Chemistry Reference
In-Depth Information
The current equations (1.54) to (1.57) can now be expressed in simple forms as follows:
for anodic current,
and for cathodic current,
where is the overpotential, which is a measure of the departure of the
potential drop in the space charge region,
shows the schematic
i-V
curves representing Eqs. (1.63)-(1.66).
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Under an anodic
from that at equilibrium,
Figure 1.15
polarization which provides a positive
increases exponentially with and is
increases exponentially
constant. On the other hand, under a cathodic polarization,
cathodic polarization but remains constant. The exponential increase for
which depends on the supply of holes, is limited for an
n
-type material by the current
of holes. Similarly, the exponential increase of the electron current
with
for
p
-type
material is limited by the current of electrons.
The net current is
This equation can be further simplified by neglecting the contribution due to the minor-
ity carriers. Thus, for an
n
-type material Eq. (1.68) becomes
The current is negative when it is cathodic and positive when it is anodic. Analogously,
the current on a
p-
type material when the contribution of minority electrons is negli-
gible can be expressed as
This form resembles that for the Schottky barrier at a metal/semiconductor interface
that is used in the literature.
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