1. Solid State Devices-I
Dr. Vaishali V. Deshmukh
Dept. of Physics
Shri Shivaji Science College, Amravati

2. Introduction to Semiconductor
Lecture -1

3. Postulates
Bohr’s Atomic Model
01
Valence band, Conduction band, Forbidden energy gap
Energy Bands in Solids
03
Properties of Semiconductor
What is Semiconductor?
04
Outline
Insulators, Conductors and Semiconductors
Classification of Solids
02
Silicon and Germanium
Commonly used semiconductors
05

4. Bohr’s Atomic Model
An atom consists of positively charged nucleus around
which negatively charged electrons revolve in different
circular orbits.
The electrons can revolve around the nucleus only in
certain permitted orbits i.e. orbits of certain radii are
allowed.
The electrons in each permitted orbit have a certain fixed
amount of energy. The larger the orbit, the greater is the
energy of electrons
If the electrons is given additional energy (e.g. Heat,
light etc.), it is lifted to the higher orbit. The atom is said to
be in state of excitation. This state does not last long,
because the electron soon falls back to the original lower
orbit. As it falls, it gives back the acquired energy in the
form of heat, light or other radiation.
Electronic distribution of various orbits or energy levels
can be calculated by the formula 2n2. Here, ‘n’ denotes
the number of orbits.
n=1
n=2
Photon

5. Classification of Solids
Semiconductor
Conductor
Insulator
Insulators are the substance
that does not allow heat or
electricity to pass through them.
There are eight valence
electrons in the outermost shell.
Conductivity low
Current flow caused by free
electrons which are negligibly
present.
Insulators are formed by ionic
bonds.
Mica, Rubber, Wood, Paper,
etc
Semiconductors are the substance
whose electrical conductivity lies
between conductors and insulators
There are four valence electrons
in the outermost shell.
Conductivity moderate
Current flow caused by free
electrons and holes.
Semiconductors are formed by
covalent bonding.
Silicon,Germanium ,Aluminium.
Conductors are the substance
that transmits heat or
electricity through them.
There is only one valence
electron in the outermost shell.
Conductivity high
Current flow Caused by the
presence of free electrons.
Conductors are formed by a
metallic bonding.
Gold, Bronze, Silver,
Mercury, Copper, Brass, etc.

6. Energy Bands in Solids

7. What is semiconductor?
Definition: Semiconductor is substance which has resistivity in between
conductors and insulators.
Properties:
The resistivity of a semiconductor is less than an insulator but more than a
conductor.
Semiconductor have negative temperature coefficient of resistance.
When a suitable metalic impurity is added to a semiconductor, its current
conducting properties changes appreciably.
S. No. Substance Nature Resistivity
1 Copper Good conductor 1.7× 10 ‒4 Ωm
2 Germanium Semiconductor 0.6 Ωm
3 Glass Insulator 9× 10 11 Ωm

8. Commonly used semiconductors
Silicon
Germanium

9. I have no
special
talents, I am
just
Passionately
curious Albert Einstein

10. THANK YOU