GaN Core-Shell Nanopillars via Inversion Etching
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Solution Overview
Problem
Conventional methods for fabricating GaN micro- and nanostructures face challenges in achieving large-area control of dimensions, morphology, and orientation, as well as reducing strain and surface defects, which are crucial for device applications.
Innovation Solution
The method involves inductively coupled plasma etching of lithographically patterned GaN epitaxial layers on silicon substrates to form vertically aligned GaN core-shell structures, followed by selective epitaxial overgrowth using Hydride Vapor Phase Epitaxy, allowing for precise control over dimensions, shape, and morphology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fabrication methods (catalyst-assisted MOVPE, selective area epitaxy, or MBE/HVPE combination) are used to produce GaN core-shell structures, then material quality is improved, but large-area control of dimensions, morphology, and orientation deteriorates
Solution Approach 1:
The patent inverts the conventional bottom-up fabrication approach by using a top-down method: starting with a continuous GaN epitaxial layer and etching it to form core structures, then growing shells selectively on the etched surfaces. This reversal enables precise control over dimensions and morphology across large areas while maintaining material quality through the selective epitaxial overgrowth process.
Solution Approach 2:
The fabrication process segments the GaN structure into distinct core and shell components through sequential etching and selective epitaxial growth steps. The continuous epitaxial layer is first etched to form nanorod cores, then shells are selectively grown on specific facets of these cores, creating segmented core-shell structures with controlled dimensions and orientation across large areas.
2Length of moving object
If high-aspect ratio nanopillar arrays (aspect ratio 10 and higher) with small diameters (150 nm to 250 nm) are fabricated, then device application potential is improved, but etch process design complexity and mask material selection requirements increase
Solution Approach 1:
The patent achieves precise control of high-aspect ratio nanopillar dimensions by systematically optimizing etch process parameters including plasma chemistry composition, radio frequency power, pressure, and temperature. These parameter changes enable consistent fabrication of structures with aspect ratios of 10 or higher and diameters of 150-250 nm while managing the complexity of the etch process design.
3Manufacturing precision
If smooth and defect-free sidewalls are obtained for subsequent selective epitaxial overgrowth, then shell growth quality is improved, but surface defect reduction requirements during etching increase
Solution Approach 1:
The patent introduces an intermediary cleaning step using a mixture of hydrogen and oxygen plasma between the etching and selective epitaxial growth processes. This intermediary treatment removes surface defects and contaminants from the etched sidewalls, creating smooth surfaces that facilitate high-quality shell growth while simplifying the overall manufacturing process by decoupling the etching and growth quality requirements.
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 results in high-quality, large-area GaN micro- and nanostructures with reduced strain and surface defects, enabling improved optical and electronic properties suitable for various device applications.
Implementation Method 1
inductively coupled plasma etching of lithographically patterned GaN epitaxial layers
Implementation Method 2
selective epitaxial overgrowth using Hydride Vapor Phase Epitaxy
Implementation Method 3
Hydride Vapor Phase Epitaxy
Data Source
AI summary
Methods of fabricating micro- and nanostructures comprise top-down etching of lithographically patterned GaN layer to form an array of micro- or nanopillar structures, followed by selective growth of GaN shells over the pillar structures via selective epitaxy. Also provided are methods of forming micro- and nanodisk structures and microstructures formed from thereby.