Temperature-dependent thermal conductivity of porous silicon

The thermal conductivity lambda(PS) of electrochemically etched porous silicon (PS) layers was determined over a wide temperature range (T = 35-320 K) using the dynamic 3 omega technique. Both the doping level of the silicon wafers (p and p(+)) and the porosity P of the porous layers (P = 64-89%) were varied. The measured thermal conductivities were three to five orders of magnitude smaller than the values for bulk silicon. Furthermore, they increase with increasing the wafer doping level and with decreasing the porosity P of the layers. For all investigated PS layers the thermal conductivity increases with temperature. The results are discussed in terms of a simple model for heat conduction in PS based on the phonon diffusion model.