Development of GaN based SiC based light emitting diode

1994 Japan Nichia chemical breakthrough key technology of nuclear growth into GaN materials, GaN soon P by annealing technology can be realized, then GaN led successfully developed. In recent years, through the extension of technology promotion, internal quantum efficiency of GaN LED is greatly improved, combined with coarsening, inversion, PSS substrate to improve the light output efficiency of GaN based technology, LED has been widely used in full-color display, traffic lights, car lights, LCD backlighting, indoor lighting and lighting and other fields, semiconductor lighting has matured into thousands of households.

At present, most of the GaN based LED are prepared with the relatively low price of sapphire as substrate material. However, the sapphire substrate and GaN material is as high as 17% lattice mismatch, so the large lattice mismatch caused by the dislocation density is very high, resulting in non radiative recombination centers of GaN in LED increased, to further enhance its internal quantum efficiency limit. SiC substrate and GaN material lattice matching degree is only 3%, far less than the sapphire substrate and GaN material between the lattice matching degree, and thus less dislocation density of epitaxial growth on SiC substrate of GaN material, the crystal quality will be higher, while the thermal conductivity of SiC (4.2W/cm.K) in great stones, is conducive to the device in the current work.

Figure 1 X-Ray half width results of epitaxial GaN on SiC substrate

However, the preparation of SiC substrate is difficult, and the nucleation of epitaxial GaN is also difficult. Therefore, the technology of preparing GaN LED on SiC substrate is limited to a few of the companies in the United States to represent CREE SiC substrate preparation technology. At present, the United States Cree company GaN LED packaging into white light, lumen efficiency has more than 200lm/W, far more than other peer manufacturers.

The first half of 2010, the substrate and SiC substrate SiC Shandong Huaguang optoelectronics Co. Ltd. and Shandong University jointly established the system of the GaN-LED epitaxial technology research and development projects to obtain a breakthrough in the domestic implementation of the SiC substrate GaN LED preparation. During the operation of the project, the Shandong University for more than 5 years of successful breakthrough SiC single crystal growth and processing in support of the National 863 project, the 3 inch SiC substrate has reached GaN LED when the extension of "open the box". Shandong Huaguang optoelectronics Co. Ltd. from experienced its epitaxy on sapphire substrates of GaN LED, by optimizing the MOCVD growth process, successful growth of high quality GaN materials, more than GaN thickness up to 4um without cracking. The X-Ray () and (102) FWHM of GaN films were up to 160S and 190s, respectively, and the dislocation density was nearly 1 orders of magnitude lower than that of GaN grown on sapphire substrates. Figure 1 shows the results of X-Ray measurements on a SiC substrate. Due to the high nucleation quality, the GaN material on the SiC substrate has better surface morphology. Figure 2 is the surface atomic force microscopy on SiC substrate and the sapphire substrate on epitaxial GaN material, it can be seen from the figure, SiC substrate surface morphology of GaN films is more smooth, the roughness Ra reached 0.3nm, better crystal quality.

Figure 2 SiC substrate (left) and sapphire substrate (right) epitaxial GaN surface atomic force microscopy morphology, the test range is 5um*5um

After optimization of growth conditions for producing SiC substrate GaN epitaxial films with high crystal quality of the epitaxial, we through theoretical simulation and optimization design of SiC LED core structure, and in the process has solved SiC LED, cutting and grinding process of ohmic contact. At present, 8 x 10mil size chip package light output power more than 16mW@20mA, much higher than the sapphire products 12mW@20mA the same size of the Guan Xin index. In addition, because of the good thermal conductivity of the SiC substrate, the LED prepared by the substrate has better saturation characteristics and is more suitable for high current density operation. Figure 3 is the saturation power of SiC substrate and sapphire substrates, 8 x 10mil size chip curve from the curve can be seen on the SiC substrate LED not only in 20mA power is higher than the sapphire products, its advantages in large current work is more obvious. Figure 4 is a picture of the blue light LED prepared on the SiC substrate by Shandong Huaguang optoelectronics Co., Ltd., the brightness of LED reached the standard of commercialization, and more than the sapphire substrate, has begun to invest in the market.

Figure 3 Comparison of saturation curves of * * * 10mil cores on SiC substrates and sapphire substrates on epitaxial LED

Figure 4 LED package on SiC substrate photo

Shandong Huaguang optoelectronics Co., Ltd. and Shandong University jointly prepared GaN LED on high quality SiC substrates. The GaN material prepared on SiC substrate has lower dislocation density and more smooth surface morphology than that of GaN on sapphire substrate. The output power of LED on the SiC substrate is higher than that of the sapphire substrate, and it has a greater advantage in large current.