LED by Tobias Schauffel

LEDs History Technologie Uses

Content

1. Introduction - What is a LED Introduction Introduction History

2. History – a brief overview

Physical effect Types+Uses

3. The physical effect, why does it glow?

4. Different types and there Uses 5. Sources English course 12/09/2009

LEDs History Technologie Uses

LED – What is it?

Overview Introduction Introduction History Physical effect Types+Uses

A light-emitting diode (LED), is a semiconductor which emits light.

LEDs are used as indicator lamps in many kinds of electronics and increasingly for lighting and communication.

LEDs work by the effect of electroluminescence, discovered by accident in 1907. The LED was introduced as a practical electronic component in 1962.

All early devices emitted low-intensity red light, but modern LEDs are available across the visible, ultraviolet and infra red wavelengths, with very high brightness. The color depends on the semiconductor material and they are available in many different shapes and sizes.

English course 12/09/2009

LEDs History Technologie Uses

History – 1907 – 1962 Key Dates Introduction History History Physical effect Types+Uses

Electroluminescence was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat's-whisker detector.

Same did a russian in 1927 Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys in 1955 In 1961, experimenters Robert Biard and Gary Pittman found that GaAs emitted infrared radiation when electric current was applied and received the patent for the infrared LED. The first practical visible-spectrum (red) LED was developed in 1962 by Nick Holonyak Jr. English course 12/09/2009

LEDs History Technologie Uses

More History ;) less names - 1972 first yellow LED was invented and Improvement of the brightness of red and red-orange LEDs by a factor of ten.

Introduction History History Physical effect Types+Uses

- 1976, first high-brightness and high efficiency LEDs for optical fiber telecommunications through invention of new semiconductor materials specifically adapted to optical fiber transmission wavelengths.

-First LEDs were very costly--Hewlett Packard (HP) introduced LEDs in 1968, initially using GaAsP. - major applications for alphanumeric displays and LEDs were integrated into HP's early handheld calculators.

-First used in 7 segment displays in expensive labratory equipment -Different LED colors 1971 - Blue LED / 1993 production 1972 - Yellow LED / 90's production 1972 - Amber LED / 90's production 1995 - White LED / late 90's production late 90's - UV LED / late 90's production

English course 12/09/2009

LEDs History Technologie Uses

Development Different color and high power output

Introduction History History Physical effect Types+Uses

The development of LED technology has caused their efficiency and light output to increase exponentially, with a doubling occurring about every 36 months since the 1960s, in a way similar to Moore's law. The advances are generally attributed to the parallel development of other semiconductor technologies and advances in optics and material science.

In February 2008, Bilkent university in Turkey reported 300 lumens of visible light per watt luminous efficacy (not per electrical watt) and warm light by using nanocrystals.

In January 2009, researchers from Cambridge University reported a process for growing gallium nitride (GaN) LEDs on silicon.

Production costs could be reduced by 90% using six-inch silicon wafers instead of two-inch sapphire wafers.

English course 12/09/2009

LEDs History Technologie Uses

Main Parts

Introduction History Physical Physicaleffect Effect Types+Uses

English course 12/09/2009

LEDs History Technologie Uses

How it works

Introduction History Physical Physicaleffect Effect Types+Uses

-Like a normal Diode made of a semiconducting material with a P and N doped part -Materials need a direct Band gap (only change in Energy, not momentum) -Current flows from P to N (electrons as charge carriers) -When an Electron meets a hole It falls into a lower energy level and emits a photon -LEDs are mainly build on a n-type substrate -It is important that as few as possible light reflects back into the substrate

English course 12/09/2009

LEDs History Technologie Uses

Wavelenght vs Material Type

Color

Material

Wavelength

Current

Voltage

Standard

Rot

GaAsP

655 nm

20 mA

1,7 V

Standard

Orange

GaAsP/GaP

610 nm

20 mA

2,0 V

History

Standard

Gelb

GaAsP/GaP

585 nm

20 mA

2,1 V

Physical Physicaleffect Effect

Standard

Grün

GaP

555 nm

20 mA

2,2 V

Types+Uses

Superhell

Blau

GaN

430 nm

20 mA

3,5 V

Ultrahell

Grün

GaInN

525 nm

20 mA

3,3 V

Ultrahell

Blau

GaInN

475 nm

20 mA

3,5 V

Ultrahell

Weiß

GaInP

20 mA

3,5V

Introduction

English course 12/09/2009

LEDs History Technologie Uses

Types SMD LED

Superflux LED wide viewing angel

Introduction History Physical effect Types+Uses Types & Uses

High Power LED

Standard LED English course 12/09/2009

LEDs History Technologie Uses

High power and superflux LEDs For ilumination Introduction

Example Seoul Semiconductor Z-LED P7 - white

History

Brightest LED on the market with a light output of 900lm by 2,8 A Cooling is important

Physical effect

415 lm equal a 40W light bulb

Types+Uses Types & Uses

English course 12/09/2009

LEDs History Technologie Uses

Comparison

Introduction History Physical effect Types+Uses Types & Uses

White high power LEDs for Ilumination

English course 12/09/2009

LEDs History Technologie Uses

Miniture LEDs for signaling Miniature LEDs Different sized LEDs. 8 mm, 5 mm and 3 mm Introduction History Physical effect Types+Uses Types & Uses

These are mostly single-die LEDs used as indicators, and they come in various-sizes from 2 mm to 8 mm,through hole and surface mount packages. They are usually simple in design, not requiring any separate cooling body.Typical current ratings ranges from around 1 mA to above 20 mA. The small scale sets a natural upper boundary on power consumption due to heat caused by the high current density and need for heat sinking.

English course 12/09/2009

LEDs History Technologie Uses

LED Display, Lights and Signals

Introduction History Physical effect Types+Uses Types & Uses

Las Vegas Nivada, USA English course 12/09/2009

LEDs History Technologie Uses

Display Backlight for Laptop and TVs Introduction History Physical effect Types+Uses Types & Uses

English course 12/09/2009

LEDs History Technologie Uses

Advantages

Introduction History Physical effect Types+Uses Types & Uses

Efficiency: more light per watt Color: LEDs can emit light of an intended color Size: LEDs can be very small On/Off time: LEDs light up very quickly. LEDs used in communications devices Cycling: LEDs are ideal for use in frequent on-off cycling Dimming: LEDs can very easily be dimmed Cool light: LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics..

Slow failure: LEDs mostly fail by dimming over time Lifetime Shock resistance Focus English course 12/09/2009

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Disadvantages High initial price.

Temperature dependence: LED performance largely depends on the ambient.

Voltage sensitivity: LEDs must be supplied with the voltage above the threshold and a current below the rating Light quality: Most cool-white LEDs have spectra that differ significantly from a black body Area light source Blue hazard Blue pollution because of emitting more blue light than other white lite sources

LEDs History Technologie Uses

Where it goes and other uses Organic light-emitting diodes (OLEDs) Introduction History

Laser diodes for communication porpuses and measuring

Physical effect Types+Uses Types & Uses

English course 12/09/2009

LEDs History Technologie Uses

Sources

Introduction History Physical effect Types+Uses

www. Wikipedia .com www.led-direkt24.de/images http://leifi.physik.uni-muenchen.de/ /www.sueddeutsche.de /www.marktechopto.com www.osram.com www.nullohm.de My university skript of semiconductores

English course 12/09/2009