Effect of ethanol on the photoelectrochemical fabrication of macroporous n-Si(100) in HF solution

The effect of ethanol on the photoelectrochemical fabrication of macroporous n-type Si(100) (pore diameter 50 nm) in 2.0 M hydrofluoric acid was investigated. A cross-sectional scanning electron microscope examination revealed the formation of rough bigger pores (diameter≈7-8 μm) in the absence of ethanol but smooth smaller ones (diameter≈3-4 μm) in the presence of ethanol when the silicon was etched at 0.250 V (vs saturated calomel electrode) under 50 W illumination for 3 h. Characteristic electrochemical properties, such as limiting current density (ilimit), half-wave current density (il2), transition potential (Etrans), and half-wave potential (Ep2) were derived from dc polarization. Electrochemical impedance spectroscopy conducted at Etrans and Ep2 was helpful to illustrate the kinetics of the photoelectrochemical reaction. An additional inductive loop in the Nyquist plot occasioned at low frequencies in the presence of ethanol was attributed to the relaxation of the adsorption of ethanol in the pores. Addition of ethanol in the etching solution led to a decrease of contact angle between the solution and the silicon. Wetting behavior of ethanol plays an important role in the formation of smooth and small macropores.