Optical investigations on thermal conductivity in n- and p-type porous silicon

Determination of thermal conductivity of top side illuminated n-type and p-type porous silicon (PS) samples have been performed by means of photo-acoustic and optical pump-probe techniques. Concerning the n-type samples, the values found can be explained in the framework of Looyenga effective medium theory, leading to a thermal conductivity of the solid phase of 13 W/mK. This result suggests that n-type thick PS samples formed by top side illumination has a complex multilayer morphology in which mesophases, nanophases and macrophases coexist. The investigation on p-type nanoporous silicon shows that the thermal conductivity does not scale with porosity p as (1-p)(3), suggesting that the percolation of the solid phase is more pronounced respect to the case of a regular "Looyoenga-like" mesophase. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.