The random motion of free electrons and holes due to thermal agitation is called

The random motion of free electrons and holes due to thermal agitation is called diffusion.

Key Points

•  Whenever the temperature of the semiconductor increases, the charge carriers within the material i.e. holes and electrons increase due to thermal agitation. As a result, the electrons diffuse from the valence to the conduction band. This process is called diffusion.
• The electrons and holes start vibrating about the mean position. They randomly start moving. 
• For example, in a p-n junction diode, because of thermal agitation, electron and hole pairs are produced. As a result, electrons diffuse from the n to the p side whereas holes diffuse from the p to the n side.