Luminescence mechanism of as-prepared and oxidized porous silicon

We have studied the photoluminescence (PL) mechanism of porous silicon (PS) with various nanocrystal sizes. In as-prepared PS without air exposure, the PL peak energy increases with a decrease of the crystalline size. After air exposure. the PL spectrum is observed in the red spectral region and is independent of the crystal size. The size-dependent PL of as-prepared PS originates from mostly delocalized states. while the red PL of partially oxidized PS originates from localized surface states in Si nanocrystals.