Absence of carrier hopping in porous silicon

It is often presumed that the stretched exponential decay of photoluminescence in porous silicon is a consequence of a variable range hopping of photoexcited carriers between the localized states of the three dimensional silicon sponge structure. We show unambiguously, however, that carrier hopping in porous silicon is absent in the microsecond time range, from ambient temperature up to 450 K. We demonstrate this by comparing resonantly and nonresonantly excited photoluminescence decays. The invariance of the decay shape is interpreted in the light of different carrier recombination models.