Photoluminescence mechanism in surface-oxidized silicon nanocrystals

We have studied photoluminescence (PL) properties of surface-oxidized Si nanocrystals fabricated with a ${\mathrm{SiH}}_4$ plasma cell. The size dependence of the PL spectrum, the PL decay dynamics, and site-selective excitation spectroscopy show that the efficient and broad PL band around ∼1.65 eV originates from excitons localized at the interface between crystalline Si and the ${\mathrm{SiO}}_2$ surface layer. The PL from the crystalline Si core state in large nanocrystals appears in the infrared spectral region. By comparison between surface-oxidized Si nanocrystals and as-prepared porous Si, the size and surface dependence of the coupling between electronic and vibrational excitations are discussed.