Double-crystal X-ray Diffractometry Research Articles

Structural properties of SI-GaAs grown in space

The structural properties of Semi-insulating gallium arsenide (SI-GaAs) crystal grown with power-travelling technique in space have been studied by double-crystal x-ray diffractometry and chemical etching. The quality of the crystal was first evaluated by x-ray rocking-curve method. The full width at half maximum of x-ray rocking curve in space-grown SI-GaAs is 9.4+/-0.08 are seconds. The average density of dislocations revealed by molten KOH is 2.0 X 10(4) cm(-2), and the highest density is 3.1 X 10(4) cm(-2). The stoichiometry in the single crystal grown in space is improved as well. Unfortunately, the rear of the ingot grown in space is polycrystalline owing to being out of control of power. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

Structural characterisation of vapour Zn-diffused waveguides in lithium niobate

All stages of vapour Zn-diffused waveguide fabrication on different cuts of lithium niobate crystals have been structurally characterised by single- and double-crystal X-ray diffractometry. Immediately after diffusion the zinc niobate (ZnNb 2O 6) phase was formed on the sample surface. After annealing, the ZnO phase appeared with the ZnNb 2O 6 on the surface of the Zn-diffused waveguides. Both these phases completely disappeared after light polishing. The lattice deformations in vapour Zn-diffused waveguides were found to differ from Zn-substituted solid solutions of lithium niobate.

Characteristics of Mg-doped GaN epilayers grown with the variation of Mg incorporation

We have studied the growth characteristics of Mg-doped GaN epilayers grown by MOCVD with the variation of Cp 2Mg flow rate. To optimize the p-type conductivity. We investigated the dependence of acceptor concentration on the dopant source (Cp 2Mg) flow rate. The van der Pauw technique, double-crystal X-ray diffractometry (DCXRD) and photoluminescence (PL) were used to characterize their crystallographic, electrical and optical properties. As the incorporation of Mg in GaN epitaxy increases, the surface morphology and crystallinity of the layers become rough and worse because of the increase of lattice distortion due to the large difference of the atomic size between Ga and Mg. With the increase of Mg incorporation, the resistivity of the epilayers increases abruptly without discontinuity because of the increase of much Mg–H complex not cracked. So, it is possible to know that only the partial amount of Mg–H complex in the layers are unbound by annealing at a certain condition. In spite of the continuous increase of Mg incorporation, the hole concentration of the epilayers first increases and then decreases from a certain Mg flow rate. As well as the results of hole concentration, the blue emission intensity of the layers in PL spectra at room temperature first increases and then decreases from a certain Mg flow rate. Therefore, it can be concluded that there is a limitation in Mg activation and the hole concentration decreases from this limit though the incorporation of Mg increases.

X-ray characterization of Rb exchanged KTP

The use of X-ray double crystal diffractometry for a nondestructive contactless determination of Rb concentration depth profile in Rb exchanged KTiOPO 4 crystals is demonstrated. Two types of layers, relaxed and strained, can be formed via the exchange process, depending on the experimental conditions. In the latter case, the exchanged layer was found to be totally strained as was determined from measurement of asymmetric X-ray reflections. The Rb and strain distribution profiles were calculated using the (0 0 8) symmetric reflection.

Characterization of strain relaxation in As ion implanted Si1−xGex epilayers grown by gas source molecular beam epitaxy

Strain relaxation in the As ion implanted Si0.57Ge0.43 epilayers was studied by double-crystal x-ray diffractometry and transmission electron microscopy, and was compared to that in the nonimplanted Si0.57Ge0.43 epilayers. Experimental results show that after rapid thermal annealing (RTA) the x-ray linewidth of the As+-implanted Si0.57Ge0.43 epilayers is narrower than that of the nonimplanted epilayers, and than that of the partially relaxed as-grown samples, which is due primarily to low density of misfit dislocations in the As+-implanted SiGe epilayers. RTA at higher than 950 °C results in the formation of misfit dislocations for the nonimplanted structures, and of combinations of dislocations and precipitates (tentatively identified as GeAs) for the As+-implanted epilayers. The results mean that the strain relaxation mechanism of the As+-implanted Si1−xGex epilayers may be different from that of the nonimplanted Si1−xGex epilayers.

Mechanical strain and defects in the end-of-range region in silicon implanted with and co-implanted with ions

Internal mechanical strain in (100) bulk Si implanted with 150 keV ions at a dose of and co-implanted with 65 keV ions over the dose range to has been investigated by double-crystal x-ray diffractometry. The crystal structure of the regrown implanted layers has been studied by plan view and cross-section TEM. These investigations have shown that there is a source of strain at the depth of the end-of-range damage in the implanted and annealed crystals. The addition of C atoms in this region reduces the mechanical strain and eliminates the formation of the extended defects. This effect is due to the trapping of Si interstitials by carbon atoms. It is speculated that strain compensation may also prevent the formation of extended defects in the end-of-range region.

High Resolution Determination of the Ge Depth Profile in SiGe Heterobipolar Transistor Structures by X-Ray Diffractometry

X-ray double crystal diffractometry is used to measure the rocking curve (RC) of SiGe heterobipolar transistor structures using CuKα 400 reflection. The depth profile of the Ge concentration is determined by simulation of RCs with a semi-kinematical theory and fitting the calculated RCs to the experimental one. The problem of achievable accuracy in the determination of the main structural parameters, Si cap layer thickness, total SiGe layer thickness, plateau layer thickness, and the maximum Ge content, is discussed in detail for three different samples by analyzing sets of independent simulations with slightly modified starting conditions. Using only one fitting procedure, it is possible to determine the thickness of the Si cap layer and the total thickness of the SiGe layer with an error of less than ±0.5 nm. The accuracy of the plateau thickness and of the maximum Ge content depends on the total SiGe layer thickness. Errors for the plateau layer thickness of less than ±2 nm and for the maximum Ge content of less than 0.5% are possible.

Room-temperature 2.2-μm InAs-InGaAs-InP highly strained multiquantum-well lasers grown by gas-source molecular beam epitaxy

We report the fabrication and performances of 2.2-/spl mu/m InAs-InGaAs-InP highly strained multiple-quantum-well (MQW) lasers grown by gas-source molecular beam epitaxy. The lasers operated at room temperature demonstrate a threshold current density of 900 A/cm/sup 2/ a maximum external quantum efficiency of 28%, and a maximum output power exceeding 60 mW per facet. To the best of our knowledge, this is the longest room-temperature emission wavelength reported for lasers grown on InP substrates to date. The effect of strain compensation on the quality of the InAs-In/sub x/Ga/sub 1-x/As MQW's was also studied using double crystal X-ray diffractometry and photoluminescence techniques. The experimental results reveal that there is no significant difference on the epilayer quality of the samples with strain compensation. However, the group V stable surface growth condition is indeed better than the group III stable surface growth condition on the epilayer quality.

Heteroepitaxial Growth of CdF2 Layers on CaF2/Si(111) by Molecular Beam Epitaxy

The effects of growth temperature and structural perfection of the CaF2 buffer layer on the crystallinity of CdF2 layers grown on CaF2/Si(111) substrates by molecular beam epitaxy (MBE) were investigated by double-crystal X-ray diffractometry (XRD). The crystal perfection of CdF2 layers grown on pseudomorphic CaF2 layers was considerably better than that of CdF2 layers grown on relaxed CaF2 layers. It was shown that epitaxial CdF2 films with high structural quality can be grown on the pseudomorphic CaF2 layer at growth temperatures as low as 50°C.

Determination of bulk mismatch values in transmission electron microscopy cross-sections of heterostructures by convergent-beam electron diffraction

Abstract The relaxation which occurs along the thinning direction of transmission electron microscopy (TEM) cross-sections of heterostructures is still poorly known. This has so far prevented the accurate determination of the corresponding bulk mismatch values from convergent-beam electron diffraction (CBED) patterns. In this paper it is demonstrated that, by using elasticity theory, it is possible to deduce a simple relationship for (001) heterostructures which relates the latice mismatches along the different crystallographic directions of the TEM specimen, as deduced from a single CBED pattern, to the bulk value. Both 〈001〉 and 〈110〉 orientations of the TEM cross-sections are considered. However, to obtain accurate results, the validity of the kinematical approach used to deduce mismatches from high-order Laue zone line patterns must be critically checked; it depends on the crystallographic projection, on the beam voltage and, in the case of Si1−xGex heterostructures, on the Ge concentration. It is found that the best results are obtained at 100kV, working in the 〈013〉 projection, and for Ge concentrations up to 20 at.%. The method has been applied to both uniform and graded Si1−xGe/x/Si heterostructures, as well as to a B+ -implanted, epitaxially regrown Si wafer. Good agreement is found between the CBED results and the bulk values obtained from double-crystal X-ray diffractometry.

Determination of bulk mismatch values in trasmission electron microscopy cross-sections of heteostructures by convergent-beam electron diffraction

Abstract The relaxation which occurs along the thinning direction of transmission electron microscopy (TEM) cross-sections of heterostructures is still poorly known. This has so far prevented the accurate determination of the corresponding bulk mismatch values from convergent-beam electron diffraction (CBED) patterns. In this paper it is demonstrated that, by using elasticity theory, it is possible to deduce a simple relationship for (001) heterostructures which relates the latice mismatches along the different crystallographic directions of the TEM specimen, as deduced from a single CBED pattern, to the bulk value. Both 〈001〉 and 〈110〉 orientations of the TEM cross-sections are considered. However, to obtain accurate results, the validity of the kinematical approach used to deduce mismatches from high-order Laue zone line patterns must be critically checked; it depends on the crystallographic projection, on the beam voltage and, in the case of Si1−xGex heterostructures, on the Ge concentration. It is found that the best results are obtained at 100kV, working in the 〈013〉 projection, and for Ge concentrations up to 20 at.%. The method has been applied to both uniform and graded Si1−xGe/x/Si heterostructures, as well as to a B+ -implanted, epitaxially regrown Si wafer. Good agreement is found between the CBED results and the bulk values obtained from double-crystal X-ray diffractometry.

Current status of GaN crystal growth by sublimation sandwich technique

The current status of GaN crystal growth using the Sublimation Sandwich Technique is discussed in the paper. We use modeling to analyze gas dynamics in the reactor and the supply of the main gaseous species into the growth cell under growth conditions used in experiments. Important features of growth process — non-equilibrium cracking of ammonia, partial sticking of ammonia at the growing surface and kinetic limitation of GaN thermal decomposition — are taken into account in the model. Growth is carried out on sapphire and 6H-SiC substrates in ammonia atmosphere using a Ga/GaN mixture as the group-III element source. Single crystals of GaN of size 15×15 mm and up to 0.5 mm thick are normally grown with the optimized growth rates of 0.25-0.35 mm/h. The GaN crystals are characterized by photoluminescence, by the Color Cathodoluminescence Scanning Electron Microscopy technique, by differential double-crystal and triple-crystal X-ray diffractometry, and by electron paramagnetic resonance. Mechanisms of sublimation growth of GaN and physical limitations of the growth process are discussed.

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.

Structure and properties of porous silicon obtained by photoanodization

The results of an investigation of layers of porous silicon (PS), which was obtained by electrochemical etching of p-Si under different illumination conditions — natural light, incandescent light, and light from a mercury lamp with and without a filter — are reported. The structure of the layers was studied by double-crystal x-ray diffractometry, the composition was monitored by means of the IR absorption spectra, and the radiative properties were monitored according to the photoluminescence (PL) spectra. It was established that electrochemical etching under illumination produces PS with a higher porosity and more intense PL whose maximum is shifted into the short-wavelength region. These changes are accompanied by a large disordering of the structure and an increase in the oxygen content in the layer. It is concluded that illumination accelerates the chemical interaction of PS with the electrolyte due to oxidation. High-porosity porous silicon stored in air exhibits quenching of PL. Conversely, PL is excited in layers with a lower porosity. Aging of PS is characterized by an increase in the microdeformation of the layers, a decrease in the crystallite sizes with a partial loss of coherence between the crystallites and the substrate, and an increase in the fraction of the amorphous phase.

Evolution of stress relaxation and yellow luminescence in GaN/sapphire by Si incorporation

We report a systematic study accomplished with a series of undoped and Si-doped GaN epilayers grown on sapphire (0001) with the carrier concentration of 4.0×1017−1.6×1019 cm−3 in order to investigate the evolution of stress relaxation and yellow luminescence by Si incorporation. As the Si doping becomes higher, the bound exciton peaks are gradually shifted to lower energy due to relaxation of the thermal residual stress with the linear coefficient of ΔE/Δσ∥=42 meV/GPa. The present results show that both the full width at half maximum of double-crystal x-ray diffractometry and the photoluminescence intensity ratio of the yellow luminescence to edge emission gradually increase as the Si incorporation becomes heavier. We suggest that the Si doping in GaN epilayers induces overall defects and gives rise to stress relaxation during the cool-down process, and the yellow luminescence may be originated from a complex of VGa and the Si-induced defect.

Crystal growth of CdTe alloyed with Zn, Se and S

Single crystals of CdTe-based quaternary alloys are grown by a vertical Bridgman method. The lattice constant of the quaternary ingot is proposed to match that of Cd 0.8Zn 0.2Te. To compensate the Zn segregation in CdTe, a suitable amount of Se or S was added along with Zn. We found that the compensate effect was not significant, particularly for the CdZnTeS alloy. Nevertheless, an ingot with a fairly uniform lattice constant was obtained for the CdZnTeSe alloy mainly because the effective segregation coefficient of Se was close to one. A study using double crystal X-ray diffractometry indicated that the addition of Se or S to CdZnTe would degrade the crystal quality.

Structures of an asymmetrically coupled double-well superlattice by double-crystal X-ray diffraction

An asymmetrically coupled (GaAs/AlAs/GaAs/AlAs)/GaAs (001) double-well supperlattice is studied by HRDCD (high resolution double-crystal X-ray diffractometry). The intensity of satellite peaks is modulated by wave packet of different sublayers. In the course of simulation, the satellite peaks in the vicinity of the node points of wave packet are very informative for precise determination of sublayer thickness and for improving accuracy.

Reduction of as carryover by PH3 overpressure in metalorganic vapor-phase epitaxy

InGaAs/InP superlattices were grown to analyze the As carryover at the InP-on-InGaAs interface in metalorganic vapor-phase epitaxy. The analysis through the double crystal X-ray diffractometry and the subsequent simulation revealed that a InAsP transient layer is formed at the interface due to As carryover to the InP layer. The change of PH3 flow rate during the growth interruption is found to be effective in controlling the desorption of As from the deposits on the reactor wall. It is believed that the increase of PH3 flow rate accelerates the As desorption and thus the As depletion is completed in a shorter time. In addition, the increased amount of desorbed As helps to protect the InGaAs surface during PH3 flow. The high PH3 flow and the corresponding interruption time provide nearly As-free InP-on-InGaAs interface.

Crystallinity improvement of Bi 2Sr 2CaCu 2O 8+δ single crystal by TSFZ method

High-quality Bi 2Sr 2CaCu 2O 8+δ single crystals have been grown successfully by the traveling solvent floationg zone (TSFZ) method with the necking technique. The crystallinity was characterized by a double-crystal X-ray diffractometry. The full-width at half maximum (FWHM) of the rocking curve was improved from 120 arcsec to 75 arcsec by the necking technique using a single crystal seed.

Double crystal X-Ray diffraction studies on chloride-VPE grown Ga xIn 1 − xAs layers with different Ga-TO-In ratio

In this paper we present the results of the growth of Ga xIn 1 − xAs epilayers using Ga-In alloy sources by chloride vapor phase epitaxial technique. The amount of indium incorporated in the epilayers with alloy source composition ranging from 3 to 12 atomic percentage (at%) of Ga is studied. Double crystal X-ray diffractometry (DXRD) has been used to characterize the epitaxial layers.