X-ray Diffraction Rocking Curve Research Articles

Impact of 3D growth and SiNx interlayer on the quality of (11–22) semi-polar GaN grown on m-plane sapphire

We report the growth of semi-polar (11−22) GaN films with low defect densities on m-plane sapphire substrates by incorporating a porous SiNx interlayer in a three-stage growth process. The linewidth of X-ray diffraction rocking curves for our semi-polar GaN films decrease with increasing SiNx deposition time. Cross-sectional transmission electron microscopy analyzes confirm that the proposed three-stage growth process greatly reduces the semi-polar GaN threading dislocation densities down to 7 × 108 cm−2. Photoluminescence measurements demonstrate that InGaN/GaN quantum wells grown on our semi-polar GaN films provide peak intensities that are 26-fold greater than those grown on semi-polar GaN by a standard method.

Single crystal growth and characterization of Ba2ScNbO6 – A novel substrate for BaSnO3 films

Large single crystals of the double-perovskite Ba2ScNbO6 were grown from the melt for the first time. With a lattice parameter at room temperature of 4.11672(1) Å, this cubic double-perovskite has an excellent lattice match to BaSnO3, PbZr0.9Ti0.1O3, LaInO3, BiScO3, and other perovskites of contemporary interest. Differential thermal analysis showed that Ba2ScNbO6 melts at 2165 ± 30 °C in an inert atmosphere. Competitive grain growth was visualized by energy dispersive Laue mapping. X-ray diffraction rocking curve measurements revealed full width at half maximum values between 21 and 33 arcsec for 002 and 004 reflections. The crystals were sufficiently large to yield (1 0 0)-oriented single-crystal substrates with surface areas as large as 10 × 10 mm2.

Fabricating GaN-based LEDs on (−2 0 1) β-Ga2O3 substrate via non-continuous/continuous growth between low-temperature undoped-GaN and high-temperature undoped-GaN in atmospheric pressure metal-organic chemical vapor deposition

This study demonstrates two approaches to the growth of GaN-based LEDs on (−2 0 1)-oriented β-Ga2O3 single crystal substrates using metal-organic CVD under atmospheric pressure. One approach induces non-continuous growth between low-temperature undoped-GaN (u-GaN) and high-temperature u-GaN, whereas the other approach induces continuous growth. We observed the following reduction in the FWHM of X-ray diffraction rocking curves: GaN (0 0 2) on (−2 0 1) β-Ga2O3 substrate (from 464 to 342 arcsec) and GaN (1 0 2) (from 886 to 493 arcsec). An LED with six pairs of InGaN/GaN multiple quantum wells was successfully fabricated on the (−2 0 1) β-Ga2O3 single crystal substrate.

A methodical approach to physico-chemical analysis of bis (potassium hydrogen l-malate).malic acid – A semi-organic single crystal for nonlinear optical applications

Bis (potassium hydrogen l-malate).malic acid (PMM), a semi-organic nonlinear optical material was synthesized and crystals were grown from aqueous solution by slow evaporation solution growth technique (SEST). The lattice parameters and space group were confirmed by single crystal X-ray diffraction study. Powder X-ray diffraction study reveals the crystalline nature of the title material. Crystalline perfection of grown crystal was analyzed using high resolution X-ray diffraction rocking curve technique. Fourier transform infrared spectral analysis revealed the vibrational behaviour of chemical bonds of various functional groups. Surface feature of the grown crystal was analyzed through atomic force microscopy. Optical transmittance study shows that the grown crystal has good transparency in the entire visible region. The luminescent property of the title crystal was investigated through photoluminescence spectroscopy. Second harmonic generation efficiency was found using Kurtz-Perry powder technique. The laser-induced surface damage threshold value for the grown crystal as measured using a Nd:YAG laser. Thermal analyses reveal that the crystal is stable up to 230 °C. The mechanical strength of the crystal was assessed by Vickers microhardness tester. The dielectric behaviour and its parameters were established through dielectric study. Piezoelectric charge coefficient (d33) of the grown crystal was determined using piezoelectric analysis.

Crystalline GaAs Thin Film Growth on a c-Plane Sapphire Substrate

Crystalline zinc blende GaAs has been grown on a trigonal c-plane sapphire substrate by molecular beam epitaxy. The initial stage of GaAs thin film growth has been investigated extensively in this paper. When grown on c-plane sapphire, it takes (111) crystal orientation with twinning as a major problem. Direct growth of GaAs on sapphire results in three-dimensional GaAs islands, almost 50% twin volume, and a weak in-plane correlation with the substrate. Introducing a thin AlAs nucleation layer results in complete wetting of the substrate, better in-plane correlation with the substrate, and reduced twinning to 16%. Further, we investigated the effect of growth temperature, pregrowth sapphire substrate surface treatment, and in-situ annealing on the quality of the GaAs epilayer. We have been able to reduce the twin volume below 2% and an X-ray diffraction rocking curve line width to 223 arcsec. A good quality GaAs on sapphire can result in the implementation of microwave photonic functionality on a photonic chip.

AlyGa1−yAs Bound GazIn1−zP Strain Compensation for Optical Enhancement of In0.07GaAs/GaAs1−xPx 940-nm Light-Emitting Diodes

The use of an AlxGa1−xAs bound GazIn1−zP strain compensation structure for optimum strain in latticed mismatched In0.07GaAs/GaAsP0.06 multiple quantum wells (MQWs) and its effect on the output power of an infrared light-emitting diode at 940-nm were investigated. A Ga0.53InP tensile strain structure, which effectively compensate excessive compressive strain in the In0.07GaAs/GaAsP0.06 MQWs, was inserted between a quantum well and a quantum barrier. The Al0.2GaAs material was used as both a growth buffer and a balancing barrier for In0.07GaAs/AlxGa1–x As-bound Ga0.53InP/GaAsP0.06 MQWs. From photoluminescence (PL) measurements and X-ray diffraction (XRD) rocking curves, we verified that the Ga0.53InP tensile strain barrier could effectively compensate the compressive strain of the In0.07GaAs/GaAsP0.06 MQWs. In addition, a further increase in the PL intensity from the In0.07GaAs/AlyGa1−yAs-bound Ga0.53InP/GaAsP0.06 MQWs was found after having adjusted the Al0.2GaAs strain tuning barrier. This result was significantly supported by the stable balance of the energy bandgap structure in the developed MQWs. From fabricated IR-LEDs chips, the LED with an In0.07GaAs/GaAsP0.06 MQW employing the Al0.2GaAs-bound Ga0.53InP strain compensation structure displayed a 48% higher light output power as compared with a conventional LED. These results suggest that the use of an Al0.2GaAs-bound Ga0.53InP strain compensation structure effectively improved both the unbalanced strain and the unbalanced energy bandgap of lattice-mismatched In0.07GaAs/GaAsP0.06 MQWs for 940-nm IR-LEDs.

Effects of indium surfactant and MgN intermediate layers on surface morphology and crystalline quality of nonpolar a-plane AlGaN epi-layers

High quality non-polar a-plane AlGaN epi-layers with dual MgN interlayers were successfully grown on semi-polar r-plane sapphire substrates with the indium-surfactant-assisted metal organic chemical vapor disposition (MOCVD) technology, and characterized with atomic force microscopy, cathode luminescence (CL), and high-resolution X-ray diffraction rocking curve. It was found that both surface morphology and crystalline quality of the non-polar AlGaN films were strongly dependent on the mass flow of indium surfactant in the MOCVD growth process. In fact, the great suppression of the deep energy level impurity-related transitions in the CL spectra indicates a significant enhancement in crystalline quality for the non-polar AlGaN films. Moreover, with the optimization of the indium surfactant mass flow, a root mean square value as small as 10.9 nm was achieved, demonstrating a remarkable improvement in surface morphology for the a-plane AlGaN epi-layer.

Control of magnetization reversal and domain structure in (Co/Ni) multilayers

Abstract We present a study of the magnetic properties of [Co(0.3 nm)/Ni(0.6 nm)] ×N multilayers as a function of bilayer repetitions N. From magnetometery measurements, magnetic force microscopy and X-ray diffraction (XRD), a correlation between the magnetic and structural properties could be made. It is shown that the multilayers exhibit square hysteresis loops for N ≤ 8 with a maximum coercivity of about 220 Oe for N = 8. The XRD scan and rocking curve measurements reveal that fcc phase of (Co/Ni) is improved for a larger value of N. Micromagnetic simulation is conducted on each multilayer at demagnetized state to reproduce the MFM images. From the best correspondence of the experimental and simulated domain structures, intrinsic parameters such as saturation magnetization M s anisotropy energy K u and average domain size were obtained. It is found that M s value of all the multilayers is about 800 emu/cm 3 with less than 3% difference. On the other hand, K u shows a continuous decrease with N down to 12 % from its largest value for 4 bilayers.

Epitaxy of GaN(0001) and GaN(10$$\bar {1}$$1) Layers on Si(100) Substrate

Two different approaches to epitaxy of 4-μm-thick layers of polar GaN(0001) and semipolar GaN(10 $$\bar {1}$$ 1) on a V-shaped nanostructured Si(100) substrate with nanometer-thick SiC and AlN buffer layers have been experimentally demonstrated. The GaN(0001) layers were synthesized by hydride vapor-phase epitaxy, and GaN(10 $$\bar {1}$$ 1) layers, by metal-organic vapor-phase epitaxy, with the growth completed by hydride vapor-phase epitaxy. It was shown that layers of the polar GaN(0002) have a longitudinal elastic stress of –0.45 GPa and the minimum full width at half-maximum of the X-ray diffraction rocking curve ωθ ~ 45 arcmin, whereas for the semipolar GaN(10 $$\bar {1}$$ 1), these values are –0.29 GPa and ωθ ~ 22 arcmin, respectively. A conclusion is drawn that the combined technology of semipolar gallium nitride on a silicon (100) substrate is promising.

Epitaxial Co50Fe50(110)/Pt(111) films on MgAl2O4(001) and its enhancement of perpendicular magnetic anisotropy

Perpendicular magnetic anisotropy (PMA) in magnetic thin films with low coercivity is desirable for magnetic memory devices. It has been found that a (111)-oriented or textured Pt seed layer can enhance PMA and is, therefore, commonly utilized in spintronic structures. We grow (111)-oriented Pt epitaxial films via off-axis sputtering on various substrates and investigate the optimal substrate and orientation for high quality, epitaxial growth. Our results show that Pt(111) epitaxial films grow remarkably well on MgAl2O4(001) with an exceptionally narrow X-ray diffraction rocking curve. This high-quality seed layer is found to promote epitaxial growth of Pt/Co50Fe50/Pt trilayers with strong PMA comparable to many repeats of the magnetic multilayers reported previously. In addition, the Pt seed layer enhances the maximum thicknesses of Co50Fe50 that can still maintain PMA up to 1.07 nm.

Study on Dislocation Annihilation Mechanism of the High-Quality GaN Grown on Sputtered AlN/PSS and Its Application in Green Light-Emitting Diodes

GaN was grown on the sputtered AlN/patterned sapphire substrate under two growth modes by metal–organic chemical vapor deposition, which was named as “rising tide” and “tsunami” growth modes, respectively, due to different characteristics of the GaN growth process. High-quality GaN epilayer was obtained under “tsunami” growth mode, and the full-width at half-maximums of GaN (002)/(102) high-resolution X-ray diffraction rocking curves were 58/90 arcsec. The green InGaN/GaN light-emitting diodes fabricated on GaN under “tsunami” growth mode exhibited both higher light output power and external quantum efficiency. By monitoring the GaN films at different growth stages using the scanning electron microscope and the transmission electron microscope as well as cathodoluminescence, the dislocation annihilation mechanisms were researched. Under “tsunami” growth mode, GaN grew into the shape of a truncated pyramid that promoted dislocations originated from flat area bend toward the inclined planes, and it was noteworthy that the propagation of dislocations in grains on the conical surface was inhibited. While under “rising tide” growth mode, the dislocations on the conical surface had chances to extend.

Growth and characterization of F-doped α-Ga2O3 thin films with low electrical resistivity

F-doped α-Ga2O3 thin films with low electrical resistivity were epitaxially grown on c-plane α-Al2O3 substrates by means of mist chemical vapor deposition. The resistivity of the α-Ga2O3 thin films was decreased dramatically by incorporating F into α-Ga2O3, achieving a minimum resistivity of 6.2 × 10−2 Ω·cm in a 1050 nm thick film grown from a precursor solution with a [F]/[Ga] ratio of 20%. Further, the carrier concentration was 1.3 × 1019 cm−3, and the Hall mobility was 4.6 cm2/Vs with the [F]/[Ga] ratio of 20% and a film thickness of 1560 nm. Secondary ion mass spectrometry revealed that the F concentration incorporated into the α-Ga2O3 thin film was approximately 1 × 1020 cm−3, and the activation ratio was approximately 10%. The higher [F]/[Ga] ratio in the precursor solution caused lower crystallinity, as demonstrated by X-ray diffraction rocking curves. For all [F]/[Ga] ratios, as the film thickness increased to approximately 1000 nm, the electrical resistivity of the thin films drastically decreased. In the thinner films, the dislocations at the interface between the α-Ga2O3 thin films and the α-Al2O3 substrates are thought to trap electrons and compensate the free carriers or deteriorate the mobility.

Shedding Light on the Intrinsic Characteristics of 3D Distorted Fluorite-Type Zirconium Tellurite Single Crystals.

Transition-metal tellurites have motivated growing research interest in both fundamental and applied chemistry, and the corresponding single crystals could serve as rich and fascinating platforms to regulate, explore, and elucidate the intrinsic characteristics of different structures from 0D to 3D architectures. In this context, a zirconium tellurite (namely, ZrTe3O8) single crystal featuring a 3D distorted fluorite-type structure with a size of 35 × 32 × 21 mm3 was successfully harvested by the top-seeded solution growth (TSSG) technique. The X-ray diffraction rocking curve reflects that the crystallinity of the as-grown ZrTe3O8 crystal is quite perfect with a small full-width at half-maximum (fwhm) value (∼39 arcsec). The temperature dependence of the thermophysical properties of the ZrTe3O8 single crystal has been systematically analyzed. The ZrTe3O8 single crystal exhibits a wide transparency window, as the UV and IR absorption cutoff edges are respectively 278 and 7788 nm. The refractive indices over the region from the visible to the near-IR have been determined and manifested relatively large values of 2.0889-2.0370 over a wavelength range of 632.8-1553 nm. Furthermore, the fundamental physical characteristics of the ZrTe3O8 single crystal associated with its distinctive 3D framework structure have been evaluated with density functional theory (DFT) calculations.

Growth, structural and optical limiting property of a new third order nonlinear optical material: piperazinium bis (2-carboxypyridine) monohydrate

Piperazinium bis (2-carboxypyridine) monohydrate (PPPA) was successfully synthesized and crystal was grown from aqueous solution. PPPA compound crystallized in centric (or achiral) space group P21/C. The lattice perfection was analyzed by high-resolution X-ray diffraction rocking curve measurement. The chemical structure was confirmed by FTIR and NMR spectral studies. The range of optical transmittance of PPPA crystal was elucidated from UV–visible spectral studies. Optical resistance was estimated from LDT studies using Nd:YAG laser. Thermal stability have also investigated for PPPA compound which shows that PPPA crystal is potentially applicable for optical applications. Mechanical stability and material’s category were established from the Vicker’s hardness studies. Growth mechanism of PPPA was revealed from etching studies. The grown crystal was investigated for third order susceptibility by Z-scan technique. It was found to that they behaved as saturable absorber and self defocused in refraction which is essential for optical switching and limiting applications. Its second molecular hyperpolarizability (γ) at 532 nm was estimated to be 3.4746 × 10−9 esu.

Epitaxial integration of high-mobility La-doped BaSnO3 thin films with silicon

La-doped BaSnO3 has been epitaxially integrated with (001) Si using an SrTiO3 buffer layer via molecular-beam epitaxy (MBE). A 254 nm thick undoped BaSnO3 buffer layer was grown to enhance the mobility of the overlying La-doped BaSnO3 layer. The x-ray diffraction rocking curve of the BaSnO3 002 peak has a full width at half maximum of 0.02°. At room temperature, the resistivity of the La-doped BaSnO3 film is 3.6 × 10−4 Ω cm and the mobility is 128 cm2 V−1 s−1 at a carrier concentration of 1.4 × 1020 cm−3. These values compare favorably to those of La-doped BaSnO3 films grown by all techniques other than MBE on single-crystal oxide substrates. Our work opens an exciting arena for integrating hyper-functional oxide electronics that make use of high-mobility oxide films with the workhorse of the semiconductor industry, silicon.

Эпитаксия слоев GaN(0001) или GaN(1011) на подложке Si(100)

AbstractTwo different approaches to epitaxy of 4-μm-thick layers of polar GaN(0001) and semipolar GaN(10 $$\bar {1}$$ 1) on a V -shaped nanostructured Si(100) substrate with nanometer-thick SiC and AlN buffer layers have been experimentally demonstrated. The GaN(0001) layers were synthesized by hydride vapor-phase epitaxy, and GaN(10 $$\bar {1}$$ 1) layers, by metal-organic vapor-phase epitaxy, with the growth completed by hydride vapor-phase epitaxy. It was shown that layers of the polar GaN(0002) have a longitudinal elastic stress of –0.45 GPa and the minimum full width at half-maximum of the X-ray diffraction rocking curve ω_θ ~ 45 arcmin, whereas for the semipolar GaN(10 $$\bar {1}$$ 1), these values are –0.29 GPa and ω_θ ~ 22 arcmin, respectively. A conclusion is drawn that the combined technology of semipolar gallium nitride on a silicon (100) substrate is promising.

Excellent structural, optical, and electrical properties of Nd-doped BaSnO3 transparent thin films

We epitaxially grew 7 mol. % Nd-doped BaSnO3 (NBSO) thin films on double-side polished SrTiO3 (001) single-crystal substrates and optimized the oxygen pressure (PO2), substrate temperature (TS), and film thickness (t) to achieve excellent structural, optical, and electrical performance. By keeping TS (=800 °C) constant, NBSO films prepared at PO2 = 10 Pa show the best crystallization, yielding a full-width at half-maximum (FWHM) of the x-ray diffraction rocking curve of 0.079° and exhibiting a room-temperature resistivity (ρ) of ∼1.85 mΩ cm and a volume carrier density (n) of ∼8.5 × 1020/cm3. By keeping PO2 (=10 Pa) constant, the room-temperature ρ of NBSO films could be reduced to as low as 0.5 mΩ cm by increasing TS from 700 to 825°; meanwhile, the volume carrier density and mobility show the maximum of 5.04 × 1020/cm3 and 24.9 cm2/Vs, respectively, for TS = 825 °C. For all as-grown NBSO thin films, the optical transmittance in the visible wavelength region is larger than 80%. The optimized comprehensive properties of the NBSO films with FWHM = 0.11°, ρ = 0.5 mΩ cm, μ = 24.9 cm2/Vs, and T > 80% are superior to those of other rare-earth and 4d- and 5d-transition metal-doped BaSnO3 thin films.

Reducing stimulated emission threshold power density of AlGaN/AlN multiple quantum wells by nano-trench-patterned AlN template

We investigate the crystal quality of epitaxy lateral overgrowth (ELOG) AlN layers and the performance of optical pumping AlGaN-based deep-ultraviolet laser diodes (LDs) on two different patterned AlN templates upon sapphire substrate. The full width at half maximum values of (0002) and (101¯2) X-ray diffraction rocking curves of the ELOG AlN layer on the nano-net-patterned AlN template are 76 and 306 arcsec, and the values of that on the nano-trench-patterned AlN template are 114 and 357 arcsec, respectively. Nevertheless, the threshold power density (Pth) of the 272-nm lasing from the multiple quantum wells (MQWs) on the nano-trench-patterned AlN template is 11% lower than that on the nano-net-patterned AlN template. The reason is that the continuous low threading dislocation density (TDD) MQWs zones above the ELOG coalescent areas upon trenched patterns are in parallel with the stimulated light emission direction. When light resonates through the continuous low TDD MQWs zones, it has higher optical gain and less non-radiative recombination than the case on the nano-net-patterned AlN template where the low TDD MQWs zones are discontinuous on the light path. The results indicate that not only the crystal quality but also the TDD distribution originated from the ELOG on the patterned templates have crucial influence on the Pth, and trench-patterned template can improve the performance of waveguide LDs with Fabry-Perot cavities.

Systematic Study on Aluminum Composition Nonuniformity in Aluminum Gallium Nitride Metal–Semiconductor–Metal Photodetectors

The influence of aluminum composition (Al%) nonuniformity on AlGaN metal–semiconductor–metal photodetectors was thoroughly studied on a device level. The Al% fluctuation was precisely measured by X-ray photoelectron spectroscopy and mapped by energy dispersive spectrometry; the dislocation density was investigated by X-ray diffraction rocking curve. Both theoretical simulation and experimental testing showed a significant difference in the responsivity, dark current, and decay time in the device with different Al%. The Al% fluctuation is also a likely cause of the long decay time of the device.

Metal organic chemical vapor deposition of m-plane GaN epi-layer using a three-step approach towards enhanced surface morphology

Specular m-plane (101¯0) gallium nitride (m-GaN) epi-layer are grown on m-plane (101¯0) sapphire substrates by metal organic chemical vapor deposition using a three-step approach. A two-step approach was used to grow m-GaN buffer layer (BL), while a three-step approach was applied to improve the surface morphology of the top m-GaN epi-layer at high temperature. The three-step approach started with growing m-aluminum nitride nucleation layer with an optimized ammonia flux during the growth of aluminum nitride. Then the temperature was ramped up during the recrystallization step before the m-GaN BL deposition at low-temperature and the growth of m-GaN layer at high-temperature for the final step. Unexpectedly, when ammonia flow was intentionally halted during the recrystallization step, the surface morphology of the BL drastically changed from three- to two- dimensional with an abrupt cross-sectional structure. This in turn facilitated the complete coalescence of the m-GaN layer as revealed by field emission scanning electron microscopy. The three-step technique was found to affect the quality of m-GaN epi-layer as the samples exhibit improved crystallinity with X-ray diffraction rocking curves widths of 4680 and 1980 arcsec along the azimuth, perpendicular and parallel to [101¯0] directions, respectively.