PhET-Simulations-for-Physics/C3/Semiconductors/English

Semiconductors

Author: Vidhi Thakur

Keywords: PhET simulation, dopants, diode, valence band, conduction band, donor, acceptor, depletion region video tutorial.

Visual Cue	Narration
Slide Number 1 Title Slide	Welcome to this spoken tutorial on Semiconductors.
Slide Number 2 Learning Objectives	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.
Slide Number 3 System Requirement	Here I am using Windows 11 (64 bit). Java Version 1.8.
Slide Number 4 Pre-requisites https://spoken-tutorial.org	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.
Slide Number 5 Link for PhET simulation point to https://phet.colorado.edu/en/simulations/conductivity/about	Please use the given link to download the PhET simulation. https://phet.colorado.edu/en/simulations/semiconductor/about
Point to the file in the Downloads folder.	I have downloaded the Semiconductors simulation to my Downloads folder.
Double click the file to open	To open the simulation double click on the file.
Cursor on the interface.	This is the interface of Semiconductors simulation.
Cursor on main panel. Cursor on input box.	The main panel consists of a circuit. The circuit has a battery with the box to input the voltage.
Cursor on electrons.	Electrons are represented as blue spheres in the circuit.
Cursor on dopants.	Two blank spaces are provided in the circuit to add two dopants. A dopant is an impurity added to semiconductors to modify their conductivity.
Point to the P Type and N Type dopants at the bottom.	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.
Cursor on dopant. Cursor on valence band.	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.
Cursor on conduction band.	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.
Cursor on right panel. Point to one(1) Segment. Two(2) Segments.	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 dopants.
Click on segment one.	Let us first select segment one(1). Here only one segment is present.
Cursor on bands.	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.
Drag and add P-type in space in the bottom of the circuit. Click on the up arrow till 4V. Cursor on circuit diagram.	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.
Click on down arrow till -4V.	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.
Click on Clear Dopants.	Let us clear dopants now.
Drag and add N-type dopant and click up arrow till 4V.	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.
Click the down arrow till -4V.	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.
Click on two segment.	Now let us select segments two(2).
Drag and add P-type dopant in the left space. Click the arrow till 4V.	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.
Cursor on internal force and battery force.	Internal force is zero and battery force is from left to right. So, there is no flow of current in the circuit.
Drag and add an N-type dopant in the right space.	Let us drag and add an N-type dopant in the right space. Such diode formation is known as pn junction diode.
Cursor on battery.	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.
Cursor on valence band and conduction band.	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.
Click on down arrow till -4V. Cursor on battery and internal force. Cursor on battery.	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.
Click on Clear Dopants. Drag and add N-type dopant in left space and click up arrow till 4V.	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.
Cursor on battery and internal force.	Internal force is zero and battery force is in the right direction. So, there is no flow of current.
Drag and add a P-type dopant in the right space. Cursor on battery	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.
Click on down arrow till -4V.	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.
Slide Number 6 Summary	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.
Slide Number 7 Assignment	As an assignment, Make various combinations of dopants at different voltages and record the observations.
Slide Number 8 About Spoken Tutorial Project	The video at the following link summarizes the Spoken Tutorial project. Please download and watch it.
Slide Number 9 Spoken tutorial workshops	We conduct workshops using spoken tutorials and give certificates. For more details, please contact us.
Slide Number 10 Answers for THIS Spoken Tutorial	Please post your timed queries in this forum.
Slide Number 12 Acknowledgement	Spoken Tutorial project is funded by the Ministry of Education (MoE), Govt. of India
	This is Vidhi Thakur, a FOSSEE summer fellow 2022, IIT Bombay signing off. Thank you for joining.

Contributors and Content Editors

Madhurig, Nancyvarkey, Vidhithakur