Correlation of photoluminescence spectra and structure of porous silicon

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Abstract
Porous silicon (PS) layers emitting red photoluminescence (PL) have been prepared by anodization of p-type (100) monocrystalline silicon substrate in aqueous HF solutions. PS layers oxidized in free air exhibit under UV photoirradiation an intense yellow-orange PL, whilst as-prepared samples emit red PL. Our aim is to explain the PL behaviour and its origin in both unetched and HF etched as-prepared and oxidized PS layers according to calculated PL based on quantum confinement formalism and to infrared spectroscopy (IRS). It was found that the PL behaviour is associated with a quantum size effect and concentration change in quantum dots and wires. It was observed that HF etching of oxidized PS may induce a preponderance of dots or wires in the PS structure, depending on the oxidation degree, and produce a PL blueshift or redshift respectively. By correlating PL spectra of unetched and HF-etched oxidized PS, we found that highly oxidized PS transforms into an matrix in which photoluminescent nanocrystalline Si quantum dots are embedded.