Vertical LED with Self-Assembled Photonic Nanostructures
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Solution Overview
Problem
Conventional vertical light emitting diodes (VLEDs) face challenges in enhancing light extraction efficiency due to surface roughening techniques that can cause cracking and have low throughput, and the use of expensive methods like electron beam lithography, while also being limited by high defect density on bulk Si substrates and costly sapphire substrate removal processes.
Innovation Solution
A method of fabricating VLEDs with generally ordered photonic nanostructures using a self-assembled template of block copolymer reverse micelles, which acts as a mask for forming pillar-type nanostructures on the surface of the LED, enhancing light extraction efficiency without causing structural damage and allowing for cost-effective production on large substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the top surface of the LED structure is roughened or patterned after layer transfer to enhance light extraction efficiency, then light extraction efficiency is improved, but the transferred LED structure cracks due to thermal expansion mismatch between the LED structure and conducting substrate
Solution Approach 1:
The photonic nanostructures are formed on the LED structure before the layer transfer process, not after. This preliminary formation of nanostructures on the sapphire substrate avoids subsequent high-temperature processing that would cause thermal stress and cracking during or after transfer to the conducting substrate.
Solution Approach 2:
The conventional sequence is inverted: instead of transferring the LED structure first and then forming photonic structures, the photonic nanostructures are formed first on the growth substrate, followed by the layer transfer process. This reversal eliminates the thermal stress problem.
2Ease of manufacture
If expensive techniques such as electron beam lithography are used to pattern the top surface, then light extraction efficiency is improved, but the fabrication throughput is reduced
Solution Approach 1:
A self-assembled monolayer is formed on the LED structure, which automatically creates a regular pattern of nanoscale features without requiring expensive lithography equipment. This self-organizing process enables high-throughput fabrication while achieving the desired photonic structures for enhanced light extraction.
3Power
If simple dry etching is used to roughen the top surface, then light output is increased, but light extraction efficiency deteriorates due to lack of ordering in the patterns formed
Solution Approach 1:
The self-assembled monolayer spontaneously forms an ordered, periodic pattern of nanoscale features through self-organization. This regular structure provides the photonic crystal effect needed for enhanced light extraction efficiency, unlike the disordered patterns from conventional roughening methods.
Solution Approach 2:
The mechanical/chemical etching process is replaced by a self-assembly process where molecules spontaneously organize into ordered structures. This substitution creates regularly spaced photonic features without requiring aggressive etching that damages the surface.
4Illumination intensity
If sapphire substrates are used for growing GaN-based LED structure, then high brightness LEDs can be produced, but the removal of expensive sapphire substrate through laser lift-off increases production cost and limits substrate size to 6 inch
Solution Approach 1:
The expensive sapphire substrate removal step is eliminated entirely. The LED structure is grown on a sacrificial substrate that is chemically removed through selective etching, and the LED is directly transferred to a conducting substrate without requiring laser lift-off processing.
Solution Approach 2:
A sacrificial substrate is used instead of expensive sapphire. This disposable substrate serves its purpose during growth and is then easily removed through selective chemical etching, replacing the costly and complex laser lift-off process.
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 approach significantly improves light extraction efficiency, achieving higher luminance efficacy compared to conventional VLEDs, with reduced defect density and lower production costs, enabling high-throughput production of high-brightness LEDs on large substrates.
Implementation Method 1
forming a self-assembled template comprising generally ordered nanoparticles on said surface of the first material layer to function as a mask for forming the photonic nanostructures
Implementation Method 2
a plurality of generally ordered photonic nanostructures at a surface of the first material layer through which light generated from the light emitting layer is emitted for enhancing light extraction efficiency
Data Source
AI summary
There is provided a method of fabricating a vertical light emitting diode which includes forming a light emitting diode structure. Forming the light emitting diode structure includes: forming a first material layer of a first conductivity type, forming a second material layer of a second conductivity type, forming a light emitting layer between the first material layer and the second material layer, and forming a plurality of generally ordered photonic nanostructures at a surface of the first material layer through which light generated from the light emitting layer is emitted for enhancing light extraction efficiency of the vertical light emitting diode. In particular, forming a plurality of generally ordered photonic nanostructures includes forming a self-assembled template including generally ordered nanoparticles on the surface of the first material layer to function as a mask for forming the photonic nanostructures at said surface of the first material layer. There is also provided a vertical light emitting diode with the self-assembly derived ordered nanoparticles.