Double-crystal X-ray Diffractometer Research Articles

Acoustic properties of La3Ga5.3Ta0.5Al0.2O14 crystal

Development and search for new advanced materials of the lanthanum gallium silicate group with unique thermal properties is of great importance for the development of acoustoelectronics based on volume and surface acoustic waves. The processes of surface acoustic wave excitation and propagation in the La3Ga5.3Ta0.5Al0.2O14 crystal was studied using a double-crystal X-ray diffractometer with a BESSY II synchrotron radiation source. The X-ray diffraction spectra of acoustically modulated crystals were used to measure the surface acoustic wave velocity and power flow angles in different acoustic cuts of the La3Ga5.3Ta0.5Al0.2O14 crystal.

Studying acoustic-wave fields in langasite-family crystals using the BESSY II synchrotron radiation source

The process of the excitation and propagation of pseudosurface acoustic waves in crystals of the langasite family is studied via X-ray diffractometry for the first time. The investigations are carried out using the BESSY II synchrotron radiation source in the double-crystal X-ray diffractometer scheme. The process of pseudosurface acoustic wave propagation is studied based on an analysis of the diffraction spectra of acoustically modulated crystals. Both the velocities of the pseudosurface acoustic waves and the power flow angles of the acoustic energy are measured for the first time. The pseudosurface acoustic wave is shown to be flowing. Surface and pseudosurface acoustic waves generated by an interdigital transducer in the Z cut of a La3Ga5.5Ta0.5O14 crystal are compared.

Investigation into the structural perfection and acoustic properties of a piezoelectric Ca3TaGa3Si2O14 crystal

Ca3TaGa3Si2O14 (CTGS) crystals are a new promising material from the lanthanum-gallium silicate family, which can be employed in high-temperature sensors and other acoustoelectronic devices. The structural perfection and acoustic properties of CTGS crystals have been investigated via X-ray topography and diffractometry at the BESSY II synchrotron radiation source in the geometry of a double-crystal X-ray diffractometer.

Transformations of microdefect structure in silicon crystals under the influence of weak magnetic field

Quantitative characterization of complex microdefect structures in annealed silicon crystals (1150 °С, 40 h) and their transformations after exposing for one day in a weak magnetic field (1 T) has been performed by analyzing the rocking curves, which have been measured by a high-resolution double-crystal X-ray diffractometer. Based on the characterization results, which have been obtained by using the formulas of the dynamical theory of X-ray diffraction by imperfect crystals with randomly distributed microdefects of several types, the concentrations and average sizes of oxygen precipitates and dislocation loops after imposing the magnetic field and their dependences on time after its removing have been determined.

Bridgman growth and defect characterization of large diameter mercury indium telluride crystals for near infrared detectors

Novel Hg3In2Te6 (MIT) single crystals with 30mm in diameter and 110mm in length have been reproducibly grown by the vertical Bridgman (VB) method. The crystalline phase was confirmed by X-ray diffraction to be free of transformation. Rocking curves using a double-crystal X-ray diffractometer showed that the full widths at half maximum of the as-grown MIT crystals were in the range of 150–317arcsec. The electrical resistivity, carrier density and mobility from Hall measurements at room temperature were 1.79×103Ωcm, 1.01×1013cm−3 and 3.44×102cm2V−1s−1, respectively. The existing defects in the as-grown MIT crystals were displayed and the average etch pits density (EPD) using the modified Chen etchant solution was (2–6)×104cm−2 in the whole ingot.

Electrical properties of thermal donors formed in silicon under elastic tensile stress

The electrical properties of thermal donors formed in the bulk and near-surface regions in silicon samples with (3–9) × 1017 cm−3 oxygen concentrations under elastic tensile stress σ of about 1 GPa have been studied. The original method allowing us to control an introduced elastic tensile stress during the thermal donor’s formation at T = 450°C by a double-crystal X-ray diffractometer has been used. The formation of thermal donors in silicon with a high oxygen concentration of 9.3 × 1017 cm−3 under tensile stress has been found to be less effective than in silicon with a low oxygen concentration of (3–5) × 1017 cm−3. Single-charged donors are formed in silicon with a low oxygen concentration under tensile stress while double-charged donors are formed in silicon with a high oxygen concentration.

The resolution function of a double-crystal X-ray diffractometer

The shape of the resolution function and the predicted and earlier detected pseudopeak in the diffraction reflection curve (DRC) were experimentally studied in detail as functions of the geometric parameters of a double-crystal dispersion-free measurement system. It has been established that the shapes of the resolution function and the pseudopeak in the DRC weakly depend on the width of the collimation slit so that this optical element, which was earlier considered necessary, is extraneous in this measurement scheme. The physical mechanism of the formation of a pseudopeak in the DRC is illustrated by the example of analyzing the Du Mond diagram.

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.

Influence of the trench depths of grooved GaN templates on the characteristics of overgrown AlGaN films

In this study, the properties of Al 0.18Ga 0.82N films grown on stripe-grooved GaN templates with different trench depths have been investigated by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), double crystal X-ray diffractometer (DCXRD), and photoluminescence (PL) measurement. Based upon the results of FESEM observations, a crack-free Al 0.18Ga 0.82N surface has been achieved using a GaN template with 1-μm-deep trenches. Moreover, from the observations of TEM, the density of threading dislocations in Al 0.18Ga 0.82N film was found to reduce during the lateral growth on the trench regions. DCXRD and PL both measurements were carried out to determine the quality of the Al 0.18Ga 0.82N films. The full-width at half-maxima of double crystal X-ray rocking curve and PL spectrum are the smallest, respectively, for the Al 0.18Ga 0.82N film grown on grooved GaN template having 1 μm-deep trenches. It is believed that the use of the grooved GaN templates effectively improves the quality of the overgrown Al 0.18Ga 0.82N films.

Structural and luminescent properties of ZnO epitaxial film grown on Si(1 1 1) substrate by atmospheric-pressure MOCVD

Epitaxial ZnO thin films have been grown on 2-in diameter Si(1 1 1) substrates by atmospheric-pressure metalorganic chemical vapor deposition. An initial Al layer with a thickness of 10 Å was deposited in order to protect the Si surface from oxidation. The structural property was characterized using a double-crystal X-ray diffractometer, and the photoluminescence spectra were measured using the excitation of 325 nm line of a He–Cd laser. The minimum full-width at half-maximum (FWHM) of the diffraction peak of ZnO(0 0 2) is 0.35° and 0.16° for the ω and ω - 2 θ scans, respectively. Free-exciton emission with a shoulder at the bound-exciton peak was observed at 10 K. Microscopic images show cracks for the sample of 3.0 μm thickness, and the crack density is about 7.6×10 2/cm −1. The maximum area of a crack-free triangular region is bout 1756 μm 2.

Characterization of Si1−xGex∕Si layers and depth profile of their heterobipolar transistor structures by high-resolution x-ray diffractometry and computer simulations

Using high-resolution x-ray diffractometry (HRXRD) and computer simulations, germanium content x, thickness T of pseudomorphic Si1−xGex layers, and Ge depth profile in their advanced heterobipolar transistor (HBT) structures grown on (001)Si substrates have been determined. High-resolution rocking curves (RCs) with well-resolved intensity oscillations have been recorded by using a double-crystal x-ray diffractometer in (+,−) geometry with CuKα1 radiation from a 12-kW rotating anode x-ray generator. The experimental RCs were simulated with the in-house developed computer program based on the semikinematical theory. In addition to the Ge depth profile, the thickness of SiGe layer, Si cap layer, and SiGe plateau layers of the HBT structures have been determined for the best fit of the experimental RCs with the theoretically simulated RCs. Due to the decay of intensity oscillations, in the case of partially relaxed layers, the values of germanium content x and relaxation R were calculated from the perpendicular and parallel (in-plane) lattice constants a⊥ and a‖ obtained by recording a pair of RCs from symmetric and asymmetric lattice planes. The simulation method using HRXRD has been described with the help of typical results obtained from samples of different structures. In this method the maximum error values of x and T are, respectively, ±0.5% and 1%. The error in the value of R is ±2% for partially relaxed samples. In the case of HBT structures, the maximum error in the value of thickness of SiGe and cap layers is ±1% and that of plateau layer is ±5%. The method is very convenient, faster, accurate, and nondestructive in comparison with other methods such as transmission electron microscopy and Secondary-ion-mass spectroscopy.

Strained InAsN/InGaAs/InP multiple quantum well structures grown by RF-plasma assisted GSMBE for mid-infrared laser applications

The authors report the growth, structural and optical characteristics of strained 10-period InAs1−xNx/In0.53Ga0.47As multiple quantum well (MQW) structures on InP substrates grown by gas-source molecular beam epitaxy. Atomic nitrogen was generated using a RF-plasma cell. Double crystal X-ray diffractometer (DXRD) measurements indicated that adding N to the InAs layer reduced the net compressive strain of the MQW. The highest nitrogen composition obtained in this study was 19.5%. It was also found that the incorporation of nitrogen resulted in red-shifted photoluminescence (PL) emission energy of the QWs. However, increased nitrogen composition broadened the DXRD linewidth and degraded PL intensity. The very broad PL linewidth might be related to alloy inhomogeneity. Finally, ridge waveguide lasers with different periods (n=2–8) of InAs0.97N0.03/InGaAs QWs as the gain medium were fabricated. A device with four QWs gave the best performance and demonstrated pulsed oscillation up to 260K at an emission wavelength of 2.38 µm with a threshold current density of 3.6 kA/cm2. This indicates the potential of InAsN as a material for mid-infrared applications.

An x-ray rocking curve technique for the absolute characterization of epitaxial layers and single-crystal solids

A rapid double-crystal x-ray diffractometer technique for the absolute measurement of lattice parameters in single crystals and epitaxial layers is introduced. The method is based on the principle that in a diffractometer aligned for rocking curve measurements within a given zone, the zero setting correction is the same for all crystal angles within the zone. The peak positions can thus be measured and corrected quickly, and the lattice parameters evaluated within each layer independently of others. The proof-of-principle tests are given for Si and InP, and the method is applied to a GaN film grown on an a-plane sapphire wafer. The method has unlimited accuracy depending only on the instrumental alignment and material quality.

Double-crystal x-ray diffractometry of single crystals withmicrodefects

The known method of the `integral' diffuse scattering has beengeneralized in the Bragg case of x-ray diffraction for crystals, which containlarge microdefects commensurable with the extinction length. In the frameworkof the developed statistical dynamical theory, relatively simpleanalytical expressions have been derived for coherent and diffuse componentsof reflectivity of single crystals with randomly distributed microdefects.To test the characterization possibilities of the proposed method, the rockingcurves (RCs) of Czochralski-grown silicon single crystal annealed at1080 °C for 6 h have been measured for 111 and 333 reflections ofCu Kα1 radiation using a high-resolution double-crystal x-raydiffractometer. The fitting results for the two RCs are in good mutualagreement and demonstrate the high information ability of the method.

Experimental characterization of bent focusing crystals

It has been established with the aid of a double-crystal X-ray diffractometer that the nonuniform curvature of cylindrically, spherically, or thoroidally bent silicon and quartz crystals is of a periodic character. It is shown that this periodicity influences the spectral (energy) resolution of a focusing crystal, which becomes noticeable at the Bragg angle θ obeying the condition tan2 ≫ 1.

Multiplicity factor and diffraction geometry factor for single crystal X-ray diffraction analysis and measurement of phase content in cubic GaN/GaAs(001) epilayers

On the basis of integrated intensity of rocking curves, the multiplicity factor and the diffraction geometry factor for single crystal X-ray diffraction (XRD) analysis were proposed and a general formula for calculating the content of mixed phases was obtained. With a multifunction four-circle X-ray double-crystal diffractometer, pole figures of cubic (002), {111} and hexagonal {1010} and reciprocal space mapping were measured to investigate the distributive character of mixed phases and to obtain their multiplicity factors and diffraction geometry factors. The contents of cubic twins and hexagonal inclusions were calculated by the integrated intensities of rocking curves of cubic (002), cubic twin {111}, hexagonal {1010} and {1011}.

Growth and characterization of large-size bismuth germanate single crystals by low thermal gradient Czochralski method

Nearly perfect Bi 4Ge 3O 12 (BGO) single crystals of ∼40 mm diameter and ∼80 mm length were grown along [0 0 1] by low thermal gradient Czochralski method employing automatic high-resolution weight control feed back loop. Optimized growth parameters were: seed pulling rate 2.5 mm/h and seed rotation rate 38 rpm. High-resolution X-ray diffractometry and topography methods were used to characterize these crystals by employing a double crystal X-ray diffractometer designed and developed at NPL. Major part of the crystal discs examined were found to have high degree of perfection with diffraction curve half-widths of ∼9 arcsec. However, small regions at the peripheries of the discs showed very low angle grain boundaries with tilt angle of ∼30 arcsec. The subgrains were directly imaged in high-resolution X-ray diffraction topographs.

Growth and characterization of GaN epilayers grown at various flow rates of trimetylgallium during growth of nucleation layers

GaN epilayers have been grown on GaN nucleation layers as a function of the flow rate of TMG (trimetylgallium) decreases by deposition (MOCVD). The size of crystalline and amorphous GaN droplets became smaller as the flow rate of TMG (10.0, 8.0, 6.0, 4.0 SCCM, respectively) decreases during the growth of nucleation layers having the same thickness. The surface morphology and crystallinity of the epilayers characterized by DCXRD (double crystal X-ray diffractometer) depend on the TMG flow rate during growth of the GaN nucleation layers. The GaN epilayers grown on a nucleation layer at a rate of 8.0 SCCM exhibits the best crystallinity.

The APS optics topography station

An in-house station for topographic testing of x-ray optical elements for the Advanced Photon Source experimental beamlines was set up by the Experimental Facilities Division of Argonne National Laboratory. A new double-crystal x-ray diffractometer was designed and built keeping in mind the need for testing large crystals possibly attached to cooling manifolds and lines. A short description of the new facility is given. The instrument performance fully satisfies imposed requirements, and the machine was successfully used for testing several silicon and diamond crystals.

Study of Biaxial Stress Induced by Cosputtered Thin Molybdenum Silicide Films in Silicon Single-Crystal Substrates

Bending of 25 mm-diameter (100) silicon wafers produced by 100 nm-thick cosputtered molybdenum–silicon films has been investigated just after deposition, after rapid thermal annealing and after etching of the deposits. Values of biaxial stress in the films were determined by the use of a widely used relation. The Mo:Si ratio in the as-deposited films was 89:11. Radii of curvature of substrates were measured by a double-crystal X-ray diffractometer. Blank wafers with three widely different radii of curvature (33, 62 and 250 m) were chosen as specimens and their curvatures were taken into account in the determination of the value of biaxial stress in wafers with deposits. All the wafers were convex when viewed from the polished surface side on which the films were deposited. Values of σ for wafers with as-deposited films were in the range 3 × 108 to 14 × 108 Nm−2 (tensile). Wafers with higher initial bending showed higher values of stress. Deposition led to degradation of perfection, as revealed by broadening of the diffraction curves and the contrast in the topographs. Rapid thermal annealing at 1273 and 1373 K (3–4 min) led to formation of the MoSi2 phase and to a notable relaxation of stress. The values of σ were in the range 1 × 107 to ~6 × 108 N m−2 (tensile). The value of the stress was lowest for the blank wafer with smallest bending. Annealing also improved the degree of crystalline perfection of the silicon. Experiments performed after etching of the annealed specimens showed no significant change in the radii of curvature.