RESONANTLY EXCITED PHOTOLUMINESCENCE IN POROUS SILICON

We report on the photoluminescence (PL) spectra of porous silicon exci ted resonantly by laser lines within the luminescence band. Measuremen ts have been performed for different excitation energies, temperatures and delay times. At low temperatures, the known step-like phonon stru cture in the PL spectra of porous silicon and a gap of the few milliel ectronvolts between the laser line and the onset of the luminescence a re observed. As the temperature is increased, the onsets of both the P L spectra and the step features shift towards higher energies whereas the peak of the spectrum moves towards lower energies by an amount whi ch depends on the delay time after excitation. Furthermore, the gap di sappears and simultaneously an exponential tail of the spectrum occurs on the high energy side of the laser line, which broadens proportiona lly to kT. These results are discussed in light of the existing theori es for the luminescence mechanism in porous silicon and for the origin of the step features in the PL spectra.