Monolithic Micro LED Wells for Etch-Free Sidewall Formation
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Solution Overview
Problem
Existing methods for forming micro LED arrays with Group III-nitrides introduce defects into sidewall surfaces during the etching process, which reduces the external quantum efficiency (EQE) of the LEDs due to increased sidewall surface area to volume ratio.
Innovation Solution
A method involving selective masking with a LED mask layer to form a monolithic LED stack without etching, where the LED stack sidewalls conform to the mask layer sidewalls, eliminating etching-induced damage and allowing for controlled sidewall geometry to enhance EQE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If reactive ion etching is used to define micro LED mesa structures, then individual micro LED structures can be formed, but defects are introduced into the sidewall surfaces reducing external quantum efficiency
Solution Approach 1:
The patent extracts and removes the harmful etching step from the fabrication process. Instead of using reactive ion etching to define micro LED mesa structures, the invention uses selective area growth to directly form LEDs with vertical sidewalls, eliminating the source of sidewall defects and charge trapping sites that reduce external quantum efficiency
Solution Approach 2:
The patent inverts the conventional fabrication approach by growing the LED structure selectively in desired locations rather than forming complete structures and then etching them down. This selective area growth method grows LEDs only where mask apertures are present, creating vertical sidewalls without etching-induced damage
2Power
If surface dimensions are reduced to micro LED sizes, then higher current density and optical power density are achieved, but the ratio of perimeter to surface area increases causing sidewall defects to have more significant effect on EQE
Solution Approach 1:
The patent applies local quality by creating micro LEDs with vertically oriented sidewalls that have different crystallographic orientation and surface properties compared to conventional etched sidewalls. This local structural difference reduces the impact of sidewall surface area on charge trapping and improves external quantum efficiency despite the high perimeter-to-area ratio inherent in micro LED dimensions
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 improves the external quantum efficiency of micro LEDs by reducing sidewall damage and enabling efficient, economic fabrication with controlled sidewall geometries that enhance light extraction and collimation.
Implementation Method 1
selectively masking the first semiconductor layer with a LED mask layer, the LED mask layer comprising an aperture defining a LED well through a thickness of the LED mask layer
Implementation Method 2
selectively forming a monolithic LED stack within the LED well on the unmasked portion of the first semiconductor layer
Data Source
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AI summary
A method of forming a monolithic LED precursor is provided. The method comprises: providing a substrate having a top surface; forming a first semiconductor layer comprising a Group Ill-nitride on the top surface of the substrate; selectively masking the first semiconductor layer with a LED mask layer, the LED mask layer comprising an aperture defining a LED well through a thickness of the LED mask layer to an unmasked portion of the first semiconductor layer, the LED well comprising LED well sidewalls extending from a top surface of the first semiconductor layer to a top surface of the LED mask layer; and selectively forming a monolithic LED stack within the LED well on the unmasked portion of the first semiconductor layer. The monolithic LED stack comprises a n-type semiconductor layer comprising a Group Ill-nitride formed on the first semiconductor layer, an active layer formed on the first semiconductor layer comprising one or more quantum well sub-layers, the active layer comprising a Group Ill-nitride, and a p-type semiconductor layer comprising a Group Ill-nitride formed on the second semiconductor layer. The LED stack sidewalls of the monolithic LED stack extend from the top surface of the first semiconductor layer conform to the LED well sidewalls of the LED mask layer.