It is a very important topic.

1. Submitted by –
ADITYA GHOSH
ARGHAYA GOSWAMI
DEBOJYOTI MUKHERJEE
PRITAM SARDAR
PROHLAD MONDAL
Department of Electronics & Communication
Engineering(6th semester)
Swami Vivekananda Institute of Science &
SEMICONDUCTORLASERPRINCIPLE

2. Content
 Introduction
 Difference between LED and Laser
 Types of Semiconductors
 Requirement of Laser
 Generation of Laser
 Classification of Semiconductor Laser
 Characteristics
 Non Semiconductor Laser
 Main application
 Advantage of Semiconductor
 Disadvantage of Semiconductor
 Conclusion

3. Introduction
In laser, light amplification is achieved via
stimulated emission.
Stimulated emission had been proposed by Albert
Einstein in 1915
Fig1:Laser

4. Difference between LED and Laser
Fig 2: Wavelength of LED and Laser
LED Laser
Principle Spontaneous Emission (Random)
Photon Emission
Stimulated Emission
Coherence Incoherent Coherent
SpectralWidth/LineWidth 50nm Less than 5nm
Directionality Not directional Highly directional
Output Power Low High

5. Types of Semiconductors
Fig 2:Wavelength of LED and Laser
Fig 3:Types of Semiconductor

6. Intrinsic & Extrinsic Semiconductors
 Intrinsic semiconductor : A perfect
material with no impurities.
 Extrinsic semiconductor : donor or
acceptor type semiconductors.
 Majority carriers: electrons in n-type or
holes in p-type.
 Minority carriers: holes in n-type or
electrons in p-type.
 The operation of semiconductor devices is
essentially based on the injection and
extraction of minority carriers.
2
inpn 

7. n-Type Semiconductor
Fig4: Donor level in an n-type semiconductor.

8. p-Type Semiconductor
Fig5: Acceptor level in an p-type semiconductor.

9. Requirement of Laser
 Conditions required:
1. Population inversion- the number of electrons in CB is greater
than the number of electrons in VB
2. Emission
3. Optical resonator or Fabry-Perot resonator
Spontaneous
emission
Stimulated emission

10. Population Inversion
Fig 6: thermal equilibrium condition for
degenerate semiconductor (without
biasing)
Fig 7: Population inversion occurs with
biasing

11. Emission
Spontaneous Emission Stimulated emission
Fig 8: spontaneous emission Fig 9: stimulated emission

12. Optical Resonator
 Mostly used the structure of Fabry-Perot resonator
 Used:
i) to increase the density of photon in active region
ii) to amplify the medium radiation
Fig 10:optical resonator cavity
Fig 11:power with phase shift

13. Generation of Laser
Fig 12: Generation diagram of Laser

14. Classification Of Semiconductor
Laser
Semiconductor Laser
Homojunction
Semiconductor Laser
Heterojunction
Semiconductor Laser
Double
Heterojunction
Semiconductor Laser
Single
Heterojunction
Semiconductor Laser

15. Homojunction Semiconductor Laser
Homojunction diode lasers are those in which P end and N end of the diode are made of
the same semiconductor material.
Example : Ga As laser
 They use Direct Band Gap
Semi- conductor material.
 P-N Junction act as the active
medium.
 The crystal is cut at a thickness of
0.5 mm
 Applied voltage is given through
metal contacts on both surfaces of
the diode.
 Pulse beam of laser of 8400 Å is
produced
Fig13: Diagram of Homojunction
Semiconductor Laser

16. Energy Level Diagram : Homojunction
Fig14: Energy level Diagram of Homojunction
Semiconductor Laser

17. Heterojunction Semiconductor Laser
Heterojunction Semiconductor lasers are those in which P end is made of one type
of semiconductor material and the N end is made of another type of semiconductor
material
Example : GaAlAs diode laser
 Use Direct Band gap
Semiconductor
 Consist of five layers namely
 GaAs – p type
 GaAlAs – p type
 GaAs – p type (Active Medium)
 GaAIAs – n type
 GaAs – n type
Fig15: Diagram of Heterojunction
Semiconductor Laser

18. Energy Level Diagram : Heterojunction
Fig 16: Energy level Diagram of
Heterojunction Semiconductor Laser

19. Characteristics
1) Type: It is a solid state semiconductor laser.
2) Active medium: A PN junction diode made from
single crystal of gallium arsenide is used as an
active medium.
3) Pumping method: The direct conversion
method is used for pumping action
4) Power output: The power output from this laser
is 1mW.
5) Nature of output: The nature of output is
continuous wave or pulsed output.

20. Non semiconductor Laser
Ruby LASER:
Fig 17:Pumping levels for Ruby Laser

21. He-Ne Laser
Fig 18: Diagram of He-Ne Laser

22. Main applications
 Optical fiber communications
 Optical storage
No diode laser
= No internet!
Diode lasers are also widely used in printers,
scanners, sensors, pumping of solid-state
lasers, etc.
The diode laser in a computer mouse costs
about 10 US cents .

23. Laser Range Finder
The laser range finder works on the principle of a radar
& use to knock down an enemy tank.
23
Fig 19: working diagram of Laser Range Finder

24. Underwater Laser
 Lasers can also be used as a source of underwater
transmission. At present, the submarines have to
rely on a sonar to find the enemy crafts and to
avoid the underwater objects.
24
Fig 19: working diagram of Underwater Laser

25. Advantages of semiconductor laser
Smaller size
Semiconductor laser are economical in
cost.
Its construction is simple.
It has high efficiency.
low power consumption.

26. Disadvantages of semiconductor laser
 Due to relatively low power production, these
lasers not suited to typical laser applications
 The temperature affects greatly the output of
the laser
 Beam divergence is much greater as compared
to all other lasers
 Cooling system required in some cases

27. Conclusion
Semiconductor laser have been around for
about forty years now, but their possible uses
continue to grow each day. We are at the new
dawn of the millennium, and Semiconductor
Laser will help bring about a new revolution
in many fields of science; the new optical
solution revolution!