Contents Introduction of different electrical materials Atomic
theory Energy band Classification of material on the basis of
energy band structure Crystal structure of semiconductor
Semiconductor material Germanium Silicon Intrinsic semiconductor
Extrinsic semiconductor N- type semiconductor P-type
semiconductor
Slide 3
Classification of Electrical and Electronics Engineering
Material The electrical and electronics material can be classified
into following types: 1.Conducting materials 2.Semi conducting
material 3.Insulating material 4.Magnetic material
Slide 4
Conducting material The conducting material are those material
in which the electric current can easily flow. In other word, we
can say that materialls which offer very low resistance to electric
current is called conducting material. The resistivity of these
materials is very low, its values lies between 10 -8 -10 -6 -m. The
most well known conducting materials are copper, aluminum, brass
bronze etc.
Slide 5
Conductor Atomic Structure The atomic structure of good
conductors usually includes only one electron in their outer
shell.atomic structure It is called a valence electron. It is
easily striped from the atom, producing current flow. Copper
Atom
Slide 6
Insulating material The insulating material are those material
which do not allow the passage of electric current or we can say
that material which offer very high resistance to electric current
is called insulating materials. The resistivity of these materials
is very high, its values lies between 10 12 -10 18 -m. The most
well known insulating material are rubber, wood, glass ceramic,
mica etc Most insulators are compounds of several elements. The
atoms are tightly bound to one another so electrons are difficult
to strip away for current flow.
Slide 7
Semi-conducting material The semi-conducting material are those
material whose resistivity is less than insulator but more than
conductor. In other word we can say that conductivity of these
material is less than conductor but more than insulator. The
resistivity of these materials is medium, its values lies between
10 0 -10 2 -m. The most well known insulating material are silicon,
germanium, gallium etc.
Slide 8
Semiconductor Valence Orbit The main characteristic of a
semiconductor element is that it has four electrons in its outer or
valence orbit.
Slide 9
Magnetic material The magnetic material are those materials
which can be magnetized and which are attracted towards the magnet.
Such material create a magnetic field on the surrounding space Iron
nickel and cobalt are most well known used magnetic materials.
Slide 10
Semi - conductor Semiconductor material are those which possess
the conductivity higher than insulators but lesser than conductor
and are used for manufacturing most of the active components.
Slide 11
Atomic Theory The atomic theory state that all the matter
weather solid, liquid or gases consist of minute particles called
molecules which can be further divided into atoms The atom is
defined as tiny discrete particles which is incapable of division.
Those substance whose molecule consist of similar atoms are called
elements and the material whose molecules consist of dissimilar
atoms are called compounds
Slide 12
Bohrs Atomic Theory Bohrs theory tell us that the atom of an
element consist of two main parts I.Nucleus II.Extra nucleus The
central part of an atom is known as nucleus. It contain proton and
neutrons. The nucleus hold the entire mass of an atom. The proton
are the positive charge particles, while neutron are chargeless
particles. Therefore the net charge on nucleus remain positive. The
outermost part of atom arround the nucleus is known as extra-
nucleus. It contain electron only. As the number of electron is
equal to no. of protons, so an atom is therefore electrically
neutral. The no. of electrons in any orbit is given by 2n 2,where n
is the number orbit from nucleus. E.g. 1 st orbit has 2(1) 2 = 2
electron as n = 1 2nd orbit has 2(2) 2 = 8 electron as n = 2 3rd
orbit has 2(3) 2 = 18 electrons as n = 3 4 th orbit has 8
electron
Slide 13
Bohrs Atomic Theory Bohrs atomic theory can be summarized as
follow: a)The atomic no. of an atom is the no. of proton present in
the nucleus b)The algebraic sum of proton and neutron of an atom is
called the atomic weight or mass of the atom. c)The number of
proton inside the nucleus is equal to the number of electron
outside of it. d)The electron on various energy level are arranged
in definite shells named as K,L,M,N e)The outermost orbit of an
atom can contain maximum 8 electron
Slide 14
Classification of material on the basis of atomic structure
a)Conducting material : On the basis of atomic structure conductor
is defined as a substance, whose atom has its outermost orbit
incomplete. Such a substance act as good conductors of an
electricity e.g. aluminum or copper
Slide 15
Classification of material on the basis of atomic structure
I.Copper : It is denoted by Cu having atomic no. = 29 and atomic
weight = 64 no. of electrons = no. of protons no. of electron =
atomic no. Hence no. of electron in Cu =29 no. of neutrons = atomic
weight - atomic no. Therefore no. of neutron = 64 29 = 35 no. of
electron in K shell = 2(1) 2 = 2 (n=1) L shell = 2(2) 2 = 8 (n=2) M
shell = 2(3) 2 = 18 (n=3) N shell = 1 So there is one electron
valence on it, it is called free electron (or valence electron)
Valence electron of an atom are defined as the electron which are
loosely attached to the nucleus at an atom and can be easily
detached
Slide 16
Classification of material on the basis of atomic structure
II.Aluminium (Al) : It is denoted by Al having atomic no. = 13 and
atomic weight 27 no. of electrons = no. of protons no. of electron
= atomic no. Hence no. of electron in Al =13 no. of neutrons =
atomic weight - atomic no. Therefore no. of neutron = 27 13 = 14
no. of electron in K shell = 2(1) 2 = 2 (n=1) L shell = 2(2) 2 = 8
(n=2) M shell = 3 (n=3) So there is 3 electron valence on it, it is
called free electron (or valence electron) Valence electron of an
atom are defined as the electron which are loosely attached to the
nucleus at an atom and can be easily detached
Slide 17
Classification of material on the basis of atomic structure
b)Semiconducting material : In semiconducting materials, if a
potential difference is applied across the end of the material, a
partial flow of electron takes place i.e. some of electron can be
detached from the atom and some of them cannot be detached, hence
the conduction is partial and therefore the properties of
semiconductor are in between those of conductor and insulator e.g.
silicon and germanium.
Slide 18
Classification of material on the basis of atomic structure
I.Silicon(Si) : it is denoted by Si having atomic no. = 14 And
atomic weight = 28 no. of electrons = no. of protons no. of
electron = atomic no. Hence no. of electron in Si =14 no. of
neutrons = atomic weight - atomic no. Therefore no. of neutron =
28-14 = 14 no. of electron in K shell = 2(1) 2 = 2 (n=1) L shell =
2(2) 2 = 8 (n=2) M shell = 4 So there is 4 electron valence in its
outermost orbit
Slide 19
Classification of material on the basis of atomic structure
II.Germanium (Ge) : it is denoted by Ge having atomic no. = 32 And
atomic weight = 73 no. of electrons = no. of protons no. of
electron = atomic no. Hence no. of electron in Si =32 no. of
neutrons = atomic weight - atomic no. Therefore no. of neutron =
73-32 = 41 no. of electron in K shell = 2(1) 2 = 2 (n=1) L shell =
2(2) 2 = 8 (n=2) M shell = 2(3) 2 = 18 (n=3) N shell = 4 So there
is 4 electron valence in its outermost orbit
Slide 20
Classification of material on the basis of atomic structure
c)Insulator : In insulating material the electron are firmly held
to their atom and hence if a potential difference is applied then a
little or no electron flow occurs There fore no electron can be
detached from outermost orbit so it is not easy to pass the
electric current through them. e.g. neon Neon (Ne) atomic no. 10
no. of electron = atomic no. =10 no. of electron in K shell =2(1) 2
= 2 n=1 L shell =2(2) 2 = 8 n=2 It outer most orbit does not
contain any free electron as its outer most orbit is completely
filled.
Slide 21
Energy band theory In an atom, the electron revolving in
different orbits possesses certain energy level. The amount of
energy on each orbit is fixed. but when we talks about solids,
where the atoms are closely packed the electron on various orbits
are influenced by energy of electrons of neighboring orbits. In
that case, energies of various bands are considered in a single
band. So the range of energy possessed by various electrons of the
same orbit of different atoms in a solid is known as energy
band.
Slide 22
Energy band theory Following are the important types of energy
bands: a)Valence band : The range of energy possessed by valence
electron (electron present in outer most orbit) is called valence
band. This band may be completely or partially filled by valence
electrons. b)Conduction band : The range of energy possesed by free
electron (electrons responsible for conduction) is called
conduction band. The conduction in solid is possible only when some
electron are present in conduction band. c)Forbidden energy gap:
The energy gap existing between a conduction band and valence band
is known as forbidden energy gap. There is no electron in this
region. The electrons can only jump to conduction band when they
receive extra energy from external source.
Slide 23
Classification of material on the basis of energy band
Insulators: Insulator are those material in which we cannot pass
the electric current easily. In insulator, conduction band remain
empty, while valence band has many electrons. In this case
forbidden energy gap between valence band and conduction band is
quite large approx 20eV) so it is not easy to conduct electric
current through them.
Slide 24
Classification of material on the basis of energy band Semi
conductor : Semiconductor material are those material whose
resistivity lies between conductor and insulator. In semiconductor
valence band is full of electron while conduction band is empty.
But in this case, energy gap is very small (1 eV) with the
application of small potential difference electron can jump from
valence band to conduction band.
Slide 25
Classification of material on the basis of energy band
Conductor : Conductor are those material which offer least
resistance to electric current. Here conduction band is overlapped
with valence band. So large no. of electrons can jump from valence
band to conduction band with the application of small potential
difference
Slide 26
Semiconductor material Semiconductor material are those which
possess the conductivity higher than insulators but lesser than
conductor and are used for manufacturing most of the active
components.
Slide 27
Semiconductor materials Silicon and germanium each have 4
electrons in their outer orbital. To fill the outer most shell each
atom acquire four more electron by sharing one electron each from
the four adjacent atoms and hence form the crystal. In a crystal
the atom are bonded together in cohesive manner. In the fig, the
core represent the nucleus and all other electron as valence
electrons. The valence electron take part in forming covalent bonds
with four neighbouring atoms. At absolute zero all four covalent
bond are intact and no electron is free to conduct. A chip, an LED
and a transistor are all made from semiconductor material.
Slide 28
Germanium Germanium (Ge) is an earth element pure germanium is
obtained from coal ash in the form of germanium dioxide, which is
then reduced to pure germanium.
Slide 29
Germanium Atomic structure : The atomic no. Ge is 32. therefore
it has 32 protons in its nucleus along with 32 neutrons and 32
electron which revolves around the necleus in fixed paths known as
orbits These 32 electrons can be distributed in various orbits or
shells according to the rule 2n 2 where n is orbit no. except that
there are four electrons in the outermost orbit. This outermost
orbit is also known as valence orbit. The germanium atom has two
electron in its first orbit four electron in second orbit eighteen
electron in its third orbit, and only four electron in its valence
shell.
Slide 30
Germanium Crystal structure : A substance in which the atoms or
molecules are arranged in an orderly pattern is known as a crystal
All semiconductor have crystalline structure. Each atom is
surrounded by a neighbouring atoms in a repetitive manner.
Therefore in a germanium crystal a large number of atoms are bonded
together This bonding is due to the fact that each atom has
tendency to complete its outermost or valence orbit by acquiring
eight electron in it. However in most of the substance the last
orbit is incomplete i.e. last orbit does not have 8 electrons. This
makes the atom active to bargain with the other atoms to acquire 8
electron in the last orbit. To do so the atom may lose gain or
share valence electron with other atoms.
Slide 31
Germanium In semiconductor bonds are formed by sharing the
valence electrons of an atom with the neighboring atoms. This type
of bonding in which which bonds are formed by sharing the valence
electrons are called covalent bonds. The various germanium atom are
held together through covalent bond to form a germanium crystal as
shown in fig The covalent bond in between the various Ge atoms are
formed by sharing their valence electron with the neighboring
atoms. Since germanium is tetravalent element each atom forms four
covalent bonds with the four neighboring atoms.
Slide 32
Silicon Atomic structure : The atomic no. Si is 14. therefore
it has 14 protons in its nucleus along with 14 neutrons and 14
electron which revolves around the nucleus in fixed paths known as
orbits The no. of electrons in first, second and third orbit are
2,8 and 4 respectively as shown in fig. The silicon has 4 electrons
in its valence shell so it is also known as tetravalent.
Slide 33
Silicon Crystal structure : Like germanium silicon atoms are
also arranged in an orderly manner to form a silicon crystal. The
crystal structure of Si is shown in fig it is quite similar to that
of germanium crystal.
Slide 34
Concept of electron and hole At absolute zero, the valence band
in the intrinsic semiconductors is totally filled and the
conduction band is empty. Since there are four covalent bond each
bond is not so strong. When the temperature is increased the
electron get sufficient energy to make a valence electron to move
away from the influence of its nucleus.when this happen the
electron becomes free to conduct and hence appears in the
conduction band. When an electron moves away to the conduction
band, a vacancy is created in the valence band. This vacancy is
called hole. Whenever a free electron is generated a hole is
created simultaneously Fig shows the generation of electron hole
pair in semiconductor. The amount of energy required to break a
covalent bond in germanium is 0.72eV and that in silicon is 1.12eV.
When such energy is supplied, one of the covalent bond is broken
and the electron appears in conduction band. This result in
generation of holes. The hole does remain stable and is quickly
filled by the electron from the adjacent covalent bond. The hole is
generated there. This way electron and hole moves in opposite
direction
Slide 35
Intrinsic semiconductor An extremely pure semiconductor is
called intrinsic semiconductor
Slide 36
INTRINSIC SEMICONDUCTOR At zero Kelvin all of the four valence
electrons of each atom in the silicon crystal form part of the
covalent bond with the four neighboring atoms. The valence band is
completely full and the conduction band completely empty. The
semiconductor behaves as a perfect insulator because there are no
conducting electrons present.
Slide 37
INTRINSIC SEMICONDUCTOR At temperatures above zero Kelvin some
of the valence electrons are able to break free from their bonds to
become free conduction electrons. The vacancy that is left behind
is referred to as a hole. This hole is treated as a positive
carrier of charge. Conduction due solely to thermally generated
electron-hole pairs is referred to as intrinsic conduction.
Slide 38
Extrinsic semiconductor An doped semiconductor is called
extrinsic semiconductor. The process by which the an impurity is
added to a semiconductor is known as doping. A semiconductor to
which an impurity at controlled rate is added to make it conductive
is known as extrinsic semiconductor.
Slide 39
Doping Silicon to Create n-Type and p-Type Silicon The process
of doping, creates p-type and n-type silicon. Materials introduce
an atom of another element into the silicon crystal to alter the
electrical properties. The "dopant has either 3 or 5 valence
electrons; silicon has 4. Substituting a phosphorus atom with 5
valence electrons for a silicon atom in a silicon crystal leaves an
extra, unbonded electron that is relatively free to move around the
crystal. Substituting a boron atom with 3 valence electrons for a
silicon atom in a silicon crystal leaves a hole (a bond missing an
electron) that is relatively free to move around the crystal.
Slide 40
When a dopant atom with a valence of less than four is
substituted into the silicon structure, a hole is created in the
structure and an acceptor energy level is created just above the
valence band. Little energy is required to excite the holes into
motion.
Slide 41
EXTRINSIC CONDUCTION A pure or intrinsic conductor has
thermally generated holes and electrons. However these are
relatively few in number. An enormous increase in the number of
charge carriers can by achieved by introducing impurities into the
semiconductor in a controlled manner. The result is the formation
of an extrinsic semiconductor. This process is referred to as
doping. There are basically two types of impurities: donor
impurities and acceptor impurities. Donor impurities are made up of
atoms (arsenic for example) which have five valence electrons.
Acceptor impurities are made up of atoms (gallium for example)
which have three valence electrons.
Slide 42
N-TYPE EXTRINSIC SEMICONDUCTOR Arsenic has 5 valence electrons,
however, only 4 of them form part of covalent bonds. The 5 th
electron is then free to take part in conduction. The electrons are
said to be the majority carriers and the holes are said to be the
minority carriers.
Slide 43
P-TYPE EXTRINSIC SEMICONDUCTOR Gallium has 3 valence electrons,
however, there are 4 covalent bonds to fill. The 4 th bond
therefore remains vacant producing a hole. The holes are said to be
the majority carriers and the electrons are said to be the minority
carriers.
Slide 44
Revision Atomic Theory Atomic Theory Energy band Energy band
Classification of material on the basis of energy band structure
Classification of material on the basis of energy band structure
Semiconductor material Semiconductor material Crystal structure of
semiconductor Crystal structure of semiconductor Germanium Silicon
Intrinsic semiconductor Intrinsic semiconductor Extrinsic
semiconductor Extrinsic semiconductor N- type semiconductor P-type
semiconductor