1. milly molly mandy

    Thread Starter Member

    Sep 4, 2008
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    To the Administrators,

    Re your request for "proofreading" for your Introduction to Diodes, I've just noticed that on about the 10th line down, it says that when forward-biased, the Diode is like a switch that is off. This is wrong isn't it? I'm only a beginner, so I could be mistaken.

    Thanks for all your excellent articles anyway which have really helped me. I'm about to see if you can clarify me a little in your various articles on pnp and npn stuff and those funny things called "holes" . I've tried other text books, but my head just spins, and basically I can't understand how they can say that the holes move, when really it's just the electrons moving in the opposite direction..Mmmmmm. Maybe tomorrow I'll ask on your forum too.

    Another thing is, I agree with you that its really ridiculous letting all those old fogeys make us think in Conventional Current terms, it's like being forced to believe in a ridiculous old heathen religion, even when you know it's all made up. And what's more, being forced to think in 2 opposite directions, when only one of them (electron flow notation) is the correct one is downright crazy. I like the way you put those electron flow black arrows under your diode diagrams, that really helped me to perceive it all a little more clearly,
     
    Last edited: Dec 3, 2008
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    You are right. Holes are some imaginary particles, in reality they do not exist as particles. Also, if say the place where an electron is missing is called hole, this hole can not move. Its the electrons which move in the opposite direction as you have already mention and it is said that holes move for simplicity. It makes things being understood better.
     
  3. Ratch

    New Member

    Mar 20, 2007
    1,068
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    milly molly mandy,

    Don't bother, I will tell you right now. Holes are a quantum phenomenon that cannot be accurately modeled as a macro event. Their drift velocity is about half that of electrons and they have a different effective mass. They are a particle in their own right. Note the snippet from Volume I, Semiconductor Fundamentals by Robert F. Perret, Second Edition, footnote on page 30 "Of prime importance is the drastic simplification resulting from the fact that the quantum-mechanical entities known as electrons and holes may be treated, both conceptually and mathematically, as classical particles."

    It is a intuitive mistake to base the mathematical current direction on the real flow direction of the charge carriers. That is because, although in metals, electrons are the charge carriers. In other cases like electrochemistry, positive ions may be the charge carrier. Or both positive and negative charge carriers may be in play. That is why the conventional current was invented. See post #26 of http://forum.allaboutcircuits.com/showthread.php?t=11410&highlight=perret&page=3 for a fuller description.

    Ratch
     
  4. Dave

    Retired Moderator

    Nov 17, 2003
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    milly molly mandy, we are glad you are getting good use from the e-book and that it is helping you in your studies.

    I have tried to find this in the e-book and I cannot see where it says it is "off"; which as written above is incorrect - when the diode is forward-biased it is like a switch which is on. I did see something similar in Volume III Chapter 3.1 (ref. http://www.allaboutcircuits.com/vol_3/chpt_3/1.html), which says:

    "Closed" and "open" are in this case referring to the physical state of the switch, i.e. the switch is closed (or "on") when forward-biased (and is open (or "off") when reverse-biased - which is correct accepting for the 0.7V forward-biased on-voltage (this is covered later in the chapter).

    You have the basic idea of holes as being physically the absence of an electron and the real physical entity in action in both cases is the electron.

    How does the "hole" move? Lets simplify the scenario at an atomic level; if you consider a hole in a body of electrons, when an EMF is applied the mobile electron respond to the stimulus accordingly. If an electron moves from right to left to occupy the space vacated by the hole, then the physical position of the hole has moved from left to right - the movement of the electron in one direction has resulted in the movement of the hole in an symmetrical direction. On a mass-action scale this is relationship is replicated.

    It causes a lot of confusion and problems. The reasons are mostly historic. We try to ensure that a distinction is made, and where possible make it clear where one methodology is preferential over another. Ultimately use whichever you are happiest with, however electron-flow is distinctly better suited for semiconductor applications.

    Dave
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    I wonder if we could use a chinese checker board and marbles. If all the spots but one are filled, it is a hole. If an extra marble is added, it is an electron. Do you think this analogy might be helpful?
     
  6. Dave

    Retired Moderator

    Nov 17, 2003
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    An analogy that is often used to illustrate the concept of doping. Naturally it can be extrapolated to the wider discussion on the mechanics of holes and electrons.

    Dave
     
  7. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    If I ever fall into a hole I sure wish there were some electrons around to pull me back out, but I doubt that will happen. ;)
     
  8. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    If you have this opportunity, don't loose it !!! You will see a little how this amazing universe works. :p
     
  9. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
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    This is why us OF's appreciate having learned about vacuum tubes first. Since you're working with FREE electrons, everything's a lot more straightforward. You can explain most of what happens in a vacuum tube with Newtonian mechanics. :)

    eric
     
  10. milly molly mandy

    Thread Starter Member

    Sep 4, 2008
    25
    0
    To: Dave the Administrator,

    Hello Dave,

    Thank you for your reply about

    A diode may be thought of as like a switch: “closed” when forward-biased and “open” when reverse-biased.

    which has cleared things up for me. I think perhaps I was getting confused, as I am a beginner. I have to get used to remembering that when a switch is "closed", this means that it is physically closed,as you put it, and that this is when the circuit is activated. Thanks.
    Edit:
    Oh! Why hasn't this message been added to my original thread I wonder?
     
  11. milly molly mandy

    Thread Starter Member

    Sep 4, 2008
    25
    0
    [​IMG] diode like a switch
    To: Dave the Administrator,

    Hello Dave,

    Thank you for your reply about

    A diode may be thought of as like a switch: “closed” when forward-biased and “open” when reverse-biased.

    which has cleared things up for me. I think perhaps I was getting confused, as I am a beginner. I have to get used to remembering that when a switch is "closed", this means that it is physically closed,as you put it, and that this is when the circuit is activated. Thanks.
    Edit:
    Oh! Why hasn't this message been added to my original thread I wonder?
     
  12. milly molly mandy

    Thread Starter Member

    Sep 4, 2008
    25
    0
    Thank you very much everyone for your helpful and interesting replies. I have begun to read through them, including the thorough and in-depth discussions you provided through the links. So far, I have the impression that it is indeed accepted by most people that it is the electrons that move And that "holes" are a concept, used to aid understanding of things like pnp junctions.

    OK, as I sat on my armchair drinking my tea , and thinking about holes and electrons, I realised that the next step for me was to be thoroughly convinced, in my own mind, that it is not illogical, (even if you are only thinking conceptually, for the sake of clarity and understanding of pnp junctions etc ) to talk about exactly the same thing (ie, electron flow), in 2 different ways, which mean exactly the same thing. I think I need to be clear about this first, as it is hard to make further progress in understanding otherwise, I have found.

    I'm about 1/3 of the way through all your replies (thanks), and I already feel I have absorbed a much greater grasp and understanding of the whole thing.

    I had to look up "quantum" in the dictionary, so I'm pleased to have added this new word to my vocabulary.I get the impression that “Quantum mechanics” is about the study of very very small particles and atoms which do not obey the laws of Newtonian physics (whatever Newtonian physics is,!) ( I’ll have to find out!)

    With regard to the Chinese Checkers board, well, I have a Solitaire game, with a circular board with holes and coloured pegs, perhaps that will serve as well. Actually, when I first read about holes and electrons I couldn't quite grasp how it worked, so I put a little row of bits of paper on the arm of my chair, the bits of paper symbolising the electrons, and moved them along one at a time, which certainly helped me see it a little more clearly.
    Dave, your clear statement verifying that as electrons move to the left, holes "move" to the right, helped clarify things a little more for me, thanks..

    Right, I'm now going back to the Diodes explanation in your textbook. So far, I am pleased to say, I have managed to understand your explanation of how the depletion region expands & contracts.















     
  13. milly molly mandy

    Thread Starter Member

    Sep 4, 2008
    25
    0
    TO DAVE THE ADMINISTRATOR

    electrons moving or holes moving?
    Thank you very much everyone for your helpful and interesting replies. I have begun to read through them, including the thorough and in-depth discussions you provided through the links. So far, I have the impression that it is indeed accepted by most people that it is the electrons that move And that "holes" are a concept, used to aid understanding of things like pnp junctions.

    OK, as I sat on my armchair drinking my tea , and thinking about holes and electrons, I realised that the next step for me was to be thoroughly convinced, in my own mind, that it is not illogical, (even if you are only thinking conceptually, for the sake of clarity and understanding of pnp junctions etc ) to talk about exactly the same thing (ie, electron flow), in 2 different ways, which mean exactly the same thing. I think I need to be clear about this first, as it is hard to make further progress in understanding otherwise, I have found.

    I'm about 1/3 of the way through all your replies (thanks), and I already feel I have absorbed a much greater grasp and understanding of the whole thing.

    I had to look up "quantum" in the dictionary, so I'm pleased to have added this new word to my vocabulary.I get the impression that “Quantum mechanics” is about the study of very very small particles and atoms which do not obey the laws of Newtonian physics (whatever Newtonian physics is,!) ( I’ll have to find out!)

    With regard to the Chinese Checkers board, well, I have a Solitaire game, with a circular board with holes and coloured pegs, perhaps that will serve as well. Actually, when I first read about holes and electrons I couldn't quite grasp how it worked, so I put a little row of bits of paper on the arm of my chair, the bits of paper symbolising the electrons, and moved them along one at a time, which certainly helped me see it a little more clearly.
    Dave, your clear statement verifying that as electrons move to the left, holes "move" to the right, helped clarify things a little more for me, thanks..

    Right, I'm now going back to the Diodes explanation in your textbook. So far, I am pleased to say, I have managed to understand your explanation of how the depletion region expands & contracts.

    I'M SORRY ABOUT THE DUPLICATION OF THIS MESSAGE. I KEEP TRYING TO ADD IT TO MY ORIGINAL MESSAGE, BUT IT KEEPS ENDING UP HERE, IN ISOLATION . I think you moved my previous message back on to the main thread? Thanks
     
  14. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    Newtonian physics normal gravity and ballistic motions. An electron in a vacuum (with no charges around) acts pretty much like a rock in a vacuum. In a vacuum tube (which also has a diode configuration) the electrons fly through the vacuum inside the tube responding to charges, ie, newtoniam physics.
     
  15. bertus

    Administrator

    Apr 5, 2008
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  16. milly molly mandy

    Thread Starter Member

    Sep 4, 2008
    25
    0
    Thanks very much everyone for your additional helpful comments which I found to be an interesting way to inwardly absorb this topic a little more.With regard to your comments about the need for simplicity of explanations for a beginner (idiot?!) like me, well I have often thought about this myself.

    Having had some experience myself of trying to teach things (to friends & relatives) I have found that it is very difficult to judge how simple/more complex one's explanations to another person can be!

    While it is good to stretch oneself as far as possible, without your brain completely collapsing (as mine sometimes does), it is indeed also true that it can often help to first build up a solid framework of facts that one has memorised. Then, further information has something it can stick to!

    Thanks Steve B for your comments, which acted for me as a kind of clarification and summing up of what the others had said.

    Right, now I'm going to examine this thread again. Thanks for your help.

    EDIT Oh Thanks Bertus, I'll have a look at it I hope someone can attach these latest posts back on to the main thread?
     
  17. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
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    Any further posts that are not on topic will be removed and if necessary privileges will be removed - this is neither constructive nor is it helping the OP - this is the first and only warning.

    milly_molly_mandy, you have directed some questions in my direction. I have been away over the weekend so let me work through them and I will give answers later.

    Dave
     
  18. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    I think some of this discussion is missing the mark and not helpful to the OP. I think Ratch raises a good point to say that the hole should be viewed as a particle. Also, others are correct to say that someone learning should at first focus on simple concepts. However, really both of these ideas are not contradictory.

    The OP need not study quantum electronics, but needs to only understand the concept of the valence and conduction bands and the distribution of electrons and what that means to charge flow in a semiconductor. These concepts are simple and need no mathematics or detailed background. Yes, it is confusing to put it all together, but that's just the nature of it.

    Basically, the term "hole" is just a short hand way of saying "lack of electron". However, when you solve the quantum mechanical equations, this lack of an electron in the valence band behaves similarly as an electron in the conduction band. Simply put, a "hole" is the lack of an electron in the valence band, while an "electron" is an electron in the conduction band. Both the hole and the electron behave similarly. (same charge magnitude but different mobility)

    Ironically, if you think about it, the confusion is not the term "hole" but the term "electron" because an electron in the valence band is not an interesting charge for current flow in a semiconductor. Only electrons that are excited to the conduction band are interesting, so why don't we give them another name like "plug" or something like that (preferably nothing perverted ;) ). To me, the poor choice of name for the excited electron is a major reason why every one of us struggles with this subject at first.
     
  19. Ratch

    New Member

    Mar 20, 2007
    1,068
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    milly molly mandy,

    Holes are not a concept, they are real. Remember the link I gave you to an authoritative source that said holes have just as much standing as electrons with respect to quantum-mechanical entities? Holes are a semiconductor phenomenon, and have an "effective mass" different from electrons. Holes even live in n-type semiconductors, although their numbers and lifetimes as minority carriers are much less the the majority electrons. Holes have a different mobility than electrons. You will never find a quantum hole in a metal wire because the ocean of electrons in metals will completely swamp a hole before it can ever form.

    Ratch
     
    Last edited by a moderator: Dec 9, 2008
  20. bertus

    Administrator

    Apr 5, 2008
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