Observation of room-temperature resonant photoluminescence in porous silicon

We have studied the room-temperature photoluminescence (PL) properties of freshly prepared and naturally oxidized porous silicon (p-Si) samples. The morphology and chemical composition of the p-Si samples are examined by means of scanning electron microscopy (SEM) and electron dispersion spectroscopy. Nanoscale pores are noticed in freshly prepared p-Si, with an average density of ∼4×109 cm−2. The surface-oxidation process in the p-Si is found to be slowly progressing in course of time. Using SEM, pores are not observed on the surface of the oxidized p-Si in plan-view geometry. A broad PL band consisting of multiple peaks together with the evolution of resonant peaks is evidenced in freshly prepared samples. A regular blue shift of the resonant peak energy is obtained with increasing excitation energy in all the p-Si samples. In addition, multiple peak structure is found slowly disappearing with increasing surface-oxide layer thickness followed by the gradual increment of the resonant PL intensity.