GaN LED DBR Structure for Wide-Angle Reflectance
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Solution Overview
Problem
Existing DBR structures in GaN-based semiconductor LEDs suffer from low overall reflectance due to poor reflectance at incident angles greater than 0°, particularly when using a patterned sapphire substrate, leading to increased light absorption and reduced luminous efficiency.
Innovation Solution
A DBR structure with alternately stacked first and second dielectric material layers, where the second layer has a lower optical thickness and higher refractive index than the first, enhancing reflectance for light incident at both small and large angles, and optionally combined with a metal reflection layer to improve luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional DBR structure with titanium oxide films and silicon oxide films is used, then the DBR structure has high reflectance for light incident at 0°, but the light absorbance of the DBR structure is high due to the titanium oxide film having greater thickness and light absorbance than the silicon oxide film
Solution Approach 1:
The patent changes the optical thickness parameter of the high refractive index layer to be less than or equal to one-quarter of the center wavelength, while maintaining the alternating layer structure. This parameter optimization reduces light absorption in the titanium oxide layer while preserving the DBR's reflectance function at normal incidence.
2Reliability
If the light-transmissive substrate is a patterned sapphire substrate (PSS), then the device structure is enhanced, but light emitted from the light-emitting layer is scattered by the pattern on the upper surface, increasing the incident angle of light incident on the lower surface, and the DBR structure has poor reflectance for light at incident angles greater than 0°
Solution Approach 1:
The patent applies local quality by creating laterally non-uniform optical thickness distribution in the DBR structure. The optical thickness varies in the lateral direction to match the scattering pattern from the PSS, providing enhanced reflectance specifically for the angular distribution of scattered light while maintaining normal reflectance performance.
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 proposed DBR structure achieves high reflectance (>90%) for light wavelengths ranging from 380 nm to 550 nm, including angles from 10° to 50°, significantly reducing light absorption and enhancing luminous efficiency.
Implementation Method 1
a distributed Bragg reflector (DBR) structure... includes a plurality of first dielectric material layers and a plurality of second dielectric material layers that are alternately stacked... The first dielectric material layer has a first refractive index, and the second dielectric material layer has a second refractive index
Implementation Method 2
the DBR structure... has a high reflection capability... reflect light emitted from the light-emitting mesa toward the chip mounting site
Data Source
AI summary
A light-emitting device includes a semiconductor light-emitting stack and a distributed Bragg reflector (DBR) structure. The semiconductor light-emitting stack includes a light-emitting layer. The DBR structure is disposed on the semiconductor light-emitting stack and includes a plurality of first dielectric material layers and a plurality of second dielectric material layers that are alternately stacked on the semiconductor light-emitting stack. The first dielectric material layer has a first refractive index, and the second dielectric material layer has a second refractive index. The first refractive index is lower than the second refractive index. The second dielectric material layer has an optical thickness that is smaller than that of the first dielectric material layer.