M. Vergnat

Evidence of light-emitting amorphous silicon clusters confined in a silicon oxide matrix

Amorphous silicon oxide thin films were prepared by the coevaporation technique in ultrahigh vacuum. Different compositions were obtained by changing the evaporation rate of silicon. The samples were then annealed to different temperatures up to 950 °C. The composition and the structure were investigated using energy dispersive x-ray spectroscopy, infrared absorption measurements, and Raman spectroscopy. This study attests the presence of amorphous silicon clusters in a silicon oxide matrix. Optical transmission measurements were performed and interpreted in the field of the composite medium theory. The obtained results are in good agreement with the presented structural model. The photoluminescence in the red-orange domain was studied in relation with the structure. The correlation between the photoluminescence energy and intensity and the structure shows that the light emission originates from the silicon clusters embedded in the silicon oxide matrix. Moreover the dependence of the photoluminescence ene...

Intense visible photoluminescence in amorphous SiOx and SiOx:H films prepared by evaporation

Visible photoluminescence (PL) can be observed in a-SiOx and a-SiOx:H alloys prepared by evaporation of SiO in ultrahigh vacuum and under a flow of hydrogen ions, respectively. The hydrogen and oxygen bonding is studied by infrared spectrometry. The hydrogen stability is followed by thermal desorption spectrometry experiments. The evolution of the PL with annealing treatments shows that the PL can be attributed to a quantum confinement effect in a-Si clusters embedded in the matrix of a-SiOx. Hydrogen does not greatly contribute to the PL efficiency and to the thermal evolution of the a-Si clusters.

Photoluminescence and electroluminescence of size-controlled silicon nanocrystallites embedded in SiO2 thin films

Silicon nanocrystallites (nc-Si) were obtained by thermal annealing treatments of SiO∕SiO2 multilayers, prepared by evaporation. The nc-Si size was controlled by the SiO thickness. In this study the SiO2 thickness was maintained at 5nm and the SiO thickness was varied from 2to6nm. The film’s microstructure was studied by transmission electron microscopy. A strong photoluminescence was obtained in the visible range which corresponds to the radiative recombination of electron-hole pairs in the nc-Si. The electroluminescence signal is weaker and broader than the photoluminescence one. A model taking into account SiO2 defects and nc-Si is proposed to explain the electroluminescence results.

Evolution with the annealing treatments of the photoluminescence mechanisms in a-SiNx:H alloys prepared by reactive evaporation

A wide range of amorphous hydrogenated silicon nitride thin films with an excess of silicon was prepared by evaporation of silicon under a flow of nitrogen and hydrogen ions. A strong visible photoluminescence at room temperature was observed for the as-deposited films as well as for films annealed up to 1100°C. The chemical composition and the structure of the films were investigated using x-ray photoelectron, thermal desorption, and Raman spectroscopies, infrared absorption measurements, grazing incidence x-ray diffraction experiments, and transmission electron microscopy. Two luminescence mechanisms were identified for the films depending on the annealing temperature. For annealing temperatures below 650°C, the films are made of amorphous silicon-rich phases mixed with nitrogen-rich phases. These inhomogeneities in the chemical composition, coupled with the evolution of the photoluminescence energies and intensities with the hydrogen content, suggest that the emission is due to the recombination proces...

Magnetic and structural properties of iron nitride thin films obtained by argon‐nitrogen reactive radio‐frequency sputtering

We have prepared iron nitride thin films by reactive rf sputtering of an iron target in an argon‐nitrogen plasma. The films present a wide variety of structures and compositions: α expanded bcc iron, amorphous Fe1−x‐Nx, γ’‐Fe4N, e‐Fe2–3N, and ζ‐Fe2N. Evolutions of the crystallographic structures and of the magnetic properties of the obtained phases are discussed versus the nitrogen concentration in the gaseous flow and the substrate temperature during deposition.

Visible photoluminescence in amorphous SiOx thin films prepared by silicon evaporation under a molecular oxygen atmosphere

A simple reactive evaporation method is proposed to prepare light-emitting amorphous SiO x thin films. By evaporating pure silicon in a controlled molecular oxygen atmosphere, it is possible to obtain a very large composition range. By changing the pressure in the preparation chamber, x can be varied from 0.7 to 1.85. The composition and the structure of the films were investigated using energy dispersive x-ray, infrared absorption and x-ray photoelectron spectroscopies. The samples contain amorphous silicon clusters dispersed inside an insulating silicon oxide matrix. The room-temperature photoluminescence properties were then measured. By conveniently choosing the oxygen pressure, the as-deposited films exhibit visible photoluminescence without any annealing post-treatments. The luminescence intensity initially increases with excess silicon concentration and then disappears for a too-high silicon excess. The above effect is interpreted in terms of confinement of the amorphous silicon clusters in the insulating matrix.

Visible photoluminescence in amorphous SiNx thin films prepared by reactive evaporation

Photoluminescence in the visible domain can be observed in amorphous silicon nitride (a-SiNx) alloys prepared by evaporation of silicon under a flow of nitrogen ions. A strong improvement of the photoluminescence intensity was obtained with annealing treatments in the range 500–1150 °C. Structural investigations were performed by infrared and Raman spectrometry experiments. The optical gap was obtained from transmission measurements in the ultraviolet, visible, and near infrared range. The evolutions of the structure and the optical properties with annealing treatments are correlated to the evolution of the photoluminescence.

Structure and photoluminescence properties of evaporated GeOx thin films

Amorphous GeOx alloys were prepared by evaporation of GeO2 powder on substrates maintained at 100°C. The evolution of the structure was investigated by infrared-absorption spectrometry, Raman spectrometry and transmission electron microscopy experiments for annealing temperatures less than 600°C. These experiments allowed us to follow the phase separation of the alloy and to observe the appearance of amorphous and crystallized Ge aggregates. The evolution of the photoluminescence in the range of 560–1550nm was correlated to the structure of the films.

Improvement of the photoluminescence properties in a-SiNx films by introduction of hydrogen

Photoluminescence properties of amorphous hydrogenated silicon nitride thin films with various compositions are presented. The as-deposited samples prepared by evaporation of silicon under a flow of nitrogen and hydrogen ions exhibit visible photoluminescence at room temperature without any annealing treatment. The evolution of the photoluminescence properties with increasing nitrogen concentration in the films is correlated to structural investigations performed with Fourier-transform infrared spectroscopy and optical characterization obtained from transmission measurements in the ultraviolet-visible-near-infrared range. It is shown that the introduction of hydrogen is of prime importance to improve the photoluminescence intensity of the films.

Structure and photoluminescence properties of evaporated GeOx∕SiO2 multilayers

Amorphous GeOx∕SiO2 multilayers were prepared by successive evaporations of GeO2 and SiO2 powders onto substrates maintained at 100°C. The evolution of the structure was investigated by x-ray reflectometry, transmission electron microscopy, infrared-absorption spectrometry and Raman spectrometry for annealing temperatures less than 800°C. These experiments allowed us to follow the phase decomposition of the GeOx alloy and to observe the appearance of amorphous and crystallized germanium aggregates. The evolution of the photoluminescence in the range of 0.8–2.2eV was correlated to the structure of the films.