Semiconductor Chip Mirror Structure for Broad-Angle LED Reflectivity
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Solution Overview
Problem
Existing optoelectronic semiconductor chips face challenges in achieving high reflectivity, particularly for thin-film LEDs, due to the angular and spectral dependence of conventional Bragg mirrors, which affects the specular reflectance and brightness of light-emitting diodes.
Innovation Solution
A dielectric Bragg mirror design with a thick low-refractive index cover layer and alternating high and low refractive index intermediate layers, optimized in thickness and number, is used to enhance reflectivity, reducing spectral and angular dependence, and integrated with a metal reflection layer for improved reflectance across a wide wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional Bragg mirror is used, then the mirror provides reflectivity, but the reflectivity exhibits strong angular and spectral dependence which reduces specular reflectance and brightness
Solution Approach 1:
The patent changes the optical parameters of the mirror system by introducing a thick cover layer with low refractive index and optimizing the thickness and refractive indices of intermediate layers. This transforms the mirror from having strong angular and spectral dependence to exhibiting flattened reflectivity characteristics across wide angular and spectral ranges, thereby improving brightness while reducing adaptability constraints.
Solution Approach 2:
The patent employs a composite mirror structure consisting of multiple dielectric layers with alternating high and low refractive indices, combined with a thick low-refractive-index cover layer and optionally a metal reflection layer. This composite design enables the mirror to achieve high reflectivity across broad angular and spectral ranges while maintaining flattened spectral dependence, resolving the contradiction between brightness and angular/spectral adaptability.
2Illumination intensity
If the number of intermediate layers is increased to improve reflectivity, then the mirror achieves higher reflectance, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent optimizes the parameters of intermediate layers (thickness, refractive index) to achieve high reflectivity with a reduced number of layers. By carefully selecting optical parameters, the mirror attains high reflectance while minimizing the number of intermediate layers required, thus reducing device complexity and manufacturing difficulty.
Solution Approach 2:
The thick cover layer with low refractive index acts as an intermediary element that enhances the overall reflectivity of the mirror system. This cover layer works in conjunction with a reduced number of intermediate layers to achieve high reflectance, thereby reducing the total layer count and simplifying the device structure while maintaining high reflectivity performance.
3Illumination intensity
If a thick cover layer with low refractive index is introduced, then the angular dependence is reduced and brightness is improved, but the device complexity increases
Solution Approach 1:
The patent introduces a thick cover layer with low refractive index as a key parameter change in the mirror structure. This single parameter modification effectively reduces angular dependence and improves specular reflectance and brightness. While it adds one layer to the structure, the overall complexity increase is minimal compared to the significant performance improvement achieved.
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 mirror design significantly increases specular reflectance and brightness of light-emitting diodes, particularly for InGaAlP and AlGaAs chips, by minimizing spectral and angular dependence, leading to improved light distribution and reduced thermal conductivity impact.
Implementation Method 1
The cover layer has a comparatively large optical thickness and is made of a material which is transparent to the radiation generated during operation and which is in particular low refractive
Implementation Method 2
In a direction away from the cover layer, the mirror comprises several intermediate layers which, together with the cover layer, have alternating high and low refractive indices for the radiation
Implementation Method 3
The intermediate layers have alternating high and low refractive indices for the radiation generated during operation
Implementation Method 4
The intermediate layers are followed in the direction away from the semiconductor layer sequence by at least one metal layer of the mirror as a reflection layer
Data Source
AI summary
In one embodiment, the optoelectronic semiconductor chip comprises a semiconductor layer sequence with an active zone for generating radiation with a wavelength of maximum intensity L. A mirror comprises a cover layer. The cover layer is made of a material transparent to the radiation and has an optical thickness between 0.5 L and 3 L inclusive. The cover layer is followed in a direction away from the semiconductor layer sequence by between inclusive two and inclusive ten intermediate layers of the mirror. The intermediate layers alternately have high and low refractive indices. An optical thickness of at least one of the intermediate layers is not equal to L/4. The intermediate layers are followed in the direction away from the semiconductor layer sequence by at least one metal layer of the mirror as a reflection layer.