X-ray Diffraction Rocking Curve Research Articles

Structural and electrical characterization of InN, InGaN, and p-InGaN grown by metal-modulated epitaxy

InN, high indium content InGaN, and Mg-doped InGaN were grown by metal modulated epitaxy (MME). Transient reflection high-energy electron diffraction intensities were analyzed during the growth of InN and found to be similar to that previously reported for GaN and AlN. The x-ray diffraction rocking curve and background electron concentration of InN grown by MME were found to be respectable in comparison to recent reports in literature. InGaN alloys grown by MME were also investigated, and a method for detecting indium surface segregation was demonstrated. It was found that the shutter modulation scheme could be modified to prevent phase separation by indium surface segregation, and a range of single-phase InGaN samples with indium contents throughout the miscibility gap were grown. Using the discovered method of suppressing phase separation, several p-InxGa1 − xN samples were grown with indium contents from x = 0 to 0.22. A maximum hole concentration of 2.4 × 1019 cm−3 was detected by Hall effect characterization, demonstrating feasibility of these p-InGaN layers for use in several device applications.

Reduced threading dislocation densities in high-T/N-rich grown InN films by plasma-assisted molecular beam epitaxy

We explore the effect of growth kinetics on the structural properties of In-polar InN films on GaN templates grown near the thermal dissociation limit by plasma-assisted molecular beam epitaxy. Unlike the common growth temperature limit (T ≈ 500 °C) for In-polar InN grown under In-rich conditions, slightly N-rich conditions are demonstrated to shift the available growth temperature window to much higher temperatures (by >50 °C). InN films grown in this high-T/N-rich regime show significantly reduced off-axis X-ray diffraction rocking curve peak widths and record low threading dislocation densities (TDD ∼ 4 × 109 cm−2) even for film thicknesses <1 μm, as compared to state of the art In-rich growth. The reduction of TDD is attributed to more effective TD inclination and annihilation under N-rich growth, delineating prospective routes for improved InN-based materials.

Effects of crystallinity on laser-induced voltage effect from Zn0.9Co0.1O thin film

Co-doped ZnO epilayer films were grown by pulsed laser deposition (PLD) on vicinal cut silicon and sapphire substrates. Changes in deposition time were observed as a moderate effect on the quality of the films, and the influence of the thickness on thermoelectric signals from Zn0.9Co0.1O thin films were discussed. The effect of one of the main deposition parameters, the deposition time, on the crystallinity and electron mobility properties of the Zn0.9Co0.1O thin films grown on sapphire was investigated by means of X-ray diffraction (XRD) and laser-induced voltage (LIV) effect. It shown that the XRD rocking curve full-width half-maximun (FWHM) decreased as time increasing, and the LIV signals were observed along the tilting angle of the substrate orientation when the pulsed KrF excimer laser of 248 nm were irradiated on the films. When the films illuminated in pulse lasers, the highest signals occurred in the films with best crystalline quality, and the signals were higher in the films grown on sapphire than those on silicon substrates. It suggested that the electrical resistivity and electron mobility have close relations with not only the crystallinity but also with the interface of the thin films.

Effects of the V/III ratio on the quality of aluminum nitride grown on (0001) sapphire by high temperature hydride vapor phase epitaxy

AbstractA High Temperature Hydride Vapor Phase Epitaxy reactor (HT‐HVPE) was used to grow 5 µm‐thick (0001) epitaxial AlN layers on sapphire. The experimental set‐up consists of a vertical cold‐wall quartz reactor working at low pressure in which the reactions take place on a graphite susceptor heated by induction. The reactants used are ammonia (NH3) and aluminum chlorides (AlClx) in situ formed via chlorine (Cl2) reaction with high purity aluminum pellets. As‐grown AlN layers have been characterized by Scanning Electron Microscopy (SEM), X‐ray diffraction rocking curves (XRC) and Raman spectroscopy. First, the influence of the V/III ratio in the gas phase on surface morphology, crystalline quality and strain into the material is investigated in order to improve the quality of epitaxial AlN layers grown at high temperature. Parameters were adjusted to keep constant growth rate of about 5 µm/h. Second, a protective layer (growth of a 200 nm‐thick AlN layer at 1200 °C) was deposited before the main growth of a 5µm layer of AlN at 1500°C. A 430 arcsec FWHM value for the 0002 reflection of the AlN layer has been obtained for such experimental conditions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

CVD growth of SiC on sapphire substrate and graphene formation from the epitaxial SiC

6H-SiC epi-layer was grown on c-plane sapphire by chemical vapor deposition (CVD) and epitaxial graphene was grown on the SiC film using the thermal decomposition method. A thin (∼300nm) AlN was employed as a buffer layer since a direct growth on sapphire did not produce SiC. Raman spectroscopy, x-ray diffraction (XRD), and atomic force microscopy (AFM) confirmed the growth of high quality 6H-SiC on the AlN/sapphire at 1450°C. The effect of AlN growth method/condition (HVPE and MBE) on the quality of final SiC film and epitaxial graphene was explored. Raman and XRD 2θ-scan did not show any significant difference between the SiC films grown on HVPE-AlN and MBE-AlN. A sharper XRD rocking curve was observed on the SiC/HVPE-AlN but a smoother SiC was grown on the MBE-AlN. Graphitization of the SiC/AlN/sapphire was done at 1300–1400°C under Ultra High Vacuum (UHV). The SiC on MBE-AlN survived at high temperatures (up to 1400°C) without cracking and graphene was grown on it. However, the SiC on HVPE-AlN cracked and peeled off at 1300°C resulting in no formation of graphene. The signatures of graphene were clearly observed by Raman spectroscopy with the 2D-peak to G-peak intensity (I2D/IG) of approximately 2, the D-peak to G-peak intensity (ID/IG) of 0.4, and the 2D-peak width of 55cm−1.

Bulk AlN single crystal growth on foreign substrate and preparation of free-standing native seeds

Physical vapour transport growth of aluminium nitride (AlN) single crystals on silicon carbide (SiC) substrates has been optimised and crack-free, large-area, free-standing (0001) AlN wafers were prepared from the grown template crystals. 28 mm diameter single crystals without any polycrystalline surroundings were obtained. Different off-oriented substrates give rise to different growth modes. Sharp and symmetric line shapes of X-ray diffraction (XRD) rocking curves and high intense Raman phonon mode peaks prove high structural quality and homogeneity of the grown crystals. Full width at half maximum of the rocking curves is 72 arcsec for symmetric 00.2 reflection and 200 arcsec for asymmetric 10.3 reflection, representing a low screw as well as edge type threading dislocations. Wet chemical etching results also confirm the above XRD results and the estimated etch pit density is as low as 2–5 × 105 cm−2. The growth surfaces of all the crystals show only Al-polarity as inferred by the etching analysis. The concentration of silicon and carbon impurities incorporated from the SiC substrate decreases with the growth length of the AlN crystals. These impurities might play a decisive role in determining the optical properties of the crystal and be responsible for the absence of near-bandgap excitonic luminescence. Confocal Raman spectra show only the phonon modes allowed by the selection rules for the measured symmetry. The observed E2(high) phonon mode frequency very closely matches the reported stress-free phonon frequency of AlN. This work demonstrates that AlN templates prepared on SiC as a foreign substrate can be used as native seeds for the growth of further homo-epitaxial layers and crystalline boules.

Nanostructural analysis of ZnO:Al thin films for carrier-transport mechanisms

The carrier mobility of sputter-deposited Al-doped ZnO transparent-conducting (ZnO:Al) thin films was controlled between 22 and 48 cm2/Vs by varying the ZnO:Al seed layer. The statistical distribution of the [001] grain misorientation was characterized from the X-ray diffraction rocking curve in the range from 0.043 (2.5°) to 0.179 rad (10.2°). The grain-boundary energy barriers (Eb) from Seto's model [1] clearly exhibit linear dependence on the grain-boundary misorientation angle (ω) according to the equation Eb = 78 ± 4 + 173 ± 32 ω meV.

Epitaxy of GaN on Si(111) substrate by the hydride vapor phase epitaxy method

GaN epilayers were grown on Si(111) at 980°C by a hydride vapor phase epitaxy (HVPE) method. AlxGa1−xN with thickness of ∼900nm was inserted between Si substrate and GaN epilayer to act as a buffer layer. The investigation of the influence of different V/III ratios on GaN epilayer qualities reveals that high GaCl flow rate can increase the growth rate and improve the surface morphologies of GaN epilayers while high NH3 flow rate is not good for reducing dislocations in GaN epilayers, which can be proved from the analysis of X-ray diffraction rocking curve (XRC), cross-sectional image of scanning electron microscopy (SEM) and image of atomic force microscopy (AFM). Finally, 1.22μm GaN epilayer without cracks was successfully obtained with a three-step growth method. The surface roughness average (Ra) was measured to be 1.45nm and the FWHM of GaN(0002) was 599arcsec. The measured lattice constants for GaN epilayer were a=3.210Å and c=5.177Å, indicating the in-plane tensile stress and out-of-plane compressive stress of GaN epilayer.

Thickness dependent residual stress in sputtered AlN thin films

Thin aluminum nitride (AlN) films of different thickness are deposited by DC-pulsed magnetron sputtering under identical conditions on sapphire (0001) and silicon (100) substrates. An investigation of the residual stress, morphology and structural properties is carried out. The thickness of the films covers the range from 17nm to 3.9μm. A higher compressive residual stress is measured for the thinner films and the presence of a stress gradient is proven. X-ray diffraction (XRD) studies show that all AlN films are achieved with perfect c-axis orientation perpendicular to the film surface and that the films are biaxially strained. XRD rocking curves reveal that AlN films on sapphire are highly oriented for all film thicknesses, whereas AlN film growth on silicon starts highly disoriented and the film quality improves with film thickness. Surface analysis by atomic force microscopy shows a continuous film roughening and decrease of grain boundary density with increasing film thickness.

Studies on synthesis, growth, structural, thermal, linear and nonlinear optical properties of organic picolinium maleate single crystals

Picolinium maleate (PM), an organic material has been synthesised and single crystals were grown by slow evaporation technique. The structure of the grown crystal was elucidated by using single crystal X-ray diffraction analysis. PM crystal belongs to the monoclinic crystallographic system with space group P21/c. The crystalline perfection of the grown crystals was analyzed by high-resolution X-ray diffraction rocking curve measurements. The presence of functional groups in PM was identified by FTIR and FT-NMR spectral analyses. Thermal behaviour and stability of picolinium maleate were studied by TGA/DTA analyses. UV–Vis spectral studies reveal that PM crystals are transparent in the wavelength region 327–1100nm. The laser damage threshold value of PM crystal was found to be 4.3GW/cm2 using Nd:YAG laser. The Kurtz and Perry powder second harmonic generation technique confirms the nonlinear optical property of the grown crystal.

Effect of Si doping in wells of AlGaN/GaN superlattice on the characteristics of epitaxial layer

An AlGaN/GaN superlattice grown on the top of a GaN buffer induces the broadening of the full width at half maximum of (102) and (002) X-ray diffraction rocking curves. With an increase in the Si-doped concentration in the GaN wells, the full width at half maximum of the (102) rocking curves decreases, while that of the (002) rocking curves increases. A significant increase of the full width at the half maximum of the (002) rocking curves when the doping concentration reaches 2.5 × 1019 cm−3 indicates the substantial increase of the inclined threading dislocation. High level doping in the AlGaN/GaN superlattice can greatly reduce the biaxial stress and optimize the surface roughness of the structures grown on the top of it.

Surfactant effects of gallium on quality of AlN epilayers grown via metal-organic chemical-vapour deposition on SiC substrates

Effects of gallium as a surfactant for the growth of AlN epilayers on SiC substrates by metal-organic chemical-vapour deposition have been studied. It was found that the use of gallium as a surfactant enables the growth of thick, crack-free AlN epilayers on SiC substrates. The photoluminescence and x-ray diffraction (XRD) analysis show that gallium surfactant can reduce some of the tensile strain in AlN epilayers and it improves the surface smoothness. XRD rocking curves yielded decreased full widths at half maximum for the (1 0 5) and (0 0 2) reflections, indicating a reduction in threading dislocation density in the AlN epilayers.

Synchrotron radiation X‐ray topography and X‐ray diffraction of homoepitaxial GaN grown on ammonothermal GaN

AbstractIn this study, homoepitaxial GaN grown on ammonothermal GaN substrates is non‐destructively investigated by synchrotron radiation X‐ray topography (SR‐XRT) and X‐ray diffraction (XRD). The homoepitaxial GaN layer was found to be of excellent crystal quality with individual dislocations clearly visible in the SR‐XRT images. SR‐XRT images and XRD rocking curves suggest the dislocations are mainly of mixed type. To the best of our knowledge the measured dislocation density is the lowest reported in a homoepitaxial GaN film (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Selective-Area Epitaxy of CdTe on CdTe/ZnTe/Si(211) Through a Nanopatterned Silicon Nitride Mask

We report here the use of molecular beam epitaxy (MBE) to achieve selective-area epitaxy (SAE) and coalescence of CdTe on nanopatterned substrates with 0.5-μm-pitch arrays of CdTe/ZnTe/Si(211) seeding areas, exposed through a silicon nitride mask. The nanopatterned substrate surface morphology, crystallinity, and chemical composition were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) both before and after exposure to CdTe flux by MBE. We find a seven times wider (422) CdTe XRD rocking curve full-width at half-maximum (FWHM) for our patterned samples, when directly compared with unpatterned samples with identical growth and pregrowth conditions. We also observe that electron beam-induced carbon deposits can serve as a mask material for SAE of CdTe by MBE. Finally, we point to possible further improvements in patterned sample architectures of the future, for use in CdTe films on Si.

In-Plane Grain Orientation Alignment of Polycrystalline Silicon Films by Normal and Oblique-Angle Ion Implantations

Random crystallographic orientations of polycrystalline silicon (poly-Si) grains in the films grown on a SiO2 substrate by chemical vapor deposition were laterally aligned by maintaining the 110 restricted pillar texture through double Si+ self-ion implantations. The in-plane X-ray diffraction pattern and rocking curve clearly indicate the lateral alignment. The oblique-angle Si+ self-ion implantation was also found to be useful for increasing the amount of the 110 pillar texture. The electron backscatter diffraction (EBSD) pattern supports the increase in the amount of the 110 pillar texture and the lateral crystal orientation alignment. The transmission electron micrography and EBSD results also suggest that grain size is increased by double Si+ self-ion implantations. Although further systematic optimization may be required, the technique will be useful for improving the electrical characteristics of poly-Si devices for future electronic systems on insulators.

Effect of Solid-Phase-Epitaxy Si Layers on Suppression of Sb Diffusion from Sb-Doped n+-BaSi2/p+-Si Tunnel Junction to Undoped BaSi2 Overlayers

A new method is proposed for the growth of undoped BaSi2 overlayers on a Sb-doped n+-BaSi2/p+-Si tunnel junction with reduced Sb diffusion. Samples with the structure of undoped-BaSi2/Si/Sb-doped n+-BaSi2/p+-Si were prepared; the inserted Si layer was grown by solid phase epitaxy and used to prevent Sb diffusion during the growth of undoped BaSi2 overlayers. Secondary ion mass spectrometry measurements indicated that Sb diffusion was effectively suppressed when the growth temperature of the undoped BaSi2 overlayers was 500 °C and lower. The X-ray diffraction (XRD) rocking curves revealed that the full width at half maximum for the BaSi2(600) intensity increased significantly for BaSi2 grown at 440 °C, indicating that the growth temperature should be higher than this temperature.

Growth, crystalline perfection and characterization of Hexaaquanickel(II) dipotassium tetrahydrogen tetra-o-phthalate tetrahydrate crystals

Pale-green single crystals of hexaaquanickel(II) dipotassium tetrahydrogen tetra-o-phthalate tetrahydrate K2[Ni(H2O)6] (C8H5O4)4·4H2O (PNHP), of dimension ∼33mm×18mm×4mm have been grown by slow evaporation solution growth technique (SEST) and modified Sankaranarayanan–Ramasamy (SR) method. The powder XRD profiles and FT-IR are used for identifying the material. The lattice parameters of the as-grown crystals obtained by single crystal X-ray diffraction analysis confirm the formulae. Lower optical cut-off at ∼300nm and optical transparency in the visible region were observed. The structural perfection of the grown crystal has been analyzed for SEST and SR method grown crystals by high-resolution X-ray diffraction (HRXRD) rocking curves (DC). The DCs of both the specimens are asymmetric with respect to Bragg position and more of scattered intensity in the negative direction is indicative of predominantly vacancy defects. Interestingly, SR method grown crystal has a better crystalline perfection than the conventionally grown crystal. The dielectric, thermal and mechanical behaviors of the specimen were also studied.

Growth and scintillation properties of pure CsI crystals grown by micro-pulling-down method

Single crystals of pure cesium iodide (CsI) have been grown from the melt using micro-pulling-down (μ-PD) method. Two kinds of crucible (graphite one and quartz one) were used for the growth and the grown crystals were investigated by X-ray diffraction (XRD) and X-ray rocking curve (XRC) analysis. The XRD analysis did not confirm any impurity phases and a sub-grain structure was observed for each sample in the rocking curve measurement. Under X-ray irradiation, strong STE emission peaks around 300nm were observed together with some luminescence related to unintentionally present impurities. The STE emission peaks are characterized by fast decay times of several ns and about 20ns which are interpreted as the on-center-type STE (VK+e) and off-center type STE (H+F) recombinations, respectively. The light yield of the STE-related emissions has been estimated to be 3000ph/MeV. Other emission peaks were observed at 410nm and 515nm. The former one can be related to Br-contamination and it is characterized by a relatively slow decay time of 6μs. Concerning the latter one at 515nm, similar luminescence was observed for the water-doped CsI grown by Bridgman method.

Structural characterization of epitaxial CrxMo1−x alloy thin films

To develop a model system containing regularly spaced misfit dislocations for studies of the radiation resistance of nanoscale defects, epitaxial thin films of Cr, Mo, and CrxMo1−x alloys were deposited on MgO(001) by molecular beam epitaxy. Film compositions were chosen to vary the lattice mismatch with MgO. The film structure was investigated by x-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and scanning transmission electron microscopy (STEM). Epitaxial films with reasonably high crystalline quality and abrupt interfaces were achieved at a relatively low deposition temperature, as confirmed by STEM. However, it was found by XRD and RBS in the channeling geometry that increasing the Mo content of the CrMo alloy films degraded the crystalline quality, despite the improved lattice match with MgO. XRD rocking curve data indicated that regions of different crystalline order may be present within the films with higher Mo content. This is tentatively ascribed to spinodal decomposition into Cr-rich and Mo-rich regions, as predicted by the CrxMo1−x phase diagram.

Synthesis, crystal growth and characterization of nonlinear optical organic crystal: p-Toluidinium p-toluenesulphonate

p-Toluidinium p-toluenesulphonate (p-TTS) an organic nonlinear optical crystal has been grown from the aqueous solution by slow evaporation solution growth technique. Single crystal X-ray diffraction analysis reveals that p-TTS crystallizes in monoclinic crystal system. The structural perfection of the grown p-TTS single crystal has been analyzed by high-resolution X-ray diffraction rocking curve measurements. Fourier transform infrared spectral studies have been performed to identify the functional groups. The optical transmittance window and the lower cutoff wavelength of the grown crystals have been identified by UV–vis–IR studies. Birefringence of p-TTS crystal has been studied using channel spectrum measurement. The laser damage threshold value was measured using Nd:YAG laser. The second harmonic conversion efficiency of p-TTS has been determined using Kurtz powder technique. Thermo gravimetric and differential thermal analyses were used to study its thermal properties. Dielectric constant, dielectric loss and AC conductivity of the grown p-TTS single crystal has been studied.