Alternating current electrochemical anodisation of silicon on insulator layers

Porous silicon (PSi) samples were prepared by electrochemical anodisation of silicon on insulator layers. Structural and optical properties of prepared samples were investigated by Raman and photoluminescence (PL) spectroscopy and field emission scanning electron microscopy (FE-SEM). The anodisation of silicon on insulator layers was performed by alternating currents (AC) of the mains frequency of 50 Hz. A very intensive PL was observed at the circular edge of the samples that exhibited micrometer sized island-like porous structure, while the central part of the samples showed moderate PL signal. The formation of such porous island-like structures with strong intensity PL was interpreted with stress induced due to difference of the piezoelectric coefficient of silicon and quartz layers (buried SiO₂). Micro-Raman spectra of islands show strong phonon confinement with the cluster size between 1.4 and 3.5 nm.