Photoluminescence from nanocrystalline silicon in Si/SiO2 superlattices

Abstract

Si/SiO 2 superlattices on oxidized silicon wafers were fabricated by successive cycles of silicon deposition and high-temperature thermal oxidation. Silicon films were deposited by low-pressure chemical vapor deposition at 580 °C. As-deposited silicon was amorphous, and it exhibited two weak photoluminescence (PL) peaks in the visible range, a stable one at ≅650 nm and an unstable one at 530–550 nm. By oxidation at 900 °C, a drastic increase of the stable PL peak was observed with an initial redshift from 650 to 800–900 nm and a subsequent blueshift down to 680–700 nm. Its position and intensity depended on the oxidation time. For prolonged oxidation, PL disappeared. The observed PL is attributed to silicon crystallites passivated by oxygen. Localized states at the Si/SiO2 interface limit the emitted wavelength. The PL peak from superlattices was at the same position as from one bilayer, while a superlinear increase in PL intensity was observed by increasing the number of bilayers.