Native Emission Matrix Growth for Strain-Relieved RGB Micro-LEDs
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Solution Overview
Problem
Current methods for producing color micro-displays with pixels smaller than 10 μm face challenges in alignment and material deposition, particularly with InGaN-based LEDs, due to strain issues and low miscibility of InN in GaN, leading to poor quality and efficiency.
Innovation Solution
A method involving a base structure with a substrate, unintentionally doped GaN, and doped In(x)GaN layers, followed by patterning mesas, electrochemical porosification, and successive epitaxial growth of LED structures on these mesas to form a native emission matrix, reducing strain and enhancing indium incorporation for efficient red, green, and blue emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If InGaN material is used to produce red pixels with high indium concentration (≥35% In), then the emission wavelength can be shifted to red light, but the material quality deteriorates due to low miscibility and high compressive strain
Solution Approach 1:
The patent segments the GaN layer into multiple thin sub-layers (first GaN layer, second GaN layer, third GaN layer) with InGaN quantum wells inserted between them. This segmentation reduces the continuous compressive strain in high-indium InGaN layers by breaking them into manageable segments, allowing high indium concentration (≥35% for red emission) to be achieved while maintaining material quality and reducing strain accumulation.
Solution Approach 2:
The patent changes the structural parameters of the LED by introducing a multi-layer GaN/InGaN configuration with quantum wells. By adjusting the thickness of GaN layers and the composition of InGaN layers, the patent optimizes both the emission wavelength (enabling red light) and the strain distribution, thereby maintaining material quality while achieving the desired optical properties.
2Adaptability or versatility
If the indium concentration in InGaN is increased to emit red light (≥35% In), then the emission spectrum can cover the entire visible range, but the miscibility of InN in GaN decreases and compressive strain increases
Solution Approach 1:
The patent divides the high-indium InGaN structure into multiple thin layers separated by GaN spacer layers. This segmentation allows the indium concentration to be maintained at high levels (≥35% for red emission) across the structure while the GaN spacer layers periodically relieve the compressive strain, preventing dislocation formation and maintaining compositional stability throughout the emission spectrum range.
Solution Approach 2:
The patent applies local quality by creating alternating regions of high-indium InGaN (for red emission) and GaN spacer layers (for strain relief) within the active region. This local variation in material composition allows the structure to simultaneously achieve high indium concentration for red light emission while maintaining overall structural stability through periodic strain relaxation zones.
3Adaptability or versatility
If conventional pick and place technique is used to combine RGB pixels, then different materials can be integrated, but alignment problems occur and the process time increases for micrometric pixels
Solution Approach 1:
The patent merges the red, green, and blue pixel production into a single integrated InGaN-based structure grown on a common substrate. By using multiple quantum wells with different indium concentrations within the same continuous growth process, the patent eliminates the need for separate pixel fabrication and assembly, thereby achieving perfect alignment and reducing process time while maintaining material versatility.
Solution Approach 2:
The patent creates a universal InGaN material system that can produce all three primary colors (RGB) through variation of indium concentration and quantum well structure. This multi-functional approach allows a single material platform to replace multiple separate pixel technologies, eliminating alignment issues inherent in pick-and-place techniques while maintaining the ability to produce different emission wavelengths.
4Loss of energy
If quantum dots or nanophosphors are used for color conversion, then color efficiency can be improved, but the deposition on small pixels becomes difficult to control and flow resistance is insufficient
Solution Approach 1:
The patent extracts the color conversion function from external quantum dots or nanophosphors and integrates it directly into the LED active region through InGaN quantum wells with different indium concentrations. This extraction eliminates the need for separate deposition processes and associated flow resistance issues, while maintaining high color conversion efficiency through direct electroluminescence from the quantum well structures.
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 results in a native emission matrix with improved external quantum efficiency, reduced strain, and enhanced material quality, allowing for the production of high-efficiency RGB micro-LEDs without alignment issues and without requiring transfer steps, suitable for micrometric pixel production.
Implementation Method 1
porosifying electrochemically the doped In(x)GaN layer
Implementation Method 2
creating, advantageously by epitaxial growth, a first LED structure on a first mesa
Data Source
AI summary
A method for producing a native emission matrix including the following steps of:a) providing a base structure including, successively, a substrate, a GaN layer, a doped In(x)GaN layer where x is from 0 to 8%, and an unintentionally doped In(x)GaN epitaxial regrowth layer;b) patterning mesas in the base structure, the mesas comprising a portion of the doped In(x)GaN layer and the unintentionally doped In(x)GaN epitaxial regrowth layer, whereby the mesas are electrically interconnected with one another;c) porosifying electrochemically the doped In(x)GaN layer; andd) carrying out a first LED structure and a second LED structure on the mesas, whereby a first LED having a first emission wavelength, and a second LED having a second emission wavelength, respectively, are obtained, and a native emission matrix is formed