# Positively charged "holes"?

Discussion in 'General Electronics Discussion' started by darren adcock, Nov 26, 2017.

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Sep 26, 2016
I realised after a conversation with a friend that I'd completely miss-understood how electrons worked especially as I was trying to explain how transistors worked....

So now I understand that electrons are negatively charged and want to move to a positively charged space.... in the tutorials I've watched they've only explained these spaces as holes which are positively charged.... is this correct? But what are these holes? are they vacant spaces on a bigger structure (by structure I mean an atom I guess, I'm really not well versed in physics, but trying to learn)

Does this also mean when I see positive and negative on a circuit that the positive rail is where less electrons are? negative rail is where more electrons are?

As said I know very little physics but have been a little embarrassed I don't know these as I'm assuming this is quite fundamental physics/electronics

I started watching orbitals on the khan academy but got quite baffled which suggests i need to do some more foundational learning.

Darren

2. ### BobK

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Jan 5, 2010
Think of a block of silicon as having a structure that has a specific number of locations for free electrons. Undoped silicon has all of these locations filled. N-doped silicon has extra free electrons, more than there are locations. P-doped silicon has fewer free electrons, not all of the locations are filled.

The unfilled locations are called holes. Electrons can jump from one of these locations to a hole, filling it, and leaving a hole where it was previously. Thus, the holes can be though of as moving in the opposite direction of the electrons.

Now think of a block of P-doped silicon, with it's holes. If we put an electric field across it, the electrons will move toward the move positive side, which means the holes move toward the more negative side. So, the holes act like positive charges.

Bob

hevans1944 and darren adcock like this.
3. ### Ratch

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Mar 10, 2013
It heartens me to observe that even though you lack understanding of some of the quantum physics basics, at least you know and acknowledge your lack. I have had arguments with folks who were clueless, but thought they knew what they were blathering about.

Holes and electrons are a simplified quantum physics model. A hole is more than a missing electron. It has its own "effective mass" and mobility constant, which are different from an electron. Quantum physics treats a hole as a particle, and gets heavily involved in describing it. But for your purposes of expounding on how a bipolar junction transistor (BJT) works, the concept of a hole being a missing electron suffices.

Pure silicon at room temperature contains some free electrons that have dissociated from the silicon atom by thermal agitation. The higher the temperature, the more of these free electrons will be present. At lower temperature the free electrons are scarce, and at absolute zero, no free electrons exist. Thermal dissociation always produces a electron hole pair, so electrical neutrality is maintained. These free electrons have a limited average lifetime because they will fill a vacant hole just as easily as they popped out and left a hole behind. Therefore, an equilibrium will be established, and some free electrons will always be present at a moderate temperature. The number of free electrons are not enough to give silicon much conductivity, so the resistivity of silicon is rather high. It sort of semi-conducts. When a atom loses an electron, it becomes an ion and has a positive charge because it lost a negative electron. i will not get into doping unless you ask a specific question. It is well covered in most transistor textbooks.

Electrons move in a conductive circuit because of electric and magnetic fields. A positive rail has a electric field existing at that position compared to another position. The positive position of the field will attract electrons and the opposite position will repel them. The polarity of the field is determined by whether it attracts or repels a charged particle of a specific polarity.

Ratch

Last edited: Nov 26, 2017

463
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Sep 26, 2016
Thanks guys. These are useful. I will go off and learn some more terms so i can understand exactly, maybe draw myself some diagrams.

I'll have to read these replies over several times as it takes me a while to process written information.

Thanks again

Darren

5. ### hevans1944Hop - AC8NS

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Jun 21, 2012
I started writing something for you, @darren adcock, but I got pulled away to replace a hardside waterbed heater. Then I read @BobK's and @Ratch's excellent replies. Wow! Very concise and to the point. You DO need to understand some quantum mechanics and the math that goes with it if you want to design semiconductors, but Ratch's description and explanation is pretty good as a starting point... and nary an equation in sight!

Darren, if you want to pursue the quantum mechanical physics of it, you are in for a bit of a ride down the rabbit hole, without Alice to guide you on this. There are people here who can and will guide you once you get started. Quantum mechanics, crystals, some chemistry, and lots of mathematics help to explain how transistors work... if you actually understand how transistors work. Sort of an egg versus a chicken problem. I think it helps if you learn the practical applications of semiconductors, even if at first it's "monkey see, monkey do" kind of learning. Then go on to deeper understanding of the how and why if you have the curiosity and an interest in circuit design. Good luck on your journey to better knowledge and understanding!

And a big Thanks! to Bob and Ratch. My reply, verging on the hopelessly pedantic, was saved for perhaps another day and another thread...

Hop

6. ### kellys_eye

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Jun 25, 2010
Personally I've always had issues with understanding the theory as it goes further 'down the rabbit hole' - the level of understanding gets incrementally more difficult the closer you look at it - which tends to leave me even more confused. As a result there comes a point at which you just 'accept the current theory' and work with the effects rather than thinking/considering the physics behind it.

Much like many people can drive a car but not understand the way they work.....

I was taught (and subsequently taught the subject to students myself some years later) but have never had cause or reason to use such knowledge. WHAT a transistor does is more relevant to most people than HOW it does it - this position often causes contortions in underwear but unless you want to be a THEORETICAL user of such knowledge or a PRACTICAL user of such is up to the individual.

hevans1944 likes this.
7. ### Cannonball

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May 6, 2017
This is a very good explanation of how electrons move through semiconductor material.

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Sep 26, 2016
I've been drawing myself some diagrams which let me have an insight at most i guess but even that is progress, but that's ok as I'm quite happily humbled... at heart i'm a geek and haven't pursued any interest without having to nibble away at it roots. My theoretical knowledge will be a drawback but won't stop my enthusiasm. Even if i learn snippets here and there which help me comprehend what's actually going on inside them circuits I'll be very happy.

I would like to understand semi-conductors much more...at the minute i'm just going through op-amp circuits...

all replies here have been most helpful and have sent me off in different ways on google.... need to get my head back into art of electronics book and maybe go through it with some youtube tuturials...

9. ### hevans1944Hop - AC8NS

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Jun 21, 2012
... or flip a light switch or watch a television program or listen the the radio... all these being sufficiently advanced technology indistinguishable from magic and, unlike real magic, requiring no skill to practice.

10. ### kellys_eye

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Jun 25, 2010
which makes 'us' GODS!!!!!!!

I never knew

11. ### Terry01

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Jul 5, 2017
Well said guys,even I understand the way you all explained it and put it in laymans terms. Wait till I tell the Mrs " I am now on my way to becoming a Quantam Mechanic ".....she'll be well chuffed with me!

12. ### kellys_eye

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Jun 25, 2010
Mine would just say "what are you wasting your time on that for?..."

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Sep 26, 2016
Hey, i'm back peeping out of the rabbit hole, maybe scrabbling for air. So I've been trying to understand electric fields (I'm not quite sure how to understand magnetic fields in terms of circuits yet, but hopefully it will pop up in khan academy lessons). I see above Ratch explained explained that electric fields have polarity thus attracting or repelling particles. So a positive rail will attract electrons as the negatively charged particle moves in the opposite direction of a negatively charged electric field? (there was some math here, but I'll struggle remembering that)....And a negative rail will repel electrons as electrons move in the same direction as a negatively charged electric field?

Is this how FET's work also, just realised field effect must mean an electric field, so the gate is usually connected closely to the positive rail which will apply a positive electric field at gate, which draws electrons through into either the source or drain depending on type?

I've come up for air, but doggy paddling at best

D

14. ### Ratch

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Mar 10, 2013
A field is a spatial distribution of a quantity. In the case of an electric field (EF), the quantity is the force exerted on a charged particle (electron, hole, positron, etc). A EF has a strength and direction, not a polarity. It is charged particles that have polarity. An EF can be represented by a vector (magnitude and direction). The EF direction convention is from positive to negative. A negatively charged particle like a electron will be attracted to the positive direction of the EF, and a positive particle will be repelled from that direction. The force direction of a charged particle is the only way to determine the direction of an EF.

FETs use EFs just like everything electrical does. Your above question is too general to be of any use. Perhaps you should stick to how semiconductors are applied before you get too involved in how they work. At least until you know the basics better.

Ratch

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Sep 26, 2016
Ok Ratch, will do. Thanks for your time.

16. ### Terry01

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Jul 5, 2017

That's what mine did say! Hmmmmm