Editing Electron mobility (section)

===Definition and units===
{{See also|Electrical mobility}}
The electron mobility is defined by the equation:
<math display="block">v_d = \mu_e E.</math>
where:
*''E'' is the [[Euclidean vector|magnitude]] of the [[electric field]] applied to a material,
*''v<sub>d</sub>'' is the [[Euclidean vector|magnitude]] of the electron drift velocity (in other words, the electron drift [[speed]]) caused by the electric field, and
*''μ''<sub>e</sub> is the electron mobility.
The hole mobility is defined by a similar equation: 
<math display="block">v_d = \mu_h E.</math>
Both electron and hole mobilities are positive by definition.

Usually, the electron drift velocity in a material is directly proportional to the electric field, which means that the electron mobility is a constant (independent of the electric field). When this is not true (for example, in very large electric fields), mobility depends on the electric field.

The SI unit of velocity is [[Metre per second|m/s]], and the SI unit of electric field is [[volt|V]]/[[metre|m]]. Therefore the SI unit of mobility is (m/s)/(V/m) = [[square metre|m<sup>2</sup>]]/([[volt|V]]⋅[[second|s]]). However, mobility is much more commonly expressed in cm<sup>2</sup>/(V⋅s) = 10<sup>−4</sup> m<sup>2</sup>/(V⋅s).

Mobility is usually a strong function of material impurities and temperature, and is determined empirically. Mobility values are typically presented in table or chart form. Mobility is also different for electrons and holes in a given material.