Impedance of porous Si

The impedance of photoelectrochemically etched n-Si was measured in a liquid junction made of a methanolic solution of oxidized and reduced dimethylferrocene. The results show that both the equivalent circuit and each of the individual elements are almost identical with those of the smooth Si that was used as a substrate. These results were interpreted in terms of a depletion layer model in which the space-charge layer is present only at the bottom of the macropores and at the interface between the electrolyte and the smooth part of the substrate. The poles that separate the pores are completely depleted of majority carriers. The nanoporous layer that is deposited on top of the macropores and can be removed by KOH is completely transparent to the impedance measurements.