STEADY-STATE AND TIME-RESOLVED SPECTROSCOPY OF POROUS SILICON

We present experimental data on steady-state properties, time-resolved properties and on polarization characteristics of porous silicon phot oluminescence and models for the decay processes of the red-orange ban d. The manifold manifestation of inhomogeneous broadening of this band in emission, excitation, polarization, kinetics and degradation suppo rts the model in which porous silicon is treated as a network of cryst allites connected via an oxide interface. Spectral inhomogeneties of t he red-orange band can be described in terms of varying shape and size of silicon clusters. The polarization of emission is explained by coe xistence of dot-like and wirelike entities, i.e. spherical and non-sph erical clusters. The relative weight of these species determines the p olarization degree, whereas the kinetics are controlled by the transpo rt of excitations among the clusters. The decay is modeled by a modifi ed stretched exponential function with the local lifetime, the migrati on lifetime, and a scaling factor. The latter is determined by the dim ensionality of the space available for migration which was found to be close to but less than unity. On the nanosecond range two distinct ba nds in the blue-green region are evaluated that need further studies f or interpretation. Generally, arguments are proposed in favor of a qua ntum confinement origin of the red-orange band and a bridge between qu antum-wire and quantum-dot models is provided.