the formation of misfit dislocations. InxGa1−xN templates (x ∼ 0.1) are grown via a modified semibulk (SB) approach, with a gradually increasing GaN interlayer thickness to provide a mechanism for backfilling of V-pits. We used high-resolution x-ray diffraction rocking curves to quantify the edge-type and screw-type dislocation density present in the SB and compared the results with the etch pit density obtained via atomic force microscopy after treating the SB with a silane etch. Device-quality InGaN templates with defect density in the mid 108 cm−2 were investigated using the above two approaches, with a quality comparable to state-of-the-art GaN.

Automatic etch pit density analysis in multicrystalline silicon

This publication contains a description and is published in combination with the source code for a tool capable of determining the etch pit density (EPD) on multicrystalline silicon image data. The algorithm is capable of classifying grain boundaries and polishing scratches and removes these structures from the analysis result. Included with the analysis code are methods for plotting EPD maps as well as relative EPD frequency. This is combined with a brief description of the experimental steps of wafer preparation and defect etching as well as a discussion of the analysis limitations.

Recent progress in basic ammonothermal GaN crystal growth

Progress in basic ammonothermal gallium nitride crystallization is reported. In order to prevent the appearance of cracks in growing GaN a new shape of native seeds is proposed. Crystallization results on irregular (old) and round (new) shapes are compared in terms of growth rate and structural quality. The new type of seeds allowed to grow crystals twice as fast without losing the very high structural quality. Etch pit density in the new-grown material is examined and compared to that in the seeds. Material deposited in vertical <000–1> and lateral <11–20> directions is analyzed. In the latter case the etch pit density is as low as 102 cm−2. An influence of growth process parameters and crystal growth configuration on the structural quality of crystallized GaN is discussed.

Vacancy Clustering in Dislocation-Free High-Purity Germanium

A germanium crystal of high purity was grown in H2 with a maximum dislocation density of 3000 cm−2, which was estimated by white beam x-ray topography. Due to a dynamical diffraction effect, the topographs revealed the existence of vacancy clusters in the form of voids in dislocation-free parts of the crystal. Etch pit density analysis, the standard technique employed for crystalline wafers to determine dislocation density, failed to reliably represent dislocations in dislocation-free parts of the crystal. On the other hand, we were able to identify a different type of etching pattern for a dislocation-free crystal. Microwave photoconductance decay was utilized to determine the charge carrier lifetime, which was found to be up to 500 μs for regions with dislocations, while being only 100 μs for dislocation-free parts of the crystal.

An atomic force microscopy study of calcite dissolution in seawater

We present the first examination of calcite dissolution in seawater using Atomic Force Microscopy (AFM). We quantify step retreat velocity and etch pit density to compare dissolution in seawater to low ionic strength water, and also to compare calcite dissolution under AFM conditions to those conducted in bulk solution experiments (e.g. Subhas et al., 2015, Dong et al., 2018). Bulk dissolution rates and step retreat velocities are slower at high and mid-saturation state (Ω) values and become comparable to low ionic strength water rates at low Ω. The onset of defect-assisted etch pit formation in seawater is at Ω ∼ 0.85 (defined as Ωcritical), higher than in low ionic strength water (Ω ∼ 0.54). There is an abrupt increase in etch pit density (from ∼106 cm−2 to ∼108 cm−2) occurring when Ω falls below 0.7 in seawater, compared to Ω ∼ 0.1 in low ionic strength water, suggesting a transition from defect-assisted dissolution to homogeneous dissolution much closer to equilibrium in seawater. The step retreat velocity (v) does not scale linearly with undersaturation (1-Ω) across an Ω range of 0.4 to 0.9 in seawater, potentially indicating a high order correlation between kink rate and Ω for non-Kossel crystals such as calcite, or surface complexation processes during calcite dissolution in seawater.

Characterization of the microstructures and optical properties of CdTe(0 0 1) and (1 1 1) thin films grown on GaAs(0 0 1) substrates by molecular beam epitaxy

In this work, CdTe(0 0 1) and CdTe(1 1 1) single-crystal films were successfully grown on GaAs(0 0 1) substrates by molecular beam epitaxy. By changing the nucleation temperature, CdTe(0 0 1) and (1 1 1) films could be controllably grown on the GaAs(0 0 1) substrates. The CdTe(0 0 1) and (1 1 1) films were grown via low-temperature nucleation followed by high-temperature growth. To optimize the quality of CdTe(0 0 1) films, a CdTe/ZnTe superlattice was used to reduce the lattice mismatch, and the CdTe(0 0 1) film was grown under a cadmium-rich atmosphere. The average surface roughness of the CdTe(1 1 1) and CdTe(0 0 1) films produced was approximately 0.76 nm and 1.37 nm, respectively. The epitaxial relationship between the CdTe(1 1 1) film and the GaAs(0 0 1) substrate was studied based on X-ray diffraction pole figures. The crystal quality of the CdTe(1 1 1) film was also characterized by X-ray diffraction and etch pit density. Finally, photoluminescence spectroscopy was used to investigate the crystal quality of CdTe(0 0 1) and (1 1 1). When the CdTe(0 0 1) film was grown under a cadmium atmosphere and using ZnTe as a buffer layer, the X-ray diffraction peak around 1.56 eV disappeared; this can be related to cadmium vacancies.

Growth of [010] oriented urea-doped triglycine sulphate (Ur-TGS) single crystals below and above Curie temperature (Tc) and comparative investigations of their physical properties

Optically transparent, urea (5 wt%)-doped triglycine sulphate (Ur-TGS) single crystals were grown along polar axis [010] by Sankaranarayanan–Ramasamy unidirectional solution growth method, below and above its Curie temperature Tc = 49.3 °C. Higher growth rate of 5 mm/day was obtained for Ur-TGS crystal grown above Tc. The phase of the grown crystals was confirmed by powder XRD. P–E hysteresis studies show well-saturated hysteresis loop for crystal grown below Tc, and the remnant polarization was 0.60 µC/cm2 with a coercive field of 1.5 kV/cm. The piezoelectric d33 coefficient for Ur-TGS crystal grown below and above Tc was 25 pC/N and 35 pC/N, indicating improved piezoelectric properties of the latter. Dielectric permittivity for Ur-TGS crystal grown above Tc was approximately 10 times higher as compared to the crystal grown below Tc. Improved Vickers microhardness and lower Meyer’s index (n) were observed for Ur-TGS crystal grown above Tc. The etch pit density (EPD) of Ur-TGS crystal grown below and above Tc was 1.8 and 1.1 × 102 dislocations/cm2, respectively, indicating that the quality of the crystals grown above Tc was better than the crystal grown below Tc. The optical transmittance of Ur-TGS crystal grown above Tc was slightly (~ 5%) more than that of crystal grown below Tc. Overall, it is concluded that the higher growth rate and improved physical properties of Ur-TGS crystal grown above its Curie temperature show its suitability for the ferroelectric device applications.

Study of the extended defects in CdZnTe crystal

Etch pit real-time observation (EPRTO) technique was employed to study the extended defects in CdZnTe materials. By tracking the pyramidal etch pits on the (1 1 1) A surface etched by Nakagawa etchant, the microstructures inside the extended defects were revealed. The extending directions of the extended defects and corresponding crystallographic orientations were determined by measuring the displacement vectors of the etch pit tips. Then the orientation distributions of the extended defects in CdZnTe samples were obtained and displayed on the [1 1 1] pole figures. The results show that the extended defects in CdZnTe material consist of dislocation lines connected by micro precipitates or dislocation jogs. The extending directions of the defects situate on the connection lines of [0 1 1], [1 0 1] and [1 1 0] on the [1 1 1] pole figure. The defects with extending directions of 〈2 1 1〉 or 〈3 2 1〉 outside the connection lines of [0 1 1], [1 0 1] and [1 1 0] cannot be revealed by Nakagawa etchant. The orientation distribution of the extended defects shows that the pyramidal etch pit density (PEPD) is not sufficient to describe the property of the extended defects in CdZnTe materials. Some additional parameters are proposed for a more comprehensive evaluation.

Trapping threading dislocations in germanium trenches on silicon wafer

We show that Ge epilayers on Si substrates with trenches filled by Ge at a different temperature have very low threading dislocation density compared to blanket Ge epilayers on Si substrates. In cross-sectional transmission electron microscopy, dislocations at the trench edges are observed to extend to the film surface, which is in agreement with the results of etch pit density measurements where two rows of etch pits are observed at the trench edge. This indicates an appreciable dislocation sink, which unlocks the potential of providing high quality Ge-on-Si virtual substrates for growing lattice matched III-V photovoltaics.

Crystallinity Evaluation and Dislocation Observation for an Aluminum Nitride Single-Crystal Substrate on a Wafer Scale

The crystallinity of a 35-mm-diameter AlN single-crystal substrate grown by physical vapor transport was investigated using x-ray diffraction and Raman spectral mapping. Dislocations in the same sample were observed using an etch pit method, synchrotron x-ray topography, and transmission electron microscopy. The central area of a diameter of 25 mm was featured with high crystallinity and high uniformity, whereas the rim area showed degradation in crystallinity. An improvement in the radius of curvature was confirmed along the growth direction of [ $$ 000\bar{1} $$ ]. The dislocations were revealed as etch pits, and the position-dependent etch pit density was analyzed across the whole wafer. Transmission electron microscopy showed that under the current chemical etching condition, the size of the etch pits in the [ $$ 11\bar{2}0] $$ diagonal direction was approximately linearly proportional to the magnitude of the Burgers vectors, and therefore could be used to classify dislocations.

Effect of xylenol orange dye on morphological, optical, piezo-/di-electric and mechanical properties of potassium hydrogen phthalate single crystals

Pure and xylenol orange (XO; C13H32N2O13S;0.1 mol%) dye doped potassium hydrogen phthalate (KAP; C8H5KO4) crystal were grown by solution technique. Only {111‾} & {110} growth sectors of KAP crystal got selectively stained by the XO dye molecules with {010} being the largest visible (morphologically important) plane. Powder XRD pattern reveals that XO dyeing did not resulted in any extra Bragg peaks and hence, didn't changed the basic structure of KAP crystal (PCa21). HRXRD and etch pit density studies were performed to investigate the effect of XO dye staining on the crystallinity of KAP crystal.The Piezoelectric charge coefficient increased (1.42–1.62 pC/N), optical transparency increased (30%–50%), mechanical strength improved (10.2–11 kg/mm2 @ 20 g), dielectric constant enhanced (ε' ~40 to 44 @ 1 kHz) and dielectric loss decreased (~0.09 to ~0.02) due to XO dye doping. Comparative optical, mechanical, piezoelectric and dielectric investigations add to the scientific insights of KAP crystals and suggest XO-dyed KAP crystal as a better alternative than pure KAP crystal for opto-electronic devices applications.

Growth of heavily-doped Germanium single crystals for mid-Infrared applications

Abstract In the growth of germanium (Ge) single crystals by Czochralski (Cz) method, a novel gas-phase doping procedure has been suggested to obtain heavily doped, both n-type (phosphorous) and p-type (boron) semiconducting crystals. The crystals were grown using the so-called “mini-Cz” technique and the pulled crystals are characterized for their structural and electrical properties. A narrow full width at half maximum (FWHM) of the X-ray diffraction rocking curves obtained for both symmetric (4 0 0) reflection (14 arcsec) and asymmetric (3 1 1) reflection (11 arcsec) indicate good crystalline quality. In addition, the grown crystals have a low dislocation density (etch pit density of ≈104 cm−2) without hot-zone optimization. Doping concentrations of up to 3 × 1018 cm−3 have been obtained so far, which implies that gas-phase doping is a viable route and may solve some of the conventional doping issues when using solids as dopants in the Cz melt. We also report here high doping of antimony (Sb) using a solid dopant source. Non-flat solid-liquid interface of the Sb-doped crystals during the growth process, as characterized by the typical ring structure of the growth striations, has been seen in lateral photovoltage scanning (LPS) measurements.

Effects of rotating magnetic field on the microstructure and properties of a GaInSb crystal

High-quality Ga0.86In0.14Sb ingots (Φ25 × 100) were prepared with vertical Bridgman method (VB) applied a rotating magnetic field (RMF). The microstructure and properties of the ingots were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), metallographic microscopy, and a Hall Effect testing system. RMF improved the crystallinity of the samples, reducing the full width at half maximum (FWHM) of the XRD characteristic peak of the GaInSb ingot from 214″ to 74". RMF significantly also reduced both of the radial and axial segregation of indium in the GaInSb crystal. The radial segregation in a 25–75 mm axial section decreased to 0.085 mol% from 0.247 mol% per mm, and the axial segregation to 0.047 mol% from 0.140 mol% per mm. RMF decreased the dislocation density (or the etch pit density; EPD) from 1.047 × 105 cm−2 to 6.988 × 103 cm−2. It also improved the electrical properties of the crystal, with the average value of the axial carrier mobility increasing from 1.437 × 103 cm2/(V·s) to 1.618 × 103 cm2/(V·s) and the average value of the axial resistivity reducing from 1.352 × 10−3 Ω·cm to 1.162 × 10−3 Ω·cm. Finally, the uniformity of the axial carrier mobility and resistivity also improved significantly.

Synthesis, vibrational, thermal, mechanical and third-order nonlinear optical properties of sodium 4-methyl-3-nitrobenzoate monohydrate crystal for optical limiting applications✰

ABSTRACT A nonlinear optical (NLO) sodium 4-methyl-3-nitrobenzoate monohydrate (Na4M3N) single crystal was synthesized and grown by the slow cooling solution growth method using an ethanol-water (1:1) mixed solvent. Powder X-ray diffraction (PXRD) reveals the crystallinity of Na4M3N compound. The Na4M3N crystal was estimated with a single crystal XRD instrument and it was identified to be in the centrosymmetric space group (P21/c) having a monoclinic system. The vibrational, proton (1H) and carbon (13C) NMR spectral analysis substantiates the functional groups, hydrogen and carbons in the synthesized compound. The Hirshfeld surfaces analysis was executed to know the different type of interactions present in the crystal. From the UV–vis spectrum, the optical band gap and cut-off wavelength of the Na4M3N crystal are endowed to be 5.06 eV and 254 nm respectively. The Na4M3N crystal was subjected to a thermogravimetric as well as differential thermal analysis for discerning the thermal characteristics. The LDT value of crystal was endowed to be 5.8 GW/cm2 using Nd: YAG laser and the value is superior to that of KDP and Urea. The emission region of the compound was identified by the photoluminescence emission spectrum. The crystalline quality was again confirmed by lifetime measurements. The thermo-optic coefficient (dn/dt) was determined to be –3.5 × 10−5 K−1. The reverse saturable absorption observed by third-order NLO studies dictates the suitability for optical limiting applications. Vickers microhardness test showed that Na4M3N crystal was a soft material. The average etch pit density (3.2 × 103 cm−2) was determined from chemical etching studies. The complex dielectric constant, electric modulus and electrical conductivity values were measured as a function of frequency to get information on the conduction mechanisms.

Growth, structural, Hirshfeld surface, optical, laser damage threshold, dielectric and chemical etching analysis of 4-dimethylaminopyridinium 4-nitrophenolate 4-nitrophenol (DMAPNP) single crystal

The organic 4-dimethylaminopyridinium 4-nitrophenolate 4-nitrophenol (DMAPNP) single crystal was grown by slow evaporation solution growth technique at 35 °C. The single crystal X-ray diffraction analysis confirms that the grown crystal belongs to the orthorhombic crystal system with the space group of P212121. Different functional groups were affirmed using FT-IR and FT-Raman analysis. The intermolecular interactions of the DMAPNP molecule were executed using Hirshfeld surface study. The Mulliken atomic charge population analysis was performed using density functional theory (DFT). The bonding interactions between two orbital atoms and groups were executed by the density of state (DOS). The optical transmittance study shows that the grown crystal has 60 to 78% transmittance in the Vis–NIR region. It has an emission peak at 482 nm in the photoluminescence (PL) spectrum. The photoconductivity analysis shows that the DMAPNP has negative photoconductive behavior. The thermal stability of the DMAPNP crystal was investigated by TG–DTA analysis. The etch pit density of the title crystal was investigated using chemical etching study. The mechanical stability of the DMAPNP crystal was tested by Vickers microhardness tester. Laser damage threshold analysis reveals that the DMAPNP is stable up to 10 mJ of laser power. The dielectric properties were assessed and the electronic polarizability of the DMAPNP was evaluated by the different empirical relations. The second harmonic generation (SHG) efficiency of DMAPNP crystal was measured by Kurtz–Perry powder technique.

Synthesis, growth and characterization of organic nonlinear optical 3-(4-fluorophenyl)-1-(4-methoxyphenyl) single crystal grown by vertical Bridgman technique

Abstract Single crystal of organic nonlinear optical material 3-(4-Fluorophenyl)-1-(4-methoxyphenyl) (FMP) was grown with the help of single walled glass ampoule in vertical Bridgman technique. The structural analysis confirmed the cell parameters and crystallinity of the single crystal with the space group of Pbca. The presences of desired components in the single crystal were confirmed by the NMR spectrum. The lower cut off wavelength of the single crystal was observed at 423 nm from the absorption spectra of the single crystal. The electrical property of grown single crystal was studied by measuring the dielectric constant and dielectric loss. The surface hardness test and amount of damage caused by incident laser beam on the surface of the single crystal determined the mechanical strength of the crystal. The FMP single crystal was found to exhibit negative photoconductive nature. The etch pit density and non-linear optical properties were determined by etching measurement and by observation of green light in Kurtz-Perry powder method. The grown crystal was studied thermal stability and melting point with TGA-DSC analysis.

Epitaxial characteristics of MBE-grown ZnTe thin films on GaAs (211)B substrates

Highly crystalline ZnTe thin films were grown on GaAs (211)B substrates by molecular beam epitaxy (MBE) for potential applications such as MCT detectors and optoelectronic devices. We investigated the effects of Te to Zn (VI/II) flux ratio on the quality of ZnTe films in terms of crystal orientation, elemental composition, surface roughness, and dislocation density. Atomic concentrations of Zn, Te, and oxygen complexes due to oxygen contamination on the film surfaces were analyzed by X-ray photoelectron spectroscopy. X-ray double crystal rocking curve full width half maximum (FWHM) of ZnTe (422) peak was observed as 233 arcseconds for a 1.66 μm thick film, which indicates high crystallinity. Wet chemical etching was applied to the films to quantify the crystal quality by calculating etch pit densities (EPD) from scanning electron microscope images. A very low EPD value of 1.7 × 107 cm−2 was measured. Additionally, the root mean square roughness values, obtained from atomic force microscopy topography images were in the range of 10–25 nm. These values were supported by FWHM values of red green blue color intensity histograms obtained from Nomarski Microscope images. The results of our analyses indicate that the VI/II flux ratios of 4 and 4.5 produce the best quality ZnTe films on GaAs (211)B substrates.