Transcript Extrinsic semiconductor

Document that explains the chosen concept to the animator
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Extrinsic Semiconductors
An extrinsic semiconductor is one in which impurities contribute a
significant fraction of the conduction band electrons and/or
valence band holes.
Course Name: Semiconducting Properties of materials.
Authors
Anura.B.Kenkre
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Learning Objectives
After interacting with this Learning Object, the learner will be able to:
•
Define an extrinsic semiconductor.
•
Predict the effect of doping on the conductivity of the extrinsic
semiconductors.
•
Interpret the difference between n type and p type
semiconductors.
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Definitions of the components/Keywords:
•An Extrinsic semiconductor is one in which impurities contribute a
significant fraction of the conduction band electrons and/or valence
band holes.
•when impurity atoms are added to a semiconductor crystal, to
increase either the number of free electrons or the number of holes,
the process is referred to as Doping.
•Impurities that contribute to the carrier density of a semiconductor are
called donors if they supply additional electrons to the conduction
band, and acceptors if they supply additional holes to (i.e. capture
electrons from)the valence band.
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IMPORTANT NOTE TO THE ANIMATOR:
•All the instructions/labels or anything WRITTEN in blue
are CONTENT NOT TO BE DISPLAYED!
•All the instructions WRITTEN in black are CONTENT TO
BE DISPLAYED!
•This is not applicable for images as there can be
overlapping of these colours there. This should be
followed for all the instructions,labels,etc…
Kindly keep a note of this while displaying text in the
animation.
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INSTRUCTIONS SLIDE
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Master layout or diagram
• Make a schematic diagram of the concept
• Explain to the animator about the beginning and ending
of the process.
• Draw image big enough for explaining.
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4
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• In above image, identify and label different components
of the process/phenomenon. (These are like characters
in a film)
• Illustrate the basic flow of action by using arrows. Use
BOLD lines in the diagram, (minimum 2pts.)
• In the slide after that, provide the definitions of ALL the
labels used in the diagram
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INSTRUCTIONS SLIDE
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2
3
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Master layout or diagram
• You may have multiple master
layouts.
– In this case, number the master
layout. ( e.g. Master layout 1)
– Each Master layout should be
followed by the stepwise description
of the animation stages related to it.
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Master Layout 1
1
This is called the energy band diagram
This is called the
conduction band
2
Electrons
-
-
-
Conduction Band
3
This is an
electron
This is called the
valence band
Valence Band
Hole
Hole
4
Hole
This is a hole
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1
Master Layout 2
This is a power
supply.
Display ‘’12 V’ here.
This is a bulb
2
-
These are
wires
+
3
4
5
This is the
sample(silicon)
and Si is the
symbol of silicon
Si
This is the
slider bar
for doping
Doping
0
max
These are the boundary
limits of the slider bar
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1
2
Master Layout 3
This is the
y axis and
σ (mho/m)
is the
heading of
the axis σ (mho/m)
This is a graph
These are the
points on the
graph
3
4
5
This is the
x axis and
ND (/m3 )
is the
heading of
the axis
ND (/m3 )
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1
2
3
4
5
Animation design
• Please see the design template
provided in the next slide.
• This is a sample template, and you
are free to change as per your design
requirements.
• Try and recreate the
sections/subsections as shown in the
template.
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Slide 3
Slide
34 - 39
Slide 4
Lets Learn!
Definitions
Slide 40
Credits
Test your understanding
(questionnaire)
Trivalent
Impurity
Pentavalent
Impurity
Slide 42
Want to know more…
(Further Reading)
Lets Sum up (summary)
Energy Band Diagram
Play/pause
Restart
Conduction Band
Experimental set up
Valence Band
-
These heading
will change
according to the
the
Graph of σ versus Nstep.follow
step
wise
σ (mho/m)
decription for
the correct
heading to be
placed
+
Si
Doping
0
max
Atomic Structure
(Display as a mouse
over)
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N
D (/m3
)
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Explain the process
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3
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In this step, use an example to explain the concept. It
can be an analogy, a scenario, or an action which
explains this concept/process/topic
Try to use examples from day-to-day life to make it
more clear
You have to describe what steps the animator should
take to make your concept come alive as a series of
moving images.
Keep the examples simple to understand, and also to
illustrate/animate.
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1
Stepwise description of process
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2
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3
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
4
5
The goal of the document is to provide instructions to an animator
who is not a expert.
You have to describe what steps the animator should take to make
your concept come alive as a moving visualization.
Use one slide per step. This will ensure clarity of the explanation.
Add a image of the step in the box, and the details in the table
below the box.
You can use any images for reference, but mention about it's
copyright status

The animator will have to re-draw / re-create the drawings

Add more slides as per the requirement of the animation
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We know that the intrinsic semiconductor has little current conduction
capability at room temperature. In order to be useful in electronic devices, how
would you alter the properties of a pure semiconductor so as to significantly
increase its conductivity?
a) By increasing number of free electrons
b) By increasing number of holes
c) Both a and b
c) Either a or b but not both
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Step 1:
Feedback
Refer to slide 15
Description of the action/ interactivity
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3
4
5
Feedback for option a:
That’s correct!
Such a semiconductor is called n type semiconductor.
There's yet another way to increase its conductivity. Go
ahead and interact with the applet to explore this further.
Feedback for option b:
That’s correct!
Such a semiconductor is called p type semiconductor.
There's yet another way to increase its conductivity. Go
ahead and interact with the applet to explore this further.
Feedback for option c:
If we increased the number of electrons as well as the
number of holes then recombination would take place and
this wouldn’t help in increasing the conductivity of the
crystal…Consider this and think about your options
again…
Feedback for option d:
That’s correct!
Such a semiconductor is called an extrinsic
semiconductor. And depending upon the type of impurity
added, It is called an n type or p type semiconductor.
Instruction for the
animator:
•Show the
feedback
according to the
options selected
by the user.
•After displaying
the feedback.let a
radio button for
‘Explore’pop up at
the bottom right
hand side corner.
•If user selects
option c let a pop
up for back also
come up..if the
user clicks on it
then go to slide 15.
•When the user
clicks on it.go to
step 2.
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Opening page
Step 2:
-
Trivalent
Impurity
Pentavalent
Impurity
+
Energy Band Diagram of a pure semiconductor
Si
Electrons
-
-
Doping
0
Conduction Band
max
σ (mho/m)
Valence Band
Hole
Hole
Hole
Atomic Structure
(Display as a mouse
over)
ND (/m3 )
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Step 2
continued:
Instructions
Description of the action/ interactivity
•Initially, let the screen be as indicated in slide 17.
•If the user clicks on the blue rectangle without selecting the options for
Pentavalent impurity or trivalent impurity, display the Image on slide 19 in
place of the Energy band diagram.
•The graph will remain blank here.
•If the user clicks on Pentavalent impurity go to slide 20.
•If the user clicks on Trivalent impurity go to slide 25.
•If the user does not click on the button for either Pentavalent or trivalent
Impurity then the scale for Doping will remain disabled.
•As soon as the user selects an option from either pentavalent or trivalent
then the scale will be enabled.
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Atomic structure
electron
Please include a little minus sign on the electrons...
It is not shown here due to space constraints…
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Step 3: If the user selects Pentavalent Impurity
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Trivalent
Impurity
Pentavalent
Impurity
+
Energy Band Diagram of a doped semiconductor
(n type)
Electrons
-
-
Si
-
Doping
0
Conduction Band
max
σ (mho/m)
Valence Band
Hole
Hole
Hole
Atomic Structure
(Display as a mouse
over)
ND (/m3 )
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Step 3
continued:
Instructions
Description of the action/ interactivity
•Initially, when the user selects pentavalent impurity without varying the
scale(the scale should be at zero), let the screen appear as indicated.
•If the user tries to vary the scale then go to next step.
•If the user clicks on the blue rectangle, go to slide 24.
•If the has not varied the slider bar then the graph will not be plotted.
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Step 3.1 :
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Trivalent
Impurity
Pentavalent
Impurity
+
Energy Band Diagram
-
-
Electrons
-
-
-
-
Si
-
Conduction Band
-
Doping
-
0
max
σ (mho/m)
Valence Band
Hole
Hole
Hole
Atomic Structure
(Display as a mouse
over)
ND (/m3 )
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Step 3.1
continued:
Instructions
Instructions for Slide22
Description of the action/ interactivity
•Let the slider bar for doping be enabled as soon as the user clicks on
Pentavalent Impurity.
•As the user varies the slider bar from zero to max let the bulb gradually glow
brighter and let more number of electrons appear in the conduction band.
•The brightness of the bulb is directly related to the number of electrons in
the conduction band..If the number of electrons in the conduction band are
more, the bulb should accordingly grow brighter.
•If the user clicks on the small blue rectangle for atomic structure show the
image on the next slide in place of the energy band diagram and replace the
mouse over on the blue rectangle with Energy Band Diagram.
•Repeat the animation for the atomic structure until the user clicks on the
small blue rectangle again..
•As the user varies the slider bar, the graph should be plotted dynamically.
•So, the graph should be plotted till the point to which the slider bar has been
dragged. If the user drags the slider bar and leaves it then the graph should
be plotted till that point to which the slider has been dragged.
•Display a pop up somewhere saying:
“Other examples of donor impurities are arsenic and antimony.”
•Display 12V on the power supply.
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P
electron
Free
electron
Free
electron
Free
electron
Free
electron
P
P
Free
electron
P
P
Please include a little minus sign on the electrons...
It is not shown here due to space constraints…
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If the user selects Trivalent
Impurity
Step 4:
-
Trivalent
Impurity
Pentavalent
Impurity
+
Energy Band Diagram of a doped semiconductor
(p type)
Si
Electrons
-
-
-
Doping
0
Conduction Band
max
σ (mho/m)
Valence Band
Hole
Hole
Hole
Atomic Structure
(Display as a mouse
over)
NA (/m3 )
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Step 4
continued:
Instructions
Description of the action/ interactivity
•Initially, when the user selects trivalent impurity, let the screen appear as
indicated.
•If the user tries to vary the scale then go to next step.
•If the user clicks on the blue rectangle, go to slide 29.
•If the has not varied the slider bar then the graph will not be plotted.
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Step 4.1 :
-
Trivalent
Impurity
Pentavalent
Impurity
+
Energy Band Diagram
Electron
-
-
Electron
Conduction Band
Si
Electron
-
Doping
0
max
σ (mho/m)
Holes
Valence Band
Atomic Structure
(Display as a mouse
over)
NA (/m3 )
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Step 4.1
continued:
Instructions
Instructions for Slides 27
Description of the action/ interactivity
•Let the slider bar for doping be enabled as soon as the user clicks on
Trivalent Impurity.
•As the user varies the slider bar from zero to max let the bulb gradually glow
brighter and let more number of holes appear in the valence band.
•The brightness of the bulb is directly related to the number of holes in the
valence band..If the number of holes in the valence band are more, the bulb
should accordingly grow brighter.
•If the user clicks on the small blue rectangle for atomic structure show the
image on the next slide in place of the energy band diagram and replace the
mouse over on the blue rectangle with Energy Band Diagram.
•Repeat the animation for the atomic structure until the user clicks on the
small blue rectangle again..
•As the user varies the slider bar,the graph should be plotted dynamically.
•So, the graph should be plotted till the point to which the slider bar has been
dragged. If the user drags the slider bar and leaves it then the graph should
be plotted till that point to which the slider has been dragged.
•Display a pop up somewhere saying:
“Other examples of acceptor impurities are boron and gallium.”
•Display 12V on the power supply.
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Al
electron
hole
hole
Al
hole
hole
Al
hole
Al
Al
Please include a little minus sign on the electrons...
It is not shown here due to space constraints…
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1
Interactivity and Boundary limits
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2
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
3

4
5

In this section, you will add the ‘Interactivity’ options to the
animation.
Use the template in the next slide to give the details.
Insert the image of the step/s (explained earlier in the
Section 3) in the box, and provide the details in the table
below.
The details of Interactivity could be:
 Types: Drop down, Slider bar, Data inputs etc.
 Options: Select one, Multiple selections etc
 Boundary Limits: Values of the parameters, which won’t
show results after a particular point
 Results: Explain the effect of the interaction in this column
Add more slides if necessary
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1 Interactivity option 1:
Step No:
2
3
Refer to slides 15 to 29.
Interactivity
type
(IO1/IO2..)
Instruction
to the
learner
Boundary
limits
Instructions for the animator
Results and Output
4
5
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INSTRUCTIONS SLIDE
Self- Assessment Questionnaire for
Learners
• Please provide a set of questions that a user
can answer based on the LO. They can be of
the following types:
– These questions should be 5 in number and can be of
objective type (like MCQ, Match the columns, Yes or
No, Sequencing, Odd One Out).
– The questions can also be open-ended. The user
would be asked to think about the question. The
author is requested to provide hints if possible, but a
full answer is not necessary.
– One can include questions, for which the user will
need to interact with the LO (with certain
parameters) in order to answer it.
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INSTRUCTIONS SLIDE
Questionnaire for users to test their
understanding
• Please make sure that the questions can be
answered by interacting with the LO. It is
better to avoid questions based purely on
recall.
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Questionnaire
1. A donor impurity has how many valence electrons?
Answers: a) three
b) four
c)
five
d)six
Correct Answers:1)c
Feedback:
 If user clicks correct answer then display
“Correct! Make sure you can explain the
reasoning!”

If user clicks incorrect answer then display
“Have a look at the atomic structure animation for
the pentavalent impurity and Try again!”

Display one question on one page..When the user selects his answer,
compare with the correct answer and display the appropriate feedback.
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Questionnaire
2. An acceptor impurity has how many valence electrons?
Answers: a) three
b) four
c)
five
d)six
Correct Answers:2)a
Feedback:
 If user clicks correct answer then display
“Correct! Make sure you can explain the
reasoning!”

If user clicks incorrect answer then display
“Have a look at the atomic structure animation for
the trivalent impurity and Try again!”

Display one question on one page..When the user selects his answer,
compare with the correct answer and display the appropriate feedback.
35
Questionnaire
3.What is the difference between the energy band diagram of an n type and p type semiconductor?
Answers: a) n type semiconductor has more number of holes in the valence band as compared to the
number of electrons in the conduction band, where as p type semiconductor has more number of electrons in
the conduction band as compared to the number of holes in the valence band,
b)
n type
semiconductor has more number of electrons in the conduction band as compared to the number of holes in
the valence band, where as p type semiconductor has more number of holes in the valence band as
compared to the number of electrons in the conduction band
c)
the energy band diagrams of
n type and p type are identicald)n type semiconductor has more number of electrons in the conduction band
as compared to the number of holes in the valence band, where as p type semiconductor has equal number
of electron and holes in the conduction and valence band respectively. e) p type semiconductor has more
number of holes in the valence band as compared to the number of electrons in the conduction band where
as n type semiconductor has equal number of electron and holes in the conduction and valence band
respectively.
Correct Answers:3)b
Feedback:

If user clicks correct answer then display “Correct! Make sure you can
explain the reasoning!”

If user clicks incorrect answer then display
“Have a look at the energy band diagrams of the n type and p type
semiconductor and try again! ”

Display one question on one page..When the user selects his answer,
compare with the correct answer and display the appropriate feedback.
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Questionnaire
4. What is the relation between the number of electrons and holes in the
n type semiconductor?
Answers: a) The density of conduction band electrons in an n type
semiconductor is greater than the density of valence band holes.
b)The density of valence band holes in an n type semiconductor is
greater than the density of conduction band electrons. c) The density of
conduction band electrons in an n type semiconductor is equal to the
density of valence band holes.
Correct Answers:4)a
Feedback:

If user clicks correct answer then display “Correct! Make sure
you can explain the reasoning!”

If user clicks incorrect answer then display
“Have a look at the energy band diagrams of the n type

semiconductor and try again! ”
37
Questionnaire
5. What is the relation between the number of electrons and holes in the
p type semiconductor?
Answers: a) The density of conduction band electrons in an p type
semiconductor is greater than the density of valence band holes.
b)The density of valence band holes in an p type semiconductor is
greater than the density of conduction band electrons. c) The density of
conduction band electrons in an p type semiconductor is equal to the
density of valence band holes.
Correct Answers:5)b
Feedback:

If user clicks correct answer then display “Correct! Make sure
you can explain the reasoning!”

If user clicks incorrect answer then display
“Have a look at the energy band diagrams of the p type

semiconductor and try again! ”
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Questionnaire
6.What happens to the conductivity of an extrinsic semiconductor as you
increase the doping?
a)Conductivity decreases as you increase the doping
b)Conductivity remains the same irrespective of the doping.
c)Conductivity increases exponentially as you increase the doping.
d)Conductivity increases as you increase the doping.
Correct Answers:6)d
Feedback:

If user clicks correct answer then display “Correct! Make sure
you can explain the reasoning!”

If user clicks incorrect answer then display
“Have a look at the graphs for the n type and p type
semiconductors and Try again!”

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Links for further reading
Books:
1)Solid state physics-MA Wahab.(chapter
13)
2)Solid state physics-Ashcroft/Mermin.
(Chapter 28)
3)Introduction to modern physicsRichtmyer, Kennard, Cooper.(Chapter 23)
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INSTRUCTIONS SLIDE
Summary
• Please provide points to remember to
understand the concept/ key terms of the
animation
• The summary will help the user in the quick
review of the concept.
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Summary
•
An Extrinsic semiconductor is one in which impurities contribute a significant
fraction of the conduction band electrons and/or valence band holes.
•
And depending upon the type of impurity added, It is called an n type or p type
semiconductor.
•
A pentavalent impurity is called a donor impurity since it supplies additional
electrons to the conduction band, and a trivalent impurity is called an acceptor
impurity since it supplies additional holes to(i.e. capture electrons from)the
valence band.
•
The conductivity of an extrinsic semiconductor goes on increasing with a rise in
the level of doping.
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