Introduction to LED epitaxial wafer growth technology

Epitaxial wafer technology and equipment are the key to epitaxial wafer manufacturing technology. Metal-Organic Chemical Vapor Deposition ( MOCVD ) technology is the main method for growing thin layers and single crystals of III-V, II-VI compounds and alloys .

Below is some information about LED epitaxial wafer technology.

1. Improve the two-step growth process

Currently, commercial production uses a two-step growth process, but the number of substrates that can be loaded at one time is limited. The 6-wafer machine is relatively mature, and the 20-wafer machine is still in the process of maturing. The large number of wafers leads to insufficient uniformity of epitaxial wafers. The development trend is in two directions: one is to develop a technology that can load more substrates into the reaction chamber at one time for epitaxial wafer growth, which is more suitable for large-scale production to reduce costs; the other direction is highly automated and repeatable single-wafer equipment.

2. Hydride Vapor Phase Epitaxy (HVPE) Technology

This technology can quickly grow a thick film with low dislocation density, which can be used as a substrate for homogeneous epitaxial wafer growth using other methods. And the GaN film separated from the substrate may become a substitute for bulk single crystal GaN chips. The disadvantage of HVPE is that it is difficult to accurately control the film thickness, and the reaction gas is corrosive to the equipment, which affects the further improvement of the purity of GaN materials.

3. Selective epitaxial wafer growth or lateral epitaxial wafer growth technology

This technology can further reduce the bit dislocation density and improve the crystal quality of the GaN epitaxial layer. First, a layer of GaN is deposited on a suitable substrate (sapphire or silicon carbide), and then a layer of polycrystalline SiO mask layer is deposited on it . Then, photolithography and etching techniques are used to form GaN windows and mask layer strips. In the subsequent growth process, the epitaxial GaN first grows on the GaN window and then grows laterally on the SiO strip.

4. Pendeo-epitaxy

This method can greatly reduce the large number of lattice defects in the epitaxial layer caused by lattice mismatch and thermal mismatch between the substrate and the epitaxial layer, thereby further improving the crystal quality of the GaN epitaxial layer. First, a GaN epitaxial layer is grown on a suitable substrate (6H-SiC or Si) using a two-step process. Then the epitaxial film is selectively etched until it reaches the substrate. This forms a columnar structure of GaN/buffer layer/substrate and an alternating groove shape. Then the GaN epitaxial layer is grown, and the grown GaN epitaxial layer is suspended above the groove, which is a lateral epitaxial growth on the side wall of the original GaN epitaxial layer. With this method, no mask is required, thus avoiding contact between GaN and the bridging material.

5. Develop short-wavelength UVLED epitaxial wafer materials

It lays a solid foundation for the development of UV tri-color phosphors White light LEDs . There are many high-efficiency phosphors that can be excited by UV light, and their luminous efficiency is much higher than that of the currently used YAG :Ce system, which can easily bring white light LEDs to a new level.

6. Develop multi-quantum well chip technology

The multi-quantum well type is to dope different impurities during the growth of the chip's light-emitting layer to create quantum wells with different structures, and directly emit white light through the combination of multiple photons emitted by different quantum wells . This method improves luminous efficiency, reduces costs, and reduces the difficulty of packaging and circuit control; but the technical difficulty is relatively large.

7. Develop “Photon Recycling” Technology

In January 1999, Sumitomo of Japan developed a white light LED made of ZnSe material. Its technology is to grow a layer of CdZnSe thin film on a ZnSe single crystal substrate. After power is turned on, the blue light emitted by the thin film interacts with the ZnSe substrate to emit complementary yellow light, thus forming a white light source. The Photonic Research Center of Boston University in the United States used the same method to stack a layer of AlInGaP semiconductor composite on a blue light GaN- LED , and also generated white light.