Multilayer Reflective Structure for LED Light Extraction
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Solution Overview
Problem
Flip-chip type LEDs face limitations in light extraction efficiency due to electrode pads absorbing light and inadequate insulation between contact electrodes, leading to reduced performance in large-sized illumination devices.
Innovation Solution
A semiconductor light emitting device with a multilayer reflective structure comprising alternately stacked dielectric layers with different refractive indices, which redirects light and provides electrical insulation between the contact electrodes and electrode pads, enhancing light extraction efficiency and insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrode pads are widely disposed on the mounting surface to ensure electrical connection, then electrical connectivity is improved, but light extraction efficiency deteriorates due to light absorption by the electrode pads
Solution Approach 1:
The electrode pad is divided into multiple segments arranged in a grid pattern, with transparent conductive material filling the gaps between segments. This segmentation reduces the continuous light-absorbing area while maintaining electrical connectivity through the distributed conductive network.
Solution Approach 2:
The electrode pad structure combines transparent conductive material with reflective material, creating a composite structure that simultaneously achieves electrical conductivity, light reflection (reducing absorption), and mechanical stability. The transparent conductive material allows light passage while conducting electricity, and the reflective material bounces absorbed light back.
2Reliability
If electrode pad area is increased to ensure insulation with contact electrodes of different polarity, then electrical insulation is improved, but light extraction efficiency deteriorates due to increased light absorption
Solution Approach 1:
The electrode pad uses transparent conductive material specifically in regions where insulation is needed, allowing light to pass through these insulating portions. The reflective material is strategically placed to provide insulation only where necessary while maintaining light extraction efficiency in other areas.
Solution Approach 2:
A transparent insulating layer is introduced between the electrode pad and the contact electrode to provide the necessary electrical insulation. This intermediary layer allows light to pass through while preventing electrical breakdown, eliminating the need to increase the electrode pad area for insulation purposes.
3Loss of energy
If reflective material is added to reduce light absorption by electrode pads, then light extraction efficiency is improved, but device complexity increases due to additional layers and materials
Solution Approach 1:
The reflective material is integrated directly into the electrode pad structure, combining the electrical conduction function and the light reflection function into a single composite element. This eliminates the need for separate reflective layers and reduces overall device complexity.
Solution Approach 2:
The electrode pad material is designed to perform multiple functions simultaneously: electrical conduction, light reflection, and structural support. This multi-functionality reduces the number of separate components needed, simplifying the overall device structure while improving light extraction efficiency.
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 increases light extraction efficiency and secures electrical insulation, improving the performance of semiconductor light emitting devices by reducing light absorption and ensuring effective electrical isolation.
Implementation Method 1
a multilayer reflective structure interposed between the first electrode pad and the second contact electrode and comprising a plurality of dielectric layers which have different refractive indices and are alternately stacked. The multilayer reflective structure is disposed on the light emitting structure to cover the light emitting structure overall and to redirect light traveling in an opposite direction of a substrate of the semiconductor light emitting device to a direction of the substrate.
Implementation Method 2
The multilayer reflective structure may form a distributed Bragg reflector in which a first dielectric layer having a first refractive index and a second dielectric layer having a second refractive index are alternately stacked. The first and second indices and thicknesses of the first and second dielectric layers of the multilayer reflective structure are adjusted to obtain a high degree of reflectivity with respect to a wavelength of light generated by the active layer.
Data Source
AI summary
Provided is a semiconductor light emitting device. The semiconductor light emitting device may include: a light emitting structure comprising a first conductivity-type semiconductor layer having an upper surface divided into first and second regions, an active layer and a second conductivity-type semiconductor layer sequentially disposed on the second region of the first conductivity-type semiconductor layer; a first contact electrode disposed on the first region of the first conductivity-type semiconductor layer; a second contact electrode disposed on the second conductivity-type semiconductor layer; a first electrode pad electrically connected to the first contact electrode and having at least a portion disposed on the second contact electrode; a second electrode pad electrically connected to the second contact electrode; and a multilayer reflective structure interposed between the first electrode pad and the second contact electrode and comprising a plurality of dielectric layers which have different refractive indices and are alternately stacked.