what is a gunn diode?

Answer 1

A Gunn diode, also known as a transferred electron device (TED) is a form of diode used in high-frequency electronics. It is somewhat unusual in that it consists only of N-doped semiconductor material, whereas most diodes consist of both P and N-doped regions. In the Gunn diode, three regions exist: two of them are heavily N-doped on each terminal, with a thin layer of lightly doped material in between. When a voltage is applied to the device, the electrical gradient will be largest across the thin middle layer. Eventually, this layer starts to conduct, reducing the gradient across it, preventing further conduction. In practice, this means a Gunn diode has a region of negative differential resistance.
It is used a lot by radio amateur.

Answer 2

Gunn diode is a transfer Electron Device ( Devices that does not have any junction or gates as that of transistor and operated with "hot" electrons ). It is not a real diode as it has no junction. It is madeup of 3 layers all of type N. A thin layer of lightly doped N type semiconductor layer sits in between two heavyly doped N type semiconductors.

Gunn diode is biased to operate in the negative resistance region ( where the differential resistance of the device is negative). When the dynamic resistance is negative it creates power ( used the power from the DC bias applied to it.. and the power is not dissipated). When the voltage across the middle layer exceed certain threshold level the current pulse starts to pass the layer. This pulse resists the developed voltage across the juntion and decreased it . The voltage again increases only when the current pulse has crossed the junction and this process continues. This produces oscillations .

Gunn Diodes are usually made of GaAs, InP and Gallium Nitride. They are used in microwave applications to generate signals of frequencies in gigahertz and tera hertz range

Answer 3

A Gunn diode is a special kind of diode used mostly in microwave applications. In a normal diode, as the current through the diode increases, the voltage across the diode increases also.

In the Gunn diode, as the current is increased, there is a small region where the voltage across the diode decreases. It exhibits negative resistance and can be used to make oscillators or parametric amplifiers.

Try this site:
http://en.wikipedia.org/wiki/Gunn_diode