Graded Dielectric Layer for LED Light Extraction
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Solution Overview
Problem
Light emitting diodes (LEDs) suffer from significant light loss due to internal reflections caused by refractive index mismatches between semiconductor materials, dielectric passivation layers, and surrounding media, leading to total internal reflections and Fresnel losses.
Innovation Solution
A graded dielectric passivation layer with varying refractive index from the semiconductor material to the surrounding medium, achieved by controlling the flow and concentration of nitrogen-containing and oxygen-containing source gases during deposition, minimizing refractive index mismatches and reducing Fresnel losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform dielectric passivation layer is used, then the manufacturing process is simple, but light loss due to internal reflections is significant
Solution Approach 1:
The patent applies parameter changes by varying the refractive index of the dielectric layer through its thickness. The dielectric layer transitions from a higher refractive index at the semiconductor interface to a lower refractive index at the outer surface, creating a graded index structure that reduces Fresnel reflections and improves light extraction efficiency without complicating the manufacturing process
Solution Approach 2:
The patent employs composite materials by creating a dielectric layer with spatially varying composition. The dielectric layer comprises multiple regions with different refractive indices, effectively combining the optical benefits of multiple materials into a single continuous structure that minimizes internal reflections while maintaining manufacturing simplicity
2Reliability
If the refractive index mismatch between semiconductor and dielectric layer is large, then the dielectric layer provides good passivation, but total internal reflections increase
Solution Approach 1:
The patent resolves this contradiction by continuously changing the refractive index parameter through the dielectric layer thickness. The graded index profile allows the layer to maintain effective passivation at the semiconductor interface while gradually transitioning to a lower refractive index that reduces total internal reflections and improves light extraction
3Device complexity
If a single-layer dielectric structure is used, then the device complexity is low, but light extraction efficiency is poor
Solution Approach 1:
The patent achieves improved light extraction efficiency within a single-layer dielectric structure by implementing a graded refractive index profile. This approach avoids the complexity of multiple discrete layers while still providing the optical benefits of index matching, thereby improving productivity without increasing device complexity
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 graded dielectric layer reduces total internal reflections and Fresnel losses, enhancing light output by allowing emitted light to refract and bend appropriately, thereby increasing the emission angle and minimizing reflectivity.
Implementation Method 1
incident light traveling in an off-normal direction toward at the interface refracts as it passes through the interface, and the refracted light propagates into the lower index layer
Implementation Method 2
If light strikes the interface at an angle sufficiently off-normal, it can be refracted to the point that it propagates in the plane of the interface, or—even worse—it can be reflected back into the high index semiconductor material. Such full reflection back into the source layer constitutes TIR
Implementation Method 3
a normally incident wave at the semiconductor surface, not refracted under Snell's law, is partially reflected based upon the difference in indices of refraction. The reflection loss in this case is computed as the square of (nhigh−nlow)/(nhigh+nlow)
Data Source
AI summary
An optoelectronic device includes a passivation layer of a dielectric material having a graded composition that varies with depth, whether continuous or stepwise, to provide a first index of refraction proximate to a semiconductor or conductor material and provide a second index of refraction adjacent to a surrounding material, such as an encapsulant. The resulting graded dielectric layer reduces Fresnel losses by reducing index of refraction mismatches between the adjacent semiconductor or conductor layer and the surrounding medium. Methods for forming graded dielectric layers include supplying a nitrogen-containing source gas at a declining flow rate or concentration, while supplying an oxygen-containing source gas an rising flow rate or concentration, to a deposition chamber.