UV Light Emitting Device Surface Patterned Substrate
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Solution Overview
Problem
Deep ultraviolet light emitting diodes (DUV LEDs) suffer from reduced light extraction efficiency due to total internal reflection at the interface between the n-type semiconductor layer and the sapphire substrate, leading to a significant portion of emitted light being absorbed rather than escaping, which is not the case with blue LEDs.
Innovation Solution
The ultraviolet light emitting device incorporates a light-transmitting layer with surface-processed pattern portions in the total internal reflection region, including random roughness and specific cut shapes, to enhance light extraction efficiency by scattering light away from the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a sapphire substrate is used for DUV LED, then the LED can emit deep ultraviolet light, but total internal reflection loss is maximized and light extraction efficiency is deteriorated
Solution Approach 1:
The patent applies curvature to the lower surface of the sapphire substrate by forming a convex upward curved surface. This curved surface structure changes the angle of incidence for light rays passing through the substrate, allowing more light to escape at angles below the critical angle for total internal reflection, thereby improving light extraction efficiency
Solution Approach 2:
The patent introduces a new dimensional aspect by creating a three-dimensional curved surface profile on the substrate rather than maintaining a flat two-dimensional surface. This dimensional change enables light extraction in additional angular directions, reducing the impact of total internal reflection
2Illumination intensity
If the AlN layer is formed in DUV LED, then the LED can emit deep ultraviolet light, but the difference in index of refraction between media greatly increases, maximizing total internal reflection loss
Solution Approach 1:
The curved surface structure on the sapphire substrate modifies the optical path of light rays, enabling them to exit the device at different angles that avoid the critical angle for total internal reflection at the AlN-sapphire interface, thus improving light extraction despite the high refractive index difference
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 surface-processed light-transmitting layer effectively increases the amount of light that escapes from the substrate, improving the light extraction efficiency of DUV LEDs compared to conventional designs.
Implementation Method 1
The ultraviolet light emitting device incorporates a light-transmitting layer with surface-processed pattern portions in the total internal reflection region, including random roughness and specific cut shapes, to enhance light extraction efficiency by scattering light away from the substrate.
Implementation Method 2
In accordance with Snell's Law, due to a difference in index of refraction between the n-type semiconductor layer 36, the AlN layer 40 and the sapphire substrate 42, a part 2 of light emitted from the active layer 34 does not escape from the sapphire substrate 42, undergoes total internal reflection and is absorbed in the semiconductor layer 30
Data Source
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AI summary
Disclosed is a light emitting device including an active layer emitting light with a wavelength band of 200 nm to 405 nm, and a light-transmitting layer disposed on the active layer, the light-transmitting layer having a lower part facing the active layer, wherein at least one of side and upper parts of the light-transmitting layer has a surface-processed pattern portion.