P-type semiconductor material

[vjee]

Ok i just want to make sure I got this. I'm also new at this..
P-type semiconductor material has large number of, Positive charge or Negative charge?
According to my understanding I would go with positive charge am I right??

 

[carbonzit]

The name is a mnemonic. Think "P" for positive, "N" for negative. So yes, your guess is correct.

P-type material has an excess of "holes". Can you tell us why? What causes "holes"?

 

[KeepItSimpleStupid]

"Hole" flow basically got invented because electron flow is opposite conventional current flow (pos to neg). "Hole" flow is in the direction of conventional current.

See: https://blog.sciencegeekgirl.com/2009/02/27/electron-flow-vs-current-flow/

 

[Ratchit]

vjee,

Ok i just want to make sure I got this. I'm also new at this..
P-type semiconductor material has large number of, Positive charge or Negative charge?
According to my understanding I would go with positive charge am I right??

No, you are not correct, but your study material is probably wrong. Let me explain.

A typical semiconductor material starts off with ultra pure crystalline silicon, to which is added a dopant. For a P-type semiconductor, the dopant is some group 3 material from the periodic table like boron. Both the silicon and boron are electrically neutral, so mixing them will not add or remove charges from the combinant P-type material. It does change the crystalline structure, however. The silicon is looking for 4 valance electrons to complete its orbital, but it only finds 3 valance electrons in the boron. This deficiency is called a "hole". So it "steals" one electron from a neighboring Si-Si bond to fill the hole, but creates another hole where it removed the electron. This action propagates throughout the crystal back and forth. Therefore, the holes are created by the perturbation of the crystal, not by a total net imbalance of charge contained within the crystal. Both P-type and N-type material are electrically neutral, but both transport (conduct) charge due to their deficiency or excess of valance electrons of the dopant. Silicon contains 5E22 atoms per cc. A typical P-type doping concentration is 1E15 atoms per cc, which makes the ratio of silicon to dopant more that 10 million to 1. Numerically the number of dopant atoms is large, but its ratio to the silcon atoms is very small.

Ratch

 

[Ratchit]

KISS,

"Hole" flow basically got invented because electron flow is opposite conventional current flow (pos to neg). "Hole" flow is in the direction of conventional current.

I thought we got you squared away on that point last December. https://www.electro-tech-online.com...how-bipolar-junction-transistors-work.114313/ , posts #8 & #9 .

There are no holes in wires, and conventional current was conceived long before transistors.

Ratch

 

[DerStrom8]

It depends on how you read the question.

You guys are correct with your explanations--Carbonzit and KISS suggest the overall charge, whereas Ratch gets much further into detail. Let's take a look at what the doping does.

Semiconductors are often based around silicon. A silicon atom has four valence electrons, so when they come together they form a sort of lattice as in the picture below:
**broken link removed**
You can see that there are very few "floating" electrons (they are only found around the edges). Because there are no free electrons, it is difficult for current to flow. That is why just pure silicon is an insulator.

Doping, however, changes the number of free electrons. First, let's look at N-type. N-type doping is often done with phosphorus. Phosphorus has five valence electrons, meaning there are five electrons around the outside. When Phosphorus atoms are bonded with silicon, each one has an extra un-bonded electron, as in the picture (sorry for the size):
**broken link removed**
Because of the "extra" electrons, which are free to "move around," it allows current to flow.

Finally, let's look at P-type doping. P-type doping is often done with boron (3 valence electrons). When bonded with silicon, they create "holes" (as carbonzit mentioned) where electrons could be:
**broken link removed**
As you can see, there is a "missing" electron on the right-hand side of the boron atom in the picture.
In this case, the electrons "fit into" the "holes", allowing current to flow, but in a different fashion.

When you have N-type doping, there are "extra" electrons, making the overall charge more negative (hence the 'N'). On the other hand, when you have P-type doping, there are "not enough" electrons, making the overall charge more positive ('P').
I have simplified some of the expressions here to make them easier to understand, so some may not be the scientific way to say it, but at least it is understandable
I hope this helps!
Der Strom

 

[Ratchit]

DerStrom8,

Thanks for correcting me on the difference between boron and phospher. That was a dumb mistake.

When you have N-type doping, there are "extra" electrons, making the overall charge more negative (hence the 'N'). On the other hand, when you have P-type doping, there are "not enough" electrons, making the overall charge more positive ('P').

I have to take issue with the above statement. Both N-type and P-type materal are electrical neutral overall. They both have the same number of electrons to balance the number of protons. A electrometer will not detect any charge on them. Only their crystalline structure is different.

Ratch

 

[DerStrom8]

I have to take issue with the above statement. Both N-type and P-type materal are electrical neutral overall. They both have the same number of electrons to balance the number of protons. A electrometer will not detect any charge on them. Only their crystalline structure is different.

I understand what you are saying, and technically you are right. I guess I should not have phrased it the way I did. The charge within each atom is neutral, as you mentioned (unless some sort of isotope was used ). What I was trying to say was that there is still an "excess" of valence electrons that are not bonded to anything. Because electrons have a negative charge, it is considered to be of a "negative" type. The same goes with the "positive" type, only the opposite.
Der Strom

 

[Ratchit]

DerStrom8,

Agreed. It is the crystalline structure that is perturbed or out of balance, not the atoms themselves.

Ratch

 

[carbonzit]

I'm actually disappointed that all you other folks answered the question I posed about holes. It was intended for the O.P., in what I thought could have been a "teachable moment". Instead, you fell all over yourselves trying to show how much you know.

 

[DerStrom8]

DerStrom8,

Agreed. It is the crystalline structure that is perturbed or out of balance, not the atoms themselves.

Ratch

Exactly. Thank you for pointing that out, Ratch

I'm actually disappointed that all you other folks answered the question I posed about holes. It was intended for the O.P., in what I thought could have been a "teachable moment". Instead, you fell all over yourselves trying to show how much you know.

I apologize, carbonzit, for answering your question directed at the OP. However, it was necessary to explain electron "holes" in order to answer vjee's actual question.
Der Strom