Pixelated Template for GaN Growth on Large Substrates
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Solution Overview
Problem
The development of high-quality GaN devices is hindered by lattice mismatch and thermal expansion coefficient differences between substrate and deposited film, leading to high dislocation densities and strain-induced wafer bending/cracking, particularly on larger substrates.
Innovation Solution
A method involving composite pixelated patterned templates is used, where a substrate with a dielectric layer features discrete groups of micro- and nano-scale patterns, decoupling lattice mismatch and thermal expansion, minimizing strain, and enabling high-quality semiconductor growth on large diameter substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heteroepitaxy is used to grow nitride layers on conventional substrates (sapphire, Si, SiC), then device fabrication can proceed, but high threading dislocation density (10^9 to 10^19 cm^-2) and strain-induced wafer bending/cracking occur due to lattice mismatch and thermal expansion coefficient differences
Solution Approach 1:
The substrate surface is segmented into an array of pixelated patterns (micropillars, nanodots, or holes) rather than a continuous surface. This segmentation isolates dislocation propagation to individual pixels, preventing the formation of high-density threading dislocations across the entire wafer. The pixelated structure divides the harmful strain effects into localized, manageable units.
Solution Approach 2:
A dielectric layer is introduced as an intermediary between the substrate and the nitride layer. This dielectric layer acts as a buffer that decouples the lattice mismatch and thermal expansion coefficient differences between the substrate and the nitride film, reducing strain transmission and preventing wafer bending and cracking.
2Stability of the object's composition
If thicker substrates are used to reduce wafer bending, then strain-induced bowing is minimized, but manufacturing cost and processing complexity increase
Solution Approach 1:
Instead of using uniformly thick substrates to prevent bending, the invention segments the substrate surface into pixelated patterns. This allows the use of thinner, more manageable substrates while maintaining wafer stability through the distributed pixel structure that locally manages strain without requiring excessive thickness.
Solution Approach 2:
The invention changes the geometric parameters of the substrate surface from a continuous flat surface to a pixelated pattern with specific dimensions (pixel size, spacing, depth). By optimizing these parameters, the substrate can maintain structural integrity and reduce bowing without requiring increased thickness, thus simplifying manufacturing.
3Productivity
If regular patterning is applied to enhance light extraction, then LED efficiency improves, but the underlying lattice mismatch and thermal expansion issues remain unresolved
Solution Approach 1:
The invention merges two previously separate functions into a single pixelated pattern structure: (1) light extraction enhancement through surface patterning, and (2) strain management through pixelated segmentation. The same micropillar/nanodot/ hole array that extracts light also serves to isolate dislocations and manage thermal expansion, eliminating the need for separate strain-management structures.
Solution Approach 2:
The pixelated pattern structure serves multiple functions simultaneously: it enhances light extraction efficiency, reduces threading dislocation density, manages strain distribution, and enables better thermal management. This multi-functional design eliminates the need for additional separate structures or processes.
Data Source
AI summary
A method of producing a template material for growing semiconductor materials and/or devices, comprises the steps of: (a) providing a substrate with a dielectric layer on the substrate; and (b) forming a pixelated pattern on the dielectric layer, the pattern comprising a plurality of discrete groups of structures.