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Semiconductor: What is Intrinsic and Extrinsic Semiconductor ? P-Type and n-Type Semiconductor - YouTube
Channel: ALL ABOUT ELECTRONICS
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Hey friends, welcome to the YouTube channel
ALL ABOUT ELECTRONICS.
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In this video, we will briefly learn about
the semiconductor materials.
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The semiconductor materials are mainly used
for manufacturing electronic devices like
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transistor, diode and the integrated circuits.
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So, if anyone wants to learn about the basic
semiconductor devices, the first of all one
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needs to understand a little bit about semiconductor
physics and the semiconductor materials.
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So, first of all, let's understand why the
semiconductors are used in the electronics.
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And to understand that first of all, let's
see the classification of the materials in
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terms of the conductivity.
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So, in terms of the conductivity, the materials
are classified into three categories.
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Conductor, insulator and the semiconductor.
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Now, for any material, the conductivity defines
how easily this material allows the flow of
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charge.
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And this conductivity is measured in siemens
per meter.
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So, the conductor has very good conductivity
or we can say that whenever the voltage is
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applied to this conductor then it allows the
generous flow of charge.
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So, silver, copper, gold, and aluminum are
the few examples of the conductors.
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And if we take the example of the copper,
then its conductivity is roughly around 10
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to the power 7 Siemens per meter.
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On the other end, if we see any insulator
then it hardly allows any flow of charge.
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Or we can say that this insulator has very
poor conductivity.
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So, the wood, glass, Teflon are the few examples
of the insulator.
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And if we take the example of dry wood, then
its conductivity is roughly around 10 to the
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power minus 14 Siemens per meter.
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So, wood is a very good insulator.
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On the other end, if we take the case of semiconductor
then its conductivity is between the insulator
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and the conductor.
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So, whenever the voltage is applied to this
semiconductor, then it allows the moderate
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amount id current.
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And moreover that by adding the impurities,
the conductivity of the semiconductor material
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can be changed.
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And this property is very useful for designing
the various electronic devices.
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So, silicon, germanium and the Gallium Arsenide
are the few examples of the semiconductor
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materials.
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And here, we will understand the behavior
of the semiconductor by taking the example
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of silicon, which is extensively used in the
electronics industry.
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Now, the atomic number of this silicon is
14.
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So, if we see the atomic structure of this
silicon, it has 14 protons and the 14 electrons.
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So, these 14 protons reside in the nucleus
and 14 electrons rotate around this nucleus.
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And if you see the outermost orbit of the
silicon, then it has 4 electrons.
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Or we can say that the silicon has 4 valence
electrons.
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Now, whenever the silicon atoms combine to
form a solid, then they arrange themselves
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in a particular pattern which is known as
the crystal.
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And in this crystal structure, each silicon
atom shares its four electrons with the neighboring
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atoms.
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And the sharing of the electrons happens in
a such a way that, each silicon atom has 8
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valence electrons.
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And in this way, by sharing the electrons
these silicon atoms forms the covalent bond.
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now, at the temperature just above the 0-degree
Kelvin, due to the thermal energy, the atoms
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in the silicon crystal starts vibrating.
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And due to this vibration, some of the electrons
may get enough energy, so that they can break
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this covalent bonds.
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And by breaking this bonds, this electron
will act as a free electron.
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So, at room temperature, you will find many
such free electrons in this silicon structure.
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Now, whenever this electron, departs from
its position then it creates a vacancy at
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that particular position.
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And this vacancy is known as the hole.
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Now, we know that the charge of the electron
is 1.6 x 10 ^ -19 C.
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And it has a negative charge.
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So, by not having an electron at a particular
position creates a positive charge.
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And this positive charge is known as the hole.
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So, this hole can attract the other free electrons
which are roaming in this vicinity.
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So, as shown in the figure, let's say in this
silicon structure, these two electrons are
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the free electrons.
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And due to this two free electrons, these
two holes have been created.
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Now, let's say, this electron gets recombine
with this hole.
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So, if it gets recombined with this hole,
then the equivalent silicon structure will
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look like this.
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And here let's say, due to the thermal energy,
this electron becomes free and it gets recombined
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with this hole.
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So, in this way, for any silicon structure,
at room temperature, the generation and the
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recombination of holes and electrons happens
continuously.
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And one more thing if you observe, for every
generated electron, the hole is also getting
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generated.
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So, we can say that at the given temperature
the equal number of holes and electrons are
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created in this silicon structure.
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And one more thing if you observe, as the
electrons are moving from one place to the
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other place, the holes are also moving from
one place to the other place.
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So, in semiconductor, we get a flow of current
due to the two types of charges.
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One is due to the electrons and the second
is due to the holes.
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Ans this the biggest difference between the
conductor and the semiconductor.
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Because in the case of a conductor, we used
to get a flow of current only due to electrons.
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Now, this semiconductor can be classified
into two categories.
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One is an intrinsic semiconductor and the
second is an extrinsic semiconductor.
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So, the intrinsic semiconductor is the pure
semiconductor without any kind of impurity
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atoms.
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So, if we take the case of silicon crystal,
then in the intrinsic semiconductor, all the
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atoms would be silicon atoms.
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On the other end, in the extrinsic semiconductor,
the external impurities are added to change
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the conductivity of this semiconductor.
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And the process of adding these impurities
is known as the doping.
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So, by doping the semiconductor, we can change
the conductivity of the semiconductor material.
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And by changing the conductivity, we can control
this semiconductor to behave in a specific
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manner.
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So, this is the reason, these semiconductor
materials are preferred in the electronics
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industry.
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So, depending on the type of impurity or the
dopant, the extrinsic semiconductors can be
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further classified as p-type or n-type semiconductors.
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So, in case of a p-type semiconductor, the
trivalent atoms are added with the silicon
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atoms.
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Now, the trivalent atom means, these atoms
have three electrons in the outer most orbit.
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And the aluminum, boron and the gallium are
the few examples of this trivalent atoms.
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So, since this trivalent atoms have three
electrons in the outer most orbit, the three
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electrons are shared with the neighboring
atoms.
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But still, if you see, the one vacancy remains
in the outer most orbit.
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And due to this vacancy, we can say that the
hole is created in the silicon structure.
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So, we can say that every trivalent atom creates
one hole.
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So, in this way, by adding the trivalent atoms
we can create an excessive amount of holes
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in the crystal structure.
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And these trivalent atoms are known as the
acceptor atoms.
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Because each hole which is created by the
atoms can accept the external free electron.
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Similarly, by adding the pentavalent impurities,
the n-type semicondcutor can be formed.
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So, in the pentavalent atoms, there are five
electrons in the outermost orbit.
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And the few examples of the pentavalent atoms
are arsenic, antimony and the phosphorus.
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So, whenever the pentavalent atom is added
with the silicon atoms then out of the five
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electrons, the four electrons of this pentavalent
atoms will be get shared with the neighbouring
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atoms.
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But still if you see, the one electron in
the valnce orbit.
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So, this electron will act as a free electron,
and it can roam around in the crystal structure.
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So, we can say that each pentavalent atom
creates the one free electron.
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So, by adding this pentavalent impurities,
we can create a excessive amount of electrons
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in the crystal strucutre.
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So, in case of a p-type semiconductor, there
is a excessive amount of holes, while in case
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of a n-type semicondcutor, there is a excessive
amount of electrons.
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So, in n-type semiconductor, the electrons
will be majority carriers, while the hole
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will be the minority carriers.
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Similarly, in case of a p-type semiconductor,
the holes will be the majority carrier and
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the electrons will be the minority carrier.
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Meaning that whenever we apply the voltage
to the p-type semiconductor, then the majority
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of the current which we will get is because
of the holes.
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So, whenever we apply voltage source to this
p-type semiconductor, then the holes will
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get attraced towards the negative termina,
while the electrons will get attracted towards
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the positive terminal.
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But as the number of electrons are less in
this p-type semicondcutor, the majority of
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the current we will get is due to the holes.
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Similarly in the n-type semiconductor, whenever
we apply a voltage source then electrons wil
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lget atteacted towards the positive terminal
and the holes will get attracted towards the
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negative terminal.
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And the majority of the flow of current is
due to the electrons.
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So, in this way, in the semiconductor, we
used to get a flow of current due to the two
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types of charges.
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So, in the next video we will see that what
will happen when we combine this n-type and
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the p-type semiconductors.
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So, I hope in this video, you understood the
basics of this semiconductor.
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So, if you have any question or suggestion,
do let me know here in the comment sectiob
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below.
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