UV LED p-type Nano-dot Layer for Conductivity and Transparency
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Solution Overview
Problem
Conventional p-type AlGaN layers in UV LEDs are highly resistive and unsuitable for serving as hole supplier or ohmic contact layers, limiting light extraction efficiency due to poor vertical conductivity and UV transparency.
Innovation Solution
A conductive UV-transparent p-type layer structure with p-type nano-dots embedded in the p-type layer structure, including a smooth p-type layer, a rough p-type layer with protrusions and depressions, and a confining p-type layer, which enhances vertical hole conductivity while maintaining UV transparency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional p-type AlGaN layers are used in UV LEDs, then UV transparency is maintained, but vertical conductivity deteriorates due to highly resistive properties
Solution Approach 1:
The patent employs a composite p-type layer structure combining multiple materials: p-type AlGaN layers with different Al compositions, p-type GaN or InGaN layers, and p-type nano-dots (GaN, InGaN, or AlGaN). This composite structure achieves both UV transparency (through high-Al composition AlGaN layers) and improved vertical conductivity (through low-Al composition layers and nano-dots), resolving the contradiction between transparency and conductivity.
Solution Approach 2:
The patent applies local quality by creating regions with different properties within the p-type layer structure. The p-type nano-dots provide localized high conductivity paths, while the surrounding AlGaN matrix maintains UV transparency. The rough layer with protrusions and depressions creates localized conductivity enhancements without compromising overall transparency.
2Ease of manufacture
If p-type GaN or InGaN layers are used as hole supplier and ohmic contact layers, then conductivity is improved, but UV transparency deteriorates due to UV opacity
Solution Approach 1:
The patent uses local quality by restricting UV-absorbing materials (GaN, InGaN) to specific locations: the p-type nano-dots and the rough layer region. The smooth layer and confining layer use high-Al composition AlGaN that maintains UV transparency. This spatial differentiation allows conductivity enhancement where needed while preserving transparency in light extraction regions.
Solution Approach 2:
The patent transitions from a planar layer structure to a three-dimensional structure with p-type nano-dots embedded in the p-type layer. The nano-dots provide vertical conductivity paths through the layer thickness, enabling conductivity improvement without requiring a continuous UV-absorbing layer that would block light extraction.
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 p-type nano-dots structure improves light extraction efficiency in UV LEDs by enabling better vertical conductivity and UV transparency, allowing for enhanced hole injection and emission efficiency.
Implementation Method 1
a layer of p-type nano-dots imbedded in the p-type layer structure, wherein the p-type nano-dots have a sheet density of 10^10 to 10^12 cm^-2, a lateral dimension of 2-20 nm, and a vertical dimension of 1-5 nm
Implementation Method 2
Since acceptor ionization energy increases linearly with Al-composition in AlGaN material, and hole concentration decreases exponentially with acceptor ionization energy, acceptor-doped AlGaN material (p-type AlGaN or p-AlGaN) possesses exponentially increasing electrical resistivity with Al-composition
Implementation Method 3
a rough p-type layer formed on the smooth p-type layer and having protrusions and depressions formed between the protrusions
Data Source
AI summary
A light emitting device includes an n-type layer, a p-type layer structure, a layer of p-type nano-dots imbedded in the p-type layer structure, and an active region sandwiched between the n-type layer and the p-type layer structure, where the p-type nano-dots possess a sheet density of 1010 to 1012 cm−2, a lateral dimension of 2-20 nm, and a vertical dimension of 1-5 nm. The p-type layer structure with a layer of p-type nano-dots imbedded therein provides good vertical conductivity and UV transparency. Also provided is a method for making the light emitting device.