Nitride Semiconductor Light Extraction Layer Refractive Index Gradient
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Solution Overview
Problem
Light emitting devices using Group III-V nitride semiconductors face reduced light extraction efficiency due to the large refractive index difference between the nitride semiconductor layer and the external atmosphere, leading to significant internal reflection and optical loss.
Innovation Solution
The implementation of a light emitting device with a first and second light extraction layer, where the refractive index of each layer decreases with distance from the semiconductor layer, and the layers are composed of nitride semiconductors with varying aluminum content, including structures with uneven portions to enhance light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a nitride semiconductor layer with large refractive index is used, then high luminance and high reliability are achieved, but light extraction efficiency reduces due to total internal reflection
Solution Approach 1:
The light extraction layer is divided into multiple layers (first light extraction layer and second light extraction layer) with different refractive indexes. The first light extraction layer includes first layers with refractive indexes reducing with distance from the first semiconductor layer, and the second light extraction layer includes second layers with refractive indexes reducing with distance from the first semiconductor layer. This segmentation allows gradual refractive index transition to reduce total internal reflection while maintaining the benefits of nitride semiconductors.
Solution Approach 2:
Different regions of the light extraction layer are assigned different refractive indexes tailored to their specific functions. The first layers and second layers have locally optimized refractive indexes that reduce with increasing distance from the first semiconductor layer, creating a gradient structure that optimizes light extraction at each interface while maintaining overall device reliability.
2Reliability
If a sealing material or substrate is used, then device protection is achieved, but critical angle for light emission becomes smaller, causing total internal reflection
Solution Approach 1:
The light extraction layer acts as an intermediary between the nitride semiconductor layer and the external atmosphere or sealing material. By introducing this intermediate layer with graded refractive indexes, the patent facilitates smoother light transition and reduces the abrupt refractive index mismatch that causes total internal reflection at the semiconductor-sealing material interface.
Solution Approach 2:
The refractive index parameter is changed gradually across the light extraction layer rather than having a sudden transition. The first layers and second layers exhibit refractive indexes that reduce with increasing distance from the first semiconductor layer, creating a parameter gradient that minimizes total internal reflection and enhances light emission intensity while maintaining device protection.
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
This configuration improves light extraction efficiency by reducing internal reflection and increasing the amount of emitted light, enhancing the luminous efficacy of the device.
Implementation Method 1
refractive indexes of the first layers reduce with increasing distance from the first semiconductor layer, refractive indexes of the second layers reduce with increasing distance from the first semiconductor layer
Data Source
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AI summary
A light emitting device is disclosed. The light emitting device includes a first semiconductor layer, a second semiconductor layer, an active layer disposed between the first semiconductor layer and the second semiconductor layer, and a first light extraction layer disposed on the first semiconductor layer and including a nitride semiconductor layer. Here, the first light extraction layer includes a plurality of first layers. The refractive indexes of the first layers reduce with increasing distance from the first semiconductor layer.