LED Reflective Layer Design for UVA and Blue Wavelengths
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Solution Overview
Problem
Conventional light emitting diodes face challenges in achieving high light extraction efficiency due to limitations in reflecting short wavelength bands, particularly with materials like aluminum which have poor ohmic contact with p-type semiconductor layers and inadequate reflectance in the UVA wavelength band.
Innovation Solution
A light emitting diode design incorporating a first reflective layer for short wavelength bands and a second reflective layer for both short and blue wavelength bands, utilizing DBR unit layers with varying Al content and a phase-matching layer, along with a silver reflective metal layer to enhance reflectance across a broad wavelength region, including UVA and blue bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If aluminum is used as a reflective layer for short wavelength bands, then reflectance is improved, but ohmic contact with p-type semiconductor layers deteriorates
Solution Approach 1:
The reflective layer is segmented into multiple functional layers: a lower reflective layer (aluminum or aluminum alloy) for short wavelength reflectance, and an upper reflective layer (silver or silver alloy) for enhanced reflectance in blue and UVA bands. This segmentation allows each layer to perform its specialized function without compromising the other, resolving the contradiction between ohmic contact and broad-spectrum reflectance.
Solution Approach 2:
The invention uses composite material structure with multiple reflective layers having different material compositions. The lower layer uses aluminum-based materials for short wavelength reflection, while the upper layer uses silver-based materials for blue and UVA reflection. This composite approach combines the advantages of different materials to achieve both good ohmic contact and high reflectance across multiple wavelength bands.
2Device complexity
If a single reflective layer is used, then device complexity is reduced, but reflectance coverage across broad wavelength regions deteriorates
Solution Approach 1:
Different regions of the reflective layer structure are assigned different material properties optimized for specific wavelength ranges. The lower reflective layer is positioned and composed to optimize short wavelength (UVA) reflection, while the upper reflective layer is optimized for blue wavelength reflection. This local quality differentiation enables broad spectrum coverage without requiring a single complex material.
Solution Approach 2:
The solution transitions from a single-layer reflective structure to a multi-layer reflective structure, adding the dimension of vertical layering. This dimensional change allows simultaneous optimization for multiple wavelength bands by stacking materials with complementary reflectance properties, achieving broad coverage while maintaining manageable structural complexity.
3Productivity
If additional reflective metal layers are added to improve reflectance, then light extraction efficiency is improved, but device complexity and manufacturing processes worsen
Solution Approach 1:
The invention merges the reflective function with the electrode structure by integrating the multi-layer reflective system into the existing electrode configuration. The lower reflective layer serves dual purposes as both electrode contact and reflector, while the upper reflective layer is integrated into the electrode assembly. This merging approach achieves high light extraction efficiency without adding separate manufacturing processes for distinct reflective components.
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 design achieves high reflectance in a broad wavelength region, significantly improving light extraction efficiency and eliminating the need for additional reflective metal layers or processes, while maintaining effective ohmic contact.
Implementation Method 1
a first reflective layer formed on the p-type semiconductor layer to reflect light of a short wavelength band propagating through the p-type semiconductor layer
Implementation Method 2
a metal electrode formed on the conductivity type semiconductor layer to further reflect light of a short wavelength band and light of a visible wavelength band
Data Source
AI summary
Disclosed is a light emitting diode comprising; a substrate having a front side and a back side; a first conductive type semiconductor layer having a front side and a back side, and formed on the back side of the substrate; a second conductive type semiconductor layer having a front side and a back side, and formed on the back side of the first conductive type semiconductor layer; an active layer having a short wavelength band of 315 to 420 nm, and formed between the back side the first conductive type semiconductor layer and the front side of the second conductive type semiconductor layer; a plurality DBR unit layers having a front side and a back side, and comprising a low refractive index layer and a high refractive index layer adjacent to the low refractive index layer; and a metal reflective layer having a front side and a back side, and formed on the back side of the plurality DBR unit layers, wherein an intermediate layer for improving ohmic contact, and formed between the back side of the plurality DBR unit layers and the front side of the metal reflective layer comprises silver.