Transparent Conductive Layer Design for LED Light Extraction
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) face challenges with opaque electrodes that reduce visibility, high material costs, and operation instability due to indium tin oxide (ITO) used in transparent electrode layers, which also lead to increased light absorption and contact resistance issues.
Innovation Solution
A light emitting diode design featuring a transparent conductive layer with a first and second transparent conductive layer of different thicknesses and electrical conductivities, incorporating a distributed Bragg reflector (DBR) layer and impurity doping to facilitate current spreading and improve light extraction efficiency, while using zinc oxide (ZnO) to reduce material costs and enhance electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick transparent electrode layer is formed using ITO, then electrical conductivity is improved, but light transmittance decreases and light absorption increases
Solution Approach 1:
The patent divides the transparent electrode into multiple layers with different materials and thicknesses. The first transparent electrode layer (closer to semiconductor) has higher conductivity, while the second transparent electrode layer (closer to observer) has higher transmittance. This segmentation allows each layer to optimize for its specific function, resolving the contradiction between overall conductivity and light transmittance.
Solution Approach 2:
Different regions of the transparent electrode structure are assigned different material properties. The first transparent electrode layer uses material with higher conductivity (even if slightly more absorbing), while the second layer uses material optimized for transmittance. This local differentiation of quality allows the system to achieve both high overall conductivity and high overall transmittance simultaneously.
2Loss of energy
If a thin transparent electrode layer is formed using ITO, then light transmittance is improved, but contact resistance becomes unstable and operation voltage increases
Solution Approach 1:
The patent segments the electrode function across two layers: the first layer provides stable ohmic contact with the semiconductor (ensuring low and stable contact resistance), while the second layer provides high transmittance. This segmentation resolves the contradiction by assigning contact stability to the first layer and transmittance to the second layer.
Solution Approach 2:
The first transparent electrode layer acts as an intermediary between the semiconductor layer and the second transparent electrode layer. It provides a stable, conductive interface that ensures reliable contact, while allowing the second layer to optimize for transmittance without compromising contact stability.
3Reliability
If ITO is used as transparent electrode material, then transparency and electrical conductivity are achieved, but material cost increases and operation stability decreases due to reducing properties in hydrogen plasma
Solution Approach 1:
The patent replaces expensive ITO (containing indium) with zinc oxide (ZnO), which uses abundant and inexpensive zinc. ZnO provides comparable or superior electrical conductivity and transparency, while being significantly cheaper and more stable in hydrogen plasma environments. This substitution directly addresses both cost and stability issues.
Solution Approach 2:
The patent uses composite material structure with two different transparent electrode materials (first and second transparent electrode layers) to achieve optimal performance. This composite approach allows selection of materials based on specific requirements (conductivity, transmittance, cost, stability) for each layer, rather than relying on a single expensive material like ITO for both functions.
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 reduces sheet and contact resistance, lowers operation voltage, and enhances luminous efficacy by evenly spreading electric current and improving light extraction efficiency, while being cost-effective and stable.
Implementation Method 1
a first transparent conductive layer formed on the second semiconductor layer and a second transparent conductive layer formed on the first transparent conductive layer and having different electrical conductivity than the first transparent conductive layer
Implementation Method 2
incorporating a distributed Bragg reflector (DBR) layer
Data Source
AI summary
A light-emitting diode includes, a semiconductor stack including a first semiconductor layer, a second semiconductor layer, and an active layer. The light-emitting diode also includes a transparent conductive layer including a first transparent conductive layer disposed on the second semiconductor layer and a second transparent conductive layer disposed on the first transparent conductive layer. The second transparent conductive layer has a conductivity different than the first transparent conductive layer.