Double-crystal X-ray Diffractometry Research Articles

Double-Crystal X-Ray Diffractometry and Topography Methods in the Analysis of the Real Structure of Crystals

The high efficiency of double-crystal X-ray diffractometry and topography methods in the characterization of crystals during refinement of the crystal-growth technology is demonstrated for the example of diamond bulk crystals and films obtained by the high pressure, high temperature method and by chemical vapor deposition, respectively. Techniques and study schemes for analysis of the real crystal structure, assessment of the chemical composition and the period of the crystal lattice, and analysis of the distinctive features of the deformation and thickness of thin films are described. Major structural defects (dislocations, stacking defects, inclusions of a different phase, and others) that emerge during the production of synthetic diamond crystals are identified.

Nanoscale tensile strain in perfect silicon crystals studied by high-resolution X-ray diffraction

A device was designed, built, and tested to apply small tensile strain to perfect single silicon crystals. It was used on the second axis of a double crystal diffractometer to obtain controllable strain fields. The strain field quality was evaluated by double crystal X-ray diffractometry. The dependence of atomic plane distances on applied stress was determined. Stress-strain curves were obtained from fitted rocking curves in the Bragg-Bragg and Bragg-Laue configurations. These results show that it is possible to obtain a tensile strained lattice with quality suitable for X-ray optics.

X-Ray Diagnostics of Microstructure Defects of Silicon Crystals Irradiated by Hydrogen Ions

Features of formation and transformation of radiation defects in near-surface layers of silicon plates that are implanted with hydrogen ions are studied. Using the method of high-resolution double-crystal X-ray diffractometry, values of the main parameters, such as mean effective thickness Leff and mean relative deformation Δa/a of a doped layer, are determined depending on the implantation dose and substrate temperature.

Рентгеновская диагностика дефектов микроструктуры кристаллов кремния, облученных ионами водорода

AbstractFeatures of formation and transformation of radiation defects in near-surface layers of silicon plates that are implanted with hydrogen ions are studied. Using the method of high-resolution double-crystal X-ray diffractometry, values of the main parameters, such as mean effective thickness L _eff and mean relative deformation Δ a / a of a doped layer, are determined depending on the implantation dose and substrate temperature.

Optimization of the Growth Technology for Crystals with Garnet Structure Based on X-Ray Diffraction Data

High efficiency of the methods of double-crystal X-ray diffractometry (DCXRD) and topography for improving the growth technology of highly homogeneous crystals has been demonstrated on the example of gadolinium gallium garnet (GGG) single crystals. The main types of structural defects observed in Czochralski-grown GGG crystals are found to be macroscopic inhomogeneity of composition distribution, caused by the facet effect manifestation; microinhomogeneous distribution of impurity and main components of the composition in striations; dislocations; and second-phase inclusions. The relationship between the type and density of newly formed defects and the technological conditions for crystal growth are considered. Optimization of the composition of crystals and their growth technology made it possible to obtain high-quality dislocation-free crystals of GGG and complex-substituted garnets on its basis for magneto-optical and microwave devices, elements of solid-state lasers, and other applications.

X-ray diffraction characterization of epitaxial CVD diamond films with natural and isotopically modified compositions

Comparative investigations of homoepitaxial diamond films with natural and modified isotopic compositions, grown by chemical vapor deposition (CVD) on type-Ib diamond substrates, are carried out using double-crystal X-ray diffractometry and topography. The lattice mismatch between the substrate and film is precisely measured. A decrease in the lattice constant on the order of (Δa/a)relax ∼ (1.1–1.2) × 10–4 is recorded in isotopically modified 13С (99.96%) films. The critical thicknesses of pseudomorphic diamond films is calculated. A significant increase in the dislocation density due to the elastic stress relaxation is revealed by X-ray topography.

X-ray diffraction characterization of synthetic garnet, diamond and sapphire crystals

The structural features of synthetic garnet, diamond, and sapphire single crystals are investigated via the nondestructive methods of double-crystal X-ray diffractometry and topography. The conditions of diffraction studies into these crystals performed with the help of Ge monochromators are optimized. The main structural defects (dislocations, stacking faults, growth striations, second-phase inclusions, etc.) of crystals arising from their generation are revealed. It is demonstrated that the experimental techniques for studying the real structure turn out to be highly efficient in optimizing crystal-growth technology.

Analysis of synthetic diamond single crystals by X-ray topography and double-crystal diffractometry

Structural features of diamond single crystals synthesized under high pressure and homoepitaxial films grown by chemical vapor deposition (CVD) have been analyzed by double-crystal X-ray diffractometry and topography. The conditions of a diffraction analysis of diamond crystals using Ge monochromators have been optimized. The main structural defects (dislocations, stacking faults, growth striations, second-phase inclusions, etc.) formed during crystal growth have been revealed. The nitrogen concentration in high-pressure/high-temperature (HPHT) diamond substrates is estimated based on X-ray diffraction data. The formation of dislocation bundles at the film-substrate interface in the epitaxial structures has been revealed by plane-wave topography; these dislocations are likely due to the relaxation of elastic macroscopic stresses caused by the lattice mismatch between the substrate and film. The critical thicknesses of plastic relaxation onset in CVD diamond films are calculated. The experimental techniques for studying the real diamond structure in optimizing crystal-growth technology are proven to be highly efficient.

Influence of the Strain of AlN Buffer Layer on the Strain Evolution of GaN Epilayer Grown on 3-in 6H-SiC Substrate

The influence of the strain of AlN buffer layers on the strain evolution of GaN epilayers grown on 3-in 6H-SiC substrates by metal-organic chemical vapor deposition was investigated by double-crystal X-ray diffractometry, and Raman scattering spectra. It was found that the tensile strain of the GaN epilayers mainly decreases with the strain of the AlN buffer layers varied from tensile to compressive. A model based on the strain evolution during the epitaxial growth is proposed to provide a valuable reference for the massive production of large scale and high quality GaN epilayers.

Molecular beam epitaxy of thermodynamically metastable GaInAsSb alloys for medium IR-range photodetectors

The features of growth of GaInAsSb alloy with In content as high as 25 mol % lattice-matched to GaSb by molecular beam epitaxy are studied. These alloys are promising for use as the active region of photodetector structures of the mid-infrared range. The results of the study of these alloys by double-crystal X-ray diffractometry, scanning electron microscopy, and photoluminescence are presented. It is shown that the GaxIn1 − xAsySb1 − y alloys with x < 0.8 grown at 500°C show the degradation of structural and optical properties as the layer thickness is increased. In layers with thicknesses above the critical one, spinodal decomposition is observed in complete agreement with thermodynamic calculations of the location of the boundaries of immiscibility regions. The possibilities to optimize the molecular beam growth of the GaxIn1 − xAsySb1 − y alloys (x < 0.75) with high optical and structural quality, as well as the characteristics of photodetectors based on the GaInAsSb/AlGaAsSb heterostructures, are discussed.

Dynamical theoretical model of the high-resolution double-crystal x-ray diffractometry of imperfect single crystals with microdefects

The dynamical diffraction model has been developed for the quantitative description of rocking curves (RCs) measured in the Bragg diffraction geometry from single crystals containing homogeneously distributed microdefects of several types and with arbitrary sizes. The analytical expressions for coherent and diffuse RC components, which take self-consistently multiple-scattering effects into account and depend explicitly on microdefect characteristics (radius, concentration, strength, etc.), have been derived with taking into account the instrumental factors. The developed model has been applied to determine the characteristics of oxygen precipitates and dislocation loops in silicon crystals grown by Czochralsky and float-zone methods using RCs measured by the high-resolution double-crystal x-ray diffractometer. It has been shown, particularly, that completely dynamical consideration of Huang as well as Stockes-Wilson diffuse scattering (DS) in both diffuse RC component and coefficient of extinction of coherent RC component due to DS, together with taking asymmetry and thermal DS effects into account, provides the possibility to distinguish contributions into RC from defects of different types, which have equal or commensurable effective radii.

Growth behaviors of GaN/Si heteroepitaxy with various terrace widths grown by the LEPS method

Epilayers of GaN were grown on patterned Si (111) substrates of various terrace widths by means of metal organic chemical vapor deposition. The technique of lateral epitaxy on a patterned substrate used the growth of GaN epilayers from the periodic and parallel stripes that form as a result of the substrate etching. Silicon substrates were patterned for various terrace widths of 3 μm, 8 μm, and 18 μm. A low temperature AlN was used as a seed layer for the growth of a 1.5 μm thick GaN epilayer. The as-grown samples were characterized by using double-crystal X-ray diffractometry (DCXRD), photoluminescence and atomic force microscopy (AFM). From the DCXRD spectra, the full width at half maximum (FWHM) of the samples was found to decrease as the terrace width decreased. This behavior indicates that there is an improvement in the crystalline quality of the GaN epilayers as the terrace width decreases. The photoluminescence spectra reveal a decrease in the FWHM and an increase in the peak intensity as the terrace width decreases. This behavior indicates that there is an improvement in the optical quality of the GaN epilayer as the terrace width decreases. The atomic force micrographs reveal a dislocation-free homogeneous surface in the trench region compared to the terrace region with defects such as pits and dislocations. The results clearly show that GaN epilayers grown on a patterned Si substrate with a terrace width 3 μm have a good crystalline quality with minimal threading dislocation and excellent band edge emission.

Investigation on Large-Sized Sapphire Crystalline Perfection by X-Ray Double-Crystal Diffraction Method

The large-sized sapphire (Ø225×205 mm, 27.5 kg) was grown successfully by SAPMAC method (sapphire growth technique with micro-pulling and shoulder-expanding at cooled center). The surface quality of the specimens was characterized by micro-Raman spectroscopy, and double crystal X-ray diffractometry (DCD) was utilized to investigate its crystalline perfection. The measurement of rocking curves was performed on various specimens from different region of large sapphire boule. The experimental results showed that CMP (chemo-mechanical polishing) with subsequent suitable chemically etching can develop the best-quality sapphire crystal surface and the values of FWHM obtained by conventional DCD were in the range from 27” to 58”. The infrared spectral transmission (2.0-4.5 5m) of sapphire crystal exceeded 82%. It is confirmed of SAPMAC growth method characteristics with in-situ annealing, small temperature gradient and low residual stress level by numerical simulation analysis.

Properties of ZnO films grown on (0 0 0 1) sapphire substrate using H 2O and N 2O as O precursors by atmospheric pressure MOCVD

In this paper, we compare the properties of ZnO thin films (0 0 0 1) sapphire substrate using diethylzinc (DEZn) as the Zn precursor and deionized water (H 2O) and nitrous oxide (N 2O) as the O precursors, respectively in the main ZnO layer growth by atmospheric pressure metal–organic chemical vapor deposition (AP-MOCVD) technique. Surface morphology studied by atomic force microscopy (AFM) showed that the N 2O-grown ZnO film had a hexagonal columnar structure with about 8 μm grain diameter and the relatively rougher surface compared to that of H 2O-grown ZnO film. The full-widths at half-maximum (FWHMs) of the (0 0 0 2) and ( 1 0 1 ¯ 2 ) ω-rocking curves of the N 2O-grown ZnO film by double-crystal X-ray diffractometry (DCXRD) measurement were 260 and 350 arcsec, respectively, indicating the smaller mosaicity and lower dislocation density of the film compared to H 2O-grown ZnO film. Compared to H 2O-grown ZnO film, the free exciton A (FX A) and its three phonon replicas could be clearly observed, the donor-bound exciton A 0X ( I 10):3.353 eV dominated the 10 K photoluminescence (PL) spectrum of N 2O-grown ZnO film and the hydrogen-related donor-bound exciton D 0X ( I 4):3.363 eV was disappeared. The electron mobility (80 cm 2/V s) of N 2O-grown ZnO film has been significantly improved by room temperature Hall measurement compared to that of H 2O-grown ZnO film.

Improved quality of InGaN/GaN multiple quantum wells by a strain relief layer

Different InGaN/GaN multi quantum wells (MQWs) structures were grown by metalorganic chemical vapor deposition (MOCVD). Samples were investigated by photoluminescence (PL), atom force microscopy (AFM) and double crystal X-ray diffractometry (DCXRD) to character their optical, morphological and crystal properties. By inserting the strain relief layer, the PL intensity was increased more than two times. The surface morphology was improved and the density of V-pits was reduced from 16–18×10 8 to 6–7×10 8/cm 2. Further, the interface abruptness was also improved. We attributed the improvements of the quality of InGaN/GaN MQWs to the relief of strain in the InGaN/GaN MQWs.

N-type doping of GaN/Si(1 1 1) using Al 0.2Ga 0.8N/ALN composite buffer layer and Al 0.2Ga 0.8N/GaN superlattice

The characteristics of Si-doped and undoped GaN/Si(1 1 1) heteroepitaxy with composite buffer layer (CBL) and superlattice are compared and discussed. While as-grown Si-doped GaN/Si(1 1 1) heteroepitaxy shows lower quality compared to undoped GaN, crack-free n-type and undoped GaN with the thickness of 1200 nm were obtained by metalorganic chemical vapor deposition (MOCVD). In order to achieve the crack-free GaN on Si(1 1 1), we have introduced the scheme of multiple buffer layers; composite buffer layer of Al 0.2Ga 0.8N/AlN and superlattice of Al 0.2Ga 0.8N/GaN on 2-in. Si(1 1 1) substrate, simultaneously. The FWHM values of the double-crystal X-ray diffractometry (DCXRD) rocking curves were 823 arcsec and 745 arcsec for n-GaN and undoped GaN/Si(1 1 1) heteroepitaxy, respectively. The average dislocation density on GaN surface was measured as 3.85×10 9 and 1.32×10 9 cm −2 for n-GaN and undoped GaN epitaxy by 2-D images of atomic force microscopy (AFM). Point analysis of photoluminescence (PL) spectra was performed for evaluating the optical properties of the GaN epitaxy. We also implemented PL mapping, which showed the distribution of edge emission peaks onto the 2 inch whole Si(1 1 1) wafers. The average FWHMs of the band edge emission peak was 367.1 and 367.0 nm related with 3.377 and 3.378 eV, respectively, using 325 nm He-Cd laser as an excitation source under room temperature.

Thickness dependent formation and properties of GdSi2/Si(100) interfaces

Epitaxial and polycrystalline orthorhombic GdSi2 films were grown on Si(100) substrates by solid phase reaction between Si and Gd films at different thicknesses of the Gd film . The most important property of these GdSi2/Si interfaces was defect formation. This was investigated by studying the properties of the Schottky barriers by means of current voltage and capacitance–voltage characteristics, deep level transient spectroscopy by double crystal X-ray diffractometry, and transmission electron microscopy. Epitaxial growth of the silicide layer ensured a relatively low interface defect density (about 1010 cm-2), while the non-epitaxial growth induced defects of a much higher density (about 1012 cm-2). The defects generated during the silicide formation are located within a depth of about 10 nm from the GdSi2/Si interface.

Low-temperature growth and doping of InP:S single crystals from melt-solution in microgravity

The effect of microgravity on the growth of bulk InP:S single crystals from a melt with an initial equilibrium composition (84 at % In, 16 at % P, and ∼2.2 × 1018 at cm−3 of S) on board the Foton-11 satellite was investigated. The growth of crystals on board the satellite and on Earth (a reference crystal) was carried out by the traveling heater method. The samples of the grown crystals were investigated by metallography, double-crystal X-ray diffractometry, single-and double-crystal X-ray topography, and secondary-ion mass spectrometry. It is shown that the mass transfer in the melt in microgravity is similar to the diffusion mode. Hence, the mass transfer in the melt results in the following: the formation of a nonstationary boundary layer, depleted in phosphorus; the constitutional supercooling at the crystallization front accompanied with the development of a cellular substructure in the early growth stage; and the hypothetical phase structurization of the transition layer with the formation of In-based associates (clusters), which were found in the grown crystals in the form of spherical defects 10–20 μm in diameter. The coefficients of sulfur distribution k0 = 0.274 and keff = 0.43, the sulfur diffusivity in the melt DS = 4.2 × 10−7 cm2/s, and the effective thickness of the transition layer δ = 0.07 cm in terrestrial gravity are determined. The data obtained are necessary to develop a mathematical model of crystallization in zero gravity.

Structural characterization of interfaces in the AlxGa1−x As/GaAs/AlxGa1−x As heterostructures by high-resolution X-ray reflectometry and diffractometry

The structural properties of multiplayer AlxGa1−xAs/GaAs/AlxGa1−xAs systems (x ≈ 0.2) grown on GaAs(001) substrates are studied by the methods of double-crystal X-ray diffractometry and reflectometry. The depth profiles of deformation, amorphization, and density of the layers are obtained. It is shown that despite small differences (5–7%) in the densities of the AlxGa1−xAs layers and the substrate and the small thickness of the AlAs layer (1–2 nm) separating the GaAs quantum well, it is possible to reconstruct the heterostructure model by the method of X-ray reflectometry and to determine the thickness of the transitional layers at a resolution of 0.1–0.2 nm. It is also established that the reflectometry data obtained complement the X-ray diffraction data considerably and allow one to estimate the roughness and the character of the aluminum distribution at the interfaces.

Determining parameters of a multilayer heterostructure by joint analysis of the X-ray rocking curves measured for various crystallographic planes

The X-ray rocking curves of (004), (113), and (115) planes of a pseudomorphous InxGa1−xAs/GaAs(001) heterostructure with a single 12-nm-thick quantum well were measured by double-crystal X-ray diffractometry. The joint fitting of the X-ray diffraction curves for various crystallographic planes has been performed for the first time, which provides more reliable information about the thickness, deformation, and amorphization of layers in the heterostructure studied.