Femtosecond nonlinear coherence spectroscopy of carrier dynamics in porous silicon

Multidimensional nonlinear coherence spectroscopy based on spectrally resolved femtosecond two-color three-pulse photon echo measurements are used to investigate carrier dynamics and energy structures in porous silicon samples, an indirect band-gap material. Short time scales for electron localization (~500 fs) and electron hopping (~3 ps) are observed which are dependent on the porosity of the samples. A spin-orbit splitting for the conduction band of 4–5 meV is deduced. The observed energy splittings of 18 and 22 meV for the 48% porosity sample and 21 and 28 meV for the 70% porosity sample are assigned to spin-orbit splitting for the valence band.