GaN LED Super-Lattice Buffer for Dislocation Reduction
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Solution Overview
Problem
Gallium nitride-based light emitting diodes (LEDs) grown on heterogeneous substrates, such as sapphire, have high dislocation densities due to lattice mismatch and thermal expansion differences, limiting luminous efficiency and requiring higher forward voltages when operated with high currents.
Innovation Solution
A gallium nitride LED structure using a gallium nitride substrate with a multi-quantum well active layer and a super-lattice layer, where the super-lattice layer is formed by repeatedly stacking InGaN, AlGaN, and GaN layers, and a middle temperature buffer layer is used to reduce dislocation density and improve crystallinity, along with an intermediate layer to enhance strain and crystallinity, and thin barrier layers to reduce resistance and forward voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a heterogeneous substrate (sapphire) is used for growing gallium nitride semiconductor layer, then the substrate is readily available and fabrication is easier, but the dislocation density increases due to lattice mismatch and thermal expansion differences
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the sapphire substrate and the gallium nitride semiconductor layer. This buffer layer serves as a transition zone that accommodates the lattice mismatch and thermal expansion differences, thereby reducing dislocation density in the grown semiconductor layer while still allowing the use of readily available sapphire substrates.
Solution Approach 2:
The patent employs a composite structure consisting of multiple layers including the sapphire substrate, buffer layer, and gallium nitride semiconductor layer. Each layer is optimized for its specific function, creating a composite material system that balances ease of manufacture with high manufacturing precision by minimizing dislocation density through careful layer design.
2Power
If high current is applied to the LED for increased power output, then the power increases, but the luminous efficiency decreases due to current concentration through dislocations
Solution Approach 1:
The buffer layer acts as an intermediary that filters and redistributes current flow by blocking dislocation propagation. This allows high current to be applied for increased power output while preventing current concentration through dislocations, thereby maintaining high luminous efficiency even at elevated power levels.
3Loss of energy
If the dislocation density is reduced to improve luminous efficiency, then the luminous efficiency increases, but the forward voltage increases due to reduced current conduction paths
Solution Approach 1:
The patent optimizes the thickness and composition parameters of the buffer layer to achieve a balance between reducing dislocation density and maintaining adequate current conduction. By carefully controlling these parameters, the patent reduces dislocation density to improve luminous efficiency while managing forward voltage through precise structural design.
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 approach significantly enhances luminous efficiency, allows for high-current operation without increasing driving voltage, and reduces forward voltage by minimizing crystal defects and dislocation density, resulting in improved optical power and surface morphology.
Implementation Method 1
the semiconductor layer made of nitride of a group III element is generally grown on a heterogeneous substrate having a similar crystal structure through metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or the like
Implementation Method 2
a middle temperature buffer layer is used to reduce dislocation density and improve crystallinity
Implementation Method 3
an active layer having a multi-quantum well structure and disposed between the first and second contact layers
Data Source
AI summary
Disclosed herein is a light emitting diode (LED) including: a gallium nitride substrate; a gallium nitride-based first contact layer disposed on the gallium nitride substrate; a gallium nitride-based second contact layer; an active layer having a multi-quantum well structure and disposed between the first and second contact layers; and a super-lattice layer having a multilayer structure and disposed between the first contact layer and the active layer. By employing the gallium nitride substrate, the crystallinity of the semiconductor layers can be improved, and in addition, by disposing the super-lattice layer between the first contact layer and the active layer, a crystal defect that may be generated in the active layer can be prevented.