question_answer

Distinguish between an intrinsic semiconductor and p-type semiconductor. Give reason, why, a p-type semiconductor crystal is electrically neutral, although \[{{n}_{h}}>>{{n}_{e}}\]?                                   

Answer:

                    The pure semiconductors (Ge or Si) in which the electrical conductivity is totally governed by electrons thermally excited from the valence band to the conduction band are called intrinsic semiconductors. They have equal number densities of free electrons and holes. A tetravalent semiconductor of Si or Ge doped with trivalent impurity atoms of B, Al or In is called a p-type semiconductor. It has \[{{n}_{h}}>>{{n}_{e}}\]. In a p-type semiconductor, the trivalent impurity atom shares its three valence electrons with the three tetravelent host atoms while the fourth bond remains unbonded. The impurity atom as a whole is electrical neutral. Hence the p-type semiconductor is also neutral.