Negative differential conductivity

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Negative differential conductivity (NDC) is a nonlinear electrical phenomenon. If J is not a monotonic function of E at some values of E, the conductivity will be negative: \sigma=\frac{dJ}{dE}<0and negative differential conductivity is experienced; that is, in some electric field, the current density decreases as the electric field strength is increased.

Negative differential conductivity has been observed experimentally in tunnel diodes, thyristors, and like structures.

The physical mechanisms that result in such effect are different, but they can be understood generally under processes such as impact ionisation.

Different shapes of the J versus E function exist, which according to the shape, S, N, and Z-type materials can be categorised. In the S-type or S-shaped negative differential conductivity (SNDC) in a range of electric field the current density is a multi-valued function of the electric field but the the electric field is a single-valued function of current density and can be calculated withouth ambiguity from the value of the current density. Thyristor is a good example of an SNDC device.