Junction Transistor Video Lecture | Physics for JAMB

hello friends this video on
semiconductors part 19 is brought to you
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exam please make sure that you have
watched all the videos and part 18
before going ahead with part 19 so we go
another level up right so far we
discussed about we started our
discussion with what is semiconductor
the types of semiconductor p-type
semiconductor n-type semiconductor PN
Junction and then Junction diodes and
now we come to Junction transistors so
Junction transistors wear an excellent
development of semiconductor electronics
this Junction transistor where helpful
and it was able to successfully replace
the valves completely as I mentioned in
our introduction slides so let us see
what is a transistor so here in this
however there are many different types
of transaction not only Junction
transistors these Junction transistors
are also known as bipolar Junction
transistors but since in this lesson we
are only discussing about bipolar
Junction transistor so we will call it
as run so what does a transistor a
device with three connections which is
capable of amplification in addition to
rectification in case of diodes we saw
that it was a two terminal device right
but in case of transistor it has got
three terminals so the transistor is
capable of amplification in addition to
rectification that means the transistor
serves the purpose which diode serve and
in diode also now helped in
rectification but in addition to
rectification the transistor can all is
also capable of amplification
it consists of three doped regions
forming two PN junctions now you must be
thinking what are these three dope
regions because in diode we have just
two regions the P region and the end
engine but in case of
mr. week since it is a three terminal
device so it has got three doped regions
forming two PN junctions that means it
is of this form we have a one type
called NPN where you have first and
n-type semiconductor then a p-type
semiconductor and then again and n-type
semiconductor and the second one is P
and P where a p-type semiconductor is
followed by a n-type semiconductor which
in turn is followed again by a p-type
semiconductor right so these are broadly
the two types of transistor PNP and NPN
right so here you can see that now we
have got two PN junctions this is one
junction between this N and P this is
another junction between this P and n so
in this case we have got two PN
junctions what is the symbol for a
transistor so this is how we denote a
transistor so when I talk about NPN
transistor we have this symbol this
denotes amitabh this denotes base and
this denotes collector you must be
wondering what are these and discuss
each of them in detail in the next slide
here I am just telling you how the
symbol looks like now what is this arrow
for this arrow shows like for example in
case of a diode we had this arrow right
so what was this arrow for this arrow
shows the direction of conveyed
conventional current similarly in this
case also you have this arrow which
shows the direction of conventional
correct in P and P if you see the symbol
remains the same just that this arrow
sign changes because the direction of
conventional current changes now why is
the arrow involves in case of PNP and
outward in case of NPN that you will
understand once I teach you about the
working of a transistor so for now just
look at the symbol whenever it is NPN
the symbol will be towards ammeter
whenever it is PNP turn it towards base
right so now let us understand what are
the different doped regions of the
transistor just now I told you there are
three doped regions what are the three
regions called
they are known as emitter base and
collector these are the three regions so
what is emitter so when I say emitter
emitter is the region at one corner
right so one end is amitabh which is
heavily doped and moderate-sized also to
note that these different doped regions
of the transistor they are of different
sizes depending upon their function they
are also doped differently depending
upon their function some will be
moderately doped some will be very
lightly doped some will be very highly
doped right so emitter is the one which
is heavily doped because as the name
suggests emitter emits the charge
carriers right so if it is heavily doped
then it is got it will be able to emit a
large number of carriers right okay but
the size of the emitter is mortal it it
is neither very large nor very thin okay
so the next region is base base is the
central segment which lies between
emitter and collector it is lightly
doped so base is lightly doped because
base is the intermediate region right so
it is not the source of current carriers
since emitter is the source of current
carriers it is heavily doped so that it
can contribute many charge carriers but
base is lightly doped and it is very
thin as well okay now why is the beach
lightly doped that you understood but
why is it very thin that we will discuss
when we discuss the working of the
transistor the third region is the
collector which is again moderately
doped so as far as doping is concerned
collector and the name again suggests
collector is the one which will collect
the charge carriers
so a meter will emit the charge carriers
and collector will collect them so the
one which which who has to connect the
charge carriers if there doesn't need to
be very highly loaded so that swipe
electric is moderately doped
however the collector is larger in size
so if you look at the three segments
selected is the one which is the largest
in size and breeze is the one which is
the smallest in size so collected is
largest in size that because its purpose
is to collect all the charge gain so it
should have enough space to collect all
the charge carriers so this is how we
define the three different regions that
is the emitter the base and a collector
so these three regions together will
form a transistor right so now the
junction between the PN junctions which
we have what do we call them this
Junction is known as the junction
between the emitter and base is known as
the emitter base Junction
similarly the junction between the base
and the collector is known as the base
collector Junction so the junction
between these two is known as base
collector collector junction junction
between emitter and base is known as
emitter base Junction so this is my
emitter base Junction and this is base
collector Junction thank you please
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