Triple-crystal Diffractometry Research Articles

Simulation of Reciprocal Space Maps with the Use of Spectral Angular Diagrams in the Triple Crystal X-Ray Diffraction Scheme

An approach to the simulation of reciprocal space maps corresponding to the maps obtained experimentally by the triple crystal X-ray diffractometry (TXD) is proposed. A specific feature of the approach is the use of spectral angular distribution diagrams of X-ray radiation, which allows one to visualize the two-dimensional pattern of the spectral angular “composition” of an X-ray beam after its interaction with each element of the scheme and thus to take into account the contribution of the hardware function of the experimental setup. The algorithms developed allow calculations for a wide class of radiation sources (from an X‑ray tube with any material of the anode to a synchrotron radiation source) and X-ray optical elements (slits, X-ray mirrors of monochromators, and analyzers). The results of simulation are compared with the experimental data for dispersive diffraction geometry, which confirms the adequacy of the proposed approach and its applicability to the simulation of a diffraction pattern corresponding to a real experiment in the triple crystal scheme.

Дисперсійна (фазова) природа структурної чутливості та інформативності однокристальної дифрактометрії дефектів і деформацій в іонно-імплантованих плівках

Дисперсійна (фазова) природа структурної чутливості та інформативності однокристальної дифрактометрії дефектів і деформацій в іонно-імплантованих плівках

X-ray diffraction methods for diagnostics of surface and nanolayers of crystalline structures (review)

X-ray diffraction methods for investigation of thin surface layers of crystals and characterization of the structures containing nanolayers are considered: double- and triple-crystal diffractometry, asymptotic diffraction, and diffraction under conditions of total external reflection of X-rays. Theoretical foundation of the methods and conditions of their experimental implementation are described and exemplified.

X-ray study of structural features of GaSb(Si) single crystals grown using a set of diffraction methods under various heat and mass transfer conditions

Structural features of GaSb(Si) single crystals grown under various heat and mass transfer conditions were studied by x-ray topography and by double- and triple-crystal diffractometry. It was shown that a decrease in the convective flow intensity during crystal growth by the vertical Bridgman method with axisymmetric upper heat supply in comparison with the Czochralski method eliminates growth striations (caused by microsegregation) and improves the uniformity of electrical parameters of materials. According to triple-crystal x-ray diffractometry data, the increased density of structural defects observed in some crystal regions causes significant lattice distortions, which makes an additional contribution to crystal inhomogeneity. Some specific features in x-ray topography images of growth striations, caused by a high silicon concentration and a dopant state deviation from an ideal substitutional solid solution, were revealed.

Acoustic Pulse Echoes Probed with Time-Resolved X-Ray Triple-Crystal Diffractometry

Acoustic pulse echoes generated by femtosecond laser irradiation were detected using time-resolved x-ray triple-crystal diffractometry. The determined time-dependent longitudinal strain component for pulse echoes in silicon and gallium arsenide plates showed that the polarity of the strain pulse was dependent on the optically induced initial stress, and that the bipolar pulse waveform was gradually deformed and broadened in the course of propagation. The three-dimensional wave front distortion of pulse echoes was shown simply as the pulse duration broadening, which was consistent with a boundary roughness for an unpolished plate.

Determination of the dynamic deformation tensor by time-resolved triple-crystal diffractometry

Triple-crystal X-ray diffractometry has been combined with time-resolved measurement techniques. A simple time-resolved technique was employed by using a digital storage oscilloscope and a fast X-ray detector. The time dependence of the deformation tensor was determined for a gallium arsenide wafer after a flash of a 130 fs laser pulse. The laser pulse produced instantaneous expansion resulting in a localized convex surface. Time-resolved measurements showed that a flexural standing wave, explained well by the classical elasticity theory for thin plates, appeared in the relaxation process.

Satellite peak splitting in the X-ray diffraction rocking curves of a crystal modulated by surface acoustic wave

A theory of the X-ray diffraction modulated by surface acoustic wave in a crystal has been developed in a kinematical approximation in application to double-and triple-crystal diffractometry. The proposed theory is applied to interpretation of the experimentally observed splitting of satellite peaks in the rocking curves.

Raman and X-ray studies of nanocrystals in porous stain-etched germanium

Using a combination of stain-etching with subsequent annealing in hydrogen, porous germanium films with a high concentration of germanium nanocrystals (NCs) were prepared for the first time. Structural studies of the films were performed by X-ray reflectometry and high-resolution triple-crystal diffractometry and Raman light spectroscopy methods. From a thorough analysis of the experimental data obtained by both methods, it was revealed that the films consist of germanium NCs with average sizes approximately 8–10 nm in annealed films. Other basic information about thickness, porosity, roughness, and lateral coherence length of the films is also presented.

X-ray diffraction determination of the interface structure of CdSe/BeTe superlattices

Structural study of CdSe/BeTe superlattices (SLs) grown by molecular beam epitaxy on GaAs substrate was performed by using double and triple crystal x-ray diffractometry. The period of the studied structures was about 5 nm, while the thickness of thin CdSe insertions varied from 0.4 to 1.5 monolayer. It is shown that new Be–Se bonds arise at the BeTe–CdSe interfaces in addition to the Be–Se bonds expected at the CdSe–BeTe interfaces. From the analysis of the diffraction curves of 002-reflection the complex composition of interfaces and thin insertions has been determined and contribution of all types of bonds in each SL period calculated. The diffraction curves of 004-reflection were used for the specification of the fine structure of the interfaces.

Influence of defects on the critical behavior at the 105 K structural phase transition ofSrTiO3:On the origin of the two length scale critical fluctuations

The temperature dependence of the sharp and the broad component of the critical scattering above the cubic-to-tetragonal phase transition of ${\mathrm{SrTiO}}_{3}$ has been studied by means of high-resolution triple-crystal diffractometry using 100--200 keV synchrotron radiation in five samples differing with respect to growth technique and oxygen vacancy concentrations. Emphasis is on changes in the critical behavior, the critical temperature, and the strain fields at the transition from bulk to surface. The sharp component was observed only in surface near regions of highly perfect crystals and is coupled to the occurrence of a long-range strain gradient that was identified by an exponential increase of mosaicity, lattice parameter fluctuations, and Bragg-peak intensity when approaching the surface from the bulk of the sample. Vanishing of the sharp component was observed at the polished/etched surface of a platelet cut off the large perfect crystal after release of strain due to free bending of the platelet. The values of the critical temperature observed in the bulk of the different samples vary between $98.7l~{T}_{c}l~105.8 \mathrm{K}.$ In the surface near regions of a highly perfect float-zone grown crystal a variation of ${T}_{c}$ of about 0.5 K has been found. Concerning the broad component the critical exponent describing the temperature dependence of the inverse correlation length ${\ensuremath{\kappa}}_{b}$ varies between $0.73l~{\ensuremath{\nu}}_{b}l~1.19,$ the exponent for the susceptibility between $1.49l~{\ensuremath{\chi}}_{b}l~2.9,$ however, the ratio of the two exponents is almost sample independent and equal to ${\ensuremath{\chi}}_{b}/{\ensuremath{\nu}}_{b}=2.1$ with a variance of 0.2, in good agreement with the theoretical value of 1.97 obtained by LeGouillou and Zinn-Justin [Phys. Rev. B 21, 3976 (1980)]. The occurrence of the sharp component did not affect significantly the critical exponents for the underlying broad component of the critical scattering. The exponents for the sharp component observed in surface near layers of about 100 $\ensuremath{\mu}\mathrm{m}$ thickness at the highly perfect float zone and flux grown crystals varied between $0.58l~{\ensuremath{\nu}}_{s}l~1.30,$ the values for the ratio varied between $3.3l~{\ensuremath{\chi}}_{s}/{\ensuremath{\nu}}_{s}l~4.6.$ The average value of ${\ensuremath{\chi}}_{s}/{\ensuremath{\nu}}_{s}$ is 3.9 with a variance of 0.5, and is about twice the ratio ${\ensuremath{\chi}}_{b}/{\ensuremath{\nu}}_{b}$ for the broad component as suggested by Harris et al. [Phys. Rev. B 52, 14 420 (1995)].

Triple crystal diffractometry, x-ray standing wave, and transmission electron microscopy investigation of shallow BF2 implantation in Si

Si wafers implanted at 5, 15, and 50 keV with different BF2+ doses and next annealed at 945 °C for 45 s, were studied by means of x-ray triple crystal diffraction, x-ray standing wave, and transmission electron microscopy methods. Due to the implantation energies used, very narrow subsurface regions with a depth ranging from a few tens of nanometers to a few nanometers were damaged. By fitting the diffraction curves and using the information obtained from the photoelectrons emitted by the x-ray standing wave field, it was possible to determine the most appropriate strain and damage profiles versus depth within the disturbed region of the crystal. The above results made it possible to find: (i) the distribution of interstitial ions produced during the implant processes; (ii) the depth of amorphization of the implanted regions at the highest doses; and (iii) the appearance of extended defects (dislocation loops band) at the amorphous/crystal interface during the restoration of the lattice by the annealing process. Transmission electron microscopy investigations and electrochemical capacitance–voltage profiling measurements were made on several annealed samples and the results obtained by the x-ray diffraction and standing wave methods were confirmed.

Damage profiles determination in ultra-shallow B + implanted Si by triple crystal X-ray diffraction and transmission electron microscopy

B + ions were implanted in Si at ultra-low energies: 0.25, 0.5 and 1 keV, respectively, and at different doses: 1×10 14, 1×10 15 cm −2. Lattice distortion and disorder due to the implantation process were investigated by means of a high resolution X-ray diffraction method. Due to the very low implantation depth (a few nm), the X-ray diffraction measurements were carried out by triple-crystal diffractometry. With this experimental configuration it was possible to separate coherent from diffuse scattering, considerably improving the signal-to-noise ratio. For the analysis of the experimental curves, the subsurface region was divided in several thin layers. The layer thickness, the static Debye–Waller factor, which is related to the lattice damage, and the lattice spacing modification (strain) were the parameters of the fitting procedure. Despite the small thickness of the ‘subsurface-damaged area’, it was possible to obtain the main parameters describing the depth distribution of the lattice distortions in the analyzed crystals. Transmission electron microscopy investigations were made on two samples implanted at the lowest energies and the results obtained by the X-ray diffraction were confirmed.

Reduction of dislocation density in GaN films on sapphire using AIN interlayers

GaN (00.1) thin films, of thickness 1.25 to 2.25 μm grown on sapphire substrate (11.0) by metallo organic chemical vapor phase deposition (MOCVD) with different number of AlN interlayers, were characterized by triple crystal diffractometry and synchrotron white beam x-ray topography (SWBXT). The full width at half maximum (FWHM) of x-ray rocking curves from symmetric and asymmetric reflections was used to estimate the dislocation density in GaN films. It has been found that the edge dislocation density decreased from 1.63 × 1010 cm−2 to 1.23 × 1010 cm−2 and the screw dislocation density decreased from 2.0 × 108 cm−2 to 1.1 × 108 cm−2 when one AlN interlayer was inserted between the high temperature GaN layer. The dislocation density decreased further with the increase in number of interlayers. On the other hand the compressive stress in the GaN film increased from −0.29 GPa to −0.86 GPa. The compressive stress further increased as the number of interlayers increased but no cracking in the GaN film was observed. This could be due to better adhesion between the film and substrate due to interlayers. SWBXT in transmission from a GaN(00.1)/Al2O3(11.0) sample confirms the orientation of GaN and indicates that it is a single crystal with high dislocation density. SWBXT from the Al2O3 substrate shows cellular structure of dislocations.

The perfection of space-grown GaSb studied by X-ray topography and high-resolution diffractometry

Space-grown GaSb single crystal doped with Te was investigated by X-ray projection topography and high-resolution triple crystal diffractometry. It was shown that a large part of the sample grown without contacting the crucible is of rather high perfection: it is striation free and only few dislocation lines are present there. However, it was found that large microdefects (exceeding 1 μm in diameter) are present, their density being ∼4×10 4 cm −3. Nevertheless, the number of small microdefects (smaller than 1 μm in diameter) is considerably less than that in terrestrially grown GaSb. A twin boundary was found between this space-grown and the other part-grown in contact with the ampoule walls. Besides the twin, it was found that dislocations at a density up to ∼10 4 cm −3 were generated. The end part of the ingot contains dislocations with a density higher than 10 6 cm −3, which were induced due to high thermal stresses at the final stage of crystallization.

Deformations in (Al,Ga)As epitaxial layers wafer bonded on dissimilar substrates

Deformations in heteroepitaxial layer stacks of AlGaAs/GaAs grown on GaAs are measured by triple crystal diffractometry before epitaxial liftoff and after subsequent wafer bonding on various substrates (GaAs, glass, Si, and LiNbO3). The tetragonal deformation present in the as-grown layer stack partially relaxes during epitaxial liftoff. The roughness of the as-grown layer stack gives rise to a bending of the atomic planes after wafer bonding. The widths of the x-ray diffraction peaks are used to estimate the misorientation of the lattice planes and compared with the atomic force microscopy measurements of the surface roughness.

The effect of high-temperature epitaxial SiC layer growth on the structure of porous silicon carbide

Porous silicon carbide layers obtained by electrochemical etching of 6H-SiC at three anode current densities were investigated. X-ray double-and triple-crystal diffractometry and scanning electron microscopy were used to study the structure of porous SiC layers before and after high-temperature sublimation growth of 6H-SiC epilayers. The density of pores in the structure is found to be independent of the current density in electrochemical etching. The effective diameter of pores increases with increasing current density, resulting in higher porosity of the structure. High-temperature annealing modifies the structure without changing the sample porosity. The structural rearrangement is accompanied by coalescence of single pores and an increase in their diameter.

Morphological and structural characteristics of homoepitaxial 4H-SiC thin films by chemical vapor deposition using bis-trimethylsilylmethane precursor

High quality 4H-SiC monocrystalline films were homoepitaxially grown on 8.0° off-oriented (0001) 4H-SiC at a low temperature (1643 K) by metal-organic chemical vapor deposition (MOCVD). The correlation between the structural properties of the films and the growth parameters, in particular, the substrate temperature, and the flow rate of source material BTMSM, was investigated to elucidate the possible benefits of a single precursor on low-temperature thin film growth. The films were examined by optical microscopy, scanning electron microscopy (SEM), triple crystal X-ray diffractometry (TCD), and photoluminescence. Reciprocal space mapping results of the (0004) Bragg spot showed that the full width at half maximum (FWHM) of the rocking curve of the epilayer grown at 1643 K was 9.3 arcsec, which is extremely low as compared with the lowest value reported (13 arcsec). The high film quality was confirmed by low-temperature photoluminescence. The homoepitaxial growth condition for high quality monocrystalline 4H-SiC was also suggested in terms of the growth temperature and supersaturation of the source material.

Triple-crystal diffractometry, x-ray standing wave and reciprocal spacemapping study of homoepitaxial grown Si layers

Homoepitaxial Si films have been synthesized by magnetron sputterepitaxy at substrate temperatures of 570 °C. The films have beencharacterized by high-resolution x-ray diffraction (HRXRD), by triple-crystaldiffractometry (TCD), by x-ray standing-wave method (XSW) and by reciprocalspace mapping (RSM). It is shown that for highly defective films, theinformation obtained from HRXRD or TCD alone might not be enough to reveal thecomplete film structure. With the addition of XSW and RSM, however, acomprehensive view of the investigated structure can be obtained.

Anisotropy of fields of stress in Si monocrystals with ordered dislocation structure

An attempt is made with X-ray triple crystal diffractometry to detect anisotropy of X-ray scattering by a structure consisting of a number of parallel dislocations, introduced into silicon by specially controlled sample deformation. Diffuse component scattering increased if the plane of scattering was perpendicular to the direction of dislocations ( ϕ=90°). The magnitude of this effect increases with increasing density of the introduced dislocations and depends on the direction of their Burgers vectors. The respective changes of the equal-intensity contours of X-ray scattering near reciprocal lattice points for the 111 reflection are investigated. The magnitudes of coherent and diffuse components of integral reflectivity were obtained experimentally. This yields quantitative information on the diffraction characteristics of structural perfection of the material. The dependencies of these characteristics are given, as well as of half-widths of a principal peak of a diffraction curve, on the angle of sample orientation relative to the X-ray beam ϕ and ϑ B. A comparison of appropriate data with those obtained for dislocation-free crystals of non-crucible zone melting silicon is carried out. The results obtained are discussed within the framework of existing theories of X-ray scattering and dislocation complexes.

Low temperature chemical vapor deposition of 3C-SiC on 6H-SiC — high resolution X-ray diffractometry and synchrotron X-ray topography study

Highly perfect 3C-SiC thin films, deposited on 6H-SiC by the chemical vapor deposition at low temperature with various Cl/Si, H/Si and C/Si ratios, were characterized by X-ray high resolution triple crystal diffractometry, synchrotron white beam X-ray topography (SWBXT) and synchrotron grazing incidence topography (SGIT) methods. The films were epitaxial with a low defect density (mostly in the range of 10 7 cm −2). The best films were produced with optimum C/Si ratio in the gas phase while the poorest quality films were produced at lower H 2/Si ratio. Synchrotron topography revealed defects like cellular dislocation structure, super screw dislocations, pores, low angle grain boundaries and double positioning boundaries.