Optical reflectivity as a simple diagnostic method for testing structural quality of icosahedral quasicrystals

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MICROSTRUCTURES DIAGRAM OF MAGNETRON SPUTTERED ALN DEPOSITS : AMORPHOUS AND NANOSTRUCTURED FILMS

International audienceIn order to get homogeneous nanostructured Aluminum Nitride deposits, thin films were grown at room temperature on [001] Si substrates by radio frequency magnetron reactive sputtering. The deposits were analysed by Transmission Electron Microscopy, energy dispersive X-ray spectroscopy and Auger electron spectroscopy. Their microstructure and chemical composition were studied versus the plasma working pressure and the radio frequency power. Systematic analysis of cross views of the films allowed the authors to draw a microstructure/process parameters map. Four microstructural types were distinguished according to the decrease of the deposition rate. One is the well-known columnar microstructure. The second one is made of interrupted columns or fibrous grains. The third one is made of nano-sized particles (size of the particles ranges from 1.7 to 8 nm). The fourth and last microstructure is amorphous. The "deposit morphology-process parameters" correlation is commented on

Elastic properties in different nano-structured AlN films

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Photoluminescence properties of Er-doped AlN films prepared by magnetron sputtering

International audienceEr-doped aluminum nitride films, containing different Er concentrations, were obtained at room temperature by reactive radio frequency magnetron sputtering. The prepared samples show a nano-columnar microstructure and the size of the columns is dependent on the magnetron power. The Er-related photoluminescence (PL) was studied in relation with the temperature, the Er content and the microstructure. Steady-state PL, PL excitation spectroscopy and time-resolved PL were performed. Both visible and near infrared PL were obtained at room temperature for the as-deposited samples. It is demonstrated that the PL intensity reaches a maximum for an Er concentration equal to 1 at. % and that the PL efficiency is an increasing function of the magnetron power. Decay time measurements show the important role of defect related non radiative recombination, assumed to be correlated to the presence of grain boundaries. Moreover PL excitation results demonstrate that an indirect excitation of Er 3+ ions occurs for excitation wavelengths lower than 600 nm. It is also suggested that Er ions occupy at least two different sites in the AlN host matrix

Influence of the magnetron power on the Er-related photoluminescence of AlN:Er films prepared by magnetron sputtering

International audienceThe effect of magnetron power on the room temperature 1.54 µm infra-red photoluminescence intensity of erbium doped AlN films grown by r. f. magnetron sputtering, has been studied. The AlN:Er thin films were deposited on (001) Silicon substrates. The study presents relative photoluminescence intensities of nanocrystallized samples prepared with identical sputtering parameters for two erbium doping levels (0.5 and 1.5 atomic %). The structural evolution of the crystallites as a function of the power is followed by transmission electron microscopy. Copyright line will be provided by the publisher 1 Introduction For some time now, rare-earth (RE)-doped semiconductors represent significant potential applications in the field of opto-electronic technology. Part of this technological interest relies on the shielded 4f levels of the RE ions as they give rise to sharp and strong luminescence peaks [1-5]. Among the RE elements, Er is preferred to its counterparts since the Er ions can produce both visible light at 558 nm (green, one of the primary colours) and IR light at 1.54 µm whose spectrum region coincides with the main low-loss region in the absorption spectrum of silica-based optical fibres, combining so potential applications towards photonic devices and towards optical communication devices operating in the infrared domain. These interesting emissions can however only be exploited when placed into host matrixes. On one side, the shielding of the intra 4f levels prevents the shifting of the RE 3+ energy levels and ensures the frequency emission stability. Moreover the intra 4f transitions are parity forbidden for the isolated ions. Matrixes can render the Er 3+ ions optically active, via a relaxation of selection rules due to crystal field effects. As silicon based materials were tested in the 1960s to the 90s with no clear industrial success it was found that th