LAYERED STRUCTURE OF LUMINESCENT POROUS SILICON

The structural and optical properties of anodized p-Si were investigat ed using a combination of transmission and scanning electron microscop y, photoluminescence, Raman scattering, and infrared transmission spec troscopy. The results obtained show clear evidence of the existence of three layers, exhibiting different luminescent and structural propert ies. The upper porous film displaying bright red-yellow luminescence, consists of small unoriented Si microcrystals and contains a substanti al amount of oxygen and hydrogen. A range of Si-O-H compounds is sugge sted to be responsible for the light emission from the surface porous film. The lower porous silicon layer has ordered microcrystalline stru cture and produces weak, hardly reproducible and unstable green lumine scence. Its origin is to be revealed. It is suggested that the presenc e of ethanol in the electrolyte is the main cause of the formation of the layered structure of porous silicon.