MadSci Network: Chemistry

Re: Why are electrons repelled from a positive charge in a semi-conductor?

Date: Tue Aug 29 11:17:56 2000
Posted By: Frank Berauer, Technology Transfer Engineer Microelectronics
Area of science: Chemistry
ID: 964025186.Ch

Hi Bilal Bhatti,

Negative and positive charge ALWAYS attract each other,
NEVER repel. This is the same in a semiconductor as any-
where else.
Maybe I don't understand your question. I will try to
explain what happens in a semiconductor and hope that
clarifies the misunderstanding.
Please feel free to contact me or other Mad Scientists
again if it doesn't.

In a non-doped semiconductor, there are exactly as many
electrons as needed to hold the inter-atomic bonds.
Electrons in bonds cannot move and therefore do not
conduct current. A non-doped semiconductor is thus an

If we, by doping, introduce excess electrons or missing
ones (=holes, which carry a positive charge), those can
move around and carry current.
If an excess electron meets a hole, they annihilate and
emit their energy as light or heat.
At a p-n-junction, all excess electrons and holes near
the junction are attracted to each other and annihilate,
thus creating a zone with no free carriers.

Hope this helps.

Greetings from Singapore,
    Frank Berauer

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