Graphene Layer Light Extraction in LED Structures
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) suffer from low light extraction efficiency due to the higher refractive index of semiconductor materials compared to air, causing large-angle light to be internally reflected and trapped within the device.
Innovation Solution
A method for manufacturing LEDs that involves applying a patterned graphene layer with apertures on a substrate to expose the epitaxial growth surface, allowing for the growth of semiconductor epitaxial layers and the formation of electrodes and reflection layers, which enhances light extraction by scattering and redirecting light emitted from the active layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional LED structure with transparent P-type electrode is used, then electrical function is achieved, but light extraction efficiency is low due to internal reflection
Solution Approach 1:
A graphene layer is introduced as an intermediary between the active layer and the P-type electrode. This graphene layer serves as both an electrical conductor and an optical scattering medium, mediating between the electrical function requirement and the light extraction enhancement requirement
Solution Approach 2:
The graphene layer is configured with a porous or patterned structure containing apertures. This porous structure enables the graphene to scatter light effectively while maintaining electrical conductivity, converting the harmful internal reflection into useful light extraction paths
2Productivity
If semiconductor materials with high refractive index are used, then electrical and optical functions are achieved, but light is trapped within the LED due to refraction differences
Solution Approach 1:
The high refractive index of semiconductor materials, which causes light trapping, is converted into a benefit by introducing the graphene layer with apertures. The graphene structure creates additional light extraction paths that utilize the refractive index difference to scatter and redirect trapped light toward the exterior
Solution Approach 2:
The optical parameters at the interface between semiconductor and air are modified by introducing the graphene layer. The graphene's unique optical properties and aperture structure change the effective refractive index transition, reducing total internal reflection and enhancing 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 method significantly improves light extraction efficiency by scattering light emitted at large angles, allowing more light to be extracted from the LED, thereby enhancing its performance.
Implementation Method 1
a graphene layer which scatters light emitted from the active layer
Data Source
AI summary
A light emitting diode includes a substrate, graphene layer, a first semiconductor layer, an active layer, a second semiconductor layer, a first electrode, a second electrode, and a reflection layer. The first semiconductor layer, the active layer, and the second semiconductor layer are stacked on the substrate in sequence. The first electrode is electrically connected with the second semiconductor layer and the second electrode electrically is connected with the second part of the carbon nanotube layer. The graphene layer is located between the active layer and the second semiconductor layer. The reflection layer covers the second semiconductor layer.