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How do electrons and holes move?

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magnetra

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In semiconductor physics, the free electrons are in conduction band while holes are in valence band. When external field (voltage) is applied across a piece of semiconductor, the free electrons are accelerated and drift forward. But what happen to the holes, how do they move about? As my understanding holes can move only with help from other valence band electrons? Please clear me out here.
M
 

Re: Electrons and Holes

the region you are talking about is n type material.... In p type material the valence band electrons are very less and holes are more in number and in p type material the movement of electrons from acceptor to acceptor atom contributes for the movement of holes....
 

Re: Electrons and Holes

Holes are not actualy moving, electrons are... But it looks like holes are moving...
 

Re: Electrons and Holes

holes are basically space left empty by electron as electron gets energy it moves out of valence band to conduction band this movement of electrons create emty regions called as holes
 

Electrons and Holes

Is the effect of external field (voltage) on conduction band electrons and valence band electrons same?
 

Re: Electrons and Holes

the effect is same in terms of field but in terms of movement it is different because conduction band electrons do not undergo that much collision....
 

Re: Electrons and Holes

the free electrons are accelerated and drift forward.

the drift velocity is so well understood by physicists & material science. i'm glad you used the term "drift" properly. the same is true in conductors, the electrons drift down the line.

how many electrical engineers would give you this answer? probably they think the electrons move from the source, through the load and back to the source "at the speed of light" when in actual fact each individual electron moves in the path of conduction at about 1 meter per second... hardly the speed of light.

why are the physicists not talking to the engineers to set them straight? do they think these facts are inconsequential? it is only a matter of application which will determine the fact's usefulness.

but.. if the engineers never know about it there will never be any application.

ho hum... let the wheel spin i guess.

Mr.Cool
 

Electrons and Holes

Flow of holes involves flow of electrons in the valence band. Since flow of electrons constitutes electric current, the flow of valence electrons also results in electric current. However since we already have mobile electrons in conduction band drifting under the influence of external field, considering the flow of valence electrons could be confusion. In order to ease the understanding, the electric current due to flow of valence electrons is explained in terms of flow of holes (which are considered as physical entities with positive charge ). Is my above understanding correct?
 

Re: Electrons and Holes

ya.... your understanding is correct... the main reason for this is the major contribution of which carrier in that region....
 

    magnetra

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Re: Electrons and Holes

in real electron can move hole cannot move
 

Electrons and Holes

keep in mind that Dirac's hole theory first contained holes as its own distinct fundamental partical. one that did not cause mutual annihilation when it met up with its counterpart. more like mutual absorption...

then he realized that this causes negative energy states and he thought this counter intuitive, so dirac ARBITRARILY decided to re-define the hole to mean the absence of an electron.

two very different concepts. yep.. its in the literature but mostly forgotten.

Mr.Cool
 

Re: Electrons and Holes

Dear All,

The discussion has been very interesting.

I quite agree with Mr. Cool, that electrons barely move on few cm (mind you not even meters...!!!! , Ref:- chap-1 M.E. Vanvalkenburg, "N/W analysis", PHI) in practise. So what we r talking is electron (or hole) "current" and not their physical movement..!! Yes, it is this electron (or Hole) current that propagates with the speed of light..!!

The concept of electrons (or holes) in energy band(s) is to convey only their relative energy levels and NOT THEIR PHYSICAL POSITION INSIDE THE ATOM..!! The idea of external biasing is to readjust these levels accordingly, remeber "forward" and "Reverse" biases??

The excitation of charge particles (Holes/Electrons) and their instantaneous movement across the conductor (or semiconductor) is a statistical affair and therefore not predictable accurately. that is why we could only specify RMS values.

Hope this is correct, Let me know if Iam wrong..!!

Sai
 

Electrons and Holes

holes cannot move. we take the flow of electron as flow of holes but in opposit direction
 

Re: Electrons and Holes

hello,
the meaning of holes is a place of electron when electon leave that place ,
so we can assume the direction of holes flow in opposite direction of electrons flow, if we let the flow of electron from right to left , then the flow of hole will be from left to right.
to be this topic clearly please read "Electonic Devices And Circuit Theory" for "Boylestad".
 

Re: Electrons and Holes

So now i concluded from this discussion that..

In both condition electron moves and creates current.

If it is n-type(excess electrons) material we call it caused by electron.

If it is p-type(electrons deficiency) material we call it caused by hole.

Am i right?
 

Re: Electrons and Holes

ya your understanding is right.... also one important thing is electron movement is in conduction band and hole movement is in valence band...
 

Electrons and Holes

Can we call the current due to movement of 'holes in valence band' to be 'conduction current'???
 

Re: Electrons and Holes

classification of current in semiconductors is usually done as drift current and diffusion current...

please tell me what you are talking of when you refer it to as conduction current....
 

Electrons and Holes

plz explain the terms if u have used them!! it actually creats curisirty :p
 

Re: Electrons and Holes

In raghuram_msc post he states the following "The excitation of charge particles (Holes/Electrons) and their instantaneous movement across the conductor (or semiconductor) is a statistical affair and therefore not predictable accurately".
I disagree with this statement. It is absolutely predictable, and controllable, it is called "current flow". As for the movement of holes and electrons (+ for holes,
- for electrons ) because they have opposite charges they both move.

Spectrabei
 

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