Electrons and Holes in Extrinsic Semiconductor

Extrinsic Semiconductor

A semiconductor doped with some suitable impurity atoms so as to increase its number of charge carriers is called Extrinsic semiconductor.

Extrinsic Semiconductors are of two types:

i)                    n-type semiconductor

 

  

This semiconductor is obtained by doping tetravalent semiconductor with pentavalent impurities. These semiconductors have free electrons obtained by donors and generated by the thermal process while holes are only due to thermal defects. Hence, electrons are majority charge carriers and holes are minority charge carriers. As most of the current is carried by negatively charged electrons, these are known as n-type semiconductors.

In n-type semiconductor n_e ≫ n_h or n ≫ p.

ii)                  p-type semiconductor

This semiconductor is obtained by doping tetravalent semiconductor with trivalent impurities. These semiconductors have holes created by acceptor atoms and generated by the thermal process while electrons are only due to thermal defects. Hence, holes are majority charge carriers and electrons are minority charge carriers. As most of the current is carried by holes which have effective positive charge, these are known as p-type semiconductors.

In p-type semiconductor n_h ≫ n_e or p ≫ n.