Principles and Processes of LED Epitaxial Wafer Technology

From the working principle of LEDs, it is evident that epitaxial wafer materials are the core component of LEDs. In fact, key optoelectronic parameters such as wavelength, brightness, and forward voltage are largely determined by the epitaxial wafer material. Epitaxial wafer technology and equipment are critical to the manufacturing process, with Metal-Organic Chemical Vapor Deposition (MOCVD) being the primary method for growing thin-layer single crystals of III-V and II-VI group compounds and alloys. Below are some future trends in LED epitaxial wafer technology.

1. Improvement of Two-Step Growth Process

Currently, commercial production employs a two-step growth process, but the number of substrates that can be loaded at once is limited. While 6-wafer machines are relatively mature, machines capable of handling around 20 wafers are still under development. Increasing the number of wafers often leads to insufficient uniformity in the epitaxial wafers. Future development will focus on two directions: first, developing technology that allows more substrates to be loaded into the reaction chamber at once, making it more suitable for large-scale production and cost reduction; second, highly automated and repeatable single-wafer equipment.

2. Hydride Vapor Phase Epitaxy (HVPE) Technology

This technology enables the rapid growth of thick films with low dislocation density, which can serve as substrates for homoepitaxial growth using other methods. Additionally, GaN films separated from the substrate may become alternatives to bulk single-crystal GaN chips. However, HVPE has drawbacks, such as difficulty in precisely controlling film thickness and the corrosive nature of reaction gases, which hinder further improvements in GaN material purity.

Si-doped HVPE-GaN

(a) Structure of Si-doped HVPE-GaN reactor; (b) Image of 800 μm- thick Si-doped HVPE-GaN;

(c) Distribution of free carrier concentration along the diameter of Si-doped HVPE-GaN

3. Selective Epitaxial Growth or Lateral Epitaxial Growth Technology

This technology can further reduce dislocation density and improve the crystal quality of GaN epitaxial layers. The process involves first depositing a layer of GaN on a suitable substrate (sapphire or silicon carbide), followed by a layer of polycrystalline SiO mask. Photolithography and etching techniques are then used to create GaN windows and mask strips. During subsequent growth, the epitaxial GaN first grows on the GaN windows and then extends laterally over the SiO strips.

ZMSH's GaN-on-Sapphire wafer

4. Pendeo-Epitaxy Technology

This method significantly reduces the large number of lattice defects in epitaxial layers caused by lattice and thermal mismatch between the substrate and the epitaxial layer, thereby further improving the crystal quality of GaN epitaxial layers. The process begins with growing a GaN epitaxial layer on a suitable substrate (6H-SiC or Si) using a two-step process. The epitaxial film is then selectively etched until the substrate is exposed, forming alternating columnar structures (GaN/buffer layer/substrate) and trenches. Subsequent GaN epitaxial growth occurs suspended above the trenches, involving lateral epitaxial growth from the sidewalls of the original GaN epitaxial layer. This method eliminates the need for a mask, avoiding contact between GaN and mask materials.

ZMSH's GaN-on-Silicon wafer

5. Development of Short-Wavelength UV LED Epitaxial Materials

This lays a solid foundation for developing UV trichromatic phosphor-based white LEDs. Many efficient phosphors can be excited by UV light, offering higher luminous efficiency than the currently used YAG:Ce system, thereby advancing white LED technology.

6. Development of Multi-Quantum Well (MQW) Chip Technology

In MQW chips, different impurities are doped during the growth of the light-emitting layer to create quantum wells with varying structures. The recombination of photons emitted from these quantum wells directly produces white light. This method improves luminous efficiency, reduces costs, and simplifies packaging and circuit control, though it presents greater technical challenges.

7. Development of "Photon Recycling" Technology

In January 1999, Japan's Sumitomo developed a white LED using ZnSe material. The technology involves growing a CdZnSe thin film on a ZnSe single-crystal substrate. When electrified, the film emits blue light, which interacts with the ZnSe substrate to produce complementary yellow light, resulting in white light. Similarly, the Photonics Research Center at Boston University in the U.S. placed an AlInGaP semiconductor composite on a blue GaN-LED to generate white light.

8. LED Epitaxial Wafer Process

Substrate >> Structural Design >> Buffer Layer Growth >> N-type GaN Layer Growth >> MQW Light-Emitting Layer Growth >> P-type GaN Layer Growth >> Annealing >> Testing (Photoluminescence, X-ray) >> Epitaxial Wafer

Epitaxial Wafer >> <｜place▁holder▁no▁80｜> and Fabrication of Mask >> Photolithography >> Ion Etching >> N-type Electrode (Deposition, Annealing, Etching) >> P-type Electrode (Deposition, Annealing, Etching) >> Dicing >> Chip Sorting and Grading

As a professional supplier in the field of LED epitaxial wafer technology, ZMSH provides comprehensive technical solutions including MOCVD epitaxial growth, HVPE thick film preparation, selective epitaxy, and quantum well structure design. We supply key materials such as sapphire/SiC substrates, GaN epitaxial wafers, UV LED materials, and supporting masks. Equipped with complete processing and testing facilities along with mature process systems, ZMSH offers one-stop services ranging from material selection and structural design to customized processing, supporting our clients in achieving technological innovation and product upgrades in lighting display, UV applications, and other related fields.

ZMSH's GaN-on-SiC wafer