G. Ghislotti

Room‐temperature visible luminescence from silicon nanocrystals in silicon implanted SiO2 layers

We report the observation of visible‐light emission at room temperature from high fluence (0.3–3×1017 cm−2) Si+ implanted thermal SiO2 layers grown on silicon substrates. Significant blue‐light emission and an intense broad luminescent band with a peak beyond 750 nm are observed after annealing at high temperature (T≥1000 °C). The red‐light emission, present only in the highest fluence implant, is attributed to the luminescence emitted from silicon nanocrystals produced by silicon precipitation. The presence of silicon nanocrystals is confirmed by transmission electron microscopy. Significant blue‐light emission is visible after thermal annealing in the 1×1017 cm−2 fluence implant. The peak position shifts from 490 to 540 nm by increasing the annealing cycles temperature.

Surface Brillouin Scattering—Extending Surface Wave Measurements to 20 GHz

Brillouin light scattering is generally referred to as the inelastic scattering of an incident optical wave field by thermally excited elastic waves (elastic waves of thermal origin are usually called acoustic phonons) in a sample. This subject was first investigated early in the century by Brillouin(1) and Mandelshtam(2) in the case of scattering from transparent materials. Since the advent of the laser as a powerful source of monochromatic light, Brillouin scattering has received considerable interest for characterizing elastic and optoelastic bulk properties of materials.3,4 More recently with the introduction of high-contrast spectrometers,(5) scattering from opaque materials can be studied, thereby permitting considerable advances in the study of surface acoustic waves in solids. In the last decade, Brillouin scattering from surfaces, more often called surface Brillouin scattering (SBS), has been widely used to investigate elastic properties of thin films, interfaces, and layered materials.

Nanosecond time-resolved emission spectroscopy from silicon implanted and annealed SiO2 layers

Photoluminescence decay curves and nanosecond time-gated spectra were measured from silicon implanted SiO2 layers after thermal annealing. Different ion fluences and annealing times were tested. Three components emitting blue-green light with lifetimes of about 0.4, 2, and 10 ns were detected. The peak position of all components moves to longer wavelengths upon increasing the ion fluence. This short-wavelength emission seems to be related to the presence of extended defects acting as precursors of nanocrystals. A slower (microsecond) component, centered in the near infrared and attributed to nanocrystals, was also identified in the highest fluence implant considered (3×1017 cm−2).

Brillouin scattering of porous silicon

Abstract Low and high porosity porous silicon samples with different microstructures were studied for the first time by Brillouin light scattering. The surface and bulk acoustic phonon spectrum was measured and the physical properties of a subsurface region 1 μm thick, about which little is known, were explored.

Elastic behaviour of TiN thin films

Abstract Thin films are increasingly being used in many technological areas. One of the problems in practical applications is the level of internal film stress, which, in severe cases, can lead to coating failure. In our laboratories we are currently studying the effect of deposition parameters and of post-deposition treatments on the stress behaviour of some coatings obtained by magnetron sputtering techniques and by ion beam assisted deposition (IBAD). In this work we concentrate on TiN since this compound is particularly valuable as a study system, in view of the good understanding of its physical properties and its wide range of applications, ranging from barrier layers in microelectronics to gas diffusion inhibition, and from optical coatings to sliding wear reduction. We have deposited thin films (ranging in thickness from 100 nm up to a few microns) of TiN in different experimental conditions, by d.c. magnetron reactive sputtering and by IBAD, and we have characterized the coatings with respect to composition, structure and microstructure by scanning electron microscopy. Auger electron spectroscopy and X-ray diffraction. The elastic response of the films has been studied in detail by surface Brillouin light scattering. Our results are in general agreement with other works in the literature; however, the Rayleigh wave velocities for IBAD samples are much lower than expected. Some preliminary explanations of this fact are presented.

Visible light emission from silicon implanted and annealed SiO2 layers

Silicon implanted and annealed SiO{sub 2} layers are studied using photoluminescence (PL) and positron annihilation spectroscopy (PAS). Two PL emission bands are observed. A band centered at 560 nm is present in as-implanted samples and it is still observed after 1,000 C annealing. The emission time is fast. A second band centered at 780 nm is detected after 1,000 C annealing. The intensity of the 780 nm band further increased when hydrogen annealing was performed. The emission time is long (1 {micro}s to 0.2 ms). PAS results show that defects produced by implantation anneal at 600 C. Based on the annealing behavior and on the emission times, the origin of the two bands is discussed.

Photoluminescence studies of light emission from silicon implanted and annealed SiO2 layers

Abstract Nanosecond time-resolved photoluminescence (PL) and the temperature dependence of continuous wave PL from high fluence ((0.3-3) × 10 17 cm −2 ) Si + implanted thermal SiO 2 layers after annealing at high temperature ( T = 1 000 °C) are reported. A green-blue light and a near-infrared signal are detected; we observed a transition from the green-blue to the near-infrared signal at the critical ion fluence 1 × 10 17 cm −2 . The green-blue light emission is very fast, characterized by 0.4, 2 and 6 ns decay times, and has decreasing intensity with the increase of measurement temperature. The near infrared light signal is peaked at approximately 800 nm and has a decay time longer than 250 ns. The intensity of the near-infrared signal grows with annealing time and shows a non-monotone behaviour with measurement temperature.

Brillouin scattering from shear horizontal surface phonons in buried SiO2 layers

Experimental evidence and a theoretical explanation of Brillouin scattering from shear horizontal surface acoustic phonons in an Si buffer with a buried SiO2 layer are given in both the discrete and continuum parts of the spectrum. This is the first experimental observation of Brillouin scattering from sheer horizontal acoustic phonons in the continuum spectral region. The intensity and position of peaks in Brillouin spectra have been qualitatively described in terms of the layer projected phonon density of states calculated for such a structure.

Characterization of SOI-SIMOX structures using Brillouin light scattering

Silicon on insulator structures prepared using separation by implanted oxygen technology are studied by means of Brillouin light scattering. The deviation in the experimental wave velocity for shear horizontal modes guided within the SiO2 buried layer is ascribed to the presence of silicon inclusions dispersed in the oxide matrix. Transmission electron microscopy (TEM) observations support this assumption. A model describing the effect of the silicon inclusions by means of an effective medium theory based on the Eshelby method is presented. The inclusion volume fraction is determined and compared with the TEM estimate.

Analysis of structural imperfections of silicon on insulator structures

Abstract Silicon-on-insulator structures prepared using the separation by implanted oxygen technology are studied by means of Brillouin light scattering. The deviation in the experimental wave velocity for modes guided within the SiO 2 buried layer is ascribed to the presence of silicon inclusions dispersed in the oxide matrix. The presence of inclusions is taken into account by means of an effective medium theory which allows to determine the inclusion volume fraction and the anisotropy of their orientation.