- The n-type semiconductor can be produced by doped some pentavalent atoms into a semiconductor.
- Pentavalent atoms are atoms that have 5 electrons in the valence shell. Examples of pentavalent atoms include antimony and phosphorus.
- The figure above shows how the silicon crystal appears after doped with a phosphorous atom, which is pentavalent.
- We can see that, the pentavalent atom form 4 covalent bonds with the silicon atoms around. Since a pentavalent atom has 5 electrons, there is an extra electron left over and it is a free electron.
- Each pentavalent in the silicon crystal produces one free electron. Therefore, the pentavalent atom is called the donour.
- The more pentavalent impurity that is added, the more free electrons in the semiconductor, and hence the greater the conductivity of the semiconductor.
- Some holes will also be formed in the semiconductor when some electrons are promoted to shell with higher energy level.
- The free electrons outnumber the holes, hence they are called the majority carrier and the holes are called the minority carriers.
- Since the negative charge carrier (the electrons) outnumber the positive charge carrier (the holes), the semiconductor is called an n-type semiconductor, where the n stands for negative.