This document provides an overview of a physics unit on semiconductors and superconductivity. It includes 20 slides on semiconductors covering topics like intrinsic and extrinsic semiconductors, doping, carrier concentrations, and the Hall effect. It also includes 37 slides on superconductivity covering critical temperature, Meissner effect, types of superconductors, flux quantization, Cooper pairs, and applications of the Josephson effect and superconductors in areas like energy transmission and magnetic levitation.

1. UNIT-5
•Semiconductors
•Superconductivity
1

2. APPLIED PHYSICS
CODE : 07A1BS05
I B.TECH
CSE, IT, ECE & EEE
UNIT-5 : CHAPTER:1
NO. OF SLIDES :20
2

3. UNIT INDEX
S.No. Module Lectur PPT Slide
e No.
No.
1 Introduction L1-2 4-8
2 Extrinsic L3 9-16
semiconducto
rs
3. EINSTEIN L4-5 17-20
EQUATION
3

4. Lecture-1
• Solids are classified as metals,
semiconductors and insulators.
• Solids with either overlapping
valence band and conduction band
or partially filled valence bands are
metals.
• Solids with finite forbidden gap in
the range 1-3ev are semi conductors.
• Insulators have much larger band
gap. 4

5. • Germanium and silicon are
important semiconductors which are
widely used in the manufacturing of
diodes and transistors.
• Germanium and silicon are
tetravalent atoms i.e they have four
valence electrons. Since all the four
valence electrons are covalently
bound to the four neighboring atoms
the crystal acts as a perfect
insulator at 0k.
5

6. • Germanium and silicon are pure
semiconductors with no impurities.
• At room temperature the thermal enrgy
is sufficient to break covalent bonds.
When a covalent bond is broken a free
electron-hole pair is generated.
• Conductivity increases with
temperature as more and more
electrons cross over the small energy
gap.
6

7. Lecture-2
• In an intrinsic semiconductor, the
Fermi energy level is at the middle of
valence and conduction bands.
• If Ev and Ec are the energy levels
respectively at the top of the
valance band and bottom of
conduction band, the enerrgygap Eg
is given by Eg =Ec-Ev
• And EF=(Ec+Ev)/2
7

8. • The density of electrons is
given by
n= 2(2пme*kT/h2)3/2 exp[ (EF-Ec)/kT]
• The density of holes is given by
p = 2(2пmh*kT/h2)3/2 exp[ (Ev-EF)/kT]
8

9. Lecture-3
Extrinsic semiconductors
• A semiconducting material in which
the charge carriers originate from
impurity atoms added to the material
is called impurity semiconductor or
extrinsic semiconductor.
• The addition of impurity increases
the carrier concentration and hence
the conductivity of the conductor.
9

10. N-type semiconductor
• There are two types of impurities
possible namely pentavalent and
trivalent.
• If a pentavalent atom is doped to the
tetravalent host crystal, four of the
five valence electrons of the
impurity atom form covalent bonds
with four neighboring host atoms
and one electron is left unpaired.
10

11. • Antimony, phosphorous, arsenic etc.,
are examples of pentavalent
elements. When they are added to Si
or Ge as impurities, they are called
donors as they donate free
electrons.
• The semiconductor prepared in this
way will have more electrons than
holes.
• Since the excess free charge is
negative, these are named as N-type 11
semiconductors.

12. • At 0k
EF =(Ed+Ec)/2
• i.e. at 0k Fermi level lies exactly at
the middle of the donor level Ed and
the bottom of the conduction band Ec.
• The density of electrons in the
conduction band is given by
n = 2(2пme*kT/h2)3/4 exp[ (Ed-Ec)/kT]
12

13. P-type semiconductor
• If a trivalent atom is doped into the
trivalent host crystal, its three
valence electrons fill only three of
the four covalent bonds of the host
atoms and one vacancy exists in the
fourth bond.
• Thus in this case one extra hole per
doped atoms is formed.
• The examples of trivalent atoms are
boron, gallium, indium etc.
13

14. L
e
c
• When they t are added to Si or Ge as
impurities, uthey are called acceptors
r
as they readily accept electrons due
e
to the presence of the hole.
-
3
• Since the holes behave like positive
charges, the acceptors are called P-
type impurities and these impure
semiconductors are called P-type
semiconductors.
14

15. • At 0k EF =(Ev+Ea)/2 i.e. Fermi level
lies exactly at the middle of the
acceptor level and the top of
the valence band.
• Density of holes in valence band
is given by
p = 2(2пmh*kT/h2)3/4 exp[ (Ev-Ea)/kT]
15

16. • For a semiconducting material
the electrical conductivity σ is
given by
σ = (neμe + peμh)
Since n=p=ni
σ = (μe + μh) 2e (2пkT/h2)3/2 (me*mh*)3/4
exp(-Eg/2kT)
16

17. Lecture-4
EINSTEIN EQUATION
• The relation between diffusion
coefficient and mobility of a
charge carrier is termed
Einstein equation.
• D n = μekT/e (For electrons)
• Dp = μfkT/e (For holes)
17

18. HALL EFFECT
• When a piece of semiconductor
carrying a current is placed in a
transverse magnetic field, an
electric field is produced inside the
conductor in a direction normal to
both the current and magnetic field.
• This phenomenon is known as the
Hall effect and the generated
voltage is known as Hall voltage.
18

19. Lecture-5
• The Hall coefficient
RH = -1/ne (for n-type
semiconductors)
= 1/pe (for p-type
semiconductors)
19

20. • Mean life time is the time taken for
the injected concentration to fall to
1/e of its initial value.
• Minority carrier life time can be
defined as the time taken for the
excess charge carriers to reduce to
1/e times its initial value, once the
source generating these excess
charge carriers is cut off.
20

21. UNIT INDEX
S.No. Module Lectur PPT
e Slide No.
No.
1 properties of superconductors. L7-8 3-11
2 Types of superconductors L9-10 12-28
3. DC & AC Josephson effect L11-12 29-33
4. Applications L13 34-37
04/10/13 21

22. APPLIED PHYSICS
CODE : 07A1BS05
I B.TECH
CSE, IT, ECE & EEE
UNIT-5: CHAPTER-2
NO. OF SLIDES :37
04/10/13 22

23. Lecture-7
SUPERCONDUCTIVITY.
• Superconductivity is a
phenomenon occurring
in certain materials at
extremely low
temperatures,
characterized by almost
zero
electrical resistance
04/10/13 23

24. • Superconductivity
occurs in a wide variety
of materials, including
simple elements like tin
and aluminium, various
metallic alloys and some
heavily-doped
semiconductors.
04/10/13 24

25. Pu
re
e
p ur
Im
Resistiv
ity
O T
TEMP(K)
c
tance of superconducter suddenly drops t

26. Critical temperature
• The temperature at which
the transition from normal
state to superconducting
state takes place on cooling
in the absence of magnetic
field is called the critical
temperature or the
transition temperature
04/10/13 26

27. • A magnet levitating
above a high-
temperature
superconductor,
cooled with liquid
nitrogen. Persistent
electric current flows
on the surface of the
superconductor,
acting to exclude the
magnetic field of the
magnet (the Meissner
effect). This current
04/10/13 27
effectively forms an

28. Lecture-8
Persistent current
• The electrical current in a
superconducter,in
superconducting state
remains for a long time .
• This current remains for
very long period without
attenuation.
• The time taken by the super
04/10/13 28

29. Effect of magnetic field.
• By applying magnetic field of
sufficient strength,
superconductivity of material
can be destroyed.
• The minimum magnetic field
strength required to destroy
superconductivity of
substance,below Tc is called
critical magnetic field (Hc) at
04/10/13 29

30. Meissner effect.
NORMAL CONDUCTER. SUPERCONDUCTER
B
B
T<Tc
T > Tc
SUPERCONDUCTER EXPELS MAGNETIC LINES OF FORCE.
04/10/13 30

31. Levitation Experiments
Magnets in repulsive mode for
levitation
Meissner Effect
High Tc Superconductor and High Energy
04/10/13 31
Permanent Magnet

32. L
Lecture-9
Types of
e
c
t
Superconductors.
u
r
e
• Depending on the way of
-
1
transition from
superconducting state to
normal state by the
application of magnetic
field, superconductors
are classified into
04/10/13 32

33. TYPE-I
SUPERCONDUCTORS
• Superconductors exhibiting
complete Meissner effect
(perfect diamagnetism) are
called Type-I
Superconductors.
• They are also known as soft
Superconductors.
04/10/13 33

34. • Transition between
normal and
superconducting states
is sharp and well
defined.
• There is only one value
of critical magnetic
04/10/13 34

35. • Critical temperatures are
low. Hence these are not
commercially useful but
are useful to understand
the exciting phenomenon
of superconductivity.
• Type-I Superconductors
are mostly of pure
04/10/13 35

36. TYPE-I SUPERCONDUCTERS
SUPER CONDUCTING
STATE
M
NORMAL
STATE.
O
Hc
RELATION BETWEEN MAGNETIZATION AND
APPLIED MAGNETIC FIELD FOR TYPE-I SUPER
CONDUCTERS.

37. TYPE-II
SUPERCONDUCTERS
• They are developed from
alloys, compounds,
ceramics, transition metals
etc.
• For any Type2 material, two
critical values of applied
magnetic field Hc1 and Hc2
can be identified. In
04/10/13 37

38. • The material behaves as
a perfect superconductor
in the range 0<H<Hc1.
• When H>Hc2 the material
returns to normal state.
• Nb and Zr are some
examples of this type.
04/10/13 38

39. TYPE-II SUPERCONDUCTERS.
SUPERCONDUCTIONG
STATE.
M MIXED
STATE NORMAL
(OR) STATE.
VORTEX
STATE
O Hc1 Hc H
2
Variation of Magnetization with applied magnetic
field for
Type –II superconducters.

40. Super electrons
• According to London
brothers, a
superconductor is
composed of two distinct
type of electrons, i.e.,
normal electrons and
super electrons. super
electrons experience no
04/10/13 40

41. Lecture-10
Penetration depth
• According to London
equations, the magnetic flux
does not drop to zero
suddenly at the surface of
Type-I superconductors, but
decreases exponentially.
The depth from the surface
at which the magnetic flux
04/10/13 41

42. BCS theory
• According to BCS theory,
superelectrons are
responsible for the
superconductivity. They
exist as Cooper pairs.
They form a bound single
system. Their motions are
correlated.
04/10/13 42

43. L
Quantum Tunneling
e
c
t
Metal
u
r Metal
e
-
1
Insulater
I
V

44. Quantum Tunneling
Super
conducter Metal
Insulater
I
Vc V

45. L Available States. QUANTUM TUNNELING
e
c
t
uE
r
e
- Ef Ef
1 E1
Super Conducter Insulater METAL

46. 04/10/13 46

47. Cooper Pairs
04/10/13 47

48. Flux quantization
•The magnetic flux
enclosed by a ring is
quantized. This
concept is known as
flux quantization.
04/10/13 48

49. Lecture-11
Josephson effect
• When a thin insulating
layer is sandwiched
between a metal and a
superconductor or two
superconductors,
electrons can tunnel
through the junction.
Their wave functions on
04/10/13 49

50. d.c. Josephson effect
•A d.c. current flows
across the junction
of two
superconductors
separated by a thin
insulating layer in
04/10/13 50

51. a.c.Josephson effect
•When d.c. voltage
applied across the
junction of the two
superconductors
separated by a thin
insulating layer then
04/10/13 51

52. Applications of
Josephson effect
Lecture-12
• Josephson effect is
used to generate
microwaves with
frequency W = 2eVo/ħ
• A.C. Josephson effect
is used to define
standard volt
04/10/13 52

53. Applications of
Josephson effect
• A.C. Josephson effect is
used to measure very low
temperatures based on the
variation of frequency of the
emitted radiation with
temperature
• A Josephson junction is
used for switching of signals
04/10/13 53

54. Applications of
Lectur
Superconductors e-13
1.It is a basis of new generation of energy saving
power system. Superconducting generators
are smaller in size and less in weight
compare with conventional generators.
These generators consume very low energy,
hence more energy will be saved.
2.All electric power companies are looking
forward to the superconducting
transmission system that would save most
of the energy now being last
04/10/13 54

55. from conventional power lines in the form of
useless radiation and heat.
.3.In japan, Superconducting magnets have been
used to levitate an experimental train above its
track and can drive it at a great speed of 500
Km/h with minimum expenditure of energy. A
similar magnetic propulsion system may be
used to launch satellites into orbits directly
from the earth without the use of rockets.
04/10/13 55

56. 4.High efficiency ore-separating machines are built
using Super-conducting magnets, which are also
used to separate tumour cells from healthy cell by
High Gradient Magnetic separation method.
5.Superconducting materials can be used as a
memory or storage device in computers, since
the current in it can flow without any change in
its value with time.
04/10/13 56

57. 6.Using Superconducting elements one
can build up an extremely fast and
large-scale computer in a compact size.
The power consumed by this computer
will be less than 0.5 watt.
7. The Josephon devices are used to
produce microwaves, which are made
up of superconductors.
04/10/13 57