Effect of potential steps on porous silicon formation

Porous silicon microstructures were fabricated by applying potential steps through which both anodic and cathodic potentials were periodically applied to silicon wafers. The electrochemical behaviors of porous silicon layers were examined by performing polarization measurements, followed by analyzing the open-circuit potential (E_ocp) and the reaction rate in terms of corrosion current density (j_corr). The surface morphologies and surface products of porous silicon were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It was found that the values of E_ocp and j_corr varied more significantly and irregularly during different polarization stages when the potentials were continuously applied to the wafer surface, while virtually unchanged after 2 min of periodic potential application. In addition, slower reaction rates were observed with applying potential steps, as indicated by smaller values of j_corr. The enhancement on refreshment of silicon surfaces by periodic potential polarization significantly accelerated the growth of porous silicon. The microstructures became more uniformed and better defined due to the improved passivating nature of wafer surfaces.