Thin Luminescent Ceramic Layer for LED Light Extraction
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Solution Overview
Problem
Existing wavelength-converting materials for semiconductor light emitting devices, such as phosphor layers, suffer from degradation in transparency at higher power and temperature, leading to reduced light extraction efficiency and optical heterogeneity causing scattering losses.
Innovation Solution
A semiconductor structure is optically coupled to a compound substrate with a luminescent ceramic layer having a thickness less than 500 µm, which is translucent or transparent, reducing scattering losses and providing mechanical robustness, allowing for improved handling and optical contact with additional elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phosphor layers are used as wavelength-converting materials, then light conversion is achieved, but transparency degrades at higher power and temperature reducing light extraction efficiency
Solution Approach 1:
The patent extracts the wavelength-converting function from the organic encapsulant matrix and places it in a separate inorganic ceramic layer. This separates the light conversion function from the transparent encapsulant, allowing the encapsulant to maintain its transparency while the ceramic layer performs wavelength conversion without degrading the overall light extraction efficiency.
Solution Approach 2:
The patent uses a composite structure combining an inorganic ceramic material (for wavelength conversion) with an organic encapsulant (for transparency and protection). The inorganic ceramic layer provides thermal and power stability for wavelength conversion, while the organic encapsulant maintains optical transparency, creating a composite system that overcomes the limitations of using either material alone.
2Loss of energy
If phosphor layers with binder materials are used, then wavelength conversion is achieved, but optical heterogeneity causes scattering losses
Solution Approach 1:
The patent employs a ceramic layer that can be formed with controlled porosity or as a dense structure, eliminating the need for binder materials that create optical heterogeneity. The ceramic particles are packed or sintered to form a homogeneous optical medium that minimizes scattering losses while maintaining structural integrity without organic binders.
Solution Approach 2:
The patent achieves optical homogeneity by using an inorganic ceramic layer with uniform refractive index and composition, eliminating the optical heterogeneity caused by binder materials in traditional phosphor layers. This homogeneous structure reduces scattering losses and improves light extraction efficiency.
3Strength
If thick luminescent ceramic layers are used, then mechanical robustness is improved, but light extraction efficiency is reduced
Solution Approach 1:
The patent optimizes the thickness parameter of the luminescent ceramic layer to achieve the right balance between mechanical robustness and light extraction efficiency. By controlling the thickness to be greater than 2 micrometers but less than 500 micrometers, the ceramic layer provides sufficient mechanical strength while remaining thin enough to allow effective light extraction and conversion.
Solution Approach 2:
The patent creates a composite substrate structure combining the luminescent ceramic layer with a support substrate. This composite structure provides the mechanical robustness needed for handling and device integration while the thin ceramic layer maintains high light extraction efficiency. The support substrate bears the mechanical load while the ceramic layer performs optical functions.
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 use of a thin luminescent ceramic layer enhances light extraction efficiency and mechanical support, reducing the need for binder materials and minimizing scattering, thus maintaining performance across varying operational conditions.
Implementation Method 1
the luminescent material is capable of absorbing the light emitted by the light emitting layer and emitting light of a second peak wavelength
Implementation Method 2
the ceramic layer including a luminescent material and having a thickness less than 500 µm. In accordance with embodiments of the invention, the compound substrate and the semiconductor structure are optically coupled such that the ceramic layer is disposed between the host and the semiconductor structure
Data Source
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AI summary
A semiconductor structure including a light emitting layer disposed between an n-type region and a p-type region is attached to a compound substrate including a host which provides mechanical support to the device and a ceramic layer including a luminescent material. In some embodiments the compound substrate includes a crystalline seed layer on which the semiconductor structure is grown. The ceramic layer is disposed between the seed layer and the host. In some embodiments, the compound substrate is attached to the semiconductor structure after growth of the structure on a conventional growth substrate. In some embodiments, the compound substrate is spaced apart from the semiconductor structure and does not provide mechanical support to the structure. The ceramic layer has a thickness less than 500 µm.