Impedance measurement for microstructure characterization and internal surface estimation of macroporous silicon

摘要

In this paper, a simple and convenient method based on impedance measurement has been proposed for the first time to evaluate the average porosity, pore radius, and internal surface area of macroporous silicon structure fabricated by electrochemical method. The porosity and the average pore radius have been obtained by developing a geometrical model and applying the generalized effective medium approximation theory to the dc and ac impedance measurement of both unoxidized and thermally oxidized macroporous silicon. The internal surface area per unit volume is then computed from the porosity and the pore radius using the same model. The method has been applied to a wide range of porosity from 30 to 58% fabricated on p-type silicon with a resistivity of 10-20 fl cm. Experimental verification of porosity, mean pore radius, and internal surface area have been performed by standard gravimetric technique and by top-view and cross-section SEM imaging, respectively. A typical mean pore radius, porosity, and internal surface area of a macroporous silicon sample has been obtained to be 1.52 μm, 54.2%, and 3565.7 cm~2/cm~3, respectively, from the impedance measurement and 1.5 μm, 55%, and 3666.7 cm~2/cm~3 from SEM and gravimetric analysis which shows that the results are within 2% of the values obtained by conventional methods. The advantages of this method over the other recently reported techniques for similar characterization have been discussed.