This PPt. helps to know about the basic fundamental of laser diode fabrication.

1. STUDY OF THE FABRICATION
OF SEMICONDUCTOR LASER
DIODES
Done At
SOLID STATE PHYSICS
LABORATORY(DRDO)
PREPARED BY:-
Uttam Singh Thakran
09196504912
Electrical and Electronics Engineering

2. TOPICS TO BE COVERED
 Introduction to lasers
 Principle and theory of lasers
 Types of lasers
 Properties of lasers
 Applications of lasers
 Introduction to semiconductor lasers
 Operation of semiconductor laser diode
 Types of semiconductor lasers
 Applications
 Overview of fabrication process
 Steps for fabrication process
 conclusion

3. Introduction to lasers
 LASER is an acronym for “Light
Amplification by Stimulated Emission of
Radiation”, coined in 1957 by the laser
pioneer Gordon Gould.
 The term “Optical Maser” (MASER=
Microwave Amplification by Stimulated
Emission of Radiation) was initially used,
but later replaced with “laser”.
 Laser technology is at the core of the
wider area of photonics, essentially
because laser light has a number of very
special properties.

4. Principle of LASER
 The principle of laser is based on the stimulated
emission of light.
 The components of a typical laser are:-
1. Gain Medium for Population energy
2. Laser Pumping energy
3. Cavity
4.Reflector
5.Laser Beam

5. Theory of LASER
 Spontaneous Emission
 Stimulated Emission
 Population Inversion
Spontaneous Emission Stimulated Emission

6. Types of LASER
 Gas Lasers
 Chemical Lasers
 Excimer(Excited Dimer) Lasers
 Dye Lasers
 Semiconductor lasers

7. Properties of LASER
Lasers show three important properties:-
 Monochromaticity
 Coherence (Properties of Lasers)
 Directionality

8. Applications of LASER
 Manufacturing
 Medical applications
 Military applications
 Communication
 Data storage

9. Introduction to semiconductor laser
diodes
 A semiconductor laser diode is formed when
a crystal is doped to produce to produce an
n-type region and a p-type region, one above
the other resulting in a p-n junction or diode.
 A laser diode is powered by injecting electric
current and therefore, they are sometimes
referred to as injection laser diodes.
 Laser diodes find a wide use in
telecommunications. Infrared and red laser
diodes are used in CD players, CDROMs and
in DVD technology.
 Violet lasers are used in HD DVD and blu-ray
technology.

10. Operation of semiconductor laser
diode
 A typical Laser diode consists of two semiconductors,
one sandwiched above the other.
 Top semiconductor is GaAs- Provides holes. It is a P-
type semiconductor.
 At Bottom we use GaAs and Se(Gallium Arsenide and
Selinium). It acts as N-type semiconductor.
 P-N junction is between both the semiconductor.
 When current is passed through semiconductors then
Electrons and Holes starts moving towards P-N junction.
 Electrons from N-type semiconductor and Holes from P-
type semiconductor combines.

11.  Since, Holes exists at lower level, hence free Electron
can combine with it only after radiating energy in the
form of Photon.
 The top and bottom of P-N junction is coated by a
mirrored material in order to trap the Photon of light.
 This Photon encourages other Electrons and Holes to
generate Photons which will be in same Phase and the
process will continue until the P-N junction is filled with
Laser light.
 Some of Laser light exits in rear side which will fall on
Photodiode and uses this information to regulate the
voltage to Laser Diode.
 Large amount of diffracted light exits through front of
laser diode and the diffracted light is then made into a
single beam by using Collimating Lens.

12. Types of semiconductor laser
diodes
 Double hetero-structure laser
 Quantum well laser
 Quantum cascade laser
 Separate confinement hetero-junction laser
 VCSEL(Vertical Cavity Surface Emitting
Lasers)
During our fabrication process of
semiconductor laser diode at SSPL, we have
only used Quantum well lasers.

13. Applications of semiconductor laser
diodes
 Laser Range Finder(LRF)……..(1)
 Proximity Fuses............................(2)
 Dazzler weapon……………....(3)
(1) (2) (3)

14. Overview of the fabrication process
 The fabrication process for Quantum well
semiconductor laser is shown here.
 Steps are performed in cleanroom facility
under contamination control because this
laser deals with micro-size features and
minor contaminations can be a critical risk.
 More attention is required in dealing with a
piece of wafer than to the whole wafer.
 Since, whole wafer is expensive
therefore a piece of wafer is suitable
to develop the process.

15. Steps for the fabrication process
There are several steps involved in the
fabrication process which are
mentioned below.

16.  EPITAXIAL GROWTH
(GaAs wafer)
Cap
Cladding
Waveguide
Active Region
Waveguide
Cladding
Substrate

17.  PHOTOLITHOGRAPHY FOR MESA
(spin coating photoresist on wafer)
(MESA patterning by photolithography process)
Photoresist
Photoresist

18.  MASK ETCHING
(wet MESA Etching of GaAs wafer)
(Removing photoresist after etching process)
Photoresist
Cap
Cap
Substrate

19.  DIECTRIC(SiO2) DEPOSITION
(oxide layer deposition on E-beam evaporator)
(stripe patterning on oxide by photolithography)
SiO2
Photoresist
SiO2

20.  METALLIZATION
(Metal deposition on P-side)
(Polishing the bottom side of GaAs Wafer)
P contact
P contact
SiO2

21. (Metal deposition on N-side)
 For P-side ohmic contact, Chromium(Cr) and Gold(Au) are
deposited by E-beam evaporator.
 The next step is the polishing of the bottom side of GaAs
substrate for N-side contact.
 For N-side ohmic contacts Ge(Germanium), Ni(Nickel) and
Au(Gold) are deposited by E-beam evaporator.
N contact

22.  CLEAVING PROCESS
 In this step, each laser is cleaved by hand. After
that, the facets of Lasers are coated with
Asymmetric Reflectivities.
 One facet is Partially Reflecting(PR), from which
Laser comes out, whereas the other facet is High
Reflecting(HR) which reflects Laser beam towards
the PR facet.
Coating the facet

23.  BONDING AND PACKAGING
(Die attach and wire bond on heat sink)
 The last step is the Bonding process between heat-sink
with Indium solder. Indium solder is widely used to
bond Semiconductor Lasers due to its simplicity and it
can bond directly to Copper(Cu).

24. THANK YOU