Electrochemical Impedance Study of Porous Silicon Prepared by Metal-Assisted Chemical Etching

Covering with thin metal facilitates the etching of p-type silicon in a solution of HF containing KBrO3, KIO3 or K2S2O8 as an oxidizing agent. Electroless deposition of Ag, Pd or Au was carried out on p-type Si (100) surface before immersion in the etchant solution. The properties of the formed porous silicon layer were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). Ag-enhanced chemical etching of p-Si in 22 M HF containing 0.1 M of KBrO3 or KIO3 led to the formation of micro pores while silicon etching in 22 M HF/0.1 M K2S2O8 after deposition of Ag gave a large-area of silicon nanowires on Si surface. Decreasing the amount of Ag deposited on Si and etching in 22 M HF/0.1 M K2S2O8 caused in formation of nanoproous layer on Si. Pd proved that it is a good assistant for etching of Si in 22 M HF/0.1 M K2S2O8 like Ag and both gave high density of small pores on Si while Au gave a small number of large pores. An appropriate electrical equivalent circuit was used to fit the experimental impedance results of the metal-modified silicon surface in aqueous solution of HF/ oxidizing agent.