Semiconductor: These are the solids with conductivities in the intermediate range from 10-6 to 104 ohm-1 m-1.Semiconductors are of two types
(i) n-type of semiconductors
(ii) p-type of semiconductors
n-type semiconductor: When a silicon or germanium crystal is doped with group 15 element like P or As, the dopant atom forms four covalent bonds like a Si or Ge atom but the fifth electron, not used in bonding, becomes delocalised and contribute its share towards electrical conduction. Thus silicon or germanium doped with P or As is called n-type semiconductor, n indicative of negative, since it is the electron that conducts electricity.
p-type semiconductor: When silicon or germanium is doped with group 13 element like B or Al, the dopant has only with three, valence electrons. An electron vacancy or a hole is created at the place of the missing fourth electron. Here, this hole moves through the crystal like a positive charge giving rise to electrical conductivity. Thus Si or Ge doped with B or Al is called p type of semiconductor, (P stands for positive hole) since it is the positive hole that is responsible for conduction.
