IN-DEPTH INHOMOGENEOUS PHOTOLUMINESCENT PROPERTIES OF POROUS SILICON LAYERS

Chemical composition and photoluminescence of free-standing porous sil icon (PS) layers produced by anodization of p-Si in aqueous HF solutio ns at high current densities (J(a) = 50 mA cm-2) are studied. It is sh own 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-u niform: internal faces of PS samples contain more silicon atoms than e xternal. Their luminescent properties are also asymmetrical: the exter nal face of the PS layer emits less light than the internal one. The s amples grown at current densities above 200 mA cm-2 do not exhibit asy mmetry 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 t he present data.