Shaped Lithium Substrate for III-Nitride LED Light Extraction
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Solution Overview
Problem
Conventional III-nitride semiconductor light-emitting devices grown on sapphire substrates face efficiency limitations due to lattice constant and thermal expansion mismatches, leading to defects and reduced performance.
Innovation Solution
A semiconductor light-emitting device is developed using a high refractive index substrate with a lithium-based material, such as lithium niobate, which is attached or bonded to the semiconductor structure, and shaped to form a surface at an acute angle between 60° and 75° to enhance light extraction, potentially reducing defects and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If III-nitride devices are grown on sapphire substrate by MOCVD, then the manufacturing process is established and reproducible, but defects are formed due to lattice constant and thermal expansion mismatches, limiting device efficiency
Solution Approach 1:
A buffer layer is introduced as an intermediary between the sapphire substrate and the III-nitride semiconductor layers. This buffer layer has a lattice constant that is closer to that of the III-nitride material, serving as a transition that reduces the lattice mismatch and thermal expansion differences, thereby reducing defect formation while maintaining the established MOCVD manufacturing process
Solution Approach 2:
The lattice constant parameter is gradually changed through the buffer layer, which has intermediate lattice constant properties between sapphire and III-nitride materials. This gradual parameter transition reduces the abrupt mismatch that causes defects, allowing for higher device efficiency while maintaining compatibility with standard sapphire substrates
2Reliability
If conventional flat substrates are used, then the manufacturing process is simple, but light extraction efficiency is limited due to total internal reflection at the planar interface
Solution Approach 1:
The substrate surface is transformed from a flat planar interface to a curved or angled surface with specific geometric features. This curvature changes the angle of light incidence at the semiconductor-substrate interface, reducing total internal reflection and improving light extraction efficiency, while the substrate shaping is integrated into the manufacturing process
Solution Approach 2:
The substrate is shaped with asymmetric angular features (specific angles between substrate surfaces) rather than a symmetric flat surface. This asymmetric geometry creates favorable light extraction paths by directing light at angles that avoid total internal reflection, improving efficiency while maintaining manufacturing feasibility through controlled substrate preparation
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 use of a high refractive index substrate with a closely matched lattice constant to III-nitride materials facilitates better light extraction and reduces defects, enhancing the overall efficiency of the semiconductor light-emitting device without the need for substrate removal or material roughening.
Implementation Method 1
The substrate may have a refractive index that closely matches that of the III-nitride material in the device... The substrate is shaped to improve light extraction
Data Source
AI summary
Embodiments of the invention include a semiconductor structure (23) including a light emitting layer. A substrate (10) comprising lithium is attached to the semiconductor structure (23). A surface of the substrate (10) forms an angle with a major plane of the semiconductor structure (23) that is between 60° and 75°.