Rocking Curve Measurements Research Articles

Structural properties of Eu doped gallium oxide films

We have investigated structural properties of Eu doped gallium oxide (Ga2O3) films grown by pulsed laser deposition at different substrate temperature. X-ray rocking curve and Raman spectroscopy measurements prove that the films grown at the substrate temperature above 400°C are of monoclinic β-Ga2O3 structure and the crystalline quality of the films depends on the substrate temperature. X-ray absorption near edge structure measurements indicate that the valence of Eu ions in the Eu doped Ga2O3 films varies from mixture of bivalent and trivalent to only trivalent with increasing substrate temperature. Extended X-ray absorption fine structure analysis reveal that the Eu atoms doped in Ga2O3 matrix are incorporated on Ga sites in Ga2O3 matrix even for the films with amorphous structure grown at low substrate temperature.

Simulated x-ray diffraction from pseudomorphic GaAs/In0.3Ga0.7As superlattice high electron mobility transistor heterostructures on GaAs (001) substrates

In this paper, the authors report a study of the simulated dynamical x-ray diffraction from GaAs/In0.3Ga0.7As superlattice high electron mobility transistor heterostructures on GaAs (001) substrates both with (metamorphic) and without (pseudomorphic) dislocations. The analysis of dynamical x-ray diffraction for 004, 115, 026, and 117 reflection profiles was conducted for the case of Cu kα1 radiation. The authors show that the threading dislocation density may be estimated from nondestructive x-ray rocking curve measurements, using the rocking curve peak intensity ratios or widths for superlattice diffraction peaks. Despite the complexity of these multilayered device structures and the resulting x-ray diffraction profiles, analysis of the 004 x-ray diffraction profile allows characterization of the pseudomorphic–metamorphic transition in them and is of considerable practical importance for device realization.

X-ray analysis of metamorphic InxGa1-xAs/InyGa1-yAs superlattices on GaAs (001) substrates

The authors present a detailed x-ray dynamical diffraction analysis of metamorphic InxGa1-xAs/InyGa1-yAs superlattices grown epitaxially on GaAs (001) substrates. The x-ray rocking curve analysis was conducted for a number of hkl reflection profiles, including 004, 115, 026, and 117, assuming Cu kα1 radiation, by using the mosaic crystal model for dynamical diffraction. The authors show that the threading dislocation density in the superlattice can be estimated from nondestructive x-ray rocking curve measurements, by observing the superlattice peak widths.

Top-Seeded Solution Crystal Growth and Linear and Nonlinear Optical Properties of Ba4B11O20F

A single crystal of Ba4B11O20F (BBOF) with dimensions of 20 × 17 × 12 mm3 was successfully grown using the top-seeded solution growth method. BBOF melts incongruently; as such several flux systems are discussed. The morphologies and growth habits of BBOF crystals grown with differently oriented seeds, [100], [010], and [001], were investigated. Using the [010]-oriented seed, the single crystal exhibits (200) and (010) faces. Rocking curve measurements indicate that the single crystal is of high quality with a full width at half-maximum (fwhm) of 0.017° (61 arcsec) from the (010) reflection. The transmission spectrum and the refractive indices from the UV to the near-infrared region are reported. BBOF is transparent from 190–2500 nm and exhibits a birefringence of 0.0146 at 1064 nm. The type-I phase matching wavelength region was determined based on the fitted Sellmeier equations to the refractive index data. BBOF is type-I phase-matchable with fundamental (second-harmonic) wavelength ranges from 1049–2348...

Single-Crystal Growth of ZnO:Ga by the Traveling-Solvent Floating-Zone Method

Transparent and blue ZnO:Ga (GZO) single crystals have been grown by the traveling-solvent floating-zone technique using the solvent B2O3 + MoO3 + Nb2O5. The crystals were typically 9–14 mm in diameter and 46–120 mm in length. The largest one was Φ12 mm × 120 mm in size. All GZO crystals were grown along the direction. The growth rate was 0.3–0.5 mm/h, which was far faster than 0.1 mm/day of that grown by the hydrothermal method. The crystalline quality has been characterized by single crystal X-ray diffraction and X-ray rocking curve measurements. Ga substituted on Zn-site and was saturated at about 0.5 wt % of Ga2O3 addition. The GZO crystal doped with 0.5 wt % Ga2O3 has the lowest electrical resistivity of 1.083 × 10–3 Ω·cm and the highest carrier concentration of 1.78 × 1020 cm–3.

Czochralski growth and characterization of cerium doped calcium scandate

A cylindrical cerium doped CaSc2O4 bulk single crystal with a diameter of 20 mm and a total length of 70 mm was grown from the melt by the Czochralski method. Due to competitive growth and grain selection, the crystal shows high crystalline quality, verified by X-ray diffraction (XRD) rocking curve measurements and by the energy dispersive Laue mapping (EDLM) method. Rocking curve measurements revealed full width at half maximum (FWHM) values of 24, 28 and 34 arcsec for 200, 020 and 002 reflexes, respectively. The anisotropic optical and thermal properties of the biaxial material were investigated by UV-vis spectroscopy, ellipsometry and by the laser flash technique along the main crystallographic orientations. TEM measurements confirmed that cerium is preferentially incorporated into the Ca-site.

Nanopipe formation as a result of boron impurity segregation in gallium nitride grown by halogen-free vapor phase epitaxy

The work reported herein demonstrated that nanopipes can be formed via a surfactant effect, in which boron impurities preferentially migrate to semipolar and nonpolar facets. Approximately 3 μm-thick GaN layers were grown using halogen-free vapor phase epitaxy. All layers grown in pyrolytic boron nitride (pBN) crucibles were found to contain a high density of nanopipes in the range of 1010 to 1011 cm−2. The structural properties of these nanopipes were analyzed by X-ray rocking curve measurements, transmission electron microscopy, and three-dimensional atom probe (3DAP) tomography. The resulting 3DAP maps showed nanopipe-sized regions of boron segregation, and these nanopipes were not associated with the presence of dislocations. A mechanism for nanopipe formation was developed based on the role of boron as a surfactant and considering energy minima. A drastic reduction in the nanopipe density was achieved upon replacing the pBN crucibles with tantalum carbide-coated carbon crucibles. Consequently, we have confirmed that nanopipes can be formed solely due to surface energy changes induced by boron impurity surface segregation. For this reason, these results also indicate that nanopipes should be formed by other surfactant impurities such as Mg and Si.

Surface modification of a-plane sapphire substrates and its effect on crystal orientation of ZnTe layer

Domain structures of ZnTe layers grown on a-plane sapphire substrates were investigated by changing the crystallographic properties of the surface and interface. Pole figure images were obtained and we investigated the domain structure in the grown film and the orientation relationships between films and substrates. It was confirmed that two kinds of {111} domains were oriented by annealing the buffer layer at 350 °C, while the (100) domain was obtained by annealing the buffer layer at 300 °C. From the results of the rocking curve measurement, the introduction of a step-terrace surface through the high-temperature treatment of the substrate resulted in an improved crystallographic quality. However, it did not affect the domain structure in the layer. The introduction of an off-angle on the substrate surface resulted in the formation of a single (111) domain layer. These crystallographic features were mainly affected by the surface atom arrangement of the sapphire substrate and its chemical nature.

Bulk growth and magneto-optical property of K3B6O10Br polar crystal

A series of K3B6O10Br (KBB) polar crystals have been grown along <110>, <210> and <001> seed directions by top seeded solution growth (TSSG) method. By optimizing the growth condition, transparent KBB crystal with the sizes of 52×29×25mm3 was successfully grown by using seed <001>-orientation from KF–PbO flux. The full-width at half-maximum (FWHM) and optical homogeneity were measured as 0.0038° and 3.3×10−5 from the rocking curve and optical interferometry measurements, respectively, indicating high optical quality of the as-grown crystals. The Verdet coefficient of KBB crystal was obtained as 5.3radT−1m−1 at 635nm by comparative method.

Improved crystalline quality of N-polar GaN epitaxial layers grown with reformed flow-rate-modulation technology

A reformed flow-rate-modulation technology was developed for the metalorganic vapor phase epitaxy (MOVPE) growth of the N-polar GaN epitaxial layers. To improve the crystalline quality of the N-polar GaN epitaxial layers, a GaN nucleation layer was grown at relatively low temperature with carefully-controlled pulsed supply of Ga source and showed diverse morphology with atomic force microscope (AFM). Furthermore, the electrical and optical properties of the grown N-polar GaN epitaxial layers were investigated extensively by means of Hall effect, photoluminescence (PL), and X-ray rocking curve (XRC) measurements. The characterization results revealed that as compared with the N-polar GaN epitaxial layer grown over the conventional GaN nucleation layer which was deposited with continuous supply of both N and Ga sources, the electrical and optical properties of the N-polar GaN epitaxial layer grown with optimized supply of Ga source for the GaN nucleation layer were significantly improved.

Top-seeded solution growth of SrTiO3 single crystals virtually free of mosaicity

Strontium titanate (SrTiO3), a well-established traditional perovskite substrate as well as a promising substrate crystal for the epitaxy of new advanced perovskite-type thin films, suffers from the unavailability in adequate quality for the latter. To improve the situation attempts have been made to grow SrTiO3 at moderate temperatures (<1535°C) well below the melting temperature and under low temperature gradients by the top-seeded solution growth method. Based on very special modifications of the growth conditions, virtually mosaicity-free SrTiO3 single crystals in the 1–2cm range were obtained. High crystalline quality was verified by defect selective etching, rocking curve measurements, energy dispersive Laue mappings and by synchrotron X-Ray diffraction topography. The production of virtually subgrain- and dislocation free substrate crystals is essential to considerably improve characteristics of SrTiO3 based SQUIDs, transistors or memory devices and to allow an in-depth analysis of intrinsic and extrinsic factors influencing the properties of epitaxially grown oxide heterostructures.

Epitaxial growth of Ge thin film on Si (001) by DC magnetron sputtering

We have demonstrated that sub-10nm-thick heteroepitaxial Ge films on Si (001) having smooth surfaces can be obtained by DC magnetron sputtering. Ge films grown at 350°C preserve the smooth surfaces with a roughness root mean square (RMS) of 0.39nm, whereas, the Ge films grown at 500°C show significant roughness with an island-like morphology. In samples grown at 350°C, it is confirmed that the Ge films are grown epitaxially by cross-section transmission electron microscopy (TEM) and X-ray diffraction (XRD) rocking curve measurements. Rapid thermal annealing (RTA) at 720°C is effective in improving the crystalline quality and the degradation in the roughness is negligible. Raman spectra and an XRD reciprocal space map reveal that the epitaxial Ge grown at 350°C show an in-plane compressive strain and that the strain continues to remain after a 720°C RTA.

Crystallization Technique for Strain-free Protein Crystals Using Cross-linked Seed Crystals

In this study, we show using X-ray diffraction (XRD) rocking-curve measurements that local strain in tetragonal hen egg white (HEW) lysozyme crystals can be removed to a large degree by utilizing seed crystals cross-linked with glutaraldehyde. We also find that misorientation between subgrains and subgrain size decrease when employing cross-linked seed crystals, which suggests that subgrain formation in tetragonal HEW lysozyme crystals can be controlled using this technique. The ideal mosaic structure of proteins that enables the collection of accurate integrated intensities of the diffracted waves is also discussed using tetragonal HEW lysozyme crystals as a model protein.

Structural transformations in highly oriented seven modulated martensite Ni–Mn–Ga thin films on an Al2O3 substrate

Abstract

A new system for sodium flux growth of bulk GaN. Part II: in situ investigation of growth processes

We report recent results of bulk GaN crystal growth using the sodium flux method in a new crucible-free growth system. We observed a (0001) Ga face (+c-plane) growth rate >50µm/h for growth at a N2 overpressure of ~5MPa and 860°C, which is the highest crystal growth rate reported for this technique to date. Omega X-ray rocking curve (ω-XRC) measurements indicated the presence of multiple grains, though full width at half maximum (FWHM) values for individual peaks were <100 arcseconds. Oxygen impurity concentrations as measured by secondary ion mass spectroscopy (SIMS) were >1020 atoms/cm3. By monitoring the nitrogen pressure decay over the course of the crystal growth, we developed an in situ method that correlates gas phase changes with precipitation of GaN from the sodium-gallium melt. Based on this analysis, the growth rate may have actually been as high as 90µm/h, as it would suggest GaN growth ceased prior to the end of the run. We also observed gas phase behavior identified as likely characteristic of GaN polynucleation.

A technique for measuring the quality of an elliptically bent pentaerythritol [PET(002)] crystal.

We present a technique for determining the X-ray spectral quality from each region of an elliptically curved PET(002) crystal. The investigative technique utilizes the shape of the crystal rocking curve which changes significantly as the radius of curvature changes. This unique quality information enables the spectroscopist to verify where in the spectral range that the spectrometer performance is satisfactory and where there are regions that would show spectral distortion. A collection of rocking curve measurements for elliptically curved PET(002) has been built up in our X-ray laboratory. The multi-lamellar model from the XOP software has been used as a guide and corrections were applied to the model based upon measurements. But, the measurement of RI at small radius of curvature shows an anomalous behavior; the multi-lamellar model fails to show this behavior. The effect of this anomalous RI behavior on an X-ray spectrometer calibration is calculated. It is compared to the multi-lamellar model calculation which is completely inadequate for predicting RI for this range of curvature and spectral energies.

GROWTH BEHAVIOR OF INTERMETALLIC LAYER ON STAINLESS STEEL IN ALUMINUM HOT-DIPPING PROCESS

A set of stainless steel plates were treated by hot-dipping into molten pure aluminum (Al) at 700[Formula: see text]C, 760[Formula: see text]C and 820[Formula: see text]C with different immersion time from 10[Formula: see text]s to 1800[Formula: see text]s. The growth behavior of the intermetallic compound layers between the substrate and Al coating is investigated. The intermetallic compounds showed a bi-layer structure consisting of FeAl3 close to Al coating and Fe2Al5 close to the substrate. The thickness of the intermetallic layers is closely related to the immersion time. Crack occurred with increasing immersion time and thickening Fe2Al5 layer. The thickness of the Fe2Al5 layers increases linearly with the square root of immersion time. Phase’s identification of each layer was confirmed using X-ray diffraction (XRD) analysis by grinding the specimens to expose different layers. The Fe2Al5 layer exhibited a single intensive peak attributable to (002) plane. The full width half maximum ([Formula: see text]) of Fe2Al5 on stainless steel substrate is 11.99[Formula: see text] by X-ray rocking curve measurement, suggesting that the Fe2Al5 grains have a strong orientation texture but not a single crystal. For comparison, [Formula: see text] of Fe2Al5 formed on mild steel by hot-dipping is 14.12[Formula: see text]. The relationship between the [Formula: see text] of Fe2Al5 layers and the growth mechanisms of crystals is discussed for the two steel substrates.

Structural, optical and electrical characterization of InAs0.83Sb0.17 p-π-n photodetector grown on GaAs substrate

High quality InAs0.83Sb0.17 mid-wavelength infrared p-π-n photodetector structure was grown with the aid of a GaSb transition layer on semi-insulating GaAs substrate by molecular beam epitaxy. The lattice mismatch and the crystal quality of the structure were investigated by high resolution X-ray diffraction rocking curve measurement. The full width at half maximum values for InAs0.83Sb0.17 and GaSb crystals were determined as 215 and 238arcsec, respectively. The lattice mismatch between InAs0.83Sb0.17/GaSb structure and GaAs substrate was identified as 8.44%. Activation energies for two different temperature regimes were extracted from Arrhenius plot which was derived from temperature dependent dark current measurements. The dominant dark current mechanisms were determined as generation-recombination limited and surface leakage based for higher- and lower-temperature regimes, respectively. The cut off wavelength and the peak quantum efficiency of the photodetector were obtained from the spectral photoresponse as 4.23μm and 24.3% at 80K, respectively.

Importance of Determination of Crystal Quality in Protein Crystals when Performing High-Resolution Structural Analysis

We show that the extinction effect explained by the dynamical theory of diffraction must be considered even in the case of protein crystals. Equal-thickness fringes, which are attributed to the Pendellösung effect, were clearly observed in the region of a tapered glucose isomerase crystal with wedge-like edges using X-ray topography carried out with a beam of monochromatic synchrotron radiation. This indicates that the perfection of this glucose isomerase crystal is high enough to produce this dynamical theory-related effect: this surely leads to difficulty in the collection of accurate integrated intensities of diffraction spots for X-ray structural analysis. Therefore, it is important to determine whether the crystal quality of a protein crystal under analysis is adequate to obtain accurate three-dimensional structures of protein molecules for X-ray structural analyses. We show that X-ray diffraction rocking-curve measurements can provide clues for this determination.

Improving the Brightness and Reliability of InGaN/GaN Near Ultraviolet Light-Emitting Diodes by Controlling the Morphology of the GaN Buffer Layer

A facile method for fabricating near ultraviolet light-emitting diodes (NUV LEDs) with better crystal quality and enhanced light emission is demonstrated by tuning total working pressure to modify the morphology of the buffer layer. With the conditions favoring the transition from 2-D to 3-D island growth in the GaN buffer layer, the crystal quality of the epitaxial GaN film is improved, leading to a decrease in the full-width at half-maximum of the (1 0 2) peak in $X$ -ray rocking curve measurement from 293 (arcsec) to 230 (arcsec). Scanning electron microscopy images imply the morphology of GaN grain boundaries at the buffer stage is different. The transmission electron microscopy analysis shows the edge dislocation can be bended due to the controlled morphology of buffer layer, leading to a better crystal quality of the GaN epitaxial film. Therefore, the reverse current is reduced with the reverse bias of $ - \hbox{40 V}$ . Moreover, the output power in lamp-formed NUV LEDs at a driving current of 20 mA can be enhanced by about 12%.