Dependence of the photoluminescence of porous silicon on the surface composition of the silicon fibers

It is shown that the luminescence of porous silicon originates mainly from a thin surface layer (1000-2000 Å). One reason for this localization is a reduction in the concentration of dangling bonds in the surface layer as a result of their passivation by hydrogen atoms and hydroxyl groups. Another cause of the enhanced brightness of radiation from the surface zone of the porous layer is an increased content of silicon oxides capable of absorbing photoluminescence-stimulating light. It is shown in this connection that the excitation of photoluminescence in the interval 410-470 nm is attributable to the absorption of light by oxides enriched with H^-, OH^-, F^-, O^-, SiF^-, and SiF^- ions.