Transcript Gunn Diode - OpenStudy

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
DYNAMIC RESISTANCE.
NEGATIVE
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
Gunn diode
Construction
 It only consists of N type
semiconductor material
 It has N+ n N+ material
No depletion region is
formed
P-N junction diode
It consists of P & N type
semiconductor material
 It has P type,N type and
depletion region between
these materials

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
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