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Theraven1982
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[SOLVED] inversion layer in a MOS
Hello,
I have some questions about MOS devices, and CCD
In a MOS or MIS after applying a voltage on the metal, the valenceband and the conduction band bend downwards (in the usual band diagram) when a positive voltage is applied. (p-type semiconductor).
When the voltage is large enough, the fermi energy (in equilibrium) is above the intrinsic energy level, so that an inversion charge will build up.
The first thing I don't understand is why the electrons make an inversion layer in the first place. I mean, why would the electrons come so close to the oxide/semiconductor boundary in the first place (I understand the electrons are drawn to this boundary by the applied voltage, but why is it such a big deal that the Fermi energy level is larger than the intrinsic level?)
The second thing I don't understand, is what is the use of this inversion layer? Why is the inversion layer necessary in a CCD?
Any help would be greatly appreciated,
thanks in advance,
Oh, and a bonus 'question': I've seen a useful formula for calculating the dark current, but I can't find a reference. It's about this formula:
amount of dark current generated = [tex]CT^{1.5}e^{-E_g/2kT} [/tex]
I've seen it in some books, but none of them make a reference to where it is derived, and I don't have a clue how to derive it myself.
(Maybe this question isn't in the right place here, then I'll try a different subforum).
Hello,
I have some questions about MOS devices, and CCD
In a MOS or MIS after applying a voltage on the metal, the valenceband and the conduction band bend downwards (in the usual band diagram) when a positive voltage is applied. (p-type semiconductor).
When the voltage is large enough, the fermi energy (in equilibrium) is above the intrinsic energy level, so that an inversion charge will build up.
The first thing I don't understand is why the electrons make an inversion layer in the first place. I mean, why would the electrons come so close to the oxide/semiconductor boundary in the first place (I understand the electrons are drawn to this boundary by the applied voltage, but why is it such a big deal that the Fermi energy level is larger than the intrinsic level?)
The second thing I don't understand, is what is the use of this inversion layer? Why is the inversion layer necessary in a CCD?
Any help would be greatly appreciated,
thanks in advance,
Oh, and a bonus 'question': I've seen a useful formula for calculating the dark current, but I can't find a reference. It's about this formula:
amount of dark current generated = [tex]CT^{1.5}e^{-E_g/2kT} [/tex]
I've seen it in some books, but none of them make a reference to where it is derived, and I don't have a clue how to derive it myself.
(Maybe this question isn't in the right place here, then I'll try a different subforum).
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