| Visual Cue
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Narration
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| Slide Number 1
Title Slide
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Welcome to this spoken tutorial on Semiconductors.
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| Slide Number 2
Learning Objectives
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In this tutorial, we will learn,
- How a battery acts as a driving force in a circuit.
- To add dopants to move the electrons in the circuit.
- How the dopants change energy levels in a semiconductor
- Why a pn junction acts as a diode
- Why a depletion region does not allow current to flow.
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| Slide Number 3
System Requirement
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Here I am using
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| Slide Number 4
Pre-requisites
https://spoken-tutorial.org
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To follow this tutorial the learner should be familiar with topics in high school science.
Please use the link below to access the tutorials on PhET simulations.
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| Slide Number 5
Link for PhET simulation
point to
https://phet.colorado.edu/en/simulations/conductivity/about
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Please use the given link to download the PhET simulation.
https://phet.colorado.edu/en/simulations/semiconductor/about
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| Point to the file in the Downloads folder.
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I have downloaded the Semiconductors simulation to my Downloads folder.
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| Double click the file to open
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To open the simulation double click on the file.
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| Cursor on the interface.
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This is the interface of Semiconductors simulation.
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| Cursor on main panel.
Cursor on input box.
Cursor on electrons.
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The main panel consists of a circuit.
The circuit has a battery with the box to input the voltage.
Electrons are represented as blue spheres in the circuit.
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| Cursor on dopants.
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Point to the P Type and N Type dopants at the bottom.
A dopant is an impurity added to semiconductors to modify their conductivity.
At the bottom right P-type dopant is represented as red spheres and N-type as green spheres.
A P Type dopant is represented as red spheres and N Type as green spheres.
P-type dopant is with more holes, whereas n-type dopant is with more electrons.
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| Cursor on dopant.
Cursor on valence band.
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An electrode is connected to each dopant.
It expands into bands represented as yellow rectangles on the left panel.
The low energy band is the valence band.
It is filled with blue spheres as electrons and plus signs as holes.
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Cursor on conduction band.
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The high energy band is the conduction band.
In semiconductors the gap between the bands is small.
Internal force arrow gives us the direction of the internal force.
Battery force arrow gives us the direction of battery force.
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| Cursor on right panel.
Point to one(1) Segment.
Two(2) Segments.
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On the right panel the Segments section is present.
It consists of one and two as options.
The one(1) Segment provides space for one dopant only.
The two(2) Segments provide space for two segments.
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| Click on segment one.
Cursor on bands.
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Let us first select segment one(1).
Here only one segment is present.
The electrode attached to the dopant expands into bands with electrons and holes.
Lower energy band is the valence band with low energy.
The higher energy band is the conduction band with high energy.
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| Drag and add P-type in space in the bottom of the circuit.
Click on the up arrow till 4V.
Cursor on circuit diagram.
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Let’s drag and place a P-type dopant to fill in the purple space in the circuit.
Increase the voltage to 4 volts and observe the movement of electrons in the circuit.
Current flows in the circuit with low energy from left-right.
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| Click on down arrow till -4V.
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Now let us decrease the voltage to -4 volts.
This way we change the terminals of the battery in the opposite direction.
There is a flow of current in the right-left direction in the circuit.
Changing the terminals, changes the direction of potential difference.
Hence direction of flow of current changes.
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| Click on Clear Dopants.
Drag and add N-type dopant and click up arrow till 4V.
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Let us clear dopants now.
Add N-type dopant to the space and increase the voltage to 4 volts.
Since N-type dopants have more electrons they are known as donors.
The flow of current is from left to right in the conduction band at high energy.
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Click the down arrow till -4V.
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Now let us change the voltage to -4 , that is. change the terminal of the battery.
This time flow of current is in the right-left direction
in the conduction band.
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| Click on two segment.
Drag and add P-type dopant in the left space.
Click the arrow till 4V.
Cursor on internal force and battery force.
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Now let us select Segments two(2).
Drag and add P-type dopant in the left space and increase the voltage to 4 volts.
Note that electrons and holes in the valence band of the left segment disappear.
This is because p-type dopant is an acceptor.
Internal force is zero and battery force is from left to right.
So, there is no flow of current in the circuit.
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| Drag and add an N-type dopant in the right space.
Cursor on battery.
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Let us drag and add an N-type dopant in the right space.
Such diode formation is known as pn junction diode.
Here the positive terminal of the battery is connected to N-type.
Negative terminal is connected to the P-type.
Such arrangement is known as reversed bias.
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| Cursor on valence band and conduction band.
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Empty space is filled by electrons in the P-type dopant.
And holes occupy the conduction band of N-type dopant.
The direction of internal force, and battery force, are in the same direction.
Hence a more resistive thicker depletion region is formed.
This is due to the diffusion of carriers across the junction of the pn diode.
So, no flow of current is observed.
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| Click on down arrow till -4V.
Cursor on battery and internal force.
Cursor on battery.
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Now let us slowly change the voltage to -4 Volts.
Notice that decrease in voltage decreases the size of the battery force arrow.
At -4 Volts the battery force changes the direction and internal force becomes zero.
At -4 Volts, P-type dopant is connected to the positive terminal and vice-versa.
Hence it is forward biased, so the depletion region is thinner here.
So, current flow is seen from N-type to P-type dopant in right-left direction.
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| Click on Clear Dopants.
Drag and add N-type dopant in left space and click up arrow till 4V.
Cursor on battery and internal force.
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Now let”s clear the dopants.
Drag and add N-type dopant in the left space and increase the voltage to 4 Volts.
Electrons and holes are visible in the left segment as N-type dopants are donors.
Internal force is zero and battery force is in the right direction.
So, there is no flow of current,
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| Drag and add a P-type dopant in the right space.
Cursor on battery
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Let us drag and add P-type dopant in the right segment.
Such diode formation is known as pn junction diode.
Here, positive terminal is connected to P-type and negative terminal to N-type.
Such an arrangement is known as forward bias.
Flow of current is seen from N-type to P-type dopant from left to right direction.
Battery force is also in the same direction.
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| Click on down arrow till -4V.
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I will now change the voltage to -4 Volts.
The electrons in the left segment of the conduction band disappear.
Only holes are left.
Internal force and battery force are in the left direction.
So, we see no flow of current.
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| Slide Number 6
Summary
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With this we come to the end of this tutorial.
Let's summarise.
In this tutorial we have learnt,* How a battery acts as a driving force in a circuit.
- To add dopants to move the electrons in the circuit.
- How the dopants change energy levels in a semiconductor
- Why a pn junction acts as a diode
- Why a depletion region does not allow current to flow.
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| Slide Number 7
Assignment
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As an assignment,
Make various combinations of dopants at different voltages and record the observations.
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| Slide Number 8
About Spoken Tutorial Project
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The video at the following link summarizes the Spoken Tutorial project.
- Please download and watch it.
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| Slide Number 9
Spoken tutorial workshops
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We conduct workshops using spoken tutorials and give certificates.
- For more details, please contact us.
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| Slide Number 10
Answers for THIS Spoken Tutorial
Do you have questions in THIS Spoken Tutorial?
Please visit this site
Choose the minute and second where you have the question.
Explain your question briefly
The spoken tutorial project will ensure answer.
You will have to register on this website to ask questions.
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* Please post your timed queries in this forum.
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| Slide Number 11
Forum
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The Spoken Tutorial forum is for specific questions on this tutorial.
- Please do not post unrelated and general questions on them.
- This will help reduce the clutter.
- With less clutter, we can use these discussions as instructional material.
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| Slide Number 12
Acknowledgement
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Spoken Tutorial project is funded by the Ministry of Education (MoE), Govt. of India
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This is Vidhi Thakur, a FOSSEE
- summer fellow 2022, IIT Bombay
- signing off
Thank you for joining.
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