Prof. Xuelun Wang | National Institute of Advanced Industrial Science and Technology (AIST): Can advanced etching techniques truly overcome the efficiency droop in small-footprint micro-LEDs?
03:19 - 07:16
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Summary of the clip:
Can advanced etching techniques truly overcome the efficiency droop in small-footprint micro-LEDs?
The neutral beam matching (NBM) technique was first applied to the fabrication of gallium nitride (GaN) micro-LEDs in 2019, demonstrating significant performance improvements. Devices, including 3.5 micron square blue GaN micro-LEDs, exhibited a remarkably high peak external quantum efficiency (EQE) of approximately 38%. Crucially, these NBM-fabricated devices showed a very slow decrease in EQE when the current density was reduced from the peak EQE point, indicating a substantial suppression of sidewall non-radiative recombination compared to conventional ICP processes.
Quantitatively, the EQE droop of NBM samples decreased with reducing chip size, reaching as low as about 26% for 3.5 micron devices. This result clearly indicates that sidewall non-radiative recombination is suppressed to a level that can be neglected compared with non-radiative recombination in the bulk material. In contrast, ICP devices showed an increase in EQE droop with decreasing chip size, confirming the strong existence of sidewall non-radiative recombination. This improved performance in NBM devices is further explained by the existence of strain relaxation near the mesa sidewall surface, which weakens the quantum-confined Stark effect (QCSE) and increases emission efficiency at low current densities.
In this short video, you can learn:
* The high peak EQE achieved with NBM-fabricated GaN micro-LEDs.
* The significant reduction in EQE droop at low current densities.
* A comparative analysis of NBM and conventional ICP etching performance.
* The mechanism of strain relaxation and its impact on QCSE and emission efficiency.
š **Clip Abstract** Neutral Beam Matching (NBM) significantly enhances micro-LED performance, achieving high EQE and dramatically reducing efficiency droop, particularly in smaller devices. This improvement is attributed to suppressed non-radiative recombination and strain relaxation near mesa sidewalls, which mitigates the quantum-confined Stark effect.
š Link in comments š
#NeutralBeamMatching, #GaNMicroLEDs, #EQEDroopSuppression, #SidewallRecombination, #MicroLEDs, #ARVRDisplays
This is a highlight of the presentation:
High-efficiency submicron GaN micro-LEDs fabricated by neutral beam etching
More Highlights from the same talk.
00:25 - 01:53
Why do conventional etching methods fundamentally limit micro-LED efficiency at critical operating conditions?
Why do conventional etching methods fundamentally limit micro-LED efficiency at critical operating conditions?
Micro-LEDs must be driven at low current densities, typically below a few amperes per square centimeter, to suppress heat generation during operation. However, fabricating sub-3 micron micro-LEDs with high efficiencies at these low current densities presents a significant challenge due to the pervasive issue of strong sidewall non-radiative recombination.
Conventional micro-LED fabrication often employs inductively coupled plasma (ICP) etching of GaN layers. This process generates a high density of defects on the sidewall surfaces, primarily due to ion bombardment and UV photon radiation. These defects substantially reduce emission efficiency, particularly as chip size decreases to the sub-3 micron region, and this efficiency decrease is especially pronounced at lower current densities where non-radiative recombination tends to dominate the overall recombination process.
In this short video, you can learn:
* The thermal management requirements for micro-LEDs.
* Challenges in achieving high efficiency at low current densities for sub-3 micron devices.
* The detrimental impact of conventional ICP etching on micro-LED performance.
* The role of sidewall defects and non-radiative recombination in efficiency degradation.
š **Clip Abstract** Micro-LEDs face significant efficiency challenges, especially at low current densities and small chip sizes, primarily due to defects introduced by conventional plasma etching. These defects lead to strong non-radiative recombination, hindering performance.
š Link in comments š
#ICPEtching, #GaNSidewallDefects, #NonRadiativeRecombination, #LowCurrentDensityEfficiency, #MicroLED, #SemiconductorEtching
01:54 - 03:15
How can we eliminate ion bombardment and UV radiation damage during micro-LED etching?
How can we eliminate ion bombardment and UV radiation damage during micro-LED etching?
To address the limitations of conventional plasma etching, a novel neutral beam matching (NBM) etching process has been developed. This technique incorporates two innovative concepts. First, the RF power for plasma discharge is supplied in a pulsed form, allowing for precise control over the plasma generation cycle.
Second, a carbon plate with a high aspect ratio aperture is strategically positioned between the plasma and the etching chamber. During the off-period of the RF power, electrons lose energy and attach to chlorine gas, which has a large electron affinity, resulting in the formation of negative ions. These negative ions are subsequently neutralized through charge exchange with the carbon plate as they pass through its aperture, which also effectively blocks UV photons. Consequently, only a beam of neutral particles is supplied to the sample surface for etching, enabling major low-damage etching of various materials.
In this short video, you can learn:
* The principles of Neutral Beam Matching (NBM) etching.
* The role of pulsed RF power in plasma discharge.
* How a carbon plate neutralizes ions and blocks UV photons.
* The mechanism for achieving low-damage etching for micro-LED fabrication.
š **Clip Abstract** Neutral Beam Matching (NBM) offers a solution to plasma etching damage by employing pulsed RF power and a carbon plate. This innovative process neutralizes ions and blocks UV photons, delivering a pure beam of neutral particles for ultra-low damage micro-LED fabrication.
š Link in comments š
#NeutralBeamMatching, #PulsedRFPlasma, #CarbonPlateAperture, #NeutralParticleEtching, #MicroLED, #SemiconductorEtching