Photoluminescence from nanocrystalline silicon in Si/SiO2 superlattices

Si/SiO2 superlattices on oxidized silicon wafers were fabricated by success ive cycles of silicon deposition and high-temperature thermal oxidation. Si licon films were deposited by low-pressure chemical vapor deposition at 580 degrees C. As-deposited silicon was amorphous, and it exhibited two weak p hotoluminescence (PL) peaks in the visible range, a stable one at congruent to 650 nm and an unstable one at 530-550 nm. By oxidation at 900 degrees C , a drastic increase of the stable PL peak was observed with an initial red shift 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 o xidation, PL disappeared. The observed PL is attributed to silicon crystall ites passivated by oxygen. Localized states at the Si/SiO2 interface limit the emitted wavelength. The PL peak from superlattices was at the same posi tion as from one bilayer, while a superlinear increase in PL intensity was observed by increasing the number of bilayers. (C) 2000 American Institute of Physics. [S0003-6951(00)00124-8].