LED Epitaxial Layer with Microlenses for Light Extraction
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) face limitations in light emitting efficiency due to lattice mismatch, low thermal conductivity of substrates, and differences in refractive index, leading to reduced internal quantum efficiency and light emission issues.
Innovation Solution
The development of a light emitting diode (LED) device with a light emitting epitaxial layer and microlenses formed on a light transmissible substrate, where the microlenses are retained after partial removal of the substrate, enhancing light extraction efficiency and reducing current crowding effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional LED structure with planar surface is used, then the device is simple to manufacture, but light extraction efficiency is low due to refractive index difference between air and semiconductor
Solution Approach 1:
The patent applies spherical microlenses on the LED chip surface to improve light extraction. The curved spherical surfaces refract light differently than planar surfaces, reducing total internal reflection at the semiconductor-air interface. This curvature transformation increases the proportion of light that can escape from the LED, directly addressing the light extraction efficiency problem while maintaining compatibility with conventional manufacturing processes.
2Loss of energy
If epitaxial layers are grown on patterned sapphire substrate, then dislocation density is reduced and light emitting efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The patent segments the sapphire substrate into an array of spherical microlenses rather than maintaining a continuous patterned substrate. This segmentation approach reduces dislocation density by creating isolated growth regions while simplifying the manufacturing process compared to complex patterned substrates. The microlenses can be formed through simpler processes like spin coating and UV curing, reducing overall manufacturing complexity while maintaining the benefit of reduced dislocation density.
3Loss of energy
If sapphire substrate is removed using laser lift-off, then lateral current distribution and light emission are improved, but manufacturing process complexity and cost increase
Solution Approach 1:
The patent incorporates a sacrificial organic layer between the sapphire substrate and the LED epitaxial structure during the initial growth process. This preliminary action allows the substrate to be easily removed later through selective etching of the organic layer, avoiding the need for complex laser lift-off processes. The organic layer acts as a pre-planned release mechanism that simplifies the overall manufacturing process while achieving the same goal of substrate removal to improve current distribution and light 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 improves light emitting efficiency and uniformity by increasing light extraction and reducing absorption, resulting in enhanced performance and operational stability of the LED device.
Implementation Method 1
The microlenses are formed on the first surface and formed of a light transmissible substrate for epitaxial growth of the light emitting epitaxial layer
Implementation Method 2
a light emitting layer that is disposed between the first and second type semiconductor layers and spaced apart from the first and second surfaces. The light emitting layer emits light toward the first surface to exit therefrom
Implementation Method 3
epitaxially growing a light emitting layer on a first type semiconductor layer; epitaxially growing a second type semiconductor layer on the light emitting layer
Data Source
AI summary
A light emitting diode (LED) device includes a light emitting epitaxial layer having opposite first and second surfaces and a plurality of microlenses formed on the first surface. The light emitting epitaxial layer includes a first type semiconductor layer defining the first surface, a second type semiconductor layer defining the second surface, and a light emitting layer disposed between the first and second type semiconductor layers and spaced apart from the first and second surfaces. The microlenses are formed on the first surface and formed of a light transmissible substrate for epitaxial growth of the light emitting epitaxial layer. A method for manufacturing the light emitting diode device is also disclosed.