Chemistry Reference
In-Depth Information
Variation of the ratio of
(see Table 5.1) with potential and type of
The fol-
108
silicon indicates that other reaction routes also exist according to Palik
et al
.
lowing reactions are suggested to be responsible for the ratio data observed under dif-
ferent polarization conditions:
According to Palik
et al.
-Si at potentials negative of the reaction is dominated
by reaction (5.22). For
n
-Si at cathodic potential it is a mix of reaction (5.22) and (5.23)
for
p
while reaction (5.24) is increasingly involved with decreasing potential. However, the
terminated
surface which is not in agreement with the later experimental findings that silicon surface
is also terminated, dynamically, by hydrogen in KOH solutions similar to that in HF
solutions.
The ratio of electrochemical to chemical dissolution rate was measured by
Allongue
et al.
22
to be 0.005 for
n
(100) and 0.075 on
n
(111) at OCP in NaOH solution.
The electrochemical portion increases with increasing potential up to the passivation
potential above which it is almost completely an electrochemical reaction. It is postu-
lated that since the silicon surface in KOH solutions is also terminated with hydrogen,
the first step must then involve a dissociation of the Si-H bond by hydrolysis to form
a Si-OH bond.
22,227
Because of the polarization by the Si-OH bond the Si-Si back bonds
are weakened and attacked by water, detaching the partially oxidized silicon atom from
the surface. The detached silicon atom is a radical and will further react with water to
generate another hydrogen molecule. The following are the reaction steps proposed by
Allongue
et al
.
22
reaction scheme described by equation (5.22) to (5.23) results in a
