n-channel enhanecement MOSFET - working: why is it an n-type

[Veek M]

In this MOSFET, when we apply a +ve voltage to the Gate, we repel holes as
the majority charge carrier in the p-type substrate downwards, thus
uncovering fixed acceptor ions/atoms which are now negativly charged
(electrons in the substrate are drawn to this region under the Gate).

We thus create a layer of fixed negative ions (a acceptor atom with a
electron) and Sedra calls this newly formed structure a n-type inversion
layer.

But in n-type materials we normally have fixed donor atoms that have donated
an electron and are now +ve ions.

So..
n-type == '+ve dopant ion, plenty of e'
inversion == '-ve dopant ion'

What am I interpreting incorrectly?

 

If you haven't crossposted this to sci.e;ectronics.design you probably should. this is definitely not a basic question. It has to do with basic semicondutors but alot of people, most engineers don't have to know too much about that kind of stuff. Give them the spec sheets and they design stuff.

Some of them come here, but some of them stay over in design because of stupid questions. Yours is not a stupid question by any means. I just go by the spec sheet so I am useless for a question like this. It is like another branch of the science.

I assume you've aready wikied it and their content was not adequate.

 

[Veek M]

jurb6006@gmail.com wrote:

If you haven't crossposted this to sci.e;ectronics.design you probably
should.
thanks for the heads up.

this is definitely not a basic question. It has to do with basic
semicondutors but alot of people, most engineers don't have to know too
much about that kind of stuff. Give them the spec sheets and they design
stuff.

it's in Sedra which is pretty basic.. you should see: Sze - Physics of Semi,
that's really hairy

Some of them come here, but some of them stay over in design because of
stupid questions. Yours is not a stupid question by any means.
thanks.

> I assume you've aready wikied it and their content was not adequate.
didn't check on the wiki till after you suggested it, but yeah, pretty much
doesn't explain the reason for why it's called: n-type inversion.

 

[whit3rd]

On Friday, April 10, 2015 at 3:13:02 AM UTC-7, Veek M wrote:

In this MOSFET, when we apply a +ve voltage to the Gate, we repel holes as
the majority charge carrier in the p-type substrate downwards, thus
uncovering fixed acceptor ions/atoms which are now negativly charged

We thus create a layer of fixed negative ions (a acceptor atom with a
electron) and Sedra calls this newly formed structure a n-type inversion
layer.

But in n-type materials we normally have fixed donor atoms that have donated
an electron and are now +ve ions.

The 'inversion layer' is still p-type material (as a material property,
in equilibrium, it has free holes and not free electrons). But, once the gate
repels the holes, n-type carriers from the end regions (the drain and source)
can freely travel in that region, and conduction occurs due to those
minority carriers, in that channel.

So, the conduction is n-type (electron) conduction, though the material
is p-doped. If there weren't any gate voltage, the electrons couldn't travel
through, because they'd react (recombine) with the free-traveling holes.

 

[Veek M]

I found this link super helpful in clarifying things:
http://www.onmyphd.com/?p=mosfet.transistor
you guys can check it out.

The key is the n+ doping which creates a asymmetric junction that allows
tunelling from S->G thus introducing charge carriers.