Experimental study of the energy-band structure of porous silicon

Porous silicon samples consisting of either as-grown films, annealed films, or powders have been studied with photoluminescence, (10-700 K) and photoluminescence excitation. In addition, absorption measurements have been carried out on powder. Results are presented and discussed in terms of current models for the luminescence properties of porous silicon. The conclusion is, that for the samples produced and studied here, the luminescence is of molecular nature. From the data, an energy-level diagram related to the luminescence is constructed, and the nature of the band structure is discussed. Of all models proposed for the photoluminescence properties of porous silicon, our data are compatible only with a recently proposed model based on oxygen-related centers.