Unique negative dimension

The saturation current or, more accurately, the reverse saturation current is that 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. (Steadman 1993, 459)

I_S, the reverse bias saturation current for an ideal p–n diode is given by (Schubert 2006, 61):

$I_{\mathrm {S} }=eA\left({\sqrt {\frac {D_{\mathrm {p} }}{\tau _{\mathrm {p} }}}}{\frac {n_{\mathrm {i} }^{2}}{N_{\mathrm {D} }}}+{\sqrt {\frac {D_{\mathrm {n} }}{\tau _{\mathrm {n} }}}}{\frac {n_{\mathrm {i} }^{2}}{N_{\mathrm {A} }}}\right),\,$

where

I_S is the reverse bias saturation current,

e is elementary charge

A is the cross-sectional area

D_p,n are the diffusion coefficients of holes and electrons, respectively,

N_D,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,

$\tau _{\mathrm {p,n} }$ are the carrier lifetimes of holes and electrons, respectively.

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. (Bogart 1986, 40)

References

• Steadman, J. W. (1993). "Electronics" in R. C. Dorf, The Electrical Engineering Handbook. Boca Raton: CRC Press.

• Schubert, E. Fred. (2006). "LED basics: Electrical properties" in Light-Emitting Diodes : Cambridge Press.

• Bogart, F. Theodore Jr. (1986). "Electronic Devices and Circuits" : Merill Publishing Company