Electrical conductivity varied at room temperature

little pixie
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Report Thread starter 7 years ago
What is the method that allows electrical conductivity of semiconductor to be varied at room temperature?

Is it complete ionisation?
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Report 7 years ago
(Original post by little pixie)
What is the method that allows electrical conductivity of semiconductor to be varied at room temperature?

Is it complete ionisation?
No. Absolutely not.

This is not something that can be described or understood without diagrams or in the space of a single paragraph. You need to search for appropriate texts to get an understanding.

The following summary applies to a diode junction only.

Look at the periodic table and notice the electron configuration of silicon and germanium.

A pure semiconductor is a poor electrical conductor because the electrons in the valence shell (4) share with the spaces available (4) in adjacent atoms to complete the shell (8). This quadruple valence electron bonding (sharing) ensures there are no free spaces to allow charge flow.

Impurities are added to the base substrate to create adjacent regions: the impurites create a lattice of excess electrons (n-type region) or spaces (p-type region also known as holes) dependent on the impurity throughout the impurity region.

At the juntion between the two regions (p-n junction), there will be a charge differential which causes a local migration of electrons from one region into the other.

The diffusion does not permeate throughout the semiconductor but is localised at the boundary between the different impurity regions.

When an electric potential is applied to the regions, the resulting electric field depletes electrons from one end which creates a potential gradient across the junction and charge is pulled across the depletion region.

i.e, a current flows.

The flow of current thus depends on the pd developed across the junction and also the polarity of the pd. Current will only flow in one direction. This is because electrons will only flow across the junction when the charge differential allows electrons to be attracted from the n-region (excess electrons) into the p-region (deficit of electrons) and not the opposite polarity rather like a fully charged capacitor cannot accept more electrons.

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