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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, 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,[link widoczny dla zalogowanych], 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, current is the longitudinal flow.
Devices made using this substrate conductivity and thermal conductivity are very good,[link widoczny dla zalogowanych], 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, 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,[link widoczny dla zalogowanych], and therefore will not be current photo diffusion layer of material absorption,[link widoczny dla zalogowanych], which also enhance the light extraction efficiency.
But relative to the sapphire substrate, the silicon carbide manufacturing costs higher, to achieve its commercial also need to reduce the corresponding costs. Performance comparison of three kinds of substrate in front of An Introduction to the LED chip is made of three commonly used substrates.
These three substrates comprehensive performance comparison shown in Table 1. In addition to these three common substrate materials, there GaAS, AlN, ZnO and other materials can also be used as a substrate, usually need to choose according to the design. Evaluation of substrate 1. Substrates and epitaxial films of structural matching: epitaxial materials and substrates on the crystal structure of the same or similar, the lattice constant mismatch is small, crystalline properties, and defect density is low;