Understanding reverse biasing

[Hazmatac]

So I get that if you hook the "positive" side of the battery up to the part of the silicon doped with negative ions, that electrons will flow from the battery into that region. What I don't get is why the electrons are pulled into the neutral zone between the p and n type silicone, making the gap wider. What principle is pulling the electrons to the neutral zone?

[Hazmatac]

It looks like I may have been wrong about electrons flowing from the battery to the p region, but what really happens is holes flow from the p region to the battery. I don't understand why that would be happening though.

[studiot]

OK so since you have posted this in Chemistry I am going to assume you understand (at least in principle) osmosis.

 

Let me start by offering a correction.

The dopant materials are atoms not ions.

The point is that the elements selected contain one more or one less outer electron than silicon ie 3 or 5.

If such an atom is substituted into a silicon lattice it creates a shortage or excess of one outer electron.

So the shortage or excess is controlled by the doping %

It is important to realise that such atoms also contain one less or one more proton so the electrical neutrality of the lattice is maintained.

Now conduction in lattices occurs by the individual atoms giving up some of their bonding electrons to participate in what amounts to giant molecular orbitals known as metallic bonds.

This form of bonding delocalises the bonds allowing the electrons free roaming from one end of the crystal lattice to the other.

This is how current flows in metals and semiconductors.

If the doped lattice has atoms that add one fewer electron than silicon to this then the material is P type

If the doped lattice has atoms that add one more electron than silicon to this then the material is N type

But remember that the lattice is electrically neutral.

If we then join a piece of P type to a piece of N type we have a chunk of material with mismatched molecular  orbitals, with excess electrons in the N material and deficit in the P type.

This sets up the electrical equivalent of osmotic pressure, that is the potential barrier across the PN junction.

 

Does this help?

[Hazmatac]

Thanks for your reply. What do you mean by electrical netrality of the lattice? What do you mean by orbital? "[metallic bonds] This form of bonding delocalises the bonds" What are metallic bonds, and it delocalises what bonds?

[studiot]

18 hours ago, Hazmatac said:

Thanks for your reply. What do you mean by electrical netrality of the lattice? What do you mean by orbital? "[metallic bonds] This form of bonding delocalises the bonds" What are metallic bonds, and it delocalises what bonds?

Electrons are not electrically neutral because they have a negative charge.

Protons have a positive charge equal but opposite sign to that on the electron.

So the charges balance out in an atom to make the atom electrically neutral, since all atoms have the same number of electrons and protons.

Take one electron away or add one and there is a net charge (positive or negative respectively).

This object is not electrically neutral and is now called an ion not an atom.

 

You posted this in chemistry so I started a chemists answer.

An electricians answer would be simpler.

 

I don't know where you are coming from on this so help me out to help you.

In particular you didn't say if you know what osmosis is.

 

Have a look at this short thread and tell me if you understand my explanation and if the explanation is too easy or what?

 

Sorry I can't do diagrams at the moment, that would make it much easier.

[Hazmatac]

So osmosis, as I understand it, is the balancing of some substance on both sides of an opening. Like, if there is and abundance of salt on one side of the opening but a lesser amount on the other side, the salt will end up in an even amount in both chambers. Less in the chamber that had more, and more in the chamber that had less. 

I understand what you are talking about in your post. Current goes from negative to positive, and the greater the difference in the positive negative gap the greater the power. 

And I get that ions have a charge, but you said that the lattice was neutral, so I didn't understand.

[studiot]

5 hours ago, Hazmatac said:

So osmosis, as I understand it, is the balancing of some substance on both sides of an opening. Like, if there is and abundance of salt on one side of the opening but a lesser amount on the other side, the salt will end up in an even amount in both chambers. Less in the chamber that had more, and more in the chamber that had less. 

I understand what you are talking about in your post. Current goes from negative to positive, and the greater the difference in the positive negative gap the greater the power. 

And I get that ions have a charge, but you said that the lattice was neutral, so I didn't understand.

No that is not osmosis that is diffusion.

When you refer to balancing, the correct term to use is concentration.

Diffusion occurs because of a difference of concentration of some substance or particles such as electrons between one place and another.
The particles of the substance tend to move from higher towards lower concentration.

When there is an opening as you describe this diffusion can take place freely.

If there is some sort of barrier then  a pressure or potential is set up where the particles want to move (diffuse) but can only do so if they can pass the  barrier.

In the case of osmosis the barrier is a semi-permeable membrane.

In the case of a PN junction the barrier is electrical.

 

Can you see how the electron concentration is different in the P and N regions?

 

 

A lattice contains atoms with the ionic central cores in a fixed array and some of the atoms electrons free to roam the lattice, but these electrons are still there.

So the net charge on a lattice is zero.

So it is electrically neutral.

 

It is vital that you understand neutrality to understand PN junctions.

Why are you making things difficult for me by not answering my questions?
They are simply there to help make a better explanatory post.