^Extrinsic or doped semiconductors
By adjusting the amount & distribution of doping the conductivity of a SC can be increased to desired amount. Generally the amount of doping is about ppm (i.e. part per million) i.e. one impurity atom is added in 106 pure atoms (i.e. 1016 impurity atoms in 1023 pure atoms per cc). This increases the conductivity more than 103 times.