High-resolution Double-crystal X-ray Research Articles

Intensity Ratio of Kβ/Kα in Selected Elements from Mg to Cu, and the Chemical Effects of Cr Kα1,2 Diagram Lines and Cr Kβ/Kα Intensity Ratio in Cr Compounds

Kα,β X-ray lines from photon excitation were measured in selected elements from Mg to Cu using a high-resolution double-crystal X-ray spectrometer with a proportional counter, and the Kβ/Kα intensity ratio for each element was obtained, after correcting for self-absorption, detection efficiency, and crystal reflectance. This intensity ratio increases rapidly from Mg to Ca but, in the 3d elements region, the increase becomes slower. This is related to the intensity of the Kβ line involving valence electrons. The slow increase of this ratio in the 3d elements region is thought to be due to the correlation between 3d and 4s electrons. Moreover, the chemical shifts, FWHM, asymmetry indices, and Kβ/Kα intensity ratios of the Cr compounds, due to different valences, were also investigated using the same double-crystal X-ray spectrometer. The chemical effects were clearly observed, and the Kβ/Kα intensity ratio was found to be compound-dependent for Cr.

X-Ray Diagnostics of Microstructure Defects of Silicon Crystals Irradiated by Hydrogen Ions

Features of formation and transformation of radiation defects in near-surface layers of silicon plates that are implanted with hydrogen ions are studied. Using the method of high-resolution double-crystal X-ray diffractometry, values of the main parameters, such as mean effective thickness Leff and mean relative deformation Δa/a of a doped layer, are determined depending on the implantation dose and substrate temperature.

Рентгеновская диагностика дефектов микроструктуры кристаллов кремния, облученных ионами водорода

AbstractFeatures of formation and transformation of radiation defects in near-surface layers of silicon plates that are implanted with hydrogen ions are studied. Using the method of high-resolution double-crystal X-ray diffractometry, values of the main parameters, such as mean effective thickness L _eff and mean relative deformation Δ a / a of a doped layer, are determined depending on the implantation dose and substrate temperature.

High performance 380-nm ultraviolet light-emitting-diodes with 3% efficiency droop by using free-standing GaN substrate manufacturing from GaAs substrate

We investigated the influence of free-standing GaN (FS-GaN) substrates on the performance of ultraviolet light-emitting-diodes (UV-LEDs) grown on top by atmospheric pressure metal-organic chemical vapor deposition. High-resolution double-crystal x-ray diffraction (HRDCXD) analysis demonstrated high-order satellite peaks and clear fringes between them for UV-LEDs grown on the FS-GaN substrate, from which the interface roughness was estimated. In addition, the full width at half maximum of the HRDCXD rocking curve in the (0002) and the (101¯2) reflections were reduced to below 90 arc sec. The Raman results indicated that the GaN-based epilayer of strain free was grown. Additionally, the effect of the FS-GaN substrate on the crystal quality of the UV-LEDs was examined in detail by transmission electron microscopy (TEM). The TEM characterizations revealed no defects and V-pits were found in the scanned area. Based on the results mentioned above, the light output power of UV-LEDs on the FS-GaN substrate can be enhanced drastically by 80% and 90% at 20 and 100 mA, respectively. Furthermore, an ultralow efficiency degradation of about 3% can be obtained for the UV-LEDs on the FS-GaN substrate at a high injection current. The use of an FS-GaN substrate is suggested to be effective for improving the emission efficiency and droop of UV-LEDs grown thereon.

High Resolution Double-Crystal X-ray Diffraction Imaging for Interfacial Defect Detection in Bonded Wafers

Wafer bonding is used for the integration of heterogeneous semiconductor materials, without the constraints of lattice constant or crystal structure mismatch. The most important aspect of such bonding is the surface flatness and the absence of particles in the bonded interface. It is very important to identify these particles, which can further result in poor bonding. The most common method for identifying has been IR imaging, but it is limited to materials which are transparent in the operating region of the CCD camera. Also, the resolution of IR image is low. X-ray diffraction imaging (topography) has been identified as the most sensitive and high resolution imaging technique capable of resolving variations due to very small particles within both the bonded and the unbonded areas. It also allows for imaging of samples which are opaque to IR, like heavily doped wafers.

High Resolution Double-Crystal X-ray Diffraction Imaging for Interfacial Defect Detection in Bonded Wafers.

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Transformations of microdefect structure in silicon crystals under the influence of weak magnetic field

Quantitative characterization of complex microdefect structures in annealed silicon crystals (1150 °С, 40 h) and their transformations after exposing for one day in a weak magnetic field (1 T) has been performed by analyzing the rocking curves, which have been measured by a high-resolution double-crystal X-ray diffractometer. Based on the characterization results, which have been obtained by using the formulas of the dynamical theory of X-ray diffraction by imperfect crystals with randomly distributed microdefects of several types, the concentrations and average sizes of oxygen precipitates and dislocation loops after imposing the magnetic field and their dependences on time after its removing have been determined.

Comparative Study of GaN—Based LED Grown on Different Substrates

The InGaN/GaN multiple quantum wells (MQWs) light emitting diodes (LEDs) were grown by metalorganic chemical vapor deposition (MOCVD) on silicon and sapphire substrates, respectively. The Optical and crystal properties of InGaN/GaN MQWs LEDs were investigated by room temperature photoluminescence (PL), temperature dependent PL measurements, Raman spectra and high-resolution double crystal X-ray diffraction(DCXRD). These results indicate that the crystal quality of InGaN/GaN MQWs growth on sapphire substrate are more preferable than that of InGaN/GaN MQWs growth on silicon substrate, and the interface of MQWs growth on substrate or silicon substrate is level. The peak positions of InGaN/GaN MQWs are 2.78 eV (446nm) and 2.64 eV (468.8nm) growth on sapphire substrate and silicon substrate, respectively.

Crystalline quality improvement in silicon films on sapphire using recrystallization from the silicon-sapphire interface

The use of the process of solid-phase recrystallization reduces to a great extent the number of defects in the silicon layer. An amorphous layer was formed by implantation of silicon ions. The crystalline quality of the SOS structures has been assessed by the method of high-resolution double-crystal X-ray diffraction. Silicon layers with a thickness d = 1000-2500 A and a high crystalline quality have been obtained after implantation of 150-keV silicon ions with subsequent high-temperature annealing.

Observation of strong virtual scattering under three-beam (220, 371) X-ray diffraction in TeO2 single crystal

A strong effect of virtual scattering has been experimentally observed when studying the nearly coplanar three-beam (220, 371) X-ray diffraction in a paratellurite single crystal under high-resolution double-crystal X-ray diffraction using MoK α1 radiation. One characteristic feature of this effect is that the angular dependence of the first (strong) reflection intensity and its shape barely change in the three-beam range of parameters, whereas very strong changes are observed for the second (weak) reflection not only in the three-beam range but also far beyond it, which is related to the variation in the two-beam diffraction parameter due to virtual scattering. The changes observed are asymmetric and make it possible to determine the triplet combination of structure-factor phases.

Defect reduction of laterally regrown GaN on GaN/patterned sapphire substrates

Structural properties of GaN epilayers on wet-etched protruding and recess-patterned sapphire substrates (PSSs) have been investigated in detail using high-resolution double-crystal X-ray diffraction (DCXRD) and etch-pit density methods. The DCXRD results reveal various dislocation configurations on both types of PSSs. The etch pits of GaN on the recess PSS exhibit a regular distribution, i.e. less etch pits or threading dislocation density (TDD) onto the recess area than those onto the sapphire mesas. On the contrary, an irregular distribution is observed for the etch pits of GaN on the protruding PSS. A higher crystal quality of the GaN epilayer grown onto the recess PSS can be achieved as compared with that onto the protruding PSS. These data reflect that the GaN epilayer on the recess PSS could be a better template for the second epitaxial lateral overgrowth (ELOG) of GaN. As a result, the GaN epilayers after the ELOG process display the TDDs of around ∼10 6 cm −2.

Dynamical theoretical model of the high-resolution double-crystal x-ray diffractometry of imperfect single crystals with microdefects

The dynamical diffraction model has been developed for the quantitative description of rocking curves (RCs) measured in the Bragg diffraction geometry from single crystals containing homogeneously distributed microdefects of several types and with arbitrary sizes. The analytical expressions for coherent and diffuse RC components, which take self-consistently multiple-scattering effects into account and depend explicitly on microdefect characteristics (radius, concentration, strength, etc.), have been derived with taking into account the instrumental factors. The developed model has been applied to determine the characteristics of oxygen precipitates and dislocation loops in silicon crystals grown by Czochralsky and float-zone methods using RCs measured by the high-resolution double-crystal x-ray diffractometer. It has been shown, particularly, that completely dynamical consideration of Huang as well as Stockes-Wilson diffuse scattering (DS) in both diffuse RC component and coefficient of extinction of coherent RC component due to DS, together with taking asymmetry and thermal DS effects into account, provides the possibility to distinguish contributions into RC from defects of different types, which have equal or commensurable effective radii.

A new method to grow high quality GaN film by MOCVD

Patterned c-plane sapphire substrate is prepared by chemical etching. GaN films are grown by LP-MOCVD on surface treated sapphire substrate and common c-plane sapphire substrate. The structure and properties of the GaN films are analyzed by high-resolution double crystal X-ray diffraction(DCXRD), scanning electron microscope(SEM) and atomic force microscope(AFM).The results indicate that the quality of GaN film grown on sapphire substrate prepared by surface treatment is superior to that grown on common c-plane sapphire substrate. High-resolution double crystal X-ray diffraction shows that for the GaN grown on surface treated sapphire substrate,the (0002) and (1012) reflections have full-width at half-maximum as low as 208.80arcsec and 320.76 acrsec, respectively. The shortcomings of procedure complexity and high crystallographic tilt in conventional lateral epitaxial overgrowth are overcome by using the new method.

Effect of Si doping on the relaxation mechanism of InGaAs on GaAs

We report measurements on the initial stages of relaxation of Si-doped In0.04Ga0.96As epitaxial layers on (001) GaAs using in situ high-resolution double-crystal x-ray topography during molecular beam epitaxial growth. For Si concentrations up to 5×1018 cm−3, the critical thickness for formation of the first B(g) misfit dislocations is modeled accurately by the Matthews–Blakeslee model, extended to include a lattice friction force varying linearly with the dopant concentration. Below a Si concentration of 2×1018 cm−3, the model can be used to predict the critical thickness for generation of the orthogonal A(g) dislocation set, with the x-ray topographs showing that the B(g) misfit multiplication occurs at damaged edges of the wafer. However, above 2×1018 cm−3 Si concentration, the critical thickness for A(g) nucleation becomes almost independent of concentration and the x-ray topographs show that cross slip becomes important in the multiplication process. For most of the Si concentrations examined, the critical thickness for nucleation of the slow A(g) misfit dislocations corresponded to that of multiplication of the fast B(g) set.

Optical functions, phonon properties, and composition of InGaAsN single layers derived from far- and near-infrared spectroscopic ellipsometry

We study the optical properties of compressively strained InxGa1−xAs1−yNy (x<0.13, y<0.03) single layers for photon energies from 0.75 to 1.3 eV (near infrared), and for wave numbers from 100 to 600 cm−1 (far infrared) using spectroscopic ellipsometry. The intentionally undoped InGaAsN layers were grown pseudomorphically on top of undoped GaAs buffer layers deposited on Te-doped (001) GaAs substrates by metalorganic vapor-phase epitaxy. We provide parametric model functions for the dielectric function spectra of InGaAsN for both spectral ranges studied here. The InGaAsN layers show a two-mode phonon behavior in the spectral range from 100 to 600 cm−1. We detect the transverse GaAs- and GaN-sublattice phonon modes at wave numbers of about 267 and 470 cm−1, respectively. The polar strength f of the GaN sublattice resonance changes with nitrogen composition y and with the biaxial strain εxx resulting from the lattice mismatch between InGaAsN and GaAs. This effect is used to derive the nitrogen and indium content of the InGaAsN layers combining the observed f dependence with results from high-resolution double-crystal x-ray diffractometry and using Vegard’s law for the lattice constants and the elastic coefficients C11 and C12. The calculated nitrogen concentrations reflect growth properties such as increasing N incorporation in InGaAsN with decreasing growth temperature, with increasing concentration of nitrogen in the gas phase, and with decreasing indium concentration in InGaAsN.

Investigation of weak damage in Al 0.25Ga 0.75As/GaAs by using RBS/C and Raman spectroscopy

The weak damage induced by 0.8 MeV Si ion implantation in the Al 0.25Ga 0.75As films epitaxially grown on GaAs substrates was studied by using Rutherford backscattering spectrometry/channeling (RBS/C) and Raman spectroscopy. RBS/C spectra measured from the implanted samples showed rather low damage level induced by the ion implantation with ion dose from 1×10 14 to 5×10 15 cm −2. The Raman spectra were measured on these samples. Two kinds of phonon modes, GaAs-like and AlAs-like, are observed, which indicate the existence of multiple phonon vibrational modes in the epitaxial Al 0.25Ga 0.75As films on the GaAs substrate. Compared with the unimplanted sample, the Raman photon peaks for the implanted sample shift gradually to lower energy with the increase of the implantation dose. The strains induced in the implanted layer were also evaluated from the Raman spectra. The result from high resolution double crystal X-ray diffractometry (HRXRD) also verified the evolution of the strains in the implanted layers.

Dependence of the critical thickness on Si doping of InGaAs on GaAs

The formation of misfit dislocations during the initial stages of relaxation of In0.04Ga0.96As epitaxial layers on (001) GaAs has been studied by in situ high-resolution double crystal x-ray topography during molecular beam epitaxy growth. Relaxation is initially anisotropic with the fast B(g) dislocations being nucleated before the slow A(g) set. On doping with Si up to a maximum concentration of 4×1018 atoms/cm3, an increase in critical thickness was observed for both dislocation sets. The data can be fitted to an extension of the Matthews–Blakeslee model that includes a lattice friction force varying linearly with the dopant concentration.

Investigation into the Role of Low-Temperature GaN in n-GaN/InGaN/p-GaN Double-Heterostructure Light-Emitting Diodes

The role of two-step low-temperature GaN (LT-GaN) layers was investigated by cathodoluminescence, high resolution double crystal X-ray diffraction, transmission electron microscopy, atomic force microscopy, and current-voltage measurements. It was shown that the introduction of the LT-GaN layer prevents In from evaporating from InGaN during the high-temperature growth of p-GaN. The trasmission electron microscopic (TEM) results showed that the LT-GaN hampers dislocation propagation from the InGaN active layer into the p-GaN, leading to reduction in the dislocation density in the p-GaN. The use of the two-step LT-GaN resulted in an increase in the output power of light-emitting diodes and a decrease in the operating forward voltage.

X-ray scattering study of quantum wires and lateral periodic heterostructures

In this work, the application of advanced X-ray scattering methods to the study of mesoscopic and low-dimensional heterostructures is briefly reviewed. Semiconductor quantum wire arrays, periodically corrugated surfaces (surface gratings) and quantum dots are investigated by high-resolution double-crystal X-ray diffraction and high- and low-angle reciprocal space mapping. It is shown that high-resolution X-ray experiments can provide useful and accurate information on the geometrical parameters and structural properties of low-dimensional semiconductor heterostructures.

The effect of post-growth cooling rate on the defect structure in MBE-grown buried layers of Si1−xGex on Si substrates

The effect of cooling rate on the defect structure in Si1−xGex layers grown on Si (100) substrates has been studied. SiGe layers 200 nm thick, with germanium fractions between 0.09 and 0.14 and capped with a 50-nm layer of Si, were grown by molecular beam epitaxy at temperatures of 550, 710, and 800°C. The defect structure in the layers was studied by means of high resolution double crystal X-ray diffractometry and transmission electron microscopy for two different modes of cool-down. In the ‘fast’ mode, the heat source was turned off abruptly, while in the ‘siew’ mode the power was lowered in small steps equal to about 2% of the initial power. The system was then allowed to reach equilibrium before the power was lowered again. X-ray rocking curves showed significant broadening after rapid cool-down from higher temperatures, whereas the corresponding strains decreased only slightly and independently of the rate of cool-down. In order to explain these results, a model is proposed in which the buried layer is distorted into small, slightly misoriented regions by rapid cooling. Thus, the original strain remains unchanged within the small regions and the X-ray profile is broadened primarily by crystalline distortion and without a significant contribution from dislocations. The distortion can lead to fracture for rapid cool-down from sufficiently high temperatures, e.g., 800°C. The model is consistent with both transmission electron microscopy and calculations of stress due to non-uniform cooling.