Porous GaN Micro-LED Structure for Uniform Light Extraction
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Solution Overview
Problem
Existing manufacturing processes for micro-LEDs suffer from variations in GaN thickness, leading to non-uniformity and reproducibility issues in the emission of micro-screens, particularly affecting the optical performance and efficiency of the LEDs.
Innovation Solution
A method involving the porosification of heavily n-doped GaN layers, followed by the formation of mesas and the application of a transparent conductive oxide electrode, which helps in achieving a uniform and repeatable emission by minimizing reflections and optimizing the optical index of the porosified GaN layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional manufacturing processes are used for micro-LEDs, then the production can be achieved with standard processes, but the uniformity and reproducibility of emission deteriorate due to GaN thickness variations
Solution Approach 1:
The patent applies porosification to the heavily n-doped GaN layer, transforming it into a porous structure. This porous GaN layer has an optical index closer to that of the encapsulation layer (SiN), reducing optical reflections at the interface. The porosity is controlled to achieve the desired optical properties while maintaining electrical functionality, thereby improving emission uniformity without requiring extremely precise thickness control
Solution Approach 2:
The patent changes the optical parameters of the GaN layer by porosification, modifying its optical index from approximately 2.4 (dense GaN) to a value closer to 1.9-2.1 (porous GaN, matching SiN). This parameter change makes the optical performance less sensitive to thickness variations, resolving the contradiction between ease of manufacture and manufacturing precision
2Device complexity
If the optical index of GaN (approximately 2.4) is used with encapsulation layer (SiN with optical index between 1.9 and 2.1), then the standard structure can be formed, but optical reflections increase leading to non-uniform emission
Solution Approach 1:
The patent introduces a porous GaN layer between the dense GaN and the SiN encapsulation layer. The porous structure reduces the optical index of GaN to be closer to SiN, minimizing the optical contrast and reducing reflections at the interface. This maintains structural simplicity while improving emission uniformity
Solution Approach 2:
The porous GaN layer acts as an optical intermediary between the dense GaN layer and the SiN encapsulation layer. Its optical index serves as a transition value between the two materials, reducing abrupt optical reflections and improving light extraction uniformity without adding significant structural complexity
3Ease of operation
If thinning processes are used to remove buffer layers, then the electrical functions can be added on the rear face and cross talk limited, but the GaN thickness variations increase affecting optical performance
Solution Approach 1:
The patent applies porosification to the heavily n-doped GaN layer after thinning processes. The porous structure compensates for thickness variations by reducing optical reflections that would otherwise be sensitive to precise thickness control. This allows aggressive thinning to achieve electrical functionality while maintaining optical performance through the porous layer's reduced optical contrast
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
The proposed method enhances the uniformity and reproducibility of micro-LED emission, making it less dependent on GaN thickness variations, and improves the extraction and stability of light, thereby increasing the efficiency of micro-LEDs.
Implementation Method 1
porosifying the layer of heavily n-doped GaN, whereby a layer of porosified GaN is obtained
Implementation Method 2
the optical index of the porosified GaN layer not varying by more than 10% relative to the optical index of the second electrode and/or relative to the optical index of the encapsulation layer
Implementation Method 3
improves the extraction and stability of light
Implementation Method 4
when the anode is a mirror, and the LED thus formed is of the resonant cavity type (emissive source in a Fabry-Pérot resonator)
Implementation Method 5
providing a stack comprising at least one layer of heavily n-doped GaN... covering the layer of porosified GaN with a second electrode formed of a layer of transparent conductive oxide
Implementation Method 6
providing a stack comprising at least one layer of heavily n-doped GaN, one layer of n-doped GaN, quantum wells and one layer of p-doped GaN
Data Source
Figure 1A~1C
Figure 1D~1F
Figure 2A~2C
AI summary
A method for manufacturing micro-LEDs comprising the following steps: i) providing a stack comprising at least one layer of n-doped GaN (104), one layer of n-doped GaN (105), quantum wells (106), one layer of p-doped GaN (107) and a first electrode (108), ii) porosifying the layer of n-doped GaN (104), to obtain a layer of porosified GaN (104'), iii) forming mesas in the stack, iv) covering the layer of porosified GaN (104') with a second electrode (301) or with an encapsulation layer (302), the second electrode (301) or the encapsulation layer (302) being in direct contact with the layer of porosified GaN (104'). Step ii) is carried out in such a way that the optical index of the porosified GaN layer (104') does not vary by more than 10% with respect to the optical index of the second electrode (301) and/or with respect to the optical index of the encapsulation layer (302).