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Carrier mobility in semiconductors is doping dependent. In silicon (Si) the electron mobility is of the order of 1,000, in germanium around 4,000, and in gallium arsenide up to 10,000 cm 2 /(V⋅s). Hole mobilities are generally lower and range from around 100 cm 2 /(V⋅s) in gallium arsenide, to 450 in silicon, and 2,000 in germanium. [1]
Free electrons in a conductor follow a random path. Without the presence of an electric field, the electrons have no net velocity. When a DC voltage is applied, the electron drift velocity will increase in speed proportionally to the strength of the electric field. The drift velocity in a 2 mm diameter copper wire in 1 ampere current is ...
Electrical mobility is the ability of charged particles (such as electrons or protons) to move through a medium in response to an electric field that is pulling them. The separation of ions according to their mobility in gas phase is called ion mobility spectrometry, in liquid phase it is called electrophoresis.
Because of collisions between electrons and atoms, the drift velocity of electrons in a conductor is on the order of millimeters per second. However, the speed at which a change of current at one point in the material causes changes in currents in other parts of the material, the velocity of propagation , is typically about 75% of light speed ...
At 60 Hz alternating current, this means that, within half a cycle (1/120th sec.), on average the electrons drift less than 0.2 μm. In context, at one ampere around 3 × 10 16 electrons will flow across the contact point twice per cycle. But out of around 1 × 10 22 movable electrons per meter of wire, this is an insignificant fraction.
Electrons are already close to the speed of light, the absolute speed limit, at a few MeV; with further acceleration, as described by relativistic mechanics, almost only their energy and momentum increase. On the other hand, with ions of this energy range, the speed also increases significantly due to further acceleration.
Typical values of saturation velocity may vary greatly for different materials, for example for Si it is in the order of 1×10 7 cm/s, for GaAs 1.2×10 7 cm/s, while for 6H-SiC, it is near 2×10 7 cm/s. Typical electric field strengths at which carrier velocity saturates is usually on the order of 10-100 kV/cm.
This is a result of two facts. Firstly, many plasma sources heat the electrons more strongly than the ions. Secondly, atoms and ions are much heavier than electrons, and energy transfer in a two-body collision is much more efficient if the masses are similar. Therefore, equilibration of the temperature happens very slowly, and is not achieved ...