In a Cmos or Finfet the current flow is due to movement of the electrons and holes. The free movement depends on the mobility of electrons/holes and factors affects the mobility are lattice scattering and impurity scattering which are dependent on the temperature.
Atoms vibrate more as the temperature increase and this results in collisions with another atoms and causing carriers (electrons/holes) to be free. This collective vibration is called phonon, thus it is also called as phonon scattering. Therefore with increase in temperature the vibrations of atoms increases and more carries are scattered from atoms, this increases the collision between the electrons and reduces the mobility. Despite the decrease in mobility, conductivity increase with the temperature as carrier concentration increases with temperature. Mathematical relation between the mobility and temperature as follows
Impurity scattering is observed in the doped semiconductors. At room temperature the impurities are ionized, and there is electrostatic attraction between the electrons travelling in the lattice and the impurities. As temperature increases the mobility of electron increased which is quite opposite to the Lattice scattering. Impurity scattering is more dominate only at low temperature in doped semiconductors. For better understanding, the electron can travel faster with increase in the temperature and it can escape the attraction forces of the impurity ions. Mathematical relation between the mobility and temperature as follows
we can observe only lattice scattering in intrinsic semiconductor where as in doped conductors we can see lattice and impurity scattering which effects the mobility of the electrons/holes.
In less doped semiconductors, the lattice scattering dominates and thus mobility decrease with increase in temperature.
For heavily doped semiconductors at low temperature as temperature increases the mobility of electrons increases since impurity scattering dominates and at high temperature the mobility decrease since lattice scattering dominates