The LED lighting epitaxial wafer knowledge introduction

 

led high bay light

 

Production wafer production process is very complex, complete exhibition epitaxial wafers, the next nine to do it at random tests to meet the requirements that the yield on each wafer, the other for defective products (voltage deviation is large, the wavelength is shorter or rather long, etc.). The wafer yield must begin electrode (P pole, N pole), followed by laser cutting the wafer, and then sorting hundred percent, depending on the voltage, wavelength, brightness fully automated sorting, which is formed german led high bay lighting factory. Then also visually put a little defective or worn electrodes, sorting out, these are behind the bulk crystal. At this point in the film has a blue ship does not comply with the normal requirements of the chip, it naturally became the edge pieces or raw footage and so on. Epitaxial wafers of defective products (mainly some parameters do not meet the requirements), they do not do the film, made directly electrode (P pole, N pole), nor do the sorting , that is currently on the market LED large circle piece (there is also a good thing, such as square tablets, etc.).

Extension products used in four aspects, CMOS Complementary Metal Oxide Semiconductor support the requirements of the small size of the device forefront of technology. CMOS products are the largest application areas epitaxial wafers, and is unrecoverable IC manufacturers for device technology, including flash memory chips and microprocessors and logic and memory applications in DRAM (dynamic random access memory). Discrete semiconductor device fabrication requires a precise characteristics for Si. "Singular" (exotic) Semiconductor contains special products that use non-Si materials, many of which use the compound is incorporated in the epitaxial layer of semiconductor material. A semiconductor buried layer in the bipolar transistor using doped region physical isolation, which is the epitaxial deposition process.
Thermal expansion coefficients of the substrate and the epitaxial film match: matches the thermal expansion coefficient is very important, an epitaxial film on the substrate material away from the thermal expansion coefficient is too large may not only decrease the quality of the epitaxial film, but also during operation of the device, due to heat causing damage to the device;
Chemical stability of the substrate 3 and an epitaxial film match: a substrate material have good chemical stability, the epitaxial growth temperature and corrosive atmosphere of the decomposition and easily, because the chemical reaction is not an epitaxial film is decreased and the quality of the epitaxial film;
Current substrate material for GaN-based LED more, but can be used for the commercialization of substrate present, only three, namely sapphire and silicon carbide and silicon substrate. Others, such as GaN, ZnO substrate is still in the development stage, is still some distance away from industrialization.
Best substrate for GaN is grown GaN single crystal material, can greatly improve the crystal quality of the epitaxial film, reducing the dislocation density and improve the life of the device, improve the luminous efficiency and device operating current density. However, the preparation of GaN single crystal is very difficult, so far there has not been an effective way.
ZnO has become a candidate substrate for GaN epitaxy, because both have very striking similarities. Two crystals of the same structure, the identification of the crystal is very small, close to the band gap (the band discontinuity value is small, the contact barrier small ). However, ZnO epitaxial GaN substrate as the fatal weakness is easily decomposed and etching the GaN epitaxial growth temperature and atmosphere. Currently, ZnO semiconductor materials not yet used to manufacture optoelectronic devices or high-temperature electronic devices, the device is not up to the level of quality of materials and the P-type doping problem is not a real solution, suitable for the growth of ZnO-based semiconductor material device has not yet developed.
The most commonly used for growing GaN substrate is Al2O3. Advantage is a good chemical stability, does not absorb visible light, affordable manufacturing technology is relatively mature. Although the poor thermal conductivity of the device is not exposed to a small current work is obviously inadequate , but at high current power type devices work very conspicuous.
SiC as a wide range of applications, second only to the extent of the sapphire substrate material, currently Professor Jiang Fengyi crystalline photovoltaic in China can be grown on Si substrates that can be used to commercialize german led high bay lighting factory epitaxial wafers. Si substrate thermal conductivity, stability is superior to sapphire, the sapphire is much lower than the price, is a promising substrate. SiC substrate has good chemical stability, good electrical conductivity, good thermal conductivity, does not absorb visible light, but also less prominent, such as the price is too high, the crystal quality Al2O3 and Si so difficult to achieve good machining performance is relatively poor, in addition, SiC substrates of absorbing ultraviolet light below 380 nm, is not suitable for the development of UV below 380 nm LED. advantageous because the conductivity of the SiC substrate and the thermal conductivity, the heat can solve the problem of power type GaNLED device, therefore, in the field of semiconductor lighting technology occupies an important position.
Compared with sapphire, SiC and GaN lattice matched epitaxial film is improved. In addition, SiC has a blue light-emitting characteristics, but also for low-resistance material, the electrodes can be made, before packing the device is fully tested for epitaxial film becomes possible to enhance the german led high bay lighting factory as a substrate material competitiveness Because of the layered structure of SiC easy cleavage, the cleavage of high quality can be obtained between the substrate and the epitaxial film surface, which will greatly simplify the structure of the device;. However , because of its layered structure, often on a surface of the substrate introduction of a large number of defects of the epitaxial film step appears.

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