A diode lamp is an incorrect and simplified name used mainly in everyday life to denote electrical semiconductor lighting devices. The principle of operation is based on the phenomenon of electroluminescence of semiconductors.
Semiconductor devices as light sources
Having got acquainted with other information on the site already know that the peak of the development of LEDs fell on the invention of the ruby laser. Then the Cold War revealed the seeds of local conflicts, and today the interests of states often run counter to each other. Let us explain: the idea of creating a laser weapon was prevalent before, but a number of difficulties did not allow working effectively with radiation: the
- Ruby laser, as well as the gas one, requires intensive cooling. It is not possible to install such units on aviation or spacecraft: heavy, bulky and require a lot of energy to work. The text has already considered the arguments on this score of Academician Ioffe. The latter was of the opinion that the thermocouples are promising in this context.
- Radiation power, concentrated in a narrow range, quickly decays in the atmosphere. Even in the windows of transparency, the use of such technologies is unprofitable. However, lasers were actively used in satellite communications. Sources will be found claiming that it has become commonplace for the military since the early 70s of the XX century. Of course, by the example of the American armed forces.
- The power of semiconductor lasers was not too big. And not only for reasons of low efficiency( hardly reached 1% for the first devices).Now there are advanced products that convert half of the energy into photons. The technological factor of the practical impracticability of creating a large pn-junction area comes into force.
It is advantageous to use the radiation of the optical and adjacent ranges for the needs of information transmission - these are the best frequencies today. Due to the small wavelength( according to the Kotelnikov theorem), it is possible to lay a large amount of data in a short area. What does the increase in transmission rate. Today, most high-quality computer networks operate in the optical range, using methods similar to those observed in LED lamps.
The history of the creation of devices is outlined in the section mentioned above, let's look at the development of technology. It is known that in the 1960s, LEDs were actively developed, but a number of difficulties were noted. For example, the efficiency of blue radiation turned out to be so small that there was no sense in applying the technology in practice. There were difficulties in studying the properties of new materials, their manufacture. Electroluminescence proceeds in three stages:
- Excitation of carrier pairs of both signs due to the applied voltage.
- Thermalization of carriers, equalization of energy for a given temperature.
- Recombination with emission of photons outside.
LED Chemical Composition
Crystal Inorganic Semiconductors From English, the abbreviation LED stands for Light-Emitting Diode. The translation into Russian is too complicated, as the professor of the Polytechnic Institute in Troy Schubert directly speaks about, and therefore the simplification is applied - the LED.To have an idea about the principles of the pn-structure, it is necessary to learn basic things. In semiconductor physics, materials are usually classified according to the periodic table from the eighth group and the seventh period. There are other graphical forms of recording the law of periodicity, but not in this context. To designate the crystal choose the first digit. If a semiconductor is formed by two elements, the groups are listed sequentially.
For example, cadmium telluride, readily used as a photon emitter and as a receiver of optical radiation, belongs to the group of materials AIIBVI.The sequence corresponds to the chemical formula. In this regard, cadmium telluride looks like CdTe. It is easy to trace that element A is in the second group, and B is in the sixth. Silicon carbide( carborundum), on the basis of which photon emission effects were first demonstrated, belongs to the rare AIVBIV group, and has become the only representative.
By properties, the hardest ore on the planet has become an analog of simple elements: diamond, silicon, germanium. The latter two are widely used in pure and doped form. The characteristics of semiconductors are completely determined by the energy states of the electrons, the width of the forbidden band. Entering into a pure crystal of an impurity, scientists try to receive new qualities. For example, when doping germanium with arsenic, the material acquires n-type conductivity due to the presence of free electrons in the region of inhomogeneities formed by impurities. So, semiconductors are considered:
- By the number of basic generators:
- Simple. Consist of a single element of the periodic system.
- Complicated. Formed by two( or more) chemical elements.
- By the source of the acquisition of the necessary qualities:
- Clean. No impurities.
- Alloyed. With the addition of other chemical elements in the crystal lattice.
The signs listed above are characterized by crystalline inorganic semiconductor materials. Among them, the most widespread, in addition to simple, compounds received: AIIIBV, AIIBIVCV2( for example, CdSnAs2, a close analogue of indium arsenide).The latter group has a chalcopyrite crystal lattice, although this material is not included in this family. Complex substances are created by fusing the original substances in the right proportion, often forming electronic or hole conductivity without the introduction of impurities. Recall that the size of quantum transitions in a material is of primary importance.
Separately from binary semiconductors, it is customary to classify oxides. Some of the materials( cuprite) are found in nature. Growth processes are currently not well understood, but copper oxide( AIIBVI) is used in engineering. Oxides are mentioned separately due to the presence of selected materials of the group( for example, La2CuO4) superconductivity at relatively high temperatures - 130 K. The crystalline structures of a number of semiconductors are characterized by layering, pronounced properties in two dimensions( film).
Non-crystalline inorganic semiconductors
By changing the technology, individual simple and complex semiconductors can be made amorphous( vitreous).Then the crystal structure of the material is not visible. All semiconductors of the group have n-type conductivity, demonstrate a bright response to photons, which allows them to be used as part of solar cells. So, the presence of specific levels suggests the possibility of creating and LEDs on a specified basis.
Globally, amorphous semiconductors are divided into groups:
- Oxide glasses are formed by fusion. The process involves oxides of elements with variable valence( transitional), oxides of the forming substance( boron, phosphorus), oxides of modifiers( calcium, lead, barium).Moreover, the transition element is contained in at least two states of valence, which determines the presence of special properties.
- Chalcogenides - compounds of elements of the sixth group of the periodic system( selenium, tellurium, sulfur) with metals. The name of the materials received for the frequent inclusion in the ore. Often used in optics, in the 60s described the possibility of using to create storage devices( including non-volatile).The disadvantages include poor chemical resistance and tendency to crystallization.
- Organic semiconductors are used to create LEDs. Predominantly polymeric structure. For the first time the effect of luminescence is demonstrated on crystals of acryca and acridine. Among organic materials, there are two groups:
- With a model based on charge transfer.
- With a system of developed conjugated double and triple bonds.
- In the crystal lattice of silicon carbide, germanium, silicon atoms are located in the corners of the tetrahedron. The amorphous structure is characterized by the lack of orderliness of individual cubic constituents of a substance.
Organic semiconductors are considered crystals, polymers or amorphous substances. The nature of origin is in the title. The effect of electroluminescence based on organic semiconductors was discovered in 1953 by Andre Bernanoz. Experiments on the study of chemiluminescence straight led the scientist to the discovery of the illumination of acrihin and acridine. The era of organic LEDs began in 1987 thanks to Codec. Dr. Tang discovered the glow of the polymer film Alq3( three-8-hydroxyquinolate aluminum).The new green LED had unique qualities and is still used in technology.
Similarly, the crystal structures of the elements of the periodic table exhibit the property of electroluminescence. Distinctive characteristics are considered high efficiency and low price. In 1989, the laboratory at the University of Cambridge learned how to produce organic polymers. The discovery of Richard Friend, Donal Bradley and Jeremy Barrow led to the creation in 1992 of Cambridge Display Technology( a division of Sumitomo Chemical) with a turnover of $ 285 million for 2007.Laboratories of the enterprise and today are engaged in the search for new polymeric materials, research of their properties.
The first black-and-white display with a passive array of organic LEDs was released by Pioneer in 1996.The screen resolution was only 256x64 pixels. In the same year, CDT presents its own work in the area mentioned. In 2000, thanks to LG, the first designs for mobile devices appeared. At the time of 2016, Samsung has invested $ 325 million in technology on OLED flexible displays with a simultaneous doubling of output, while new Mercedes will be equipped with 12.3-inch screens.
Today, organic LEDs are already used in the backlight of the matrix. LG has developed and manufactured special printers capable of printing to produce panels for lighting purposes. This solves the question of the price of organic LEDs. The big advantage was the ability to adjust the brightness. Not far off is the day when diode lamps begin to function at the expense of organic matter.
The advantages of LED lamps
Despite the low efficiency of LEDs, lamps based on them have tremendous characteristics. Energy consumption, other things being equal, is reduced by an order of magnitude. That allows you to recoup the cost of devices during the year, the manufacturer usually gives a guarantee of 3 or more. However, getting it on Chinese products sold under various European brands is not easy. The cunning manufacturer in the instructions indicates the need to return products by the seller, and the latter is not always ready to go for it.
The main thing - the segment today is booming. LED lamp tomorrow will become the de facto standard for the needs of lighting.