the LED lights, lighting technology route includes the extension, the substrate, the type of packaging, white LED lamp bead, etc. Red, green, blue LED lamp bead is by III - phosphorus, arsenic, nitrogen, etc V compounds such as gallium arsenide ( GaAs) , gallium phosphide ( GaP) And phosphorus gallium arsenide ( GaAsP) And gallium nitride ( GaN) Such as made of semiconductor.
1, LED lamp bead epitaxy technology
in the last ten years in the industry by improving the epitaxial growth process makes the dislocation density are improved greatly. But the mainstream white light lighting blue LED lamp bead, GaN GaN lattice and the mismatch of thermal expansion coefficient between the substrate and still LED to a high dislocation density. For a long time, by studying the LED lamp bead epitaxy technique to minimize the defect density, improve the quality of crystal is the goal of the LED lamp bead technology.
LED lamp bead epitaxial wafer is the core part of the LED lamp bead, the wavelength of LED diode, forward voltage, brightness, or count was largely depends on the epitaxial wafer photoelectric parameters, such as material. Epitaxy technology is the key of the epitaxial wafer manufacturing technology and equipment, metal organic vapor deposition technology ( 金属 Is III - growth V, II - VI and alloy thin layer of the main method of single crystal. Epitaxial wafer dislocation as a non-luminous non radiative recombination centers, photoelectric performance has very important influence on the device.
LED lamp bead epitaxial structures and epitaxy technology research:
(1) the growth of the LED lamp bead conventional techniques including multiple quantum well before the low growth In components of the InGaN well to release stress, and ACTS as a carrier 'reservoir', warming grow GaN base layer to improve the quality of the base layer of crystal, the lattice mismatch through a new growth of InGaAlN base layer or complementary InGaN/AlGaN growth stress structure, etc. Quantum well active area InGaN/GaN quantum well active area is the core of the LED lamp bead epitaxial material growth InGaN quantum well is the key to control the stress of the quantum well, reduce the influence of polarization effect.
2. After years of development, the epitaxial layer structure and extension of the LED lamp bead technology has been more mature, LED lamp bead, internal quantum efficiency can reach more than 90%, internal quantum efficiency of red light LED lamp bead have even close to 100%. But in the study of high power LED lamp bead, found that the quantum efficiency decreased significantly under large current injection, is known as Droop effect. Effect of GaN LED lamp bead the Droop of the tendency and the reason for the carrier localization, spillage from the source region, as well as auger recombination. It was found that the quantum well with wide to reduce the carrier density and electron blocking layer can be optimized P type area slow Droop effect.
LED diode epitaxial structures and epitaxy technique in the study of other specific techniques are:
1) surface coarsening technology
LED lamp bead epitaxial surface coarsening is equivalent to change the emergent Angle to avoid emergence of total reflection light increase the rate of the light, due to the refractive index of epitaxial materials and packaging materials lead to different part of the emergent light will be reflected back to the epitaxial layer. Directly on process of epitaxial surface processing, easy to damage the extension of active layer, and the transparent electrode is harder to make, by changing the epitaxial layer growth conditions to achieve surface coarsening is a feasible way.
(2) the substrate stripping technology
LED lamp bead sapphire substrate laser stripping technology is based on GaN homogeneous epitaxial stripping of the development of technology, using uv laser irradiation substrate, melting transition layer stripping, stripping sapphire OSRAM 2003 using this process, will the light rate up to 75%, is one of the traditional three times, and formed the production line.
3. LED lamp bead flip chip technology according to the American Lumileds company data, sapphire substrate LED lamp bead about increase the rate of a light one. 6 times.
(4) the LED lamp bead omni-directional reflection film, except a positive light to other emergent light as much as possible of the total reflection back to within the epitaxial layer, ultimately ascend out of the positive rate of light.
5. LED diode microstructure of two-dimensional photonic crystals can improve the efficiency of the light, in September 2003, Japan's matsushita made 1 in diameter. 5 microns, 0. 5 micron bump photonic crystal LED lamp bead, light yield increased by 60%.
2, substrate technology
LED lamp bead commonly used chip substrate technology mainly include sapphire substrate, silicon carbide substrate, three categories of silicon substrate, and development of gallium nitride, zinc oxide, etc. To the substrate material request:
1. LED lamp bead substrate chemical stability matching with the epitaxial film layer, substrate material to have a good chemical stability, not easy to decompose in epitaxial growth temperature and atmosphere and corrosion, not with the decrease of the quality of the epitaxial film epitaxial produce chemical reaction film;
2. LED lamp bead substrate and epitaxial film layer match, the thermal expansion coefficient of thermal expansion coefficient difference is too big, will lead to the decrease of the quality of the epitaxial film growth, in the working process of the device, may also damage caused by heating device;
(3) the LED lamp bead substrate and the structure of the epitaxial film layer match, both the crystal structure of the same or similar material, the small lattice constant mismatch, good crystallization properties, low defect density.
LED lamp bead silicon substrate technology at present in our country has got a technical breakthrough, is trying to to the large-scale industrialization application development. At present, has a large number of used for commercialization of GaN LED lamp bead only sapphire substrate and silicon carbide substrate. Can be used for other GaN LED lamp bead, substrate material and there is quite a distance away from the industrialization of GaN homogeneous substrate, ZnO substrate.
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