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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).
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where the js are the current densities of electrons (e) and holes (p), the μs the charge carrier mobilities, E is the electric field, n and p the number densities of charge carriers, the Ds are diffusion coefficients, and x is position.
The carrier particles, namely the holes and electrons of a semiconductor, move from a place of higher concentration to a place of lower concentration. Hence, due to the flow of holes and electrons there is a current. This current is called the diffusion current. The drift current and the diffusion current make up the total current in the conductor.
The formula for evaluating the drift velocity of charge carriers in a material of constant cross-sectional area is given by: [1] =, where u is the drift velocity of electrons, j is the current density flowing through the material, n is the charge-carrier number density, and q is the charge on the charge-carrier.
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.
Measured carrier mobilities for electrons and holes are shown in Figure 4. The mobility of carriers in Ga 0.47 In 0.53 As is unusual in two regards: The very high value of electron mobility; The unusually large ratio of electron to hole mobility. The room temperature electron mobility for reasonably pure samples of Ga 0.47 In