Vertical GaN LED Light Extraction via Wet Etching Roughness
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Solution Overview
Problem
Conventional vertical GaN-based LEDs face reduced external quantum efficiency due to photon confinement and manufacturing challenges, particularly with thin GaN structures, where forming hemispherical convex patterns is difficult, leading to low yield and insufficient efficiency improvement.
Innovation Solution
A method involving the formation of a p-type GaN layer on a silicon substrate using a nitride-based buffer layer without separate doping, followed by wet etching to create surface roughness for light scattering, simplifying the process and enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If hemispherical convex patterns are formed on the surface of the n-type GaN layer to reduce the incident angle of photons, then the external quantum efficiency is improved, but the manufacturing process becomes more complex and the yield decreases for thin GaN structures
Solution Approach 1:
Instead of forming convex patterns on the emission surface (top surface), the patent inverts the approach by forming concave patterns on the bottom surface of the GaN layer facing the sapphire substrate. This inversion simplifies the manufacturing process while achieving the same light extraction enhancement through total internal reflection modification.
Solution Approach 2:
The concave patterns are formed on the bottom surface before the GaN layer is fully grown and before device assembly. This preliminary action allows the light extraction enhancement to be built into the structure during manufacturing, avoiding post-processing complexity and improving yield.
2Temperature
If the sapphire substrate is removed using laser lift-off to create a vertical GaN-based LED, then the thermal conductivity is improved, but the external quantum efficiency is degraded due to photon confinement
Solution Approach 1:
The patent applies local quality modification by creating localized concave patterns only on specific regions of the bottom GaN surface. These localized structures selectively enhance light extraction in critical areas while maintaining the overall vertical structure and thermal management benefits of the LLO process.
Solution Approach 2:
The patent converts the harmful photon confinement effect into a benefit by using the bottom surface of the GaN layer, which would normally be a simple flat interface, and transforming it into a light-scattering surface through concave patterning. This turns the previously harmful total internal reflection into useful light extraction.
3Manufacturing precision
If a separate doping process is used to form the p-type GaN layer, then the doping precision is improved, but the manufacturing process complexity increases
Solution Approach 1:
The patent merges the p-type doping process with the GaN layer growth process itself. By incorporating doping elements during the epitaxial growth, the separate doping step is eliminated, reducing manufacturing complexity while maintaining adequate doping precision for device operation.
Solution Approach 2:
The GaN layer growth process is given multi-functionality: it simultaneously forms the GaN layer structure and incorporates the p-type doping. This universal process eliminates the need for separate doping equipment and process steps, simplifying the overall manufacturing flow.
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 improves external quantum efficiency by scattering light and simplifies the manufacturing process, increasing production yield and enhancing LED characteristics.
Implementation Method 1
removing the silicon substrate through wet etching and forming roughness on the surface of the p-type GaN layer through over-etching
Implementation Method 2
the surface of the p-type GaN layer is formed to have roughness through a wet etching process for removing the silicon substrate, the roughness being capable of scattering light
Implementation Method 3
there has been proposed a vertical GaN-based LED in which a sapphire substrate is removed using a laser lift-off (LLO)
Data Source
AI summary
A method of manufacturing a vertical GaN-based LED includes forming a nitride-based buffer layer on a silicon substrate; sequentially forming a p-type GaN layer, an active layer, and an n-type GaN layer on the nitride-based buffer layer; forming an n-electrode on the n-type GaN layer; forming a plating seed layer on the n-electrode; forming a structure supporting layer on the plating seed layer; removing the silicon substrate through wet etching and forming roughness on the surface of the p-type GaN layer through over-etching; and forming a p-electrode on the p-type GaN layer having the roughness formed.