The drift velocity is the average velocity that a particle, such as an electron, attains due to an electric field.
It can also be referred to as axial drift velocity since particles
defined are assumed to be moving along a plane. In general, an electron
will ‘rattle around’ randomly in a conductor at the Fermi velocity. An applied electric field will give this random motion a small net velocity in one direction.
In a semiconductor, the two main carrier scattering mechanisms are ionized impurity scattering and lattice scattering.
Because current is proportional to drift velocity, which is, in turn,
proportional to the magnitude of an external electric field, Ohm's law can be explained in terms of drift velocity.
Drift velocity is expressed in the following equations:
where is the current density, is charge density (in units C/m3), and is the drift velocity, and where is the electron mobility (in units m2/V·s) and is the electric field (in units V/m).