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The hole mobility is defined by a similar equation: =. 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).
is the mobility (m 2 /(V·s)). In other words, the electrical mobility of the particle is defined as the ratio of the drift velocity to the magnitude of the electric field: =. For example, the mobility of the sodium ion (Na +) in water at 25 °C is 5.19 × 10 −8 m 2 /(V·s). [1]
Electron and hole trapping in the Shockley-Read-Hall model. In the SRH model, four things can happen involving trap levels: [11] An electron in the conduction band can be trapped in an intragap state. An electron can be emitted into the conduction band from a trap level. A hole in the valence band can be captured by a trap.
The "holes" are, in effect, electron vacancies in the valence-band electron population of the semiconductor and are treated as charge carriers because they are mobile, moving from atom site to atom site. In n-type semiconductors, electrons in the conduction band move through the crystal, resulting in an electric current.
The proportionality constant is known as mobility of the carrier, which is a material property. A good conductor would have a high mobility value for its charge carrier, which means higher velocity, and consequently higher current values for a given electric field strength. There is a limit though to this process and at some high field value, a ...
Drift current density due to the charge carriers such as free electrons and holes is the current passing through a square centimeter area perpendicular to the direction of flow. (i) Drift current density J n {\displaystyle J_{n}} , due to free electrons is given by:
In physics, drift velocity is the average velocity attained by charged particles, such as electrons, in a material due to an electric field. In general, an electron in a conductor will propagate randomly at the Fermi velocity, resulting in an average velocity of zero. Applying an electric field adds to this random motion a small net flow in one ...
In a semiconductor with an arbitrary density of states, i.e. a relation of the form = between the density of holes or electrons and the corresponding quasi Fermi level (or electrochemical potential) , the Einstein relation is [11] [12] =, where is the electrical mobility (see § Proof of the general case for a proof of this relation).