Environmental Engineering Reference
In-Depth Information
being the thermal voltage defined as
where
is the temperature in degrees Kelvin at room temperature),
k
is the Boltzmann's constant and
q
is the charge of an
electron At room temperature, is approximately equal to
26 mV. Typical values of the built-in potential are around 0.9 V.
Under open circuit and steady-state conditions, it can be shown that the
widths of depletion regions are given by the following equations
T
where
is the permittivity of free space
and
is the
relative permittivity of silicon (equal to 11.8).
Dividing (1.7a) by (1.7b) yields
which justifies the fact that
is greater than
if
Moreover,
under this condition, we can further simplify (1.7) in
The charge stored in the depletion region, per unit device area, is found
by multiplying the width of the depleted area by the concentration of the
immobile charge, which can be considered equal to
q
times the doping
concentration. So for both the sides of the device we have
