Resonant Coupling between Surface Vibrations and Electronic States in Silicon Nanocrystals at the Strong Confinement Regime

A striking correlation between infrared photoinduced absorption spectra and the photoluminescence from silicon nanocrystals indicates that quantized electronic sublevels of the nanocrystals are resonantly coupled to surface vibrational modes via a polarization field produced by coherent longitudinal polar vibrations. Our experimental results and model support the assumption that the mechanism responsible for the efficient photoluminescence from silicon nanocrystals should be assigned to inhibition of nonradiative channels rather than enhancement of radiative channels. The current interest in the optical properties of silicon nanocrystals (nc’s) is driven by both fundamental questions concerning the origin of the photoluminescence (PL) from these nc’s1-3 as well as the possibility to develop silicon-based optoelectronic devices.4,5 Canham6 in his pioneering work on porous silicon (PS) suggested that quantum confine-ment (QC) of carriers in small silicon nc’s is responsible for the strong, room temperature PL from PS. However, shortly after, numerous models that do not rely on QC wer