Variable Al Composition Contact Layer for UV Light Extraction
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Solution Overview
Problem
Nitride-based semiconductor light-emitting devices face challenges in forming a reflective electrode and achieving efficient light extraction, particularly for ultraviolet light emission, due to low hole concentration in p-type AlGaN layers and high light absorption by the contact layer.
Innovation Solution
A semiconductor light-emitting device structure is introduced, featuring a contact layer with a variable Al composition ratio, facilitating the formation of a reflective electrode by minimizing light absorption, where the Al composition ratio is higher near the p-type nitride semiconductor layer and lower near the reflective electrode, and an electron blocking layer with a high Al composition ratio is included to enhance light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an additional contact layer is formed between the p-type semiconductor layer and the electrode to form the p-side electrode, then the electrode formation is achieved, but the absorption of the light emitted from the active layer degrades efficiency of light extraction
Solution Approach 1:
The contact layer is designed with a non-uniform Al composition ratio that varies in the thickness direction. The Al composition ratio is higher near the p-type nitride semiconductor layer interface and lower near the reflective electrode interface. This local variation in material composition allows the contact layer to simultaneously achieve good electrical contact properties near the semiconductor layer while maintaining low light absorption near the reflective electrode, thus resolving the contradiction between ease of electrode formation and light extraction efficiency
Solution Approach 2:
The Al composition ratio in the contact layer is changed as a continuous or discontinuous gradient through its thickness. By controlling the Al composition ratio to be greater than 0% and smaller than about 50%, and specifically varying it from higher values near the p-type layer to lower values near the electrode, the optical and electrical properties of the contact layer are optimized to balance electrode formation capability with minimal light absorption
2Illumination intensity
If p-AlGaN is used for the p-type semiconductor layer to achieve desired wavelength emission, then the light emission capability is improved, but the hole concentration is very low making it difficult to form ohmic contact with metal electrode
Solution Approach 1:
The contact layer acts as an intermediary between the p-type AlGaN semiconductor layer and the metal reflective electrode. This intermediate layer with its specific Al composition ratio and thickness provides a transition zone that facilitates ohmic contact formation, bridging the gap between the low-hole-concentration p-AlGaN layer and the metal electrode, thus enabling effective electrical contact while preserving the light emission properties of the p-type 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
The proposed structure improves light extraction efficiency and facilitates the formation of a reflective electrode, effectively addressing the absorption issues in nitride-based semiconductor light-emitting devices, especially for ultraviolet light emission.
Implementation Method 1
a reflective electrode disposed on the contact layer
Data Source
AI summary
A semiconductor light-emitting device includes a contact layer. The contact layer has the composition ratio of Al elements which varies gradually therein. A region formed by an Al element in the contact layer of the semiconductor light-emitting device may improve light extraction efficiency of the light emitted from an active layer and facilitate a formation of the reflective electrode.