TOPIC OF PRESENTATION

Gunn Diode

GUNN DIODE

• Definition

• History

• Construction

Definition:

Such type of semiconductor device which have only N type doped

(semiconductor) material, is called “Gunn Diode.”

It’s a unique component.

Gunn Diode is also known as:

Transferred Electron Device (TED).

Microwave Semiconductor Device.

Symbols for Circuit Diagram:

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.

Construction:

Gunn diodes are fabricated from a single piece of n-type

semiconductor,

Source Material:

Tri-methylgallium and arsenic (10% in H2).

Most Common Materials :

Gallium Arsenide (GaAs)

and Indium Phosphide (InP).

Three main areas:

Top/Upper Area,

Middle Area,

Bottom Area.

Middle area (Active layer) has a doping level between

1014 cm-3 to 1016 cm-3 .

Substrate has doping

density

n = 1.3x10 ^18 cm-³.

Thickness varies according to the

frequency required.

Metal contacts consist of three layers, namely a

80 nm layer of AuGe sandwiched between two

layers of 10 nm of Ni.

Additional AuGe is evaporated on the

existing contacts to a depth of 0.7μm.

Use Of Gold.

Its relative stability,

and high conductivity.

Requirements:

The material must be defect free , and it must also

have a very uniform level of doping.

Types of Materials Used For Gunn Diodes

To Get Different Frequencies:

Gallium arsenide for frequencies up

to 200 GHz,

Gallium nitride can reach up to 3 THz.

GUNN DIODE

Negative

Resistance

In Gunn Diode

GaAs (Galliam Arsenide ) has a property of

negative resistance.

) The negative resistance in Gunn diode is due to

(a) electron transfer to a less mobile energy level

(b) high reverse bias

(c) electron domain formation at the junction

(a)

How electron move into low mobility ?

According to Einstien Equation

E=mc2

(b) High reverse bias

(c) Electron domain formation at the

junction

EFFECT OF NEGATIVE RESISTANCE

ON CURRENT

GUNN DIODE

Gunn Effect

GUNN DIODE WHICH HAS A NEGATIVE DYNAMIC

RESISTANCE.

GRAPH BETWEEN RESISTANCE

AND VOLTAGE

As a result we arrange that average

voltage on the Gunn diode is as

illustrated in figure. The diode is said

to be biased into the negative

resistance region.

CHANGE IN ENERGY

R= RL + R(V)

WHEN R >0

THE ENERGY OF ANY OSCILLATION TENDS TO BE

REDUCED BY RESISTIVE DISSIPATION.

WHEN R < 0

The oscillation energy tends to be increased.

According to law of conservation of energy

The amount of energy at r > 0 = The amount of

energy at r < 0

GRAPH BETWEEN RESISTANCE AND

CURRENT

WORKING OF GUNN DIODE

COAXIAL CAVITY

In this case, each diode induced fluctuation travels

up the cavity and reflected from the far end,

returning to the diode after a time

L = length of cavity

c= speed of light

The oscillator may therefore

oscillate at any frequency such

that.

n= the “number of half-

waves”

FOR A BETTER RESULT

n=1 The system won't oscillate at a lower

frequency because the cavity is too short to

permit it. It can't oscillate at a higher

frequency because the diode is „too slow‟,

hence we ensure a single-valued oscillation

frequency.

Real Gunn devices have a

response time which varies

with the applied voltage, hence

we can electronically tune the

oscillation frequency by slightly

adjusting the bias voltage

GUNN DIODE

Difference between Gunn diode and P-N junction

DIFFERENCE BETWEEN GUNN DIODE AND P-N

JUNCTION

Construction

It only consists of N type

semiconductor material

It has N+ n N+ material

No depletion region is

formed

It consists of P & N type

semiconductor material

It has P type,N type and

depletion region between

these materials

Gunn diode P-N junction diode

DIFFERENCE BETWEEN GUNN DIODE AND P-N

JUNCTION

Gunn Doiode P-N junction Diode

DIFFERENCE BETWEEN GUNN DIODE AND P-N

JUNCTION

Symbols of Gunn Diode P-N junction

DIFFERENCE BETWEEN GUNN DIODE AND P-N

JUNCTION

Gunn Doiode P-N junction Diode

DIFFERENCE BETWEEN GUNN DIODE AND P-N

JUNCTION

Gunn Doiode P-N junction Diode

DIFFERENCE BETWEEN GUNN DIODE AND P-N

JUNCTION

I-V characteristics

Of Gunn diode

I-V characteristics

Of P-N junction Diode

GUNN DIODE

Applications

A Gunn diode can be used to amplify signals because of

the apparent "negative resistance". Gunn diodes are

commonly used as a source of high frequency and high

power signals

Sensors and measuring

Instruments

Anti-lock brakes

Sensors for monitoring the flow of traffic

Pedestrian safety systems

Distance traveled" recorders

Traffic signal controllers

Automatic traffic gates

AUTOMATIC DOOR OPENERS

CAR SPEED DETECTORS

SENSORS TO AVOID DERAILMENT OF

TRAINS

MOTION DETECTOR

RADIO AMATEUR USE

GUN OSCILLATOR

Thanks!