UV Light-Emitting Element With Side-Surface Extraction Control
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Solution Overview
Problem
Existing ultraviolet light-emitting elements struggle to achieve high light emission output and uniform light distribution, particularly when used in devices with a lens-equipped SMD, where light emission in all directions is desirable.
Innovation Solution
The ultraviolet light-emitting element features a transparent substrate with a rough side surface and a p-side semiconductor layer thickness determined by the formula 2L/cos θ = λ(2k + 1)/2n, where λ is the central emission wavelength, n is the refractive index, and θ is the emission angle, ensuring light extraction from both the main and side surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the light emission is optimized for high axial output with a narrow light distribution angle, then the axial light emission efficiency is improved, but the light emission output in other directions is reduced
Solution Approach 1:
The patent segments the light extraction function by creating two distinct extraction paths: one through the main surface for axial light and another through the side surface for oblique light. The side surface is specifically roughened to enable light extraction in directions other than axial, thereby distributing light emission across multiple directions while maintaining high axial output.
Solution Approach 2:
The patent adds a spatial dimension to light extraction by utilizing the side surface of the substrate in addition to the main surface. By roughening the side surface and controlling the p-side semiconductor layer thickness, light can be extracted through both the top (main surface) and sides of the device, transforming the light emission from a single-directional (axial only) to multi-directional output.
2Manufacturing precision
If the p-side semiconductor layer thickness is increased to improve flatness, then the manufacturing precision is improved, but the light extraction efficiency in specific angle ranges is reduced
Solution Approach 1:
The patent applies precise parameter control by setting the p-side semiconductor layer thickness to satisfy the specific formula 2L/cosθ = λ(2k+1)/2n. This parameter optimization ensures that light within the critical angle range (where total internal reflection would normally occur at flat surfaces) can be effectively extracted through the roughened side surface, thereby maintaining both manufacturing feasibility and high light extraction efficiency.
Solution Approach 2:
The patent applies different surface qualities to different regions of the substrate. The main surface remains flat for standard light extraction, while the side surface is specifically roughened to enable light extraction at oblique angles. This localized differentiation of surface quality allows the device to maintain manufacturing precision while enhancing light extraction in specific angular ranges.
3Illumination intensity
If the side surface of the transparent substrate is made rough to enhance light extraction, then the light emission output is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent segments the surface treatment process by applying roughening only to the side surface of the substrate while keeping the main surface flat. This selective segmentation allows light extraction enhancement in oblique directions without compromising the optical quality of the main light extraction surface, thereby improving light emission output with controlled manufacturing complexity.
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
This configuration enhances light emission output and results in a light distribution pattern with a peak angle between 24° and 37°, improving overall light extraction efficiency.
Implementation Method 1
a side surface of the transparent substrate is a rough surface
Implementation Method 2
thickness L (nm) of the p-side semiconductor layer satisfies formula (1)... 2L/cos θ = λ(2k + 1)/2n
Implementation Method 3
a quantum well-type light-emitting layer on the n-type semiconductor layer
Data Source
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AI summary
Provided are an ultraviolet light-emitting element with which high light emission output is obtained and a method of producing the same. The ultraviolet light-emitting element includes a transparent substrate having a main surface that constitutes a light extraction surface, an AlN layer on the transparent substrate, an n-type semiconductor layer on the AlN layer, a quantum well-type light-emitting layer on the n-type semiconductor layer, a p-side semiconductor layer directly on the quantum well-type light-emitting layer, and a reflective electrode directly on the p-side semiconductor layer. A side surface of the transparent substrate is a rough surface. Thickness L (nm) of the p-side semiconductor layer satisfies 2L/cos θ = λ(2k + 1)/2n with respect to a central emission wavelength λ (nm) of the quantum well-type light emitting layer, a refractive index n of the p-side semiconductor layer, a natural number k, and an emission angle θ of light traveling toward inside of the p-side semiconductor layer from the quantum well-type light-emitting layer, and is within a range where the emission angle θ is an angle at which light extraction from the transparent substrate into air would not occur in a case in which the main surface and the side surface of the transparent substrate are flat surfaces.