FET operation

[pyz]

Hi all,

This is probably a silly question: what is the reason that conductance is not modulated when we gate a metal? Is it because the metal screens the effect of the gate, or is it because there is such a huge carrier concentration that the added (or depleted) carriers due to the gate go unnoticed?

Cheers,

pyz

[Enthalpy]

The number of charges added or subtracted from a metal is the same as in a semiconductor (if the gate oxide layer or depleted region are as thick), but with a metal

- There are usually many more charge carriers, unaffected by the gate voltage. Or equivalently, the gate influences an extremely shallow portion of a metal;

- Metals have no bandgap. Even if you add or remove charge carriers, you get no situation where all the mobile charge carriers have been removed.

 

There might be some way out - please take with caution, that's hypothetical. We can make extremely thin layers of anything presently, for instance single-atom layers. The band structure differs in thin layers, so some metals might have a bandgap as a thin layer. Also, the number of charge carriers to remove isn't that big in a monoatomic layer. Then a FET might be possible with a metal channel.

 

The next question is: how useful could it be? We are limited by the number of charge carriers that are controlled by the gate: the same for a semiconductor and a metal - but charge carriers are more mobile in a semiconductor than in a metal (at least a bulk metal), which permits to control a bigger conductance.

 

FET are being experimented with a graphene channel, which is allegedly interesting because charge carriers are so mobile in graphene - advantage over silicon and metal.

[pyz]

Graphene is actually proof that even a monoatomic metal (or zero band gap semiconductor to be precise) can't be used successfully in a FET (af least not a conventional one).

[Delbert]

 

Hi all,

This is probably a silly question: what is the reason that conductance is not modulated when we gate a metal?

What do you mean by 'gate a metal'?

 

I understand it's the squeezing by varying the depletion layer in an FET. How would one do that with a conductor like a metal?