Gallium Nitride LEDs are on the way to replace light-bulbs and fluorescent tubes, and GaN lasers have many applications including Blue-Ray storage. This presentation introduces the basic technologies
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Gerhard Fasol is President and Chief Executive Officer of Eurotechnology Japan KK, a boutique consultancy firm for leaders that he founded in 1996 in Tokyo. Eurotechnology Japan KK advises several of the world’s largest blue-chip corporations, financial institutions, the Government of Finland and the European Union on strategy and mergers and acquisitions. Fasol has been working with Japan’s high-tech sector since 1984. He was manager of one of Hitachi’s research-and-development labs, and was Associate Professor of the NTT Telecommunications Chair at Tokyo University.
Regarding the field of this report, Fasol is the co-author, with key inventor Shuji Nakamura, of The blue laser diode: The complete story (2nd ed, Springer-Verlag, October 2000). As well, he has worked for about 12 years in compound-semiconductor research. He has briefed the President of Germany, Horst Koehler, and many other global leaders about Japan’s technology sector. In August 1995, Fasol briefed US Senator Jeff Bingaman about gallium-nitride light-emitting diodes. Senator Bingaman’s bill for energy-efficient lighting is mentioned in this report.
Fasol graduated with a PhD in Semiconductor Physics from Cambridge University and Trinity College, Cambridge
The global lighting industry is about to change with the emergence of solid state lighting. This revolution is: ➔ motivated by the resulting energy savings and reduction of environmental impact ➔ Enabled by the invention of GaN and OLED technology ➔ And accelerated by politics and government (“Ban the Bulb” legislation)
Today’s size and impact of the lighting industry: ➔ US$100bn for lighting fixtures (of which US$30bn is for lamps). ➔ A total of 15bn installed screw-based light sockets (4bn in the US; 3.6bn in the EU). ➔ US$230bn for electricity + US$50bn for kerosene in the developing world. ➔ Energy-efficient lighting could save US$67bn (100 nuclear-power plants), 600m tonnes of CO2 emission or more and
10,000kg of mercury emission.
Ban the bulb - Politics accelerates move to energy-efficient lighting: ➔ The California Lighting Efficiency and Toxics Reduction Act (signed by Governor Arnold Schwarzenegger on 12 October
2007). ➔ Senator Jeff Bingaman: “Energy Efficient Lighting for a Brighter Tomorrow Act”. ➔ Well positioned companies (eg, Philips) push for energy-efficient lighting, GE closes its incandescent light-bulb factories.
Gallium-nitride LED-based solid-state lighting on the way to replace bulbs and tubes: ➔ Can cut the lighting electricity bill by 90%. ➔ LEDs have 50,000 hours lifetime compared to 1,000 hours for incandescent bulbs. ➔ Moore’s law for semiconductors: progress is faster-than-expected. ➔ GaN Light Emitting Diodes (LEDs) and lasers were developed by Shuji Nakamura at Nichia Chemical Industries (located in
Anan, Tokushima-ken, Japan) based on InGaN/AlGaN. The first GaN light emitter was demonstrated by Jack Pankove in the 1970s, and Isamu Akasaki (Matsushita, Univ of Nagoya and Meijo Univ) developed many inventions which enabled Shuji Nakamura’s first commercialization. Largely invented in Japan, Asia-Pacific companies at important positions today in the GaN field.
Agenda� Executive Summary The solid state lighting revolution
➔ Today’s lighting industry ➔ Energy consumption, efficiency and environmental impact ➔ Government action, legislation, “Ban the bulb” ➔ Developing countries
Physics and technology ➔ GaN devices: the three key steps for the breakthrough ➔ White LEDs ➔ Lasers ➔ Why did Shuji Nakamura at Nichia succeed where many much larger corporations failed?
Markets for GaN LEDs ➔ Traffic signals, street lights, displays and signage, architectural, automotive, backlights, general lighting
Markets for GaN Lasers Patent issues and the “Club of Five” The emerging new industry structure
➔ Nichia ➔ Frontline LED makers ➔ Equipment makers and supplies
The solid state lighting revolution is about to disrupt the global lighting industry
What drives the solid state lighting revolution?� Enabled by technology
➔ The solid state lighting revolution is only possible because of the discovery of GaN LEDs and OLEDs in the 1990s
Driven by economics and environmental considerations ➔ Today’s lighting (incandescent bulbs and fluorescent tubes) wastes
energy, creates more greenhouse gases than necessary, and releases harmful poisons (mercury, lead) into the environment
➔ 2 billion people have no electricity. They use kerosene for lighting, and they need to pay 5000 times more to get the same amount of light as they would pay would they use GaN LEDs
Accelerated by politics and government ➔ All major countries have legislation in place or on the way to enforce
energy efficient lighting. It is very likely that incandescent light bulbs are gone within a few years
Some years ago the active elements in radios and TV-sets were vacuum tubes. Many years ago these vacuum tubes have been replaced first by discrete transistors and now by integrated circuits (ICs).
Still today, the lighting industry is dominated by glass bulbs and glass tubes (fluorescent tubes), which despite gradual improvements are essentially a 100 year old technology with many disadvantages (short lifetime, bulky and breakable, difficult to recycle, causing environmental damage, inefficient: most energy input is converted into heat not desired light, etc)
GaN based blue, green, white LEDs for the first time allow to replace light bulbs and fluorescent tubes with semiconductors
GaN LEDs have started to replace light bulbs and fluorescent tubes starting with high-value applications (e.g. traffic lights, specialty lighting, medical applications)
Blue (violet) GaN based semiconductor lasers allow to store information with approx. 4 times higher density and therefore are the basis for the next generation DVDs
Blue (violet) GaN based lasers have many other applications in medicine, printing, copying machines and other areas
Who invented GaN blue LEDs and lasers? Three people:�
Jacques (Jack) Pankove (1970s at RCA Laboratories, now at the University of Colorado and Astralux Inc.) found that Gallium Nitride (GaN) can emit blue light. Jack Pankove’s memories of his early work can be found here: ➔ http://nsr.mij.mrs.org/2/19/text.html#section1
Professor Isamu Akasaki (1980s & 1990s initially at Matsushita Electrical Industries, then at Nagoya University and now at Meijo University) in patient and systematic research work in cooperation with Hiroshi Amano and others over many years developed methods to deposit device quality GaN films, developed and demonstrated p-type and n-type doping and developed GaN based light emitting diodes
Shuji Nakamura (1990s at Nichia Chemical Industries, and now at University of Santa Barbara) invented a long list of technologies and processes necessary for commercial application, and developed GaN LEDs and Lasers to the point of commercial products. His most important discovery is the “two-flow MOCVD process” to grow GaN films.
Light spectrum of an LED, a light bulb and a laser� Light bulb: tungsten filament heated to about 3000 C emits “black body” radiation over a broad spectrum.
Most emission is invisible infrared heat radition. The efficiency is low, because most input energy is converted into heat, not into light.
LED: Light is emitted by the transition of electrons between energy levels, and therefore within a relatively narrow range of wavelenghts
Laser: the emission of a laser is determined by the resonance of an “optical amplifier” and an optical cavity. The light emitted is coherent (this means that the light waves are continuous without break in phase over a considerable range in time and space). Lasers can emit light in a very narrow beam in a very narrow wave length spectrum
Diffraction limits the size of a focused laser beam to a spot with a width of the order of the wavelength of the light used, therefore the wavelengths limits the density of data storage: shorter wavelengths (blue, violet, UV) enable higher storage density
In principle, an optical near-field microprobe allows a much higher density of optical storage, however access is VERY slow using current knowledge
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Diffraction spots ofred, green, blue and violet lasers
Schematic of information storage on CD-ROMand magneto-optical disc
What is a blue light emi"ing diode (LED)� A light-emitting semiconductor diode (LED) or a laser
diode (LD) both consist of a stack of extremely thin and precisely grown semiconductor layers of different materials
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A light emitting diode (LED) consists of a stack of n-type (left hand side) and a stack of p-type (right hand side) material, forming a “p-n junction”. Electrons (red) and holes (green) follow the potential gradient of an applied voltage and recombine in the region of the p-n junction. The photons of the emitted light have an energy similar to the value of the energy gap.
What is a laser diode (LD)?� LASER = Light Amplification by Stimulate Emission of Radiation
➔ Every laser consists of a light amplifier (which amplifies light by stimulated emission) combined with an optical resonant cavity: Laser = Light Amplifier + Resonant Cavity
➔ In most semiconductor lasers, the light amplifier and the resonant cavity are grown in the same structure, are strongly interlinked and some components may be shared.
Light Amplifier: a light amplifier increases the intensity of light in a certain wavelength range, when it is pumped above a threshold. Above this threshold, “stimulated emission” occurs. A light amplifier can be “pumped” electrically, optically, or by other methods. In the case of a semiconductor laser diode, pumping is optically in the first stages of research, however for devices pumping is almost always electrically ➔ In a semiconductor Laser Diode (LD) the light amplifier consists of a structure similar to a light emitting
diode (LED) with a pn-junction. However, the requirements for accuracy of design, accuracy of growth, purity, freedom from impurities and crystal defects are much more stringent that for LEDs.
Resonant Optical Cavity: an optical cavity has certain resonant frequencies. When the amplification spectrum of a light amplifier within a resonant cavity coincides with the resonant frequencies of the optical cavity lasing can occur. ➔ The resonant cavity of a semiconductor laser can in the simplest case consist of the cleaved (broken) edges
of the semiconductor, or in more sophisticated cases of multi-layer dielectric mirrors. ➔ A resonant cavity has “eigen-modes” or resonant modes, the transmission spectrum, the reflection
spectrum, spontaneous noise spectrum of a well-formed resonant cavity shows narrow peaks �
Surface emi"ing lasers (VCSELs) vs. Edge emi"ing lasers� Conventional edge emitting semiconductor lasers: the light emission is through the
cleaved edge of the laser. Conventional edge emitting lasers are normally handled one-by-one are almost impossible to integrate in large numbers.
Surface emitting laser (Vertical Cavity Surface Emitting Laser = VCSEL). VCSELs are usually much smaller, can be integrated in large numbers on a substrate wafer, and are much easier to test one-by-one while still on the wafer
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Ref
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Surface emitting laser(VCSEL)
internal or external reflectorsto form resonant cavity
When light is emitted in an electronic transmission, two types of emission are possible: ➔ Spontaneous emission: in the case of a laser, spontaneous emission gives
rise to “phase noise” and is not usually desirable. Methods to suppress spontaneous emission in lasers are desirable and have been proposed by researchers. In a laser spontaneous emission is necessary to start laser action, before the lasing threshold is crossed
➔ Stimulated emission: stimulated emission is the emission of photons stimulated (in resonance) with the electric field of other photons present in the amplifier. Stimulated emission occurs at sufficiently high intensities, an usually “population inversion” is necessary, the upper electronic level of the transition is stronger populated than the lower level. Therefore optical or electronic pumping is necessary to achieve stimulated emission
Light entering the amplifier is amplified by resonant emission, if the amplifier is pumped sufficiently for stimulated emission to occur and to overcome the losses due to absorption and scattering
In optics a resonant cavity is usually called a “Fabry-Perot Cavity”, or “Fabry-Perot Resonator” In the simplest case, a resonant optical cavity consists of two highly reflective flat mirrors
which are very accurately parallel. Actually, An optical resonant cavity has resonant modes, I.e. the transmission spectrum, the
reflectance spectrum, noise spectrum etc. show very sharp resonances. The higher the quality and the better the design of the cavity, the sharper these resonances are.
In a VCSEL (vertical cavity semiconductor laser the resonant cavity is formed by stacks of layers grown on top of the substrate. The axis of the optical cavity, and laser emission is perpendicular to the substrate.
In a traditional edge emitting semiconductor laser the cavity is formed by the cleaved edges of the laser chip, usually the cleaved edge have to be coated by evaporating thin layers of dielectric material.
In semiconductor lasers, the optical amplifier and the resonant cavity are tightly integrated, strongly interact and influence each other: e.g. during laser operation the electron density in the structure changes, which changes the refractive index, and both the amplifier and the resonant cavity become inter-dependent. Therefore in a semiconductor laser, amplifier and resonant cavity must be designed together, not independently as is sometimes possible in large gas lasers.
AlN, GaN, InN materials all have a direct band gap, i.e. the optical transitions across the bandgap are “allowed” and therefore much stronger than in the case of indirect bandgaps (which have “forbidden” transitions), as in the case of Silicon Carbide (SiC).
Before Nichia brought GaN blue LEDs on the market, commercial blue LEDs used SiC, which are much less efficient due to the indirect bandgap
Before Shuji Nakamura commercialized GaN blue LEDs it was generally thought that II-VI compounds were the path to blue LEDs and Lasers however defects in these materials could not be controlled sufficiently and the life-time of the devices was too short
Lattice mismatch ➔ GaN is grown on Sapphire, which has a 15% smaller lattice constant than GaN, and different
thermal expansion, leading to a very high defect density and cracking of the layers when the structures are cooled down after growth
➔ Akasaki solved this problem by developing AlN buffer layers ➔ Nakamura grew GaAlN buffer layers
High growth temperature ➔ thermal convection inhibits growth ➔ Nakamura solved this problem with his two-flow growth reactor (this invention by Shuji
Nakamura is at the core of the US$ 600 million law suits before the Courts of Japan between Shuji Nakamura and Nichia Chemical Industries)
p-doping was impossible ➔ A semiconductor laser, semiconductor light emitting diode, transistor structures and other
device structures require pn-junctions, I.e. junctions between p-type and n-type materials. Previous to Akasaki’s work p-type doping of GaN was impossibly
➔ Akasaki demonstrated p-type material which was e-beam annealed ➔ Nakamura found that annealing in Ammonia gas passivated the acceptors and solved this
Choice of substrate ➔ Silicon Carbide (SiC): good lattice matching, very expensive, patent issues ➔ Sapphire: used at present for most devices ➔ Ideally: GaN. However, GaN substrate wafers have not been available. Once they
become available, it is expected that GaN devices grown on GaN will have much better properties than devices grown on Sapphire with high lattice mismatch
Sapphire as substrate ➔ 15% difference in lattice constants between Sapphire and GaN and very large
difference in thermal expansion initially made growth of devices impossible. ➔ Akasaki solved this issue by designing and growing a AlN buffer layer (Akasaki US-
Problem: Pankove (1971 at RCA Laboratories) reported metal-insulator-semiconductor Gallium-Nitride light emitting diodes, but found p-type doping to be impossible
Proof of p-type doping: Akasaki (1988 at Nagoya University) found that samples after Low Energy Electron Beam Irradiation treatment (LEEBI) showed p-type conductivity. Thus Akasaki demonstrated that in principle p-type doping of GaN compounds was possible
Solution: Nakamura (1992 at Nichia, US-Patent 5306662) found the solution to the puzzle of p-type doping (see image on left hand side): ➔ Nakamura found that previous investigators had annealed the
samples in Ammonia (NH3) atmosphere at high temperatures. Ammonia dissociates above 400 Celsius, producing atomic hydrogen. Atomic hydrogen passivates acceptors, so that p-type characteristics are not observed.
➔ Nakamura solved this problem by annealing the samples in Nitrogen gas, instead of Ammonia
Although commercial GaN devices are routinely produced today, several materials issues still remain and are under intensive research investigation: ➔ GaN substrate: at the moment GaN devices are mainly
grown on Sapphire substrates, since GaN wafers of sufficient size and quality are not available. It is expected that growth on GaN wafers will lead to much lower defect densities, because the lattice constant mismatch will be much smaller
➔ High defect density: it is very puzzling that commercial GaN devices and particularly lasers operate with defect densities which are dramatically higher than in comparable GaAs or Silicon devices. This fact is not understood at the moment. It is expected that understanding this fact will lead to improvements to device quality.
Development of long-lifetime GaN lasers� Lasers are much more difficult to develop than LEDs, and in the case of
GaAs-based red and infrared lasers it took many years for the development of commercial semiconductor lasers.
The research path in semiconductor laser development is first to develop lasers which only work at very low temperatures (liquid Nitrogen temperatures) and under optically pulsed conditions. The development work leads: ➔ from optical pumping to electrical pumping ➔ from low temperature to room temperature ➔ from pulsed pumping to continuous pumping ➔ from short life-time to long life-time
Some of the most difficult issues to solve is high-defect density, and defect migration under the high currents of laser operation
Nakamura applied Epitaxially Laterally OverGrown (ELOG) GaN substrates to control defect density for laser structures �
Why did Shuji Nakamura at Nichia succeed where many MUCH larger multinationals and famous Universities failed?�
A quick direct answer is, that all other labs (with the exception of Akasaki in Nagoya) looked at II-VI compounds (ZnSe/ZnS) - and had given up working on Gallium-Nitrides because they thought it was hopeless. Work on ZnSe/ZnS did not succeed because II-VI compounds have low stability and are grown at low temperatures. Only Professor Akasaki (at Nagoya University and later at Meijo University) continued systematic work on GaN over many years.
Nichia’s Chairman and Founder (Nobuo Ogawa) gave Shuji Nakamura + 2 Assistants YEN 300 Million (approx. US$ 3 Million) to “gamble” on Gallium Nitride. This was about 1.5% of annual sales for Nichia. In addition, Nakamura had to learn MOCVD growth. For this purpose Nichia sent Nakamura for one year to the University of Florida to learn MOCVD in Professor Ramaswamy’s laboratory.
Large corporations tend to avoid risks more, and tend to take a more conservative approach to research - even in fundamental research (“jumping on the band-wagon” phenomenon)
Large corporations and research institutes tend to spend less research budget per researcher on average, e.g. NTT and other corporations spend on the order of US$ 250,000 to US$ 400,000 per researcher per year on average, so that it is very seldom that US$ 3 million + 1 year training in the US is available for the gamble on a new fundamental research project, which has not yet shown any proven results
As widely reported in the press internationally there has been a number of court cases between Shuji Nakamura and Nichia concerning the patents covering Shuji Nakamura’s research work while he was still at Nichia (he has since moved to the University of Santa Barbara)
To our knowledge, the present status is, that the judgments have confirmed Nichia’s ownership of the key patent which Shuji Nakamura claimed to own
To our knowledge, the Tokyo District Court has decided that Shuji Nakamura deserves a 50% share of profits of his invention, and the Court estimated Nichia’s profits to be on the order of US$ 1.2 billion, so that Shuji Nakamura would deserve US$ 600 million in reward for his invention. Since Shuji Nakamura claimed US$ 200 million the court granted his demand in full.
The court case was taken by Nichia to a higher court, and a court supervised settlement between Nichia and Shuji Nakamura was reached, where Nichia agreed to Shuji Nakamura approximately US$ 8 million reward for his inventions – a dramatically smaller sum than initially awarded by the Tokyo District Court. �
LEDs for tra!ic signals� Traffic signals together with large area out-
door flat panel displays where the first applications of GaN LEDs. The reasons are the initially high price of LEDs
LEDs are much more suitable for traffic lights than light-bulbs and in the near future it is expected that all traffic lights will operate with LEDs. The main reasons are: ➔ much lower energy consumption ➔ long lifetime (10 years and longer) ➔ better light quality (no filters)
Trend: at the moment most traffic light designs use a very large number of LEDs. In the future it is expected that traffic lights will be developed to include a much smaller number of LEDs reducing cost and energy consumption
LEDs are starting to replace fluorescent tubes in outdoor signage� LEDs are starting to
appear in applications where fluorescent tubes would have been used in the past in outdoor signage and advertising applications.
LEDs consume less energy, live much longer, don’t show flicker when aging, can be controlled to show images, messages and movies, change color, and have far more flexibility�
All lighting for cars including headlights and fog lamps will be soon replaceable by LED lamps
At recent Tokyo Motorshows most leading automotive electrical makers showed LEDs for car lighting applications based on red, yellow and white GaN based light emitting diodes
In the future semiconductor LEDs will enable “intelligent” lighting, e.g. lighting where the color composition corresponds to the external lighting conditions and other built-in intelligence and control which is impossible for traditional incandescent lamps
Markets for GaN lasers� The main application for GaN is for data storage and music storage. Due
to the shorter wavelength, violet and UV GaN lasers allow a much higher data density.
The next generation DVD standards use blue GaN lasers with a wavelength of 405nm for reading and writing data. Two competing standards competed for prominence, however Blue-Ray won the race: ➔ Blu-Ray: promoted by SONY and the Blu-Disc Founders consortium of 11 consumer
electronics companies plus Hewlett-Packard and Dell ➔ HD-DVD (Advanced Optical Disc) promoted by NEC and Toshiba (lost the race…)
Many other applications exist and are about to be developed, e.g. in the medical area
Today’s global lighting industry amounts to approximately US$380bn annually for lighting fixtures, lamps, electricity and kerosene fuel (in the third world). Energy consumption, and environmental impact due to CO2 emission and release of poisons can be much reduced by replacing traditional light bulbs and fluorescent tubes with GaN based LEDs.
Legislation, environmental groups, and well positioned companies push for energy-efficient lighting solutions and reduction of toxic emissions. Incandescent bulbs are on the way out (“Ban the bulb” movement).
Japanese researchers at Nichia and Toyoda Gosei in the 1990s invented gallium-nitride (GaN)-based light-emitting diodes (LEDs), which made it possible for the first time to replace light bulbs and fluorescent tubes, starting the solid-state lighting revolution.
Moore’s law brings semiconductor-innovation cycles to the lighting industry. GaN-based LEDs revolutionize the lighting industry, change industry structure and
business models, break established market positions and allow newcomers (Nichia, Toyoda Gosei, Seoul Semiconductors) to enter the mainstream lighting industry.
From the investor perspective, in addition to the front-line LED manufacturers, luminaire makers, manufacturing equipment makers, and materials makers are also very important, as well as the impact on incumbents.
Shuji Nakamura, Gerhard Fasol, Stephen J Pearton “The Blue Laser Diode: The Complete Story” ISBN 3540665056, Springer-Verlag, (Second Edition, September 2000)
Gerhard Fasol: "Room-Temperature Blue Gallium Nitride Laser Diode" SCIENCE, 272, p. 1751-1752 (21 June 1996)
Gerhard Fasol: "Fast, Cheap and Very Bright" SCIENCE, 275, p. 941-942 (14 Feb 1997)
Gerhard Fasol: "Longer Live for the Blue Laser" SCIENCE, 278, p. 1902-1903 (12 Dec 1997)
Roland Haitz et al, “The case for a national research program on semiconductor lighting” (White paper presented at the 1999 Optoelectronics Industry Development Association in Washington, DC, on 6 October 1999)
Evan Mills, “The US$230 Billion Global Lighting Energy Bill” (manuscript dated June 2002, and Proceedings of the 5th International Conference on Energy-Efficient Lighting, May 2002, Nice, France)
At the core of a light-emitting diode (LED) is a p-n junction - a junction of a p-type-doped and an n-type-doped semiconductor. When a voltage is applied to the LED, electrons are injected into the n-type side of the LED, and holes into the p-type side. The injected electrons and holes recombine at the location of the p-n junction and emit light. The photon energy (wavelength) of the light corresponds to the bandgap of the semiconductor material from which the LED is manufactured. Practical red and infra-red LEDs were invented by Nick Holonyak in 1962 at the R&D labs of General Electric (GE). (The first LED was made in 1907 by H.J. Round, who was assistant to Guglielmo Marconi at Marconi Company in the UK, however these first LEDs were not practically used.) Until Shuji Nakamura’s invention and commercialisation of blue LEDs, essentially only red and infra-red LEDs were commercially available for meaningful applications (weaker blue LEDs were available before Nakamura’s invention, but their light was too weak and the lifetime too short for common applications). �
Compact fluorescent lamps (CFL) are essentially small versions of the common fluorescent tubes. CFLs use about one-fifth to one-quarter of the energy of incandescent-light bulbs for a given light output. Therefore, about 70-80% of the electricity used for lighting could be saved by replacing incandescent lamps with CFLs. Although CFLs are substantially more expensive than incandescent lamps to buy, they have a much longer life.
The CFL was invented by Edward Hammer at General Electric in 1976. General Electric did not manufacture CFLs at that time. However, other companies began making and selling them from 1995. Hammer was awarded the IEEE Edison Medal 2002 for inventing the CFL.
CFLs contain mercury. In the US, the National Electrical Manufacturers Association is committed to limiting the amount of mercury used in CFLs. If broken, CFLs are a health hazard because of evaporating mercury. When CFLs are disposed of in landfills, they are likely to be crushed, enabling the mercury to escape into the atmosphere. Proper recycling is necessary to avoid this mercury load on the environment.
➔ GLS are lamps for general lighting Luminaire (lighting fixture)
➔ The lighting industry uses the term luminaire (lighting fixture) to describe devices used to create artificial light. A complete luminaire may include some or all of the following components: light source (lamp); reflector to direct the light; aperture; lens; housing or shell; protective covers; electric ballast (if required, such as for fluorescent tubes); electronic driver circuitry (as for LED lamps); and wires or connectors to link the luminaire to a power source.
Luminous efficacy (luminous efficiency) ➔ The energy efficiency of light sources is the amount of light produced divided by the electricity consumed
and is measured in lumens per Watt (lm/W). Gallium Nitride (GaN)
➔ Gallium nitride is a III-V semiconductor crystal with a direct bandgap. Solid-state lighting
➔ The light emitters for solid-state lighting (SSL) are solid-state devices, usually gallium-nitride (GaN) light-emitting diodes (LED) or organic light-emitting diodes (OLEDs).
Organic light-emitting diodes (OLEDs) ➔ Organic light-emitting diodes have applications in lighting and for flatpanel displays. The first OLED-based commercial
flatpanel displays were introduced for mobile phones in Japan about 2006, and Sony introduced the first commercial, stand-alone OLED flatpanel display in the autumn of 2007. Development is also progressing on lighting applications of OLEDs.
MOCVD ➔ Metal organic chemical vapor epitaxy is a common crystal-growth method used to develop and manufacture GaN
semiconductor light-emitting diodes and lasers. MOCVD allows the growth of device layers with single-atom-layer precision.
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