X-ray Rocking Curve Research Articles

Growth, first-principles calculations and optical properties of a novel near-infrared Ho: NLGW laser crystal

A rigid structure was constructed using an isotopic doping strategy, and a novel near-infrared 1 at% Ho3+: NaLa0.93Gd0.06(WO4)2 (Ho: NLGW) laser crystal with a size of Φ 18 mm × 30 mm was successfully grown by the Czochralski method. X-ray rocking curves and Rietveld refinement indicate that the grown crystal possesses high crystalline quality and crystallizes in the I41/a space group with lattice parameters: a = b = 5.3518 Å, c = 11.6438 Å and V = 333.5051 Å3. The Ho: NLGW crystal exhibits a low coefficient of thermal expansion (8.472 × 10−6 K−1), and the c-axis thermal conductivity increases from 1.235 W/(m × K) to 1.404 W/(m × K). The thermal properties of the Ho: NLGW crystal surpass those of other Ho3+-doped tungstate series and mainstream near-infrared laser crystals, suggesting that it is easier to obtain excellent laser gain. For revealing the excellent thermal properties, the elastic moduli of the NLW and NLGW crystals have been calculated by first principles. With the introduction of Gd3+, the structural stiffness of the NLW as a whole has been increased to optimize the mechanical properties in each axial direction and to obtain the reason for the larger Debye temperature. Finally, the transmission, absorption and near-infrared emission spectra of the Ho: NLGW crystal were investigated. The crystal exhibits a high transmittance of 88.5 % and an emission cross-section of 0.84 × 10−20 cm2 calculated according to the J-O theory. Experimental results indicate that the grown Ho: NLGW crystal can achieve large laser output more easily and are expected to be an excellent medium for 2 μm solid-state lasers.

Epilayer thickness effect on the electrical and breakdown characteristics of vertical β-Ga2O3 Schottky barrier diode

The current–voltage and breakdown characteristics of Au/Ni/β-Ga2O3 Schottky barrier diodes were investigated as a function of β-Ga2O3 epilayer thickness in the range of 6–19 μm. The X-ray rocking curves indicated that the full-width half-maximum is reduced with increasing epilayer thickness, implying an improvement in the crystallinity of β-Ga2O3 epilayer. The barrier heights of the field-plated β-Ga2O3 Schottky barrier diode with epitaxial layer thickness of 6, 12, and 19 μm were obtained as 1.01, 1.03, and 1.04 eV, with the ideality factor values being 1.21, 1.19, and 1.46, respectively. The higher ideality factors could be associated with the existence of inhomogeneity at the metal–semiconductor interface. The series resistance of the Schottky diode obtained increased with increasing epilayer thickness. The Schottky diode fabricated on 19 μm thick epitaxial layer exhibited a higher breakdown voltage of 490 V. The increase in epilayer thickness led to the widening of depletion region, resulting in lower electric field over a larger distance. This could be a main cause of the enhancement of the breakdown voltage characteristics of β-Ga2O3 Schottky barrier diode.

(10–13)-oriented semipolar GaN growth on (10–10) m-plane ScAlMgO4 substrate

Abstract We report the growth of a GaN layer on (10–10) m-plane ScAlMgO4 (SAM) substrate. The GaN layer demonstrated (10–13) preference growth orientation. The anisotropy of the crystalline quality was distinctly observed through X-ray rocking curve taken across the sample surface over various azimuths across the orthogonal directions [0001] and [1–210] of the SAM substrate. Notably, the crystalline quality exhibited gradual degradation as the substrate is rotated around its surface normal away from the c-direction [0001] of the SAM substrate toward the a-direction [11–20]. Additionally, basal stacking faults in the (10–13)-oriented GaN were observed along [0001] direction using scanning transmission electron microscopy. Moreover, the selected area electron diffraction analysis was utilized to confirm the (10–13) growth orientation that was found to be consistent with the X-ray diffraction result. The (10–13) GaN layer exhibited a metal face through integrated differential phase contrast imaging.

Growth Conditions and Interfacial Misfit Array in SnTe (111) Films Grown on InP (111)A Substrates by Molecular Beam Epitaxy.

Tin telluride (SnTe) is an IV-VI semiconductor with a topological crystalline insulator band structure, high thermoelectric performance, and in-plane ferroelectricity. Despite its many applications, there has been little work focused on understanding the growth mechanisms of SnTe thin films. In this manuscript, we investigate the molecular beam epitaxy synthesis of SnTe (111) thin films on InP (111)A substrates. We explore the effect of substrate temperature, Te/Sn flux ratio, and growth rate on the film quality. Using a substrate temperature of 340 °C, a Te/Sn flux ratio of 3, and a growth rate of 0.48 Å/s, fully coalesced and single crystalline SnTe (111) epitaxial layers with X-ray rocking curve full-width-at-half-maxima of 0.09° and root-mean-square surface roughness as low as 0.2 nm have been obtained. Despite the 7.5% lattice mismatch between the SnTe (111) film and the InP (111)A substrate, reciprocal space mapping indicates that the 15 nm SnTe layer is fully relaxed. We show that a periodic interfacial misfit (IMF) dislocation array forms at the SnTe/InP heterointerface, where each IMF dislocation is separated by 14 InP lattice sites/13 SnTe lattice sites, providing rapid strain relaxation and yielding the high quality SnTe layer. This is the first report of an IMF array forming in a rock-salt on zinc-blende material system and at an IV-VI on III-V heterointerface, and highlights the potential for SnTe as a buffer layer for epitaxial telluride film growth. This work represents an important milestone in enabling the heterointegration between IV-VI and III-V semiconductors to create multifunctional devices.

New Possibilities for the Analysis of Vibrating Crystal Deformations Using X-ray Rocking Curve Imaging

New Possibilities for the Analysis of Vibrating Crystal Deformations Using X-ray Rocking Curve Imaging

Cold Seeded Epitaxy and Flexomagnetism in GdAuGe Membranes Exfoliated From Graphene/Ge(111).

Remote and van der Waals epitaxy are promising approaches for synthesizing single crystalline membranes for flexible electronics and discovery of new properties via extreme strain; however, a fundamental challenge is that most materials do not wet the graphene surface. We develop a cold seed approach for synthesizing smooth intermetallic films on graphene that can be exfoliated to form few nanometer thick single crystalline membranes. Our seeded GdAuGe films have narrow X-ray rocking curve widths of 9-24 arc seconds, which is 2 orders of magnitude lower than their counterparts grown by typical high temperature methods, and have atomically sharp interfaces observed by transmission electron microscopy. Upon exfoliation and rippling, strain gradients in GdAuGe membranes induce an antiferromagnetic to ferri/ferromagnetic transition. Our smooth, ultrathin membranes provide a clean platform for discovering new flexomagnetic effects in quantum materials.

Measuring of the surface acoustic wave amplitude in the X-112° Y-cut of a LiTaO3 crystal using X-ray diffraction at the laboratory X-ray source

The SAW excitation and propagation on the X-112° Y-cut of a LiTaO3 crystal were studied using a triple-axis X-ray diffractometer with a laboratory X-ray source. Simulation of X-ray rocking curves with the Takagi equation system enabled the determination of surface acoustic wave amplitudes on the crystal surface. The SAW excitation process in the frequency range of an acoustoelectronic device, determined by the excitation band or interdigital transducer structure, was studied.

Improved characteristics of (11 [formula omitted]) plane AlGaN films grown on SiNx interlayer

SiNx interlayer was introduced in the epitaxial process of (11 2‾2) AlGaN film, and the influences of SiNx on the properties of (11 2‾2) AlGaN were characterized. It was revealed that the morphologic properties and crystal quality of (11 2‾2) AlGaN could be refined remarkably by optimizing SiNx growth time. Especially, a low root mean square value of 1.02 nm was obtained for S3 with a SiNx growth time of 10 min, which was 56.7 % less than S0 that grown without SiNx. Meanwhile, compared with S0, the full width at half maximum values of X-ray rocking curves for S3 were reduced by 39.6 % along [11 2‾3‾] direction and 41.2 % along [1 1‾00] direction. Besides, the background electron concentration and basal stacking faults related emission of (11 2‾2) AlGaN could also be suppressed remarkably by optimizing SiNx growth time to 10 min. These improvements could be originated from the formation of SiNx islands, leading to the lateral growth of AlGaN overlayer, the relaxation of strain in the AlGaN, and the annihilation of dislocations.

Growth of bulk β-Ga2O3 crystals from melt without precious-metal crucible by pulling from a cold container

We report the growth of bulk β-Ga2O3 crystals based on crystal pulling from a melt using a cold container without employing a precious-metal crucible. Our approach, named oxide crystal growth from cold crucible (OCCC), is a fusion between the skull-melting and Czochralski methods. The absence of an expensive precious-metal crucible makes this a cost-effective crystal growth method, which is a critical factor in the semiconductor industry. An original construction 0.4–0.5 MHz SiC MOSFET transistor generator with power up to 35 kW was used to successfully grow bulk β-Ga2O3 crystals with diameters up to 46 mm. Also, an original diameter control system by generator frequency change was applied. In this preliminary study, the full width at half maximum of the X-ray rocking curve from the obtained β-Ga2O3 crystals with diameters ≤ 46 mm was comparable to those of β-Ga2O3 produced by edge-defined film fed growth. Moreover, as expected, the purity of the obtained crystals was high because only raw material-derived impurities were detected, and contamination from the process, such as insulation and noble metals, was below the detection limit. Our results indicate that the OCCC technique can be used to produce high-purity bulk β-Ga2O3 single crystalline substrate.

Reproducible high-quality perovskite single crystals by flux-regulated crystallization with a feedback loop

Controlling the linear growth rate, a critical factor that determines crystal quality, has been a challenge in solution-grown single crystals due to complex crystallization kinetics influenced by multiple parameters. Here we introduce a flux-regulated crystallization (FRC) method to directly monitor and feedback-control the linear growth rate, circumventing the need to control individual growth conditions. When applied to metal halide perovskites, the FRC maintains a stable linear growth rate for over 40 h in synthesizing CH3NH3PbBr3 and CsPbBr3 single crystals, achieving outstanding crystallinity (quantified by a full width at half-maximum of 15.3 arcsec in the X-ray rocking curve) in a centimetre-scale single crystal. The FRC is a reliable platform for synthesizing high-quality crystals essential for commercialization and systematically exploring crystallization conditions, maintaining a key parameter—the linear growth rate—constant, which enables a comprehensive understanding of the impact of other influencing factors.

Improved characteristics of [formula omitted] Al0.62Ga0.38N film grown with pulsed flow growth technique

Pulsed flow growth (PFG) technique is a simple and effective method to improve the quality of aluminum gallium nitride (AlGaN) alloys. In this work, a reformed three-way PFG was applied to deposit (11 2‾2) plane Al0.62Ga0.38N film, and the separate ammonia (NH3) supply time in a PFG cycle was modulated carefully. It was revealed that the full width at half maximum (FWHM) values of on-axis X-ray rocking curves (XRCs) along [11 2‾3‾]- and [1 1‾00]-direction decreased conspicuously from 0.496 ° to 0.28 ° and from 0.674 ° to 0.451 ° by modifying the separate NH3 supply time to 3 s. Meanwhile, the FWHM values of basal stacking faults (BSFs)-related and prismatic stacking faults (PSFs)-related off-axis XRCs exhibited a reduction of 21.2 % and 17.2 %, respectively. Besides, the ratio of the intensity of BSF-related emission to that of near band emission (NBE) could be suppressed from 0.45 to 0.17. In other words, the crystal quality of (11 2‾2) AlGaN could be ameliorated significantly by optimizing separate NH3 supply time. Furthermore, the root mean square value was also reduced to 0.78 nm. These improvements could be interpreted as the reduced parasitic reaction between TMA and NH3 as well as the boosted migration of Al adatoms.

Liquid phase epitaxy of GaN films on sapphire substrates under an atmospheric pressure nitrogen ambience

GaN films were grown on sapphire substrates using liquid phase epitaxy under an atmospheric pressure nitrogen ambience, employing molten Ga and Fe3N as a source mixture. Single-crystal GaN (0001) films were successfully grown on sapphire (0001) substrates within a growth temperature (T g) range of 750 °C–900 °C. When varying the Fe3N concentration in the range of 0.05–3 mol%, lower iron nitride resulted in high crystallinity of GaN (0001) films. The incorporation of iron atoms in GaN can negatively impact crystal quality. Parameterizing T g at a concentration of 0.1 mol% Fe3N showed that higher T g led to a reduction in the peak width of GaN (0002) X-ray rocking curves. However, at 3 mol%, elevating T g resulted in the degradation of the crystallinity of GaN. This degradation may be attributed to the increased solubility of iron atoms in GaN with increasing T g.

Characterization of a HPHT boron ion-implanted diamond X-ray mirror following high vacuum annealing

The incorporation of boron into a diamond lattice holds the potential to advance X-ray optics, offering the capability to manipulate various parameters of the lattice. This includes enhancing near-infrared absorption relative to pure diamond, thereby enabling Q-switchable optics. The use of MeV boron implantation emerges as a promising method for precisely doping the diamond lattice. However, for these optics to function effectively as Bragg-reflecting mirrors, ion implantation must be executed with meticulous attention to maintaining a strain-free, perfect diamond lattice. This study aimed to investigate the feasibility of utilizing a 9 MeV ion beam for high energy boron implantation. Different areas of a high-pressure, high-temperature (HPHT) diamond sample were subjected to irradiation with 9 MeV Boron ions, ranging in fluences from 5×1015 to 2.5×1016ions/cm2. Following boron implantation, high-temperature vacuum annealing was performed to restore the diamond lattice. Our assessment utilized X-ray rocking curve imaging, surface profilometry, and micro-Raman spectroscopy, with additional observations on near-infrared transmission properties. Our measurement of high-quality Bragg reflection through X-ray rocking curve imaging, sensitive to implantation-induced strain and defects, served as an key diagnostic for the effectiveness of this ion-implanted sample as a Bragg-reflecting optic.

High-temperature growth of ZnSnN2 layer via radiofrequency magnetron sputter epitaxy

ZnSnN2 layers were grown directly on Al2O3 (0001) substrates via RF magnetron sputter epitaxy at various substrate temperatures using N2 gas and a ZnSn alloy target. The crystalline quality and surface morphology of the ZnSnN2 layers were examined. X-ray diffraction patterns indicated that ZnSnN2 layers grown at substrate temperatures of 600 °C and 700 °C had wurtzite-type structures. The gross full width at half maximum (FWHM) value of the X-ray rocking curve (XRC) for the (0002) plane of the ZnSnN2 layer grown at 700 °C was 324 arcsec. The XRC for the (0002) plane contained two components, and the FWHM values of these components were 206 and 1520 arcsec for the highly c-axis-oriented columnar domains and disordered structure inside the ZnSnN2 layer, respectively. Metallic Sn was detected in a ZnSnN2 layer grown at 800 °C.

Study of AlN Epitaxial Growth on Si (111) Substrate Using Pulsed Metal–Organic Chemical Vapour Deposition

A dense and smooth aluminium nitride thin film grown on a silicon (111) substrates using pulsed metal–organic chemical vapor deposition is presented. The influence of the pulsed cycle numbers on the surface morphology and crystalline quality of the aluminium nitride films are discussed in detail. It was found that 70 cycle numbers produced the most optimized aluminium nitride films. Field emission scanning electron microscopy and atomic force microscopy images show a dense and smooth morphology with a root-mean-square-roughness of 2.13 nm. The narrowest FWHM of the X-ray rocking curve for the AlN 0002 and 10–12 reflections are 2756 arcsec and 3450 arcsec, respectively. Furthermore, reciprocal space mapping reveals an in-plane tensile strain of 0.28%, which was induced by the heteroepitaxial growth on the silicon (111) substrate. This work provides an alternative approach to grow aluminium nitride for possible application in optoelectronic and power devices.

High-Performance Solar-Blind Photodetector Based on (010)-Plane β-Ga2O3 Thermally Oxidized from Nonpolar (110)-Plane GaN.

A high-performance planar structure metal-semiconductor-metal-type solar-blind photodetector (SBPD) was fabricated on the basis of (010)-plane β-Ga2O3 thermally oxidized from nonpolar (110)-plane GaN. A full width at half maximum of 0.486° was achieved for the X-ray rocking curve associated with (020)-plane β-Ga2O3, which is better than most reported results for the heteroepitaxially grown (-201)-plane β-Ga2O3. As a result of the relatively high crystalline quality, a dark current as low as 6.30 × 10-12 A was achieved at 5 V, while the photocurrent reached 1.86 × 10-5 A under 254 nm illumination at 600 μW/cm2. As a result, the photo-to-dark current ratio, specific detectivity, responsivity, and external quantum efficiency were calculated to be 2.95 × 106, 2.39 × 1012 Jones, 3.72 A/W, and 1815%, respectively. Moreover, the SBPD showed excellent repeatability and stability in the time-dependent photoresponse characteristics with fast relaxation time constants for the rise and decay processes of only 0.238 and 0.062 s, respectively. This study provides a promising approach to fabricate the device-level (010)-plane β-Ga2O3 film and a new way for the epitaxial growth of (010)-plane β-Ga2O3 and (110)-plane GaN as mutual substrates.

Growth optimization, optical, and dielectric properties of heteroepitaxially grown ultrawide-bandgap ZnGa2O4 (111) thin film

Ultrawide bandgap ZnGa2O4 (ZGO) thin films were grown on sapphire (0001) substrates at various growth temperatures with a perspective to investigate the electrical and optical characteristics required for high-power electronic applications. Due to the variation in the vapor pressure of Zn and Ga, severe loss of Zn was observed during pulsed laser deposition, which was solved by using a zinc-rich Zn0.98Ga0.02O target. A pure phase single-crystalline ZGO thin film was obtained at a deposition temperature of 750 °C and an oxygen pressure of 1 × 10−2 Torr. The out-of-plane epitaxial relationship between the sapphire and ZGO thin film was obtained from φ-scan. The x-ray rocking curve of the ZGO thin film grown at 750 °C exhibits a full width at half maximum of ∼0.098°, which indicates a good crystalline phase and quality of the thin film. Core-level x-ray photoelectron spectroscopy of ZGO grown at 750 °C indicated that Zn and Ga were in the 2+ and 3+ oxidation states, respectively, and the atomic ratio of Zn/Ga was estimated to be ∼0.48 from the fitted values of Zn-2p3/2 and Ga-2p3/2. The high-resolution transmission electron microscopy images revealed a sharp interface with the thickness of the ZGO film of ∼265 nm, and the signature of minor secondary phases was observed. The bandgap of the ZGO film at different growth temperatures was calculated from the ultraviolet-diffuse reflectance spectroscopy spectra, and its value was obtained to be ∼5.08 eV for the 750 °C grown sample. The refractive index (n) and the extinction coefficient (k) were determined to be ∼1.94 and 0.023 from the ellipsometric data, respectively, and the real dielectric function (ɛr) was estimated to be ∼6.8 at energy 5 eV. The ultrawide bandgap and dielectric function of ZGO recommend its possible potential applications in deep-ultraviolet optoelectronic devices and high-power electronics.

Single crystal growth of complex layered oxychalcogenide by melt-solidification method

We have successfully grown single crystals of layered mixed-anion compound Sr2ZnCu2Se2O2 by a simple melt-growth method. Single crystals of the layered oxychalcogenides Sr2ZnCu2Se2O2 were grown by melt-solidification of stoichiometric raw materials. Plate-like single crystals were obtained, and the maximum size of crystals was 2.5 × 1.4 mm2. Thermal analysis result indicates simple melting-solidification-like behavior, and the size of crystals increases significantly above the melting point revealed by this measurement. X-ray rocking curve (XRC) measurement results of the single crystal showed no peak splitting, with a narrow full width half maximum of 30 and 97 arcsec in (105) and (0012) peaks, respectively. The electrical conductivity of single crystals on the a(b) plane was 4.34 × 10−1 S/cm at room temperature. Obtained single crystals were transparent, and the absorption edge was observed around 560 nm in the transmittance measurement. Although layered oxychalcogenide Sr2ZnCu2Se2O2 has a complex composition and structure, this compound exhibits congruent melting behavior in a sealed environment. This feature enables us to grow single crystals of mixed-anion compounds easily by the melt-growth method.

Threading dislocations reduction of GaN-on-Si by introducing AlN/3D-GaN with SiN interlayer for photodetectors

Gallium nitride-on-Silicon epitaxy technology has enabled a high level of large-scale GaN integrated manufacturing. However, the poor crystalline quality of GaN on Si substrates dramatically deteriorates device performance. This work demonstrates the application of a buffer layer structure of AlN/3D-GaN with a SiN interlayer to obtain GaN films with high crystalline quality on Si substrates. Transmission electron microscopy and X-ray diffraction reveal reductions in GaN dislocation density. The full width at half maximum values of the X-ray rocking curve for the GaN(0002) and (10–12) planes have decreased from 499 to 710 arcsec to 339 and 350 arcsec, respectively. Ultraviolet photodetectors based on the optimized GaN-on-Si substrates exhibit low dark currents (34 pA@10 V) and high responsivity (6.8 A/W@10 V). Our reported novel buffer architecture provides an important reference for improving the performance of other GaN-based optoelectronics and power electronic devices on Si substrates.

Magnetic and electrical properties of Co2Te3 single crystal

The Co-Te system has become a prominent field of research in recent times. CoTe2 is confirmed to be a Dirac semimetal, while Co2Te is predicted to host the quantum anomalous Hall effect. Here, we have successfully grown high-quality Co2Te3 single crystals using the solid-state reaction method and have characterized them using the energy dispersive X-ray spectroscopy, the X-ray diffraction and Laue diffraction. The X-ray rocking curve with a full-width at half-maximum of 0.067° shows Co2Te3 single crystals have good crystalline quality and mosaicity. Co2Te3 single crystals possess a hexagonal structure with the space group of P63/mmc. Resistivity measurements reveal typical metallic behavior with a transition from Non-Fermi liquid to low-temperature Landau Fermi-liquid behavior around 50 K, which can be fitted by the parallel resistance model. Magnetic measurements show no obvious anisotropy between the in-plane and out-of-plane directions with the presence of a small magnetic hysteresis at 1.8 K. Furthermore, Co2Te3 single crystals undergo a magnetic phase transition around 50 K and an antiferromagnetic transition modulated by the magnetic field below 8 K.