The width and integrated intensity of the 220 X-ray double-diffraction profile and the shift of the Bragg condition due to refraction have been measured in a channel-cut Ge crystal in an angular range near the critical angle of total external reflection. The Bragg angle and incidence condition were varied by changing the X-ray energy. In agreement with the extended dynamical theory of X-ray diffraction, the integrated intensity of the double diffraction remained almost constant, even for the grazing-incidence condition very close to the critical angle for total external reflection. A broadening of the diffraction profile not predicted by the extended theory of X-ray diffraction was observed when the Bragg condition was at angles of incidence lower than 0.6°. Plane wave topographs revealed a contrast that could be explained by a slight residual crystal surface undulation of 0.3° due to etching to remove the cutting damage and the increasing effect of refraction at glancing angles close to the critical angle. These findings confirm that highly asymmetric channel-cut Ge crystals can also work as efficient monochromators or image magnifiers at glancing angles close to the critical angle, the main limitation being the crystal surface preparation.

The influence of the substrate on composition and CuPt-type spontaneous order of MOVPE lattice matched InGaP/GaAs layers was studied. The study was carried out by microRaman and microphotoluminescence. The order was determined by the band gap, while the Raman parameters were also contributed by the surface topography that was also related to the type of substrate. The spontaneous order increases with Si- doping of the substrates. Doping the layers with Zn randomises the alloy.

The optimization of the electronic properties of InGaP/GaAs MQWs, to be inserted in multilayers heterostructure for novel photovoltaic devices, was performed by structural, optical and photoelectrical measurements. Different sequences of nominally undoped InGaP and GaAs alternated layers were grown by low-pressure metalorganic vapour phase epitaxy, employing tertiarybutylarsine and tertiarybutylphosphine as metalorganic precursors for the V-group elements. In order to minimize the As/P exchange effect, the interface In segregation, and to control the whole lattice matching, single and multi-quantum wells (MQWs) with different: (i) periods, (ii) well widths, (iii) growth temperatures, (iv) gas-switching sequences at the interfaces and (v) indium concentrations in the InGaP alloy, were prepared and investigated. The interface sharpness and the compositional fluctuation of thick MQW region containing up to 40 well-barrier sequences were investigated for the modelling, realization and evaluation of test structures based on low-dimensional systems for third generation solar cells.

The chemically sensitive (200) diffraction in the dark field (DF) mode of transmission electron microscopy has been used to detect, identify, and evaluate the composition of the parasitic interlayer at the GaAs-on-InGaP interface in metallorganic vapor-phase epitaxy (MOVPE) In(x)Ga(1-x)P/GaAs heterostructures. The latter were grown at 600 degrees C with no growth interruption. The composition range determined by (200) DF was further refined by using the X-ray diffraction result that the interlayer has a negative lattice mismatch to GaAs. The parasitic interlayer can be either GaAs(0.45)P(0.55) or In(x)Ga(1-x)As(1-y)P(y) with 0 <= x < 0.069 and 0.55 <= y < 0.707. P/As intermixing and In segregation are assumed to drive the formation of the interlayer. The low In content in the quaternary is ascribed to the reduced In segregation at 600 degrees C. In segregation is likely favored by the tensile strain associated with the interlayer in its process of growth.

MgS/ZnSe/GaAs multilayers with the MgS thickness ranging from 20 to 140 nm were grown at 300 degrees C by molecular-beam epitaxy on [001] GaAs substrates. The samples were studied by using several x-ray methods and transmission electron microscopy. The coexistence of metastable zinc-blende (ZB) and rocksalt MgS structural phases was evidenced and discussed. The analysis of reciprocal space maps of the x-ray intensity distribution around asymmetrical reciprocal-lattice nodes allowed us to determine the strain status of the MgS layers and to show that the ZB-MgS phase was pseudomorphic also in the case of the thickest film. The lattice parameter of the pure ZB-MgS phase ranging between 0.563 33<a(MgS)<0.563 67 nm was obtained by extrapolation from x-ray diffraction data and predicted ab initio elastic constants, taking into account that there was a Zn incorporation during the MgS growth estimated in the range 0.005 <= x(Zn)<= 0.02.

The article shows the application of (200) dark field TEM to the detection and analysis of the extra interlayer that typically forms at the GaAs-on-InGaP interface in metal organic vapour phase epitaxy (MOVPE) InGaP/GaAs heterojunctions. Calculations of the dark field (DF) contrast function in the kinematical approximation show that the interlayer can be either GaAsP or InGaAsP for some values of the composition. Comparison with high-resolution X-ray diffraction results allowed to better estimate the composition ranges of the two compounds. The possible mechanisms responsible for the formation of either GaAsP or InGaAsP are briefly discussed.

InAs/GaAs quantum dot (QD) structures were grown by molecular beam epitaxy (MBE) with InAs coverages θ continuously graded from 1.5 ML to 2.9 ML. A critical coverage of 2.23 ML is found, above which the islands undergo ripening, which causes a fraction of quantum dots to increase in size and to eventually relax through the formation of pure, edge-type misfit dislocations which propagate towards the surface in the form of V-shaped defects. Concomitant with ripening, extended-defect related traps with activation energies of 0.52 and 0.84 eV were observed, and regarded as the cause of the significant worsening of the optical and electrical properties in high coverage structures. Their relationship with the observed dislocations is discussed.

The development of high resolution X-ray measurements and imaging in real and reciprocal space is related to the improvement of the optical elements available for use. Crystal diffractive optics still give the highest resolution ill reciprocal space and in energy, and progress has also been made in improving resolution in real space. In this chapter a short introduction to the dynamical theory behind crystal diffractors and their coupling is given and modern one- and two-dimensional elements based on symmetric, asymmetric and inclined diffractions are introduced. The design, the modeling of the output parameters and the experimental results are presented for a special 2-bounce V-shaped monochromator, for a monolithic 4-bounce monochromator and for a monolithic 2D beam de/magnifier.

This paper presents a detailed study of structure, morphology, and magnetic properties in FePt thin films epitaxially grown on MgO(100) at intermediate temperatures (≅380°C). It focuses on the effects obtained by in situ annealing the FePt films after deposition. We have demonstrated that the annealing allows one to complete the ordering, thus obtaining an epitaxial L10-FePt film with large perpendicular anisotropy (up to 3×107erg∕cm3) and high perpendicular squareness and remanence ratio (both higher than 0.85). At the same time, we have found a peculiar morphology evolution by increasing the annealing time: the interconnected mazelike grains evolve towards interconnected dotlike grains of reduced size (down to 10nm). Due to the interconnection at the grains basis, the increase in the film perpendicular coercivity with the annealing process is moderate (up to 4.1kOe), leading to an increasing anisotropy/coercivity ratio with the annealing time. As a further step towards the understanding of the properties evolution with annealing, we have investigated the magnetic domain pattern and analyzed the domain-period dependence on the anisotropy constant in comparison with the behavior expected by the Kooy–Enz theory [C. Kooy and U. Enz, Philips Res. Rep. 15, 7 (1960)]. The main magnetic properties and reduced grain size obtained after the in situ annealing are promising to realize perpendicular recording media with reduced bit size, high thermal stability, and suitable switching field.

An evaluation of the composition of the extra interlayer at the GaAs-on-InGaP inverted interface in MOVPE grown In(x)Ga(1-x)P/ GaAs heterostructures has been carried out by chemically sensitive (200) dark field TEM in the kinematical approximation. X-ray diffraction measurements have also been performed that showed that the extra interlayer had a negative strain to GaAs. in combination with this result the (200) dark field measurements allowed to establish that the extra interlayer can be either GaAs(1-y)P(y) (y = 0.55) or In(x)Ga(1-x)As(1-y)P(y) with 0 < x < 0.069 and 0.55 < y < 0.707. P/As intermixing is suggested to be the basic mechanism for the formation of either one of these two alloys. The formation of an interlayer of the quaternary compound additionally requires that In carry-over also occurs. (C) 2008 Elsevier Ltd. All rights reserved.

The presence of interlayers at the inverted GaAs-on-InGaP interfaces in MOVPE grown InxGa1-xP/GaAs heterojunctions has been evidenced by (200) dark field (DF) transmission electron microscopy and high resolution X-ray diffraction. A relatively large negative strain is associated with the interlayers. Analysis of the kinematical DF contrast has allowed to establish which kind of InxGa1-xAs1-yPy compound the interlayer can be made of and the possible ranges for the compositions x and y. The localization of the interlayer at the bottom of the GaAs layer and inside it would suggest that its formation can be due to the incorporation into GaAs of P atoms remained in the reactor after PH3 was switched off and In carry-over. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The diffusion phenomena at interfaces between GaAs/InGaP layers grown by low pressure MOVPE have been studied by dark field (DF) transmission Electron Microscopy (TEM) and High resolution X‐ray Diffractometry (HRXRD). By comparing the results of the two techniques a mismatched layer containing P or P and In has been evidenced. The causes of this behavior are briefly discussed.

We report a detailed study of InAs∕GaAs quantum dot (QD) structures grown by molecular beam epitaxy with InAs coverages θ continuously graded from 1.5 to 2.9 ML. The effect of coverage on the properties of QD structures was investigated by combining atomic force microscopy, transmission electron microscopy, x-ray diffraction, photoluminescence, capacitance-voltage, and deep level transient spectroscopy. In the 1.5–2.9 ML range small-sized coherent QDs are formed with diameters and densities that increase up to 15nm and 2×1011cm−2, respectively. For θ>2.4 ML large-sized QDs with diameters of 25nm and densities ranging from 2×108to1.5×109cm−2 coexist with small-sized QDs. We explain the occurrence of large-sized QDs as the inevitable consequence of ripening, as predicted for highly lattice-mismatched systems under thermodynamic equilibrium conditions, when the coverage of the epitaxial layer exceeds a critical value. The fraction of ripened islands which plastically relax increases with θ, leading to the formation of V-shaped defects at the interface between QDs and upper confining layers that propagate toward the surface. Island relaxation substantially affects the properties of QD structures: (i) free carrier concentration is reduced near the QD plane, (ii) the QD photoluminescence intensity is significantly quenched, and (iii) deep levels show up with typical features related to extended structural defects.

This work deals with the strain relaxation mechanism in InGaAs metamorphic buffers (MBs) grown on GaAs substrates and overgrown by InAs quantum dots (QD). The residual strain is measured by using Raman scattering and X-ray diffraction, both in Reciprocal Space Map and in single ω-2θ scan modes (ω and θ being the incidence angles on the sample surface and on the scattering planes, respectively). By relating the GaAs-like longitudinal optical phonon frequency ωLO of InGaAs MBs to the in-plane residual strain ε measured by means of photoreflectance (PR), the linear ε-vs.-ωLO working curve is obtained. The results of Raman and XRD measurements, as well as those obtained by PR, are in a very satisfactory agreement. The respective advantages of the techniques are discussed. The measurements confirm that strain relaxation depends on the thickness t of the buffer layer following a ~t-1/2 power law, that can be explained by an energy-balance model.

The stable crystal structure of magnesium sulfide (MgS) is rocksalt. However, the metastable zinc-blende structure is obtained when MgS is deposited by molecular beam epitaxy (MBE) on (001) zinc-blende substrates with a relatively small misfit. In the present work, the zinc blende to rocksalt phase transition is analyzed in MgS∕ZnSe∕GaAs multilayer samples grown by MBE with different MgS layer thicknesses. By x-ray diffraction and transmission electron microscopy methods, a partial nucleation of MgS rocksalt is evidenced and correlated to the presence of stacking faults at the bottom interface. The unexpected coexistence of both rocksalt and zinc-blende MgS structural phases is discussed.

Si wafers implanted at 80keV with different As doses, and next annealed at different temperatures for different times, were studied by means of x-ray triple crystal diffraction, x-ray standing wave, transmission electron microscopy, spreading resistance profile, and electrochemical C-V profiling methods. The implantation processes produced heavily damaged subsurface regions hundreds of nanometers deep. By fitting both the x-ray diffraction curves and the x-ray standing wave photoelectron emission profiles, it was possible to determine the most appropriate strain and atomic static displacement behavior versus depth within the disturbed region of the crystal. The results obtained by x-ray diffraction measurements were confirmed by transmission electron microscopy investigations. Therefore, making use of different structural and electrical characterization techniques it was possible to find: (i) the depth of amorphization of the implanted regions, (ii) the appearance of extended defects (dislocation loops band) during the restoration of the lattice by the annealing processes and the dependence of their size and density on the implant dose and the annealing time and temperature, (iii) the dopant profiles versus depth as a function of the implant dose and the annealing parameters, (iv) the effect on the total strain of the doping induced variation of the conduction band minima. The experimental evidence of a screen electronic effect on the As+–Si distance in the restored crystal lattice was confirmed by ab initio calculations.

Lattice-matched, single and multiple InGaP/GaAs/InGaP quantum wells (QWs) were grown at 600 degreesC by low-pressure metalorganic vapour phase epitaxy (LP-MOVPE), with the use of the tertiarybuthylarsine (TBAs) and tertiarybuthylphosphine (TBP) group-V sources. In order to enhance the interface abruptness, different gas switching sequences were exploited during the growth of the interface, and the best results were obtained by inserting a few monolayer-thick GaAsP interlayers (IL), at the direct GaAs-on-InGaP interface. Low-temperature photoluminescence (PL), high resolution X-ray diffraction, transmission electron microscopy and photoreflectance spectroscopy analysis were performed on the grown heterostructures, to correlate the adopted growth sequence with the interface properties and the QW optical transitions.Promising results were obtained, among which: (a) the suppression of the anomalous PL emission at low energy, (b) optical emission from the InGaP/GaAs/InGaP QWs, exhibiting a good correlation with theoretical expectations, (c) direct interface fluctuations within 1 nm. (C) 2003 Elsevier B.V. All rights reserved.

Si wafers implanted at 5, 15, and 50 keV with different BF2+ doses and next annealed at 945 °C for 45 s, were studied by means of x-ray triple crystal diffraction, x-ray standing wave, and transmission electron microscopy methods. Due to the implantation energies used, very narrow subsurface regions with a depth ranging from a few tens of nanometers to a few nanometers were damaged. By fitting the diffraction curves and using the information obtained from the photoelectrons emitted by the x-ray standing wave field, it was possible to determine the most appropriate strain and damage profiles versus depth within the disturbed region of the crystal. The above results made it possible to find: (i) the distribution of interstitial ions produced during the implant processes; (ii) the depth of amorphization of the implanted regions at the highest doses; and (iii) the appearance of extended defects (dislocation loops band) at the amorphous/crystal interface during the restoration of the lattice by the annealing process. Transmission electron microscopy investigations and electrochemical capacitance–voltage profiling measurements were made on several annealed samples and the results obtained by the x-ray diffraction and standing wave methods were confirmed.

Lattice matched InGaP alloys grown by Low Pressure Metal Organic Vapor Phase Epitaxy were studied by Atomic Force Microscopy, X-ray diffraction, microRaman spectroscopy and Photoluminescence mapping. The study is devoted to the analysis of both the composition fluctuations and spontaneous CuPt-type order. N-type (Si-doped) and semi-insulating substrates were used. Order seems to occur in a higher amount in layers grown on Si-doped substrates; the morphology and the properties of the layers are shown to depend on the type of substrate. The Raman study of the layers allows to establish the influence of CuPt-type order on the Raman spectrum of lattice matched InGaP. The relation between the Raman parameters and the spontaneous CuPt-type order is discussed.

B+ ions were implanted in Si at ultra-low energies: 0.25, 0.5 and 1 keV, respectively, and at different doses: 1 x 10(14), 1 x 10(15) cm(-2). Lattice distortion and disorder due to the implantation process were investigated by means of a high resolution X-ray diffraction method. Due to the very low implantation depth (a few nm), the X-ray diffraction measurements were carried out by triple-crystal diffractometry. With this experimental configuration it was possible to separate coherent from diffuse scattering, considerably improving the signal-to-noise ratio. For the analysis of the experimental curves, the subsurface region was divided in several thin layers. The layer thickness, the static Debye-Waller factor, which is related to the lattice damage, and the lattice spacing modification (strain) were the parameters of the fitting procedure. Despite the small thickness of the 'subsurface-damaged area', it was possible to obtain the main parameters describing the depth distribution of the lattice distortions in the analyzed crystals. Transmission electron microscopy investigations were made on two samples implanted at the lowest energies and the results obtained by the X-ray diffraction were confirmed. (C) 2002 Elsevier Science B.V. All rights reserved.