AlN Template Substrate Structure for UV LED Light Extraction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing methods for forming AlN layers on sapphire substrates for UV LEDs suffer from high defect density and inefficient light extraction due to the AlN/sapphire interface roughness, which affects the optical output power efficiency and reliability of the LEDs.
Innovation Solution
A substrate structure with sealed depressions formed on the sapphire substrate, where discrete AlN nuclei are grown and etched to create a smooth AlN template layer, reducing defect density and enhancing light extraction efficiency by forming sealed depressions and voids within the AlN layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a low-temperature deposited non-single-crystalline AlN buffer is used, then the manufacturing process is simplified, but the defect density increases to high levels (~10^10 cm^-2)
Solution Approach 1:
The patent applies preliminary action by performing high-temperature annealing (1600-1700°C) on the AlN buffer layer before growing the light-emitting structure. This pre-treatment reduces defect density in the AlN layer, creating a high-quality foundation that prevents defect propagation into subsequent layers, thereby solving the reliability issue while maintaining process simplicity.
Solution Approach 2:
The patent changes the temperature parameter by annealing the AlN buffer at extremely high temperatures (1600-1700°C), which transforms the material's crystalline structure and reduces dislocation density. This parameter change converts the low-quality non-single-crystalline AlN into a high-quality template layer suitable for UV LED growth.
2Manufacturing precision
If the AlN/sapphire interface is made smooth, then the manufacturing precision is improved, but the light extraction efficiency decreases due to total internal reflection
Solution Approach 1:
The patent applies local quality by creating localized roughness features (depressions and voids) at specific positions within the AlN layer rather than making the entire interface rough. These localized features are strategically positioned to interrupt total internal reflection paths while maintaining overall interface quality, thus improving light extraction without sacrificing manufacturing precision.
Solution Approach 2:
The patent introduces an intermediary structure (the pattern of depressions and voids within the AlN layer) that mediates between the smooth sapphire substrate and the light-emitting structure. This intermediary layer provides both mechanical support and optical function by scattering light to improve extraction efficiency while maintaining structural integrity.
3Reliability
If high-temperature annealing is applied to reduce defect density, then the material quality is improved, but the device complexity increases due to multiple reactor steps
Solution Approach 1:
The patent merges the annealing process with the existing MOCVD reactor by implementing the high-temperature annealing step (1600-1700°C) within the same equipment used for AlN deposition. This consolidation combines two previously separate processes (deposition in one reactor, annealing in another) into a single integrated process, reducing device complexity while maintaining the defect-reduction benefit.
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 improves the material quality and light extraction efficiency of UV LEDs by reducing defect density and optimizing the AlN/sapphire interface, leading to enhanced optical output power and reliability.
Implementation Method 1
an AlN template layer formed on a surface of the substrate... discrete AlN nuclei are grown and etched to create a smooth AlN template layer
Implementation Method 2
This AlN layer serves as an epitaxial template to support a light-emitting structure
Data Source
AI summary
A substrate structure includes an AlN template layer formed on a substrate. Depressions sealed by the AlN template layer are formed on a surface of the substrate at an interface between the substrate and the AlN template layer, the sealed depressions contain discrete depressions and depression networks and have a lateral size in the range of 20-100 nm, a vertical dimension in the range of 20-100 nm, and a density in the range of 1.0×109-2.0×1010 cm−2. The substrate structure is used for light-emitting diodes with improved optical output power efficiency.