Mesa Sidewall Epitaxy for Strain-Tunable Micro-LED Efficiency
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Solution Overview
Problem
Micro-LEDs face efficiency losses due to non-radiative recombination at the sidewalls, particularly due to defects and high surface-to-volume ratio, which reduces internal and external quantum efficiency, and existing manufacturing processes are not suitable for producing high-efficiency micro-LEDs with desired color performance and longevity.
Innovation Solution
The formation of epitaxial layers over the sidewalls of the LED mesa through mesa sidewall epitaxy (MSE) reduces non-radiative recombination by using semiconductor materials with a wider bandgap, and inducing tensile or compressive strain to modify light emission characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the size of LEDs is reduced to micro-LED scale, then pixel density for high resolution is improved, but efficiency losses due to surface recombination increase
Solution Approach 1:
The patent applies local quality by forming a dielectric layer specifically at the mesa sidewalls where non-radiative recombination occurs. This localized treatment addresses the surface recombination problem at the critical sidewall region without affecting the bulk active region, thereby improving overall device efficiency while maintaining the micro-LED's high pixel density capability
Solution Approach 2:
The dielectric layer acts as an intermediary between the semiconductor mesa sidewall and the external environment. It passivates the sidewall surface, preventing charge carrier interaction with defect states and reducing non-radiative recombination, thus mitigating efficiency losses in scaled-down micro-LED structures
2Ease of manufacture
If traditional LED manufacturing processes are used, then manufacturing simplicity is maintained, but color performance and device longevity are insufficient
Solution Approach 1:
The patent implements preliminary action by forming the dielectric layer on the mesa sidewalls before completing the micro-LED fabrication process. This early passivation step prevents sidewall degradation and non-radiative recombination throughout subsequent processing, ensuring improved device longevity and color performance are achieved without complicating the overall manufacturing workflow
3Shape
If mesa etching is performed, then LED structure formation is achieved, but non-radiative recombination increases due to defects and dangling bonds
Solution Approach 1:
The patent converts the harmful effect of mesa etching (creation of defects and dangling bonds) into a beneficial outcome by subsequently forming a dielectric passivation layer on the etched sidewalls. This layer neutralizes the harmful defects created during etching, transforming the previously harmful sidewall surface into a protective interface that reduces non-radiative recombination while maintaining the necessary LED mesa structure
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 enhances the quantum efficiency of micro-LEDs by reducing non-radiative recombination and allowing for tunable light emission characteristics, improving both efficiency and reliability.
Implementation Method 1
forming one or more epitaxial layers over the sidewalls of an LED mesa such that the epitaxial layer(s) induce a predetermined amount of tensile or compressive strain along the sidewalls
Implementation Method 2
non-radiative recombination of charge carriers at and/or near the sidewalls of an LED mesa is a major contributor to reduced internal quantum efficiency
Data Source
AI summary
A light-emitting diode (LED) device can include a mesa with a sidewall encompassing a first semiconductor layer, a second semiconductor layer, and an active region between the first semiconductor layer and the second semiconductor layer. The first semiconductor layer and the second semiconductor layer are oppositely doped. The active region includes a quantum well. The LED device can further include at least one epitaxial layer grown over the sidewall of the mesa. The at least one epitaxial layer comprises a semiconductor material having a wider bandgap than a semiconductor material of the quantum well and is configured to induce compressive or tensile strain in the quantum well. The compressive or tensile strain causes a bandgap of a peripheral portion of the quantum well to differ from a bandgap of a central portion of the quantum well, thereby tuning an emission profile (e.g., wavelength and/or intensity) of the LED device.