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Thermionic diode
Thermionic diode
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Old 30th December 2010, 09:16 AM   #1
ravaner is offline ravaner
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Join Date: Apr 2010
Default Thermionic diode

Hello ! I just discovered in an old document (Dupont Nemours 1952) that Shockley Law is also available for thermionic diode with inverted bias (plate < cathode), this for low currents < 200 ľA, and before space charge appears (Child-Lagmuir). I'm very surprised, where is Fermi level ? where are N & P ? If someone knows a demonstration of this, thanks by advance.
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Old 30th December 2010, 10:28 AM   #2
SemperFi is offline SemperFi  Wake Island
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So what?

...before space charge appears? Cold cathode? In other words in conditions we never use rectifiers?
There are no N & P, just free electrons in the space charge area over the hot cathode.
There may be some leakage going the 'wrong' way, but if so, it's so small it can be effectively ignored.
Actually, I'm no physics master, so can't say for sure.
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Old 30th December 2010, 11:13 AM   #3
DF96 is offline DF96  England
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If you erect a potential barrier (reverse bias) near an electron 'gas' (in the cathode) then classical/quantum physics says that the tail of the Boltzmann/Fermi distribution will allow some electrons to overcome/tunnel the barrier. The result is an exponential response.

The Fermi level is in the cathode.
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Old 30th December 2010, 11:48 AM   #4
ravaner is offline ravaner
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Of courses N & P carriers were a joke . Thanks for your explanation which shows why we retieve the Boltzmann / Fermi statistic from which Shockley law is issued. For info the diode uses indirect heating (filament) and is parallelized with very high value resistors in a transimpedance amplifier (electrometer).
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