Question #d8b67

An intrinsec semiconductor is made by a single and pure substance, like Silicon or Germanium, which have 4 electrons in the last layer.

The atoms are united by covalent connections, sharing those electrons between the atoms, and for this reason each atom keeps 8 electrons in the last layer. At -273°C, it does not have free electrons and is not a conductor.

As the temperature increases, free electrons appear due to the covalent connections breakdown. For each free electron, there is a "hole" (the space previously occupied by the electron). There is nothinh there, but is behaves as it was a positive particle. In the intrinsec semiconductor, the number of electrons and holes is the same.

Now, if we introduce an "impurity" wlth 5 electrons in the last layer, 4 of them will make covelent connections and there will be one more electron. This is called a "N" type crystal, because there are more electrons than holes. This is an extrinsic semiconductor.

If we introduce a substance with only 3 electrons in the last layer, they will make covalent connections and there will be a missing one. Therefore, a hole will appear in the space left by the missing electron. This is the type "P" crystal, because there are more holes than electrons, and is another extrinsic semiconductor.