Strong linear polarization in scanning tunneling microscopy-induced luminescence from porous silicon

Visible luminescence with strong linear polarization (up to 80%) from porous silicon induced with scanning tunneling microscopy is reported. The external quantum efficiency is found to be close to that of the semiconductors with direct band gaps such as GaAs and CdS. These observations agree with the theoretical predictions of direct band gap and strong optical anisotropy for quantum Si wires. The observation of a strong linear polarization indicates that the delocalized states, which extend throughout the entire Si clusters and undergo quantum confinement, play an important role in the luminescence.