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
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 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
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!