Deep-UV Light Extraction Surface With Cone Asperities
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Solution Overview
Problem
The external quantum efficiency of deep ultraviolet light output from semiconductor light emitting devices is low, particularly for shorter wavelengths, due to total reflection issues at the light extraction surface.
Innovation Solution
A semiconductor light emitting device with a light extraction surface featuring an asperity structure comprising an array of cone-shaped parts and granular parts, formed through a single mask dry-etching process, which inhibits total reflection and enhances light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat light extraction surface is used, then the device structure is simple, but the light extraction efficiency is low due to total reflection
Solution Approach 1:
The patent applies curvature by forming cone-shaped protrusions on the light extraction surface instead of using a flat surface. The conical geometry with specific aspect ratios (height/diameter) creates curved interfaces that reduce total internal reflection of deep ultraviolet light, thereby improving light extraction efficiency while maintaining manufacturing feasibility through standard lithography and etching processes
Solution Approach 2:
The patent creates a porous-like structure by forming an array of cone-shaped protrusions with controlled spacing. The spaces between adjacent cones create a periodic structure that functions similarly to porous materials in scattering and extracting light, improving external quantum efficiency without requiring actual porous materials
2Reliability
If the wavelength of emitted light is shortened to achieve deep ultraviolet output, then the sterilization capability is improved, but the external quantum efficiency decreases
Solution Approach 1:
The patent changes the geometric parameters of the light extraction surface by forming cones with specific height-to-diameter ratios (0.5 to 2.0) and controlled densities (10^4 to 10^6 cones per mm²). These parameter optimizations are specifically tailored for deep ultraviolet wavelengths, enabling efficient light extraction at shorter wavelengths where sterilization capability is maximized
3Loss of energy
If a complex asperity structure is formed on the light extraction surface, then the light extraction efficiency is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The patent segments the light extraction surface into discrete cone-shaped units arranged in a periodic array. This segmentation allows the complex asperity structure to be formed using standard lithography masks with periodic patterns followed by conventional etching processes, making the manufacturing feasible with existing semiconductor fabrication equipment
Solution Approach 2:
The cone-shaped asperity structure serves multiple functions simultaneously: it acts as a light extraction enhancement structure, provides mechanical support, and can be integrated with the underlying LED chip structure. This multi-functionality reduces the need for additional separate components or processing steps
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 asperity structure significantly improves light extraction efficiency by reducing total reflection, resulting in a 32% increase in output intensity compared to devices with flat or single-asperity light extraction surfaces.
Implementation Method 1
the external quantum efficiency of deep ultraviolet light output via the light extraction surface of the substrate of a deep ultraviolet light emitting device is as low as several % and that the shorter the wavelength of emitted light, the lower the external quantum efficiency
Data Source
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AI summary
A semiconductor light emitting device 10 includes a light extraction layer (substrate 22) having a light extraction surface (principal surface 22b). The light extraction layer includes: a plurality of cone-shaped parts 52 formed in an array on the light extraction surface, and a plurality of granular parts 56 formed both on a side part of the cone-shaped part 52 and in a space between adjacent cone-shaped parts 52. A method of manufacturing the semiconductor light emitting device 10 includes: forming a mask having an array pattern on the light extraction layer; and etching the mask and the light extraction layer from above the mask. The etching includes first dry-etching performed until an entirety of the mask is removed and second dry-etching performed to further dry-etch the light extraction layer after the mask is removed.