arXiv subjects

Filipe Camarneiro

Publications and source records attributed to Filipe Camarneiro.

3 recordsLinked to original sources

arXiv2025

Widefield Quantum Sensor for Vector Magnetic Field Imaging of Micromagnetic Structures

Many spintronic, magnetic-memory, and neuromorphic devices rely on spatially varying magnetic fields. Quantitatively imaging these fields with full vector information over extended areas remains a major challenge. Existing probes either offer nanoscale resolution at the cost of slow scanning, or widefield imaging with limited vector sensitivity or material constraints. Quantum sensing with nitrogen-vacancy (NV) centers in diamond promises to bridge this gap, but a practical camera-based vector magnetometry implementation on relevant microstructures has not been demonstrated. Here we adapt a commercial widefield microscope to implement a camera-compatible pulsed optically detected magnetic resonance protocol to reconstruct stray-field vectors from microscale devices. By resolving the Zeeman shifts of the four NV orientations, we reconstruct the stray-field vector generated by microfabricated permalloy structures that host multiple stable remanent states. Our implementation achieves a spatial resolution of $\approx 0.52 ~μ\mathrm{m}$ across an $83~μ\mathrm{m} \times 83~μ\mathrm{m}$ field of view and a peak sensitivity of $ (828 \pm 142)~\mathrm{nT\,Hz^{-1}}$, with acquisition times of only a few minutes. These results establish pulsed widefield NV magnetometry on standard microscopes as a practical and scalable tool for routine vector-resolved imaging of complex magnetic devices.

quant-ph↗

arXiv2025

Impact of Surface Passivation on the Efficiency and High-speed Modulation of III-V GaAs/AlGaAs Nanopillar Array LEDs

III-V semiconductor nanolight sources with deep-subwavelength dimensions ($<<$1 $μ$m) are essential for miniaturized photonic devices such as nanoLEDs and nanolasers. However, these nanoscale emitters suffer from substantial non-radiative recombination at room temperature, resulting in low efficiency and ultrashort lifetimes ($<$100 ps). Previous works have predominantly studied surface passivation of nanoLEDs under optical pumping conditions, while practical applications require electrically driven nanoLEDs. Here, we investigate the influence of surface passivation on the efficiency and high-speed modulation response of electrically pumped III-V GaAs/AlGaAs nanopillar array LEDs. Surface passivation was performed using ammonium sulphide chemical treatment followed by encapsulation with a 100 nm silicon nitride layer deposited via low-frequency plasma-enhanced chemical vapour deposition. Time-resolved electroluminescence measurements reveal differential carrier lifetimes ($τ$) of ~0.61 ns for nanoarray LEDs with pillar diameters of ~440 nm, a record-long lifetime for electrically driven GaAs-based nanopillar arrays. Under low injection conditions, the devices exhibited carrier lifetimes of ~0.41 ns, indicating successful suppression of non-radiative effects and a low surface velocity, ranging from $S$~0.7$\times$10$^4$ cm/s to 2.7$\times$10$^4$ cm/s. This reveals a potential high internal quantum efficiency $IQE$~0.45 for our nanoLEDs operating under very high injection conditions, limited only by Auger recombination and self-heating effects at high current density. These miniaturized nanoLEDs with high radiative recombination efficiency and sub-ns modulation response pave the way for optical data communications, energy efficient optical interconnects, AR/VR displays, and neuromorphic computing applications.

physics.optics↗

arXiv2022

Surface Passivation of III-V GaAs Nanopillars by Low Frequency Plasma Deposition of Silicon Nitride for Active Nanophotonic Devices

Numerous efforts have been devoted to improve the electronic and optical properties of III-V compound materials via reduction of their nonradiative states, aiming at highly-efficient III-V sub-micrometer devices. Despite many advances, there is still a controversial debate on which combination of chemical treatment and capping dielectric layer can best reproducibly protect the crystal surface of III-Vs, while being compatible with readily available plasma deposition methods. This work reports on a systematic experimental study on the role of sulfide ammonium chemical treatment followed by dielectric coating in the passivation effect of GaAs/AlGaAs nanopillars. Our results conclusively show that the best surface passivation is achieved using ammonium sulfide followed by encapsulation with a thin layer of silicon nitride by low frequency plasma enhanced chemical deposition. Here, the sulfurized GaAs surfaces, the high level of hydrogen ions and the low frequency (380 kHz) excitation plasma that enable intense bombardment of hydrogen, all seem to provide a combined active role in the passivation mechanism of the pillars. We observe up to a 29-fold increase of the photoluminescence (PL) integrated intensity for the best samples as compared to untreated nanopillars. X-ray photoelectron spectroscopy analysis confirms the best treatments show remarkable removal of gallium and arsenic native oxides. Time-resolved micro-PL measurements display nanosecond lifetimes resulting in a record-low surface recombination velocity for dry etched GaAs nanopillars. We achieve robust, stable and long-term passivated nanopillar surfaces which creates expectations for remarkable high internal quantum efficiency (IQE>0.5) in nanoscale light-emitting diodes. The enhanced performance paves the way to many other nanostructures and devices such as miniature resonators, lasers, photodetectors and solar cells.

physics.optics↗