ENERGY MANAGEMENT POTENTIAL FOR PAKISTAN

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New trends in Optoelectronics

• DR SALEEM FAROOQ SHAUKAT
• COMSATS

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• Optics Electronics
• Main important industry of 21st century
• Far wider meaning and more applications than just
  optical communications, storing, displaying,
  printing images,

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• information retrieval, processing, transport,
  internet, CD, DVD, digital camera and flat panel
  displays, etc.
• Human characteristics, such as fingerprint
  identification, facial recognition, iris
  recognition, retina scanning, e-banking, online
  shopping

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• In medicine, various types of lasers are being
  used in corneal reshaping, dentistry,
  dermatology, urology and cardiology
• According to Optoelectronics Industry Development
  Association (OIDA), USA, optoelectronics industry
  will bring 460 billion by 2010. This represents
  a compound annual growth rate of 9.5

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• Data storage, A remote sensing satellite sends
  down more than 1 Gbyte of images data per second
• Displaying the image, pixels

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Photonics

• Photonics is the science and technology of
  generating, controlling, and detecting photons,
  particularly in the visible light and near
  infra-red spectrum
• Photons carry information at the speed of light
  and two photons dont interfere each other
• An optical computer is a computer that uses
  photons / light, instead of electricity, to
  perform computations

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Photonic Integrated Circuit
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Applications of Photonics

• Consumer Equipment Barcode scanner, printer,
  CD/DVD/Blu-ray devices, remote control devices
• Telecommunications Optical fiber communications
• Medicine correction of poor eyesight, laser
  surgery, surgical endoscopy, tattoo removal

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Applications of Photonics

• Industrial manufacturing the use of lasers for
  welding, drilling, cutting, and various kinds of
  surface modification
• Construction laser levelling, laser
  rangefinding, smart structures
• Aviation photonic gyroscopes lacking any moving
  parts
• Military IR sensors, command and control,
  navigation, search and rescue, mine laying and
  detection

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Applications of Photonics

• Entertainment laser shows, beam effects,
  holographic art
• Information processing
• Metrology time and frequency measurements,
  rangefinding
• Photonic computing clock distribution and
  communication between computers, circuit boards,
  or within optoelectronic integrated circuits in
  the future quantum computing

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Refraction of photons by a prism
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Optical Communication

• Creating the optical signal using a transmitter
• Relaying the signal along the fiber
• Receiving the optical signal and converting it
  into an electrical signal

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• The most commonly used optical transmitters are
  semiconductor devices such as Light-emitting
  diodes (LEDs) and laser diodes
• The main component of an optical receiver is a
  photodetector that converts light into
  electricity through the photoelectric effect

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• The impact is more on the broadband information
  services
• The fourth generation of fiber-optic
  communication systems used the wavelength-division
  multiplexing to increase fiber capacity

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• Wavelength-division multiplexing (WDM) is the
  practice of dividing the wavelength capacity of
  an optical fiber into multiple channels in order
  to send more than one signal over the same fiber
• Systems with more than 8 active wavelengths per
  fiber are generally considered Dense WDM (DWDM)

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Wavelength Division Multiplexing
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Another presentation of Wavelength Division
Multiplexing phenomenon
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• Remarkable progress has been made in the field of
  optical communication system
• Today, the capacity of optical communications has
  expanded gigabits per second into terabits per
  second, enough to meet the current traffic demand
  due to the explosive growth of data transfer and
  internet services

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Wavelength Division Multiplexing Deplexing
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• Inexpensive disposable fiber optics can relay
  real time information about drilling process
• Optoelectronics field provides a wealth of
  opportunities for scientists, technologists and
  those with modern manufacturing skills. One can
  work across a number of different disciplines

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Emerging Disciplines

• Recognition of human characteristics (finger
  print, face iris, hand geometry)
• Surveillance and tracking
• Lip reading and behavioral analysis

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• Tagging of targets and network implications
• Rapid analysis of video information
• Pattern recognition

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• Broadband optical communication and networks
• Laser communication
• Trends in holography

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• Optical signal processing
• Optical instrumentation and metrology
• DVDs and blu-ray discs
• Trends in optical memory

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Light Emitting Diodes (LEDs)

• Silicon is the most abundant elemental
  semiconductor and makes 21 of earth crust
• Porous Silicon (P S) is an interconnected network
  of air holes in silicon.  The size of these air
  holes, called pores, is of a few nanometers

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• P S offer promises of powerful NANOTECHNOLOGY
  tool
• The production of long life, stable and highly
  efficient electroluminescence (EL )

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Fabrication of Porous Silicon

• Silicon wafers used were 1 inch diameter (111)-
  oriented n-type substrate with resistivities
  between 5 10 Ocm
• Porous Silicon (PS) is formed during
  electrochemical dissolution of silicon in
  Hydrogen Fluoride (HF) based solution

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• PS formation results from the passivation of
  insoluble silicates in the pore walls.
• PS formation is due to reverse bias break down in
  n-type silicon.

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• Hydrogen plays an important role in the surface
  formation of PS
• The back side of the Si wafer acts as a secondary
  cathode and the front side as secondary anode
• PS formed layer was of 3 to 5 microns observed
  by SEM

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Fabrication of Porous Silicon ANODIZATION CELL
Schematic diagram of a double-tank cell
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• A number of direct contacting schemes have been
  tried semi transparent metal layers, indium tin
  oxide, silicon carbide and conducting polymers
• Poly-4-dicyanomethylene-4H-cyclopenta dithiophene
  monolayer (PCDM) is a good candidate for
  fabrication of a transparent conducting contact
  to PS

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• PCDM has a transmission window over part of the
  visible spectrum
• PS and PCDM contact make a good p-n junction
• SEM shows that a PCDM coated surface is smoother
  than bare porous silicon

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EXPERIMENTAL
Schematic structure of Au/PCDM/Si/Al
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• A layer of Al evaporated on the back of the
  substrate and annealed at 500 oC to make an ohmic
  contact
• PCDM dissolved in nitrobenzene was used for
  wetting the PS layer
• A very thin layer of Au was evaporated on the
  PCDM to make a better contact

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Electroluminescence from PS

• The deposition of PCDM provides not only
  electrons under the external electric field but
  holes as well
• The presence of PCDM results in a higher electron
  hole recombination rate, a higher intensity
  emission and a larger emission rate

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• Red / orange stable luminescence bands
  originating from the recombination in the Si
  crystal nanostructure
• Emission area significantly large.

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EL of PCDM coated porous Si (solid line)
compared with that of In Sn porous Si (dotted
line)
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Electrical Measurements

• Electrical transport characteristics show
  Schottky behavior.
• The Schottky junction provides more chance for
  carriers passing through the nanowire surface and
  more electron-hole recombination occurs. This
  increases both the brightness and emission area
  of the Nano-wire based Photonic devices
• The rectification ratio at 15 V is 450

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IV characteristics of typical Au/PCDM/PS/Si/Al
LED, showing rectifying behavior
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Structural Studies

• Cross-sectional micrographs (High Resolution
  Scanning Electron Microscope) of PS layers
  obtained from Si Substrate

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APPLICATIONS

• Sensors
• Solar Cells
• Memory Chips
• Optical switches
• Photonic Devices
• Coupling Devices, coupling light and electronics
  to build very fast optoelectronics devices

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CONCLUSIONS

• EL has been observed from Au-PCDM-PS-Si-Al
  device structures
• More stable than any reported solid PS-based
  contact LED
• Visible light emission can be observed under
  normal daylight

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• Electrical transport characteristics show
  Schottky behavior
• The rectification ratio at 15 V is 450
• The time stability and reproducibility was good
  for all the devices tested
• PCDM is a very promising material for stabilizing
  PS devices

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• Thank You