ORIGIN OF THE BLUE AND RED PHOTOLUMINESCENCE FROM OXIDIZED POROUS SILICON

We have studied the origin of the visible photoluminescence (PL) from oxidized porous Si fabricated by rapid-thermal-oxidization processes. At low oxidation temperature (T(ox)), the PL spectrum with a peak near 750 nm is observed, and silicon oxyhydrides and silicon oxides are formed at the surface of nanocrystallites. At high T(ox) above 800-degrees-C, strong blue PL is observed around 400 nm and the surface of crystallites is covered by SiO2. The electronic state of porous Si is very sensitive to the surface structure of crystallites. Spectroscopic data indicate that the red PL originates from the near-surface region in the crystallite, while the blue PL originates from the core region in the crystallite.