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We have used an experimental strategy that, combining nuclear reaction analysis and Rutherford backscattering spectrometry both in random and channeling geometry, allowed an accurate quantification of the total amount of N in InxGa1−xNyAs1−y/GaAs and GaNyAs1−y/GaAs epitaxial systems (0.038

A new phenomenon of strain relaxation will be presented. In a series of In x Ga 1− x As graded composition buffer layers grown on well cut (001) GaAs substrates, a curvature of the epilayer lattice has been found, i.e. a tilt of the epilayer lattice orientation with respect to the substrate which varies coherently along the sample surface on the scale of several mm. The most recent data analysis performed on a buffer layer compositionally graded with a six-step profile shows also a thickness functional dependence of the curvature. The epilayer lattice curvature has been attributed to a coherent lateral distribution of the Burgers’ vectors. An analytical model has been developed in the framework of the continuum elasticity theory to compute the related strain field. The results show small but unexpected contributions to the parallel strain.

A combined method for structural characterization of strained epitaxial heterostructures involving different techniques such as Rutherford backscattering spectrometry (RBS), multiple crystal X-ray diffractometry (MCD) and transmission electron microscopy (TEM) is presented. In order to obtain a complete characterization of the analysed structure, three different quantities are measured independently: the epilayer thickness, the density of misfit dislocations which may appear at the interface, and the significant components of the strain tensor, mainly the tetragonal distortion, affecting the epilayer lattice. In this way the thermodynamic state and the mechanisms of plastic deformation of the structures can be fully investigated. In this contribution we present and discuss the experimental results concerning a set of InP/GaAs samples having different layer thicknesses ranging from 5 to 500 nm. The thickness of the samples has been determined by RBS. Measurements of in-plane strain and tetragonal distortion have been performed by MCD and RBS-channelling respectively, finally TEM has been used for determining the defects densities and distribution.

The structural characterization of ZnS epilayers grown on (100) GaAs by H 2 transport vapour-phase epitaxy is reported. High-resolution X-ray diffraction and ion channelling Rutherford backscattering spectrometric measurements were used to evaluate the overall crystalline perfection of the epilayers and the distortion and reciprocal orientation of the ZnS and GaAs lattices and to measure the epilayer built-in lattice strain. High crystalline quality can be achieved at the surface of relatively thick (above ca. 1 μm) ZnS layers, although a dense distribution of extended defects was observed close to the ZnS/GaAs interface. It turns out that the ZnS unit cell is orthorombically distorted, although its deviation from a purely tetragonal distortion is very small. Systematic measurements of the ZnS lattice strain were performed on the epilayers and the results were compared with the thermal strain value obtained by temperature-dependent X-ray diffraction measurements. The data indicate that the ZnS built-in lattice strain can be entirely ascribed to a thickness-dependent thermal strain contribution, the initial lattice misfit at the growth temperature being almost totally relaxed even for relatively thin epilayers. Finally, no appreciable strain was found for epilayer thicknesses above about 3 μm.

We report on the structural characterization by ion channelling Rutherford backscattering spectrometry (RBS) of thin (less than 3 μm) CdS epitaxial layers grown on {111}A-oriented CdTe substrates by chemical vapour deposition. The overall crystalline quality of the present epilayers has been studied as a function of their thickness. Also, the occurrence of single crystal growth vs. highly textured polycrystalline growth has been checked by studying channelling angular dips at different 4 He + beam energies. The CdS epilayers turned out to be essentially single crystalline, although the present RBS measurements show that extended defects are contained in the layers and at the CdS/CdTe interfaces. The dechannelling beam energy dependence allows us to identify these defects as stacking faults, whose concentration profile in the epilayers is reported.

This work reports on the use of the dechanneling technique for the determination of the misfit dislocation distribution at the interface between mismatched III–V semiconductor heterostructures grown on (001) substrates. In this case the dislocations are oriented along the [110] and [110] and the depth distribution is nearly planar and close to the chemical interface. The displacement field caused by one misfit dislocation is calculated in the frame of the linear elasticity theory. An analytical treatment of the dechanneling cross section dependence on both the dislocation line and Burgers vector orientation and on the beam direction in the channeling plane is performed within the Quere model. It is shown that (110) planar channeling is most sensitive to the dislocation orientation. Experimental data concerning a set of In x Ga 1− x As/GaAs single layer samples are presented and analyzed. The two {110} planes perpendicular to the interface show distinct dechanneling probabilities. In the light of the dechanneling cross section properties this fact reflects the difference between the dislocation densities in the two directions. The obtained dislocation densities are in agreement with those derived indirectly from strain measurements. It is shown that the sensitivity of the dechanneling technique is of the order of 10 4 dislocation lines cm −1 .

In this work the silicon self-interstitial (I) diffusion in trap-containing molecular beam epitaxy Si layers is investigated. The I’s are produced by Si ion implantation, and the I supersaturation is reported as a function of the depth and the annealing time. These data are discussed on the basis of two alternative models proposed in literature (“effective diffusivity” model and “filling trap” model). This analysis demonstrates that the second model is more appropriate to describe the proposed phenomenology, since it explains both the increase of the I penetration depth as a function of the implant dose and the very rapid change of the supersaturation versus time. Moreover, the proposed model takes account for the I recombination at the surface.

In this work, we have investigated the strain induced in a Si crystal by Boron-interstitial clusters (BICs). BICs were formed by Si implantation and subsequent annealing of two Si samples, grown by molecular beam epitaxy (MBE), containing thin buried layers doped with different B concentrations (10 19 and 10 20 at./cm 3 ). By B chemical profile diffusion analysis the doses of Si self-interstitials (Is) and Boron atoms trapped in the BICs were extracted. The B/I stoichiometric ratio is about 1 for the low B concentration and about 3.5 for the high B concentration sample. High-resolution X-ray diffraction (HRXRD) analyses provided a measure of the strain profile. While in the low B concentration sample, no appreciable strain was detected after BICs formation, at the higher B concentration, we found that the tensile strain present in the as-grown B doped layer changes to a strong compressive strain as a consequence of BIC formation. For this kind of clusters, the mean volume expansion with respect to the Si matrix is 29 ± 6 A 3 for each B atom trapped in the BICs.

In this work, we have investigated the stoichiometry of boron-interstitial clusters (BICs) produced in a molecular-beam-epitaxy-grown B box by Si implantation and annealing, and their dissolution during further prolonged annealing cycles. Low-concentration B delta doping was used to quantitatively monitor the interstitial (I) flux. A stoichiometric ratio of about 1.2 between I and B was found for the BICs formed at 815 °C. The BIC dissolution kinetics was investigated by analyzing the concentration profiles at different times and temperatures (in the range 815–950 °C) with a simulation code able to deconvolve the processes of B diffusion and B release from clusters. We found that the main mechanism for cluster dissolution is the release of interstitial boron atoms, with a thermal activation energy of 3.2±0.4 eV. These data are discussed and compared with existing literature data.

We report on the direct measurements of surface lattice strain in ZnTe epitaxial layers on {100}GaAs substrates by ion channeling Rutherford backscattering spectrometry and low-temperature (10 K) reflectance spectroscopy measurements. The measured ZnTe strain is the superposition of the expected thermal (tensile) strain and a thickness-dependent residual compressive strain. Our data indicate that the removal of this residual strain is slower than the rate predicted by the equilibrium theory, following an apparent h^(-1/2) power-law dependence on the epilayer thickness h, above approximately 100 nm.

In this work we investigated the diffusion and clustering of supersaturated substitutional carbon 200nm thick SiGeC layers buried under a silicon cap layer of 40nm. The samples were annealed in inert (N2) or oxidizing (O2) ambient at 850°C for times ranging from 2 to 10 hours. The silicon self-interstitial (I) flux coming from the surface under oxidation enhances the C diffusion with respect to the N2 annealed samples. In the early stages of the oxidation process, carbon escape by diffusion across the layer/cap interface dominates. This phenomenon saturates after an initial period (2-4h) which depends on the C concentration. This saturation is due to the formation and growth of C containing precipitates which are promoted by the I injection and act as a sink for mobile C atoms. The competition between clustering and diffusion is discussed for two different C concentrations.

Ion channeling analysis and x-ray diffraction reciprocal space maps have been performed on InxGa1−xAs buffer layers grown with different composition profiles on well-cut (001) GaAs substrates. On all of the samples analyzed we detect a curvature of the layer lattice, i.e., a tilt of the lattice with respect to the substrate which varies coherently along the sample surface. The layer tilt is directed inward defining a curvature that is concave, large (up to 2.5° cm−1) and that decreases when approaching the substrate. We describe this new phenomenon in terms of a coherent lateral distribution of the orientations of the misfit dislocation Burgers’ vectors.

It is well-known that in the case of high lattice mismatch the growth of semiconductor structures proceeds via island formation. The growth and characterization of the so obtained nanostructures has attracted increasing interest in the last few years due to their fascinating potential applications in integrated microelectronics. Apart from optical and electrical characterization, the structural analysis of these structures is usually performed by Scanning Electron Microscopy, Transmission Electron Microscopy or Atomic Force Microscopy. However, none of these techniques is suitable to exactly measure the total amount of deposited materials which is, together with the statistical distribution of the dimensions of the nanostructures, the most important information to be obtained. We have developed a new experimental set up for RBS analysis which, in connection with a computer simulation code, improves the thickness resolution of the technique of nearly one order of magnitude. With this experimental arrangement InAs/GaAs, InP/GaAs and InGaAs/GaAs nanostructures, nominally few monolayers (ML) thick can be analyzed by obtaining the total amount of deposited material, the fraction of the surface covered by the nanostructures and their maximum thickness.

Titanium nitride films were produced on silicon substrate by ion beam assisted deposition in the alternate mode: first, thin titanium layers were deposited by electron beam evaporation and then titanium nitride was formed by nitrogen implantation at room temperature; this cycle was then iterated many times in order to obtain thicker titanium nitride layers. The obtained films were characterized with respect to atomic composition by Rutherford backscattering spectrometry and nuclear reaction analysis techniques, while chemical bonding was investigated by Auger line-shape analysis. We observe that nitrogen implantation, along with the production of titanium nitride, induces silicon migration into the film. Silicon transport is connected to point defects produced by ion implantation as well as by chemical driving forces associated with silicides formation.

This work reports on the use of the dechanneling technique for the determination of the misfit dislocation distribution at the interface between mismatched III–V semiconductor heterostructures grown on (001) substrates. Planar channeling is employed because of the higher sensitivity with respect to the axial case. For low misfit heterostructures, dislocations are oriented along the [110] and [110] and the depth distribution is nearly planar and close to the chemical interface. We show that, for this kind of structure, dechanneling measurements allow one to determine the dislocation densities along the two quoted directions. This is done by using a fitting procedure based on a numerical simulation program of the RBS-channeling spectra. As a result of this procedure, an estimation of the dislocation distribution thickness can also be obtained, besides the ratio of the energy loss under channeling conditions to that under non-channeling conditions. Experimental data concerning a set of InxGa1−xAs/GaAs single layer samples having different thicknesses and indium concentrations are presented and discussed in the framework of this model. The dechanneling probability due to the misfit dislocations is obtained from the RBS-channeling spectra at several beam energies for all the samples. In some cases we note two distinct dechanneling probabilities for the two {110} channeling planes perpendicular to the interface. In light of the dechanneling cross section properties, this fact reflects the difference between the dislocation densities in the two directions.

The thermal oxidation of polycrystalline zirconium implanted with 21 different ion species has been studied by using the nuclear reaction 16 O( d , p 1 ) 17 O. A very good agreement has been found between the oxidation kinetics of unimplanted zirconium as determined by the nuclear reaction and those previously measured gravimetrically. Oxidation kinetics show a time dependence which is cubic or parabolic depending upon the surface treatment before oxidation. Ion implantation produces significant changes in oxidation rate but the time dependence remains the same. A strong correlation has been found between the behaviour of ion implanted systems and that reported for binary alloys, confirming the hypothesis that the ionic size of the additive is the major parameter governing the influence upon the oxidation of zirconium. The implanted species which inhibit oxidation possess ionic radii lying between 80% and 100% of that of Zr 4+ . An explanation of their beneficial effect based on an increase of the plasticity of the growing oxide is presented.

Nous avons utilisk des techniques d'analyses nuclkaires et de spectrom6trie de masse d'ions secondaires pour Ctudier le comportement d'oxydes natifs de GaAs enrichis h 1'180 et irradids sous vide au moyen d'un laser Rubis dCclench6. Nous avons examin6 Itincorporation d'160, l'incorporation et les pertes dl180 ainsi que le ddplacement des cations As et Ga hors des sites du rCseau en fonction de la densitd d'dnergie du faisceau laser. Nos rdsultats d&montrent qu'il est nkcessaire d'irradier avec une densitd d'knergie de I'ordre de 0,8 J/cmZ, afin d'dliminer compl6tement les oxydes de surface. Toutefois, avant Climination compl&te, nous observons une dissolution partielle de ces oxydes dans le mat6riau liquide sous-jacent, ce qui a pour effet d'induire un important piCgeage d'oxygine dans les couches resolidifikes. Nous observons de plus que la surface passe de facon continue d'un dtat riche en Ga & un

Channeling experiments have been performed on [111] yttria stabilized zirconia (YSZ) single crystals with uniform Y concentration of 19 mol %. These crystals have the fluorite structure and contain 5% of oxygen vacancies. Various axial and planar, mixed (ZrO) and single crystallographic directions have been investigated. The results show a strong oxygen-oxygen vacancy interaction: the nearest neighbours of a vacancy (i.e. 6 oxygen atoms) are displaced from regular lattice sites by a distance greater than 0.5 A. The other oxygen atoms are also certainly displaced but by smaller quantities. No preferential direction could be evidenced for this displacement. A cation relaxation is not excluded by our results but its amplitude should not exceed ≅0.1 A . Some YSZ crystals were implanted with 1.2×1016 and 1.2×1017 Yb atoms/cm2 at 210 keV. The lattice parameters of YSZ and ytterbium stabilized zirconia are identical. For the low implantation dose, a full crystalline recovery is observed after a 1000°C annealing and Yb is 100% substitutional. A 1300°C annealing is required for the high implantation dose, for which the concentration ratio [Yb]/[Zr]≅1.1 in the implanted region. This region appears, after annealing, in full epitaxy with the substrate and the behaviour of Yb and Zr atoms is identical. However, the rather high minimum yields measured are indicative of strong atom relaxation.

Angular and energy distributions of protons transmitted through thin Si single crystals have been measured as a function of the impinging angle between the beam direction and the {110} planar direction. The angular distributions have been obtained by means of a mobile small-acceptance angle (∼10 −7 sr) surface barrier detector. The investigation has been performed for different crystal thicknesses (3–7 μm) and beam energies (0.5−2.5 MeV). The observed anisotropies in the angular intensity distributions have been interpreted in terms of feeding-in and blocking processes. The relative contribution from each phenomenon is determined by the target thickness t , beam energy E , and angular position ϕ of the plane with respect to the beam direction through the combination ϕE /√ t , at least in the adopted range of the experimental parameters.

The planar to axial transition for channeled 1.8 MeV He + ions has been studied. The transition between the planar mode and the axial mode appears in a very narrow angular range. The planar spectra were fitted using a stochastic model described previously. In order to check the hypothesis that the structure observed in axial spectra is of planar origin, the axial spectrum was fitted using a linear combination of the spectra obtained for the two major planes which intercept along the axis. The fit obtained is rather good and leads to the conclusion that the oscillations observed in axial spectra can be due to particles non-channeled with respect to the axis but sensitive to a planar potential and hence having quasi-periodic oscillating trajectories.

The existence of radiation-induced (or enhanced) migration of undersized impurities in a number of metal hosts is now well established. This paper reports a study of radiation-induced impurity segregation during the impurity implantation itself. P and Si impurities were implanted at room-temperature respectively into Ni and Pd films and their distribution profiles measured by 1.8 MeV- 4 He Rutherford backscattering experiments. The implantation energies were adjusted to obtain implantation profiles centered well below the surface (taking into account sputtering effects) and hence a very low impurity concentration in a layer 0–200 A under it. In Ni, the P impurities were shown to migrate under implantation towards the film surface; there is no evidence for Si diffusion in the Pd implanted film.

The results of a systematic investigation by transmission electron microscopy (TEM), cathodoluminescence (CL), Rutherford backscattering (RBS), X-ray diffraction and topography and scanning force microscopy (SFM) techniques on several InGaAs/InP compressive and tensile strained layers covering the misfit range from −2.3 to 1.5×10−2 and grown by the metal organic vapor phase epitaxy (MOVPE) technique are reported. In compressively strained films the same dependence for the residual strain vs the film thickness as for the InGaAs/GaAs is found whereas a different strain release rate and different extended defects are found in tensile stressed InGaAs alloy. In particular in tensile stressed samples, grooves, planar defects and cracks are present in addition to the interfacial network of misfit dislocations. The correlation between the observed planar defects and the mechanisms of strain relaxation in the case of tensile strained layers is discussed.

Preliminary measurements on temperature and energy dependence of planar channeling in Si thin crystals are reported. Backscattering and transmission of MeV H+ have been used to obtain information on the half-thickness x 1 2 for escape on the critical angle and on the energy loss of channeled particles. The x 1 2 values extracted from the backscattering data are smaller than those obtained by transmission measurements in crystals of thicknesses comparable with x 1 2 values. A change of about 15–20% has been measured in x 1 2 on going from 80 K to 300 K for both backscattering and transmission techniques. An increase at 80 K of about 20% has also been measured in the full-width at half-maximum of the transmitted angular distributions for particles impinging around the {110} plane. A comparison of these results with theoretical predictions suggest a value of the screening distance lower than the Thomas-Fermi radius. A small but systematic decrease with temperature has been also found in the energy losses of the well channeled particles.