# Direction of electron flow in semiconductors

This picture shows how the electrical current actually flows in Silicon material. So current obviously flows from the negative pole of voltage source to the positive. What about holes? Are they moving in reverse direction? Are they even moving in any direction? Do electrons moving from negative to positive pole fill up the holes to move forward?

I have read a few articles about this process but I still have some basic questions. I would be very tankful if anyone would share their knowledge here. Thanks :D

• Sep 3, 2016 at 20:59

There's a little backstory here.

This picture shows how the electrical current actually flows in Silicon material. So current obviously flows from the negative pole of voltage source to the positive.

Conventionally, the direction of current is from positive pole to the negative pole, though the actual direction of electrons is from negative to positive as in the image.

What about holes? Are they moving in reverse direction? Are they even moving in any direction?

The term 'holes' is used in this circuit just because silicon is a semiconductor, which means it can have characteristics of both conductors and insulators. Holes are a term given to absence of electrons. The holes do not move by themselves. But, yes, holes appear to be moving in the opposite direction to electrons, when the electrons in the semiconductor device move from one vacancy to the another.

Hence, here you can say the direction of the current is the direction of the holes!

Do electrons moving from negative to positive pole fill up the holes to move forward?

Yes. With a sufficient amount of kinetic energy (applied voltage), the valence electron of one atom moves out and occupies the hole in its adjacent atom; consequently creating a hole in the atom which the valence electron left. This goes on and appears as if the holes are moving.

This sounds peculiar at the beginning, but as you proceed to learning pn-junctions and diodes, you'll gain a better insight.

Let me know if I cleared you.

• Holes do move, in fact they are every bit as real a quantum mechanical particle as an electron or photon. They have velocity, energy, momentum, charge. Get your physics facts straight before spouting rubbish. The atom that the hole temporariliy resides on does not move. Aug 28, 2016 at 14:31
• In addition to Neil_UKs comment, I will note that the majority carrier (electrons or holes depending on device) determine many characteristics of transistors, because they are at different energy levels (but holes are every bit as real as electrons at the energy level). Aug 28, 2016 at 14:40
• @Neil_UK Thank you for your insight. I tried to stress on the fact that holes don't move by themselves but appear to, when electrons move. I'll edit my answer there. I tried to recheck texts and most of them like Millman and Streetman Banerjee, in their Solid state theory say: "In attempting to form four covalent bonds the three electrons move around trying to form four bonds. This makes the hole appear to move. " or ""An electron moving from a bond to fill a hole leaves a hole in its initial position. Hence the hole effectively moves in the direction opposite to that of the electron." Aug 28, 2016 at 15:08
• @PeterSmith Thanks for your comment. I realize the cognizance of the concepts of majority and minority carriers in differently doped semiconductors, but owing to the OP's very basic knowledge, I preferred to answer so. But, yes, I implicitly made a false point that holes aren't real, which I corrected now. Aug 28, 2016 at 15:13
• @Neil_UK and electronics: I'm very satisfied with your definitions and answers to my question. And I really hope those definitions are as accurate as they can be because I'm just beginning to learn basics of transistors and its details and some of these definitions are gonna be (probably) my knowledge basics. Thank you all for your time! Aug 28, 2016 at 23:34

A hole is the physical absence of an electron where there should (or could) be one.

Think of the marble game "Solitaire". You move a marble from one place to a vacant place. Where the marble was there is now a vacant space. The marble moved in one direction, but the "hole" it moved into has moved in the opposite direction.

While the electron (marble) is a physical item the hole is more of a logical concept that is created by the movement of the electron.

• Both electrons and holes are quantum mechanical particles with energy, charge, velocity, momentum. I'm not sure how you say one is real and the other is conceptual. Aug 28, 2016 at 14:33
• An electron is a physical object. A hole is an absence of a physical object. The charge of both a hole and an electron are real, but the hole isn't a physical thing you can hold in your hand. Aug 28, 2016 at 14:58
• Nothing in quantum mechanics is able to be held in your hand (i.e. localized in both position and momentum) Including electrons. Aug 28, 2016 at 15:24
• I must remind you that quantum mechanics is merely a theory. Quantum mechanics has no place in this discussion. An electron is a real physical object. It can be smashed into other particles (and is done regularly). A hole, at the physical level, is merely an absence of a physical particle. Now if you call the electron a wave, then yes a hole is as real as the electron. But then the electron isn't real either, it's merely a possibility. At the quantum level everything exists and nothing exists. Through observation you collapse it into either the presence or absence of an electron. Aug 28, 2016 at 15:29
• Classical physics describes an electron as a particle, and is what we use when describing the world as we would like it to behave if it were simpler. When we want to describe the world as it actually behaves, we use quantum mechanics. That says that an electron is not a particle, though it has particle-like behaviours in certain circumstances, which is exactly the same that could be said for a hole. In the semiconductor, the way they both contribute to conductivity is best described with quantum mechanics, so there is no huge philosophical difference between them. Aug 28, 2016 at 20:01