Editing Electron mobility (section)

===Drift velocity in an electric field===
{{Main|Drift velocity}}
Without any applied electric field, in a solid, [[electron]]s  and [[electron hole|holes]] [[Brownian motion|move around randomly]].{{What|reason=Electrons are bound by metallic bond in silicon... how could they move randomly?|date=May 2025}} Therefore, on average there will be no overall motion of charge carriers in any particular direction over time.

However, when an electric field is applied, each electron or hole is accelerated by the electric field. If the electron were in a vacuum, it would be accelerated to ever-increasing velocity (called [[ballistic transport]]). However, in a solid, the electron repeatedly scatters off [[Crystallographic defect|crystal defects]], [[phonons]], impurities, etc., so that it loses some energy and changes direction. The final result is that the electron moves with a finite average velocity, called the [[drift velocity]]. This net electron motion is usually much slower than the normally occurring random motion.

The two charge carriers, electrons and holes, will typically have different drift velocities for the same electric field.

Quasi-[[ballistic transport]] is possible in solids if the electrons are accelerated across a very small distance (as small as the [[mean free path]]), or for a very short time (as short as the [[mean free time]]). In these cases, drift velocity and mobility are not meaningful.