The saturation current (or scale current), more accurately the reverse saturation current, is the part of the reverse current in a

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...

caused by diffusion of minority carriers from the neutral regions to the

depletion region 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 ...

. This current is almost independent of the reverse voltage. ''I''_S, the reverse bias saturation current for an ideal p–n

, is given by: :

I_\text = e A n_\text^2 \left( \frac \sqrt + \frac \sqrt \right),\,

where :''e'' is

elementary charge The elementary charge, usually denoted by is the electric charge carried by a single proton or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge −1 . This elementary charge is a fundame ...

:''A'' is the cross-sectional area :''D''_p, ''D''_n are the

diffusion coefficient Diffusivity, mass diffusivity or diffusion coefficient is a proportionality constant between the molar flux due to molecular diffusion and the gradient in the concentration of the species (or the driving force for diffusion). Diffusivity is enco ...

s of holes and electrons, respectively, :''N''_D, ''N''_A are the donor and acceptor concentrations at the n side and p side, respectively, :''n''_i is the intrinsic carrier concentration in the semiconductor material, :

\tau_\text, \tau_\text

are the carrier lifetimes of holes and electrons, respectively. Increase in reverse bias does not allow the majority charge carriers to diffuse across the junction. However, this potential helps some minority charge carriers in crossing the junction. Since the minority charge carriers in the n-region and p-region are produced by thermally generated electron-hole pairs, these minority charge carriers are extremely temperature dependent and independent of the applied bias voltage. The applied bias voltage acts as a forward bias voltage for these minority charge carriers and a current of small magnitude flows in the external circuit in the direction opposite to that of the conventional current due to the moment of majority charge carriers. Note that the saturation current is ''not'' a constant for a given device; it varies with temperature; this variance is the dominant term in the temperature coefficient for a diode. A common rule of thumb is that it doubles for every 10°C rise in temperature.

References

{{DEFAULTSORT:Saturation Current Diodes