AlGaN UV Light-Emitting Element With Optimized Sapphire Off Angle
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Solution Overview
Problem
Conventional nitride semiconductor light-emitting elements using sapphire substrates with off angles between 0.05° to 0.5° face challenges in maintaining optimal crystal quality and light-emitting output, particularly for ultraviolet light-emitting elements with emission wavelengths below 365 nm, due to increased RMS surface roughness and Ga segregation, leading to wider wavelength distribution and reduced performance.
Innovation Solution
Optimizing the off angle of the sapphire substrate to between 0.6° and 3.0°, with an AlN molar fraction of 50% or higher in the n-type cladding layer, and a film thickness of the AlN layer between 2.2 µm and 6.6 µm, to enhance crystallinity and light-emitting output while controlling emission wavelength distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the off angle of the sapphire substrate is increased to reduce dislocation, then the crystallinity is improved, but the RMS surface roughness increases and Ga segregation occurs
Solution Approach 1:
The patent changes the off angle parameter from the conventional range (0.05° to 0.5°) to a new optimized range (0.6° to 3.0°). This parameter change resolves the contradiction by finding an optimal value that provides sufficient dislocation reduction while controlling surface roughness and Ga segregation through the specific angular range.
2Reliability
If the off angle is increased to form macro steps for dislocation reduction, then the dislocation density is reduced, but the wavelength distribution widens due to Ga segregation
Solution Approach 1:
The patent optimizes the off angle parameter to a specific range (0.6° to 3.0°) that balances two competing requirements: forming sufficient macro steps to reduce dislocation density while limiting the degree of Ga segregation that would cause wavelength distribution widening. This parameter optimization resolves the contradiction between dislocation reduction and wavelength control.
3Reliability
If the AlN molar fraction in the n-type cladding layer is increased to improve crystallinity, then the light-emitting output is enhanced, but the manufacturing complexity increases
Solution Approach 1:
The patent sets the AlN molar fraction to a specific range (50% or higher) that achieves optimal crystallinity and light-emitting output. This parameter specification resolves the contradiction by defining a clear manufacturing target that balances performance enhancement with manufacturing feasibility, avoiding excessively high AlN fractions that would increase complexity.
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 significantly improves the light-emitting output and crystallinity of AlGaN-based ultraviolet light-emitting elements, achieving a peak emission wavelength of 300 nm or less with a reduced full width at half maximum (FWHM) of the emission wavelength distribution, thereby stabilizing and enhancing the light-emitting performance.
Implementation Method 1
a nitride semiconductor light-emitting element obtained by forming an n-type cladding layer, an active layer and a p-type cladding layer, each of which is an AlGaN based semiconductor layer, above a sapphire (0001) substrate
Data Source
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AI summary
A nitride semiconductor ultraviolet light-emitting element is provided with: an underlying structure portion including a sapphire (0001) substrate and an AlN layer formed on the substrate; and a light-emitting element structure portion including an n-type cladding layer of an n-type AlGaN based semiconductor layer, an active layer having an AlGaN based semiconductor layer, and a p-type cladding layer of a p-type AlGaN based semiconductor layer, formed on the underlying structure portion. The (0001) surface of the substrate is inclined at an off angle which is equal to or greater than 0.6° and is equal to or smaller than 3.0°, and an AlN molar fraction of the n-type cladding layer is equal to or higher than 50%.