Amélie DUSSAIGNE | CEA-Leti: Can we break the 25% Indium limit in GaN to conquer the "Green Gap" and reach native Red microLEDs?
00:01:06.585 - 00:03:14.245
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Can we break the 25% Indium limit in GaN to conquer the "Green Gap" and reach native Red microLEDs?
Achieving monolithic red, green, and blue microdisplay integration on a single substrate requires tuning the Indium content of InGaN layers across the entire visible spectrum. However, a severe drop in external quantum efficiency occurs above 500 nanometers due to thermodynamic alloy instability, severe lattice mismatch, and high compressive strain. This mismatch triggers composition pulling and Indium surface segregation, capping Indium incorporation at just 25% when grown on traditional gallium nitride templates.
Furthermore, the polarization-induced internal electric field within traditional polar c-plane quantum wells dramatically reduces radiative recombination efficiency. To mitigate this quantum-confined Stark effect and prevent screening under high injection currents, quantum well thicknesses must be restricted to under 3 nanometers. To emit red light under these physical constraints, the Indium content must reach 35% on polar c-planes and up to 40% on semi-polar or non-polar planes.
These stringent parameters far exceed the thermodynamic limits of conventional GaN-on-sapphire epitaxy. This technical overview highlights the critical material science bottlenecks of InGaN microLED scaling, defining the structural boundaries that next-generation strain-engineered substrate architectures must bypass to achieve efficient native red emission.
In this short video, you can learn:
* Why lattice mismatch between InGaN and GaN limits Indium incorporation to a thermodynamic threshold of 25%.
* How the composition pulling effect and Indium surface segregation push Indium atoms out of the GaN matrix during growth.
* The structural requirements of maintaining quantum well widths below 3 nm with 35% to 40% Indium to minimize the quantum-confined Stark effect.
📋 **Clip Abstract** This clip outlines the thermodynamic and strain-induced limitations that restrict Indium incorporation in InGaN layers grown on conventional GaN templates. It establishes the critical material science criteria required to achieve efficient green-to-red microLEDs.
#InGaNEpitaxy, #GreenGap, #QuantumConfinedStarkEffect, #IndiumIncorporation, #MicroLEDDisplays, #ARMicrodisplays
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00:05:57.925 - 00:07:58.435
Why did CEA-Leti abandon planar InGaN growth on Graphene to embrace 3D Nanopyramids?
Why did CEA-Leti abandon planar InGaN growth on Graphene to embrace 3D Nanopyramids?
To bypass lattice-mismatch constraints and grow strain-free InGaN layers, researchers are leveraging 2D materials like graphene to enable Van der Waals epitaxy. The absence of dangling bonds and covalent surface polarization on graphene theoretically allows the growth of relaxed InGaN layers. However, growing a continuous planar InGaN thin film on pristine graphene via molecular beam epitaxy or metal-organic vapor-phase epitaxy has proven exceptionally difficult due to poor nucleation kinetics.
To overcome this nucleation barrier, CEA-Leti developed an in-situ patterning method that creates small, approximately 100-nanometer apertures in the graphene layer down to the underlying silicon carbide substrate. These nano-apertures act as localized nucleation centers, promoting the growth of highly ordered, c-axis-aligned InGaN cores that laterally expand over the graphene surface.
This hybrid approach successfully yields perfect 3D pyramidal nanostructures rather than defect-ridden planar films. By taking advantage of the high adatom diffusion length of Indium on graphene and lateral strain relaxation, the sidewalls of these pyramids form highly uniform InGaN quantum wells capable of wide wavelength tuning in a single epitaxy run.
In this short video, you can learn:
* The fundamental materials science behind using 2D graphene to enable strain-free Van der Waals epitaxy of InGaN.
* The technological challenges of planar InGaN growth on graphene and how in-situ patterning of 100 nm apertures solves the nucleation problem.
* How 3D lateral growth over graphene relaxes strain and allows high-quality multi-quantum well active regions.
📋 **Clip Abstract** This clip explains how CEA-Leti uses patterned graphene on silicon carbide to initiate localized nucleation of strain-free InGaN nanopyramids. It demonstrates a path toward high-efficiency active regions by exploiting Van der Waals epitaxy.
#VanDerWaalsEpitaxy, #InGaNNanopyramids, #GrapheneNucleation, #StrainRelaxation, #MicroLEDDisplays, #Optoelectronics
00:05:57.925 - 00:07:58.435
Why did CEA-Leti abandon planar InGaN growth on Graphene to embrace 3D Nanopyramids?
Why did CEA-Leti abandon planar InGaN growth on Graphene to embrace 3D Nanopyramids?
To bypass lattice-mismatch constraints and grow strain-free InGaN layers, researchers are leveraging 2D materials like graphene to enable Van der Waals epitaxy. The absence of dangling bonds and covalent surface polarization on graphene theoretically allows the growth of relaxed InGaN layers. However, growing a continuous planar InGaN thin film on pristine graphene via molecular beam epitaxy or metal-organic vapor-phase epitaxy has proven exceptionally difficult due to poor nucleation kinetics.
To overcome this nucleation barrier, CEA-Leti developed an in-situ patterning method that creates small, approximately 100-nanometer apertures in the graphene layer down to the underlying silicon carbide substrate. These nano-apertures act as localized nucleation centers, promoting the growth of highly ordered, c-axis-aligned InGaN cores that laterally expand over the graphene surface.
This hybrid approach successfully yields perfect 3D pyramidal nanostructures rather than defect-ridden planar films. By taking advantage of the high adatom diffusion length of Indium on graphene and lateral strain relaxation, the sidewalls of these pyramids form highly uniform InGaN quantum wells capable of wide wavelength tuning in a single epitaxy run.
In this short video, you can learn:
* The fundamental materials science behind using 2D graphene to enable strain-free Van der Waals epitaxy of InGaN.
* The technological challenges of planar InGaN growth on graphene and how in-situ patterning of 100 nm apertures solves the nucleation problem.
* How 3D lateral growth over graphene relaxes strain and allows high-quality multi-quantum well active regions.
📋 **Clip Abstract** This clip explains how CEA-Leti uses patterned graphene on silicon carbide to initiate localized nucleation of strain-free InGaN nanopyramids. It demonstrates a path toward high-efficiency active regions by exploiting Van der Waals epitaxy.
00:09:07.645 - 00:11:31.965
How did researchers achieve 45% Indium incorporation in MQWs with near-zero piezoelectric polarization?
How did researchers achieve 45% Indium incorporation in MQWs with near-zero piezoelectric polarization?
Characterization of the red-emitting InGaN nanopyramids reveals a unique strain-relaxation profile enabled by the 2D graphene interface. Deep inside the core of the nanostructures, Indium content transitions from 13% directly above the 100-nanometer graphene openings to 30% above the graphene itself. This structural relaxation of the core provides an ideal template for the subsequent growth of high-indium multi-quantum wells on the pyramid's semi-polar facets.
Using electron holography and strain mapping on transmission electron microscopy lamellas, CEA-Leti scientists confirmed a complete mitigation of the piezoelectric polarization. While traditional c-plane InGaN structures suffer from massive internal electric fields that degrade radiative recombination, the semi-polar sidewalls of these pyramids exhibit only mean inner potential differences, indicating a near-zero piezoelectric field.
This lack of internal polarization field allows the active layers to maintain highly stable and efficient red emission centered at 620 nanometers. The strain mapping reveals 5.5% deformation in the quantum wells, correlating to an unprecedented 42% to 45% Indium incorporation rate without generating structural defects.
In this short video, you can learn:
* How 100 nm graphene apertures allow core strain relaxation, permitting up to 30% Indium in the core template.
* The use of electron holography to prove the elimination of piezoelectric polarization on semi-polar nanopyramid facets.
* The structural verification of 42% to 45% Indium incorporation in the multi-quantum wells, enabling native red emission at 620 nm.
📋 **Clip Abstract** This clip presents a detailed TEM, strain-mapping, and electron holography analysis of red-emitting InGaN nanopyramids grown on graphene templates. It proves that semi-polar facets eliminate piezoelectric polarization fields while enabling up to 45% Indium incorporation in the quantum wells.
#InGaNNanopyramids, #GrapheneTemplates, #ElectronHolography, #PiezoelectricPolarization, #RedMicroLEDs, #ARDisplays