Investigation of thermal transport in n-type porous silicon by photo-acoustic technique

Non-destructive thermal and optical characterization of materials can be successfully performed by the photo-acoustic technique. In this work, this technique has been applied to the measure of thermal conductivity in porous silicon by considering the photo-acoustic response at fixed frequency of samples having the same porosity but different thicknesses. Experimental data are interpreted in terms of a model which takes into account both scattering effects and the contribution to the photo-acoustic signal of the interstitial gas expansion. The measured thermal conductivity is found to be lower than the one reported for crystalline silicon by two orders of magnitude. A discussion of the photo-acoustic signal dependence on the morphology of the porous medium is also presented.