M. G. Grimaldi

Origin and perspectives of the 1.54 μm luminescence from ion-beam-synthesized β-FeSi2 precipitates in Si

The structural and optical properties of β-FeSi2 precipitates in Si have been analyzed. Float zone Si samples were implanted at 250 °C with 350 keV Fe ions to fluences in the range 1–5×1015/cm2 and annealed in vacuum at 800 °C for times up to 24 h. Detailed morphological analyses of these samples, using transmission electron microscopy, reveal the presence of (i) a band of small (with a diameter 100 nm diameter) fully relaxed β-FeSi2 precipitates centered at a depth of ∼320 nm, and (iii) residual extended defects. A sharp photoluminescence peak at 1.54 μm is measured at 17 K. This peak remains unchanged when the region containing the small precipitates is removed, using Ar sputtering. On the other hand, it is also fully suppressed when the large precipitates region is removed and a high concentration of extended defects remains in the samples. This allowed us to identify the large unstrained precipitates as...

Solute trapping by moving interface in ion‐implanted silicon

Experiments are reported for Te and Ag implantation in silicon, as examples of slow and fast diffusers, after furnace or laser annealing. Slow diffusers are substitutionally located at concentrations in great excess of the maximum solid solubility after both processes. Fast diffusers inhibit the solid‐phase epitaxial regrowth or are rejected at the sample surface after laser irradiation. Although the epitaxial growth occurs with velocities which differ up to ten orders of magnitude after furnace or laser annealing, the supersaturation is interpreted as due to the same basic mechanism: solute trapping at the moving interface when the residence time is larger than the one monolayer regrowth time. This process is controlled by the diffusion coefficient in the two adjacent phases.

Atomic force microscopy study of the growth mechanisms of nanostructured sputtered Au film on Si(111): Evolution with film thickness and annealing time

Nanostructured Au films were deposited on Si(111) by room-temperature sputtering. By the atomic force microscopy technique we studied the evolution of the Au film morphology as a function of the film thickness h and annealing time t at 873 K. By the study of the evolution of the mean vertical and horizontal sizes of the islands forming the film and of their fraction of covered area as a function of h from 1.7×1017 to 1.0×1018 Au/cm2 we identified four different growth stages such as: (1) 1.7×1017≤h≤3.0×1017 Au/cm2, nucleation of nanometric three-dimensional (3D) hemispherical Au clusters; (2) 3.0×1017<h≤5.2×1017 Au/cm2, lateral growth of the Au clusters; (3) 5.2×1017<h≤7.7×1017 Au/cm2, coalescence of the Au clusters; (4) 7.7×1017<h≤1.0×1018 Au/cm2, vertical growth of the coalesced Au clusters. The application of the dynamic scaling theory of growing interfaces allowed us to calculate the dynamic scaling exponent z=3.8±0.3, the dynamic growth exponent β=0.38±0.03, the roughness exponent α=1.4±0.1 and the A...

Activation and carrier mobility in high fluence B implanted germanium

High doping regimes of B implanted Ge have been accurately characterized combining Hall effect technique and nuclear reaction analysis. Preamorphized Ge was implanted with B at 35keV (spanning the 0.25–25×1020B∕cm3 concentration range) and recrystallized by solid phase epitaxy at 360°C. The Hall scattering factor and the maximum concentration of active B resulted rH=1.21 and ∼5.7×1020B∕cm3, respectively. The room-temperature carrier mobility was accurately measured, decreasing from ∼300to50cm2∕Vs in the investigated dopant density, and a fitting empirical law is given. These results allow reliable evaluation for Ge application in future microelectronic devices.

Self-organization of gold nanoclusters on hexagonal SiC and SiO2 surfaces

Very thin Au layers were deposited on SiC hexagonal and SiO2 substrates by sputtering. The Au surface diffusion, clustering, and self-organization of Au nanoclusters on these substrates, induced by thermal processes, were investigated by Rutherford backscattering spectrometry, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. On both types of substrates, clustering is shown to be a ripening process of three-dimensional structures controlled by surface diffusion and the application of the ripening theory allowed us to derive the surface diffusion coefficient and all other parameters necessary to describe the entire process. The system Au nanoclusters/SiC and Au nanoclusters/SiO2 are proposed as nanostructured materials for nanoelectronic and nanotechnology applications.

Novel approach to the fabrication of Au/silica core?shell nanostructures based on nanosecond laser irradiation of thin Au films on Si

We demonstrate the possibility of producing Au/SiO(2) core-shell nanoparticles by nanosecond laser irradiation of thin (5 and 20 nm) Au films on Si. The Au/Si eutectic reaction and dewetting process caused by the fast melting and solidification dynamics induced by the nanosecond laser irradiations are investigated as the origin of the formation of core-shell nanoparticles. Using several microscopic techniques (Rutherford backscattering spectrometry, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and energy filtered transmission electron microscopy) the formation and evolution of the core-shell structures are investigated as a function of the laser fluence in the 500-1500 mJ cm(-2) range for both film thicknesses. In particular, the mean height and diameter and surface density evolution of the core-shell structures are quantified and correlated to the laser fluence and Au film thickness.

Amorphization and defect recombination in ion implanted silicon carbide

The damage produced in silicon carbide single crystals by ion implantation was investigated by Rutherford backscattering channeling and transmission electron microscopy techniques. Implantations were performed at liquid nitrogen and at room temperatures with several ions to examine the effect of the ion mass and of the substrate temperature on the damaging process. The damage accumulation is approximately linear with fluence until amorphization occurs when the elastic energy density deposited by the ions overcomes a critical value. The critical energy density for amorphization depends on the substrate temperature and is greatest at 300 K indicating that defects recombination occurs already at room temperature. Formation of extended defects never occurred and point defects and uncollapsed clusters of point defects were found before amorphization even in the case of light ion implantation. The atomic displacement energy has been estimated to be ∼12 eV/atom from the analysis of the damage process in dilute c...

Nanostructuring in Ge by self-ion implantation

We report here a detailed study about the formation and self-organization of nanoscale structures during ion beam implantation at room temperature of 300 keV Ge+ in Ge as a function of the ion fluence in the range between 1×1014 to 4×1016 cm−2. “Microexplosions” characterize the morphology of the swelled material; a random cellular structure consisting of cells surrounded by amorphous Ge ripples has been observed and studied in details by combining atomic force microscopy, scanning electron microscopy, and transmission electron microscopy.

Relaxation and crystallization of amorphous silicon carbide probed by optical measurements

Abstract Optical spectroscopy in the visible (300–1100 nm) and in the infrared (400–4000cm−1) regions was used to monitor the relaxation and crystallization processes of pure amorphous silicon carbide (a-SiC) thin films upon annealing at temperatures between 200 and 1000°C. These films were obtained by ion implantation of crystalline material with 200keVkr+ at a fluence of 2 × 10 ions cm−2. The refractive index n and the absorption index k were calculated from the ultraviolet-visible transmittance and reflectance, and information on the vibration modes of the Si-C bonds was detected from infrared transmittance. Thermal treatment changes the optical properties of a-SiC; in particular, annealing at temperatures lower than 800°C resulted in a continuous variation in both the refractive index and the absorption index and in a decrease in the infrared silicon-carbon peak width. Annealing at higher temperatures produces sudden variations in the shape of the refractive index and in the infrared silicon-carbon pe...

Ga-implantation in Ge: Electrical activation and clustering

The electrical activation and clustering of Ga implanted in crystalline Ge was investigated in the (0.3–1.2)×1021 Ga/cm3 concentration range. To this aim, Ge samples implanted with 50 keV gallium, and annealed at several temperatures up to 650 °C, have been subjected to a detailed structural and electrical characterization. The substrate was maintained at 77 K during implantation to avoid the formation of the honeycomb structure that occurs during implantation at room temperature of heavy ions at high fluence. Secondary ion mass spectrometry analyses indicated a negligible Ga diffusion and dopant loss during the thermal annealing. The carrier concentration in the recrystallized samples measured by Hall effect showed a maximum concentration of active Ga of ∼6.6×1020 Ga/cm3. A remarkable Ga deactivation occurred with increasing the annealing temperature from 450 to 650 °C although the sheet resistance did not change considerably in this temperature range. It turned out that the carrier concentration reducti...