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Extrinsic Semiconductors

The addition of a small percentage of foreign atoms in the regular crystal lattice of silicon or germanium produces dramatic changes in their electrical properties, producing n type and p-type semiconductors.

Pentavalent impurities

Impurity atoms with 5 valence electrons produce n-type semiconductors by contributing extra electrons.

Trivalent impurities

Impurity atoms with 3 valence electrons produce p-type semiconductors by producing a "hole" or electron deficiency.

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N-type SC

The addition of pentavalent impurities such as antimony, arsenic or phosphorous contributes free electrons, greatly increasing the conductivity of the intrinsic semiconductor.

the 2-d lattice looks like this

while the enrgy-band diagram is like this

).

P-type SC

The addition of trivalent impurities such as boron, aluminum or gallium to an intrinsic semiconductor creates deficiencies of valence electrons,called "holes".

the 2-d lattice is as this

while the energy band diagram is as this

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