Conduction in semiconductors

Natural germanium (silicon etc.) has a small number of electrons with enough thermal energy in the lattice to occupy states in the conduction band. Increasing the temperature makes more electrons available and the conductivity increases.

As an electron in the conduction band moves through the lattice it leaves behind a hole (vacancy). In response to an applied electric field positive holes move in the direction of the field, and electrons move in the opposite direction.

n-type

Adding a low level of phosphorous from Group 5 adds extra electrons to the conduction band. The doped semiconductor now has electrons as majority carriers.

p-type

Adding a low level of arsenic from Group 3 adds extra holes to the conduction band. The doped semiconductor now has holes as majority carriers.

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