Ultraviolet LED Contact Layer Reducing Resistance
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Solution Overview
Problem
High contact resistance between n-AlGaN and the n electrode in ultraviolet LEDs limits the efficiency of the device, requiring a larger n electrode area and a narrower light-emitting area, which hampers the development of highly efficient ultraviolet light emitting devices.
Innovation Solution
Incorporating a contact layer made of n-AlGaN with a lower Al composition ratio between the n layer and the n electrode, where the contact area between the n electrode and the contact layer is wider than between the contact layer and the n layer, effectively reducing the resistance by using n-GaN as the contact layer material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an intermediate layer made of n-AlyGa1-yN is provided between n-AlxGa1-xN and an n electrode, then contact resistance between n-AlxGa1-xN and the n electrode is reduced, but when the Al composition ratio in n-AlGaN is high, the contact resistance cannot be sufficiently reduced and the n electrode area must be increased
Solution Approach 1:
The patent applies parameter changes by introducing a contact layer with a lower Al composition ratio (0≤y<x) than the n layer (x≥0.7). This parameter change in material composition enables sufficient reduction of contact resistance between the n electrode and the high-Al-content n layer, eliminating the need to increase the n electrode area while maintaining low contact resistance.
2Reliability
If the n electrode area is increased to reduce contact resistance, then contact resistance is reduced, but the light emitting area becomes narrow
Solution Approach 1:
The patent resolves this contradiction by changing the material parameter of the contact layer to have a lower Al composition ratio than the n layer. This enables the n electrode to maintain a smaller area while achieving low contact resistance, thereby preserving a larger light emitting area for high device efficiency.
3Reliability
If a contact layer made of n-AlGaN with lower Al composition ratio is provided between the n layer and the n electrode, then resistance between the n layer and the n electrode is reduced, but the device structure becomes more complex
Solution Approach 1:
The patent introduces a contact layer as an intermediary between the n layer and the n electrode. This contact layer, made of n-AlGaN with lower Al composition ratio, serves as a mediator that facilitates low-resistance electrical contact while maintaining structural simplicity through epitaxial growth, thus resolving the contradiction between reduced resistance and increased device complexity.
Data Source
AI summary
In an ultraviolet light emitting device made of a group III nitride semiconductor, a contact layer is provided on a reflective insulating film along a bottom surface, a side surface, and an upper surface of a hole. The contact layer and an n layer are in contact with each other via a plurality of holes. The contact layer is made of Si-doped n-GaN. A lower surface of the contact layer is in contact with the n layer, and an upper surface thereof is in contact with an n electrode. The contact layer is not in contact with the n layer except for regions of the holes. The n electrode is provided on almost the entire upper surface of the contact layer. Therefore, a contact area between the n electrode and the contact layer is wider than a contact area between the contact layer and the n layer.