Chemistry Reference
In-Depth Information
as potential is increased from OCP to At potentials larger than the anodic reac-
tion is limited by the dissolution rate of the oxide, which, unlike in fluoride solu-
tions, is completely kinetically controlled in KOH solutions. Table 5.7 summarizes
the rate-determining processes identified for the anodic reactions on silicon under
different conditions.
5.12. REACTION MECHANISMS
The rich phenomena observed on silicon electrodes suggest that the detailed
mechanisms of anodic reactions on silicon are extremely complicated. Any successful
model for the mechanisms must account for the essential aspects: (1) variation of effec-
tive dissolution valence of silicon atoms, (2) hydrogen surface termination and evolu-
tion, (3) participation of minority and majority bands, (4) formation and dissolution of
and (5) the effect of doping, potential, solution composition, and illumination.
Numerous models have been proposed focusing on various aspects of anodic reaction
mechanisms since the early works of Turner
33
in the late 1950s and Memming and
Schwandt in the mid-1960s. In this section, a review of the models on the reaction
mechanisms will be given to provide a historical connection among the different
models. Based on these models, an overall reaction scheme is then proposed to account
for the reactions in both HF and KOH solutions and the specific kinetic characteristics.
5.12.1. Tu
rn
er-Memming Model
The reactions involved in the anodization of silicon in aqueous solution, depend-
ing on whether or not fluoride ions are present, as originally proposed by Turner
33
and
Memming and Schwandt,
34
have two different paths determined by the two essential
reactants,
and HF.
