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# Photodiode IV characteristics

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Two p+-n abrupt junction diodes are made from silicon and are identical except that the donor levels in the 2 diodes are ND_1=10^15 and ND_2 = 1x10^17 cm-3. Sketch on one set of axes the I-V characteristics of the diodes for operation at room temperature. Label each curve. Also sketch on the same (or similar) axes the I-V curves for the diodes at - 100 C. Repeat for 100 C. As the temperature is lowered much further below - 100C, what phenomena would limit the operation of the diodes?

Don't I need to know the saturation current for each of the two diodes? How do I find this based on the donor levels? Do I need to find the built-in voltage as well? I had intended to utilize the diode equation:
I = I_0(exp(eV/kT)-1), but I am not sure how to find the saturation current (I_0) with the dopant concentrations. If you can guide me in the right direction on finding I_0 I can do the rest on my own.

##### Solution Summary

Step wise guide to find saturation current of Photodiode with different dopent concentrations from I-V Characteristics of given diode at different temperatures.

##### Solution Preview

PLEASE SEE ATTACHED pdf FILE FOR PROPER VIEW OF EQUATIONS

As student knows how to perform calculation of current I = I_0(exp(eV/kT)-1), Following discussion explains step-wise method for finding I_0 only. (For Properly readability of equations in this solution it is recommended to see attached pdf file).

In this problem you will need to have idea of saturation current for both diodes as ultimately for considering current for I-V curve you will need value of saturation current. For p-n junction diode the saturation current is given by(Ref.1),

I_0=q A ((D_N∙n_i^2)/(L_N∙N_A )+ (D_P∙n_i^2)/(L_P∙N_D ))

Where,
q = charge of charge carrier = 1.6E-19
A = are of junction
DN & DP are diffusion constant in N type and P type respectively.
LN & LP are diffusion length in N type and P type respectively.
NA and ND are acceptor and donor level respectively.
n_i is intrinsic charge carrier ...

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