LED (LightEmittingDiode), light-emitting diode, is a solid state semiconductor devices, which can be directly put electricity into light. LED is the heart of a semiconductor chip, the chip attached to one end of a stent, is the negative side, the other end of the positive power supply, so that the whole chip is epoxy encapsulated. Semiconductor chip consists of two parts, part of P-type semiconductor, the hole in it dominates the other side is N-type semiconductor, here is mainly electronic. But when the two semiconductor connected between them to form a PN junction. When the current through the wire, when applied to the chip, electronics will be pushed to P zone, with the P zone electron hole recombination, and then will be issued in the form of photon energy, which is the principle of LED light. The wavelength is the color of light is the formation of PN junction of the material by the decision.
50 years ago, people have to understand the semiconductor material can produce light of the basic knowledge, the first commercially available diodes in 1960. LED is in English lightemittingdiode (light-emitting diode) acronym, and its basic structure is an electroluminescent semiconductor material, placed in a wire rack, then four weeks sealed with epoxy resin, that is solid package, it can play the role of protecting the internal core wire, so the LED's seismic performance.
The core part of the light-emitting diode is a p-type semiconductor and n-type semiconductor chip formed in the p-type semiconductor and n-type semiconductor between a transition layer, called the pn junction. In certain semiconductor materials, PN junction, the injection of minority carrier and majority carrier recombination, when will the excess energy released in the form of light to convert light energy directly into electrical energy. PN junction reverse voltage, minority-carrier injection is difficult, it is not light. The use of injection electroluminescent diodes called the principle of making light emitting diodes, commonly known as LED. When it is in working condition when a positive (that ends with a positive voltage), current from the LED anode to the cathode, the semiconductor crystals to the making of different colors from the ultraviolet to infrared light, light intensity and current.
Instrumentation for the first LED light source direction, then a variety of light-colored LED in traffic lights and large screen has been widely used and produced good economic and social benefits. 12-inch red traffic lights, for example, is used in the United States would have long life, low-efficiency 140-watt incandescent lamp as a light source, it produces 2000 lumens of white light. The red filter, 90% light loss, only 200 lumens of red light. In light of the new design, Lumileds has used a red LED light source 18, including circuit losses, including a total power of 14 watts of light to produce the same effect. Automotive LED lights are also important areas of light application.
For general lighting purposes, people need a white light. 1998 white LED developed. This is the GaN LED chip and yttrium aluminum garnet (YAG) packaged together to make. GaN blue chip fat (λp = 465nm, Wd = 30nm), made of high-temperature sintering of YAG phosphors with Ce3 + excited by this blue light yellow light shot, peak 550nm. Blue LED substrate cavity installed in the reflective bowl, cover with thin layer of resin mixed with YAG, about 200-500nm. LED substrate phosphor emitted blue light is absorbed, and some blue and yellow light emitted phosphor mixture can be too white. Now, for the InGaN / YAG white LED, YAG phosphor by changing the chemical composition and adjust the thickness of the phosphor layer can be obtained color temperature 3500-10000K in colored white. The white light through the blue LED by means of simple structure, low cost, high degree of technological maturity, and the use most.
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