C.2
We find for the constants A and B:
The full solution for the excess electron concentration is therefore
We find for the electron current density
If the emitter is much more highly doped than the base, the current is virtually only carried
by the electrons. This current should be constant anywhere in the device, so also for x = 0,
we find
Using
and
, we finally obtain for the saturation current density
Surface recombination velocity S = 0
Also in this case, we first need to work out the minority carrier distribution. Again, we
start with the continuity equation
Taking into account that in the quasi-neutral region the electric field is zero, that there is
no generation, and that we are considering the steady-state condition, this equation
reduces to
The general solution for this reduced continuity equation is