Optoelectronics Materials Optoelectronics Materials (An

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Optoelectronics Materials
Optoelectronics Materials

• (An Introduction)

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Outline

• Introduction
• Basic Aspects
• Properties of lights
• Structure of materials
• Electrical properties of semiconductor
• Optical properties of semiconductor
• Light Detection and Imaging
• Photo-detectors
• Charged Couple Devices (CCD)

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Optoelectronics?
Fiber optic

• Opto optics, lights, photons
• Electronic involves electron movements
• Optoelectronics converts light into electricity
• Applications
• Optical storage (CD, DVD)
• Communications (fiber optics)
• Imaging/Display (CRT, LCD, TFT)
• Publishing (Laser printer)
• Guidance and control (Laser devices)
• Env. energy supply (Solar cell)
• Health (Painless therapy)
• Defense (Night vision - military)
• More..

LED
Display Frame
Solar-powered PDA
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Optoelectronic devices

• Laser Diodes
• Light Emitting Diodes (LED)
• Optical Detectors
• Display Devices
• Solar Cells
• etc.

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Basic questionHow to change lights into
electronic applications?
The miracle of Electron
Lights
Current (Electron)
Other type of energy
semiconductor
Applications
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Lights free energy source

• Light has a dual nature!
• an electromagnetic wave (Maxwell Theory), has
  certain ?
• Has propagation speed, c
• Radio waves, Microwaves, IR, Visible (0.7-0.4?m),
  UV, X-Ray, ?-Ray
• an energy package, photon or particle (Planck,
  Einstein)
• Properties of Light
• Propagation (can be guided..)
• Polarization (can be twisted..)
• Interference
• Diffraction
• Radiation

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Properties of Light

• Light with wavelength lo lt 400 nm is called
  ultraviolet (UV).
• Light with wavelength lo gt 700 nm is called
  infrared (IR).
• We cannot see light of these wavelengths,
  however, we can sense it in other ways, e.g.,
  through its heating effects (IR) and its tendency
  to cause sunburn (UV).

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Basic Materials Structure

• Solids
• Crystalline periodicity, Long Range Order (LRO)
• Polycrystalline LRO several microns
• Amorphous good SRO, no LRO
• Liquid and Gaseous
• No ordering
• Can flow and take the containers shape
• Liquid Crystal (Organic)
• LRO
• Flow of atoms/molecules
• Has both properties of solid crystalline and
  liquid

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Solid matters

• Crystalline
• Periodicity 14 Bravais lattices
• Most electronic materials are FCC and only few
  HCP
• Imperfections
• Point defects Vacancy, Interstitial,
  Substitution
• Dislocations
• Planar (Volume) defect

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Solid matters

• Polycrystalline
• Grain size 1 microns
• Amorphous
• Dangling bonds
• Passivation by H

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Conduction properties of solid

• Electron has energy levels
• Energy Band gap
• Direct and Indirect band gap

Conductor
Isolator
Semiconductor
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Optical Generation of Free Electrons and Holes
Bond Model
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Optical Generation of Free Electrons and Holes
Band Model

• If a photon has an energy larger than the energy
  gap, the photon will be absorbed by the
  semiconductor, exciting an electron from the
  valence band into the conduction band, where it
  is free to move.
• A free hole is left behind in the valence band.
• This absorption process underlies the operation
  of photoconductive light detectors, photodiodes,
  photovoltaic (solar) cells, and solid state
  camera chips.

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Intrinsic and Extrinsic Semiconductors

• Ex. Silicon

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Carrier Generations and Recombinations

• Through electron hole pairs mechanism
• Transport scattering may occurs from various
  imperfections in the crystal

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Semiconductor (p-n) junction
Band to band transition is the most important
optoelectronic interaction in semiconductor !!!
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Optical properties

• The energy of the photons (hf) must equal or
  exceed the energy gap of the semiconductor (Eg) .
• Scattering affects the transport of electrons and
  holes
• Two classes of scattering
• absorption of photon
• emission of photon (from recombination of e- and
  hole)

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Photon Absorptions

• Photon energy must be higher than Energy band gap
  
• Absorption coefficient
• Example Solar cell

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Photon Emissions (Radiative recombination)

• Spontaneous emission
• Even requires NO incident photon
• Incoherent emission
• Example LED
• Stimulated emission
• Requires sufficient incident photon
• Coherent emission
• Example Laser diode
• Radiative recombination
• Electron-hole pairs from charge injection (from
  light or external battery)
• Gain (Emission - Absorption)
• An optical beam will grow as a result of positive
  gain
• Non-radiative recombination
• When recombination produces heat or phonon

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Color Imaging (Phosphors and Fluorescence)

• Light emission can also be occurred after
  excitation
• Organic and Inorganic materials with impurities
  emit different light colors

• Widely used in CRT and TV screens
• RGB (Red, Green, Blue) system

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Outline

• Introduction
• Basic Aspects
• Properties of lights
• Structure of materials
• Electrical properties of semiconductor
• Optical properties of semiconductor
• Light Detection and Imaging
• Photodetectors
• Charged Couple Devices (CCD)

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Photoconductive Light Detectors

• Photons having energy greater than the energy gap
  of the semiconductor are absorbed,
• then creating free electrons and free holes,
• and thus the resistivity, r, of the semiconductor
  decreases.

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Types of Photon Detectors
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MS and MIS/MOS diodes
Metal Semiconductor (Schottky detector)
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Charge-Coupled Device (CCD)

• Principle an array of MOS diode

1. Exposure 2. Charge transfer 3.
Charge-to-voltage conversion and output
amplification
MOS

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Charge-Coupled Device (CCD)
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Resolutions

• Denoted in Pixels
• Related to the number and form of detectors
• Device 4 million pixels
• Human eye 120 million pixels

New FUJI super CCD
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Outline

• Introduction
• Basic Aspects
• Properties of lights
• Structure of materials
• Electrical properties of semiconductor
• Optical properties of semiconductor
• Light Detection and Imaging
• Photodetectors
• Charged Couple Devices (CCD)

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Concluding remarks

• light and electron