Effects of phonon pore scattering and pore randomness on effective conductivity of porous silicon

The observed low effective thermal conductivity of porous silicon makes for its convenient fabrication and integration as a thermal insulation layer i n microelectronics. The observed average pore size is controlled by the etc hing process and ranges between 1 and 100 nm, which on the low end is much less than the bulk phonon mean-free path. This low effective conductivity, i.e., low effective phonon mean-free path, can be explained with the inclus ion of the effects of the phonon pore scattering and the pore randomness. T he available two-dimensional porous silicon pore-network simulations are us ed along with the Boltzmann transport equation to determine the effective c onductivity. It is shown that the hindering effect of the phonon pore scatt ering (due to reflection from the solid-pore interface) is significant for small pore size. Also, due to the dendritic structure of the pores, the hin dering effect of the pore-network randomness is significant. The prediction s are compared with the existing experiments and a good agreement is found. (C) 1999 Elsevier Science Ltd. All rights reserved.