Isn't it
just like the current flowing from positive to negative?
"Hole flow", ugh...one little mistake soooo long ago...
Err yes... And of course the affor on a semiconductor diode or bipolar
transistor symbol points i nthe direction of conventional (+ve to -ve)
current flow through the device.
[As an aside, and nothing to do with hole/conventional current, at one
time, the _cathode_ of a semiconductor rectifier was labelled with a '+'
sign -- like this :
\ | +
----->|--------
/ |
The explaination was that this is the side you connectto the +ve output
terminal when maing a half-wave recrtifier (!).]
I once tied a physics teacher up in mental knots... Whe had bee
discussing what happens if you pass a current through a slab of material
with a perpendicualr maginetic field. Obviousl ythe moving charge
carriers are deflected by said field towards the other 2 faces of the
slab, and a voltaeg is thus set up between them. This is the Hall Effect,
of coruse, as used in Hall Effect sensors and the like.
Now it turns out that hhat if you keep the polarity of the current source
and magneitc field constant, the driection that the charge carriers are
deflected is independant of their sign -- if the sign is reversd, the
direction of motion of the charge carriers along the slave is reversed,
which compentsates for the fact that the magnetic force's direction also
depends on the polarity of the moving charge. The othe polarity of the
voltage tyhat's set up does depend o nthe sign of the charge carriers.
This is an experimentlaly-observed fact, and is one way of telling n-type
from p-type materials.
I then pointed out that he had told us the week befroe that the hole
current was actually an electron current goign the other way, filling up
the holes.
So my question was 'OK, if that's the case, why does the Hall voltage
reverse in sign?'
Yes, OK, I was evil. There is acutaly no classical explanation for this...
-tony
