This document discusses a lecture on tunnel diodes given by Arpan Deyasi of RCC Institute of Information Technology, Kolkata, India. The lecture covers the mechanism of carrier transport in tunnel diodes, which is tunneling. It also discusses the criteria for tunneling to occur, including a lower depletion width, lower effective mass, and degenerate doping. Examples are given of materials that can satisfy these criteria, such as semiconductors with large bandgaps or lower effective masses. The characteristic I-V curve of a tunnel diode is presented, showing its negative differential resistance region. Finally, applications of tunnel diodes such as in oscillators are mentioned.

1. Course: Electronic Devices
paper code: EC301
Course Coordinator: Arpan Deyasi
Department of Electronics and Communication Engineering
RCC Institute of Information Technology
Kolkata, India
9/17/2020 1Arpan Deyasi, RCCIIT, India
Topic: Tunnel Diode

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Tunnel diode
Mechanism of carrier
transport: tunneling
Operating mode: Forward bias

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Criteria for tunneling process
Lower width of depletion region
Lower effective mass
Complete filled conduction band in n-side and
completely empty valence band in p-side
How could these conditions be satisfied?

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Solution: Large bandgap semiconductor
Tunnel diode
Requirement 1: Lower width of depletion region
d

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Solution: Semiconductor with lower effective mass
Tunnel diode
Requirement 2: Lower effective mass

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Solution: Degenerate semiconductor
Tunnel diode
Requirement 3: Complete filled conduction band in
n-side and complete empty valence band in p-side
EC
EV
EFI
EF
n- degenerate
EC
EV
EFI
p- degenerate
EF

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V=0
V
I

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V>0
V
I
I
VP>
Tunneling Current

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V
I
I
V=VP
Tunneling Current
VP
IP

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V
I
I
V>VP
Tunneling Current
IP
VP

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V
II
V=VV
Tunneling Current
VV
IV

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V
II
V>VV
Thermionic Current
VV
IV

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

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I-V Characteristics of Tunnel Diode
0
dV
R
dI
= <
dV>0
dI<0
V
I
NDR

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Criteria for Tunnel diode operation
Degenerate semiconductor so that Fermi level
should be within the band
Material should have lower effective mass
Large bandgap semiconductor to get thin depletion layer
At operating temperature, all states above Fermi level
should be empty and below Fermi level should be occupied
There must be filled energy states on the side from which
electron will tunnel and allowed empty energy states on
the other side where electron will stay in the same
energy level

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Tunnel diode oscillator
Zin
C
-R
RS LS
Equivalent circuit
of tunnel diode oscillator

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Tunnel diode oscillator
Input impedance
.
in S S
j
R
C
Z R j L
j
R
C
ω
ω
ω
 
 
 = + +
− −

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Tunnel diode oscillator
Resistive cut-off frequency
1
1
2
r
S
R
f
RC Rπ
= −
Reactive cut-off frequency
2 2
1 1 1
2
x
S
f
L C R Cπ
= −