GaN LED Light Extraction via DBR and Scatter Elements
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Solution Overview
Problem
Gallium nitride-based LEDs experience light loss due to internal total reflection and prolonged light paths within nitride semiconductor layers, limiting their light extraction efficiency, especially in vertical-type LEDs where sapphire substrates restrict the structure and reflectance is not sufficient to prevent light trapping.
Innovation Solution
Incorporating a distributed Bragg reflector (DBR) with a multi-layered structure and scatter elements within the nitride semiconductor layers to enhance light reflectance across the visible spectrum, combined with a roughened surface and air gaps to scatter light and prevent trapping, thereby improving light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a reflection metal layer is formed on the bottom surface of the sapphire substrate, then light reflectance is improved, but light loss still occurs due to insufficient reflectance and internal total reflection
Solution Approach 1:
The patent combines a distributed Bragg reflector (DBR) with a metal reflection layer to create a composite reflection structure. The DBR provides wavelength-selective high reflectance while the metal layer provides broadband reflection, together achieving superior light extraction efficiency compared to either layer alone.
Solution Approach 2:
The reflection structure is divided into multiple functional layers: the DBR consists of alternating high and low refractive index layers, and the metal reflection layer is separated from the sapphire substrate by an insulation layer. This segmentation allows each layer to perform its specific function optimally.
2Illumination intensity
If light is scattered on the surface of the sapphire substrate, then light extraction is improved, but light path length is prolonged causing internal total reflection and light loss
Solution Approach 1:
The patent introduces scatter elements at specific locations within the nitride semiconductor layer to create localized scattering centers. This provides effective light extraction enhancement at critical positions without requiring extensive scattering throughout the entire light path.
Solution Approach 2:
The scatter elements act as intermediary structures between the light-generating active layer and the light extraction surface, facilitating light extraction by scattering light at optimal positions before it can be trapped by internal total reflection.
3Illumination intensity
If a distributed Bragg reflector with multi-layered structure is used, then light reflectance across visible spectrum is enhanced, but device complexity increases
Solution Approach 1:
The DBR structure serves multiple functions: it provides high reflectance across the visible spectrum, acts as a protective insulation layer, and contributes to the overall mechanical stability of the LED structure. This multi-functionality justifies the increased structural 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 enhances light extraction efficiency by reducing light loss through internal reflection, achieving high reflectance across the visible spectrum and improving luminous efficiency, making it suitable for white LED packages.
Implementation Method 1
a distributed Bragg reflector (DBR) having a multi-layered structure
Implementation Method 2
enhance light reflectance across the visible spectrum
Implementation Method 3
scatter elements within the third nitride semiconductor layer
Implementation Method 4
roughened surface and air gaps to scatter light
Implementation Method 5
air gaps to scatter light and prevent trapping
Data Source
AI summary
An exemplary embodiment of the present invention relates to a light emitting diode (LED) including a substrate, a first nitride semiconductor layer arranged on the substrate, an active layer arranged on the first nitride semiconductor layer, a second nitride semiconductor layer arranged on the active layer, a third nitride semiconductor layer disposed between the first nitride semiconductor layer or between the second nitride semiconductor layer and the active layer, the third nitride semiconductor layer comprising a plurality of scatter elements within the third nitride semiconductor layer, and a distributed Bragg reflector (DBR) comprising a multi-layered structure, the substrate being arranged between the DBR and the third nitride semiconductor layer.