Gunn Diode Dr I Srinivasa Rao VIT University S1

8/9/2019 Gunn Diode Dr I Srinivasa Rao VIT University S1

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Session – 1Session Name: Gunn Diode

Author Name: Dr. I. Srinivasa Rao

Department: School of Electronics Engineering

Subject/Course: Microwave Engineering


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Page 2 Ver 1.01 Gunn DiodeDr. I. Srinivasa Rao, VIT University

Session Objectives

At the end of this session, the learner will be able to:

Define Gunn Effect.Identify the importance of semi conducting materials like GaAs, InP etc.Elucidate the theory of operation of Gunn diode.Illustrate the formation of Gunn domains.List the different applications of Gunn diode.

Teaching Learning Material

Presentation Slides2D Animation VideoBoard and Chalk


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Gunn Diode Page 3Dr. I. Srinivasa Rao, VIT University

Session Plan

Time(in min)

ContentLearning Aid

andMethodology

FacultyApproach

Typical StudentActivity

Learning Outcomes(Blooms + Gardeners)

10Recap: Tunnel Diode

2D AnimationQuiz

FacilitatesMonitors

RecapitulatesParticipates

Answers

Remembering

IntrapersonalInterpersonal

Spatial

10Introduction to Gunn

DiodeChalk and Talk

ExplainsFacilitates

ListensRememberingUnderstanding

Intrapersonal

15Theory & Operation

of Gunn Diode2D AnimationPresentation

ExplainsFacilitatesMonitors

ParticipatesListens

RememberingUnderstanding

SpatialIntrapersonal

10Formation of Gunn

DomainGroup View Facilitates

GuidesParticipates

Discusses

ApplyingUnderstanding

InterpersonalIntrapersonal

05Conclusion

Recall by KeyWords

FacilitatesLists

IdentifiesExplains

RememberingUnderstanding

Intrapersonal


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Session Inputs

Recap: Tunnel Diode

Since the learners are familiar with Tunnel diode operation, thesame can be recapped through an animation and an interac tivequiz.

Suggested Activity: 2D Animation and Quiz

Download the flash animation from the following link and play theanimation of operation of Tunnel diode, so that learners can recap.Link: http://www.mission10x.com/mission-10x/Documents/Tunnel_Diode.swf

Ask some questions related to the Tunnel Diode. Some of the samplequestions for the quiz could be as follows:

1. What is tunneling effect?2. What is the effect of high doping to a semiconductor?3. What is the advantage of having negative resistance region for

tunnel diode?4. List the applications of tunnel diode

The possible answers from the learners could be:1. It refers to the phenomena of a particle's ability to penetrate energy

barriers within electronic structures.2. Effects:

It reduces the width of the depletion region to a small valueIt reduces the reverse breakdown voltage to a small valueIt exhibits an important feature of negative resistance over aportion of its I-V characteristics

3. It is able to produce oscillations of high frequency.4. Applications:

It can be used as an ultra high speed switchIt can be used as logic memory storage deviceIt can be used in RF & Microwave oscillator circuits.


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Introduction to Gunn Diode

Having recapitulation of tunnel diode, we shall now focus onGunn diode and transferred electron mechanism. We can startwith the history of the electron mechanism through the chalk andtalk methodology.

In 1963 J . B. Gunn discovered the transferred electronmechanism, since then we are calling it asGunn Effe c t . The device that uses Gunn Effect known asGunn Diod e orTransferred Elec tron Devic e .In the transferred electron mechanism, the conduction ofelectrons of some semiconductors is shifted from a state ofhigh mobility to a state of low mobility by the influence of

strong electric field. This process is known as Gunn Effect. During this processnegative resistance occurs at some point of c riticalvoltage.Gunn diode is only found in N-type semiconductormaterials, so that it must be associated with electrons ratherthan with holes.

For better understanding of the learners’ knowledge, it would bea good idea to ask the learners to list out the semiconductor

devices that exhibit negative resistance region in its V-Icharacteristics. We can list their responses on the board.

The semiconductor devices that exhibit negative resistance are:1. Uni J unction Transistor2. Silicon Control Rectifier3. Tunnel diode4. Gunn diode5. IMPATT diode6. TRAPATT diode7. BARIT diode

Theory and Operation of Gunn Diode

We shall now introduce the various materials used for thepreparation of Gunn diode and we can depict the energy band


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diagram of GaAs material with the help of a PPT presentation.

Show the following figure in the PPT and explain it in the blackboard.

In N-type GaAs the valence band is filled with electronsand conduction band is partly filled. The forbidden energy gap between valence band andconduction band is about 1.43 eV.

In ordinary semiconductors conduction band is the highestenergy band.But in N-type GaAs the conduction band consists ofdifferent energy levels.Here conduction band is referred to as central valley.Above the conduction band we have another higherempty energy band separated by 0.3 eV from conductionband. This empty energy band is referred as satellite valley. In thesatellite valley mobility of electrons is less than central

valley.

For better explanation, the operation of the Gunn diode can beillustrated by showing an animation.


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Suggested Activity: 2D Animation

Get the animation from the following link:

Link: http://www.mission10x.com/mission-10x/Documents/Gunn%20diode1.swf

We can play the animation of operation of Gunn diode with properexplanation in the middle, so that the learners can easily understand thewhole concept. Animation at different stages is shown with the help of thefollowing figures

1. On application of electric filed or voltage across the GaAsslice, electrons start travel from cathode to anode.

2. The greater the potential across the slice, the higher is the


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veloc ity of electrons and therefore greater the current.3. Once the electrons have gained enough energy i.e. at the

threshold level, they transferred to higher energy band thatis to satellite valley from central valley

4.

In the satellite valley electrons become less mobile and soget slowed down. Now there is a fall in current and thusnegative resistance is exhibited

5. As the voltage rises further, the gradient become sufficientto remove electrons from the satellite valley so that currentagain starts rising with voltage

Formation of Gunn Domains

After the above animation, the learners are familiar with the

operation of Gunn diode. Now the formation of Gunn domainscan be introduced with a group view activity.

Suggested Activity: Group View

Here the learners are divided into 4 groups and subjected to the interactivediscussion about the conditions, difficulties and limitations for the formationof Gunn domains. All learners have to think what will happen when dopingconcentration is not uniform?

Formation of Gunn domains can be easily understand with thehelp of the following figure:


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1. Domain is a bunch of electrons. Negative resistance effectin the Gunn diode is mainly because of formation ofdomains.

2. In a heavily doped N-type GaAs slice, it is realistic toassume that the density of doping material may not beuniform throughout the GaAs sample.

3. The region where the impurity concentration is lessbecomes less conductive than other regions of the sample.So the resistance of this region is high. As a result thevoltage drop across this region is high compared with otherregions.

4. If we start rising D.C. voltage across the GaAs sample,current start rising. Further increase in the DC voltagecauses a high voltage drop across this region, which means

a high electric field is set up inside the region.5. With this electric field electrons in the conduction band

have enough energy to jump into the higher energy levelsi.e. to the satellite valley.

6. Now current inside the less conductive region starting todecrease and this region will become a negativeresistance domain. Such a domain is very unstable. Thishigh energetic bunch comes out as a pulse of voltage.

7. If a suitable tank circuit is connected at the output of thediode, this pulse turns tank circuit into oscillating mode.

Conclusion

We can conclude the session by revising the key conceptsdiscussed in the session by using the following recall by key wordsactivity.

Suggested Activity: Recall by Key Words

We can list the following key words discussed in the session, randomly picka learner for every keyword and ask the learner to tell something about the

key word. Transferred electron effect or Gunn effectGaAs or InPSatellite valleyGunn domainGunn oscillator


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Assignment

1. Why Gunn Effec t is assoc iated only with electrons rather than holes?

2.

What is the concentration of doping used for Gunn diode? What willhappen if doping concentration decreases?

3. Compare the Tunnel diode and Gunn diode.4. List the various limitations of Gunn diode in the generation of MW

power and MW oscillations.


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References

Solid State Electronic Devices by Benz. Streetman

Physics of Semiconductor Devices by S. M. SzeMicrowave Devices and C ircuits by Samuel Y. Leo

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