Carrier Mobility

Carrier Mobility (μn,p) is the measure of ease of charge carrier drift. That is, a measure of how quickly a charge carrier can move through a material. For example, how quickly an electron can travel through a semiconductor.

## Overview

When an electric field is applied across a material, the electrons gain a net velocity in the direction of the field called the drift velocity, defined as

Where the carrier mobility [cm2/Vs] is defined as

Note that this is for both electrons () and holes ().

## Characteristics

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It's worth noting that as the time between collisions () increases, then mobility increases. Likewise, the lighter the particle (), then mobility also increases.

In the case of a semiconductor such as silicon, at a fixed temperature (e.g., ambient temperature), the mobility will depend on doping. For the same doping level, > , therefore holes are "heavier" than electrons. Additionally, for low doping level, will be mostly limited by collisions with lattice (as temperature is increased, will decrease). With medium and high doping levels collisions with ionized impurities will limit mobility.