L23 : Doping with impurity - Solid States , Chemistry, Class 12 Video Lecture

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poking not so doping can be done by two
method one is electron-rich
you add electron rich impurity as
compared to the intrinsic semiconductor
for example if I am taking silicon add
something which is richer than silicon
or electron deficient which is again
compared to the intrinsic semiconductor
case silicon right so let us try and
understand the electron rich impurity
doping you dope the silicon dope silicon
with electron rich in purity silicon has
4 valence electron so in this case I
will take phosphorous which has 5
valence liquor
correct since this silicon is a group 14
element I will pick something from group
15 correct of the periodic table has 4
valence Ektron says 5 so when you do
this this is my typical silicon
structure now when I do this silicon
with phosphorous or arsenic that is 5
electron what will happen is they'll
occupy some lattice site some silicon
will be replaced with german IAM and
what will happen is 4 out of 5 electrons
will be used to form where for example
if you see now all the 4 valence
electrons are used in formation of
covalent bonds right now if i pick out
this silicon and a sheet of silicon i
put some phosphorus so what happen here
if you see will be borne from here
they'll be gone from here they will be
borne from here will you form bond here
so one bond one electron is extra right
now there are five na this the per
electron is extra so since this electron
is extra this electron comes delocalized
this electron is delocalized this
electron delocalized electron will
increase the conductivity of this doped
silicon or germanium
right so this doped silicon or germanium
is dope with electron-rich impurity
since it has more electron if you see
electrons are negative charge they are
called n-type semiconductor n-type
semiconductor the
let's understand the doping with
electron deficient impurity so you see
this silicon is again group 14 we have
just discussed so if you disk if we do
with something with this group 13 or 12
also then we'll have electron deficit in
guilty so this is the impurity here this
is the impurity this is electron
deficient compared to silicon we'll talk
about electron rich or electron
deficient we compare with silicon or
whatever is the main element right so
here the main solid state is silicon
then the impurity is burrow this silicon
has 4 valence electron this spoon has 3
years left on so this electron deficient
right let's see what happens this is a
silicon structure remove silicon and put
a boron in this case if you see what
happens is this will form a bond this
will hold on this will form what what
will happen is this electron silicon
electron will be free correct if you see
there will be hole created here there is
a hole this is a hole that is created
here correct and until there is a hole
here the neighboring electrons can jump
in this hole so when they can jump in
this hole will see electron traveling
right so if you the direction the if you
see the hole travels if you apply
electric field will you see that the
hole is moving in the direction opposite
of electron flow right if hole moves in
this direction you can see that the
electron is moving in
this direction alright so under the
influence of electric field electric
field the electron will move towards
positively charged clay the electron
holes and this type of transistor is
called p-type for this type of
semiconductor is called p-type silly
connector if you see the application of
n-type and p-type semiconductor these
are used to create transistors is also
used to create solar cells like their
various combination of n time and P
times are used for making lot of
electronic components for example diets
are also used right ICS we use this
transition this diode a told they have
light-emitting that it's normal diet
this also has composition of n-type and
p-type use for dye light-emitting small
tuning bulbs or also used for rectifiers
these transistors they are used by
sandwiching a layer of semiconductor
between our 2 type example you have NPN
transistor or PNP so you take 2 n
semiconductor sandwich with the P or 2 P
sandwich at the end and so this is also
used to detect or amplify radio signals
if solar cells this is also efficient
photo diodes used to convert solar
energy to electrical energy and please
known as gallium arsenide semiconductor
is a very very popular similar traits
very very fast response
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