Anodisation-related structural variations of porous silicon nanostructures investigated by photoluminescence and Raman spectroscopy

Porous silicon layers (PSLs) were prepared in ethanoic and aqueous HF solutions using the conventional electrochemical etching technique. The microscopic structure of the PSLs has been studied by polarised photoluminescence (PL), Raman scattering and atomic force microscopy (AFM). We found that parallel (I//) and perpendicular (I⊥) polarised PL present quite different line shapes. By assuming PS as a mixture of quantum wires (QWs) and quantum dots (QDs) nanocrystallites having specific mean diameter sizes and proportions, we give an explanation to the polarised PL behaviour. This PS modelling enable us to obtain calculated Raman spectra that fit very well the experimental ones for PSLs formed in ethanoic HF solution. AFM images of PSLs prepared in pure aqueous HF solution show morphological inhomogeneities as anodisation time increases, leading to non-conventional and reproducible PL and Raman behaviours. The latter PL behaviour was explained as being due to the non-uniformity of etching in aqueous HF, while that of the Raman spectra was described by introducing an amorphous phase beside the QWs and QDs contribution.