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# how does tunneling take place in a tunnel diode?

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#### sambireddy

##### Junior Member level 1
do not post the basics of tunnel doide but tell the theory behind the principle of tunnelling.
Tunnelling also takes place in the mos transistors in the form of leakage throught the reverse baised pn junction at the diffusion regions.

heavily doped,1 for every 10*3 atoms,depletion region width is 1 angstrom

thank u for ur reply, but i want to know abt the principle behind the tunnelling..

Tunnelling takes place in diodes having narrow depletion region, which is obtained by increasing the doping concentration. An electron which wants to pass to the other side of the depletion barrier takes an energy equal to the difference between the barrier height and its own energy from the external environment (this will be a little bit confusing), climbs the barrier using the energy it acquired and then reaches the other side.

It doesn't occurr because of an increase in energy - that would be normal conduction.

Let me see if I can explain it a different way. When the doping concentration is very high on both sides of the junction, the depletion region is very thin. In general, carriers are repelled by this barrier since they are not energetic enough to surmount it.

However, as the barrier gets thinner and thinner, quantum mechanics tells us that there is some small but finite probability a carrier is not repelled and instead is found on the other side - and !blink! - it is.

It's the equivalent of throwing a ball against a wall. The probability that it will bounce back is enormous, but after billions of years qm says that one day it will simply pass through and appear on the other side. Try it and see!

electronrancher said:
It doesn't occurr because of an increase in energy - that would be normal conduction.

Let me see if I can explain it a different way. When the doping concentration is very high on both sides of the junction, the depletion region is very thin. In general, carriers are repelled by this barrier since they are not energetic enough to surmount it.

However, as the barrier gets thinner and thinner, quantum mechanics tells us that there is some small but finite probability a carrier is not repelled and instead is found on the other side - and !blink! - it is.

It's the equivalent of throwing a ball against a wall. The probability that it will bounce back is enormous, but after billions of years qm says that one day it will simply pass through and appear on the other side. Try it and see!

Different and nice perspective by electronrancher ...

Yeah as our friend told,it has got to do with Quantum Mechanics. This is the reason why we start to look for nano devices in future.
As the wall gets thinner and thinner(our channel length),so Silicon Dioxide will be still small, then the electron has finite probability to tunnel through the wall and this will not serve the purpose of MOSFET.( As we start to conduct current from Gate.). This theory is also used in teleportation.

avlsi said:
this will not serve the purpose of MOSFET.( As we start to conduct current from Gate.). This theory is also used in teleportation.

avlsi,
how your are correlating MOSFET with tunneling phenomena!

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