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E-Photon One Curriculum
2B- Optical Technologies
Coordinator: António Teixeira, Co-Coordinator: K. Heggarty
António Teixeira, Paulo André, Rogério
Nogueira, Tiago Silveira, Ana Ferreira,
Mário Lima, Ferreira da Rocha, João
Andrade
© 2005, it - instituto de telecomunicações. Todos os direitos reservados.
This tutorial is licensed under the Creative Commons
http://creativecommons.org/licenses/by-nc-sa/3.0/
Program
1.
2.
3.
4.
Basic Photonic Measurements
Material growth and processing
Semiconductor materials
Transmission systems
performance assessment tools
5. Optical Amplifiers
a)
b)
c)
d)
Semiconductor Optical Amplifiers
(SOAs)
Erbium Doped Fiber Amplifiers
(EDFAs)
Fiber Amplifiers- Raman
Other Amplifiers
6. Emitters
a)
b)
Semiconductor
Fiber
7. Receivers
a)
b)
PIN
APD
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8. Modulators
a) Mach Zehnder
b) Electro-absorption
c) Acoust-optic
9. Filters
a) Fiber Bragg gratings
b) Fabry Perot
c) Mach-Zehnder
10. Isolators
11. Couplers
12. Switches
a) Mechanical
b) Wavelength converters
c) Multiplexers/ Demultiplexers
Paulo André
Material Growth and Processing
© 2005, it - instituto de telecomunicações. Todos os direitos reservados.
This tutorial is licensed under the Creative Commons
http://creativecommons.org/licenses/by-nc-sa/3.0/
2. Material Growth and Processing
1.1. States of Matter (2)
1.2. Material Structure (16)
1.3. Brillouin zones (2)
1.4. Miller indexes (2)
1.5. Growing Steps and Processes (13)
1.6. Manufacture of Microelectronic devices (1)
1.6.1. Photolithography (9)
1.6.2. p-n junction manufacture (4)
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States of Matter
 Gaseous
 Liquid
 Solid
Crystalline: the long range crystalline
order extends to the all of the material.
Polycrystalline: the long range crystalline
order is about the same size of the crystals
Amorphous: short range order
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States of matter
 The macroscopic properties (electrical, optical and mechanical, …)
of a material depend on the internal organization of the atoms and
also from the interatomic forces that bind them.
Diamond
Graphyte
Most electronic and optoelectronic devices are made of
crystalline materials where the long range order between atoms is
dominant.
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http://www.iit.edu/~felfkri/report.htm
SiO2 Structure
Crystalline Lattice
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Non-Crystalline Lattice
Structure
In a crystalline lattice equivalent points (R and R`) are connected by a
lattice vector
 



r '  r  u a1  va2  wa3
Primitive Cell – cell defined by primitive vectors
(vectors defined by the lesser integer numbers) serves
the purpose of being an elementary building block to
build the lattice. It can only contain 1 lattice point.
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Structure - Wigner-Seitz Cell
Wigner-Seitz primitive Cell
- It’s built not from primitive vectors but
from each lattice point, complying to the
translation symmetry that binds each
point to it’s neighbor.
Building:
- Connect a lattice point to all its adjacent
neighbors;
- Draw lines (or a plane) that bisect the
previous drawn lines;
- An area or volumes that is delimited by
these planes is said to be a Wigner-Seitz cell.
http://www.chembio.uoguelph.ca/educmat/chm729/wscells/construction.htm
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Structure – Bravais Lattice
August Bravais showed that
there are only 14 ways to
group 3-dimensional points: 14
Bravais lattices.
These lattices can be grouped
on 7 crystallographic systems.
E1- 2b Optical technologies http://folk.uio.no/dragos/Solid/FYS230-Exercises.html
10 Jan 2006
Structure
O coordination number (CN) is the number of adjacent
neighbors near a given atom.
The spatial arrangement depends
on:
- the ions' relative size
- the electrical charge balance
Normally there is a tendency to
have bigger packaging in order to
minimize the energy
The bigger the number of cations
that surrounds the central cation,
the bigger the stability.
A: CN = 4
B: CN = 6
C: CN = 8
D, E: CN = 12
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Structure - cubic - simple cubic (sc)
1 atom per unitary cell
8x(1/8 dos vertices)=1
Conventional cell volume : ao3
APF=0.524
Number of adjacent neighbors: 6
Distance to closer neighbors: ao



V  a1  (a2  a3 )
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Structure - cubic - Corpus centered cubic (CCC)
2 atoms per unitary cell
8x(1/8 of the vertices)+1=2
conventional cell volume : ao3
APF=0.68
http://tftlcd.kyunghee.ac.kr/lecture/solid_state_physics/chapter1.html
Number of adjacent neighbors : 8
Distance to closer neighbors :
3a / 2
http://www.jwave.vt.edu/crcd/farkas/lectures/structure/tsld005.htm
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Structure - cubic – Face Centered Cubic (FCC)
4 atoms per unitary cell
8x(1/8 of the vertices)+
6x(1/2 of the faces)=4
Volume of each conventional cell : ao3
APF=0.74
Number of adjacent neighbors : 12
Distance to closer neighbors :
http://www.jwave.vt.edu/crcd/farkas/lectures/structure/tsld002.htm
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Structure - compact - hexagonal (CH)
6 atoms per unitary cell
APF=0.74
Number of adjacent neighbors : 12
 The spatial lattice is
simply hexagonal, with a
two atoms base
associated to each
lattice point
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Structure - Crystalline - NaCl (sodium chloride) type
 Coordination Number = 6
 Anion with FCC structure
 Cation placed centrally in the
cube and in the middle of each
of its 12 edges
=> Two interpenetrated FCC
lattices
MgO, FeO, MnS, LiF
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Structure - Crystalline - CsCl (Cesium Chloride) type
 Coordination Number = 8
 Anions on the cube vertices
 Cation on the center of the
cube
 CsBr, CsI
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Structure – Crystalline-type CdS (Wurtzite)
 Coordination Number = 4
 Anions with a CH arrangement
 Cations with a CH arrangement
=> 2 interpenetrated CH lattices
 ZnO, AlN, GaN, ZnS
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Structure - Crystalline structures of ZnS (zinc-blende)
 Coordination Number = 4
 Anions with a FCC
arrangement
 Cations occupy tetrahedric
positions
 SiC, BeO, CuCl, GaAs
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Structure - diamond type
 8 atoms per unitary cell
 FCC lattice com um motivo de dois
átomos
 Coordination Number = 4
=> 2 FCC lattices interpenetrated at ¼ of
the diagonal of the body structure)
Si, C, Ge
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Structure - Reciprocal Lattice
Each crystalline structure has two lattices: the crystalline lattice and
the reciprocal lattice.
The set of all wave vectors that generate plane waves with a periodicity
taken from the Bravais lattices, is the reciprocal lattice.
The vectors that define the reciprocal lattice’s axis are deduced from
the primitive vectors of the crystalline network.









a2  a3
a 3  a1
a1  a 2
b1  2 

 , b 2  2 

 , b 3  2 


a 1  a 2  a 3 
a 1  a 2  a 3 
a 1  a 2  a 3 
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Structure
The reciprocal lattice vector can be defined by:
Ghkl = h b1+k b2+ l b3
with h, k and l integer
numbers
The crystalline lattice vectors have dimension L
The reciprocal lattice vectors have dimension L-1
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1st Brillouin zone
As in the case of a direct lattice, where a
primitive cell containing a single lattice
point using translational symmetry can build
the entire sapce without superposition and
still mantain full lattice symmetry –
Wigner-Seitz cell
Also in the reciprocal space, and by analogy
with the Wigner-Seitz cell, a 1st Brillouin
zone can be built
If a Wigner-Seitz cell has volume V, the
Brillouin zone will have 2/V
1st Brillouin zone for a
1-D lattice
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1st Brillouin zone for
a simple cubic lattice
1st Brillouin zone for an
hexagonal lattice
1st Brillouin zone for a face
centered cubic lattice : truncated
Octahedral
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1st Brillouin zone for a face
centered cubic lattice : rhombic
dodecahedral
http://cst-www.nrl.navy.mil/bind/kpts/
Miller indexes
In order to identify the planes and directions of a crystalline lattice, Miller indexes are used.
- Choose an axis system whose origin isn’t over the plane
- determine the plane intersections with the crystallographic axis
- Invert
- Simplify the fractions to minimum integer possible
- This values are the Miller indexes (h,k,l) of the plane
- The negative direction must be signaled with a line above
Identical plane family.
...
Z
Y
X
(100)
(001)
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(002)
(111)
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Growing Steps
Initial Material
Quimical Processing
Polycrystalline Material
Growth Techniques
monocrystalline Material
Cutting and polishing
Wafers
Devices
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Semiconductor Layer
Deposition
Monocrystal Growing
 The purpose of the growing techniques:
- produce ingots with the least amount of imperfections and
with the biggest diameter.
For Si, it is possible to grow ingots
with about l=100cm and = 30cm.
- For Si, GaAs and InP semiconductors, there are well
developed growth technologies. However, for most
semiconductors it is difficult to get high quality materials
and big dimension substrates.
http://www.ent.ohiou.edu/~juwt/HTMLS/semicondmanufactureprocess/crystalgrowing.htm
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Semiconductor Growth
Czochralski – single crystal Wafers
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Czochralski Method
A
solid material seed is dived in the molten material
The
seed is slowly pulled in order to promote the
solidification of the grasped molten material
O
crystal is slowly turned around its axis in order to get a
circular section.
http://www.ent.ohiou.edu/~juwt/HTMLS/semicondmanufactureprocess/crystalgrowing.htm
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Si monocrystal Growth
Typical Growth Environment:
Fusion Temperature = 1420ºC
Growth Speed = 2mm/min
Growth Atmosphere = Argon
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http://www.sumitomometals.co.jp/e/business/silicon.html
After growing the ingot, several steps have to be taken until actually having a
substrate;
Remove the seed and the other ingot end;
Rectify the surface and define the diameter;
Mark the crystallographic orientations, by making one or more plain
regions over the ingot length;
Rectify the surface and
define the diameter;
Mark the crystallographic
orientations, by making one or
more plain regions over the ingot
length;
Cut in a disc shaped way;
Polish the discs.
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Crystal Characterization
Real crystals aren’t perfect since they have crystalline periodicity
irregularities - flaws.
The presence of this flaws affects the electrical, mechanical and optical
properties.
Point defects:
a) substitutional impurities
b) interstitial impurities
c) hole
d) Frenkel and Schottky flaw
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Epitaxial Growth
The wafers grown through the described techniques are rarely used in
direct device manufacture, but are used as substrates instead.
Solution : grow one or more layers (of some m thickness) over them.
The epitaxial growth techniques have low growth rate (as low as one
single layer per second in some techniques) which allows an high
precision size control in the growth direction, which is essential for
the heterostructure variety that is nowadays used in optoelectronic
devices.
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Molecular Beam Epitaxy (MBE)
The MBE technique is one of the
more important heterostructure
manufacture techniques for
optoelectronic devices
Almost all semiconductors have been
grown through this technique
 MBE is a growth technique that involvs the reaction
of one or more atom beams with the substract surface
http://www.elettra.trieste.it/experiments/beamlines/lilit/htdocs/people/luca/tesihtml/node24.html
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When an effusion cell is heated, atoms or charged molecules evaporate in
the direction of the heated substrate.
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 An atom or molecule beam is
direccioned to the substrate's
crystalline lattice, giving rise to a
new deposited material layer.
 When heating the surface, each
atom has enough time to migrate
find a new place in the new
crystalline lattice.
The MBE growth rate is about one single layer per second.
This low growth rate in association to the shutters placed in
front of the effusion ovens allows the change of the crystal
composition with a single layer control.

http://www.wsi.tu-muenchen.de/E24/resources/facilities.htm
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Photolithography
The photolithography technique allows
the manufacture of complex and dense
circuits, improving this way the
performance of the devices since it
allows for its dimension reductions to
happen.
Recurring to the lithography technique,
it’s possible to manufacture on the same
wafer both active and passive devices.
The process consists in transferring a
previously created pattern/model to the
wafer’s surface, in order to define the
several regions of an integrated circuit
This process has several steps, so all
advances in the overall process depend on
the development of each of the individual
steps.
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Photolithographic Process Steps
The photolithography process must be implemented in a clean room,
in order to avoid dust to be deposited in the mask and wafer.
1 - Deposition of the photosensitive film
Spin Coating
A little piece of photosensitive material is placed on the center of
the wafer. The wafer is then spinned over its axis in order to promote a
uniform spacing of the material.
Base Material : polyisopropene
Conditions:
rotation speed: 2000-8000rpm
time: 10-60s
thickness: 0.7 - 1.0m
thermical treatment : 100ºC
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2- Photosensitive film
to radiation
The transfer of the model
from the mask to the wafer can
be done using optic equipment
(for details bigger than 0.25m),
X-rays or by an electron beam.

The photosensitive film when
receiving radiation can behave as:
- Positive photosensitive : The
images formed are the same as the
ones in the mask.
- Negative photosensitive: The
images formed are complementary to
the ones in the mask. The radiation
exposed regions become insoluble
and therefore can not be removed.
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Positive Photosensitive : It’s built by 3
components: a resin, a photosensitive
element and an organic solvent. The region
exposed to radiation changes its chemical
structure becoming soluble. The broken
connections between the molecules allow an
easy removal.
Negative Photosensitive : Polymers are
combined with a photosensitive element.
The region exposed to radiation become
insoluble due to the cross connections
formed between the molecules. The high
molecular weight of the molecules prevents
their removal.
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Exposure Response Curves and their transversal
sections
Photosensitive film
Photosensitive film
fully soluble for an
energy equaling ET
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fully insoluble for
an energy equaling
2ET
3- Writing/Recording Process
The next step is the Writing/Recording process, That must allow the
removal of material in the regions where the photosensitive film
doesn’t exist.
SiO2 is selectively attacked, whereas the substrate remains unaltered
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The simplest recording process is chemical
recording:
- It involves a chemical reaction
followed by the removal of reaction
elements.
- The elements used for chemical
attacks are mostly acids
(HF, HNO3, H4C2O2, H2SO4).
E.g. :
SiO2 + 6HF -> H2SiF6 + 2H2O
Water can be used as diluent for this attacker
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The Attack depends on the
orientation degree:
Some solutions are more easily
solved in some specific
crystallographic planes.
The material used in the
attack should attack only one
layer at a time and should be
self-limitative.
Chemical recording is simple and cheap, however it’s neither compatible
with submicrometric technologies nor permits an anisotropic attack.
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4 – Film Removal
After the recording, the photosensitive film must be removed
Usually, the film removal is made by chemical attack
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Manufacture Steps of
a p-n junction
Oxidation
- Forming a SiO2 layer.
- Works as an insulator or barrier to
diffusion or implantation
Litographic Process
- The wafer is covered by a
photosensitive film;
- Radiation Exposure through a mask;
- The non-polymerized regions are solved;
- Thermical Treatment (120-180ºC) to
boost the film adhering;
- Attack with HF to remove the
uncovered SiO2;
- Photosensitive film removal through a
chemical solution or through an attack
of oxygen plasma.
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In order to form active elements in integrated
circuits it’s necessary to selectively
introduce dopants in the substrate;
The surface is exposed to an high ion dopant
concentration, that are incorporated in the
semiconductor crystal lattice;
The SiO2 layer is a barrier to diffusion and to
the impurity implantation.
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Doping techniques:
- Diffusion: Thermical Treatment in an oven at 1000-1100ºC on rich
doping environment (e.g. Phosphorus or boron)
- Ionic Implantation : the doping atoms are ionized and accelerated
against the surface in order to be implanted in the substrate
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Metallization
Ohmic Contact Formation, through a phased
chemical or physical vapor deposition of a
metallic film.
A lithographic process is used in order to define
contact zones.
Metallization of the backside of the
semiconductor.
Thermical Treatment at ~500ºC in order to get
low contact resistance between metallic layers
and the semiconductor.
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