Sub-wavelength Antireflection Grating for Optoelectronic Devices
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Solution Overview
Problem
Existing opto-electronic light emission devices, such as LEDs and VCSELS, face challenges in reducing retro-reflexions at the exit surface, leading to reduced light delivery due to high reflection coefficients caused by the difference in optical indices between the semiconductor material and the environment.
Innovation Solution
An opto-electronic device with an anti-reflective structure featuring a sub-wavelength periodic network with hollow and protruding parts, forming a regular periodic structure with a spatial period less than λ/(2n), which modifies the angular opening of the emission cone and enhances light efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional anti-reflective layer is used, then the reflection coefficient is reduced, but the emission angle is spread over a very wide angle (approximately 120 degrees)
Solution Approach 1:
The anti-reflective layer is segmented into a periodic lattice structure with recessed and protruding parts, where each element has dimensions smaller than λ/(2n). This segmentation allows the structure to function as an effective medium with tailored optical properties while maintaining manufacturing compatibility with planar techniques.
Solution Approach 2:
The optical parameters of the anti-reflective layer are changed by controlling the geometry of the periodic lattice (pitch, depth, filling factor) rather than relying on material composition alone. This enables precise control of both the reflection coefficient and emission angle through geometric parameter optimization.
2Object-affected harmful factors
If a disordered nanostructured anti-reflective layer is used, then the reflection coefficient is reduced, but the manufacturing process is complex and not suitable for planar integration
Solution Approach 1:
The anti-reflective layer is segmented into a periodic lattice structure with recessed and protruding parts, where each element has dimensions smaller than λ/(2n). This segmentation allows the structure to function as an effective medium with tailored optical properties while maintaining manufacturing compatibility with planar techniques.
Solution Approach 2:
The manufacturing process replaces complex vapor deposition with inclined flux (mechanical/process complexity) with standard planar lithography and etching techniques. The periodic lattice can be fabricated using conventional semiconductor manufacturing steps, eliminating the need for specialized equipment or processes.
3Object-affected harmful factors
If a disordered nanostructured anti-reflective layer is used, then the reflection coefficient is reduced, but the characteristics vary substantially from one micro-LED to another
Solution Approach 1:
The anti-reflective layer is segmented into a periodic lattice structure with recessed and protruding parts, where each element has dimensions smaller than λ/(2n). This segmentation allows the structure to function as an effective medium with tailored optical properties while maintaining manufacturing compatibility with planar techniques.
Solution Approach 2:
The periodic lattice structure provides uniform local geometry across the device surface, ensuring that each micro-LED experiences the same anti-reflective effect. This local uniformity in structure leads to consistent optical characteristics and reduces device-to-device variability.
4Ease of manufacture
If the pitch of the periodic lattice is increased, then the manufacturing becomes easier, but the sub-wavelength condition is violated and diffraction effects occur
Solution Approach 1:
The anti-reflective layer is segmented into a periodic lattice structure with recessed and protruding parts, where each element has dimensions smaller than λ/(2n). This segmentation allows the structure to function as an effective medium with tailored optical properties while maintaining manufacturing compatibility with planar techniques.
Solution Approach 2:
The optical parameters of the anti-reflective layer are changed by controlling the geometry of the periodic lattice (pitch, depth, filling factor) rather than relying on material composition alone. This enables precise control of both the reflection coefficient and emission angle through geometric parameter optimization.
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 sub-wavelength periodic network effectively reduces the reflection coefficient, concentrating the emission in a narrower cone, improving light efficiency and reproducibility, especially in micro-LEDs, while being compatible with planar integration techniques.
Implementation Method 1
the refractive index nAR, which can be deposited on this surface. Maximum transmission is obtained when the anti-reflective layer has a thickness equal to λ/(4nAR), and when the refractive index nAR is equal to √(n·n out)
Implementation Method 2
an important challenge is to limit back-reflections at the level of the radiation output surface. Indeed, the semiconductor material(s) forming these emitting structures have optical indices that are generally much higher than the optical index of the medium into which the radiation emerges
Data Source
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Figure 6~7
AI summary
Optoelectronic device (1) comprising an emitting structure (2) at least a part of which is formed of one or more semiconductor materials, configured to produce light radiation when an electric current passes through it, said light radiation being produced within the emitting structure and having an average wavelength λ, the emitting structure having an average optical index n and being delimited by an exit surface (4), through which at least a part of said light radiation exits, the device further comprising an anti-reflective structure (3) comprising a sub-wavelength periodic grating which has recessed parts (7) and protruding parts (6) forming a periodic structure of pitch (a) less than λ/[2.n].