Faceted GaN LED Mesa for Photon Extraction
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) face inefficiencies in external photon emission due to internal reflection and reabsorption, with existing methods failing to effectively increase the fraction of photons emitted in a desired direction, particularly for blue light which requires high energy and is crucial for full-color and white light devices.
Innovation Solution
The method involves forming a light emitting diode with a Group III-nitride active structure mesa having faceted top surfaces and sidewalls along chemically developed indexed crystal planes, achieved through anisotropic wet etching using potassium hydroxide, which enhances light extraction by aligning crystal facets to optimize photon emission angles and reduce internal reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional LED structures are used, then manufacturing is simple, but external photon emission efficiency is low due to internal reflection and reabsorption
Solution Approach 1:
The patent applies curvature by forming the LED active structure into a mesa with rounded top corners and curved sidewalls rather than sharp angular features. This curvature modifies light propagation paths, reducing internal reflection at interfaces and enabling more photons to escape the device. The rounded geometry acts as a form of optical lensing that directs light outward more effectively.
Solution Approach 2:
The patent introduces dimensional complexity by creating a three-dimensional mesa structure with controlled corner rounding and sidewall curvature. This moves beyond conventional planar LED designs, utilizing vertical and lateral dimensional variations to manipulate light extraction. The rounded top corners specifically create additional light extraction pathways at the edges where total internal reflection typically traps photons.
2Illumination intensity
If blue light emission is achieved using Group III nitride materials, then full-color and white light applications are enabled, but internal reflection prevents photons from escaping the diode
Solution Approach 1:
The rounded top corners and curved sidewalls of the mesa structure modify the geometry at light-extraction interfaces. This curvature changes the angles at which photons encounter the semiconductor-air or semiconductor-lens interface, reducing the incidence of total internal reflection. By rounding corners rather than leaving them sharp, the design creates gradual transitions that facilitate photon escape.
Solution Approach 2:
The patent changes geometric parameters of the LED structure, specifically the radius of curvature at top corners and the profile of sidewalls. By adjusting these dimensional parameters, the light extraction efficiency is optimized for blue wavelengths from Group III nitride materials. The curvature radius becomes a critical parameter that controls the balance between maintaining structural integrity and maximizing photon emission.
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 increases the external emission of photons by aligning crystal facets to minimize internal reflection, thereby enhancing the visible output and efficiency of LEDs, particularly for blue light emission, making them more suitable for full-color and white light applications.
Implementation Method 1
The method comprises anisotropically wet etching the Group III-nitride light emitting active structure to form a faceted emitting surface and indexed crystal plane sidewalls
Implementation Method 2
achieved through anisotropic wet etching using potassium hydroxide
Implementation Method 3
enhances light extraction by aligning crystal facets to optimize photon emission angles and reduce internal reflection
Implementation Method 4
not every recombination-generated photon externally exits the physical diode... the photons are subject to competing factors including reabsorption and internal reflection
Implementation Method 5
A light emitting diode is a semiconductor photonic device that emits light upon the recombination of electrons and holes in the semiconductor material or material system
Data Source
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AI summary
A light-emitting diode (20) with improved light extraction is made by anisotropically etching the surface of a Group III nitride layer (33,35) to develop crystal facets on the group III nitride surface (24,32) in which the facets are along a small integer Miller index plane of the Group III nitride surface.