LED Reflective Contact via Segmented Metal-Dielectric Stack
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Solution Overview
Problem
Conventional LEDs suffer from low light-extraction efficiency due to total internal reflection and absorption, with existing reflective contacts being either too absorptive or complex to manufacture in high volumes at low cost, while maintaining low resistance and high reflectivity.
Innovation Solution
A multi-layer reflective stack comprising a transparent ohmic contact layer, a thick low-index dielectric layer for total internal reflection, and a distributed Bragg reflector, along with a metal layer for high reflectivity and low resistance contacts, which can be manufactured at low cost and high volumes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a thick metal layer is used for reflective contact, then reflectivity is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The reflective contact is segmented into multiple functional layers: a thin metal layer (50-200 nm) for electrical conductivity and a dielectric layer for optical reflection. This segmentation allows each layer to be optimized for its specific function, achieving high reflectivity without requiring a thick metal layer that would complicate manufacturing.
Solution Approach 2:
The invention uses a composite structure combining metal and dielectric materials. The metal layer (Al, Ag, Au, or their alloys) provides electrical conductivity and partial reflection, while the dielectric layer (SiO2, Si3N4, TiO2, or their combinations) provides enhanced optical reflection. This composite approach achieves superior overall performance compared to using a single thick metal layer.
2Ease of manufacture
If a simple metal contact is used, then manufacturing is easier, but light absorption increases and reflectivity decreases
Solution Approach 1:
By combining a thin metal layer with a dielectric layer, the structure achieves high reflectivity while maintaining manufacturing simplicity. The dielectric layer compensates for the light absorption of the metal, creating a composite contact that is both easy to manufacture and highly reflective.
Solution Approach 2:
The dielectric layer acts as an intermediary between the metal contact and the semiconductor substrate. It mediates the optical interaction by providing a high-refractive-index interface that enhances reflection, while the thin metal layer provides the necessary electrical contact. This intermediary layer reduces overall light absorption.
3Illumination intensity
If multiple metal layers are stacked to achieve high reflectivity, then light extraction efficiency is improved, but contact resistance increases
Solution Approach 1:
The contact structure is segmented into distinct functional zones: the metal layer provides electrical conduction with low resistance, while the dielectric layer handles optical reflection. This segmentation allows the metal layer to be kept thin (maintaining low contact resistance) while the dielectric layer provides the necessary optical performance.
Solution Approach 2:
Different regions of the contact structure have different properties optimized for their specific functions. The metal layer has high electrical conductivity for low contact resistance, while the dielectric layer has high refractive index for optical reflection. This local optimization achieves both low resistance and high light extraction efficiency.
4Ease of manufacture
If conventional reflective contacts are used, then manufacturing is simpler, but light extraction efficiency remains low due to absorption
Solution Approach 1:
The composite metal-dielectric contact structure achieves high light extraction efficiency by combining the advantages of both materials. The thin metal layer provides electrical contact while the dielectric layer provides optical reflection, together achieving high reflectivity with minimal absorption and simplified manufacturing.
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 extraction efficiency by achieving high reflectivity for light incident at all angles with low contact resistance and uniform current injection, balancing cost and performance.
Implementation Method 1
Light that reaches a semiconductor surface at angles greater than θC will experience total internal reflection. This light is reflected back into the LED chip where it can be absorbed within the chip or in metal contact layers that are attached to the chip.
Implementation Method 2
The reflector stack comprises a relatively thick, low-index dielectric film and a metallic layer. The reflector stack can be incorporated into a variety of light emitting devices, including light emitting diodes (LEDs).
Data Source
AI summary
A semiconductor device emitting light about a predetermined wavelength comprising a structure comprising a plurality of layers, sometimes referred to as a stack, providing low resistance, high reflectivity and ohmic contacts to at least one semiconductor material.