ABSENCE OF CARRIER HOPPING IN POROUS SILICON

It is often presumed that the stretched exponential decay of photolumi nescence in porous silicon is a consequence of a variable range hoppin g of photoexcited carriers between the localized states of the three d imensional silicon sponge structure. We show unambiguously, however, t hat carrier hopping in porous silicon is absent in the microsecond tim e range, from ambient temperature up to 450 K. We demonstrate this by comparing resonantly and nonresonantly excited photoluminescence decay s. The invariance of the decay shape is interpreted in the light of di fferent carrier recombination models.