Editing Electron mobility (section)

{{Short description|Quantity in solid-state physics}}
{{About|the mobility for electrons and holes in metals and semiconductors|the general concept|Electrical mobility}}

In [[solid-state physics]], the '''electron mobility''' characterizes how quickly an [[electron]] can move through a [[metal]] or [[semiconductor]] when pushed or pulled by an [[electric field]]. There is an analogous quantity for [[Electron hole|holes]], called '''hole mobility'''. The term '''carrier mobility''' refers in general to both electron and hole mobility.

Electron and hole mobility are [[special case]]s of [[electrical mobility]] of charged particles in a fluid under an applied electric field.

When an electric field ''E'' is applied across a piece of material, the electrons respond by moving with an average velocity called the [[drift velocity]], <math> v_d</math>. Then the electron mobility ''μ'' is defined as
<math display="block">v_d = \mu E.</math>

Electron mobility is almost always specified in units of [[square centimetre|cm<sup>2</sup>]]/([[volt|V]]⋅[[second|s]]). This is different from the [[SI]] unit of mobility, [[square metre|m<sup>2</sup>]]/([[volt|V]]⋅[[second|s]]). They are related by 1 m<sup>2</sup>/(V⋅s) = 10<sup>4</sup> cm<sup>2</sup>/(V⋅s).

[[Electrical resistivity and conductivity|Conductivity]] is proportional to the product of mobility and carrier concentration. For example, the same conductivity could come from a small number of electrons with high mobility for each, or a large number of electrons with a small mobility for each. For semiconductors, the behavior of [[transistor]]s and other devices can be very different depending on whether there are many electrons with low mobility or few electrons with high mobility. Therefore mobility is a very important parameter for semiconductor materials. Almost always, higher mobility leads to better device performance, with other things equal.

Semiconductor mobility depends on the impurity concentrations (including donor and acceptor concentrations), defect concentration, temperature, and electron and hole concentrations. It also depends on the electric field, particularly at high fields when [[velocity saturation]] occurs. It can be determined by the [[Hall effect]], or inferred from transistor behavior.