Third, the surface microstructure technology
The surface micro-structure process is another effective technology to improve the light extraction efficiency of the device. The basic point of this technology is to etch a large number of small structures with the size of light wavelength on the surface of the chip, each structure is in the form of a truncated tetrahedron, and thus not only expands The light exit area changes the direction of light refraction at the surface of the chip, resulting in a significant increase in light transmission efficiency. Measurements indicate that the efficiency of light extraction can increase by 30% for devices with a window layer thickness of 20μm. When the thickness of the window layer is reduced to 10 μm, the light extraction efficiency will be improved by 60%. For the 585-625nm wavelength LED device, the luminous efficiency can reach 30lm/w after the texture structure is made, and its value is close to that of the transparent substrate device.
Fourth, flip chip technology
A GaN-based LED structure layer is grown on a sapphire substrate by MOCVD technology, and light emitted from the P/N junction light emitting region is emitted through the above P-type region. Due to poor conductivity of P-type GaN, in order to obtain good current spreading, a layer of Ni—Au metal electrode layer needs to be formed on the surface of P region by vapor deposition technology. P zone leads are drawn through the layer of metal film. For good current spreading, the Ni-Au metal electrode layer should not be too thin. For this reason, the luminous efficiency of the device will be greatly affected, usually at the same time taking into account the two factors of current spreading and light extraction efficiency. However, in any case, the presence of the metal film will always deteriorate the light transmission performance. In addition, the presence of wire bonds also affects the light extraction efficiency of the device. The GaN LED flip chip structure can fundamentally eliminate the above problems.