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REALISATION ET ETUDE DE STRUCTURES A MODULATION D'INDICE OPTIQUE EN SILICIUM POREUX

Abstract : Abstract : This work concerns the study of the vertical and lateral modulation of the optical index in the porous silicon.To realise performing optical structures, we focused our efforts on the optical losses due to the p-type porous silicon samples interfaces. A study on the changes induced by the formation temperature on the interface roughness has been performed to reduce the losses. For a formation temperature of –35°C, and using the most critical formation currents, we obtained a striking improvement, reducing the interface roughness by a factor of 6.This roughness decrease allowed us to realise Bragg mirrors and microcavities of very high optical quality, with reflectivity coefficients as high as 99.5% and cavity mode widths of 5nm. The determination of such high reflection coefficients was realised using very precise measurements by “ring down” spectroscopy, with a precision of 0.01%. Thanks to the characterisation of these structures we were able to evidence a difference in the optical properties between simple layers and underlying layers. The modifications of the refractive index and of the formation velocity have been determined quantitatively by studying the photoluminescence and by simulating the reflection spectra. We also show that dye molecules can be used to efficiently fill the porous silicon cavities,independent on the low or high porosity degree. Moreover, the filling of the pores may be eased by oxidation of the porous silicon layer prior to the filling. Our results show that porous silicon can be a very good matrix for dye molecules, that stay enough dispersed to emit light. The use of dye-filled porous silicon microcavities allow for a sharpening and an amplification of the dye emission. To characterise the lateral refractive index modulation, obtained by photodissolution and photo-electro-formation of the porous silicon layer, we studied the influence of the presence of light on the porosity and on the optical properties of p- and n+-type porous silicon monolayers. Based on this study, we were able to determine the optimal formation parameters for gratings with lateral refractive index modulation. The light diffraction from these samples has also been studied. Keywords: Porous Silicon, optical index modulation, reflectivity, interface roughness, Bragg mirrors, laser dye
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Susanna Setzu. REALISATION ET ETUDE DE STRUCTURES A MODULATION D'INDICE OPTIQUE EN SILICIUM POREUX. Matière Condensée [cond-mat]. Université Joseph-Fourier - Grenoble I, 1999. Français. ⟨tel-00004131⟩

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