MAYURBHANJ SCHOOL OF ENGINEERING � LAXMIPOSI ,BARIPADA,757107

Prepared by Er. Viswanath Behera (Lecturer E & TC Engineering Department)

Subject – WAVE PROPAGATION & BROADBAND COMMUNICATION ENGINEERING

Chapter – 4 – Microwave Engineering

Topic – Tunnel Diode

Semester – 5^th

Branch – Electronics & Telecommunication

AY-2021-2022, WINTER-2021

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TUNNEL DIODE (ESAKI DIODE)

• It was introduced by Leo Esaki in 1958.
• Heavily-doped p-n junction
• Impurity concentration is 1 part in 10^3 as compared to 1 part in 10^8 in p-n junction diode
• Width of the depletion layer is very small�(about 100 A).
• It is generally made up of Ge and GaAs.
• It shows tunneling phenomenon.
• Circuit symbol of tunnel diode is :

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E_V

WHAT IS TUNNELING

• Classically, carrier must have energy at least equal to potential-barrier height to cross the junction .
• But according to Quantum mechanics there is finite probability that it can penetrate through the barrier for a thin width.
• This phenomenon is

called tunneling and

hence the Esaki Diode

is know as

Tunnel Diode.

CHARACTERISTIC OF TUNNEL DIODE

Ip:- Peak Current

Iv :- Valley Current

Vp:- Peak Voltage

Vv:- Valley Voltage

Vf:- Peak Forward

Voltage

ENERGY BAND DIAGRAM

Energy-band diagram of pn junction in thermal equilibrium in which both the n and p region are degenerately doped.

-Zero current on the I-V diagram;

• All energy states are filled below E_F on both sides of the junction;

AT ZERO BIAS

Simplified energy-band diagram and I-V characteristics of the tunnel diode at zero bias.

• Electrons in the conduction band of the n region are directly opposite to the empty states in the valence band of the p region.
• So a finite probability that some electrons tunnel directly into the empty states resulting in forward-bias tunneling current.

AT SMALL FORWARD VOLTAGE

Simplified energy-band diagram and I-V characteristics of the tunnel diode at a slight forward bias.

• The maximum number of electrons in the n region are opposite to the maximum number of empty states in the p region.
• Hence tunneling current is maximum.

AT MAXIMUM TUNNELING CURENT

Simplified energy-band diagraam and I-V characteristics of the tunnel diode at a forward bias producing maximum tunneling current.

• The forward-bias voltage increases so the number of electrons on the n side, directly opposite empty states on the p side decreases.
• Hence the tunneling current decreases.

AT DECREASING CURRENT REGION

Simplified energy-band diagram and I-V characteristics of the tunnel diode at a higher forward bias producing less tunneling current.

• No electrons on the n side are directly opposite to the empty states on the p side.
• The tunneling current is zero.
• The normal ideal diffusion current exists in the device.

AT HIGHER FORWARD VOLTAGE

Simplified energy-band diagram and I-V characteristics of the tunnel diode at a forward bias for which the diffusion current dominates.

• Electrons in the valence band on the p side are directly opposite to empty states in the conduction band on the n side.
• Electrons tunnel directly from the p region into the n region.
• The reverse-bias current increases monotonically and rapidly with reverse-bias voltage.

AT REVERSE BIAS VOLTAGE

TUNNEL DIODE EQUIVALENT CIRCUIT

• This is the equivalent circuit of tunnel diode when biased in negative resistance region.
• At higher frequencies the series R and L can be ignored.

• Hence equivalent circuit can be reduced to parallel combination of junction capacitance and negative resistance.

THANK YOU