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Semiconductors

Intrinsic semiconductors
In the intrinsic semiconductor the valence band is full, but the conduction band is empty at very low temperatures. The energy gap between the two bands is so very small that electrons can jump across it by the addition of thermal energy alone or even light energy of a suitable wavelength. Heating the specimen or shining a light on it maybe sufficient to cause electrical conduction. The conductivity increases with temperature as more and more electrons are liberated. Intrinsic semiconductors have negative temperature coefficients of resistance.

Extrinsic semiconductors
These are semiconductors to which a very small amount of impurity has been added, this process is called doping. Doping with an impurity can have quite marked effects on the electrical properties of the material. The addition of one impurity atom in one hundred million will increase the conductivity of germanium by twelve times at 300 K.


 
 
 
© Keith Gibbs 2009