Positive, Negative charge flow and Holes in PNP : Confusion

Thread Starter

Willen

Joined Nov 13, 2015
294
Recently I read and knew that when pentavalent (Si) element mixed with tetravalent (Phosphorus), the mixer compound semiconductor becomes NPN because there's an electron extra on its outer cell (8+1). The extra electron is carrier.

And when pentavalent (Si) element mixed with trivalent (Boron), the mixer compound semiconductor becomes PNP because there's a space empty (hole) on its outer cell (7+0). The hole travels for conduction.

This is 'HUGE' thing I just learned as a chemistry. More than this in books are hard to understand for me. So I wish to use simple words and example while answering. One of my confusions is:

- it mean, the battery has electrons and holes both? And and we need electrons or holes (any one) to get the circuit working? And NPN conducts electrons & PNP conducts holes?

My confusion is in concept, so it might sound silly.
 
Last edited:

nsaspook

Joined Aug 27, 2009
7,479
A battery and its wire connections are not semiconductors so 'current' flow and the particles/ions associated with that current flow are different.

I'm not sure what you have learned yet but once you get past the basic explanations you eventually need to understand a 'hole' in a semiconductor is a Quasiparticle. The important thing to know is they have some of the properties of the real particle (positron) but its characteristics are determined by the bulk properties of the compound and lack the full energy properties (electron-positron pair annihilation energy for one) of the real particle.
A hole is a quasiparticle consisting of the lack of an electron in a state; it is most commonly used in the context of empty states in the valence band of a semiconductor.[1] A hole has the opposite charge of an electron.
http://sciexplorer.blogspot.com/2012/05/quasiparticles.html
Example 1: When an electron moves through a semiconductor it interacts with all the other electrons as well as the atomic nuclei in that conductor. These interactions can be very complex. They disturb the electron's motion in such a way that it begins to look like an electron with a different mass altogether moving through empty space.

Example 2: Even more strangely, the general movement of electrons in the valence band of a semiconductor (this is the region where electrons are bound to individual atoms in contrast with mobile conduction electrons elsewhere in the material) resembles what would happen if the semiconductor contained positively charged particles instead of electrons. Physicists call these positively charged quasiparticles holes.
 

Thread Starter

Willen

Joined Nov 13, 2015
294
I thought the positive charge is Hole, comes from positive supply of battery and goes to negative through PNP.
And I thought the negative charge is electrons, comes from negative supply of a battery and goes to positive through NPN.
What are the mistakes I made?
 

nsaspook

Joined Aug 27, 2009
7,479
I know it seems confusing but there is really only electron charge physically moving in all parts of the circuit past the +- terminals of the battery. The local conduction effect of that charge movement changes due to the material structure. They move easily in the wiring ('sea' of electrons in metals) as electrons, electrons to the conduction band or accepting holes in the valence band in (doped) semiconductors or as full atomic species ions with each carrying an electrical charge inside a battery electrolyte.

The individual electron that leaves the battery - terminal doesn't need to fly around the circuit to cause the transistor to operate, the electromagnetic field from the battery is propagated through the metal at nearly light speed to the device causing the local electron or hole effects inside the PNP/NPN transistor while it's still just a electron slowly moving in a wire.
 

Veracohr

Joined Jan 3, 2011
721
In N-type silicon electrons are the majority carrier. In P-type silicon holes are the majority carrier. Both carriers move in both types, but one is the majority. NPN and PNP transistors both have both types of carriers moving in them.
 

Nawaz Zia

Joined Mar 6, 2016
10
Sorry, but that statement makes no sense. :confused:
What's a "bipolar system"?
What do you mean "accurate"?
OH SORRY...............u r right sir..............actually i was dnt knows abt type of material like semi conductor n conductor.....i got this knowledge from senior member nsaspook's statement or reply.....
 

dl324

Joined Mar 30, 2015
11,282
OH SORRY...............u r right sir..............actually i was dnt knows abt type of material like semi conductor n conductor.....i got this knowledge from senior member nsaspook's statement or reply.....
Please take the time to spell out complete words. It'll make reading your posts easier for people who don't do text speak.

Correct sentence structure and capitalization would also be appreciated.
 
Last edited:

MrSoftware

Joined Oct 29, 2013
1,865
Someone with knowledge please correct me, but I've always simplified it in my head by thinking of holes as places where electrons could be, but are not. Like the sliding puzzle game below. As you slide the pieces around, it appears that the "hole" is moving, but in reality it's the real pieces (electrons) that are moving. The hole is just a space, it's not a physical thing. Is my analogy good?

temp.jpg

Also I always thought of a wire, which is full of electrons, as similar to a straw that is full of water. You insert a drop of water in one end and a different drop pops out the other end. The flow of water is nearly instant, but your original drop will take some time to propagate through the straw. The same with a wire; you put an electron in one end and a different electron pops out the other end. Eventually your original electron will propagate through the wire, and while the charge moves at almost the speed of light, the electron itself moves at a slower speed than you would expect.
 

nsaspook

Joined Aug 27, 2009
7,479
Pretty good analogy.

I think a large amount of the confusion comes from people trying to use the atomic physics of single atoms/electrons when the correct behaviors are predicted using the solid-state physics of material science (semiconductors) where there are a gazillion atoms all connected together as a solid. The electrical/physical properties of solid structures made from a single type of atom can be completely different from those of a single atom in isolation. Carbon is a good example.

https://en.wikipedia.org/wiki/Solid-state_physics
 
Top