Elongate Light Extracting Elements for LED Efficiency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Light emitting diodes (LEDs) face inefficiencies due to trapped photons within high refractive index materials, leading to reduced light extraction and overall performance in solid-state lighting applications, particularly in vertical type n-p contact configurations where optically lossy metal contacts exacerbate the issue.
Innovation Solution
A light emitting device with a network of elongate indentations or etches on the top surface, known as elongate light extracting elements (ELEE), which are designed to couple light out of the device and modify the far field emission profile by extending orthogonally without penetrating the light emitting region, thereby enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If light emitting devices use high refractive index epi-material to achieve high brightness and efficiency, then internal quantum efficiency and injection efficiency are improved, but light extraction efficiency deteriorates due to total internal reflection and trapped photons
Solution Approach 1:
The patent introduces periodic texturing on the LED interface to create a multi-dimensional light extraction pathway. The textured surface with periodic patterns (gratings, ridges, or grooves) adds a spatial dimension to light extraction, enabling photons to escape through diffraction and scattering effects that operate in addition to the conventional vertical extraction path, thereby overcoming the limitations of total internal reflection in high refractive index materials
Solution Approach 2:
The patent modifies the physical parameters of the LED interface by introducing periodic structures with specific pitch, depth, and geometry. These parameter changes alter the optical properties of the interface, creating conditions for enhanced light extraction through diffraction orders and modified escape cones, directly addressing the light trapping problem while maintaining the high refractive index benefit
2Power
If vertical type n-p contact configuration is adopted to improve current and thermal driving capabilities, then electrical and thermal performance are improved, but light extraction efficiency deteriorates due to optically lossy metal contacts in close vicinity of light emitting heterostructure
Solution Approach 1:
The patent extracts or removes the problematic metal contacts from the immediate vicinity of the light emitting heterostructure. By separating the metal contacts from the active light emitting region, the design eliminates the primary source of optical losses while preserving the vertical current path configuration that provides excellent electrical and thermal performance
Solution Approach 2:
The patent introduces periodic texturing as an intermediary structure between the metal contacts and the light emitting heterostructure. This intermediary textured interface serves to redirect and extract light before it reaches the lossy metal contacts, acting as a protective layer that maintains both the electrical performance of vertical contacts and the optical efficiency by preventing photon absorption in the metal
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
The ELEE elements significantly improve light extraction efficiency by allowing more light to be emitted on the first pass, reducing recombination rates of trapped photons, and achieving higher luminous output while maintaining high wall plug efficiency.
Implementation Method 1
The elongate light extracting elements (ELEE) are designed to couple light out of the device... improve light extraction efficiency by allowing more light to be emitted on the first pass
Implementation Method 2
One of the main limiting factors reducing the extraction efficiency in LEDs is the emitted photons being totally internally reflected and trapped in the high refractive index of the epi-material
Implementation Method 3
These trapped waveguide-modes propagate in the LED structure until they are scattered, escape or reabsorbed
Data Source
AI summary
A light emitting device having a plurality of light extracting elements defined on an upper surface of a semiconductor layer of the device, wherein the light extracting elements are adapted to couple light out of the device and to modify the far field emission profile of the device. Each element comprises an elongate region having a length at least twice its width and also greater than the effective dominant wavelength of light generated in the device. The elongate region extends orthogonal to the upper surface but not into the light emitting region of the device and may be oriented at an angle of less than 45° relative to one of a pair of basis axis defining a plane parallel to the semiconductor layer. Each elongate region is spatially separated from neighboring elongate regions such that it perturbs light generated in the light emitting region independently of the neighboring regions.