Monolithic Micro LED Precursor Growth Without Sidewall Etch Damage
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Solution Overview
Problem
Existing methods for forming Group III-nitride LEDs introduce defects into the sidewalls of micro LED structures, which reduce the external quantum efficiency (EQE), and the shape of the sidewalls is not well-controlled, affecting the light extraction efficiency.
Innovation Solution
A method is developed to form a monolithic LED precursor by selectively masking a semiconductor layer with a LED mask layer, defining apertures for LED wells, and growing the LED stack within these wells, ensuring the sidewalls conform to the mask layer, thereby avoiding etching-induced damage and allowing controlled sidewall shapes for improved EQE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reactive ion etching is used to define micro LED mesa structures, then the LED structures can be formed with defined geometry, but defects are introduced into the sidewall surfaces reducing external quantum efficiency
Solution Approach 1:
The patent removes the harmful etching step from the process entirely. Instead of forming mesas by etching away material, the invention uses selective area growth to grow LED structures only in desired locations through mask apertures, eliminating the source of sidewall defects while maintaining geometric definition
Solution Approach 2:
The patent inverts the conventional approach: rather than removing material to define structures (etching), material is selectively grown to define structures (selective area growth). This fundamental reversal eliminates etching-induced defects while achieving the same structural definition goal
2Reliability
If dielectric passivation layer is deposited over sidewall surfaces, then sidewall defects can be passivated to improve EQE, but additional process steps and device complexity are introduced
Solution Approach 1:
The patent performs preliminary action by preventing sidewall defect formation in the first place through selective area growth, rather than requiring subsequent passivation steps. The sidewalls are formed clean during growth, eliminating the need for additional dielectric deposition and simplifying the overall process
3Reliability
If selective area growth is used to form LED precursors, then sidewall defects are avoided, but the sidewall shape is determined by mask aperture rather than direct control
Solution Approach 1:
The mask layer serves as an intermediary that defines the initial growth region, while the selective area growth process itself becomes the mechanism for achieving clean sidewalls. The combination allows both defect-free formation and geometric control through the mask aperture design
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 method improves the external quantum efficiency of LEDs by reducing sidewall defects and enabling controlled sidewall geometries for enhanced light extraction, facilitating efficient fabrication without etching steps.
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
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 III-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 III-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 III-nitride, and a p-type semiconductor layer comprising a Group III-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.