Strain-Controlled AlN Heterostructure Growth for UV LED Reliability
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Solution Overview
Problem
The challenge in improving the reliability and lifetime of ultraviolet light emitting diodes (UV LEDs) lies in the high threading dislocation density due to heteroepitaxial growth on foreign substrates, which leads to cracking and poor yield, and current methods for improving substrate quality are cost-prohibitive for large-scale production.
Innovation Solution
A method for fabricating group III nitride heterostructures on lattice mismatched substrates by optimizing nucleation and aluminum nitride layer growth parameters, including specific V/III ratios and temperatures, to control strain and dislocation formation, resulting in reduced dislocation density and improved crystal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If heteroepitaxial growth is performed on foreign substrates, then substrate availability and manufacturing cost are improved, but threading dislocation density increases leading to poor reliability
Solution Approach 1:
The patent introduces a multi-layer buffer structure including AlN nucleation layer, AlN barrier layer, and AlGaN transition layer as intermediary layers between the foreign substrate and the active device layers. These buffer layers act as mediators that gradually transition from the substrate lattice structure to the GaN lattice structure, reducing the abrupt lattice mismatch and minimizing threading dislocation propagation into the active region.
Solution Approach 2:
The patent performs preliminary actions by growing multiple buffer layers with specific compositions and thicknesses before depositing the active device layers. The AlN nucleation layer is grown first to establish a stable foundation, followed by the AlN barrier layer and AlGaN transition layer, which are prepared in advance to reduce dislocation density before the critical active region growth.
2Reliability
If buffer layer thickness is increased to reduce dislocation density, then threading dislocation density is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies local quality by creating buffer layers with spatially varying composition and thickness. The AlGaN transition layer has a graded composition that changes locally from high Al content near the substrate to lower Al content near the active region. Each buffer layer serves a specific local function: AlN nucleation for initial stabilization, AlN barrier for dislocation blocking, and AlGaN transition for gradual lattice matching.
Solution Approach 2:
The patent employs composite material structures by combining different aluminum gallium nitride compositions (AlN, AlGaN with varying Al content) in a layered buffer structure. This composite approach allows optimization of each layer's properties for specific functions while maintaining overall structural integrity and reducing dislocation density more effectively than a single uniform layer.
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 enhances the reliability and lifetime of UV LEDs by reducing dislocation density and strain, leading to improved light intensity and current-voltage characteristics, while being cost-effective for large-scale production.
Implementation Method 1
growing an aluminum nitride nucleation layer directly on a substrate using a set of nucleation layer growth parameters
Data Source
AI summary
A solution for fabricating a group III nitride heterostructure and/or a corresponding device is provided. The heterostructure can include a nucleation layer, which can be grown on a lattice mismatched substrate using a set of nucleation layer growth parameters. An aluminum nitride layer can be grown on the nucleation layer using a set of aluminum nitride layer growth parameters. The respective growth parameters can be configured to result in a target type and level of strain in the aluminum nitride layer that is conducive for growth of additional heterostructure layers resulting in strains and strain energies not exceeding threshold values which can cause relaxation and/or dislocation formation.