In Spectra Simulation program (Link Corpotration), I tried to reach full depleted stage for this photodiode without applying the bias voltage or changing the doping concentration. Whenever I change the NFermi value in IN file, the potential voltage changes according to the NFermi level. At Z=0, When the NFermi=3.3, the potential voltage equals 4 but when NFermi=13, the potential voltage equals 12.
I'm very confused about the reason.
"Changing" the Fermi level is actually quite similar to applying a voltage on the semiconductor (or to changing of the carrier density, in equilibrium they're all related).
In other words: in the simulation you've artificially increased the potential of the free carriers and you're observing a change in the overall voltage drop...
Absolute values of Fermi Level dont have any meaning. It is important to know what it is being referenced to. In this case I dont know how the zero potential is defined. In any case, the difference in fermi level is equal to the applied external voltage. The difference is all that you should care about.
Hi Nam,
Hope you are doing good,
Fermi level is decided by the doping concentration and type of extrinsic semiconductor. Moreover, fermi level is always measured from the vacuum level. If you dope your p and n-type semiconductor (like Si) heavily, the during junctioning these two semiconductors, fermi level matching and results in Large built-in potential. That means (in other way) that the energy required to match the two fermi level is high.
You can also go to this (http://ecee.colorado.edu/~bart/book/book/chapter4/ch4_2.htm)
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