GaN Micro-LED Array Light Extraction via Mesa Reflection
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Solution Overview
Problem
Traditional LEDs face challenges in extracting emitted light due to total internal reflection and high absorption, especially in GaN-based LEDs with sapphire and silicon carbide substrates, which are difficult to shape mechanically, limiting light extraction efficiency and thermal management.
Innovation Solution
The design features a semiconductor material with a first surface forming a mesa structure to reflect light toward a second surface, which is shaped to allow light to escape at angles outside the critical range, and optionally includes a sub-mesa structure to enhance light extraction, potentially with a Fresnel lens and reflective layer for improved efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional cuboid-shaped LED structure is used, then manufacturing is simple, but light extraction efficiency is low due to total internal reflection and long path lengths
Solution Approach 1:
The LED chip is divided into multiple micro-LED elements arranged in an array, where each micro-LED has a reduced lateral dimension that allows light to escape before undergoing total internal reflection, thereby improving light extraction efficiency while maintaining manufacturability through standard fabrication processes
Solution Approach 2:
The invention transitions from a two-dimensional planar LED structure to a three-dimensional array of micro-LEDs with controlled aspect ratios, utilizing the vertical dimension to allow light escape paths that avoid total internal reflection while maintaining a planar footprint for manufacturing compatibility
2Loss of energy
If chip shaping is used to improve light extraction, then extraction efficiency increases, but the technique is not suitable for GaN-based LEDs with hard substrates that are difficult to shape mechanically
Solution Approach 1:
Instead of mechanically shaping the entire GaN chip, the invention segments the chip into micro-LED elements defined by photolithography and etching processes that are compatible with standard GaN fabrication, avoiding the need for mechanical shaping of hard substrates while achieving improved light extraction
Solution Approach 2:
The invention replaces mechanical chip shaping with semiconductor fabrication processes (photolithography, etching, deposition) that are chemically-based and compatible with GaN-based LEDs, eliminating the need for mechanical contact with hard substrates while achieving the desired micro-scale geometry for improved light extraction
3Loss of energy
If micro-LED array is used to reduce path length, then light extraction efficiency improves, but device complexity increases
Solution Approach 1:
The invention merges multiple micro-LED elements into a single integrated array structure that functions as one device, sharing common substrate, contact structures, and packaging, thereby achieving improved light extraction through the micro-LED geometry while minimizing the increase in overall device complexity through consolidation of common elements
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 light extraction efficiency by approximately a factor of two, allowing more light to escape and maintaining high optical flux per unit area, while also improving thermal management by reducing the need for thick sapphire substrates.
Implementation Method 1
Total internal reflection is a common problem for LED devices, as the refractive index of the substrate materials used is typically much greater than air, which typically surrounds the LED. This allows light to escape from only a very narrow range of escape angles (or critical angle range) around the normal to the exit surface.
Implementation Method 2
the first surface defines a first structure comprising the active layer and configured to reflect light emitted from the active layer toward the second surface
Implementation Method 3
the second surface defines a second structure configured to permit light incident on the second surface at an angle outside a critical angle range to the planar normal to pass therethrough
Data Source
Figure 1~2a
Figure 2b~3b
Figure 4~6
AI summary
An optical device and method for fabricating an optical device. The optical device comprising: a semiconductor material comprising an active layer configured to emit light when an electrical current is applied to the device and/or to generate an electrical current when light is incident on the active layer, wherein the semiconductor material comprises a first surface and an opposed second surface, from which light is emitted from and/or received by the device, and wherein the first surface defines a first structure comprising the active layer and configured to reflect light emitted from the active layer toward the second surface and/or to reflect light received by the device toward the active layer, and the second surface defines a second structure configured to permit light incident on the second surface at an angle outside a critical angle range to the planar normal to pass therethrough.