P-Type Semiconductor

n-type Semiconductor

1. A p-type semiconductor can be produced by doped some trivalent atoms into a semiconductor.
2. Trivalent atom is atom has only three valence electrons. Examples include aluminum, boron, and gallium.
   
3. Figure above shows an aluminium atom (which is trivalent ) in the center, surrounded by four silicon atoms.
4. We can see that, the trivalent atom form 4 covalent bonds with the silicon atoms around. Since the trivalent atom has only three valence electrons and each neighbour shares one electron, only seven electrons are in the valence orbit..
5. This means a hole exists in the valence orbit of each trivalent atom. A trivalent tom is also called an acceptor atom because each hole it contributes can accept a free electron.
6. The more trivalent impurity that is added, the more holes in the semiconductor, and hence the greater the conductivity of the semiconductor.
7. Some free electrons will also formed in the semiconductor when some electrons are promoted to shell with higher energy level.
8. The holes outnumber the free electrons, hence they are called the majority carrier and the free electrons are called the minority carriers.
9. Since the positive charge carrier (the holes) outnumber the negative charge carrier (the free electrons), the semiconductor is called a p-type semiconductor, where the p stands for positive.