Vertical GaN LED with Patterned Substrate for Light Extraction
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Solution Overview
Problem
Conventional vertical GaN-based LEDs face issues with reduced external quantum efficiency due to photon confinement and limited manufacturing yield, especially when the LED thickness is 10 μm or less, and current crowding occurs at the n-electrode, degrading light-extraction efficiency and lifespan.
Innovation Solution
The formation of uneven patterns with protuberances on the surface of the n-type GaN layer increases the surface area and light-scattering structures, combined with a heterojunction structure using AlGaN/GaN layers to enhance current dispersion and light-extraction efficiency, and a method involving patterning, etching, and annealing processes to create these features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a sapphire substrate is used for GaN-based LED growth, then the LED can be manufactured, but the thermal conductivity is poor and manufacturing costs cannot be reduced
Solution Approach 1:
The patent extracts and removes the sapphire substrate from the final LED structure through laser lift-off (LLO) process. The GaN layer is grown on the sapphire substrate during manufacturing, then the substrate is separated and removed, leaving only the GaN-based LED structure mounted on a heat-sink optimized substrate, thereby eliminating the thermal conductivity limitation of sapphire
Solution Approach 2:
The patent segments the manufacturing process into two distinct phases: growth phase (using sapphire substrate for its crystalline quality) and final device phase (using removed sapphire and mounting on alternative substrate optimized for thermal management and cost). This allows each phase to use the most appropriate substrate for its specific requirements
2Length of moving object
If the LED thickness is reduced to 10 μm or less, then manufacturing costs may be reduced, but manufacturing yield decreases significantly
Solution Approach 1:
The patent performs preliminary actions by forming uneven patterns on the substrate before growing the GaN layer. This pre-structuring ensures that even when the GaN layer is thin (10 μm or less), the underlying patterned substrate provides mechanical support and optical function, enabling thin-fabrication while maintaining manufacturing yield
Solution Approach 2:
The patent transitions from a flat, two-dimensional LED structure to a three-dimensional structure with uneven patterns (convex portions) on the substrate surface. This dimensional change allows the substrate to provide both mechanical support and optical light-extraction enhancement, enabling thin LED fabrication while maintaining yield
3Ease of manufacture
If conventional flat surface structures are used, then manufacturing is simple, but external quantum efficiency is reduced due to photon confinement
Solution Approach 1:
The patent applies spheroidality by forming convex portions (hemispherical or dome-shaped structures) on the substrate surface. These curved surfaces reduce the critical angle for light extraction and increase the surface area for photon emission, thereby improving external quantum efficiency while maintaining manufacturing simplicity through standard photolithography and etching processes
4Reliability
If current is concentrated at the n-electrode contact point, then electrical connection is efficient, but current crowding occurs degrading light-extraction efficiency and lifespan
Solution Approach 1:
The patent applies local quality by creating regions of different electrical conductivity within the n-type GaN layer. By forming uneven patterns and potentially varying doping concentrations locally, the patent creates pathways that guide and disperse current flow from the central n-electrode contact toward the edges, reducing current crowding at the contact point while maintaining efficient electrical connection
Solution Approach 2:
The patent uses the three-dimensional uneven patterns (convex portions) to create additional current diffusion pathways in the lateral dimension. The extended surface area and varied topography provide multiple routes for current flow, transforming the current distribution from a concentrated point-source pattern to a more distributed two-dimensional flow pattern, reducing current density at the contact point
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 maximizes external quantum efficiency, improves current dispersion, and enhances light-extraction efficiency, leading to higher power characteristics and increased manufacturing yield while simplifying the process.
Implementation Method 1
formation of uneven patterns with protuberances on the surface of the n-type GaN layer increases the surface area and light-scattering structures
Implementation Method 2
forming a GaN layer on the first AlGaN layer such that a 2D-electron gas layer is formed in a junction interface of the first AlGaN layer
Implementation Method 3
a sapphire substrate is removed using a laser lift-off (LLO)
Implementation Method 4
a method involving patterning, etching, and annealing processes to create these features
Data Source
AI summary
A vertical GaN-based LED and a method of manufacturing the same are provided. The vertical GaN-based LED includes an n-electrode, a first n-type GaN layer, a first AlGaN layer, a GaN layer, a second AlGaN layer, a second n-type GaN layer, an active layer, a p-type GaN layer, and a structure support layer. The first n-type GaN layer has uneven patterns having a plurality of protuberances. The first AlGaN layer is formed under the first n-type GaN layer, and the GaN layer is formed under the first AlGaN layer. The active layer is formed under the second n-type GaN layer, and the p-type GaN layer is formed under the active layer. A p-electrode is formed under the p-type GaN layer, and the structure support layer is formed under the p-electrode.