Structure and optical properties of porous silicon prepared on thin epitaxial silicon layer on silicon substrates

Porous silicon (PSi) samples were prepared by electrochemical etching of silicon-on-insulator wafers, consisting of 45 μm thick p-type (111) silicon epitaxial layer grown on a thin 100 nm SiO2 layer on silicon substrates, by varying the concentration of 48% HF in ethanol solution. Within the epitaxial layer micro- and nano-sized pores of different sizes in dependence on HF concentration were obtained. The structural and optical properties of prepared samples were investigated by Raman spectroscopy, infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). SEM images showed high density of micrometer sized pores whose morphology and density depend on the HF concentration. Nanometer sized silicon structures were observed by phonon confinement effects of TO and TA phonon bands in the Raman spectra. The broadening of crystalline silicon (c-Si) vibrational band at 520 cm−1, that indicates phonon confinement, increased with decreasing the HF concentration. At the same time the TA-like phonon vibrational band at 150 cm−1, that characterizes the short range confinement, also appeared in same samples. All samples showed photoluminescence (PL) peak in visible spectral range. The change in intensity and position of the PL peak showed strong sensitivity to the influence of different environment conditions; air, vacuum and acetone.