RAMO4 Substrate Curvature for LED Light Extraction
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Solution Overview
Problem
Conventional sapphire substrates used in flip-chip LEDs suffer from low light extraction efficiency due to refractive index differences between the Group III nitride semiconductor layered product and the sapphire substrate, leading to reflection losses at the interfaces, which hinder the extraction of light emitted from the light emitting layer.
Innovation Solution
A flip-chip Group III nitride semiconductor light emitting diode is developed using a RAMO4 substrate with a ScAlMgO4 layer, where a large part of the substrate is peeled off to create a surface with irregularities, reducing the flatness difference between the substrate and the layered product, thereby enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sapphire substrate is used in a flip-chip LED, then the substrate provides good thermal insulation and electrical insulation, but light extraction efficiency is reduced due to refractive index differences causing reflection at interfaces
Solution Approach 1:
The invention applies surface curvature by forming convex and concave portions on the sapphire substrate surface. The convex portions have curved outer surfaces with radii of curvature between 1-10 μm, and the concave portions have curved inner surfaces. This curvature modifies light propagation paths, reducing total internal reflection at the sapphire-LED interface and improving light extraction efficiency while preserving the substrate's thermal and electrical insulation properties
Solution Approach 2:
The invention creates a porous-like structure on the sapphire substrate surface through the pattern of convex and concave portions. This surface topology increases the effective surface area and creates multiple interfaces for light extraction, allowing light to escape through multiple paths rather than being reflected back into the LED structure
2Temperature
If a flip-chip configuration is used, then the LED structure allows for better thermal management, but light extraction through the sapphire substrate is hindered by reflection at the interface between the Group III nitride semiconductor and sapphire
Solution Approach 1:
The convex and concave portions on the sapphire substrate create curved interfaces that alter light propagation angles. When light travels from the high-refractive-index Group III nitride semiconductor through the sapphire substrate, the curved surfaces prevent uniform total internal reflection by creating varying incident angles, thereby improving light extraction while maintaining the flip-chip's thermal management advantages
3Ease of operation
If a flip-chip configuration is used with sapphire substrate, then the structure enables electrode placement on one surface, but light extraction is further reduced by reflection at the interface between sapphire substrate and air or fluorescent material layer
Solution Approach 1:
The curved surfaces of the convex and concave portions extend to the top surface of the sapphire substrate, creating optimized light extraction interfaces at both the LED-sapphire and sapphire-air boundaries. This dual-interface curvature design addresses reflection losses at both interfaces simultaneously while preserving the flip-chip electrode configuration
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 approach significantly improves light extraction efficiency by reducing reflection losses and increasing the probability of light being extracted outside, resulting in higher light output compared to conventional LEDs.
Implementation Method 1
due to a difference in refractive index of layered product 820 formed of a Group III nitride semiconductor and a refractive index of sapphire substrate 801, reflection occurs at an interface between layered product 820 and sapphire substrate 801
Implementation Method 2
reflection also occurs at an interface between sapphire substrate 801 and air or a fluorescent material layer
Data Source
AI summary
The object of the present invention is to provide a Group III nitride semiconductor light emitting diode having improved light extraction efficiency. A Group III nitride semiconductor light emitting diode according to the present disclosure includes an RAMO4 layer including a single crystal represented by the general formula RAMO4 (wherein R represents one or more trivalent elements selected from the group consisting of Sc, In, Y and lanthanoid elements, A represents one or more trivalent elements selected from the group consisting of Fe (III), Ga and Al, and M represents one or more divalent elements selected from the group consisting of Mg, Mn, Fe (II), Co, Cu, Zn and Cd); and a layered product stacked on the RAMO4 layer. The layered product includes at least a light emitting layer including a Group III nitride semiconductor. A degree of flatness of a surface, of the RAMO4 layer, opposite to the layered product is lower than a degree of flatness of a surface, of the RAMO4 layer, adjacent to the layered product.