View source for 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.'''


{|border=1
|-
||'''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 to 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.
|-
||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 to 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.
|-
|}