Gunn diode

Transferred Electron Device
Course coordinator: Arpan Deyasi
1/30/2021 1
Arpan Deyasi, RCCIIT, India

1/30/2021 2
Transfer of Carrier
transfer of carrier at interband
transfer of carrier at intraband

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Transferred Electron Effect
All types of transitions (interband/intraband) are
possible due to application of external electric field
Q: Why these transitions are important?
To produce negative conductivity
Ridley-Watkins-Hilsum Effect

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Q: Why negative conductivity is important?
Within the circuit/device, generator is present
It works as an amplifier!

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Q: Is it possible to realize?
A few semiconductor materials can exhibit these
properties under specific external conditions
Those devices are called

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Q: What are those materials?
Q: What are the conditions?
Q: How they exhibit?
Materials: GaAs, InP

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Transferred Electron Mechanism
1.43
eV
GaAs
0.36 eV
m=0.068m0
μ=8000 cm2V-1s-1
<000>
<100> m=1.2m0
μ=180 cm2V-1s-1

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higher effective mass
lower mobility
decrease of current
Negative Differential Conductivity
J
E
Gunn Effect

1/30/2021 Arpan Deyasi, RCCIIT, India 9
Gunn Diode

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Condition for TED
 Two conduction valleys should be present with energy
difference greater than thermal energy ΔE>kBT
For GaAs ΔE=0.36 eV>0.0259 eV
 Electrons at lower valley of CB should have lower m* and
higher μ, higher valley of CB have higher m* and lower μ
mlv < muv & μlv > μlv
For GaAs mlv = 0.068m0, μlv = 8000 cm2V-1s-1
muv = 1.2m0, μuv = 180 cm2V-1s-1
 Energy difference should be less than bandgap ΔE<Eg
For GaAs ΔE=0.36 eV<1.427 eV

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Mathematical Formulation
l u
n n n
= +
Total carrier concentration
0
l u
dn dn
dn
dE dE dE
= + =
l u
dn dn
dE dE
= −

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p
E
µ ∝
Mobility is related with electric field
( )
p
d d
E
dE dE
µ
∝
1
p
d p
pE
dE E
µ µ
−
= =

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Net conductivity
( )
l l u u
q n n
σ µ µ
= +
l u
l u
l u
l u
dn dn
d
q
dE dE dE
d d
q n n
dE dE
σ
µ µ
µ µ
 
= +
 
 
 
+ +
 
 

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[ ]
( ) u
l u
l l u u
dn
d
q
dE dE
p
q n n
E
σ
µ µ
µ µ
 
= −
 
 
+ +

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Differential form of Ohm’s law
J E
σ
=
dJ d
E
dE dE
σ
σ
= +

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( )
( )
1
1
d
dJ dE
dE
E
σ
σ
σ
= +
under NDC condition 0
dJ
dE
<

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( )
( )
1 0
d
dE
E
σ
σ
+ <
( )
( )
1
d
dE
E
σ
σ
< −

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[ ]
( ) u
l u l l u u
dn
d p
q q n n
dE dE E
σ
µ µ µ µ
 
= − + +
 
 
( )
l l u u
q n n
σ µ µ
= +
[ ]
( )
( )
u
l u l l u u
l l u u
dn p
n n
d
dE E
dE
n n
µ µ µ µ
σ
σ µ µ
 
− + +
 
 
=
+

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We assume
u
l
n
n
η =
[ ]
( )
( )
u
l u l l u u
l l u u
dn
E n n p
d
dE
dE
n n
E
µ µ µ µ
σ
σ µ µ
 
− + +
 
 
=
+

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( )
( )
l u l
l u l
d
dn
E
dE p
n dE
E
σ
µ µ
σ µ ηµ
 
 
   
−  
 
+
 
  
  
+  
 
 
   
 
 
( )
1
( )
l u l
l u l
dn
E
p
n dE
µ µ
µ ηµ
 
 
   
−  
 
+ < −
 
  
  
+  
 
 
   
 
 

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To satisfy the inequality
l u
µ µ
>
0
l
dn
dE
<
Electron at lower valley has higher mobility
concentration of lower valley electron
decreases with increasing electric field,
i.e., they are transferred to upper valley

I-V Characteristics of Gunn Diode
VP VV
IP
IV
peak point
valley
point
V
I

Different Modes of I-V Characteristics
E
J
E
J
Voltage-controlled Mode
Current-
controlled Mode

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Formation of Domain
Applied voltage is very large
Charge density and electric field becomes non-uniform
Cluster of charges inside the sample creates domain
Domains cause inter-valley transfer
Current decreases

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Formation
of
Domain
ΔE
z
E
z

Properties of High-field Domain
Domain will start to form when electric field in a region of
the sample increases above the threshold electric field
Domain will drift through the device
If additional voltage is applied to a device containing a
domain, it will enhance in size and absorb more voltage
and corresponding current will decrease
Domain will in general disappear after reaching the anode

Properties of High-field Domain
Domain will modulate current as it asses through different
regions of doping and cross-sectional area
Length of domain is inversely proportional to doping
Presence of domain anywhere inside the sample can be
detected by change of differential impedance

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Movement
of
Domain

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Movement
of
Domain

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Modes of Operation
I. Transit Time Domain Mode
fL = 107 cm.s-1
transit time = oscillation period
efficiency is below 10% as current is collected only
when domain arrives at anode
doesn’t require external circuit for operation

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Modes of Operation
II. Delayed Domain Mode / Inhibited Mode
106 cm.s-1 < fL < 107 cm.s-1
transit time < oscillation period
efficiency is approximately 20%
domain is only collected when applied field is less
than critical field

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Modes of Operation
III. Quenched Domain Mode
fL = 107 cm.s-1
transit time >> oscillation period
efficiency is approximately 13%
domain collapses when it reaches the anode
device oscillates at resonant frequency of the circuit

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Modes of Operation
IV. Limited Space Charge Accumulation Mode
fL > 2×107 cm.s-1
transit time >> oscillation period
efficiency is 20%
current is proportional to drift velocity

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Gunn Diode Oscillator Circuit

High bandwidth
High reliability
Low manufacturing cost
Fair noise performance
Relatively low operating voltage
Advantages of Gunn Diode

Low efficiency below about 10 GHz
Poor stability – frequency varies with bias and temperature
FM noise high for some applications
Small tuning range
Disadvantages of Gunn Diode

Applications of Gunn Diode
Gunn oscillators are used in radio communication,
RADAR source, military application
Sensor
Efficient microwave generator
Remote vibration detector

Gunn diode

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