Rough Adhesive Contact for DUV LED Light Extraction
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Solution Overview
Problem
Group III nitride semiconductor materials pose challenges in forming good ohmic contacts due to their wide band-gap, leading to resistive losses and instability in deep ultraviolet light emitting diodes (DUV LEDs), particularly in thermal management and light extraction efficiency.
Innovation Solution
A contact interface with a roughness profile having a characteristic height of at least three nanometers and a characteristic width of at least 0.1 micron is introduced, enhancing adhesion and reducing contact resistance by increasing the surface area between the contact and the semiconductor layer, while promoting light scattering and reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If aluminum is used as contact material for DUV LEDs, then reflectivity is improved, but ohmic contact stability deteriorates
Solution Approach 1:
The patent uses a composite contact structure consisting of multiple layers including Pd, Ni, Al, Ti, and Au. This composite structure combines the high reflectivity of Al with the stability and adhesion properties of Pd-Ni-Ga compounds, resolving the contradiction between reflectivity and contact stability.
2Stability of the object's composition
If Pd/Ni/Al/Ti/Au metallization scheme is used, then thermal stability and reflectivity are improved, but contact resistance increases
Solution Approach 1:
The patent optimizes the thickness parameters of each layer in the Pd/Ni/Al/Ti/Au stack and introduces a roughness profile with specific height (≥3 nm) and width (≥0.1 micron) parameters. These parameter changes reduce contact resistance while maintaining thermal stability and reflectivity.
Solution Approach 2:
The patent introduces a roughness profile (curved surface) at the contact interface instead of a flat surface. This curvature increases the contact area and improves adhesion, thereby reducing contact resistance while maintaining the thermal stability provided by the Pd-Ni-Ga compound formation.
3Strength
If Ni-based contacts are used, then adhesion is improved, but oxidation resistance deteriorates at high temperature
Solution Approach 1:
The patent introduces Pd as an intermediary layer between Ni and the environment. The Pd layer forms stable Pd-Ga compounds that protect the underlying Ni from oxidation at high temperatures, while Ni maintains its adhesion function to the GaN layer.
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 solution improves light extraction efficiency and maintains low electrical resistance, achieving a stable and efficient ohmic contact for DUV LEDs, enhancing thermal stability and reflectivity.
Implementation Method 1
enhancing adhesion and reducing contact resistance by increasing the surface area between the contact and the semiconductor layer
Implementation Method 2
promoting light scattering and reflectivity
Data Source
AI summary
A device including a first semiconductor layer and a contact to the first semiconductor layer is disclosed. An interface between the first semiconductor layer and the contact includes a first roughness profile having a characteristic height and a characteristic width. The characteristic height can correspond to an average vertical distance between crests and adjacent valleys in the first roughness profile. The characteristic width can correspond to an average lateral distance between the crests and adjacent valleys in the first roughness profile.