LED lighting is a set of equipment for illumination of various kinds, based on the radiation produced by electric current in special semiconductor devices. Plus, this technical solution in significant savings. The efficiency of LED lighting is much higher than incandescent lamps.
LEDs and lighting
It turned out to be difficult to believe half a century ago, but today LED lighting is considered the most economical of all. An additional plus in a wide range of shades, characterized by a special parameter - temperature, information is located on the package. Savings in comparison with incandescent bulbs is 10 times, LED lighting is undoubtedly characterized by better color reproduction than halogen bit sources.
Developers promise incredible durability of their own products. The average lifetime of LED lighting is 30,000 hours and reaches 50,000. These are many decades of trouble-free operation. Thanks to the built-in driver, the LED light bulb is not terrible voltage surges, dramatically reducing service life. There are also difficulties in using switches with light indication.
On sale there will be branded products priced at up to 2,000 rubles apiece, Chinese consumer goods are ten times cheaper. And it is impossible to say anything bad about the latter. Choose LED lighting relies on power and the absence of flicker. Revealing a negative effect is not difficult with a poor quality camera. An old phone or iPad will do. Not a professional camera. Focus on a glass flask and carefully see if flicker is present.
From the history of the development of semiconductor technology
A prerequisite for the creation of the first LED from silicon carbide was the 1907 article in the magazine Electric World, published in New York by McGraw and Hill. The text said that Henry Joseph Round was experimenting with carborundum crystal and discovered an amazing, previously unseen phenomenon. At connection of electrodes of a direct current the luminescence was noted. Only selected samples showed an effect at a voltage of 10 V, but any crystal began to luminesce as the value increased to 110 V.
In most cases, the luminescence was yellow and located near the negative pole, the positive periodically flashed greenish-blue sparks. In addition to this, samples of the crystals showed light green, blue and orange colors. The round tried to place the negative electrode in the middle of the crystal, then the only pole( positive) became to emit light. Thus, the scientist brings readers to the concept of a metal-semiconductor transition, then unknown in science( the Schottky rectifying contact).
The origin of the carborundum is enmeshed in deep mystery. This is apparently the only mineral originally obtained in the laboratory by Edward Godrich Acheson( 1890).Three years later, Henri Moissan discovered something similar in the fragments of a meteorite that overtook the Devil's Valley of Arizona, and decided that there was a diamond in front of him. A long 11 years was spent on understanding the true chemical composition of the find, while carborundum continued to be used by industry as the strongest abrasives.
Being a silicon carbide by chemical formula, the mineral moissanite shows a Mohs scale of 9.5 points and is truly comparable to natural diamond: only a precious mineral( and boron nitride, but the compound was first obtained exclusively in 1957) and is inferior to an alien from space. For obvious reasons, it was suggested that the "diamond" hit a meteorite during the development of the excavators, having broken away from the mining tool.
Mineral, which became a prerequisite for the creation of LED lighting, was named after the discoverer in 1904, several years before the death of the latter. In nature, moissanite is extremely rare. Among the likely places of residence, in addition to meteorites, are called corundum deposits and deposits of diamonds. And until 1959, even these foci were not called: Henri Moissan ran into something extremely rare. In the late 50s of the 20th century, natural moissanite was found at once in two points of the globe:
- Yakut diamond mines.
- Formation of the Green River Wyoming.
Spectral analysis data suggests that carborundum is considered a frequent visitor to rocks hovering around the carbon-rich stars of the galaxy. It is surprising, but the discovery of the LEDs was forgotten for a long time. Information emerged already during the Cold War, when the first semiconductor lasers were demonstrated simultaneously in several places. About LED lighting then did not think.
LEDs based on silicon carbide
Electroluminescence discovered recently, at the beginning of the XX century. The great advantage of the new phenomenon is the fact that the glow is noticeable at room temperatures. An ordinary incandescent light bulb, as you know, was greeted with applause from theater visitors for comparative safety with regard to gas horns. LED lighting by all signs surpassed predecessors by an order of magnitude: even after hours of work, the glass bulb remains slightly warm.
Industrial production of silicon carbide began in 1891.Developed by Acheson, proceeded at high temperatures in a coal crucible, where the conditions for the transformation of ordinary glass into a superhard mineral were created using an electric current. The reaction goes in two stages. Carbon reduces tetravalent silica to two valent, then a similar reaction occurs. Carbon monoxide released needed intensive oxidation to deactivate.
Carborundum shows extreme hardness in the first place, due to the similarity of the crystal lattice with the diamond. The low cost of synthesis led to high popularity as an abrasive of a new chemical compound. Henry Joseph Round experimented with detectors for the first electromagnetic wave receivers, and discovered a new phenomenon. Semiconductor rectifiers were called to replace an expensive vacuum diode, as LED lighting gradually replaces the incandescent light bulbs.
The phenomenon detected by the Round would have been noticed in some Schottky diodes, if we apply a voltage much higher than the operating one. In this case, avalanche multiplication of minority charge carriers( holes) in the metal occurs. They are injected into a semiconductor, where they are recombined with electrons, and the difference in energy levels just falls within the visible range of radiation. The phenomenon can also be observed with a strong reverse displacement of the transition. There are even special studies on this score.
Russian Losev usually does not appear in the scientific literature, but the author’s merit in creating LED lighting is indisputable. The experimenter found that some diodes glow when turned on in the forward direction, others - in all cases. He derived a formula for the dependence of the radiation frequency on the magnitude of the voltage drop at the junction, patented the world's first optical relay. Work continued from 1924 until the beginning of the Second World War.
In 1939, Zoltan Bay and Georgy Zhigeti patented a silicon carbide-based LED with the option of replacing boron carbide that emitted colors: white, pale yellow, and pale green, depending on the impurities introduced into the materials. Along the way, we note the developments of Kurt Lekhovits, doped silicon carbide with arsenic to obtain n-conductivity and boron - for p-conductivity. According to the text of the patent, it is said about the possibility of introducing into the material of the LEDs a number of other impurities: lead, tin, copper, zinc, europium, samarium, bismuth, thallium, manganese, silver and cerium.
Losev's work was actively interested in Lebner, an employee of the US embassy, who patented the green LED in 1958.A decade later, they learned how to make thin-film silicon carbide structures, which made it possible to create LED lighting, where the correct shape is used as a working element.
Development of LEDs and lighting
It turned out to be harder to get blue. Already in the middle of the 20th century, it became clear that the devices had a great future; to use( not for lighting) in television, it was necessary to allow one of the color schemes. For example, the famous RGB.A blue LED was required. The efficiency at the beginning of the 60s of such a device was only 0.005%.Silicon carbide was not the best solution for such problems, the brightest samples worked at a wave of 470 nm with an efficiency of 0.03%.For LED lighting, this is clearly not suitable.
Attention of researchers attracted the publication of the French scientist Destrio, who suggested using zinc sulfide as the main material of LEDs. As a result, semiconductors of class AIII BV gained popularity, to which GaAs, which is found everywhere today, belongs. The era of the new compound started in 1954, when they learned to melt thin plates from the melt, and the epitaxy made it possible to form pn junctions on the surface, which is used today in LED lighting.
In 1962, there were reports of the creation of the first semiconductor lasers in the infrared range, with a wave from 870 to 890 nm. The devices were clearly called to replace the ruby, without targeting the creation of LED lighting. New devices operated in continuous mode at temperatures of 77 K. Then the temperature rose to 300 K( room temperature).Much attention was paid to the technological aspect of LED production, which became the basis of success in the task of creating LED lighting. In the 60s, a horizontal method was developed for growing gallium arsenide crystals according to the Bridgeman method.
Radiation of LEDs from gallium arsenide with silicon impurities went above the absorption range of the substrate of pure gallium arsenide. As a result, all the power of the flow went to destination without weakening. And gallium arsenide behaved like clear glass. The output of quanta increased 5 times in comparison with materials obtained by zinc diffusion methods. IBM employees Rupprecht and Woodall worked underground, in their free time. Everyone was engaged in their own material. Accordingly, GaAsP and AlGaAs. The first alloy was considered hopeless. The difficulty manifested itself in technology. It was difficult to grow the correct form of stable crystals. Aluminum, among other things, actively added oxygen from the air, the oxidation centers extinguished the luminescence phenomena.
Woodall when he was a graduate student specialized in metallurgy and heard something about the phase transitions of metals. And I decided to experiment with the concentration of aluminum in the melt. As a result of the fulfillment of certain conditions, it was possible to obtain a film with a thickness of 100 microns, which made it possible to create LEDs with a spectrum in the region of a dark red hue. Further increase in the concentration of aluminum shifted the area of transparency of the substance, it was possible to create on the basis of the same material a working pn-junction and a substrate for it.
A working circuit from a GaAsP-based instrument with a power source on a conventional battery was immediately assembled and demonstrated to IBM management. Some people have recognized the invention as very promising. The first application was found in the display area on motherboards. At the same time, Texas Instruments has established a serial production of infrared devices with an amazing price of $ 130 per piece.