GaN LED Epitaxial Structure on YAG Substrate
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Solution Overview
Problem
GaN based LED epitaxial structures face issues with low optoelectronic converting efficiency, high heat generation, and high dislocation density due to lattice mismatch with sapphire substrates, leading to reduced luminous efficiency and stability.
Innovation Solution
A GaN based white light LED epitaxial structure is grown on a rare earth element doped Yttrium Aluminum Garnet series ceramic or single crystal substrate without phosphor powder, utilizing a photoluminescence fluorescent material to enhance efficiency and reduce heat generation, with a layered structure including low temperature AlN and GaN buffer layers, n-type GaN layers, and p-type GaN electrode contact layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a sapphire substrate is used for GaN based LED epitaxial wafer, then the crystalline structure compatibility is improved, but the lattice mismatch increases leading to high dislocation density
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the sapphire substrate and the GaN epitaxial layer. This buffer layer serves as a transition zone that accommodates the lattice mismatch and reduces dislocation propagation, thereby maintaining crystalline structure compatibility while improving manufacturing precision and reducing dislocation density in the active GaN layers.
Solution Approach 2:
The patent segments the epitaxial structure into multiple distinct layers including buffer layers, active layers, and contact layers. By dividing the structure into functional segments, each layer can be optimized independently - the buffer layers handle the lattice mismatch issue while the active layers maintain high crystalline quality, thus resolving the contradiction between structure compatibility and dislocation density.
2Illumination intensity
If phosphor powder is used to convert blue light to white light, then the color temperature can be adjusted, but the light scattering and absorption increase reducing emitting efficiency
Solution Approach 1:
The patent extracts and eliminates the phosphor powder component from the LED structure. Instead of using phosphor materials that cause light scattering and absorption, the invention directly generates white light through the epitaxial structure, thereby removing the source of energy loss while maintaining the ability to control illumination characteristics.
Solution Approach 2:
The patent merges the functions of light generation and color control into a single integrated epitaxial structure. By combining multiple semiconductor layers with different bandgaps in the epitaxial stack, the structure directly emits white light with adjustable color temperature, eliminating the need for separate phosphor conversion and reducing energy loss from scattering and absorption.
3Illumination intensity
If high current is applied to achieve high luminous output, then the brightness increases, but the heat generation increases reducing optoelectronic converting efficiency
Solution Approach 1:
The patent changes the structural parameters of the epitaxial layers to optimize carrier transport and reduce resistive heating. By adjusting layer thicknesses, doping concentrations, and material compositions, the structure achieves higher electroluminescence efficiency at lower current densities, thereby increasing luminous output while controlling heat generation and maintaining optoelectronic converting efficiency.
4Reliability
If multiple layers are added to improve LED performance, then the luminous efficiency increases, but the device complexity increases
Solution Approach 1:
The patent designs the epitaxial layers to perform multiple functions simultaneously. Each layer is engineered to contribute to both light emission and structural stability, with buffer layers providing both mechanical support and dislocation management, and active layers providing both electroluminescence and carrier confinement. This multi-functionality increases luminous efficiency while minimizing the number of separate components needed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances photoelectric efficiency, reduces heat generation, and simplifies the manufacturing process, resulting in improved luminous efficiency and stability of the LED light source while avoiding the drawbacks of phosphor-based systems.
Implementation Method 1
a Japanese company of Nichia possesses a groundbreaking invention (U.S. Pat. No. 5,998,925A), which utilizes a Blue GaN chip to excite a YAG yellow phosphor powder to obtain a white light
Implementation Method 2
When a current is applied across the chip by a wire, the electrons are pushed towards the P region in which the electrons recombines with the holes to radiate energy in a form of photons
Data Source
AI summary
A GaN based LED epitaxial structure and a method for manufacturing the same. The GaN based LED epitaxial structure may include: a substrate; and a GaN based LED epitaxial structure grown on the substrate, wherein the substrate is a substrate containing a photoluminescence fluorescent material. The photoelectric efficiency of the LED epitaxial structure is enhanced and the amount of heat generated from a device is reduced by utilizing a rare earth element doped Re3Al5O12 substrate; since the LED epitaxial structure takes a fluorescence material as a substrate, a direct white light emission may be implemented by such an LED chip manufactured by the epitaxial structure, so as to simplify the manufacturing procedure of the white light LED light source and to reduce production cost. The defect density of the epitaxial structure is reduced by firstly epitaxial growing, patterning the substrate and then laterally growing a GaN based epitaxial structure.