1, metal film reflection technology
The transparent substrate technology originated from Hewlett-Packard, Lumileds and other companies in the United States, and the metal film reflection method was mainly developed by Japanese and Taiwan Province manufacturers. This process not only avoids the patent of transparent substrate, but also is more conducive to mass production.
Its effect can be said to be similar to the transparent substrate method. This process is usually called MB process. Firstly, the GaAs substrate is removed, then Al metal films are simultaneously evaporated on its surface and Si substrate surface, and then welded together at a certain temperature and pressure.
In this way, the light irradiated from the luminescent layer to the substrate is reflected by the Al metal film to the surface of the chip, which improves the luminous efficiency of the device by more than 2.5 times.
2. Surface microstructure technology
Surface microstructure technology is another effective technology to improve the luminous efficiency of devices. The basic point of this technology is to etch a large number of small structures with light wavelength on the chip surface, and each structure is in the shape of truncated tetrahedron, which not only expands the light emitting area, but also changes the refraction direction of light on the chip surface, thus obviously improving the light transmission efficiency.
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Other technical requirements
1, flip chip technology
GaN-based LED structure layer is grown on sapphire substrate by MOCVD technology, and the light emitted from the P/N junction light-emitting region is emitted through the upper P-type region. Because of the poor conductivity of P-type GaN, in order to obtain good current expansion, it is necessary to form a metal electrode layer composed of Ni-Au on the surface of P region by evaporation technology.
P-area leads are led out through the metal film. In order to obtain good current diffusion, the Ni-Au metal electrode layer should not be too thin. Therefore, the luminous efficiency of the device will be greatly affected, and it is usually necessary to give consideration to current expansion and light extraction efficiency.
2. Chip bonding technology
Optoelectronic devices have certain requirements for the properties of required materials, usually requiring large bandwidth difference and large refractive index change of materials. Unfortunately, there is generally no natural such material.
Generally, the required bandwidth difference and refractive index difference cannot be formed by homoepitaxial growth technology. However, ordinary heteroepitaxial technologies, such as epitaxial GaAs and InP on silicon wafer, are not only expensive, but also have very high dislocation density, so it is difficult to form high-quality optoelectronic integrated devices.