Patterned GaN Substrate for Epitaxial Growth
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Solution Overview
Problem
GaN-based semiconductor light emitting elements face challenges in enhancing light-emitting efficiency due to high dislocation defects and limited light extraction efficiency, particularly when using inexpensive substrates like sapphire and silicon.
Innovation Solution
A substrate for epitaxial growth with a novel uneven surface pattern featuring convex portions arranged at 120-degree intervals, forming equilateral hexagonal growth spaces that promote the growth of hexagonal pyramidal or truncated pyramidal crystals, reducing dislocation density and enhancing light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat sapphire substrate is used for epitaxial growth, then the manufacturing process is simple, but the GaN-based semiconductor crystal contains high density dislocation defects
Solution Approach 1:
The substrate surface is segmented into multiple convex portions with growth spaces between them. This segmentation prevents the formation of large continuous crystal domains, allowing independent growth control in each region and reducing the propagation of dislocation defects across the entire substrate.
Solution Approach 2:
The substrate surface is given non-uniform local structure with convex portions having specific crystal orientations (c-plane, a-plane, or r-plane) in different regions. This local quality variation enables controlled epitaxial growth with reduced dislocations in each local area, improving overall crystal quality.
2Manufacturing precision
If the growth surface is processed to an uneven surface by etching, then dislocation defects are reduced, but the light extraction efficiency is not maximized
Solution Approach 1:
The convex portions are formed with curved surfaces having specific radii of curvature. This curvature design optimizes both the reduction of dislocation defects during epitaxial growth and the extraction of light from the grown crystal by creating favorable refraction and scattering conditions at the curved interfaces.
3Manufacturing precision
If conventional uneven surface patterns are used, then some dislocation reduction is achieved, but the density of hexagonal crystals is not maximized
Solution Approach 1:
The convex portions are arranged in an asymmetric pattern where each convex portion has three closest convex portions at 120-degree intervals, creating equilateral hexagonal growth spaces. This asymmetric arrangement optimizes the nucleation and growth of hexagonal GaN crystals, maximizing crystal density while maintaining low dislocation levels.
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
The substrate achieves low-dislocation-density GaN-based semiconductor films with high light extraction efficiency, suitable for high-output applications like illumination, by delaying two-dimensionalization of the growth surface and maximizing the density of hexagonal crystals.
Implementation Method 1
a substrate for epitaxial growth which has an uneven surface, as a surface for epitaxial growth
Implementation Method 2
there has been developed an epitaxial growth technique which generates a lateral growth mode of a GaN-based semiconductor crystal by processing a substrate surface to an uneven surface by a method such as etching (LEPS: Lateral Epitaxy on a Patterned Substrate)
Implementation Method 3
a dislocation line propagating in the c-axis direction in the inside of the crystal is bent in a lateral direction
Implementation Method 4
an effect of increasing the light extraction efficiency is obtained
Implementation Method 5
when the growth surface of the crystal is two-dimensionalized... the density of threading dislocation reaching the surface of the finally obtained film decreases
Data Source
AI summary
A substrate for epitaxial growth of the present invention comprises: a single crystal part comprising a material different from a GaN-based semiconductor at least in a surface layer part; and an uneven surface, as a surface for epitaxial growth, comprising a plurality of convex portions arranged so that each of the convex portions has three other closest convex portions in directions different from each other by 120 degrees and a plurality of growth spaces, each of which is surrounded by six of the convex portions, wherein the single crystal part is exposed at least on the growth space, which enables a c-axis-oriented GaN-based semiconductor crystal to grow from the growth space.