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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] It is necessary to consider the part of diffusion current when describing many semiconductor devices. For example, the current near the depletion region of a p–n ...
Shockley derives an equation for the voltage across a p-n junction in a long article published in 1949. [2] Later he gives a corresponding equation for current as a function of voltage under additional assumptions, which is the equation we call the Shockley ideal diode equation. [3]
The Shockley diode equation relates the diode current of a p-n junction diode to the diode voltage .This relationship is the diode I-V characteristic: = (), where is the saturation current or scale current of the diode (the magnitude of the current that flows for negative in excess of a few , typically 10 −12 A).
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 first term of the equations is the drift current, and the second term is the diffusion current.
In a p-n junction diode, electrons and holes are the minority charge carriers in the p-region and the n-region, respectively. In an unbiased junction, due to the diffusion of charge carriers, the diffusion current, which flows from the p to n region, is exactly balanced by the equal and opposite drift current. [1]
In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region, space charge region, or space charge layer, is an insulating region within a conductive, doped semiconductor material where the mobile charge carriers have diffused away, or been forced away by an electric field.
One-dimensional current; Negligible recombination-generation in space charge regions; Negligible electric fields outside of space charge regions. It is important to characterize the minority diffusion currents induced by injection of carriers. With regard to pn-junction diode, a key relation is the diffusion equation.
The saturation current (or scale current), more accurately the reverse saturation current, is the part of the reverse current in a semiconductor diode caused by diffusion of minority carriers from the neutral regions to the depletion region. This current is almost independent of the reverse voltage.