Chemistry Reference
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large positive potential values. The thickness of the inversion layer is on the same
order of magnitude as that of the accumulation layer, namely, about 100 Å. An inver-
sion layer does not usually occur at an electrode surface because the electrochemical
reactions generally consume quickly the minority carriers and prevent their accumula-
tion in the surface region. An inversion layer has been found to form on
n
-Si electrode
in a solution of
containing redox couples of high potential
values.
587
The capacitances for the accumulation layer and inversion layer are respectively
given by
The change of capacitance of the charged layer in the surface region of the semicon-
ductor with band bending is illustrated schematically in Fig. 1.8. For negative values
of the surface is in an accumulation and the capacitance is very large because the
thickness of the accumulation layer is thin. As becomes positive, the capacity
decreases as the thickness of the space charge layer increases. When an inversion layer
forms at a large the surface has an excess of minority carriers. In this case the mobile
minority carriers are mostly located near the surface so that the thickness is small com-
pared with the depletion layer thickness and the capacitance increases again. In the case
when minority carriers are consumed by electrode reactions and do not accumulate at
