High-resolution X-ray Diffraction Curves Research Articles

Effect of Neutron Irradiation on the Electronic and Optical Properties of AlGaAs/InGaAs-Based Quantum Well Structures.

The effect of neutron irradiation on the structural, optical, and electronic properties of doped strained heterostructures with AlGaAs/InGaAs/GaAs and AlGaAs/InGaAs/AlGaAs quantum wells was experimentally studied. Heterostructures with a two-dimensional electron gas of different layer constructions were subjected to neutron irradiation in the reactor channel with the fluence range of 2 × 1014 cm-2 ÷ 1.2 × 1016 cm-2. The low-temperature photoluminescence spectra, electron concentration and mobility, and high-resolution X-ray diffraction curves were measured after the deactivation. The paper discusses the effect of neutron dose on the conductivity and optical spectra of structures based on InGaAs quantum wells depending on the doping level. The limiting dose of neutron irradiation was also estimated for the successful utilization of AlGaAs/InGaAs/GaAs and AlGaAs/InGaAs/AlGaAs heterostructures in electronic applications.

Hydrothermal crystal growth of tetralithium octafluoridozirconate (Li4ZrF8) and its physicochemical properties

A single crystal of tetralithium octafluridozirconate (Li4ZrF8) has been obtained by using a hydrothermal process. The crystal phase was analyzed using a powder X-ray diffraction pattern and matched with standard reference data. The high-resolution X-ray diffraction curve indicates that the crystal has good crystalline perfection. The thermal behavior of the crystal sample was investigated by TGA/DSC analysis. The optical bandgap of the crystal sample was calculated from the Tauc plot and found to be 5.8 eV. The crystal sample exhibits intrinsic X-ray excited luminescence with a peak maximum of 265 nm. The thermoluminescence measurement shows two peaks, one is at the high-temperature region of 545 K and another one is at the low-temperature region at 383 K. TL kinetic parameters such as activation energy (E) and frequency factor (s) for the peak at 545 K was estimated as 1.20 eV and 2.06 × 10−10 respectively. The sample has good TL sensitivity to the neutron dose in the order of µsv. The low-temperature thermoluminescence measurements were carried out to study the trap levels and found two major glow peaks at 108 and 130 K. Scintillation properties were analyzed under α-rays from a 241Am source. The decay time profile was well fitted with three components and the fitted values show the fast component of 500 ns (9 %), the medium component of 2.4 μs (24 %), and a slow component of 12.8 μs (67 %).

Photoluminescence Properties of InGaN/InGaN MQWs with Different Electron Injection Layers

The structural and optical properties of InxGa1-xN/InyGa1-yN multi quantum well (MQW) light emitting devices with/without electron injection layers were studied. The samples with electron injection layer consist of step-graded (GIE) and two step staircase (SEI) electron injection layer between n-type GaN and MQWs active region. Edge and screw type of dislocation densities were deduced from High Resolution X-Ray Diffraction (HR-XRD) curves and no significant difference were realized. The zeroth and higher order satellite peaks were more clearly observed in the sample without electron injection layer. Optical characterization was carried out by temperature dependent photoluminescence (PL) technique. It was found that the PL densities of samples with step-graded and two step-staircase electron injection layers had almost two times lower temperature dependence compared to the reference sample without electron injection layer. On the other hand, the line width of the photoluminescence peak associated with MQWs is much narrower at low temperature for sample without electron injection layer than the other two samples.

Interface effect on superlattice quality and optical properties of InAs/GaSb type-II superlattices grown by molecular beam epitaxy

We systematically investigate the influence of InSb interface (IF) engineering on the crystal quality and optical properties of strain-balanced InAs/GaSb type-II superlattices (T2SLs). The type-II superlattice structure is 120 periods InAs (8 ML)/GaSb (6 ML) with different thicknesses of InSb interface grown by molecular beam epitaxy (MBE). The high-resolution x-ray diffraction (XRD) curves display sharp satellite peaks, and the narrow full width at half maximum (FWHM) of the 0th is only 30–39 arcsec. From high-resolution cross-sectional transmission electron microscopy (HRTEM) characterization, the InSb heterointerfaces and the clear spatial separation between the InAs and GaSb layers can be more intuitively distinguished. As the InSb interface thickness increases, the compressive strain increases, and the surface “bright spots” appear to be more apparent from the atomic force microscopy (AFM) results. Also, photoluminescence (PL) measurements verify that, with the increase in the strain, the bandgap of the superlattice narrows. By optimizing the InSb interface, a high-quality crystal with a well-defined surface and interface is obtained with a PL wavelength of 4.78 μm, which can be used for mid-wave infrared (MWIR) detection.

Crystal growth and physico-chemical characterization of semi-organic [C4H12N2] ZnCl4·H2O single crystal for laser applications

Optical high-quality semi-organic piperazinium tetrachlorozincate monohydrate, [C4H12N2] ZnCl4·H2O (PTCZ), single crystals were grown by conventional solution method. The structure of grown crystal was confirmed by the single-crystal X-ray diffraction (SXRD) analysis. The material phase purities and its various (hkl) planes have been confirmed by the powder X-ray diffraction (PXRD) analysis at room temperature. The different functional groups were confirmed by the Fourier transform infrared (FTIR) spectroscopy. The optical quality of the PTCZ single crystal and band gap energy have been identified by the UV–Vis–NIR spectral analysis and also calculated refractive index of the material. The thermal stability of the PTCZ single crystal was investigated by TG–DTA. The hardness-related properties were analyzed by microhardness tester. The dielectric properties have been measured on the grown single crystal and the electronic polarizability value has been calculated with various theoretical approaches. The etching was carried out on the grown crystal to find the dislocation density. The crystal atomic perfection has been investigated by the high-resolution X-ray diffraction (HRXRD) or Rocking curve (RC) analysis. The Z-scan measurement has been carried out to find third-order optical susceptibility (χ(3)) of the grown single crystal using solid-state laser (640 nm).

Growth of high-quality organic single crystal of 2-aminopyridinium 4-nitrophenolate 4-nitrophenol (2AP4N) by a novel Rotational Sankaranarayanan–Ramasamy (RSR) method

The good quality 2-aminopyridinium 4-nitrophenolate 4-nitrophenol (2AP4N) single crystals have been grown by (i) Sankaranarayanan–Ramasamy (SR) method and (ii) Rotational Sankaranarayanan–Ramasamy (RSR) method. The effect of rotation on unidirectional crystal growth method (RSR) has been reported for the first time. The apparatus was specially designed and developed for the growth of high-quality crystals by slow cooling under rotational conditions. The high-quality crystals have been achieved under forced convection and the quality of the crystal is compared to the crystals grown under free convection conditions. The crystal structure was analyzed by single crystal X-ray diffraction (SXRD) measurement. The grown crystal was subjected to the powder X-ray diffraction (PXRD) analysis to confirm the growth direction along (0 0 1) plane. The optical quality of the grown crystals has been analyzed by UV–Vis NIR spectrophotometer. It confirms that the grown crystal is highly transparent in the visible and near IR region. The photoluminescence behaviour was recorded in the wavelength region between 450 and 700 nm. It confirms that the grown crystal has emission at 500 nm. The electro-optical properties of the grown crystal were analyzed by photoconductivity measurement and it has positive photoconductivity nature. The grown crystal has less dislocation densities as confirmed by chemical etching analysis. The mechanical strength was investigated by Vickers microhardness tester. The frequency dependent dielectric properties of the crystals were investigated. The laser damage threshold (LDT) was measured for both SR and RSR method grown crystals. The full-width at half maximum (FWHM) of high-resolution X-ray diffraction (HRXRD) curves indicate that the grown crystal has high crystalline perfection. The results obtained from the SR and RSR method grown 2AP4N crystals were compared. The RSR method grown crystal has higher optical transparency, higher photoluminescence, higher photoconductivity, higher mechanical strength, higher laser damage threshold, higher crystalline perfection, less dislocation density, low dielectric loss and low full with at half maximum (FWHM). The second harmonic generation (SHG) of 2AP4N was analyzed by Kurtz-Perry powder technique. The SHG efficiency was found to be 4.5 times that of reference KDP material. The above studies reveal that the RSR method grown crystals are more useful for device applications.

Structural and optical characterization of GaSb on Si (001) grown by Molecular Beam Epitaxy

GaSb epilayers were grown on Si (001) using molecular beam epitaxy via AlSb quantum dots as an interfacial misfit (IMF) array between the Si substrates and GaSb epilayers. The effect of IMF array thickness, growth temperature and post annealing on the surface morphology, structural and optical properties of the GaSb on Si were investigated. Among five different IMF array thicknesses (5, 10, 20, 40 and 80 ML) that were used in this study, the best result was obtained from the sample with a 20 ML AlSb IMF array. Additionally, it was found that although the full width at half maximum (FWHM) and threading dislocation (TD) densities obtained from high resolution x-ray diffraction curves can be improved by increasing the growth temperature, a decrease in the photoluminescence (PL) signal and an increase in the surface roughness (RMS) emerged. On the other hand, the results indicate that by applying post annealing the GaSb epilayer crystal quality can be improved in terms of FWHM, TD density, PL signal or RMS depending on the post annealing temperature. By applying post annealing at 570 °C for 30 min we achieve a FWHM value of 260 arcsec for a 1 μm thick GaSb epilayer on Si (001) and improve the PL signal intensity without worsening the RMS value.

In situ monitoring of InAsBi alloy grown under alternated bismuth flows by metalorganic vapor phase epitaxy

We suggest a successful growth method for InAsBi layer epitaxy on (0 0 1) GaAs substrate. An alternated trimethylbismuth flows was used during growth. For real time monitoring of the metalorganic vapor-phase epitaxy of InAsBi layer, we use spectral reflectance. Reflectivity signal is found to change significantly during both InAsBi and InAs growth stages. High-resolution X-ray diffraction (HRXRD) curve shows a wide peak that can be attributed to InAsBi inhomogeneous layer. Based on the signals of several wavelengths in situ monitoring system, the related information of growth rate, refractive index n and the extinction coefficient k of InAs and InAsBi sequences were determined. Simulation results indicate different Bi regions. Theoretical simulation of reflectivity signals was carried out by recurrence method using a multilayer model. Results were ex-situ correlated with atomic force microscopy measurements.

Performance of Nanostructures within InGaN-Based Multiquantum-Well Light-Emitting Devices

We introduced multiquantum-barrier (MQB) nanostructures into the barrier layers of InGaN/GaN multiquantum-well (MQW) heterostructures to improve the operation characteristics of the light-emitting devices. The electroluminescence (EL) spectra were examined over a broad range of temperatures for the samples. We observed inhibited carrier leakage for the sample with the MQB nanostructures. Greater inhomogeneity of nanocrystallite size and a stronger localization effect were also observed for the sample. To interpret this phenomenon, high-resolution X-ray diffraction curves were measured and analyzed using the Warren–Averbach model. External quantum efficiency as a function of temperature was also evaluated. The calculation results correspond with the inference the EL measurements provided. We determined that the performance of the light-emitting devices is enhanced by the MQB nanostructures within InGaN/GaN MQWs.

WITHDRAWN: Microstructure and optoelectronic performance of SiGe/Si heterostructures

Abstract The best way to produce silicon-based Ge infrared detectors with lower dark current density is to develop high-quality buffer layers with low dislocation density and high relaxation degree. In this paper, we grew both Ge/Si and Si 1 − x Ge x /Si heterostructures and studied the effects of Ge composition, annealing-influenced dislocation density, and strain relaxation. Using high-resolution X-ray diffraction and swing curve (224) analysis, we found that the thin films after annealing exhibited strain relaxation of > 90%. Their dislocation density was lower than 8.0 × 10 5 /cm 2 , while their average roughness was 1.4–2.0 nm. These results show that such heterostructure buffer layers can be used to produce Ge-alloy infrared photodetectors with good performance.

Strain study of GaAs/In x Ga 1−x As/GaAs structures grown by MOVPE

Abstract GaAs/InxGa1 − xAs/GaAs strained and partially relaxed structures were grown by metalorganic vapor phase epitaxy and in situ monitored by laser reflectometry (LR). Two structures were formed by a single InxGa1 − xAs layer, and the third comprises three superposed InxGa1 − xAs layers having increasing indium contents. LR plots as function of time were recorded to extract growth rates and thicknesses of active and cap layers. In order to study the strain effect on structural and optical properties of these heterostructures, high resolution X-ray diffraction (HRXRD) and photoreflectance (PR) measurements were performed. HRXRD curves are developed to calculate strain tensor components, indium composition, and thicknesses of strained and partially relaxed layers. Besides, valence-band splitting and band-gap energy shift were measured by best fitting PR spectra at 300 K. Experimental energy values determined as a function of indium composition and relaxation rate were compared to those obtained by the elastic strain theory. For single and superposed InxGa1 − xAs active layers, a good correlation between experimental results and theoretical predictions was obtained.

High-resolution X-ray diffraction analysis of AlxGa1−xN/InxGa1−xN/GaN on sapphire multilayer structures: Theoretical, simulations, and experimental observations

The work presents a comparative study on the effects of In incorporation in the channel layer of AlGaN/GaN type-II heterostructures grown on c-plane sapphire by Plasma Assisted Molecular Beam Epitaxy. The structural characterizations of these samples were performed by High-Resolution X-Ray Diffraction (HRXRD), X-ray Reflectivity (XRR), Field Emission Scanning Electron Microscopy, and High Resolution Transmission Electron Microscopy. The two-dimensional electron gas in the AlGaN/GaN and AlGaN/InGaN interface was analyzed by electrochemical capacitance voltage and compared with theoretical results based on self-consistent solution of Schördinger–Poisson equations. The carrier profile shows enhanced confinement in InGaN channel (1.4393 × 1013 cm−2 compared to 1.096 × 1013 cm−2 in GaN). On the basis of HRXRD measurements, the stress-strain of the layers was examined. The c- and a-lattice parameters of the epilayers as well as in-plane and out-of plane strains were determined from the ω-2θ for symmetric scan and ω-Xθ (X represents the coupling coefficient) for asymmetric scan. Strain, tilt, and correlation lengths were calculated from Williamson–Hall plots, whereas stress was examined from modified plot of the same data assuming Uniform Stress Deformation Model. Moreover, the twist angle was measured from skew symmetric scan of (102), (103), and (105) plane along with (002) symmetric plane. The composition and strain/relaxation state of the epilayers were observed in detail by reciprocal space mapping (RSM). The symmetric (002) triple axis RSM and asymmetric (105 and 114) double axis RSM of grazing incidence and exit geometry were carried out on each sample. The defect density was measured from HRXRD curves of skew symmetric (002) and (102) reflection plane. The Al and In mole fraction and strain states of the layers were calculated by fitting the experimental curves with computer simulations and compared with theoretical findings based on elastic theory. The thicknesses of the layers and roughness of the interfaces were measured from simulation of the nominal structure by fitting with XRR experimental curves. The HRXRD measured thicknesses of the layers were further confirmed by cross sectional electron micrographs.

Influence of the Nitridation Time after the Al Pre-Seeded Layer on the Properties of GaN Layer Grown on Si (1 1 1)

The epitaxial growth of Gallium Nitride (GaN) on 2 inch Si (1 1 1) substrates was investigated, and it was found that by inserting a surface nitridation layer prior to Aluminum Nitride (AlN) nucleation upon substrate, the discoid defects and cracks on the surface were suppressed. Furthermore, compared with the GaN epitaxial layer grown without nitridation, the one with a 30 sec. nitridation layer showed a twice brighter integrated photoluminescence (PL) spectra intensity and a (0 0 2) High-resolution X-ray diffraction (HRXRD) curve width of 13.6 arcminute. The crystalline quality of GaN epitaxial layer became worse when the nitridation time exceeded a critical value, and even more cracks appeared on the surface although no discoid defect appeared anymore.

Determination of indium and nitrogen contents of InGaAsN quantum wells by HRXRD study supported by BAC calculation of the measured energy gap

Determination of indium and nitrogen content in InGaAsN quantum wells (QWs) is often based on the analysis of high-resolution X-ray diffraction (HRXRD) measurements. The comparison of diffraction curves of two similar samples, with and without nitrogen, together with an assumption of constant indium incorporation efficiency during the growth of layers with and without nitrogen, may lead to a large deviation in the determined In and N content. The HRXRD curve simulations supported by bandgap determination and calculations seem to be a solution of this problem. Comparison of the results achieved from simulated HRXRD curves with the calculations of all QWs transitions measured by contactless electro-reflectance (CER) can lead to reduction of deviations in composition determination of InGaAsN quantum wells. The proposed algorithm was applied for investigation of InGaAsN QWs grown by atmospheric pressure metalorganic vapor phase epitaxy (APMOVPE).

Studies on vibrational, thermal, optical, dielectric and mechanical properties of a molecular salt: 2-Methylimidazolium hydrogen succinate

Good quality single crystal of 2-methylimidazolium hydrogen succinate (2MISA) was grown by slow evaporation solution growth method. The grown crystal was investigated using various characterization techniques to study its properties. Single crystal of 2MISA was confirmed by single crystal XRD. The high resolution X-ray diffraction curve shows the structural perfection of the grown crystal. Factor group analysis predicts 153 possible modes of vibrations. IR and Raman measurements confirm the functional groups present in the title crystal. From the UV–vis spectrum the optical bandgap and refractive index were evaluated. The PL spectrum of the title compound shows green emission. Dielectric tensorial behavior of the grown single crystal was studied with varying frequencies. The thermal stability of 2MISA was analyzed using TGA/DTA measurements, which infer the thermally stability. Mechanical stability of the grown crystal was studied by Vickers hardness tester.

Evaluation of critical thickness of GaP0.98N0.02 layer on GaP substrate by synchrotron X-ray diffraction topography

GaP0.98N0.02 layers having a thickness from 75nm to 600nm are grown on GaP substrates by metalorganic vapor phase epitaxy. Back-reflection X-ray topographs made with a synchrotron radiation of the thick GaP0.98N0.02 layers reveal images of misfit dislocations. The critical thickness of the grown GaP0.98N0.02 layer on GaP substrate is evaluated from the topographs to be about 200nm. The strain relaxation is also observed from high resolution X-ray diffraction curves. X-ray diffraction curves and atomic force microscopy studies indicate that the GaP0.98N0.02 layers with thickness smaller than 200nm possess a very good crystal quality, an atomically smooth surface with a roughness less than 0.3nm and a well-defined interface without misfit dislocations between the layer and the substrate.

High-quality Ge1-xSnx alloys grown on Ge(001) substrates by molecular beam epitaxy

As a new group-IV semiconductor alloy, Ge1-xSnx is a very promising material for applications in photonic and microelectronic devices. In this work, high-quality germanium-tin (Ge1-xSnx) alloys are grown on Ge(001) substrates by molecular beam epitaxy, with x=1.5%, 2.4%, 2.8%, 5.3%, and 14%. The Ge1-xSnx alloys are characterized by high resolution X-ray diffraction (HR-XRD), Rutherford backscattering spectra (RBS), and transmission electron micrograph (TEM). For the samples with Sn composition x 5.3%, the Ge1-xSnx alloys each exhibit a very high crystalline quality. The ratio of channel yield to random yield (min) in the RBS spectrum is only about 5%, and the full width at half maximum (FWHM) of the Ge1-xSnx peak in HR-XRD curve is 100''. For the sample with x=14%, the crystalline quality of the alloy is degraded and FWHM is 264.6''.

Investigations on growth and crystalline perfection of an organic Schiff base material: 4-Chloro-4′bromobenzylidene aniline

Single crystal of an organic material, 4-chloro-4′bromobenzylidene aniline (CBBA), was synthesized and grown by slow evaporation method at room temperature. 1H and 13C NMR spectra were recorded to elucidate the molecular structure and functional groups of CBBA were identified using FTIR and FT Raman spectral analyses. The lattice parameters were calculated from single crystal X-ray diffraction data. Single and reasonably sharp peak observed in the high resolution X-ray diffraction curve indicates that the quality of the crystal is good. Thermal properties of CBBA were carried out using thermogravimetric, differential thermal and differential scanning calorimetric analyses and the melting point of the CBBA material is ∼123°C. The dielectric properties of CBBA crystal was studied as the function of frequency (100Hz–500kHz). The optical properties were ascertained by recording UV–vis–NIR and fluorescence spectrum. Further the mechanical properties were studied using Vickers microhardness test.

Crystal growth, structural and photoluminescence studies of L-tyrosine hydrobromide semi organic single crystal

Nearly perfect single crystal of L-tyrosine hydrobromide (LTHB) has been grown at room temperature from the saturated solution prepared from the solvent with optimised normality (2N) using slow evaporation solution growth technique. Crystal system and lattice parameters have been estimated by single crystal X-ray diffraction analysis. Prominent peeks of powder X-ray diffraction pattern have been indexed and diffraction data have been presented. The presence of various functional groups in LTHB has been identified by vibrational and Nuclear Magnetic Resonance spectral study. The crystalline nature and defect during the growth has been studied by obtaining high resolution X-ray diffraction curve (rocking curve) for the title crystal and detailed explanation is given in this paper. Cyclic voltammetric behaviour and photoluminescence properties of LTHB have also been investigated.

High-Dose Phosphorus-Implanted 4H-SiC: Microwave and Conventional Post-Implantation Annealing at Temperatures ≥1700°C

Semi-insulating 4H-SiC ⟨0001⟩ wafers have been phosphorus ion implanted at 500°C to obtain phosphorus box depth profiles with dopant concentration from 5 × 1019 cm−3 to 8 × 1020 cm−3. These samples have been annealed by microwave and conventional inductively heated systems in the temperature range 1700°C to 2050°C. Resistivity, Hall electron density, and Hall mobility of the phosphorus-implanted and annealed 4H-SiC layers have been measured in the temperature range from room temperature to 450°C. The high-resolution x-ray diffraction and rocking curve of both virgin and processed 4H-SiC samples have been analyzed to obtain the sample crystal quality up to about 3 μm depth from the wafer surface. For both increasing implanted phosphorus concentration and increasing post-implantation annealing temperature the implanted material resistivity decreases to an asymptotic value of about 1.5 × 10−3 Ω cm. Increasing the implanted phosphorus concentration and post-implantation annealing temperature beyond 4 × 1020 cm−3 and 2000°C, respectively, does not bring any apparent benefit with respect to the minimum obtainable resistivity. Sheet resistance and sheet electron density increase with increasing measurement temperature. Electron density saturates at 1.5 × 1020 cm−3 for implanted phosphorus plateau values ≥4 × 1020 cm−3, irrespective of the post-implantation annealing method. Implantation produces an increase of the lattice parameter in the bulk 4H-SiC underneath the phosphorus-implanted layer. Microwave and conventional annealing produce a further increase of the lattice parameter in such a depth region and an equivalent recovered lattice in the phosphorus-implanted layers.