Doping semiconductors - n-type, p-type

 

John Robert Woodyard (1904 - 1981) a U.S. physicist invented "doping" to improve the performance of semiconductors. Doping means to insert impurities of foreign atoms (e.g. boron (p-type) and phosphor (n-type)) into the existing silicon crystal structure.

 

Semiconductors doped with donor impurities are called n-type, while those doped with acceptor impurities are known as p-type.

By adding an impurity of a valence-five elements - phosphorus - to a valence-four semiconductor in order to increase the number of free charge carriers. The purpose of p-type doping is to create an abundance of holes. In the case of silicon, a trivalent atom - is substituted into the crystal lattice.

Generally, the n-type layer is only some tenth µm thick (approx. 0.2 µm). The layer underneath with approximately 300µm thickness is p-doped positively with boron (i.e. 3 instead of 4 electrons in the outer shell).

It applies for all manufacturing processes, that doping with boron is already conducted during the production of blocks or ingots or poles respectively. The n-doping with phosphor is carried out in a later process step.