Layered structure of luminescent porous silicon

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Abstract
The structural and optical properties of anodized p-Si were investigated using a combination of transmission and scanning electron microscopy, photoluminescence, Raman scattering, and infrared transmission spectroscopy. The results obtained show clear evidence of the existence of three layers, exhibiting different luminescent and structural properties. The upper porous film displaying bright red-yellow luminescence, consists of small unoriented Si microcrystals and contains a substantial amount of oxygen and hydrogen. A range of Si-O-H compounds is suggested to be responsible for the light emission from the surface porous film. The lower porous silicon layer has ordered microcrystalline structure and produces weak, hardly reproducible and unstable green luminescence. Its origin is to be revealed. It is suggested that the presence of ethanol in the electrolyte is the main cause of the formation of the layered structure of porous silicon.