and the V exposure

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Thermal conductivity of sapphire is not very good (at 100 ℃ approximately 25W / (m?; K)). Therefore, the use of LED devices, it will transfer a large amount of heat; particularly for larger power devices, thermal conductivity is a very important consideration.
In order to overcome these difficulties, many people tried to direct the growth of GaN optoelectronic devices on silicon substrate,display signs, thereby improving the thermal and electrical conductivity. There are currently part of the silicon substrate LED chip silicon substrate.
Chip silicon substrate electrode can be two kinds of contact methods, namely L exposure (Laterial-contact, the level of exposure) and the V exposure (Vertical-contact, vertical contact), hereafter referred to as L-type electrode and V-type electrode. By these two means of contact, LED chip current flow can be horizontal,LED billboard, or vertical movement. Since current can flow vertically, thus increasing the LED light-emitting area, thereby improving the extraction efficiency of LED.
Because silicon is a good conductor of heat, so the device can be significantly improved thermal performance, thus extending the life of the device. SiC substrate SiC substrates (CREE company specializes in the United States as a substrate material using SiC) LED chip electrode is L-type electrode,business signs, current is the longitudinal flow.
Devices made using this substrate conductivity and thermal conductivity are very good, is conducive to high-power devices made larger. LED chips using silicon carbide substrate shown in Figure 2. Thermal conductivity of SiC substrate (SiC the thermal conductivity of 490W / (m?; K)) than in more than 10 times higher than the sapphire substrate. Sapphire itself is a poor conductor of heat, and in the production of the device need to use the silver plastic while the bottom of the solid crystal,vinyl banner, silver plastic that the heat transfer performance is also poor.
Chips using silicon carbide substrates for the L-type electrodes, two electrodes located in the surface and bottom of the device, the heat generated can be exported through the electrode; the same time that the substrate does not require conductive layer, and therefore will not be current photo diffusion layer of material absorption, which also enhance the light extraction efficiency.