LED Devices with Patterned Substrates and Selective Dielectric Layers
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Solution Overview
Problem
Light emitting diode (LED) devices with patterned sapphire substrates face limitations in light extraction efficiency due to trapped photons and broad angular emission patterns, which are exacerbated by side-coating materials that reduce light extraction efficiency and increase light trapping.
Innovation Solution
The implementation of a light emitting diode (LED) device with a patterned substrate featuring integral features and a selective dielectric layer on the surfaces of these features, but not on the base surface, allows for epitaxial growth of a III-nitride layer, enhancing light out-coupling and reducing absorption losses by using a low refractive index material like silicon dioxide for the dielectric layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If 3D features are packed closely together to maximize light out-coupling, then light extraction efficiency is improved, but it becomes difficult to grow a continuous GaN layer with a smooth surface
Solution Approach 1:
A dielectric material layer is introduced as an intermediary between the closely packed 3D features and the GaN layer. This intermediary layer enables the GaN to be deposited conformally on high-aspect-ratio structures without direct contact between adjacent GaN regions, preventing formation errors while maintaining high light extraction efficiency through the textured interface
Solution Approach 2:
The solution moves from a two-dimensional planar interface to a three-dimensional textured interface by depositing dielectric material conformally on vertical sidewalls of 3D features. This dimensional transition allows light extraction enhancement through angular diversity while maintaining manufacturability through conformal deposition processes
2Ease of operation
If side-coating materials are used to prevent light escaping from sides, then angular emission control is improved, but light extraction efficiency is significantly penalized due to increased light trapping
Solution Approach 1:
The harmful side-coating layer is completely removed from the device structure. Instead of using side-coats to control angular emission, the invention relies on the inherent directional emission properties of vertical LED structures and the optical confinement provided by the textured interface between the GaN layer and patterned substrate
Solution Approach 2:
The vertical sidewalls of the 3D features, which could potentially cause side emission, are converted into beneficial light-trapping structures through conformal dielectric coating. These textured sidewalls enhance light extraction for photons attempting to escape laterally, while the overall device geometry maintains narrow angular emission patterns
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 increases light extraction efficiency by allowing a wider range of incident angles to pass through, narrowing angular radiation patterns, and improving brightness by minimizing side emission and absorption losses, thereby enhancing the overall efficiency of the LED device.
Implementation Method 1
using a low refractive index material like silicon dioxide for the dielectric layer... allowing a wider range of incident angles to pass through
Implementation Method 2
most of the emitted photons are trapped inside the device due to a relatively small critical angle (∼45 deg.) for total internal reflection at the GaN/sapphire interface
Implementation Method 3
When a III-nitride material, such as GaN, is epitaxially-grown on a substrate... epitaxially growing a III-nitride layer therein
Data Source
AI summary
Light emitting diode (LED) devices comprise: a patterned substrate comprising a substrate body, a plurality of integral features protruding from the substrate body, and a base surface defined by spaces between the plurality of integral features; a selective layer comprising a dielectric material located on the surfaces of the integral features, wherein there is an absence of the selective layer on the base surface; and a III-nitride layer comprising a III-nitride material on the selective layer and the base surface.