## Band Gap Theory of Conduction

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• I know that conduction of electricity involves the movement of free electrons. Which electrons are not bound to atoms. I m looking at an electron energy chart
Message 1 of 12 , Aug 19, 2013
I know that conduction of electricity involves the movement of free electrons. Which electrons are not bound to atoms.

I'm looking at an electron energy chart of N-type material. I see that many electrons are in the conduction band. Most have got there because of the donor atoms, and a few there from the valence band.

I see that since there are lots electrons in the conduction band, they can be used to effect a current.

I have a similar chart shown almost the same thing, but in that case, there care few electrons in the conduction band, but lots of holes in the valence band.

Okay, I have some questions, but first, let's talk about copper. What is the situation with copper, if you were to draw an energy or band gap chart? I mean, what would be the state of play with electrons and holes? Thanks.
• In a metal the valence band and conduction band overlap. There is no gap, so the electrons can travel freely from one atom to the next without the need to put
Message 2 of 12 , Aug 19, 2013
In a metal the valence band and conduction band overlap.
There is no gap, so the electrons can travel freely from one atom to the
next without the need to put in extra energy.

At least that's how I understand it, never was very good with semiconductor
physics.

ST

On Mon, Aug 19, 2013 at 7:09 PM, Richard59854 <
hobby_electronics@...> wrote:

> I know that conduction of electricity involves the movement of free
> electrons. Which electrons are not bound to atoms.
>
> I'm looking at an electron energy chart of N-type material. I see that
> many electrons are in the conduction band. Most have got there because of
> the donor atoms, and a few there from the valence band.
>
> I see that since there are lots electrons in the conduction band, they can
> be used to effect a current.
>
> I have a similar chart shown almost the same thing, but in that case,
> there care few electrons in the conduction band, but lots of holes in the
> valence band.
>
> Okay, I have some questions, but first, let's talk about copper. What is
> the situation with copper, if you were to draw an energy or band gap chart?
> I mean, what would be the state of play with electrons and holes? Thanks.
>
>
>
> ------------------------------------
>
>
>
>
>

[Non-text portions of this message have been removed]
• I m guessing that at room temperature, in copper, because the outermost electron is so weakly bound, there are large numbers of electrons in the conduction
Message 3 of 12 , Aug 19, 2013
I'm guessing that at room temperature, in copper, because the outermost electron is so weakly bound, there are large numbers of electrons in the conduction band, that is, free electrons wandering around quite haphazardly in-between the atoms.

--- In Electronics_101@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:
>
> In a metal the valence band and conduction band overlap.
> There is no gap, so the electrons can travel freely from one atom to the
> next without the need to put in extra energy.
>
> At least that's how I understand it, never was very good with semiconductor
> physics.
>
> ST
• That s what I m told. Apparently the electrons fizz about by themselves from thermal motion and applying an electric field just makes them go ever so slightly
Message 4 of 12 , Aug 19, 2013
That's what I'm told. Apparently the electrons fizz about by themselves
from thermal motion and applying an electric field just makes them go ever
so slightly more in one direction, on average.

The numbers of available mobile electrons are so vast it makes more sense
to think of them as a gas or fog rather than individual particles.

If you could move just a tiny fraction of them from one piece of metal to
another you'd measure a huge voltage differential. I don't recall the
numbers but it was quite impressive.

ST

On Mon, Aug 19, 2013 at 7:49 PM, Richard59854 <
hobby_electronics@...> wrote:

> I'm guessing that at room temperature, in copper, because the outermost
> electron is so weakly bound, there are large numbers of electrons in the
> conduction band, that is, free electrons wandering around quite haphazardly
> in-between the atoms.
>
> --- In Electronics_101@yahoogroups.com, Stefan Trethan <stefan_trethan@...>
> wrote:
> >
> > In a metal the valence band and conduction band overlap.
> > There is no gap, so the electrons can travel freely from one atom to the
> > next without the need to put in extra energy.
> >
> > At least that's how I understand it, never was very good with
> semiconductor
> > physics.
> >
> > ST
>
>
>
>
> ------------------------------------
>
>
>
>
>

[Non-text portions of this message have been removed]
• As I understand it, movement of electrons (current) in metals happens in two ways: * by movement of free electrons, whose energy levels puts them into the
Message 5 of 12 , Aug 20, 2013
As I understand it, movement of electrons (current) in metals happens in two ways:

* by movement of free electrons, whose energy levels puts them into the conduction band spread of energy levels. These electrons are free, that is, not bound to atoms.

and

* by movement of holes in the outmost orbitals of atoms. whose energy levels puts them into the valence band spread of energy levels. Movements of holes is actually a movement of electrons between atoms, These electrons have not the energy to be classed as free electrons.

In N type doped semiconductor, doping introduces into the metal a lot of electrons whose energy levels are withing the conduction band. A very few of these conduction band electrons have come out of the valence band, leaving holes.

So, in N type the majority carriers are free electrons, the minority carriers movement of the few holes.

In P type, there are few electrons with energies within the conduction band. But doping has made a large number of holes in that pool of electrons whose energies lie within the valence band. In P type the majority carriers are holes, or movement of electrons whose energies lie withing the valence band, a few electrons make it out of the valence band and make it into the conduction band. These electrons are then the minority carriers.
• I never heard about holes with regards to conduction in metals. Why are you asking this? If one can call these statements asking. You aren t that smiling cat
Message 6 of 12 , Aug 20, 2013
I never heard about holes with regards to conduction in metals.

Why are you asking this? If one can call these statements asking.

You aren't that smiling cat person per chance, right?

ST

On Tue, Aug 20, 2013 at 12:34 PM, Richard59854 <
hobby_electronics@...> wrote:

> As I understand it, movement of electrons (current) in metals happens in
> two ways:
>
> * by movement of free electrons, whose energy levels puts them into the
> conduction band spread of energy levels. These electrons are free, that is,
> not bound to atoms.
>
> and
>
> * by movement of holes in the outmost orbitals of atoms. whose energy
> levels puts them into the valence band spread of energy levels. Movements
> of holes is actually a movement of electrons between atoms, These electrons
> have not the energy to be classed as free electrons.
>
> In N type doped semiconductor, doping introduces into the metal a lot of
> electrons whose energy levels are withing the conduction band. A very few
> of these conduction band electrons have come out of the valence band,
> leaving holes.
>
> So, in N type the majority carriers are free electrons, the minority
> carriers movement of the few holes.
>
> In P type, there are few electrons with energies within the conduction
> band. But doping has made a large number of holes in that pool of electrons
> whose energies lie within the valence band. In P type the majority carriers
> are holes, or movement of electrons whose energies lie withing the valence
> band, a few electrons make it out of the valence band and make it into the
> conduction band. These electrons are then the minority carriers.
>
>
>
> ------------------------------------
>
>
>
>
>

[Non-text portions of this message have been removed]
• I don t know your level of knowledge, so forgive me if I seem to be talking down to you. Your first description of conduction in metals is accurate. The second
Message 7 of 12 , Aug 20, 2013
I don't know your level of knowledge, so forgive me if I seem to be talking down to you.

Your first description of conduction in metals is accurate. The second describes conduction in semiconductors, not metals.

Metals are not used to make semiconductor parts. Semiconductors like silicon, germanium, and now carbon (diamond) are semiconductors. They have four electrons in the outer valance band. The outer valance band, for lack of a better word, "needs" to have 8 electrons. In a crystal structure they link up with four other atoms to share electrons and fill the entire 8 available electron spaces, while still remaining neutral.

Not a very good conductor. But that can be changed.

Doping is the process of replacing some of those atoms with other atoms that have either 5 electrons in the outer band, so there is a "free" electron as there are in metals (N type), or with atoms that have 3 electrons in the outer valance band (P type). In which case, you have a virtual "hole", sort of a virtual positive charge that can move around as if it were an actual positive electron. In fact, electrons are moving in the opposite direction, popping from "hole" to "hole".

For more details, and more accuracy than my extemporaneous babblings, I suggest you do some online searching for sites and videos about semiconductor physics. There are some good videos with great graphics, images always help me understand.

Steve Greenfield AE7HD

--- In Electronics_101@yahoogroups.com, "Richard59854" <hobby_electronics@...> wrote:
>
> As I understand it, movement of electrons (current) in metals happens in two ways:
>
> * by movement of free electrons, whose energy levels puts them into the conduction band spread of energy levels. These electrons are free, that is, not bound to atoms.
>
> and
>
> * by movement of holes in the outmost orbitals of atoms. whose energy levels puts them into the valence band spread of energy levels. Movements of holes is actually a movement of electrons between atoms, These electrons have not the energy to be classed as free electrons.
>
> In N type doped semiconductor, doping introduces into the metal a lot of electrons whose energy levels are withing the conduction band. A very few of these conduction band electrons have come out of the valence band, leaving holes.
>
> So, in N type the majority carriers are free electrons, the minority carriers movement of the few holes.
>
> In P type, there are few electrons with energies within the conduction band. But doping has made a large number of holes in that pool of electrons whose energies lie within the valence band. In P type the majority carriers are holes, or movement of electrons whose energies lie withing the valence band, a few electrons make it out of the valence band and make it into the conduction band. These electrons are then the minority carriers.
>
• As to holes as minority carriers in metals. I think I ve been looking at P type conduction, and making a wrong asumption. In P type I see that some of the
Message 8 of 12 , Aug 20, 2013
As to holes as minority carriers in metals.

I think I've been looking at P type conduction, and making a wrong asumption.

In P type I see that some of the electrons in the valence band will acquire sufficient energy to become minority carriers in the conduction band. And in doing so, will leave holes. These holes would be in addition to the holes made by the doping.

So, I then think of copper and apply similar thinking. And imagine some few electrons in the valence band of copper making it to the conduction band, leaving holes that are minority carriers.

I know, it shows a lack of understanding. Because, as you say, there are no minority carriers, consisting of movement of holes in copper. Well, I don't think so. It's all movement of free electrons in copper.

I don't think movement of holes involves the concept of free electrons.

--- In Electronics_101@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:
>
> I never heard about holes with regards to conduction in metals.
>
>
> Why are you asking this? If one can call these statements asking.
>
> You aren't that smiling cat person per chance, right?
>
> ST
• Something that bugs me: I know that electric current is always the movement of electrons, whether that conduction is in n-type or p-type material. I mean, even
Message 9 of 12 , Aug 20, 2013
Something that bugs me: I know that electric current is always the movement of electrons, whether that conduction is in n-type or p-type material. I mean, even in p-type material, which involves holes as the majority charge carriers, it's stiil electrons moving.

But, are the moving electrons, even in p-type, called free electrons?
• No, they are not free electrons. You might think of each hole as kind of a vacuum pulling on nearby electrons. So if you give an electron a little push with
Message 10 of 12 , Aug 20, 2013
No, they are not free electrons. You might think of each "hole" as kind of a vacuum pulling on nearby electrons. So if you give an electron a little push with an electric field, it doesn't take much to move it from one atom's orbit into the "hole" in another. And although this is really electrons moving, we use the model of a hole, a virtual positive charge, moving in the opposite direction.

Steve Greenfield AE7HD

--- In Electronics_101@yahoogroups.com, "Richard59854" <hobby_electronics@...> wrote:
>
> Something that bugs me: I know that electric current is always the movement of electrons, whether that conduction is in n-type or p-type material. I mean, even in p-type material, which involves holes as the majority charge carriers, it's stiil electrons moving.
>
> But, are the moving electrons, even in p-type, called free electrons?
>
• I remember in college semiconductor physics was the number one weed out class. If you try to make sense of it you will just go mad. Think the average grade
Message 11 of 12 , Aug 20, 2013
I remember in college semiconductor physics was the number one weed out class. If you try to make sense of it you will just go mad. Think the average grade was a D.
Doping a non conducting silicon crystal at 1 part per billion and magically turning it into a conductor doesn't make much logical sense.
The interesting stuff happens at the neutral junction.
• Another question: In a pn junction you get a depletion layer, and what checks it progress is an electric field which builds up beween the two ends of the
Message 12 of 12 , Aug 21, 2013
Another question: In a pn junction you get a depletion layer, and what checks it progress is an electric field which builds up beween the two ends of the junction/diode.

Okay, so that means if I take a diode in hand, there is a potential difference of about 0.7v between the wires?
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