Nanofils AlxGa1-xN et AlN pour la réalisation de diodes émettant dans l'UV-C

Because of their band gap value extending from 0.68 eV (for InN) up to 3.5 eV (GaN) and 6.2 eV (AlN), nitride family is potentially well adapted to the realization of light emitting diodes (LEDs) or detectors in a wavelength range spanning from infrared to ultraviolet. In particular, the possibility to realize devices emitting in the UV C range (200-280 nm) is a current subject of interest, in relation with numerous applications such as air and water sanitization, counterfeiting detection, sensors etc… Contrary to the visible LEDs which exhibit an excellent efficiency (at least for blue emission, which, coupled to a yellow phosphor is at the base of standard white LEDs currently available on the market), UV LEDs efficiency is currently limited to a few percent, as a consequence of the lack of suitable substrates, which results in defective material, and of doping difficulties, which limit current injection. One innovative solution to overcome these difficulties consists of using nanowires (NWs): the remarkable geometry (small diameter) and aspect ratio (height/diameter) of these objects make them favorable to the realization of heterostructures free of extended defects, therefore limiting carrier non radiative recombination. Furthermore, as a major advantage, electrical doping of NWs (type n with Si, type p with Mg) is considerably eased in NWs, as a result of an improved elastic strain relaxation, which significantly pushes away the dopant incorporation limit to values higher than in 2D layers used for conventional UV LEDs to date. The combination of these advantages make UV emitting NWs a subject of intense interest, with the prospect of realizing a breakthrough in efficiency. We are partially funded by an ANR project to explore this road. In this context, the proposed PhD project will consist of growing and fully characterizing the structural and optical properties of AlxGa1-xN/ AlyGa1-yN / AlxGa1-xN NW heterostructures (cathodo- and photo-luminescence, high resolution electron microscopy, atom probe and Kelvin probe measurement, etc…) with the prospect of realizing innovative, highly efficient UV LEDs in the range 240-270 nm. The process of the final structures and their electrical characterization will be performed by CNRS-Néel, after deposition of a doped-diamond upper contact. The work will be mostly performed in the Nanophysics and semiconductor CNRS/CEA group in CEA-INAC, which has an internationally recognized expertise in the academic studies on nitride materials, in close collaboration with several academic groups in France and abroad (CNRS-Néel, CNRS-LPS, University of Valencia….).La thèse sera consacrée à la croissance par épitaxie par jets moléculaires d’hétérostructures AlGaN/GaN de type filaire, incluant leur dopage de type n et de type p. La caractérisation des propriétés structurales et optiques de ces hétérostructures sera menée à bien en combinant des expériences de microscopie électronique à balayage, de spectroscopie de la photoluminescence, de diffraction de RX. Dans le cadre d’un partenariat national et international, des études de nanocathodoluminescence à haute résolution et de Kelvin probe seront également menées. Finalement, on réalisera des structures complètes de LEDs émettant dans la gamme de l’UV C (environ 250-280 nm), en collaboration étroite (dans le cadre d’un projet ANR) avec le CNRS/Institut Néel qui prendra en charge le dépôt d’une électrode conductrice en diamant, l’étape de processing et les caractérisations électriques