Relaxed GaN/InGaN Mesa Regrowth for Stress-Reduced Micro-LED Pixels
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Solution Overview
Problem
Current methods for manufacturing color microdisplays with pixels smaller than 10 μm face challenges in aligning red, green, and blue pixels due to alignment problems and the difficulty in controlling deposition of quantum dot or nanophosphor materials, leading to stress issues in GaN/InGaN structures which affect the quality and efficiency of micro-LEDs.
Innovation Solution
A process involving electrochemical porosification of a GaN/InGaN structure by selectively porosifying the doped InGaN layer of mesas, followed by epitaxial regrowth, which reduces stress and allows for the growth of relaxed InGaN layers, enabling the production of red, green, and blue pixels on the same substrate with improved efficiency and alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If InGaN material is used to cover the entire visible spectrum with high indium concentration (≥25% for green, ≥35% for red), then the luminance and spectral coverage are improved, but the material quality degrades due to low miscibility of InN in GaN and strong compressive stress
Solution Approach 1:
The patent applies porosification to the GaN layer, transforming it from a dense structure to a porous structure with controlled porosity (5-50%). This porous structure reduces the compressive stress in high-indium InGaN layers by providing void space that accommodates lattice mismatch, thereby maintaining material quality while enabling high indium concentration for green and red emission
Solution Approach 2:
The patent changes the physical state and structural parameters of the GaN layer by controlling porosity through electrochemical or photoelectrochemical treatments. By adjusting porosity parameters ( pore size, distribution, and density), the stress state of the InGaN layer is modified, enabling stable growth of high-indium compositions without material quality degradation
2Manufacturing precision
If the pick and place technique is used to combine red, green, and blue pixels on the same substrate, then the alignment precision and manufacturing efficiency are improved for microdisplays with pixels smaller than 10 μm, but the process complexity and time required increase significantly
Solution Approach 1:
The patent merges the manufacturing process of red, green, and blue pixels by growing all three color InGaN layers sequentially on the same substrate in a single epitaxial process. This eliminates the need for separate pixel fabrication and assembly steps, significantly reducing process complexity while maintaining alignment precision through in-situ growth
Solution Approach 2:
The patent applies local quality by creating spatially varying indium concentration profiles in different regions of the same InGaN layer. By controlling local indium content (higher for red, intermediate for green, lower for blue), all three pixel types are formed with distinct optical properties from a single continuous growth process on the same substrate
3Manufacturing precision
If quantum dot or nanophosphor materials are used for color conversion, then the spectral purity and color accuracy are improved, but the control of deposition on small pixels becomes difficult and flow resistance is insufficient
Solution Approach 1:
The patent extracts the color conversion function from separate quantum dot or nanophosphor layers and integrates it directly into the InGaN active region itself. By incorporating indium-rich InGaN quantum wells that naturally emit at specific wavelengths (red, green, blue), the need for additional color conversion materials is eliminated, simplifying the manufacturing process while maintaining spectral purity
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 process simplifies the manufacturing of micro-LEDs by reducing stress and piezoelectric polarization, enabling the production of micrometric or sub-micrometric pixels with enhanced optical and electrical properties, and allows for the creation of multispectral devices without the need for complex alignment techniques.
Implementation Method 1
applying a voltage or current between the electrically conductive doped GaN layer and the second electrode so as to porosify the doped InGaN layer of the mesas
Implementation Method 2
forming a layer of InGaN by epitaxy on the InGaN mesas, whereby a relaxed epitaxially grown InGaN layer is obtained
Data Source
AI summary
A process comprising the following steps of: a) providing a device comprising: a GaN/InGaN structure comprising an electrically conductive doped GaN layer locally covered with InGaN mesas comprising a doped InGaN layer and an undoped or weakly doped InGaN layer, an electrically insulating layer covering the electrically conductive doped GaN layer between the mesas, b) connecting the electrically conductive doped GaN layer and a counter-electrode (500) to a voltage or current generator, c) dipping the device and the counter-electrode into an electrolyte solution, d) applying a voltage or current between the electrically conductive doped GaN layer and the second electrode to porosify the doped InGaN layer, e) forming an InGaN layer by epitaxy on the InGaN mesas, whereby a relaxed epitaxially grown InGaN layer is obtained.