N-type semiconductor :
When pentavelent impurities are mixed in pure Germanium (e.g. Anti mony or Arsenic are pantavalent) then in newly formed material there is excess of electrons. Therefor valence electrons of four Germanium atom form covalent bond with four electrons of impurity atom one electron is left. It moves freely inside crystal and perform process of conduction. Since on mixing pentavelant material large number of negative charge carries are produced so this type of semiconductor is called N-type semiconductor
P-type semiconductor:
when in Germanium, trivalent impurity atom like Boron, Aluminium etc. are mixed then three electrons of this atom form covalent bond with three electrons of Germanium. For tetrahedral one electron is needed. The place evacuated by electron is called .Here main charge carries are . Such type of semiconductor is called p-type semiconductor.
