Nanowire LED Spacer Layer for Light Extraction
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Solution Overview
Problem
Micro-LED displays face challenges in achieving high light extraction efficiency due to total internal reflection issues caused by the high refractive index of semiconductor materials, which limits their power consumption and battery life in mobile devices compared to OLED displays.
Innovation Solution
The use of a spacer layer with a refractive index lower than the semiconductor materials, combined with textured surfaces on the nanowire LEDs, helps to reduce total internal reflections by acting as an index matching layer and providing light scattering locations, thereby enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If semiconductor materials with high refractive index are used for micro-LEDs, then light emission is achieved, but total internal reflection occurs which reduces light extraction efficiency
Solution Approach 1:
The patent introduces a spacer layer with intermediate refractive index (e.g., SiO2 with n=1.46) between the high refractive index semiconductor material (GaN with n=2.2-3.8) and the low refractive index air or encapsulant. This intermediary layer acts as a refractive index transition medium, reducing the abrupt refractive index mismatch that causes total internal reflection, thereby improving light extraction efficiency while maintaining the benefits of semiconductor LED materials
Solution Approach 2:
The patent modifies the refractive index parameter by introducing the spacer layer with a specific refractive index value (1.46 for SiO2) that is lower than the semiconductor material but higher than air. This parameter change creates a gradual refractive index transition, allowing more light to escape the semiconductor material without requiring a complete change of the semiconductor material itself
2Use of energy by stationary object
If micro-LED displays are used to reduce power consumption, then energy efficiency improves, but total internal reflection limits the achievable light extraction efficiency
Solution Approach 1:
The spacer layer serves as a mediator between the micro-LED structure and the external environment, providing a refractive index transition that improves light extraction efficiency. This allows micro-LED displays to achieve higher power efficiency by reducing the energy loss from total internal reflection, making them more reliable alternatives to OLED displays for low-power applications
3Loss of energy
If a spacer layer with lower refractive index is introduced, then total internal reflection is reduced, but device structure becomes more complex
Solution Approach 1:
The patent implements the spacer layer as a thin film structure that can be deposited conformally on the nanowire LED surface. This thin film approach adds minimal structural complexity while effectively providing the refractive index transition function. The spacer layer can be formed as a continuous coating that follows the nanowire geometry, avoiding the need for complex three-dimensional structures
Solution Approach 2:
The patent creates a composite structure by combining the semiconductor nanowire core with a dielectric spacer layer material (such as SiO2). This composite material approach allows the device to benefit from both the light-emitting properties of the semiconductor and the optical impedance matching properties of the dielectric spacer, achieving improved light extraction without requiring entirely new material systems
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 results in micro-LED displays that consume two-fold less power than OLED displays, providing approximately 8 additional hours of battery life and outperforming low power consumption CPUs, while maintaining high light extraction efficiency.
Implementation Method 1
total internal reflection issues caused by the high refractive index of semiconductor materials
Implementation Method 2
acting as an index matching layer
Implementation Method 3
providing light scattering locations, thereby enhancing light extraction efficiency
Data Source
AI summary
Embodiments described herein comprise micro light emitting diodes (LEDs) and methods of forming such micro LEDs. In an embodiment, a nanowire LED comprises a nanowire core that includes GaN, an active layer shell around the nanowire core, where the active layer shell includes InGaN, a cladding layer shell around the active layer shell, where the cladding layer comprises p-type GaN, a conductive layer over the cladding layer, and a spacer surrounding the conductive layer. In an embodiment, a refractive index of the spacer is less than a refractive index of the cladding layer shell.