Re: mobility of holes

jason wrote:
<deleted>

Since both nmos and pmos currents are due to electron flows, what
really make the mobility different? Just imagine for both type of
devices, the current is due to electron flow, what actually happen in
the mechanism of electron flow in pmos that required us to have a hole
mobility?

Basically, holes can only move one atom at time, since a hole moves by an electron from an adjacent atom filling the existing hole, but leaving a hole associated with the atom from which the electron came.

Conduction band electrons aren't tied to a specific atom in the same way that valence band holes are, so they're free to move more than one atom at a time.

As flow of electron can be explained by the flow of holes to the
opposite direction, then can I say that there is hole flows in the nmos
as well?

I *suppose* so. (I could be wrong.) As far as I can tell, it's basically a matter of convention that people refer to electrons moving in the conduction band vs. holes moving in the valence band.

Kindly enlighten why there cant be a universal mobility parameter for
both pmos and nmos?


See my comments a couple paragraphs above.


Another silly question, when we analyse circuit using KCL, say we use
the conventional current flow from positive terminal to negative
terminal of battery. Is this current flow the flow of hole?

Not really. The concept of holes and electrons really only has meaning when one is talking about energy band diagrams and related concepts. With KCL and conventional current flow, you're basically making the (incorrect) assumption that current flow is due to the motion of positive charges. However, there's no difference in most situations between positive charges moving up/right and negative charges moving down/left. (Off-hand, the Hall effect is the only case I can think of where the sign of the moving charge matters. If the moving charge flips sign, the resulting Hall voltage changes polarity. I *believe* (but could easily be wrong) that Hall effect measurements were what lead to the conclusion that in p-type semiconductors, it is more appropriate to talk about positive holes moving than negative electrons moving.)

Are we
talking about the same "hole" for circuit and those in valance bands?


As discussed above, the answer is "No".

Bob Pownall
.

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