UV LED Lateral Tunnel Junctions for Hole Injection
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Solution Overview
Problem
Conventional UV LEDs with p-type AlGaN layers are highly resistive and unsuitable for hole injection, leading to limited light extraction efficiency due to strong UV absorption and poor vertical conductivity, which restricts their application in UVB and UVC regimes.
Innovation Solution
The development of UV transparent AlGaN PN tunnel junction structures with alternately laminated p-AlGaN barrier and well layers and n-AlGaN barrier and n-AlInGaN well layers, where the p-AlGaN barrier layers have a higher Al-composition than the well layers to ensure a valence band offset of at least 300 meV, and n-AlGaN barrier layers have a higher Al-composition than n-AlInGaN well layers to ensure a conduction band offset of at least 200 meV, enhancing vertical conductivity and light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional p-type AlGaN layers are used for hole injection, then the structure is simple, but the electrical resistivity is high and light extraction efficiency is poor
Solution Approach 1:
The patent divides the p-type AlGaN layer into multiple alternating layers of p-AlGaN barrier layers and p-AlGaN well layers, forming a superlattice structure. This segmentation creates numerous interfaces that accumulate holes through valence band and polarization discontinuities, thereby improving hole concentration and light extraction efficiency while maintaining UV transparency
Solution Approach 2:
The patent creates a composite superlattice structure by combining p-AlGaN barrier layers with different Al-composition than p-AlGaN well layers. This composite structure leverages the band alignment and polarization effects at the interfaces to achieve enhanced hole accumulation and improved electrical properties without sacrificing UV transparency
2Reliability
If p-type GaN or InGaN layers are used as hole supplier layer, then hole injection is improved, but UV absorption increases and light extraction efficiency decreases
Solution Approach 1:
The patent applies local quality by using AlGaN materials with specific Al-compositions tailored for different functions: barrier layers with higher Al-composition for UV transparency and hole accumulation, and well layers with lower Al-composition for hole supply. This localized optimization ensures UV transparency in barrier regions while maintaining hole injection capability in well regions
3Illumination intensity
If p-type AlGaN layers with high Al-composition are used, then UV transparency is maintained, but electrical resistivity increases exponentially
Solution Approach 1:
The patent segments the high-Al-composition AlGaN into thin barrier layers alternating with lower-Al-composition well layers. The barrier layers maintain UV transparency while the well layers provide pathways for hole transport. The numerous interfaces between layers create hole accumulation that effectively bridges the conductivity gap
Solution Approach 2:
The p-AlGaN well layers with lower Al-composition act as intermediaries that facilitate hole transport between the high-Al-composition barrier layers. These intermediary layers reduce the overall resistivity while the barrier layers maintain UV transparency, creating a balanced structure
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 proposed solution significantly improves the light extraction efficiency of UV LEDs by facilitating efficient hole injection and tunneling, overcoming the limitations of conventional p-type AlGaN layers, and achieving higher tunnel current densities, thereby enhancing the performance of UV LEDs in UVB and UVC regimes.
Implementation Method 1
PN tunnel junctions are formed on the p-type layer... facilitating efficient hole injection and tunneling
Data Source
AI summary
An ultraviolet light-emitting device with a lateral tunnel junction for hole injection includes a PN tunnel junction structure formed on a p-type layer at one side of an active region. The PN tunnel junction structure includes a p-type structure containing a plurality of alternately laminated p-AlGaN barrier layers and p-AlGaN well layers, and an n-type structure containing a plurality of alternately laminated n-AlGaN barrier layers and n-AlInGaN well layers, with the p-type structure facing the p-type layer. Both the p-type structure and the n-type structure have a plurality of projections extending from their surface. The n-type structure is formed on the p-type structure with the projections of the n-type structure fully filling void portions of the p-type structure.