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Your search keyword '"Rochat, Nevine"' showing total 19 results
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19 results on '"Rochat, Nevine"'

1. Effect of extended defects on AlGaN QDs for electron-pumped UV-emitters

Author

Cañas, Jesus, Rochat, Névine, Grenier, Adeline, Jannaud, Audrey, Saghi, Zineb, Rouviere, Jean-Luc, Bellet-Amalric, Edith, Harikumar, Anjali, Bougerol, Catherine, Rigutti, Lorenzo, and Monroy, Eva

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science
Abstract

We study the origin of bimodal emission in AlGaN/AlN QD superlattices displaying high internal quantum efficiency (around 50%) in the 230-300 nm spectral range. The secondary emission at longer wavelengths is linked to the presence of cone-like defects starting at the first AlN buffer/superlattice interface and propagating vertically. These defects are associated with a dislocation that produces strong shear strain, which favors the formation of 30{\deg} faceted pits. The cone-like structures present Ga enrichment at the boundary facets and larger QDs within the defect. The bimodality is attributed to the differing dot size/composition within the defects and at the defect boundaries, which is confirmed by the correlation of microscopy results and Schr\"odinger-Poisson calculations.

Published
2023
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2. AlGaN/AlN Stranski-Krastanov quantum dots for highly efficient electron beam pumped emitters: The role of miniaturization and composition to attain far UV-C emission

Author

Cañas, Jesus, Harikumar, Anjali, Purcell, Stephen T., Rochat, Nevine, Grenier, Adeline, Jannaud, Audrey, Bellet-Amalric, Edith, Donatini, Fabrice, and Monroy, Eva

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science
Abstract

Conventional ultraviolet (UV) lamps for disinfection emit radiation in the 255-270 nm range, which poses a high risk of causing cancer and cataracts. To address these concerns, solid-state far UV-C sources emitting below 240 nm are gaining attention as a safe and sustainable disinfection solution for occupied spaces. Here, we delve into the extension of the AlxGa1-xN/AlN quantum dot (QD) technology towards the far UV-C range, which presents various challenges associated with the reduction of the lattice mismatch and band offset when Al is incorporated in the QDs. We explore the structural and optical impact of increasing the Al content through the increase of the Al flux and eventual correction of the Ga flux to maintain a constant metal/N ratio. We also examine the impact of extreme miniaturization of the QDs, achieved through a reduction of their growth time, on the spectral behavior and internal quantum efficiency (IQE). The high Al content results in QDs with a reduced aspect ratio (height/diameter) and thicker wetting layer when compared to the GaN/AlN system. Self-assembled QDs grown with a metal/N ratio ranging from 0.5 to 0.8 show an IQE around 50%, independent of the Al content (up to 65%) or emission wavelength (300-230 nm). However, samples emitting at wavelengths below 270 nm exhibit a bimodal luminescence associated with inhomogeneous in-plane emission attributed to fluctuations of the QD shape associated with extended defects. Reducing the QD size exacerbates the bimodality without reducing the emission wavelength. The power efficiencies under electron beam pumping range from 0.4% to 1%, with clear potential for improvement through surface treatments that enhance light extraction efficiency., Comment: 31 pages, 7 figures, 4 tables

Published
2023
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15. Selective area growth of AlGaN nanopyramids by conventional and pulsed MOVPE.

Author

Boughaleb, Sofia, Martin, Brigitte, Matei, Constantin, Templier, Roselyne, Borowik, Łukasz, Rochat, Nevine, Gil, Bernard, and Dussaigne, Amélie

Subjects
METAL organic chemical vapor deposition, LIGHT emitting diodes
Abstract

Planar UV-C light emitting diodes still suffer from low efficiency, mainly due to substrate crystalline quality, p doped conductivity and extraction efficiency. One possible way to overcome partly these issues is to realize the whole UV structure on AlGaN pyramids by selective area growth in order to benefit from the advantages of such structures, i.e. the dislocation filtering and the semi polar planes. We present here a detailed study about the epitaxy of AlGaN nano-sized pyramids by metal organic vapor phase epitaxy on patterned templates presenting different holes apertures and pitches as 1.5 μm and 4 μm or 100 nm and 250 nm respectively. While increasing the Al content, their height decreases while the thickness of the deposition on the mask increases whatever the design of the mask. Those changes of the pyramid shapes and deposition are directly linked to the properties of Al adatoms, i.e. low Al diffusion length. Using the conventional growth mode for the epitaxy of those pyramids did not permit the incorporation of Al from the base of the pyramids to their truncated apex. Its presence was concentrated on the edges and top of the pyramids. On the contrary, a pulsed growth mode, coupled with a strongly reduced pitch, allowed an incorporation of Al since the base of the nanopyramid, and a decrease of the deposition height on the mask. These results can be explained by the desorption of Ga species, due to the presence of H2 in the reactor chamber during the step without the metal precursors, leading to a higher Al/Ga ratio. It is even enhanced inside the holes by the reduced pitch. [ABSTRACT FROM AUTHOR]

Published
2021
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