Electrodissolution and Passivation of Silicon in Aqueous Alkaline Media:  A Voltammetric and Impedance Investigation

Abstract

The behavior of Si electrodes in aqueous alkaline media has been investigated by voltammetric and impedance techniques. The flatband potential has been estimated on the basis of Mott−Schottky plots and photocurrent onset as E FB = −1.15 V (SCE) for n-Si and E FB = −0.45 V(SCE) for p-Si. A dissolution/passivation mechanism is proposed, assuming: (1) irreversible electrochemical oxidation of H-terminated Si to a monohydroxylated surface species, which may undergo either (2) irreversible electrochemical oxidation to a dihydroxylated species responsible of 2D surface blocking or (3) chemical dissolution as Si(II) regenerating an H-terminated surface; furthermore, (4) the blocking species may be dissolved chemically as Si(IV); (5) a chemical reaction with water generating monohydroxilated Si (and H2) is also considered. A kinetic model is developed for the case of n-Si, assuming Helmholtz-layer control. The model reproduces the essential experimental features of both J − E curves and impedance diagrams in the active dissolution and passivation regions but is not expected to be realistic in the passive region where 3D surface blocking should be considered.

Anisotropy in the Anodic Oxidation of Silicon in KOH Solution.

“…In both cases, the initial scan prior to anisotropic etching shows a single peak at lower potential, characteristic of the (100) surface. 7,21,22 The anodic current is due to oxidation of the silicon; below the peak potential the semiconductor dissolves, while passivation occurs at higher potential. Subsequently, voltammograms were measured at regular intervals during anisotropic etching.…”

Low Frequency Impedance Studies on Covalently Modified Glassy Carbon Paste

“…On the other hand impedance studies can be used to isolate the faradaic response of a system from the associated effects of double layer. Impedance studies are no longer a new method, it has been used to study semiconductor electrodes [16,17,18], porous paste electrodes [19,20] and redox polymers [21,22]. In most of the studies the electrodes were modeled to a simple R-C combination, which may be suitable in the high frequency spectra.…”

“…In most of the studies the electrodes were modeled to a simple R-C combination, which may be suitable in the high frequency spectra. There are only a few reports on the low frequency region [5,17,18,21]. But in order to study chemical processes at the electrode surfaces it is the low frequency studies, which can provide a better insight.…”

“…As all these enzyme substrate reaction at the electrode surfaces (faradaic processes) are slow processes due to diffusion limitations, slow electron transfer reactions and all these tend to impede the electron transfer processes. Hence simple R-C circuit model is not a good one and a little more complex circuit [17] has to be used. An impedance study can be viewed in more a general way by considering an electrochemical cell as a black box to which certain perturbation is given and output is obtained.…”

Degradation of silicon photonic biosensors in cell culture media: analysis and prevention

“…1 ). Silicon oxide has previously been reported as a passivation layer for silicon devices in aqueous environments [ 9 , 10 ]. Secondly, we show that the SOI etching rate can be greatly reduced by improving the pH buffering of the CCM.…”