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This project is a contribution to the development of high-brightness, mercury-free, 100% recyclable and high-gloss ultraviolet (UV) lamps for disinfection at 270 nm. The performance of AlGaN-based UV LEDs remains limited by carrier injection problems, due to the high activation energy of dopants in this material and the difficulties to implement ohmic contacts. To circumvent these problems, we propose to pump an active region based on AlGaN nanostructures with an electron beam. For investigating the active media for electron-pumped UV lamps for disinfection, two types of heterostructures are considered, namely AlGaN/AlN quantum dots (QDs) embedded in GaN nanowires (NWs) synthesized on Si(111) substrates and AlGaN/AlN QDs grown by the Stranski-Krastanov (SK) method on AlN-on-sapphire templates. These choices were based on the high internal quantum efficiency (IQE) that can be achieved in QDs thanks to the three dimensional confinement of carriers. The growth of all the structures was performed by plasma-assisted molecular beam epitaxy.The first stage of the work involved establishing the feasibility of QDs on NWs for this application. Structural and optical studies demonstrated that the QD dimensions were quite homogeneous along the 400-nm-long superlattice (SL), giving a single emission line tunable in the range from 340 to 258 nm. We demonstrated IQE levels higher than 60% at 340 nm at room temperature, decreasing when reducing the emission wavelength. At 270 nm, the IQE was around 30%. These values were obtained under low injection, but remain stable for pumping densities up to 200 kW/cm2. Under electron beam pumping, channeling effects due to the NW geometry can be compensated by increasing the active region length by 60% in comparison to planar layers. The external quantum efficiency under optical pumping provides promising results (3.42±0.55%).The second stage of the work involved studying AlGaN/AlN SK-QD SLs. It is demonstrated that by modifying the III/V ratio and/or the composition of the QDs, the peak emission wavelength can be tuned from 225 nm to 335 nm while keeping the IQE around 50% in the 250-335 nm range, and higher than 35% in the 225-250 nm range. The IQE of these nanostructures remain stable from low to high injection power densities up to 200 kW/cm2. An average power efficiency of 0.38% is measured for as-grown structures, and that without any treatment to improve the light extraction efficiency or thermal management. These results are very promising for the development of an efficient, environment friendly UV technology for disinfection.; Ce projet est une contribution au développement de lampes ultraviolettes (UV) à haute luminosité, sans mercure, 100 % recyclables et à haute brillance, pour la désinfection à 270 nm. Les performances des LED UV à base d'AlGaN restent limitées par des problèmes d'injection de porteurs, dus à la haute énergie d'activation des dopants dans ce matériau et aux difficultés de mise en œuvre des contacts ohmiques. Pour contourner ces problèmes, nous proposons de pomper une région active à base de nanostructures d'AlGaN avec un faisceau d'électrons. Pour étudier les milieux actifs des lampes UV à pompage électronique pour la désinfection, deux types d'hétérostructures sont considérés, à savoir les boîtes quantiques (BQs) AlGaN/AlN intégrées dans des nanofils (NFs) GaN synthétisés sur des substrats Si(111) et les BQs AlGaN/AlN développées par la méthode Stranski-Krastanov (SK) sur des matrices AlN sur saphir. Ces choix étaient basés sur la haute efficacité quantique interne (IQE) qui peut être atteinte dans les BQ grâce au confinement tridimensionnel des porteurs. La croissance de toutes les structures a été réalisée par épitaxie par jets moléculaires assistée par plasma.La première étape du travail a consisté à établir la faisabilité des BQ dans les NFs pour cette application. Des études structurelles et optiques ont démontré que les dimensions des BQs étaient assez homogènes le long du super-réseau (SR) de 400 nm de long, donnant une seule raie d'émission accordable dans la plage de 340 à 258 nm. Nous avons démontré des niveaux d'IQE supérieurs à 60% à 340 nm à température ambiante, diminuant lors de la réduction de la longueur d'onde d'émission. A 270 nm, l'IQE était d'environ 30 %. Ces valeurs ont été obtenues sous faible injection, mais restent stables pour des densités de pompage jusqu'à 200 kW/cm2. Sous pompage par faisceau d'électrons, les effets de canalisation dus à la géométrie NF peuvent être compensés en augmentant la longueur de la région active de 60 % par rapport aux couches planaires. L'efficacité quantique externe sous pompage optique donne des résultats prometteurs (3,42±0,55%).La deuxième étape du travail a consisté à étudier les SRs de BQs SK AlGaN/AlN. Il est démontré qu'en modifiant le rapport III/V et/ou la composition des BQs, la longueur d'onde d'émission maximale peut être réglée de 225 nm à 335 nm, tout en maintenant l'IQE autour de 50 % dans la gamme 250-335 nm, et plus de 35 % dans la gamme 225-250 nm. L'IQE de ces nanostructures reste stable des densités de puissance d'injection faibles jusqu'à 200 kW/cm2. Un rendement énergétique moyen de 0,38 % est mesuré pour les structures brutes de croissance, et cela sans aucun traitement pour améliorer l'efficacité d'extraction de la lumière ou la gestion thermique. Ces résultats sont très prometteurs pour le développement d'une technologie UV efficace et respectueuse de l'environnement pour la désinfection.

International audience; UV disinfection is receiving renewed attention due to the global pandemic, as an immediately deployable and cost-effective option. The common sources used for this application are low-pressure arc lamps, emitting at 254 nm and containing toxic mercury, which Europe is trying to phase out. Furthermore, this radiation is highly carcinogenic and cataractogenic, which represents a health hazard. Recently different replacements for mercury lamps have been proposed, e.g. excimer lamps that emit at 222 nm, supposedly harmless. However, most of the focus is now on AlGaN-based UV LEDs, with numerous advantages (fast on/off switching, longer lifetime, reduced ozone generation, wider wavelength selection). Yet the wall plug efficiency of commercial LEDs at  260 nm is WPE < 1%, far below that of mercury lamps, and drops dramatically at shorter wavelengths. Therefore, there is still a need and opportunity for alternative UV sources.This work proposes electron-beam pumped UV lamps as an alternative to LEDs to overcome issues related to doping, transport and contacting. This approach obviates the need for p-type doping and efficient and homogeneous carrier injection is achieved without an electron blocking layer. Furthermore, the WPE should not vary much over 210−350 nm. Here, we study the performance of AlGaN/AlN dots-in-a-wire [1] and Stranski-Krastanov quantum dot superlattices [2], whose UV emission can be tailored in the 230-330 nm range. The three-dimensional (3D) carrier confinement in such nanostructures results in high internal quantum efficiency (IQE = 50% on average) and promising external quantum efficiency (EQE up to 5% for as-grown structures). Studies conducted under operation conditions (high injection) show no degradation of the IQE for excitation power densities up to 1 MW/cm2, obtained by pumping with a pulsed Nd-YAG laser. With e-beam excitation, the emission efficiency remains stable up to 10 kV of acceleration voltage and 0.5 mA of injected current (current limit of our setup). E-beam pumping offers also an interesting alternative for the fabrication of UV lasers, highly demanded in the fields of medicine and biotechnology, as well as in 3D printing and non-line-of-sight communication. Today, this spectral range is covered by gas lasers (ArF, KrF, XeF) or lasers based on frequency conversion (Nd:YAG). III-nitride semiconductor laser diodes are promising candidates to provide an efficient semiconductor-based alternative, but current injection is a major problem for wavelengths shorter than 360 nm.For this application, advantages of the e-beam pumping include higher flexibility in the choice of materials for the active medium due to the absence of doping or electrical contacts, as well as higher radiative recombination efficiency since the electrons and holes generated by impact ionization share the same distribution in the active medium. This technology has enabled the fabrication of ZnSe-based pulsed lasers that emit up to 600 W at 535 nm. There are some studies of e-beam pumped UV lasers using AlGaN/GaN separate confinement heterostructures (SCH), but they are limited to pulsed electron beam excitation at cryogenic temperatures [3,4]. New device architectures are required with the prospect of achieving room temperature lasers. Here, we present a study of undoped AlGaN/GaN SCHs designed to operate under e-beam injection with an acceleration voltage  10 kV. We discuss the effect of spontaneous and piezoelectric polarization on the carrier diffusion and demonstrate that the performance is improved using an asymmetric graded-index separate-confinement heterostructure (GRINSCH).[1] H. Arkumar et al., Nanotechnology 31 505205 (2020).[2] I. Dimkou et al., Nanotechnology 31 204001 (2020).[3] T. Wunderer et al., IEEE Photonics Technology Letters 29 1344 (2017).[4] T. Hayashi et al., Scientific Reports 7 2944 (2017).