AlGaN UV Light-Emitting Structure for Strain and Optical Confinement
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Solution Overview
Problem
Nitride semiconductor light-emitting elements face challenges in emitting ultraviolet light due to increased tensile strain from high Al composition ratio AlGaN layers, leading to wafer cracking and reduced optical confinement factors.
Innovation Solution
The introduction of a nitride semiconductor light-emitting element structure with N-type and P-type cladding layers, guide layers, and an active layer with specific band gap energies and refractive indices, including N-side and P-side guide layers, and an electron barrier layer, to reduce strain and enhance optical confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Al composition ratio of the barrier layer is increased to increase the band gap energy, then the refractive index of the barrier layer decreases, but the tensile strain on the substrate from the cladding layer increases causing wafer cracking
Solution Approach 1:
The patent divides the cladding structure into multiple segments: N-type cladding layer, N-side guide layers (first and second), active layer with barrier layer, P-side guide layer, and P-type cladding layer. Each segment has optimized Al composition ratio and thickness to distribute strain while maintaining optical confinement. The barrier layer with high Al composition (0.05-0.3) is segmented and positioned specifically to provide band gap energy without requiring the entire cladding structure to have high Al content, thus reducing overall tensile strain on the wafer.
Solution Approach 2:
Different regions of the semiconductor stack are assigned different Al composition ratios tailored to local requirements. The barrier layer has high Al composition (0.05-0.3) for sufficient band gap energy, while the guide layers have moderate Al composition (0.01-0.05) to balance optical confinement and strain reduction. The N-type and P-type cladding layers have optimized compositions for their respective functions. This local optimization allows each region to contribute to band gap energy without uniformly increasing strain across the entire structure.
2Strength
If the thickness of the P-type cladding layer is reduced to reduce strain on the substrate, then the electrical resistance increases and the refractive index increases, but the optical confinement factor decreases reducing light output
Solution Approach 1:
The P-side guide layer acts as an intermediary between the active layer and the P-type cladding layer. It has moderate Al composition (0.01-0.05) and is positioned to provide optical confinement assistance without the high strain of high-Al cladding material. This intermediary layer helps maintain the optical confinement factor while allowing the P-type cladding layer to be thinner and have lower strain. The guide layer mediates the transition between the high-confinement requirement and the low-strain requirement.
Solution Approach 2:
The cladding structure uses composite material design with multiple AlGaN layers having different Al composition ratios. The P-type cladding layer is composite with the P-side guide layer and N-side guide layers, creating a graded structure that provides both optical confinement and strain management. This composite approach allows the system to achieve the optical confinement factor of a thick high-Al layer while the actual thick high-Al portion is replaced by lower-Al guide layers that impose less strain.
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 reduces strain on the semiconductor stack, increases the optical confinement factor, and enhances light output stability, allowing for higher power ultraviolet light emission without wafer cracking.
Implementation Method 1
The band gap energy of the barrier layer is larger than the band gap energy of the N-side second guide layer
Implementation Method 2
the refractive index of the cladding layer, which is for confining ultraviolet light to the active layer
Implementation Method 3
nitride semiconductor light-emitting elements that emit blue light have been known, but there is a demand for high-power nitride semiconductor light-emitting elements that emit ultraviolet light
Data Source
AI summary
A nitride semiconductor light-emitting element includes: an N-type cladding layer; an N-side first guide layer; an N-side second guide layer; an active layer including a well layer and a barrier layer; and a P-type cladding layer. The band gap energy of the barrier layer is larger than the band gap energy of the N-side second guide layer. The band gap energy of the N-side second guide layer is smaller than the band gap energy of the N-side first guide layer. The band gap energy of the N-side first guide layer is smaller than the band gap energy of the N-type cladding layer. The cladding layers, the guide layers, and the barrier layer each comprise a nitride semiconductor including Al.