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Photodiodes
Photodiodes 45
Figure 3.4. Measured current–voltage charateristic of a real photodiode. a) Forward
bias. b) Reverse bias, in the dark, and under illumination.
ue. In practice, the measured forward current is many orders of mag-
nitude less than Eq. 3.13 predicts. This difference is usually modeled
by assuming an ideality factor n (or fudge factor!) in the relationship
between current and voltage:
I = A(e qV/kT – 1) A(e qV/nkT – 1), where n is greater than 1 (3.16)
The ideality factor for a perfect diode is 1. This means that there is
perfect transport of electrons and holes across the junction. When n
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