[UPSC CSE 1987] Semiconductors/Solar cell (Q293, 60M)

Define Fermi energy. Show that the Fermi level lays half-way between the top of the valence band and the bottom of the conduction band of an intrinsic semiconductor. Explain why an extrinsic semiconductor, such as an N-type crystal, has more free electrons than holes but is found to be electrically uncharged.