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Sapphire substrate has many advantages: First, the sapphire substrate production technology is mature, good quality components; Secondly, the stability of sapphire good to use in high-temperature growth process; Finally, the sapphire of high mechanical strength, easy to handle and cleaning.
Therefore, most processes are generally on sapphire as a substrate. Figure 1 Example of the use made of sapphire LED chip. Use of sapphire as a substrate, there are some problems, such as lattice mismatch and thermal mismatch stress, which will generate a large number of defects in epitaxial layer, while the device for subsequent processing difficult.
Sapphire is an insulator, the resistivity at room temperature is greater than 1011Ω?; Cm, in which case the vertical structure of the device can not be produced; usually produced in the epitaxial layer on the surface of n-and p-type electrode (as shown in Figure 1 shown). In the production of two electrodes on the surface, resulting in a reduction of the effective emitting area, while increasing the device fabrication process of photolithography and etching process,light signs, resulting in lower material utilization,menu board, the cost increase.
Since P-type GaN doping difficulties,illuminated signage, the current widely used in the preparation of p-GaN metal transparent electrodes on the ways in which current spread, in order to achieve the purpose of uniform light. But the metal transparent electrode generally absorb about 30% to 40% of the light, while the chemical properties of GaN-based materials stability, high mechanical strength,LED outdoor sign, its not easy to etch, so the etching process of the need for better equipment,

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