Deep Ultraviolet LED With Hemispherical Lens and Transparent Contact Layer
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Solution Overview
Problem
Deep ultraviolet LEDs have low wall-plug power conversion efficiency (WPE) and light extraction efficiency (LEE) due to light absorption in the p-GaN contact layer and total internal reflection, limiting their practical applications.
Innovation Solution
A deep ultraviolet LED design incorporating a transparent p-AlGaN contact layer with a photonic crystal periodic structure and a hemispherical lens on the sapphire substrate, enhancing light extraction efficiency through multiple reflections and minimizing total internal reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-GaN contact layer is used, then electrical contact is achieved, but light absorption occurs reducing light extraction efficiency
Solution Approach 1:
The patent changes the material composition parameter of the contact layer by using p-AlGaN with high Al content (x≥0.6) instead of conventional p-GaN. This parameter change makes the contact layer transparent to deep ultraviolet light at 265-280 nm wavelength while maintaining electrical conductivity, thereby eliminating light absorption losses.
Solution Approach 2:
The patent employs a composite structure combining p-AlGaN contact layer with photonic crystal periodic structures and highly reflective electrode layers. This composite approach integrates multiple functional materials to simultaneously achieve electrical contact, light transparency, and enhanced light extraction through photonic band gap effects and optical reflection.
2Device complexity
If conventional contact layer structures are used, then device simplicity is maintained, but light extraction efficiency remains below 10%
Solution Approach 1:
The patent segments the contact layer into multiple functional components: a p-AlGaN contact layer for electrical conduction, a photonic crystal periodic structure for light manipulation, and a highly reflective electrode layer for light redirection. This segmentation allows each component to perform its specific function optimally, achieving over 50% light extraction efficiency.
Solution Approach 2:
The patent introduces photonic crystal periodic structures that create photonic band gaps in the optical dimension, preventing light propagation in certain directions and enhancing extraction. This adds a dimensional aspect to light control that goes beyond conventional planar contact layer designs.
3Device complexity
If total internal reflection is not addressed, then device structure remains simple, but light is confined and converted to heat reducing efficiency
Solution Approach 1:
The patent introduces a hemispherical lens as an intermediary optical element between the LED chip and external environment. This lens acts as a mediator that refracts and redirects light rays, preventing total internal reflection at the semiconductor-air interface and enabling more light to escape the device, thereby reducing heat conversion losses.
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 significantly increases the LEE and WPE of deep ultraviolet LEDs, achieving higher efficiency and enabling their practical use in applications such as food and water purification and medical treatment.
Implementation Method 1
the photonic crystal periodic structure has a photonic band gap; the photonic band gap opens for TE polarized components
Implementation Method 2
light with the wavelength λ can be efficiently reflected through multiple reflections
Implementation Method 3
total internal reflection can be minimized and high LEE can be obtained
Implementation Method 4
the light is emitted in the direction of the normal to the lens surface even when there is a distribution in the angle of incidence of light on the sapphire substrate
Implementation Method 5
the Al reflecting electrode layer has reflectivity as high as 90% with respect to light
Implementation Method 6
the p-AlGaN contact layer is transparent to light with the wavelength λ; the amount of absorption of light by the ultrathin Ni layer is small
Data Source
Figure 1
Figure 2A
Figure 2B~2B(b)
AI summary
Provided is a deep ultraviolet LED with a design wavelength λ, including a reflecting electrode layer, an ultra-thin metal layer, and a p-type contact layer that are arranged in this order from a side opposite to a substrate; and a hemispherical lens bonded to a rear surface of the substrate on a side of the p-type contact layer, the hemispherical lens being transparent to light with the wavelength X. The refractive index of the hemispherical lens is greater than or equal to the average value of the refractive index of the substrate and the refractive index of air and is less than or equal to the refractive index of the substrate. The hemispherical lens has a radius that is greater than or equal to the radius of an inscribed circle of the substrate and is about equal to the radius of a circumscribed circle of the substrate.