Gunn Diode

transcript

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

(b) high reverse bias

(c) electron domain formation at the junction

(a) How electron move into low mobility ?

According to Einstien Equation

(b) High reverse bias

(c) Electron domain formation at the junction

EFFECT OF NEGATIVE RESISTANCEON 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

Gunn Doiode P-N junction Diode

Symbols of Gunn Diode 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!

Gunn Diode

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