Nitride Underlayer Fabrication via Annealing for Crack-Free Growth
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Solution Overview
Problem
Current deep ultraviolet LEDs suffer from low light-emitting efficiency due to the large mismatch between AlGaN and common substrates, leading to surface cracks in nitride films grown over sputtered AlN buffer layers.
Innovation Solution
A fabrication method involving sputtering an AlN layer with doped non-Al materials like Ga or In, followed by high-temperature annealing to create a rough surface, and subsequent growth of AlxGa1-xN layers via MOCVD to release stress through 3D-2D mode conversion, thereby improving crystalline quality and reducing cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sputtered AlN buffer layer is used to improve crystalline quality, then light output efficiency is improved, but surface cracks occur due to the extremely flat surface unable to provide stress release path
Solution Approach 1:
The patent introduces localized roughness features on the AlN buffer layer surface through controlled surface treatment processes. This creates local variations in surface morphology that provide stress release paths while maintaining overall surface quality suitable for subsequent epitaxial growth, resolving the contradiction between surface flatness and crack prevention.
Solution Approach 2:
The patent transforms the extremely flat surface into a microscopically rough surface with curved features. This curvature at the micro-scale provides stress release pathways that prevent crack formation, while the overall surface remains sufficiently flat for high-quality epitaxial growth of AlGaN layers.
2Reliability
If AlN layer is sputtered with doped non-Al materials and annealed to form rough surface, then stress is released through 3D-2D mode conversion, but process complexity increases
Solution Approach 1:
The patent combines multiple functions into the annealing process: surface roughening, stress relief, and phase transformation (3D-2D mode conversion) are all achieved in a single annealing step. This integration reduces the number of separate process steps while achieving multiple beneficial effects simultaneously.
Solution Approach 2:
The patent utilizes changes in temperature and material composition parameters during annealing to achieve surface roughening and stress release. By controlling the annealing temperature and dopant concentration, the process transforms the surface morphology and stress state without requiring additional complex processing steps.
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 method enables the production of crack-free AlN underlayers with high lattice quality, resulting in deep-ultraviolet light-emitting diodes with enhanced light-emitting efficiency and reduced surface cracks.
Implementation Method 1
sputtering an AlN layer over a surface of the substrate
Implementation Method 2
annealing the AlN layer to form a rough surface
Implementation Method 3
the non-Al material is desorbed during annealing to form a rough surface
Implementation Method 4
depositing an AlxGa1-xN layer (0≤x≤1) over the AlN layer via MOCVD
Data Source
AI summary
A fabrication method of a nitride underlayer structure includes, during AlN layer sputtering with PVD, a small amount of non-Al material is doped to form nitride with decomposition temperature lower than that of AlN. A high-temperature annealing is then performed. After annealing, the AlN layer has a rough surface with microscopic ups and downs instead of a flat surface. By continuing AlGaN growth via MOCVD over this surface, the stress can be released via 3D-2D mode conversion, thus improving AlN cracks.