Transcript Optoelectronics Materials

Optoelectronics Materials
(An Introduction)
무니르
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)
Fiber optic
Optoelectronics?
Opto ~ optics, lights, photons
Electronic ~ involves electron movements
Optoelectronics “converts light into electricity”
Applications:
LED
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……..
Display Frame
Solar-powered PDA
Optoelectronic devices
Laser Diodes
Light Emitting Diodes (LED)
Optical Detectors
Display Devices
Solar Cells
etc….
Basic question:
How to change lights into
electronic applications?
The miracle of “Electron”
Lights
Other type
of energy
Current
(Electron)
semiconductor
Applications
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)
E
hc 1240eV  nm

o
o
Properties of Light
Propagation (can be guided..)
Polarization (can be twisted..)
Interference
Diffraction
Radiation
Properties of Light
Color
lo (nm)
red
orange
yellow
green
blue
violet
630-760
590-630
560-590
500-560
450-500
380-450
f (Hz)
~4.5 x 1014
~4.9 x 1014
~5.2 x 1014
~5.7 x 1014
~6.3 x 1014
~7.1 x 1014
Ephoton (eV)
~1.9
~2.0
~2.15
~2.35
~2.6
~2.9
Light with wavelength o < 400 nm is called ultraviolet (UV).
Light with wavelength o > 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).
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 container’s shape
Liquid Crystal (Organic)
LRO
Flow of atoms/molecules
Has both properties of solid crystalline and liquid
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
Solid matters
Polycrystalline
Grain size ~ 1 microns
Amorphous
Dangling bonds
Passivation by H
Conduction properties of solid
Electron has energy levels
Energy Band gap
Direct and Indirect band gap
GaAs
Conductor
Isolator
Semiconductor
Si
Optical Generation of Free Electrons and Holes ~
Bond Model
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Photons
free
electro
n
free
hole
“Conduction Band”
(Nearly) Empty
“Forbidden”
“Valence Band”
(Nearly) Filled with Electrons
Energy
Gap
Electron Energy
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”.
Intrinsic and Extrinsic Semiconductors
Ex. Silicon
N-type (P-doped)
P-type (B-doped)
Carrier Generations and Recombinations
Through electron – hole pairs mechanism
Transport scattering may occurs from various imperfections in
the crystal
Conduction Band
Valence Band
at thermal equilibrium
Under optical illumination
Semiconductor (p-n) junction
Band to band transition is the most important
optoelectronic interaction in semiconductor !!!
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)
Photon Absorptions
Photon energy must be higher than Energy band gap
Absorption coefficient
Example: Solar cell
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’
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
Materials
Impurities
Emission Color
Silver
Blue
Yttrium Sulfide
Cerium
Purplish Blue
Zinc Sulfide
Copper
Green
Zinc Orthosilicate
Manganese
Yellowish Green
Yttrium Oxysulfide
Europium
Red
Zinc Sulfide
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)
Photoconductive Light Detectors
hf
semiconductor
I
Vo
ut
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.
Types of Photon Detectors
MS and MIS/MOS diodes
Metal – Semiconductor
(Schottky detector)
Electron concentrations ‘Well’
Charge-Coupled Device (CCD)
Principle: an array of MOS diode
1. Exposure
2. Charge transfer
3. Charge-to-voltage conversion and output amplification
MOS
Charge-Coupled Device (CCD)
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
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)
Concluding remarks:
light and electron