semiconductor

bloguetronica

Joined Apr 27, 2007
1,372
In a p-semiconductor, an electron moves by filling the hole from a adjacent atom and leaving a hole behind. In a sense, the holes are "moving" against the electron flow.
 

bloguetronica

Joined Apr 27, 2007
1,372
If the electrons are not moving, then holes are not moving either.
But when electrons do move, they jump from hole to hole. In a p-semiconductor material, electrons prefer vacant valence shells since those have a lower energy than a complete shell. In a n-semiconductor material, the story is different, since all valence shells around are filled, and the excedentary electrons already have the energy required to create a new valence shell since they are already promoted to this level of energy (they are already in a 1 electron shell and don't need much energy to move to another). In a n-p junction, excedentary electrons from the n-semicondutor tend to fill the holes in the n-semiconductor, creating a i-semiconductor layer (i from intrinsic) and releasing energy in form of light (because electrons are promoted to a lower level of energy). This happens until a potential barrier is created, typically 0.6V in Si.
 

steeve_wai

Joined Sep 13, 2007
47
an anlogy might be of help..(i personally avoid analogies,because they rarely give the "correct" picture):

consider a water tank with a bubble at the bottom.this bubble may be considered as the absence of water.the bubble is less dense and rises up.water fills the place that the bubble leaves.finally the bubble reaches the surface.the situation is similar to the mechanism of conduction in semiconductors,the water is like the electrons and the hole is like the bubble.

the hole is nothing but absence of an electron.it is created when an electron in valence band goes to conduction band.
but this does not mean that valence band electrons have no role to play in conduction in semiconductors.when the appropriate voltage is applied to a semiconducting material,conduction electrons move in the conduction band.
an electron in the valence band occupies a hole in the same band,there by leaving a hole at "its place".this process goes on and on and the hole has effectively "moved".hence we say that:

electronic current occurs in the conduction band whereas hole current occurs in the valence band.

the mechanism is similar to the bubble example...anyway i hope that helped...
 
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