Wideband Distributed Bragg Reflector for LED Chips
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Solution Overview
Problem
Current distributed Bragg reflectors in light emitting diode (LED) chips exhibit high reflectivity only for specific wavelength ranges, limiting the light emission efficiency of LED packages emitting white light, as they do not efficiently reflect green and red wavelengths.
Innovation Solution
A light emitting diode chip with a distributed Bragg reflector designed to have high reflectivity across a wide wavelength range, including blue, green, and red, achieved by stacking multiple layers of materials with varying refractive indices on a substrate with controlled surface roughness, and a metal layer to enhance reflectivity and protect the Bragg reflector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a distributed Bragg reflector is formed using conventional materials (TiO2/SiO2) to reflect blue light, then reflectivity in the blue wavelength range reaches approximately 100%, but reflectivity for green and red wavelengths is considerably lower than 50%
Solution Approach 1:
The patent changes the material parameters of the Bragg reflector by using alternating layers of high refractive index material (AlN with n≈2.1) and low refractive index material (Al2O3 with n≈1.7). This parameter change in refractive index contrast enables the reflector to achieve high reflectivity across a broader wavelength range including blue, green, and red light, resolving the limitation of conventional TiO2/SiO2 reflectors that only work for blue wavelengths.
2Illumination intensity
If a metal reflector (aluminum layer) is formed on the bottom surface of the substrate, then reflectivity increases to about 80% over the visible wavelength range, but it cannot achieve the high reflectivity and wavelength selectivity of a DBR
Solution Approach 1:
The patent creates a composite structure combining the advantages of both metal reflectors and DBRs. The AlN/Al2O3 layered structure provides DBR-like high reflectivity and wavelength selectivity, while the overall design maintains the simplicity and broad-spectrum reflection capability similar to metal reflectors. This composite approach achieves over 90% reflectivity across blue, green, and red wavelengths simultaneously.
3Ease of manufacture
If the substrate surface roughness is not controlled, then the fabrication process is simpler, but the optical performance and reflectivity of the Bragg reflector are significantly reduced
Solution Approach 1:
The patent applies preliminary surface treatment to the sapphire substrate before depositing the AlN/Al2O3 layers. By controlling the surface roughness to be 0.1 μm or less through polishing or chemical treatment prior to deposition, the patent ensures optimal optical performance and high reflectivity of the Bragg reflector, while maintaining reasonable fabrication 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
The solution significantly improves light emission efficiency of LED packages by maintaining high reflectivity across the visible spectrum, enhancing the performance of white light emission and reducing light loss, while also ensuring the reliability of the reflector's properties.
Implementation Method 1
a distributed Bragg reflector arranged on the second surface of the substrate, the distributed Bragg reflector to reflect light emitted from the light emitting structure
Implementation Method 2
stacking multiple layers of materials with varying refractive indices on a substrate
Implementation Method 3
a metal layer arranged on the distributed Bragg reflector
Data Source
AI summary
Exemplary embodiments of the present invention disclose a light emitting diode chip including a substrate having a first surface and a second surface, a light emitting structure arranged on the first surface of the substrate and including an active layer arranged between a first conductive-type semiconductor layer and a second conductive-type semiconductor layer, a distributed Bragg reflector arranged on the second surface of the substrate, the distributed Bragg reflector to reflect light emitted from the light emitting structure, and a metal layer arranged on the distributed Bragg reflector, wherein the distributed Bragg reflector has a reflectivity of at least 90% for light of a first wavelength in a blue wavelength range, light of a second wavelength in a green wavelength range, and light of a third wavelength in a red wavelength range.