What are transistors made of?

• Transistors are made of chemical elements in Group IV in the periodic table of elements.
• Most commonly Silicon is used; Germanium is less common.
• These elements form crystals in such a way that the four valence electrons of each atom are shared between neighbors.
• Then, at any time each atom has eight valence electrons on its outer shell.
• This is a very stable state and there are no freely available electrons for conducting a current.
• However, this perfect balance can be disturbed by replacing some of the silicon atoms with atoms from Group V (phosphorus or arsenic) or group III (boron).
• For example, if phosphorus is introduced an extra freely available electron per phosphorus atom is introduced.
• The resulting material is called n-type material.
• Similarly, by introducing Group III atoms, p-type material results.
• By placing p-type and n-type materials next to each other p-n junctions are formed.