Semiconductors + p-n junction doubt

1. Apr 20, 2012

HyDraZin3

When electrons from N region diffuse to P region, the electrons combine with holes to form a -ve negative ion leaving behind a +ve ion in P region.So, my doubt is how the holes accept the electrons and get a negative charge because as the holes are positively charged, when they accept the electron which is negatively charged the net charge should be neutral.

THANKS

2. Apr 20, 2012

Staff: Mentor

The holes do not have a positive charge, if they are induced by your doping. The holes are just positions in the lattice where no electron is present. As you have a different nucleus with a different charge there, doping gives you holes without any charges.

3. Apr 27, 2012

HyDraZin3

can you tell me the reason why holes do not have a positive charge on induced doping?

4. Apr 27, 2012

nasu

The net charge of the whole structure (p and n regions) is indeed neutral.
The point is that electrons from the n region combine with holes from the p region (so not from the same region). Before recombination both regions were neutral.
As a consequence of recombination, region n looses some electrons so from neutral becomes positive. Region p gains some electrons (or looses some holes) so it becomes negative. Overall, the n and p regions together have zero charge.

5. Apr 27, 2012

Staff: Mentor

Imagine a perfect, neutral lattice of silicon. Now, at a single position, remove one proton from a nucleus and one electron. It is still neutral, as you removed one positive charge and one negative charge. The silicon atom became an aluminium atom, and as you removed one electron there is a position where a new electron from somewhere else can fit in.
You have a hole, but no charge. If an electron moves to this position, you have a filled hole, and a negative charge.

6. Apr 28, 2012

HyDraZin3

Thank you all for your help but i have a question:-In wikipedia it is stated that electrons recombines with holes, exactly what does recombination mean, do electrons and holes pair together?