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Porous Silicon Prepared on a Thin Epitaxial Silicon Layer: Structure and Optical properties

Commercially available silicon-on-insulator (SOI) wafers, consisting of 45  m tick p-type (111) epitaxial layer grown on a thin 100 nm SiO2 layer on n-type silicon substrate were electrochemical etched to produce porous silicon (PSi) samples. At 50% concentration of 48% hydrofluoric acid (HF) in ethanol solution the micro- and nano-sized pores were obtained. The structural and the optical properties of prepared sample were investigated by Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). SEM images showed high density of micrometer sized pores. Nanometer sized structures were observed by the phonon confinement effects of the optical and acoustic phonon bands in the Raman spectra. The broadening of crystal silicon (c-Si) transversal optical TO( ) band at 520 cm-1, was observed in substrate sample. At the same time the wide transversal acoustical (TA)-like phonon band at 150 cm-1, that characterizes the short range confinement, also appeared in the same sample. FT-IR spectra exhibited numerous bands from Si-Hx and H-Si(Si3-nOn) groups. The sample also showed photoluminescence (PL) peak in the visible spectral range. The change in the intensity, width and the position of the PL peak showed strong sensitivity to the influence of different environment conditions such as air, vacuum and acetone.

Porous silicon; nanostructures; Raman and FT-IR spectroscopy; SEM images

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