Anodic Passivation of {111} Silicon in  KOH

Abstract

As part of a comprehensive electrochemical investigation of silicon etching and anodic passivation in KOH , chronoamperometric experiments were performed on precisely oriented {111} silicon to elucidate the mechanistic course of silicon {111} passivation. The resulting current vs. time relationships display multiple current maxima that obey two‐dimensional nucleation and first‐order reaction rate laws. Each current peak has been associated with either the formation of an anodic oxide or the dissolution of an open‐circuit oxide film. Data analysis confirms previous results which show that anodic oxide formation on {111} silicon consumes a fixed quantity of charge of approximately 2.4×10−3C/cm2 for both n‐ and p‐type silicon.

In-situ infrared study of silicon in KOH electrolyte: Surface hydrogenation and hydrogen penetration

“…The current transient following the positive-potential step exhibits a fast and a slow component, like those reported in the literature [11,15]. However, here the current maximum is barely seen.…”

“…At OCP, dissolution proceeds via step flow and, to a lesser extent, by pitting on the terraces [10]. Surprisingly, when the potential is scanned positive of OCP in the dark, a current peak comparable to that on p-Si is also observed, despite the absence of valence band holes [11,12,15]. This anodic current has been attributed to electron injection into the conduction band from surface states associated with intermediates of the chemical etching reaction [10,12,13].…”

“…Consequently, we used the Si(111) surface which has added advantages for a spectroscopic investigation of anodic processes: the chemical etch rate is very low and as a result the rate of evolution of hydrogen bubbles from the surface is limited. Previous studies involving potential-step measurements with n-Si(111) have shown an unexpectedly long induction time for oxide film formation, a feature attractive for kinetic studies [11,15]. These various considerations led us to the choice of atomically flat n-Si(111) as the starting electrode for our study.…”

Oxide Formation and Dissolution on Silicon in KOH Electrolyte: An In-Situ Infrared Study

“…9 Though the initial state of the surface is actually hydrogenated, we have retained the idea of a two-step mechanism, the first step now consisting in the oxidation of SiH groups to NBO sites, and the second step being similar to that proposed by Smith et al, leading to the mechanism summarized in Scheme I. Note that this model implies that there is no direct silicon dissolution channel, i.e., dissolution proceeds solely through oxide formation / oxide dissolution.…”

Macroporous Semiconductors

“…This time constant does not only depend on the general electrolyte composition, pH, and temperature, but also on the crystallography. For example, {111} planes in Si passivate faster and are more stable than {100} planes [ 83 , 84 , 85 ]. It is thus not too difficult to conceive scenarios, where a current flowing through some semiconductor surface is originally uniform, i.e.…”