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Introduction to LED
LED structure and luminescence principle
LED (Light Emitting Diode), light-emitting diode, is a solid state semiconductor devices, which can be directly converted into electricity to light. LED is the heart of a semiconductor wafer, the wafer is attached to a support, one end is negative, the other end of the power of the cathode, the entire chip package to be epoxy resin. Semiconductor chip is composed of two parts, one part is a P type semiconductor, it inside the hole dominated, the other side is the N type semiconductor, here is mainly electronic. But linking the two semiconductor, among them the formation of a P-N junction. When the current through the wires role in this chip, the electron will be to P area, complex in area P electrons and holes, and then to form a photonic energy, this is LED light-emitting principle. The wavelength of light that is the color of light, is decided by the formation of P-N junction material.
The initial LED is used as the light source instrument, then all kinds of colored LED has been widely used in traffic lights and large screen, resulting in good economic benefit and social benefit. The 12 inch red traffic lights as an example, in America was long-lived, low light efficiency 140 watt incandescent lamp as the light source, it produces 2000 lumens of white light. The red filter, the optical loss of 90%, only 200 lumens of light. In the light of the new design, Lumileds uses 18 red LED light source, including the loss of circuit, a total power consumption of 14 watts, to generate the same optical effect. An important field of car lights and LED light source applications.
For general lighting, people need more white light sources. The success of LED development in 1998 white. The LED is the GaN chip and yttrium aluminum garnet (YAG) package together. GaN chip blue light (λ p=465nm, Wd=30nm, YAG) phosphor with high temperature sintering of Ce3+ made by the blue light after excitation of a yellow light, the peak 550nm. The blue LED chip are arranged in a bowl shaped reflection cavity, covered with a resin mixed with thin layer of YAG, about 200-500nm. The blue part of the LED based tablets issued by the fluorescent powder absorption, another part of the Blu ray and the phosphors emit yellow light mixed, can be a white. Now, the InGaN/YAG white LED, YAG phosphor by changing the chemical composition of the phosphor layer and adjust the thickness, 3500-10000K color temperature can be colored white. The blue LED through the method by white, has the advantages of simple structure, low cost, high technology is mature, so use the most

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