Introduction to optoelectronic devices


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Introduction to optoelectronic devices

  1. 1. Introduction to Optoelectronic Devices Prepaired by:Aditya kumar sahu
  2. 2. Outline  What is optoelectronics?  Major optoelectronic devices LED,OLED  Current trend on optoelectronic devices
  3. 3. What Did the Word “Opto-Electronics” Mean?  Optoelectronics is the study and application of electronic devices that interact with light. Electronics Optics (electrons) (light or photons) Optoelectronics
  4. 4. Examples of Optoelectronic Devices 4
  5. 5. Major Optoelectronic Devices ─ Direct Conversion Between Electrons and Photons Light-emitting diodes (LEDs) (display, lighting,···)  Laser diodes (LDs) (data storage, telecommunication, ···)  Photodiodes (PDs) (telecommunication, ··· )  Solar Cells (energy conversion) 
  6. 6. Light- Emitting Diodes LEDs Red LED LED for displays White LED Blue LED LED for traffic light
  7. 7. Diode Lasers Diode lasers have been used for cutting, surgery, communication (optical fibre), CD writing and reading etc
  8. 8. Producing Laser in the Lab
  9. 9. Optoelectronic devices for Photovoltaic Applications
  10. 10. Solar Cells
  11. 11. 2007 marks a century of optoelectronics 1907 - H.J. Round discovered electroluminescence when using silicon carbide and a cats whisker. Oleg Losev independently discovered the phenomena the same year. London, United Kingdom 1920s - Oleg V. Losev studied the phenomena of light emitting diodes in radio sets. His first work on 'LEDs' involved a report on light emission from SiC. In 1927 he published a detailed report but his work was not well known until the 1950s when his papers resurfaced. Saint Petersburg, Russia
  12. 12. 1961 - Bob Biard and Gary Pittman developed the Infrared LED at Texas instruments. This was the first modern LED. It was discovered by 'accident' while TI tried to make a laser diode. The discovery was made during a test of a tunnel diode using a zinc diffused area of a GaAs (Gallium Arsenide) semi-insulating substrate. Dallas, Texas 1962 - Nick Holonyack Jr. develops the red LED, the first LED of visible light. He used GaAsP (Gallium Arsenide Phosphide) on a GaAs substrate. General Electric. Syracuse, New York 1972 - M. George Craford creates the first yellow LED at Monsanto using GaAsP. He also develops a brighter red LED. St. Louis, Missouri
  13. 13. 1979 - Shuji Nakamura develops the world's first blue LED using GaN (Gallium nitride). It wouldn't be until the 1990s that the blue LED would become low cost for commercial production. Tokushima, Japan 1976 - Thomas P. Pearsall develops special high brightness LEDs for fiber optic use. This improves communications technology worldwide. Paris, France
  14. 14. What is an LED? Light Emitting Diode Colour White
  15. 15. A light emitting diode (LED) is essentially a PN junction optosemiconductor that emits a monochromatic (single color) light when operated in a forward biased direction. LEDs convert electrical energy into light energy. They are frequently used as "pilot" lights in electronic appliances to indicate whether the circuit is closed or not.
  16. 16. About LEDs The most important part of a light emitting diode (LED) is the semi-conductor chip located in the center of the bulb as shown at the right. The chip has two regions separated by a junction. The p region is dominated by positive electric charges, and the n region is dominated by negative electric charges. The junction acts as a barrier to the flow of electrons between the p and the n regions. Only when sufficient voltage is applied to the semi-conductor chip, can the current flow, and the electrons cross the junction into the p region.
  17. 17. How Does A LED Work? When sufficient voltage is applied to the chip across the leads of the LED, electrons can move easily in only one direction across the junction between the p and n regions. In the p region there are many more positive than negative charges. When a voltage is applied and the current starts to flow, electrons in the n region have sufficient energy to move across the junction into the p region.
  18. 18. How Does A LED Work? Each time an electron recombines with a positive charge, electric potential energy is converted into electromagnetic energy. For each recombination of a negative and a positive charge, a quantum of electromagnetic energy is emitted in the form of a photon of light with a frequency characteristic of the semi-conductor material (usually a combination of the chemical elements gallium, arsenic and phosphorus)..
  19. 19. Testing LEDs Never connect an LED directly to a battery or power supply! It will be destroyed almost instantly because too much current will pass through and burn it out. LEDs must have a resistor in series to limit the current to a safe value, for quick testing purposes a 1k resistor is suitable for most LEDs if your supply voltage is 12V or less. Remember to connect the LED the correct way round!
  20. 20. How Much Energy Does an LED Emit? The energy (E) of the light emitted by an LED is related to the electric charge (q) of an electron and the voltage (V) required to light the LED by the expression: E = qV Joules. This expression simply says that the voltage is proportional to the electric energy, and is a general statement which applies to any circuit, as well as to LED's. The constant q is the electric charge of a single electron, -1.6 x 10-19 Coulomb.
  21. 21. Currently Most LED’s Are Directional The LED chip is located in a little reflective cup that sends the light in a direction. Which makes them good for applications requiring a spot light.
  22. 22. LED Light Distribution Some LEDs have diffusion lenses to spread out the light, or don't have the reflective cap.
  23. 23. Colours of LEDs LEDs are made from galliumbased crystals that contain one or more additional materials such as phosphorous to produce a distinct color. Different LED chip technologies emit light in specific regions of the visible light spectrum and produce different intensity levels. LEDs are available in red, orange, amber, yellow, green, blue and white. Blue and white LEDs are much more expensive than the other colours. The colour of an LED is determined by the semiconductor material, not by the colouring of the 'package' (the plastic body). LEDs of all colours are available in uncoloured packages which may be diffused (milky) or clear (often described as 'water clear'). The coloured packages are also available as diffused (the standard type) or transparent.
  24. 24. Colours of LEDs Bi-colour LEDs A bi-colour LED has two LEDs wired in 'inverse parallel' (one forwards, one backwards) combined in one package with two leads. Only one of the LEDs can be lit at one time and they are less useful than the tri-colour LEDs described above.
  25. 25. Colours of LEDs Tri-colour LEDs The most popular type of tri-colour LED has a red and a green LED combined in one package with three leads. They are called tri-colour because mixed red and green light appears to be yellow and this is produced when both the red and green LEDs are on. The diagram shows the construction of a tri - colour LED. Note the different lengths of the three leads. The centre lead (k) is the common cathode for both LEDs, the outer leads (a1 and a2) are the anodes to the LEDs allowing each one to be lit separately, or both together to give the third colour.
  26. 26. LED Performance LED performance is based on a few primary characteristics: • • • • • • • Color White light Intensity Eye safety information Visibility Operating Life Voltage/Design Current
  27. 27. LED Performance Colour Peak wavelength is a function of the LED chip material. Although process variations are 10 NM, the 565 to 600 NM wavelength spectral region is where the sensitivity level of the human eye is highest. Therefore, it is easier to perceive color variations in yellow and amber LEDs than other colors.
  28. 28. LED Performance White Light When light from all parts of the visible spectrum overlap one another, the additive mixture of colors appears white. However, the eye does not require a mixture of all the colors of the spectrum to perceive white light. Primary colors from the upper, middle, and lower parts of the spectrum (red, green, and blue), when combined, appear white.
  29. 29. LED Performance Intensity LED light output varies with the type of chip, encapsulation, efficiency of individual wafer lots and other variables. Several LED manufacturers use terms such as "super-bright," and "ultra-bright“ to describe LED intensity. Such terminology is entirely subjective, as there is no industry standard for LED brightness.
  30. 30. LED Performance Eye Safety The need to place eye safety labeling on LED products is dependent upon the product design and the application. Only a few LEDs produce sufficient intensity to require eye safety labeling. However, for eye safety, do not stare into the light beam of any LED at close range
  31. 31. LED Performance Visibility Luminous intensity (Iv) does not represent the total light output from an LED. Both the luminous intensity and the spatial radiation pattern (viewing angle) must be taken into account. If two LEDs have the same luminous intensity value, the lamp with the larger viewing angle will have the higher total light output.
  32. 32. LED Performance Operating Life Because LEDs are solid-state devices they are not subject to catastrophic failure when operated within design parameters. DDP® LEDs are designed to operate upwards of 100,000 hours at 25 C ambient temperature. Operating life is characterized by the degradation of LED intensity over time. When the LED degrades to half of its original intensity after 100,000 hours it is at the end of its useful life although the LED will continue to operate as output diminishes. Unlike standard incandescent bulbs, DDP® LEDs resist shock and vibration and can be cycled on and off without excessive degradation.
  33. 33. LED Performance Voltage/Design Current LEDs are current-driven devices, not voltage driven. Although drive current and light output are directly related, exceeding the maximum current rating will produce excessive heat within the LED chip due to excessive power dissipation. The result will be reduced light output and reduced operating life. LEDs that are designed to operate at a specific voltage contain a built-in current-limiting resistor. Additional circuitry may include a protection diode for AC operation or full-bridge rectifier for bipolar operation. The operating current for a particular voltage is designed to maintain LED reliability over its operating life.
  34. 34. Customer says “I want to use LEDs” What is their goal? Saving energy? Saving Money? Better Lighting? Being “Green”?
  35. 35. The advantages of LED’S
  36. 36. • Size • Efficiency • Life expectancy • Dimmable • Low temperatures • Toxin free
  37. 37. Applications • Sensor Applications • Mobile Applications • Sign Applications • Automative Uses • LED Signals • Illuminations • Indicators
  38. 38. Sensor Applications • • • • • • Medical Instrumentation Bar Code Readers Color & Money Sensors Encoders Optical Switches Fiber Optic Communication
  39. 39. Mobile Applications • • • • • Mobile Phone PDA's Digital Cameras Lap Tops General Backlighting
  40. 40. Sign Applications • • • • Full Color Video Monochrome Message Boards Traffic/VMS Transportation - Passenger Information
  41. 41. Automative Applications • Interior Lighting - Instrument Panels & Switches, Courtesy Lighting • Exterior Lighting - CHMSL, Rear Stop/Turn/Tail • Truck/Bus Lighting - Retrofits, New Turn/Tail/Marker Lights
  42. 42. Signal Appications • • • • • • Traffic Rail Aviation Tower Lights Runway Lights Emergency/Police Vehicle Lighting LEDs offer enormous benefits over traditional incandescent lamps including: • Energy savings (up to 85% less power than incandescent) • Reduction in maintenance costs • Increased visibility in daylight and adverse weather conditions
  43. 43. Illumination Architectural Lighting Signage (Channel Letters) Machine Vision Retail Displays Emergency Lighting (Exit Signs) Neon Replacement Bulb Replacements Flashlights Outdoor Accent Lighting - Pathway, Marker Lights
  44. 44. Illumination LEDs not only consume far less electricity than traditional forms of illumination, resulting in reduced energy costs, but require less maintenance and repair. Studies have shown that the use of LEDs in illumination applications can offer: Greater visual appeal Reduced energy costs Increased attention capture Savings in maintenance and lighting replacements As white LED technology continues to improve, the use of LEDs for general illumination applications will become more prevalent in the industry.
  45. 45. Indication  Household appliances  VCR/ DVD/ Stereo and other audio and video devices  Toys/Games  Instrumentation  Security Equipment  Switches
  46. 46. Organic Light-Emitting Diodes
  47. 47. What is an OLED? • An OLED is an electronic device made by placing a series of organic thin films between two conductors. When electrical current is applied, a bright light is emitted. • A device that is 100 to 500 nanometers thick or about 200 times smaller than a human hair.
  48. 48. The OLED Structure
  49. 49. Electrons in a Lattice •E •V(r) • Atom has bound states – Discrete energy levels – Partially filled by electrons •r • Periodic array of atoms (cf. QM textbook) – Effectively continuous bands of energy levels – Also partially filled •E •V(x) •r
  50. 50. The Bands on Stage •E •E •E •E •E •N •S o •Gap ma G ll a Ga p p •Semiconductor •Doped Semiconduct •Insulator•Conductor
  51. 51. Doping – Add Impurities •Ntyp e •Ptyp e
  52. 52. The Bands on Stage •E •E •E •E •E •Ntyp e •Ptyp e •N •S o •Gap ma G ll a Ga p p •Semiconductor •Doped Semiconduct •Insulator•Conductor
  53. 53. Diode: p-type meets n-type •E •E
  54. 54. Diode: p-type meets n-type •E •E
  55. 55. Diode: p-type meets n-type •E •E
  56. 56. Diode: p-type meets n-type •E •E •Electric Field •Excess Negative Ions •Excess Positive Ions
  57. 57. Diode: p-type meets n-type •Try to make current flow to left? •Electric Field •Depletion Zone Grows
  58. 58. Diode: p-type meets n-type •Try to make current flow to right? •Current Flows! •Electric Field •Current •Electrons in higher band meet Holes in lower band
  59. 59. Excitons • Electron in higher band meets a hole in lower band • The two form a hydrogen-like bound state! Exciton! •N– Like “positronium” • Can have any orbital angular momentum •E typ • Can have spin 0 or spin 1 e – Annihilation • Rate is slow • Electron falls into hole • Energy emitted • Energy released as electron falls into hole – May turn into vibrations of lattice (“phonons”) – heat – May turn into photons (only in some materials) • Infrared light (if gap ~ 1 eV) – remote control • Visible light (if gap ~ 2-3 eV) – LED – May excite other molecules in the material (if any; see below)
  60. 60. How OLEDs Emit Light
  61. 61. The battery or power supply of the device containing the OLED applies a voltage across the OLED. An electrical current flows from the cathode to the anode through the organic layers. (an electrical current is a flow of electrons) At the boundary between the emissive and the conductive layers, electrons find electron holes. The OLED emits light.
  62. 62. Types of OLEDs • Passive-matrix • Active-matrix • Transparent • Top-emitting • Flexible • White
  63. 63. Passive-Matrix
  64. 64. Active-Matrix
  65. 65. Transparent
  66. 66. Top-Emitting
  67. 67. Flexible
  68. 68. White
  69. 69. Current Research for OLEDs • Manufacturers focusing on finding a cheap way to produce o "Roll-to-Roll" Manufacturing • Increasing efficiency of blue luminance • Boosting overall lifespan
  70. 70. Applications of OLEDs • • • • • • TVs Cell Phone screens Computer Screens Keyboards (Optimus Maximus) Lights Portable Divice displays
  71. 71. OLEDs as a Light Source
  72. 72. OLED Televisions • Sony • • • • • • • Released XEL-1 in February 2009. First OLED TV sold in stores. 11'' screen, 3mm thin $2,500 MSRP Weighs approximately 1.9 kg Wide 178 degree viewing angle 1,000,000:1 Contrast ratio
  73. 73. Optimus Maximus Keyboard • Small OLED screen on every key • 113 OLED screens total • Each key can be programmed to preform a series of functions • Keys can be linked to applications • Display notes, numerals, special symbols, HTML codes,
  74. 74. Advantages of OLEDs •OLED Displays Vs. LCD and Plasma • Much faster response time • Consume significantly less energy • Able to display "True Black" picture • Wider viewing angles • Thinner display • Better contrast ratio • Safer for the environment • Has potential to be mass produced inexpensively • OLEDs refresh almost 1,000 times faster then LCDs OLED Lighting Vs. Incandescent and Fluorescent • Cheaper way to create flexible lighting. • Require less power • Better quality of light. • New design concepts for interior lighting
  75. 75. Disadvantages of OLEDs OLED Displays Vs. LCD and Plasma • Cost to manufacture is high • • • • Overall luminance degradation Constraints with lifespan Easily damaged by water Limited market availability OLED Lighting Vs. Incandescent and Fluorescent • Not as easy as changing a light bulb
  76. 76. Future Uses for OLED Lighting • Flexible / bendable lighting • Wallpaper lighting defining new ways to light a space • Transparent lighting doubles as a window Cell Phones • Nokia 888
  77. 77. Future Uses for OLED Transparent Car Navigation System on Windshield • Using Samsungs' transparent OLED technology • Heads up display • GPS system Scroll Laptop • Nokia concept OLED Laptop
  78. 78. Major areas of commercial growth in the optoelectronics marketplace • Flat-panel displays: recorded sales are up 30% year on year: currently, 8% growth in Europe & USA and 9% in Japan • Solid-state vehicle lighting: much more than just brake lights! • Solid-state domestic lighting: replacement of incandescent lighting with LED-based sources would reduce CO2 emissions by many millions of tonnes worldwide! • Power generation: solar cell technologies are progressing steadily – for example, in Germany a new power station based on solar cells is producing 5MW to power up 1800 households
  79. 79. Preferences • • • • • • •
  80. 80. ::The END:: Thank you for your Attention!