Light propagation in porous silicon: application to photonics ; Propagation de la lumière dans le silicium poreux: application à la photonique

This work deals with the optical characterisation of porous silicon and its application in order to obtain refractive index modulation (superlattices). In the first part, we demonstrate the homogeneity of this material on the scale of the wavelength of light studying scattering. This observation justifies the use of a mean refractive index to describe the material. Although the thickness remains well defined, velocity fluctuations appear during the electrochemical process of formation which give rise to an interface roughness. Owing this effect we had to develop a method to analyse optical measurements taking into account the scattering at the interface. Optical constants were determined using two techniques firstly by measuring the transmission of the thin layers at low temperature by photoconduction in the substrate and secondly by measuring and fitting the reflectance spectra. Although the dispersion remains low, the absorption coefficient varies exponentially over a large energy range. In the second part, from the previous characterisation it is demonstrated that weakly doped porous silicon could be used to obtain periodic structures such as Bragg reflectors, Fabry- Perot filters and luminescent microcavities. The characterisation of the structures was complicated by differences between the formation of a single layer and buried one. The structures display a high optical quality. Owing to the high quantum efficiency of the low doped p-type porous silicon, we obtain very efficient luminescent microcavities. The last part, a new type of in-depth grating is developed using a combination of holography and photochemistry. It has enabled us to obtain lateral periodic structures few microns thick and with submicron lateral periodicity. The localised photodissolution has been demonstrated during or after the formation of the porous silicon layer and for all the types of porous silicon, including the macroporous one. ; Ce travail porte sur la caractérisation optique du silicium poreux et son application à la ...