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The LED chip, also known as the LED light-emitting chip, is the core component of the LED lamp, which is also referred to as the PN junction. Its main function is to convert electrical energy into light energy. The main material of the chip is monocrystalline silicon. The semiconductor wafer consists of two parts, one part is a P-type semiconductor, in which the hole dominates, and the other end is an N-type semiconductor, which is mainly electrons here. But when the two semiconductors are connected, they form a PN junction. When a current is applied to the wafer through the wire, the electrons are pushed toward the P region. In the P region, the electrons recombine with the holes, and then the energy is emitted in the form of photons. This is the principle of LED illumination. The wavelength of light, which is the color of light, is determined by the material that forms the PN junction.
Led history
Fifty years ago, people learned about the basics of semiconductor materials that produced light. In 1962, General Electric's Nick Holonyak Jr. developed the first practical use of visible light-emitting diodes. LED is the abbreviation of English lightemitTIngdiode (light-emitting diode), its basic structure is an electroluminescent semiconductor material, placed on a leaded shelf, and then sealed with epoxy resin, that is, solid package, so it can protect The role of the internal core wire, so the LED's seismic performance is good.
The LED was originally used as an indicator light source for instrumentation. Later, various light-colored LEDs were widely used in traffic lights and large-area displays, resulting in good economic and social benefits. Taking a 12-inch red traffic light as an example, in the United States, a long-life, low-efficiency 140-watt incandescent lamp was used as a light source, which produced 2000 lumens of white light. After passing the red filter, the light loss is 90%, leaving only 200 lumens of red light. In the newly designed lamp, Lumileds used 18 red LED light sources, including circuit losses, to consume 14 watts of electricity, which would produce the same light effect. Automotive signal lights are also an important area for LED light source applications.
classification
Uses: According to the use, it is divided into high-power LED chip and low-power LED chip;
Color: Mainly divided into three types: red, green, blue (raw materials for white light);
Shape: Generally divided into square pieces and round pieces;
Size: Small power chips are generally divided into 8mil, 9mil, 12mil, 14mil, etc.
Chip size
High-power LED chips are available in three sizes: 38*38mil, 40*40mil, and 45*45mil. Of course, the chip size is customizable. This is just a common specification. Mil is a unit of size, a mil is one thousandth of an inch. 40mil is almost 1 mm. 38mil, 40mil, and 45mil are common size specifications for 1W high power chips. In theory, the larger the chip, the greater the current and power it can withstand. However, the chip material and process are also the main factors affecting the chip power. For example, CREE40mil chips can withstand 1W to 3W, and other chips of the same size can withstand up to 2W.
Luminance
General brightness: R (red GaAs P655nm), H (high red GaP697nm), G (green GaP565nm), Y (yellow GaAsP/GaP585nm), E (orange GaAsP/GaP635nm), etc.;
High brightness: VG (lighter green GaP565nm), VY (lighter yellow GaAsP/GaP585nm), SR (lighter red GaA/AS660nm);
Ultra high brightness: UG, UY, UR, UYS, URF, UE, etc.
Binary wafer (phosphorus, gallium): H, G, etc.;
Ternary wafers (phosphorus, gallium, arsenic): SR (bright red GaA/AS 660 nm), HR (super bright red GaAlAs 660 nm), UR (bright red GaAlAs 660 nm), etc.;
Quaternary wafers (phosphorus, aluminum, gallium, indium): SRF (bright red AlGalnP), HRF (ultra bright red AlGalnP), URF (bright red AlGalnP630nm), VY (bright yellow GaAsP/GaP585nm), HY (super Bright yellow AlGalnP595nm), UY (brightest yellow AlGalnP595nm), UYS (brightest yellow AlGalnP587nm), UE (brightest orange AlGalnP620nm), HE (super bright orange AlGalnP620nm), UG (brightest green AIGalnP574nm) LED, etc.
Substrate
The selection of substrate materials is a primary consideration for the fabrication of LED chips. Which suitable substrate should be used depends on the requirements of the device and the LED device. Three substrate materials: sapphire (Al2O3), silicon (Si), silicon carbide (SiC).
Advantages of sapphire: 1. Mature production technology and good device quality; 2. Good stability, can be used in high temperature growth process; 3. High mechanical strength, easy to handle and clean.
Insufficient sapphire: 1. Lattice mismatch and thermal stress mismatch, will produce a large number of defects in the epitaxial layer; 2. Sapphire is an insulator, two electrodes are fabricated on the upper surface, resulting in a reduction in effective light-emitting area; The lithography and etching processes are added, and the manufacturing cost is high.
Silicon is a good conductor of heat, so the thermal conductivity of the device can be significantly improved, thus extending the life of the device.
An LED chip of a silicon carbide substrate (CREE specializes in SiC material as a substrate), the electrode is an L-type electrode, and the current flows longitudinally. Devices fabricated using such substrates have very good electrical and thermal conductivity properties, which facilitates the fabrication of large power devices with large areas. Advantages: The thermal conductivity of silicon carbide is 490 W/m·K, which is more than 10 times higher than that of sapphire substrates. Insufficient: The cost of manufacturing silicon carbide is high, and the commercialization of it needs to reduce the corresponding cost.
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