Search

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.

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.

The known models describing the breakdown of coherency between layer and substrate in mismatched heterostructures are based on the isotropic elastic continuum approximation. As a matter of fact an internal contribution to the misfit accommodation, that is a deviation from the so-called “virtual crystal approximation”, is expected in ternary or more complex alloy structures. This effect is clearly seen in a set of In x Ga 1− x As / GaAs low misfit samples in the presence of misfit dislocations. The complete structural characterisation including the elastic distortion field and the dislocation density and distribution has been performed by means of Rutherford backscattering based techniques and double crystal X-ray diffraction.

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 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.