Textured Light Guide LED Structure for Current Crowding Relief
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Solution Overview
Problem
GaN-based light emitting diodes face issues with current crowding and heat generation due to small n-type GaN layer thickness, leading to reduced external quantum efficiency and increased forward voltage, while GaN substrates suffer from crystal defects and light loss through total internal reflection.
Innovation Solution
Incorporating an optical trap with a light absorption layer between light guide layers and a side reflector to prevent light loss and reduce substrate resistance, allowing for increased dopant concentration and optical amplification to enhance external quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the n-type GaN layer is increased to reduce current crowding, then current distribution is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent divides the n-type GaN layer into multiple sub-layers with different thicknesses and doping concentrations. This segmentation allows each sub-layer to be optimized independently for current distribution while maintaining overall manufacturability and reducing the complexity of controlling a single thick layer.
2Power
If dopant concentration is increased to reduce substrate resistance, then forward voltage is reduced, but free carrier absorption increases causing deterioration in external quantum efficiency
Solution Approach 1:
The patent applies different dopant concentrations to different regions and layers of the device. High dopant concentration is used in regions where low resistance is critical, while lower concentrations are used in regions where light propagation occurs, thereby locally optimizing both forward voltage and minimizing free carrier absorption losses.
Solution Approach 2:
The patent changes the dopant concentration parameter across different layers and regions of the device. By varying this parameter spatially, the device achieves low forward voltage in contact regions while maintaining low free carrier absorption in light-emitting and light-propagating regions.
3Reliability
If the thickness of the n-type GaN layer is increased to distribute electric current, then current crowding is relieved, but photons subjected to total internal reflection are absorbed and lost over long distances
Solution Approach 1:
The patent segments the thick n-type GaN layer into multiple thinner sub-layers. This segmentation maintains the current distribution benefit of increased thickness while reducing the total distance photons must travel through the material, thereby minimizing absorption losses from total internal reflection.
4Reliability
If a bulk GaN substrate is used to improve current distribution, then reliability is improved, but light extraction efficiency deteriorates due to total internal reflection and absorption
Solution Approach 1:
The patent segments the bulk GaN substrate into multiple thinner layers, reducing the distance light must propagate through the substrate. This maintains the current distribution advantages of a thick substrate while minimizing light absorption losses and improving light extraction efficiency.
Solution Approach 2:
The patent optimizes different regions of the substrate with different properties. The substrate structure is designed to provide good current distribution in the electrical contact regions while having reduced thickness or modified optical properties in regions where light extraction occurs, thereby locally optimizing both reliability and productivity.
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 solution improves light extraction efficiency, reduces forward voltage, and relieves the droop phenomenon, achieving high output and efficiency at high current densities by minimizing light absorption and promoting optical amplification.
Implementation Method 1
a light absorption layer interposed between light guide layers... the light absorption layer includes a semiconductor layer having an energy band gap narrower than or equal to an energy band gap of the active layer
Implementation Method 2
photons incident on the interface between the n-type GaN and air at a certain angle (critical angle) or more cannot be discharged outside and return back to the interior of the light emitting diode due to total internal reflection
Data Source
AI summary
A light-emitting device includes a light generating portion including an active layer interposed between a first conductivity type layer and a second conductivity type layer. The active layer generates light. The light-emitting device further includes a light guide layer disposed on an optical path of light generated from the active layer. The light guide layer includes a textured structure on the optical path. The light guide layer can have a same conductivity type as the first conductivity type layer.