Ultraviolet Reflective Rough Adhesive Contact for DUV LEDs
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Solution Overview
Problem
Group III nitride semiconductors face challenges in forming good ohmic contacts, leading to resistive losses and instability, particularly for deep ultraviolet light emitting diodes (DUV LEDs), due to their wide band-gap and thermal sensitivity.
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, while promoting light extraction and reflectivity through a combination of metallic and nitride layers with specific thicknesses and compositions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If aluminum is used as a reflective contact material, then light reflectivity is improved, but ohmic contact and thermal stability deteriorate
Solution Approach 1:
The patent employs a composite contact structure consisting of multiple layers including aluminum (for reflectivity), nickel (for adhesion and oxidation resistance), and gold (for stability and low contact resistance). This composite approach allows each material to contribute its strengths: aluminum provides high reflectivity for UV light extraction, while the nickel and gold layers ensure thermal stability and maintain ohmic contact properties during thermal cycling.
2Reliability
If nickel is used to improve adhesion and ohmic contact, then contact resistance is reduced, but oxidation resistance and thermal stability worsen above 400°C
Solution Approach 1:
The patent uses gold as an intermediary protective layer over the nickel contact layer. The gold layer serves as a barrier that prevents oxidation of the nickel, while the nickel underneath maintains low contact resistance and good adhesion to the semiconductor. This intermediary structure allows the nickel to provide its beneficial electrical properties without suffering from its susceptibility to oxidation at elevated temperatures.
3Stability of the object's composition
If contact layers are made thicker to improve stability, then thermal stability is improved, but light extraction efficiency and device complexity worsen
Solution Approach 1:
The patent optimizes the thickness parameters of each contact layer to achieve a balance between stability and light extraction. The aluminum layer is kept thin (e.g., 50-200 nm) to maintain UV reflectivity while providing sufficient thermal stability, the nickel layer is controlled at moderate thickness (e.g., 10-50 nm) for adhesion without excessive absorption, and the gold layer is applied as a thin protective capping layer. These parameter optimizations ensure that the contact structure provides thermal stability during packaging and operation while minimizing impact on light extraction efficiency.
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 solution improves light extraction efficiency and maintains low electrical resistance, achieving stable ohmic contact and adhesion between the contact and semiconductor layer, even under thermal cycling.
Implementation Method 1
An interface between the first semiconductor layer and the contact includes a first roughness profile having a characteristic height and a characteristic width
Implementation Method 2
it is desirable for the p-type contact 6 and the n-type contact 8 to be both ohmic and reflective, which allows each contact 6, 8 to serve as an electrode as well as a mirror for reflecting light emitted by an active region 4 out of the device 2
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.