Light Coupling Layers with Recessed Electrodes for LED Stress Management
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Solution Overview
Problem
The formation of Group III-V semiconductor-based LEDs on silicon substrates faces challenges due to lattice mismatch and thermal expansion mismatch, leading to structural stresses, defect densities, and cracking issues, which affect the extraction efficiency and current spreading.
Innovation Solution
The implementation of a light coupling structure with a roughened u-type Group III-V semiconductor layer over an n-type Group III-V semiconductor layer, which reduces stress and eliminates cracking, while optimizing current spreading and extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If Group III-V semiconductor layers are formed on silicon substrates, then LED device integration is achieved, but lattice mismatch and thermal expansion mismatch cause structural stresses and cracking
Solution Approach 1:
A light coupling layer comprising a buffer layer and a roughened layer is introduced as an intermediary structure between the silicon substrate and the n-type Group III-V semiconductor layer. This intermediary layer accommodates the lattice mismatch and thermal expansion differences, reducing structural stresses and preventing cracking while enabling successful LED device integration on silicon substrates.
Solution Approach 2:
The buffer layer and roughened layer are designed with specific thickness parameters (buffer layer: 1-10 µm, roughened layer: 0.1-1 µm) and controlled surface roughness (RMS: 10-100 nm). By optimizing these physical parameters, the structure effectively manages stress distribution and thermal expansion mismatches, maintaining structural integrity during LED operation.
2Ease of manufacture
If conventional planar electrode structures are used, then manufacturing is simple, but light extraction efficiency is limited due to total internal reflection
Solution Approach 1:
The light coupling layer incorporates a roughened layer with controlled surface roughness (RMS: 10-100 nm) that introduces curvature and non-planar features to the electrode structure. This roughened surface morphology reduces total internal reflection at the semiconductor-air interface, significantly improving light extraction efficiency while maintaining compatibility with standard semiconductor fabrication processes.
3Manufacturing precision
If smooth semiconductor surfaces are used, then manufacturing precision is easier to achieve, but current spreading is insufficient leading to hot spots
Solution Approach 1:
The roughened layer is designed with locally varied surface morphology (RMS: 10-100 nm) that creates multiple local contact points for current injection. This local quality variation enhances current spreading uniformity across the semiconductor surface, preventing hot spot formation while remaining compatible with precision manufacturing techniques.
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 approach enables the formation of LEDs with improved external quantum efficiency and reduced defect densities, maintaining desirable performance characteristics while minimizing cracking and stress.
Implementation Method 1
structural limitations, which may limit transmission of light generated by an LED out of the device
Implementation Method 2
lattice mismatch and thermal expansion mismatch, leading to structural stresses, defect densities, and cracking issues
Implementation Method 3
An LED typically includes a chip of semiconducting material doped with impurities to create a p-n junction. When electrons meet holes, the electrons recombine with the holes in a process that may result in the radiative emission of energy in the form of photons (hν)
Data Source
AI summary
A light emitting device comprises a first layer of an n-type semiconductor material, a second layer of a p-type semiconductor material, and an active layer between the first layer and the second layer. A light coupling structure is disposed adjacent to one of the first layer and the second layer. In some cases, the light coupling structure is disposed adjacent to the first layer. An orifice formed in the light coupling structure extends to the first layer. An electrode formed in the orifice is in electrical communication with the first layer.