Confused about Holes :S.. (1 Viewer)

[FrozenSky]

3.2.3 Identify absences of electrons in a nearly full band as holes, and recognises that both electrons and holes help to carry current

I understand this bit.. When an electron in a semiconductor leaves the valence band it leaves a positive “hole”, that is, an atom with one less valence electron than normal. An electron from a nearby atom’s valence band can move and fill the hole, creating a new hole in that valence band.

But i don't understand the bit how they ask me to recognise how both the holes and electrons help to carry current. Isn't the movement of electron from negative to positive itself a current? I'm really confused :S And if that is correct, then how does positive holes help to carry current?

 

[Pwnage101]

Well you're quite right, in that it is the electrons doing the work when we refer to a "hole current". The reason we say it is a hole current, is because if we simply focus on what's going on in the big picture, the hole seems to be moving, and not the electron [however, as you mentioned, yes it is the electrons moving]. Without the hole, conduction in this manner would not be possible. Consider the diagram:

Time 1: *****[ ]*****
Time 2: ******[ ]****
Time 3: *******[ ]***
Time 4: ********[ ]**
Time 5: *********[ ]*
Time 6: **********[ ]

Here *= electron, and [ ] is a hole.

It looks like the hole is moving, hence the name.

 

[darkchild69]

In reality both electrons and holes are responsible for current in a semiconductor and it depends on what is termed their "mobility"

As far as we're concerned in the HSC course, "holes" make it easier for electrons to move, as there are free spaces for the electrons to move into.

Electrons can travel between different positions in the semiconductor lattice to fill the positions left by the electrons which have been promoted into the conduction band.

It is termed "hole current" as it seems as though the holes are moving in the opposite direction to the electron migration in the semiconductor material

decent video on it:

http://www.youtube.com/watch?v=MCe1JXaLEwQ

 

[FrozenSky]

So would be correct if i said this:


When an electron in a semiconductor leaves the valence band it leaves a positive “hole”, that is, an atom with one less valence electron than normal. An electron from a nearby atom’s valence band can move and fill the hole, creating a new hole in that valence band.
When a voltage is applied holes act as a positive flow of current in the valence band moving towards the negative potential, and electrons act as a negative flow of current in the conduction band moving towards the positive potential, therefore electrons and holes may help to carry current