2 MEYER-NELDEL RULES IN POROUS SILICON

We observe two Meyer-Neldel rules for the dc conductivity in porous si licon. One rule corresponds to extended-states transport and the other to transport by thermally activated hopping. The quantitative resembl ance of the first rule to the one found in hydrogenated amorphous sili con (a-Si:H) indicates that in samples in which it is observed the con duction takes place in an a-Si:H-like tissue that wraps the luminescen t crystallites. In samples where the second rule is observed the condu ction appears to be either by activated hopping in this disordered tis sue, or by intercrystallite hopping.