IN-DEPTH INHOMOGENEOUS PHOTOLUMINESCENT PROPERTIES OF POROUS SILICON LAYERS

Chemical composition and photoluminescence of free-standing porous silicon (PS) layers produced by anodization of p-Si in aqueous HF solutions at high current densities (J(a) = 50 mA cm-2) are studied. It is shown that the PS layers are enriched in oxide phase, presumably due to silicic acid formation during the pore growth. Chemical composition of PS films produced at current densities about 100-150 mA cm-2 is non-uniform: internal faces of PS samples contain more silicon atoms than external. Their luminescent properties are also asymmetrical: the external face of the PS layer emits less light than the internal one. The samples grown at current densities above 200 mA cm-2 do not exhibit asymmetry of chemical composition and luminescence. The obtained results are considered based on existing models for PS luminescence and it is shown that the quantum confinement and siloxene-based models may fit the present data.