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Re: HOLES AS CARRIERS



William Beaty wrote:

In truth, a hole acts to "expose" the positive charge of the
silicon's protons which normally would be canceled out.
It's easy to concentrate on the emptiness of the "hole"
while forgetting that a hole is most definitely a positive
charge carrier.

After being satisfied with the explanation of the "positivity
of holes" I started thinking about it and I am less satisfied.
All materials are made of atoms, systems containing
charged particles (electrons and protons). We learn that
there are no particles called holes, unless the "emptiness",
full of fields, is treated as a set of holes.

A uniform semiconductor, n or p, is electrically neutral. It
remains neutral when a current flows through it due to an
applied difference of potentials. The same is true for metals.
But we do not say that a free electron, drifting from point
A to point B, creates a positively charged region near A.
Why not? What we are saying is that the drift of electrons in
one direction is equivalent to the drift of positive charges.

I am not able to make a good connection between the idea
of donors/acceptors and holes. Thermal transfers of trapped
electrons (from donor atoms or to acceptor atoms), and
reverse processes near-by, can probably be visualized as
random displacements. They occur even when the imposed
electric field is zero. Note that I am referring to uniform
materials, not to junctions.

If presence of acceptors is equivalent to holes then presence
of donors should also be equivalent to holes, unless a hole
is not simply a place in which neutrality is locally destroyed
for a short period of time. Clearly something is missing in
my mental image of reality. Is it because I am using the
semi-classical way of thinking about tiny particles (accepting
the QM band structure without abandoning the idea of
classical drifting) ?

In a message I already deleted Bill wrote that it is wrong to
identify a macroscopic current I (measured by an instrument)
with electrons drifting in metallic conductors. I do not agree.
Consider a wire element dL and the force BIdL acting on it,
for example, in an ammeter. The current density J = I/A=
n*q*v, where v is the mean velocity of drifting electrons.
Ludwik Kowalski