Heterostructure Stress Management via Alternating Sub-layers
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Solution Overview
Problem
The growth of high-quality aluminum nitride (AlN) buffer layers on substrates like sapphire, silicon carbide, and silicon is challenging due to high dislocation density and stress issues, which affects the efficiency and reliability of deep ultraviolet light emitting diodes (DUV LEDs).
Innovation Solution
A heterostructure with alternating sub-layers of different group III nitride materials, where the thin sub-layers have a distinct composition from the intervening sub-layers, are used to control stresses and reduce wafer bowing during epitaxial growth, incorporating thin sub-layers of AlN or other nitride materials with varying gallium molar fractions to manage tensile and compressive stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If thick AlGaN epitaxial layers are grown to reduce current crowding, then device efficiency improves, but tensile strain and cracking increase
Solution Approach 1:
The thick AlGaN layer is segmented into multiple sub-layers with alternating compositions (Al-rich and Ga-rich regions), allowing the total thickness to be maintained for current spreading while individual sub-layers remain thin enough to avoid cracking from tensile strain
Solution Approach 2:
The patent uses composite AlGaN structures with varying aluminum compositions (x values) arranged in specific patterns, creating a material system that combines the current-spreading benefit of thick layers with the strain-resistance of compositionally modulated regions
2Reliability
If AlN buffer layers are grown on sapphire or SiC substrates to improve crystal quality, then dislocation density decreases, but growth difficulty increases due to lattice mismatch
Solution Approach 1:
The buffer layer structure is designed with locally varying compositions, including graded AlN layers transitioning to AlGaN layers with specific aluminum fractions, allowing optimal lattice matching at each interface while maintaining overall crystal quality
Solution Approach 2:
The patent systematically varies composition parameters (aluminum fraction x), layer thickness parameters, and growth conditions across different layers to optimize both crystal quality and growth feasibility on different substrate types
3Stability of the object's composition
If superlattice structures are used to reduce biaxial tensile strain, then layer stability improves, but manufacturing complexity increases
Solution Approach 1:
The superlattice is segmented into repeating units of thin AlN and AlGaN layers, where each unit cell is relatively simple to grow but the repeated pattern provides cumulative strain management over the thickness of the layer
Solution Approach 2:
The patent employs periodic alternation of AlN and AlGaN layers with specific thickness ratios, creating a regular pattern that systematically manages strain accumulation while maintaining a manageable manufacturing process through repetition
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 effectively reduces internal stresses and wafer bowing, leading to improved crystal quality and reduced dislocation density, enhancing the efficiency and reliability of DUV LEDs by balancing tensile and compressive stresses during growth and cool-down processes.
Implementation Method 1
The thin sub-layers can have a distinct composition from the intervening sub-layers, which alters stresses present during growth of the heterostructure
Data Source
AI summary
A heterostructure for use in fabricating an optoelectronic device is provided. The heterostructure includes a layer, such as an n-type contact or cladding layer, that includes thin sub-layers inserted therein. The thin sub-layers can be spaced throughout the layer and separated by intervening sub-layers fabricated of the material for the layer. The thin sub-layers can have a distinct composition from the intervening sub-layers, which alters stresses present during growth of the heterostructure.