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The drift current, by contrast, is due to the motion of charge carriers due to the force exerted on them by an electric field. Diffusion current can be in the same or opposite direction of a drift current. The diffusion current and drift current together are described by the drift–diffusion equation. [1]
The drift velocity is the average velocity of the charge carriers in the drift current. The drift velocity, and resulting current, is characterized by the mobility; for details, see electron mobility (for solids) or electrical mobility (for a more general discussion). See drift–diffusion equation for the way that the drift current, diffusion ...
This diffusion current is governed by Fick's law: = where: F is flux. D e is the diffusion coefficient or diffusivity; is the concentration gradient of electrons; The diffusion coefficient for a charge carrier is related to its mobility by the Einstein relation.
The convection–diffusion equation can be derived in a straightforward way [4] from the continuity equation, which states that the rate of change for a scalar quantity in a differential control volume is given by flow and diffusion into and out of that part of the system along with any generation or consumption inside the control volume: + =, where j is the total flux and R is a net ...
drift of carriers, driven by the electric field, with electrons being pushed one way and holes the other way; diffusion of carriers from zones of higher carrier concentration to zones of lower carrier concentration (following a gradient of chemical potential). These two "forces" may work one against the other at any given point in the cell.
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Current is the movement of charge. The continuity equation says that if charge is moving out of a differential volume (i.e., divergence of current density is positive) then the amount of charge within that volume is going to decrease, so the rate of change of charge density is negative.
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