When a small amount of impurity atoms are added to a semiconductor then generally its resistivity

Step-by-step solution

The conductivity of a semiconductor is given by ( =n_ e e _ e +n_ h e _ h ) where (n_ e ) and (n_ h ) = number of electrons and holes per unit volume and ( _ e ) and ( _ h = ) mobility of electrons and holes. When impurity atoms are added in a semiconductor, then the concentration of holes and electrons increases. So, the conductivity Increases and hence the resistivity ( ( = 1 ) ) of semiconductors decreases.