Effect of Ethanol on the Photoelectrochemical Fabrication of Macroporous n-Si(100) in HF Solution

Abstract

The effect of ethanol on the photoelectrochemical fabrication of macroporous n-type Si͑100͒ ͑pore diameter Ͼ 50 nm͒ in 2.0 M hydrofluoric acid was investigated. A cross-sectional scanning electron microscope examination revealed the formation of rough bigger pores ͑diameter Ϸ 7-8 m͒ in the absence of ethanol but smooth smaller ones ͑diameter Ϸ 3-4 m͒ in the presence of ethanol when the silicon was etched at 0.250 V ͑vs saturated calomel electrode͒ under 50 W illumination for 3 h. Characteristic electrochemical properties, such as limiting current density ͑i limit ͒, half-wave current density ͑i l/2 ͒, transition potential ͑E trans ͒, and half-wave potential ͑E p/2 ͒ were derived from dc polarization. Electrochemical impedance spectroscopy conducted at E trans and E p/2 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.

Photoelectrochemical Performance of Anatase TiO[sub 2] Thin Films Deposited by Self-Limiting Growth Techniques

“…ITO has a limited stability during cathodic polarization in acidic solutions. 22 Hydrogen intercalation into ITO and the resulting changes in optical properties have been shown to occur at potentials Ͻ−0.7 V, 23 again consistent with the finding reported here. At a potential of Ϫ0.75 V the absorption edge is shifted to lower wavelengths.…”

Fabrication of Ordered Silicon Wire Structures via Macropores without Pore Wall by Electrochemical Etching

“…In addition, the slope (dJ/dV) of the current density (J) -potential (V) curve decreased largely. This indicates that the resistance of the electrochemical etching process involving the charge transfer increases 16,29 toward the thickness direction of the metal (Ag) as compared to other back contact materials (i.e. Pt, Al, Ti/Au).…”

Galvanic Deposition of Nanoporous Si onto 6061 Al Alloy from Aqueous HF

“…35 They distinguish between different surface conditions partly by the magnitude of the measured capacitance, which is expected to be in the nF cm 2 , F cm −2 , and mF cm −2 range for a space charge layer, Helmholtz layer, and oxide layer, respectively. 35,36 Thus, a best-fit capacitance value in the F cm −2 range is considered as evidence of a Helmholtz layer in potential regimes and at dopant conditions where the surface is not oxidized and no space charge layer forms. The results in Table I are consistent with this criterion, supporting our assertion that Si oxide does not form in the solutions studied here.…”