Asymmetric Micro LED Mesa Structure for Current Confinement
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Solution Overview
Problem
Micro light emitting diodes (μ-LEDs) face issues such as red-shift, low maximum efficiency, and inhomogeneous emission due to high current density, nonradiative recombination at unoptimized quantum well sidewalls, and electron leakage, which decrease external and internal quantum efficiencies and lead to reliability concerns.
Innovation Solution
A micro LED structure is designed with a mesa structure featuring a first semiconductor layer, a light emitting layer, and a second semiconductor layer, where the top surface area of the second type semiconductor layer is greater than the first, and a sidewall protective and reflective layer is added to enhance light extraction efficiency and reduce crosstalk, along with an ion implantation region to manage current density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If space is formed between adjacent μ-LEDs to avoid carrier spreading, then carrier isolation is improved, but active light emitting area is reduced and light extraction efficiency decreases
Solution Approach 1:
The patent applies local quality by creating an asymmetric mesa structure where the second semiconductor layer has a larger top surface area than the first semiconductor layer. This local geometric modification allows carriers to be confined in the narrower lower region while providing sufficient light extraction area at the broader upper region, thus simultaneously achieving carrier isolation and maintaining large active light emitting area.
2Area of stationary object
If space between adjacent mesas is eliminated to increase active light emitting area, then active light emitting area is improved, but carrier spreading across adjacent mesas occurs and light emitting efficiency decreases
Solution Approach 1:
The asymmetric mesa structure creates a local geometric feature where the narrowing of the mesa towards the first semiconductor layer acts as a carrier confinement region. This local geometric modification provides sufficient carrier isolation without requiring spacing between adjacent mesas, thus achieving both large active area and good carrier confinement.
3Power
If quantum well sidewall area is reduced to improve current injection, then current injection is improved, but nonradiative recombination at sidewalls decreases and EQE/IQE decrease
Solution Approach 1:
The asymmetric mesa structure locally modifies the quantum well region by creating a narrower base, which reduces the sidewall area where nonradiative recombination occurs. This local geometric modification simultaneously improves current injection uniformity and reduces parasitic recombination losses, thereby increasing both internal and external quantum efficiencies.
Solution Approach 2:
The patent employs asymmetry by making the top surface area of the second semiconductor layer larger than that of the first semiconductor layer. This asymmetric geometry creates a tapered mesa structure that optimizes both current distribution and sidewall area, reducing nonradiative recombination while maintaining efficient current injection.
4Manufacturing precision
If chip size is decreased to achieve higher resolution, then resolution is improved, but peak EQE and IQE are greatly decreased due to poor current injection and electron leakage
Solution Approach 1:
The asymmetric mesa structure provides a locally optimized geometry for small-sized μ-LEDs. The narrower base region improves current confinement and injection uniformity, while the broader top region provides sufficient area for effective current injection, thereby reducing electron leakage and maintaining high quantum efficiencies even at reduced chip sizes.
Solution Approach 2:
The asymmetric design with different top surface areas for the two semiconductor layers creates an optimized current distribution pattern that is particularly beneficial for small-sized devices. This asymmetry helps prevent electron leakage and poor current injection that typically plague miniaturized LEDs, thereby maintaining high resolution with preserved quantum efficiency.
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 design improves light extraction efficiency, reduces red-shift and inhomogeneous emission, and enhances the reliability of μ-LEDs by optimizing the quantum well sidewall area and current injection, thereby increasing external and internal quantum efficiencies.
Implementation Method 1
a sidewall reflective layer formed on the surface of the sidewall protective layer
Implementation Method 2
an ion implantation region formed around the first type semiconductor region, the ion implantation region having a resistance higher than a resistance of the first type semiconductor region
Implementation Method 3
The top surface area of the second type semiconductor layer is made greater than a top surface area of the first semiconductor layer, the top surface area of the second type semiconductor layer is made greater than a bottom surface area of the second semiconductor layer
Data Source
AI summary
A micro light emitting diode (LED) structure, includes a mesa structure. The mesa structure further includes a first type semiconductor layer having a first conductive type, a light emitting layer formed on the first semiconductor layer, a second type semiconductor layer formed on the light emitting layer, the second type semiconductor layer having a second conductive type different from the first conductive type. The first type semiconductor layer further includes a first type semiconductor region and an ion implantation region formed around the first type semiconductor region, the ion implantation region having a resistance higher than a resistance of the semiconductor region.