III-Nitride LED Light Extracting Structure
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Solution Overview
Problem
Semiconductor light-emitting devices, particularly III-nitride devices, face challenges in light extraction and strain relief due to the use of conventional substrates, leading to defects and poor performance, as the lattice mismatch and thermal expansion issues affect the quality of the grown layers.
Innovation Solution
A composite substrate structure is employed, featuring a host substrate and a seed layer bonded together, with a light extracting structure that includes a variation in refractive index between the host and the light emitting layer, which can be organized or random, such as a quasi-crystal photonic structure, to enhance light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional substrate is used for growing III-nitride semiconductor layers, then the device structure is simple, but lattice mismatch and thermal expansion issues cause strain in the light emitting layer leading to poor performance and defects
Solution Approach 1:
The substrate is segmented into multiple functional layers: a host substrate providing mechanical support and a separate seed layer bonded to the host substrate. This segmentation allows the seed layer to be optimized for lattice matching with the III-nitride semiconductor layers, reducing strain and improving device performance while maintaining structural integrity through the host substrate.
2Manufacturing precision
If a composite substrate with host and seed layer is used, then strain in the light emitting layer is reduced, but the device structure becomes more complex
Solution Approach 1:
The seed layer acts as an intermediary between the host substrate and the III-nitride semiconductor layers. It provides a lattice-matched interface that reduces strain during epitaxial growth, while the host substrate serves as a mechanical carrier. This intermediary layer enables high-quality layer growth without requiring the entire substrate structure to be complex.
3Illumination intensity
If a light extracting structure with refractive index variation is added, then light extraction is improved, but the device structure becomes more complex
Solution Approach 1:
The light extracting structure introduces local variations in refractive index at specific interfaces within the device, such as between the seed layer and host substrate or within the semiconductor layers. These localized optical property changes enhance light extraction efficiency without requiring a complete redesign of the entire device structure, maintaining relative simplicity while improving illumination intensity.
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 composite substrate structure reduces strain in the light emitting layer, improves device performance by facilitating better light extraction, and allows for the growth of high-quality III-nitride semiconductor layers with reduced defects.
Implementation Method 1
A light extracting structure is disposed between the host substrate and the light emitting layer. The light extracting structure may be, for example, a variation in index of refraction in a direction perpendicular to a growth direction of the III-nitride device layers.
Data Source
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AI summary
Embodiments of the invention include a substrate comprising a host and a seed layer bonded to the host, and a semiconductor structure comprising a light emitting layer disposed between an n-type region and a p-type region grown over the seed layer. A variation in index of refraction in a direction perpendicular to a growth direction of the semiconductor structure is disposed between the host and the light emitting layer.