X-ray Rocking Curve Measurements Research Articles

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.

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.

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.

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.

Warpage Structure of 4H-SiC after Implantation and Annealing Processes

The warpage structure of 4°-off-axis (0001) 4H-SiC samples after implantation and annealing processes was investigated using white light interferometry (WLI) and X-ray rocking curve (XRC) measurements. The WLI images showed that the surface warpage of the 300 °C-implanted/annealed SiC sample was small and almost the same as that of the un-implanted SiC sample, but the 30 and 150 °C-implanted/annealed SiC samples had a typically saddle-like warpage. The XRCs of the 0008-reflection were measured using monochromatic X-rays with different energies to change the X-ray penetration depth. The subtracted XRCs were reconstructed, and then the depth-dependence of the curvature radius of the 0008-reflection was evaluated. The results indicated that the saddle-like warpage of the 30 and 150 °C-implanted/annealed samples relaxed with increasing depth.

Growth of N-benzyl-2-methyl-4-nitroaniline (BNA) single crystal fibers by micro-pulling down method

N-benzyl-2-methyl-4-nitroaniline (BNA) fiber single crystals were grown by the micro-pulling down (µ-PD) method. Crucible material and its shape were selected based on wetting of the crucible material by liquid BNA. As a result, BNA fiber single crystal with about 1–2mm diameter was successfully grown. Powder XRD analysis and X-ray rocking curve measurements were performed. Widely-tunable THz-wave generation from 4THz to 14THz was demonstrated using the BNA fiber crystal grown by µ-PD method.

Optical and Electric Properties of Cu-Doped ZnO Films Grown on MgO (100) Substrate

This work studied the luminescent and electric properties of Cu-doped ZnO films grown on MgO (100) substrate by plasma-assisted molecular beam epitaxy. The doping quantity was controlled by regulating Cu Kundsen cell temperature. The crystallinity and surface morphology of the Cu-doped ZnO films were characterized by high resolution X-ray diffraction, atomic force microscopy, and scanning electron microscopy. The chemical state and elemental compositions was analyzed by X-ray photoelectron spectroscopy (XPS). The near-band-edge emission (NBE) and defect-related emission (DLE) were analyzed by photoluminescence spectroscopy. The electric properties were determined by Hall measurement and four-point probe measurement. The experimental results revealed that ZnO films grown epitaxially on MgO substrate with (10-10)ZnO//(100)MgO. X-ray rocking curve measurements showed that the (10-10)ZnO reflection exhibits a full width at half maximum value of about 0.7o-1.0o. The XPS analysis showed that the doped copper atoms have a monovalent state in the ZnO films grown at Cu Kundsen cell temperatures lower than 900oC. The amount of Cu incorporation was estimated to be in the range of 1x1019 to 1x1021 atoms/cm3. The NBE peak of the Cu-doped ZnO films can be deconvoluted into three sub-peaks: a free exciton emission at 3.29 eV, a basal-plane stacking fault emission at 3.19 eV, and a third peak at 3.25 eV. The third peak might be related to an acceptor-bound excitons due to the doping of copper, since it disappeared after annealing. Hall measurement indicated that both pure and Cu-doped ZnO films are n-type semiconductor. The electron concentration of undoped ZnO film is 1x1018 cm-3, whereas that of the Cu-doped ZnO films are in the range of 5x1015~5x1016 cm-3. Obviously, the electron concentration of ZnO is compensated by the substitution of Cu+ to Zn2+ which generates acceptor levels. However, the electron concentration of the Cu-doped ZnO films rose back to the order of magnitudes 1018 cm-3 after annealed in oxygen or hygrogen, indicating the acceptor states were eliminated. Moreover, in this study, the incorporation of copper in ZnO does not result in an increase of the yellow-green luminescence.

Deep boron diffusion induced surface damage in silicon

This paper presents deep boron diffusion induced damages in silicon (100), (110) and (111) surfaces. The silicon (100) and (110) samples showed a broad hump at the higher angle (ω) side during x-ray Rocking curve measurement; whereas, the (111) sample shows an additional broad peak at higher angle side. All the diffused samples showed two distinct contours in reciprocal space mapping measurements. Due to the diffusion process, surface roughness of the silicon samples is found to be increased from 10nm to 110nm, 70nm and 30nm for the silicon (100), (110) and (111) samples respectively.

Influence of laser repetition rate on the structural and optical properties of GaN layers grown on sapphire (0001) by laser molecular beam epitaxy

High-quality GaN layers were grown on sapphire (0001) substrates using laser molecular beam epitaxy (LMBE) by laser ablating a solid GaN target at different laser repetition rates (10–40 Hz) under a constant supply of r.f. nitrogen plasma. The effect of laser repetition rate on the structural and optical properties of GaN layers was systematically studied using high-resolution X-ray diffraction (HRXRD), field emission scanning electron microscopy, atomic force microscopy, Raman spectroscopy and photoluminescence (PL) spectroscopy. High-resolution X-ray rocking curve measurements revealed highly c-axis oriented GaN layers on sapphire grown at 30 Hz with a calculated screw dislocation density of ~1.42 × 107 cm−2, whereas the GaN layers grown at 10 or 40 Hz consisted the screw dislocation density in the range of 108–109 cm−2. Surface morphological analysis revealed a change in grain size as well as surface roughness as a function of laser repetition rate and is explained on the basis of growth kinetics. Vibrational Raman spectroscopy revealed that the GaN layer grown at 10 Hz shows an in-plane compressive stress of ~1 GPa, while the film grown at 30 Hz exhibits a minimum stress of ~0.3 GPa. The PL measurements show a highly luminescent band-to-band emission of GaN at 3.44 eV for the 10 Hz grown highly strained GaN layer and at 3.41 eV for the less strained film grown at 30 Hz along with a broad defect band emission centered around 2.28 eV. It is found that the GaN layers grown at 30 Hz have excellent structural and optical properties. We expect that the less strained thin and highly oriented GaN film grown by LMBE can further be utilized for developing prodigious low-temperature-grown nitride-based multilayer structures and devices.

MPCVD growth of 13C-enriched diamond single crystals with nitrogen addition

This study describes the growth of 13C-enriched (100)-oriented diamond single crystals by the MPCVD (microwave plasma chemical vapour deposition) process. All crystals are at least 6×6mm2 in area and 0.5–1.0mm in thickness. The samples with nominal 13C percentages (R=[13C]/[13C+12C]) of 0.011 (natural abundance), 0.10, 0.21, 0.24 and 0.34 were obtained by controlling the flow of the carbon-13 and carbon-12 methane feed gases. To obtain thicker and near-colourless quality 13C-enriched diamond, 190ppm of nitrogen was added into the gas mixture. The shift towards lower frequency in the Raman peak positions and decrease in the thermal conductivities of the near-colourless crystals with increasing 13C percentages are similar to previous studies of isotopically-controlled diamond grown with no nitrogen additive. The images of the structural defects associated with 13C-enrichment obtained by spatially-resolved X-ray rocking curve measurement show distinct patterned structures that runs parallel to the <100> direction. Moreover, the broadening in the line width of the nuclear magnetic resonance (NMR) peak from sp313C correlates with increasing R. We also expand the study by injecting 500ppm of nitrogen. Higher nitrogen concentration leads to the formation of brown crystals. The brown crystals show far greater 13C NMR peak intensity than the near-colourless. This suggests that paramagnetic nitrogen impurities in the brown crystals hasten the spin-lattice relaxation time of the 13C nuclear spin that resulted in higher intensity. The isotopic splitting observed for the localized vibrational mode of the NVH0 defect in brown crystals is attributed to the co-existence of both the 13C (3114.2cm−1) and 12C (3123.5cm−1). Unlike the isotopic splitting observed for NVH0 defect, the peak position of the Ns+ defect shifts towards lower frequency as R increases. Not only have we demonstrate the growth of bigger isotopically-controlled diamond single crystals, the results shown here have provided a framework to further investigate the interplay between 13C atoms and nitrogen impurity.

Resolution of X-Ray Rocking Curve Measurements Made with Finite Counting Statistics

We have analyzed the strain resolution of x-ray rocking curve profiles from measurements of the peak position and peak width made with finite counting statistics. In this work, we have considered x-ray rocking curves which may be Gaussian or Lorentzian in character and have analyzed the influence of the effective number of counts, full-width-at-half-maximum (FWHM) and the Bragg angle on the resolution. Often experimental resolution values are estimated on the order of 10−5 whereas this work predicts more sensitive values (10−9) with smaller FWHM and larger effective counts and Bragg angles.

HPHT synthesis and crystalline quality of large high-quality (001) and (111) diamond crystals

High-quality type IIa diamond crystals measuring up to 12mm in diameter (8 to 10 carats) were successfully grown by the temperature gradient method at high pressure and high temperature (HPHT) on defect-free (001)-oriented and (111)-oriented seed crystals. The crystalline quality of the grown crystals was qualitatively evaluated by synchrotron based X-ray topograph and rocking curve (RC) measurements. The results revealed that the crystals grown on (001)-oriented seeds have extremely high quality in the (001) growth sector, which extends straight upward from the seed surface. This sector contains very few dislocations and stacking faults in the upper part in particular, where the RC almost agrees with the theoretical curve. For the crystals grown on (111)-oriented seeds, it was confirmed that crystal defects are fewer in the outer (100), (010), and (001) growth sectors than in the central (111) growth sector extending straight upward from the seed surface. The RCs in selected regions of these {100} growth sectors are close to the theoretical curve, indicating high crystalline quality.

Homoepitaxial growth of a-plane GaN layers by reaction between Ga2O vapor and NH3 gas

Growth of high-quality a-plane GaN layers was performed by reaction between Ga2O vapor and NH3 gas at a high temperature. Smooth a-plane GaN epitaxial layers were obtained on a-plane GaN seed substrates sliced from thick c-plane GaN crystals. Growth rate increased with increasing Ga2O partial pressure. An a-plane GaN layer with a growth rate of 48 µm/h was obtained. The X-ray rocking curve (XRC) measurement showed that the full widths at half maximum (FWHMs) of GaN with the incident beam parallel and perpendicular to the [0001] direction were 29–43 and 29–42 arcsec, respectively. Secondary ion mass spectrometry (SIMS) measurement revealed that oxygen concentration decreased at a high temperature. These results suggest that growth of a-GaN layers using Ga2O vapor and NH3 gas at a high temperature enables the generation of high-quality crystals.

(Invited) High Efficiency Green-Yellow Emission from InGaN/GaN Quantum Well Structures Grown on Overgrown Semi-Polar (11-22) GaN on Regularly Arrayed Micro-Rod Templates

A simple but cost-effective overgrowth technique has been developed for the growth of semi-polar (11-22) GaN on mask-patterned micro-rod array templates fabricated on thin (11-22) GaN layers on sapphire. As a result, a fast coalescence with a thickness of ~1 μm has been obtained. Massively improved crystalline quality has been achieved, confirmed by detailed X-ray rocking curve measurements, which show that the full width at half maximum (FWHM) has been reduced to 0.096° and 0.097° at both 0° and 90° azimuth angle measured on an overgrown sample with a total thickness of 4.5 μm. The root mean square (RMS) roughness measured by atomic force microscopy is 1.47 nm. A number of InGaN/GaN multiple quantum well (MQW) structures with high In composition have been grown on the overgrown semi-polar GaN templates, showing strong photoluminescence (PL) emission with a wavelength from 495 to 590 nm at room temperature. Temperature dependent PL measurements have been performed to estimate their internal quantum efficiency (IQE), demonstrating ~ 8% of IQE for the sample with an emission wavelength of 590 nm. Power dependent PL measurements indicate weak quantum confined Stark effects (QCSE).

Highly transparent terbium gallium garnet crystal fabricated by the floating zone method for visible–infrared optical isolators

Highly transparent terbium gallium garnet (Tb3Ga5O12; TGG) single crystal having a large Verdet constant based on the visible and near-infrared region (VIS–NIR) Faraday rotator was grown by Floating Zone (FZ) growth machine. We successfully grew TGG single-crystal rods of 8–10mm in diameter, which was suitable for the use in optical devices. The crystal showed a full-width at half-maximum as little as 18arcsec by the X-ray rocking curve measurement. The Faraday rotation (B=0.55T) was investigated at wavelength of 532, 632.8, 1064nm at room temperature. The lower weak absorption coefficient, higher Verdet constant, thermal conductivity and laser induced damage threshold (LIDT) compared to the commercial TGG gives the great potential of using this new method to meet the increasing demand of VIS–NIR Faraday rotators (FRs).

Achieving high thermal conductivity from AlN films deposited by high-power impulse magnetron sputtering

We report on thermal conductivity measurements of aluminum nitride (AlN) films using the fast pulsed photo-thermal technique. The films were deposited by high-power impulse magnetron sputtering with different thicknesses ranging from 1000 to 8000 nm on (1 0 0) oriented silicon substrates. The films were characterized by x-ray diffraction (XRD), Raman spectroscopy, profilometry, scanning electron microscopy and atomic force microscopy. The XRD measurements showed that AlN films were textured along the (0 0 2) direction. Moreover, x-ray rocking curve measurements indicated that the crystalline quality of AlN was improved with the increase in film thickness. The thermal conductivities of the samples were found to rapidly increase when the film thickness increased up to 3300 nm and then showed a tendency to remain constant. A thermal boundary resistance as low as 8 × 10−9 W−1 K m2 and a thermal conductivity as high as 250 ± 50 W K−1 m−1 were obtained for the AlN films, at room temperature. This high thermal conductivity value is close to that of an AlN single crystal and highlights the potential of these films as a dielectric material for thermal management.

Structural and electronic properties of epitaxial GaN layer grown on sapphire (0001) using laser molecular beam epitaxy

Epitaxial GaN films were grown on sapphire (0001) substrates by an ultra-high vacuum laser assisted molecular beam epitaxy (MBE) system using GaN solid target with laser energy density of ∼3 J cm−2 at various growth conditions. The influence of growth temperature, layer thickness and growth rate on the structural properties of the GaN layers have been studied using high resolution x-ray diffraction, field emission scanning electron microscopy and scanning tunneling microscopy at room temperature. The epitaxial GaN layers grown at 700 °C exhibited good crystalline properties with a screw dislocation density of 3.1 × 108 cm−2 as calculated from the x-ray rocking curve measurements. The electronic properties such as core levels and valence band of GaN film were examined using x-ray photoelectron spectroscopy. Chemical composition of the GaN layer was determined using core level spectroscopy.

Accurate determination of surface orientation of single-crystal wafers using high-resolution X-ray rocking curve measurements

Theoretical models of the variations of the peak positions of X-ray rocking curves as a function of the azimuthal angle of a single-crystal wafer have been proposed. These models completely describe the variations of the peak positions both when the surface normal of a wafer is parallel and when it is not parallel to the rotation axis of the goniometer used. Based on the models, an accurate measurement method for the surface orientation of a single-crystal wafer with a small surface miscut of &lt;∼3° has been proposed through rocking curve measurements using a high-resolution X-ray diffractometer. The method measures the misalignment of the sample surface normal with respect to the rotation axis of the goniometer as well as the surface orientation of the wafer. The surface orientation has been measured for a 6 inch (152.4 mm) single-crystal sapphire wafer, and the misalignment of the surface normal from the rotation axis was determined. The results were compared with those from a different method. In addition, a simple and accurate method to obtain the surface orientation of a wafer is proposed by measuring only four rocking curves, two each at two sample azimuths 180° apart.

Advancements in THM-Grown CdZnTe for Use as Substrates for HgCdTe

The focus of this work is to evaluate the suitability and substrate potential of Cd0.9Zn0.1Te and Cd0.96Zn0.04Te crystals grown by the traveling heater method (THM). THM-grown Cd0.9Zn0.1Te crystals used for gamma spectroscopy have shown very good spectral performance owing partly to the very low concentration of Te inclusions and precipitates. Inspection in the infrared (IR) of annealed THM-grown CdZnTe wafers reveals no inclusions >3 μm, and Fourier-transform infrared measurements show IR transmission values in excess of 60%. Wafer etch pit density values are typically less than 4 × 10−4 pits/cm2, and double-crystal x-ray rocking-curve measurements show full-width at half-maximum values approaching 40 arcsec. 〈211〉 wafers have been produced with off orientation within 0.3°. (111)-Oriented, seeded THM growth runs have the ability to provide 10 60 mm × 60 mm × 2 mm wafers from a 75-mm-diameter boule or 20 90 mm × 90 mm × 2 mm wafers from a 100-mm-diameter boule.