LED epitaxial wafer growth technology introduction

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

The following is some information about LED epitaxial wafer technology.

1. Improve the two-step growth process

At present, the commercial production adopts a two-step growth process, but the number of substrates that can be loaded at one time is limited, the six-piece machine is relatively mature, and the 20-piece machine is still mature, and the number of sheets is large, resulting in insufficient uniformity of the epitaxial wafer. The development trend is two directions: one is to develop more epitaxial wafer growth in the reaction chamber at one time, which is more suitable for large-scale production technology to reduce costs; the other is highly automated repeatability. Monolithic device.

2. Hydride vapor phase epitaxial wafer (HVPE) technology

With this technique, a thick film having a low bit error density can be rapidly grown, and can be used as a substrate for homoepitaxial growth using other methods. And the GaN thin film separated from the substrate is likely to be a substitute for the bulk single crystal GaN chip. The disadvantage of HVPE is that it is difficult to precisely control the film thickness, the reaction gas is corrosive to the device, and the purity of the GaN material is further improved.

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

This technique can further reduce the bit error density and improve the crystal quality of the GaN epitaxial layer. First deposit a layer of GaN on a suitable substrate (sapphire or silicon carbide), deposit a polycrystalline SiO mask layer on it, and then use lithography and etching techniques to form a GaN window and mask layer. Article. During the subsequent growth process, the epitaxial wafer GaN is first grown on the GaN window and then laterally grown on the SiO strip.

4. Suspended epitaxial wafer technology (Pendeo-epitaxy)

By adopting this method, a large number of lattice defects in the epitaxial layer due to lattice mismatch and thermal mismatch between the substrate and the epitaxial layer can be greatly reduced, thereby further improving the crystal quality of the GaN epitaxial layer. The GaN epitaxial wafer is first grown using a two-step process on a suitable substrate (6H-SiC or Si). The epitaxial film is then selectively etched down to the substrate. This forms the columnar structure of the GaN/buffer layer/substrate and the alternate shape of the grooves. Then, the GaN epitaxial wafer layer is grown, and the grown GaN epitaxial wafer layer is suspended above the trench, which is a lateral epitaxial wafer growth on the sidewall of the original GaN epitaxial wafer layer. With this method, no mask is required, thus avoiding contact between the GaN and the pickle material.

5. Development of UV LED epitaxial wafer material with short wavelength

It lays a solid foundation for the development of UV trichromatic phosphor white LEDs. There are many high-efficiency fluorescent powders that can be excited by UV light, and the luminous efficiency is much higher than that of the currently used YAG:Ce system, which makes it easy to bring white LEDs to a new level.

6. Develop multiple quantum well chip technology

The multi-quantum well type is a quantum well doped with different impurities during the growth process of the light-emitting layer of the chip to directly emit white light by a plurality of photon recombinations emitted by different quantum wells. The method improves the luminous efficiency, can reduce the cost, and reduces the control difficulty of the packaging and the circuit; but the technical difficulty is relatively large.

7. Develop "photon recirculation" technology

In January 1999, Sumitomo of Japan developed a white LED of ZnSe material. The technology is to first grow a layer of CdZnSe film on the ZnSe single crystal substrate. After energization, the blue light emitted by the film and the substrate ZnSe act to generate complementary yellow light, thereby forming a white light source. In the same way, the Photonics Research Center of Boston University in the United States stacked a layer of AlInGaP semiconductor composite on a blue GaN-LED, which also produced white light.

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