Since the last century since 90 time junior village built two invention of high bright blueLED, white light semiconductor lighting technology combination of GaN based blue LED and yellow fluorescent powder to emit got wide attention and rapid development in the world scope based on. So far, the commodity of white LED light efficiency is more than 150 lm/W, level has exceeded 200 lm/W, much higher than the traditional incandescent lamp (15 lm/W) and fluorescent lamp (80 lm/W)level. From the market perspective, LED has been widely used in display, LCD backlight, traffic lights, outdoor lighting and other fields, and has already begun topenetrate to the interior lighting, automotive lighting, stage lighting, special lightingand other markets, the future is expected to fully replace the traditional light source.
The quality of semiconductor lighting quality and is closely related to the LED chip.Further improve the efficiency of LED (especially the light efficiency and high powerworking condition), reliability, service life is LED material and chip technologydevelopment goals. The key technology of LED material and chip and its development trend in the future to do the following analysis:
A, epitaxial materials
The 1 epitaxial technology
Metal organic chemical vapor deposition (MOCVD) technology is the mainstream technology in the growth of LED. In recent years, thanks to the progress of MOCVDequipment, LED epitaxial materials cost has dropped significantly. Currently on the market the main equipment from Germany's Aixtron and America Veeco. The formercan provide the level of planetary type reaction chamber and a close coupledshowerhead reactor two types of devices, the utility model has the advantages of raw material saving, LED epitaxial growth are good uniformity. High speed rotating trayusing the laminar flow device, the utility model has the advantages of simple maintenance, large capacity. In addition, the acid production of atmospheric MOCVD for the Japanese enterprises to use, can obtain better crystal quality. Americanapplied materials, the original multi reaction chamber of MOCVD equipment, and has already begun in the industrial field trial.
Including the future development direction of MOCVD equipment: to further expand the reaction chamber volume to increase production capacity, to further improve theutilization of the MO source, ammonia and other raw material ratio, further improve themonitoring capacity in the epitaxial wafers, further optimize the control of temperaturefield and flow field in order to enhance the ability to support large size substrateepitaxial etc..
The 2 substrate
(1) patterned substrate
The substrate is a substrate support epitaxial films, due to the lack of homogeneous substrate, GaN based LED growth on sapphire, SiC, Si and other heterogeneous substrate. Development so far, has become the highest price of the sapphiresubstrate, the most widely used. Because the refractive index of GaN than sapphirehigh, in order to reduce the light emitted in the transmitting substrate interface from LED, is currently being generally in the graphics chip substrate for epitaxial materialsto improve the light scattering. Patterned substrate pattern common are conical arrayaccording to the hexagonal close packed size is micrometer, the LED light extraction efficiency increased to 60%. Research also shows that, using the patterned substrateand extending direction can be controlled in GaN dislocation combined with the growthprocess so as to effectively reduce the dislocation density of GaN epitaxial layer. In the future a considerable period of time in the patterned substrate is still the maintechnical means to take forward chip.
The future direction of development is to develop graphical substrate size smaller. At present, due to the cost of production, patterned sapphire substrate is produced bycontact exposure and ICP dry etching, can only achieve micron size. If can further reduce the size and the wavelength is comparable to several hundred nm, can further improve the scattering capability. Can even cause periodic structure, and furtherenhance the light extraction efficiency by the physical effect of two-dimensional photonic crystal. Production including electron beam lithography, nano imprint lithography, nanoparticle self-assembly method of nano pattern, from cost considerations, which is more suitable for substrate processing.
(2) the large size substrate
At present, the industry is based on 2 inch sapphire substrate for the mainstream,some international companies have been using 3 inch or 4 inch substrate, the future is expected to expand to 6 inch substrate. Expand the substrate size is conducive to the edge effect in reducing extension plate, improve the yield of LED. But the large size sapphire substrate prices are still expensive, epitaxial equipment and chipprocess equipment and expand the substrate size matching are faced with upgrading,the manufacturer is a not a small investment.
(3) SiC substrate
Between the SiC substrate and GaN substrate lattice mismatch is smaller, that quality of GaN crystal was grown on SiC is slightly better than on sapphire substrate results in the fact. But the SiC substrate, especially SiC substrate manufacturing cost and high quality is very high, so few manufacturers for material extension LED. But AmericanCree company by virtue of its own high quality SiC substrate manufacturing advantages, to become the industry's only a growth of LED on SiC substratemanufacturers, so as to avoid patent barriers to growth of GaN on sapphire substrates. At present the mainstream size SiC substrate is 3 inches, the future is expected to expand to 4 inches. The SiC substrate than sapphire substrate is moresuitable for the production of GaN based electronic devices, the future with thedevelopment of wide band gap semiconductor power electronic devices, the SiC substrate is expected to further reduce the cost.