Jim said:
As someone else pointed out, the 1N4xxx devices are also very lightly
doped (almost PIN-diode-like) to get the "high-voltage" performance.
But, Fred, your dissertation sounds just like that... dissertation out
of the mouth of some _twisted_ PhD ;-)
...Jim Thompson
I am miles ahead of you, and this using the most elemental analysis of
the diode Is*(exp(V/VT)-1) diode equation. For low level injection,
which is certainly the case in the example measurements, the
volts-per-decade characteristic derives precisely from Vt and nothing
else. The measurement deviations are not about non-linearity due to Is
dependence on injection level or anything like that. So the explanation
of the behavior goes directly to the estimation of THE POTENTIAL DROP
ACROSS THE TRANSITION REGION AND THE ACCOMPANYING MINORITY CARRIER
CHARGE DENSITIES AT THE BOUNDARIES! Charge neutrality in steady state
requires that the majority carrier densities increase by the same amount
as the minority density at the boundaries, and this creates the
dependence of each minority carrier density upon the other. The
simplified model of say n-sub-P being in ratio to n-sub-N by the factor
exp(V/Vt) no longer holds when the doping densities in the two
complementary regions are of the same order. Anything having to due with
surface diffusion, recombination rates, and/or diffusion lengths all
influence an Is non-linearity and having nothing to do with transition
region fields and potentials. The transition region is the purest
structure in the device, and it is this that determines the
volts-per-decade current dependence.