When you see a picture in
which EC or EV are drawn as straight lines, then they should be
respectively taken simply as the bottom of conduction band energy levels
and top of valence band energy levels 2 In elemental semiconductors (Si or Ge), the n-type or p-type
semiconductors are obtained by introducing ‘dopants’ as defects In
compound semiconductors, the change in relative stoichiometric ratio
can also change the type of semiconductor