Re: gEDA-user: Depletion zone

[John Doty <jpd@xxxxxxxxxxxxx>]

On Nov 24, 2006, at 3:46 AM, Karel Kulhavy wrote:

> When a depletion zone in a diode is created, holes are on one side and
> electrons on the other side and the zone is middle.
>
> But electrons and holes attract and they should be attracted  
> together and
> refill the depletion zone again. Why doesn't this happen?

Because in the P part of the zone, the added electrons create a  
negative space charge, while in the N part of the zone, the removed  
electrons create a positive space charge. Remember that on the N  
side, each dopant nucleus has an extra electron *and* *proton*  
relative to the adjacent group IV element, so if you remove its extra  
electron, you have a net positive charge. Similarly, the dopant  
nuclei on on the P side have a proton and electron deficiency: fill  
in the hole, and you get a net negative charge.

There is thus a bulk electric field across the zone that sweeps  
electrons toward the N side and holes toward the P side. That's what  
keeps the zone depleted at equilibrium.

John Doty              Noqsi Aerospace, Ltd.
jpd@xxxxxxxxx




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