Polarized optical gain and polarization-narrowing of heavily oxidized porous silicon.

We report on a polarization-sensitive optical gain in a blue-emitting Si/SiO(2) nanocrystalline system having a high degree of emission polarization memory. This system can show a positive optical gain or optical loss depending on the polarization state of the pump and emitted light. Under optical gain conditions, the degree of polarization of the amplified spontaneous emission increases with the pumping fluence. This effect has been attributed to an increase in the stimulated emission efficiency occurring for the linearly polarized emission component characterized by high photon occupation numbers (stimulating photon flux). This finding is independently supported by other experimental observations. The occurrence of polarization dependent stimulated emission strongly indicates the relevance of morphological effects in light emission from ultrasmall elongated silicon nanostructures.