Types of Semiconductors - Semiconductor Electronics Video Lecture - Class 12

types of semiconductors
intrinsic semiconductor an intrinsic
semiconductor is one which is pure
enough that impurities do not
appreciably affect its electrical
behavior example germanium and silicon
at room temperature the valence electron
absorb thermal energy and get excited
due to absorption of energy the valence
electron jump from the valence band to
the conduction band whenever a valence
electron drips from the valence band to
the conduction band a vacancy is created
in the valence band and such a vacancy
is called a hole thus an electron hole
pair is produced now if a potential
difference is applied across a
semiconductor current will flow through
the external circuit electrons and holes
flow in opposite directions in an
electric field though they contribute to
the current in the same direction since
they are oppositely charged this type of
semiconductor where the conductivity is
due to the movement of electrons and
holes is called the intrinsic
semiconductor thus equal numbers of
electrons and holes are present in an
intrinsic semiconductor extensive
semiconductors conductivity of intrinsic
semiconductor is very less at room
temperature to increase the conductivity
a small amount of external impurities
added to the pure semiconductor such a
semiconductor then becomes impure or
extrinsic semiconductor the process of
deliberate addition of a very small
amount of impurity into an intrinsic
semiconductor to increase its
conductivity is called doping and the
impurities are called dopants
impurities are classified into donor
impurities and acceptor impurities donor
impurities are those elements which
donates excess electron for conduction
pentavalent elements like antimony
phosphorus arsenic our donor impurities
acceptor impurities are those elements
which creates positive carriers all
goals that can accept electrons try
valence elements like boron gallium or
indium our acceptor impurities dominant
carrier concentrations in an extrinsic
semiconductor classify it as either an
n-type or p-type semiconductor n-type
semiconductors if a small amount of
pentavalent impurity is added to an
intrinsic semiconductor then four of the
five valence electrons form a covalent
bond with the four valence electrons of
the intrinsic semiconductor and the
fifth one will be available for
conduction this type of semiconductor
where electron are the current carriers
are known as n-type semiconductor the
phrase n-type comes from the negative
charge of the electron in n-type
semiconductors electrons are the
majority carriers and holes are the
minority carriers n-type semiconductors
are created by doping and intrinsic
semiconductor with donor impurities now
there
and electric field is applied the
current flow is shown in the animation
in an n-type semiconductor the Fermi
energy level is greater than that of the
intrinsic semiconductor and lies closer
to the conduction band than the valence
band p-type semiconductors if a small
amount of trivalent impurity is added to
an intrinsic semiconductor only three
covalent bonds are formed and there
exists a vacancy in the fourth bond
creating a hole this type of
semiconductor where positively charged
holes are the current carriers are known
as p-type semiconductor the phrase
p-type refers to the positive charge of
the hole in p-type semiconductors holes
are the majority carriers and electrons
are the minority carriers p-type
semiconductors are created by doping an
intrinsic semiconductor with acceptor
impurities now when an electric field is
applied the current flow is shown in the
animation