CBSE Class 12-science Answered

The solids with intermediate conductivities between insulators and conductors are termed semiconductors.

(i) n- type semiconductor : It is obtained by doping Si or Ge with a group 15 element like P. Out of 5 valence electrons , only 4 are involved in bond formation and the fifth electron is delocalized and can be easily provided to the conduction band. The conduction is thus mainly caused by the movement of electron.

(ii) p - type semi conductor : It is obtained by doping Si or Ge with a group 13 element like Gallium which contains only 3 valence electrons. Due to missing of 4^th valence electron, electron hole or electron vacancy is created The movement of these positively charged hole is responsible for the conduction.