1. Transport phenomena in metals

Most metals, but also very heavily doped semiconductors, have a very large number of free electrons (of the order of one per lattice atom). These electrons are permanently agitated by random motion with an average velocity, called Fermiv velocity _F , which is of the order of 10 ⁶ m/s (Table 1).This thermal velocity is always very large in front of the velocity acquired by the effect of an applied electric field, called drift velocityv, which is of the order of cm/s as we'll see later. The relatively high value of v _F is due to that of the Fermi energy, which varies from one metal to another. The two quantities are linked by :