Extrinsic Semiconductors

The carrier concentration of an intrinsic semiconductor is far too small for practical electronic devices. Extrinsic semiconductors solve this by doping -- deliberately adding a small, controlled concentration of impurity atoms (dopants, typically about 100 parts per million) to the pure crystal, which increases the concentration of one type of charge carrier by orders of magnitude and hence increases the material's electrical conductivity in a controllable way. Depending on which group of the periodic table the dopant comes from, …