Photonic Crystal LED Extraction Efficiency
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) face limitations in extraction efficiency due to full reflection of light within the device, leading to absorption and reduced output, with existing methods like hemispherical lenses and rough surfaces facing manufacturing challenges and inefficiencies.
Innovation Solution
The introduction of a photonic crystal structure with a spatially-periodic refractive index arrangement, which enhances extraction efficiency by cutting off light movement in the plane direction and coupling light with modes outside the light cone, allowing for external extraction through diffraction, while maintaining desired electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional LED structures are used, then manufacturing is simple, but extraction efficiency is low due to full reflection of light within the device
Solution Approach 1:
The patent introduces a photonic crystal structure with periodic modulation in the vertical dimension (depth direction) to control light propagation. This dimensional approach creates a photonic bandgap that prevents light from propagating in the plane direction, forcing it to couple with external modes for extraction, thereby resolving the contradiction between manufacturing simplicity and extraction efficiency.
Solution Approach 2:
The patent modifies the refractive index parameter by introducing a photonic crystal layer with spatially-periodic refractive index arrangement. This parameter change creates conditions for photonic bandgap formation, enabling control over light movement and significantly improving extraction efficiency while maintaining manufacturing feasibility through standard semiconductor fabrication processes.
2Loss of energy
If light extraction structures are introduced to improve extraction efficiency, then light extraction is enhanced, but electrical characteristics may be compromised
Solution Approach 1:
The photonic crystal structure is implemented as a localized layer with specific periodicity and depth parameters, affecting only the optical properties in the light extraction region while leaving the bulk electrical properties of the LED structure unchanged. This local modification approach enhances extraction efficiency without compromising overall electrical characteristics.
3Loss of energy
If photonic crystal structure is used, then extraction efficiency increases up to 2.4 times, but device complexity increases
Solution Approach 1:
The patent addresses the complexity issue by confining the photonic crystal structure to a single vertical layer with controlled depth, rather than implementing complex three-dimensional structures. This dimensional simplification maintains the extraction efficiency benefits while reducing manufacturing complexity to a single etching and deposition process step.
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 approach significantly enhances extraction efficiency, achieving up to 2.4 times the conventional extraction efficiency, with the ability to adjust directionality and minimize absorption losses, making it a practical solution for improving LED performance.
Implementation Method 1
The introduction of a photonic crystal structure with a spatially-periodic refractive index arrangement, which enhances extraction efficiency by cutting off light movement in the plane direction and coupling light with modes outside the light cone, allowing for external extraction through diffraction
Data Source
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AI summary
A light emitting device is disclosed, which comprises: a reflective electrode (530); a semiconductor layer (510) over the reflective electrode, the semiconductor layer comprising a p-type semiconductor layer (513) disposed on the reflective electrode (530), a light emitting layer (512) disposed on the p-type semiconductor layer (513), and an n-type semiconductor layer (511) disposed on the light emitting layer (512); and a photonic crystal (520) disposed on the semiconductor layer (510), the photonic crystal (520) having an etching depth of λ/n or more, where "λ" represents a wavelength of light emitted from the light emitting layer (512) and "n" represents a refractive index of the semiconductor layer (510), wherein a distance (d) between the reflective electrode (530) and a center of the light emitting layer (512) is within the ranges represented by 0.65 λ/n to 0.85 λ/n or an odd multiple of λ/(4n).