Semiconductor materials and pn junction by sarmad baloch
I AM SARMAD KHOSA
BSIT (5TH A)
(ISP)
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2. An Atom
This model was proposed by
Niels Bohr in 1915.
• electrons circle the nucleus.
• nucleus made of:
i) +protons
ii) Neutral:neutron
Bohr model of an atom
3. What is Conductor?
•An element that can easily pass current
•We can also say that an atom that can easily lose an electron from
its outermost shell.
•Conductors have loosely bound electrons in their outer shell
•These electrons require a small amount of energy to free them for
conduction
•The force on each electron is enough to free it from its orbit and it
can jump from atom to atom – the conductor conducts
•Conductors have a low resistance.
5. •Insulators have tightly bound electrons in their outer shell
•These electrons require a very large amount of energy to free
them for conduction
•The force on each electron is not enough to free it from its
orbit and the insulator does not conduct
•Insulators are said to have a high resistivity / resistance
Insulator
6. Semiconductor
•Definition: Semiconductors are those materials that have
a resistance between that of conductors and insulators
•Their electrons are not free to move but a little energy will
free them for conduction
•The two most common semiconductors are silicon and
germanium
7. Conductor, Insulator, Semiconductor
Energy Band
Energy Bands
•Energy gap-the difference between the energy levels of any two orbital shells
•Band-another name for an orbital shell (valence shell=valence band)
•Conduction band –the band outside the valence shell
8. Silicon Atom and Covalent Bond
•Silicon has a valency
of 4 i.e. 4 electrons in
its outer shell
•Each silicon atom
shares its 4 outer
electrons with 4
neighbouring atoms
•These shared
electrons – bonds – are
shown as horizontal
and vertical lines
between the atoms
Slide 8
This picture shows the
shared electrons
9. Heating Silicon
•We have seen that, in
silicon, heat releases
electrons from their
bond.
•This creates electron-
hole pairs which are then
available for conduction
Slide 9
10. Heating Silicon
•If more heat is applies the
process continues…
Slide 10
•More heat…
•More current…
•Less resistance…
•The silicon is acting as a
thermistor
Its resistance decreases with
temperature
12. Intrinsic And Extrinsic
Semiconductor
•Intrinsic Semiconductor: A semiconductor in its pure from is called
Intrinsic Semiconductor. It is undoped.
• Extrinsic Semiconductor: A semiconductor in its impure form or
semi conductor which is doped is called is called extrinsic
Semiconductor.
13. Doping Of An Intrinsic Semiconductor
• Definition: Doping is a process of adding impurity to a
pure semiconductor is called the doping of a
semiconductor.
•When semiconductor is doped, P-Type or N-Type
Semiconductor material is form.
•N-Type semiconductor material have majority of
electrons.
•P-Type semiconductor material have majority of holes.
15. N-Type Semiconductor Material
Slide 15
•Phosphorus is
number 15 in the
periodic table
•It has 15 protons and
15 electrons – 5 of
these electrons are in
its outer shell
16. N-Type Semiconductor Material
•Suppose we
remove a silicon
atom from the
crystal lattice.
•We replace it with
a phosphorus atom
•We now have an
electron that is not
bonded – it is thus
free for conduction
Slide 16
17. N-Type Semiconductor Material
•Let’s remove another
silicon atom and replace it
with a phosphorus atom.
Slide 17
•As more electrons are
available for
conduction we have
increased the
conductivity of the
material
•If we now apply a potential difference across the
silicon
•Phosphorus is called the
dopant
18. Extrinsic Conduction In N-Type
Semiconductor Material
•A current will
flow
•Note: The
negative
electrons move
towards the
positive terminal
Slide 18
19. N-Type Silicon Material
This type of silicon is called n-type
This is because the majority charge carriers are negative
electrons
A small number of minority charge carriers – holes – will
exist due to electrons-hole pairs being created in the silicon
atoms due to heat
The silicon is still electrically neutral as the number of
protons is equal to the number of electrons
Slide 19
21. How P-Type Material Is Forming Using
Boron Atom
Slide 21
•Boron is
number 5 in the
periodic table
•It has 5 protons and
5 electrons – 3 of
these electrons are
in its outer shell
22. Doping – Making p-type Silicon
•As before, we
remove a silicon
atom from the
crystal lattice
•This time we
replace it with a
boron atom
•Notice we have a
hole in a bond – this
hole is thus free for
conduction Slide 22
23. Doping – Making p-type Silicon
•Let’s remove another
silicon atom. and replace it
with another boron atom
•As more holes are available
for conduction we have
increased the conductivity of
the material
Slide 23
•If we now apply a potential difference across the
silicon.
•Boron is the dopant in
this case.
24. Extrinsic Conduction – p-type silicon
A current will
flow – this time
carried by
positive holes
Note:
The positive
holes move
towards the
negative terminal
Slide 24
25. Holes & Hole Current
+ + ++
+
+
+
+
+
+
+
+
+
Hole Movement
Electron Movement
26. P-type Silicon
This type of silicon is called p-type
This is because the majority charge carriers are positive
holes
A small number of minority charge carriers – electrons –
will exist due to electrons-hole pairs being created in the
silicon atoms due to heat
The silicon is still electrically neutral as the number of
protons is equal to the number of electrons
27. Donor And Acceptor Impurity Atom
• Acceptor Dopant: an acceptor is a dopant atom that when
added to a semiconductor can form a p-type region.
•Donor Dopant: a donor is a dopant atom that, when added
to a semiconductor, can form an n-type region.
•Trivalent Impurity: P-type material is formed. Boron is
trivalent impurity
•Pentavalent Impurity: N-Type Material is formed.
Phosphorus is pentavalent impurity.
