Patterned Substrate for Group III Nitride Light Extraction
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Solution Overview
Problem
Semiconductor emitting devices, such as LEDs and laser diodes, face issues with light trapping due to abrupt changes in refractive index at interfaces between semiconductor layers, leading to reduced light extraction efficiency and increased absorption.
Innovation Solution
A patterned substrate with substantially flat top surfaces and a plurality of openings is used to improve the growth of group III nitride-based semiconductor layers, featuring a root mean square roughness less than 0.5 nanometers and opening sizes between 0.1 micron and five microns, which helps in reducing light trapping by providing additional surfaces for light escape and alleviating stress buildup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a planar substrate is used for layer growth, then the manufacturing process is simple, but light extraction efficiency is reduced due to total internal reflection at interfaces
Solution Approach 1:
The substrate surface is segmented into multiple discrete patterns (protrusions and openings) rather than remaining planar. This segmentation creates multiple light extraction pathways and interfaces, reducing total internal reflection and improving light extraction efficiency while maintaining a manufacturable structured surface.
Solution Approach 2:
The substrate surface is transformed from a two-dimensional planar interface to a three-dimensional structured surface with protrusions and openings. This dimensional change creates additional light extraction interfaces and angles, reducing total internal reflection and improving light extraction efficiency.
2Loss of energy
If interface roughness is increased to reduce light trapping, then light extraction improves, but stress fields in semiconductor layers worsen
Solution Approach 1:
The substrate surface exhibits local quality variation with distinct protruding regions and opening regions. The protruding regions provide controlled roughness for light extraction enhancement, while the overall structured pattern manages stress distribution, achieving both light extraction improvement and stress field mitigation.
Solution Approach 2:
The substrate incorporates a porous-like structure with openings distributed across the surface. This porous configuration increases surface area for light extraction while the controlled geometry of openings and protrusions manages stress field distribution in the semiconductor layers.
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 patterned substrate enhances light extraction efficiency and reduces stress in semiconductor layers, leading to improved performance and efficiency of semiconductor emitting devices by allowing more light to be transmitted without total internal reflection.
Implementation Method 1
A larger change in the index of refraction between the layers, and between the substrate and its surroundings, results in a smaller total internal reflection (TIR) angle
Implementation Method 2
Roughness at an interface allows for partial alleviation of the light trapping by providing additional surfaces through which light can escape without totally internally reflecting from the interface
Data Source
AI summary
A patterned surface for improving the growth of semiconductor layers, such as group III nitride-based semiconductor layers, is provided. The patterned surface can include a set of substantially flat top surfaces and a plurality of openings. Each substantially flat top surface can have a root mean square roughness less than approximately 0.5 nanometers, and the openings can have a characteristic size between approximately 0.1 micron and five microns. One or more of the substantially flat top surfaces can be patterned based on target radiation.