Gun Diode

History Gunn diode was invented by a Physicist, John Battiscombe Gunn, in 1963, in IBM .

Transferred Electron Effect was first published by :Ridley and Watkins in 1961 .Further work by Hilsum in 1962 ,

Finally J.B. Gunn, observed it, using GaAs semiconductor, in 1963 .

What is Gun Diode?

A Gunn diode is also known as a transferred electron device (TED). It is a form of diode used in high-frequency electronics. it consists only of n-doped semiconductor material, whereas most diodes consist of both P and N-doped regions. In practice, a Gunn diode has a region of negative differential resistance.

Gallium Arsenide Gunn Diodes are made for frequencies up to 200GHz whereas Gallium Nitride can reach upto 3THz.

1x 3A703A Military GaAs Gunn diode 8.24 - 12.5GHz

UkraineItem sold in:

US $13.95price

3 725 A VMilitary GaAs Gunn Oscillator dio

8.25 1de GHz Oty

Item sold in: Ukraine

price 14.00$

715 / 8625 / -AA E DGB ex USSR GaAs

11.Gunn Oscillator Diode5 =1GHz QTY UkraineItem sold in:

price $22.95

3 736 , 736 , A A AA A GaAs 18Gunn Oscillator diode

35 GHz mWOty 10

Item sold in:

price 99.0$

Romania

3 703 A BMilitary GaAs 12.5Gunn diode GHz :10Oty

Item sold in: price

Romania99.$

0

Gunn Diode ConstructionThe top and bottom areas of the device are heavily doped to give N+ material. The device is mounted on a conducting base to which a wire connection is made.

It also acts as a heat-sink for the heat which is generated. The connection to the other terminal of the diode is made via a gold connection deposited onto the top surface.

The centre area of the device is the active region .This region is also less heavily doped and this means that virtually all the voltage placed across the device appears across this region.

In view of the fact that the device consists only of n type material there is no p-n junction and in fact it is not a true diode, and it operates on totally different principles.

Gunn diode operation basicsThe operation of the Gunn diode can be explained in basic terms. When a voltage is placed across the device, most of the voltage appears across the inner active region. As this is particularly thin this means that the voltage gradient that exists in this region is exceedingly high.

The device exhibits a negative resistance region on its V/I curve as seen below. This negative resistance area enables the Gunn diode to amplify signals. This can be used both in amplifiers and oscillators. However Gunn diode oscillators are the most commonly found.

This negative resistance region means that the current flow in diode increases in the negative resistance region when the voltage falls - the inverse of the normal effect in any other positive resistance element. This phase reversal enables the Gunn diode to act as an amplifier and oscillator.

Gunn diode operation at microwave frequencies

When the voltage across the active region reaches a certain point a current is initiated and travels across the active region. During the time when the current pulse is moving across the active region the potential gradient falls preventing any further pulses from forming. Only when the pulse has reached the far side of the active region will the potential gradient rise, allowing the next pulse to be created

It can be seen that the time taken for the current pulse to traverse the active region largely determines the rate at which current pulses are generated, and hence it determines the frequency of operation.

To see how this occurs, it is necessary to look at the electron concentration across the active region. Under normal conditions the concentration of free electrons would be the same regardless of the distance across the active diode region. However a small perturbation may occur resulting from noise from the current flow, or even external noise - this form of noise will always be present and acts as the seed for the oscillation. This grows as it passes across the active region of the Gunn diode.

The increase in free electrons in one area cause the free electrons in another area to decrease forming a form of wave. It also results in a higher field for the electrons in this region. This higher field slows down these electrons relative to the remainder. As a result the region of excess electrons will grow because the electrons in the trailing path arrive with a higher velocity. Similarly the area depleted of electrons will also grow because the electrons slightly ahead of the area with excess electrons can move faster. In this way, more electrons enter the region of excess making it larger, and more electrons leave the depleted region because they too can move faster. In this way the perturbation increases.

ADVANTAGES It has much lower noise than IMPATT diodes

Gunn amplifiers are capable of broad-band operation.

Higher peak-to-valley ratio in its –ve resistance characteristics.

High fundamental frequency operation.Increased efficiency.

GUNN DIODE