GaN LED Light Extraction via Scattering Layer
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) face challenges in achieving high light extraction efficiency, reducing dislocation density, and improving current spreading due to lattice mismatch and thermal expansion differences between epitaxial layers and substrates, leading to limitations in luminous efficacy and forward voltage.
Innovation Solution
The development of a light emitting diode structure with a gallium nitride substrate and a method involving the formation of grooves and protrusions on the conductive type clad layer, along with a light scattering pattern, to enhance light extraction and current spreading, using techniques like impurity implantation and wet etching, and the incorporation of a super-lattice layer to reduce crystal defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gallium nitride substrate is used to reduce dislocation density, then crystal quality improves, but light extraction efficiency deteriorates due to matching refractive indices
Solution Approach 1:
The patent applies local quality by forming a light scattering layer with specific refractive index properties at the substrate interface, while maintaining the bulk substrate material properties for low dislocation density. The light scattering layer is localized at the interface region where light extraction occurs, allowing different optical properties in different spatial locations of the substrate structure.
Solution Approach 2:
The patent uses composite materials by combining the gallium nitride substrate with a light scattering layer having different refractive index properties. This composite structure allows the substrate to provide crystal quality while the light scattering layer provides enhanced light extraction through refractive index contrast.
2Loss of energy
If a patterned sapphire substrate is used to enhance light extraction, then light scattering improves, but dislocation density increases due to lattice mismatch
Solution Approach 1:
The patent applies local quality by concentrating the light scattering function in a specific light scattering layer at the substrate interface, rather than relying on the bulk substrate structure. This allows the majority of the substrate to maintain homogeneous crystal quality while only the interface region provides light scattering functionality.
Solution Approach 2:
The light scattering layer acts as an intermediary between the gallium nitride epitaxial layer and the substrate, providing the necessary refractive index contrast for light extraction without requiring the substrate itself to have mismatched lattice properties. This intermediary layer mediates between the optical extraction requirement and the crystal quality requirement.
3Strength
If the gallium nitride substrate thickness is increased to reduce light loss, then substrate strength improves, but light extraction efficiency worsens due to increased absorption path
Solution Approach 1:
The patent applies local quality by creating a light scattering layer at the substrate interface that enhances light extraction efficiency without requiring changes to the bulk substrate thickness. The light scattering functionality is localized at the interface where light enters the substrate, allowing thin substrates to achieve high light extraction while maintaining structural integrity.
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 significantly improves light extraction efficiency, reduces dislocation density, and enhances current spreading, leading to increased luminous efficacy and reduced forward voltage, enabling high current operation while maintaining device reliability.
Implementation Method 1
a light scattering pattern, to enhance light extraction and current spreading
Implementation Method 2
forming a plurality of grooves within a surface of the first conductive type clad layer by forming defects within the surface of the first conductive type clad layer and etching the defects
Implementation Method 3
etching the defects
Data Source
AI summary
A light-emitting diode including a support substrate, a semiconductor stack disposed on the support substrate and including a p-type compound semiconductor layer, an active layer, and an n-type compound semiconductor layer, a reflective metal layer disposed between the support substrate and the semiconductor stack, the reflective metal layer being in ohmic contact with the p-type compound semiconductor layer of the semiconductor stack and including a groove exposing a portion of the semiconductor stack, an insulation layer disposed between the support substrate and the semiconductor stack and disposed in the groove, and a first electrode including a first electrode pad and a first electrode extension and contacting the n-type compound semiconductor layer of the semiconductor stack, in which the first electrode extension is connected to the first electrode pad, and the first electrode extension is formed along an outer boundary of the light-emitting diode.