| Summary: | 碩士 === 國立中央大學 === 能源工程研究所 === 101 === Porous silicon has unique characteristics of optics, photoelectric, thermal ,chemistry etc.. It has been used in different area, for example, in photodetectors, biosensors, chemical sensors, and gas sensor. Recently, porous silicon has been found as a potential thermoelectric material due to its low thermal conductivity. In general, porous silicon can be made using dry etching, wet etching, and electrochemical
etching, in which electrochemical etching is the most common method to fabricate directional pores due to its low-cost and etching anisotropy. In this study, we fabricate porous silicon on silicon wafer using electrochemical etching. Different porous layer thickness and porosity are made by adjusting the current density and etching time. Thermal diffusivity of porous silicon is measured using transient laser flash method that can avoid the damages of the sample. Since the measured sample is composed of the porous silicon layer and the silicon substrate. To obtain the thermal transport properties of the porous silicon, finite element simulation is performed with the two-layer construction model. In the fabrication of the porous silicon, it is shown that the change of current density can increase the etching rate and the increase in etching time can lead to thicker thickness and higher porosity. The measurement results show
that the thermal conductivity of the porous silicon increase from 150 K to 400 K and reach a plateau. In addition, the thermal conductivity decrease as the porosity increae.
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