Transcript Lecture-7 - Dr. Imtiaz Hussain

Electronic workshop
Lecture-7
Diodes and Transistors
Dr. Imtiaz Hussain
email: [email protected]
URL :http://imtiazhussainkalwar.weebly.com/
Semiconductor Diodes
• Diode is constructed by fusing two different types
of doped semiconductors (P-type and N-type)
together.
What Are Diodes Made Out Of?
• Silicon (Si) and Germanium (Ge) are the two
most common single elements that are used to
make Diodes.
• Silicon and Germanium are both group 4
elements, meaning they have
4 valence
electrons. Their structure allows them to grow
in a shape called the diamond lattice.
• In diamond lattice lattice, each atom shares its
valence electrons with its four closest
neighbors.
• This sharing of electrons is what ultimately
allows diodes to be build. When dopants from
groups 3 or 5 (in most cases) are added to Si or
Ge it changes the properties of the material so
we are able to make the P- and N-type materials
that become the diode.
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
N-Type Material
• When extra valence electrons are introduced
into a material such as silicon an n-type
material is produced.
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+5
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• The extra valence electrons are introduced
by putting impurities or dopants into the
silicon.
• The dopants used to create an n-type
material are Group V elements. The most
commonly used dopants from Group V are
arsenic, antimony and phosphorus.
• The 2D diagram to the left shows the extra
electron that will be present when a Group V
dopant is introduced to a material such as
silicon. This extra electron is very mobile.
P-Type Material
• P-type material is produced when the
dopant that is introduced is from Group III.
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• Group III elements have only 3 valence
electrons and therefore there is an electron
missing.
• This creates a hole (h+), or a positive charge
that can move around in the material.
Commonly used Group III dopants are
aluminum, boron, and gallium.
• The 2D diagram to the left shows the hole
that will be present when a Group III dopant
is introduced to a material such as silicon.
This hole is quite mobile in the same way the
extra electron is mobile in a n-type material.
What Are Diodes Made Out Of?
• Silicon (Si) and Germanium (Ge) are the two most
common single elements that are used to make
Diodes. Gallium is a group 3 element while
Arsenide is a group 5 element. When put together
as a compound, GaAs creates a zincblend lattice
structure.
• In zincblend lattice, each atom shares its valence
electrons with its four closest neighbors. This
sharing of electrons is what ultimately allows diodes
to be build. When dopants from groups 3 or 5 (in
most cases) are added to Si, Ge or GaAs it changes
the properties of the material so we are able to make
the P- and N-type materials that become the diode.
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Si
+4
Diode Terminals
Diode Biasing
Short Circuit
Forward Biased Diode
Open Circuit
Reverse Biased Diode
Light Emitting Diode (LED)
• A compound that is commonly used for LEDs construction
is Gallium Arsenide (GaAs), because of it’s large bandgap.
• Gallium is a group 3 element while Arsenide is a group 5
element.
• When put together as a compound, GaAs creates a
zincblend lattice structure.
Light Emitting Diode (LED)
Task#1
• Take few diodes and check it using multimeter’s continuity function and
fill in the following table.
S. N.o
1.
2.
3.
4.
5.
Model
Voltage
Implication
Reverse Bias Forward Bias
Task#2
• Take few LEDs and check it using the same method as task#1 and fill in
the following table.
S. N.o
1.
2.
3.
4.
5.
Color
On/Off
Implication
Reverse Bias Forward Bias
Transistor
• A transistor is a 3 terminal device that is used in
a variety of applications such as amplification
and switching.
• There are two types of transistors categorized
according to their construction:
– Bipolar Junction Transistor (BJT)
– Field Effect Transistor (FET)
BJT
• The Bipolar Junction Transistor (BJT) comes in two
flavors
FET
• It is a two layer three terminal device made up of
two pieces of semiconductors.
• Like the BJT, this comes in two flavors too
Task#3
S N.o Terminals of the BJT Type of Transistor
A
B
C
NPN/PNP
1.
2.
3.
4.
5.
Implication
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END OF LECTURE-7