Epitaxial Substrate with AlN Projections for UV LED Crystallinity
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Solution Overview
Problem
Current epitaxial substrates for light-emitting diodes, particularly those using nano-patterned sapphire substrates, still exhibit high dislocation densities, which hinder the efficiency and crystallinity of ultraviolet light-emitting diodes.
Innovation Solution
An epitaxial substrate with a single crystal sapphire substrate featuring conical or pyramidal projections and a specific AlN layer structure, including a first AlN crystal covering the substrate, second AlN crystals protruding from the projections, and a third AlN crystal interconnecting these, is used to reduce dislocation density and enhance crystallinity through metal organic vapor phase epitaxy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AlN is grown on a nano-patterned sapphire substrate, then dislocation density is reduced, but the dislocation density remains high and crystallinity is insufficient
Solution Approach 1:
The invention segments the AlN layer into three distinct crystal structures: a first AlN crystal covering the substrate plane, multiple second AlN crystals growing from projection tips, and a third AlN crystal interconnecting the second crystals. This segmentation allows each region to serve a specific function in reducing dislocations and improving crystallinity.
Solution Approach 2:
The invention transitions from a conventional planar AlN layer to a three-dimensional hierarchical structure with AlN crystals growing vertically from conical or pyramidal projections. The second AlN crystals extend in the thickness direction from the projection tips, creating a multi-layered architecture that effectively filters dislocations.
2Ease of manufacture
If conventional planar AlN growth is used, then manufacturing is simple, but dislocation density remains high
Solution Approach 1:
The sapphire substrate is pre-patterned with conical or pyramidal projections before AlN growth. These projections serve as predetermined nucleation sites that guide the formation of the hierarchical AlN crystal structure, ensuring that second AlN crystals grow vertically from the tips with proper orientation to filter dislocations.
Solution Approach 2:
The invention changes the surface morphology parameter of the substrate from planar to three-dimensional projections, and controls the crystal growth parameters to form distinct first, second, and third AlN crystal regions. This parameter transformation enables the hierarchical structure that reduces dislocations while maintaining manufacturing feasibility through established epitaxial techniques.
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 configuration significantly reduces dislocation density and improves the crystallinity of the AlN layer, leading to enhanced performance of ultraviolet light-emitting diodes by minimizing dislocations and stress-related issues.
Implementation Method 1
an AlN layer on the plane of the single crystal substrate... formed as a layer interconnecting ends of the plurality of second AlN crystals
Data Source
AI summary
An epitaxial substrate includes: a single crystal substrate including projections arranged in an array on a plane. Each projection has a conical or pyramidal shape tapered in a normal direction to the plane. The AlN layer includes: a first AlN crystal covering the plane and the projections with tips of the projections being exposed; second AlN crystals protruding from the tips of the projections along the normal direction and each having a shape of a column whose cross-sectional area increases as a distance from a tip of a corresponding projection increases; and a third AlN crystal as a layer interconnecting ends of the second AlN crystals, opposite the single crystal substrate.