Rare earth-doped aluminum nitride thin films for optical applications

Ce projet est consacré à l'étude des propriétés optiques des films minces en nitrure d'aluminium dopé par des terres rares. Plus particulièrement, le travail est orienté pour étudier les mécanismes de luminescence des éléments RE sélectionnés incorporés dans des films minces AlN pour être utilisés comme candidats aux dispositifs d'éclairage. Au cours de cette thèse, la technique de pulvérisation de magnétron réactif est utilisée pour synthétiser les films minces AlN non dopés et dopés. La technique et le traitement des films sont discutés en détail. L'effet des conditions de pulvérisation sur la structure et les propriétés optiques des films préparés est étudié. La corrélation entre les conditions de pulvérisation cathodique, l'orientation cristallographique, la morphologie, la microstructure et les propriétés optiques sont établies. Les analyses de structure et de composition des échantillons préparés ont été étudiées par plusieurs moyens, tels que la microscopie électronique à transmission, la spectroscopie à rayons X à énergie dispersive et la spectrométrie de rétrodiffusion Rutherford. Les propriétés optiques des films sont caractérisées par une transmission UV-Visible, une spectroscopie d'Ellipsometry et une spectroscopie de photoluminescenceThis project is dedicated to study the optical properties of rare earth-doped aluminum nitride thin films. More particularly, the work is oriented to investigate the luminescence mechanisms of selected RE elements incorporated in AlN thin films to be used as a candidate for lighting devices. During this thesis, reactive magnetron sputtering (RMS) technique is used to synthesize the undoped and doped AlN thin films. The technique and films processing are discussed in details. The effect of sputtering conditions on the structure and optical properties of the prepared films are investigated. The correlation between the sputtering conditions, the crystallographic orientation, the morphology, the microstructure and the optical properties are established. The structure and composition analyses of the prepared samples have been investigated by several means, such as transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS), and Rutherford backscattering spectrometry (RBS). The optical properties of the films are characterized by UV-Visible transmission, Ellipsometry spectroscopy, and Photoluminescence spectroscop

Rare earth-doped aluminum nitride thin films for optical applications

This project is dedicated to study the optical properties of rare earth-doped aluminum nitride thin films. In particular, to investigate the luminescence mechanisms of selected RE elements incorporated in AlN thin films. Reactive magnetron sputtering (RMS) technique is used to synthesize the undoped and doped AlN thin films. The effect of sputtering conditions on the structure and optical properties of the prepared samples are investigated. In addition, the optimum experimental conditions that will be used during this work are determined. The structure and composition analyses have been investigated by several means, such as transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS), and Rutherford backscattering spectrometry (RBS). The optical properties of the films are characterized by UV-Visible transmission, Ellipsometry spectroscopy, and Photoluminescence spectroscopy. For undoped AlN, well crystallized AlN thin films with high degree of c-axis orientation were prepared. Controlling the preferred orientation by only tuning the N 2 % in the gas phase has been achieved. It was found that, the synthesis of highly c-axis oriented crystalline AlN is favored by depositing the coatings in nitrogen-rich reactive ambiance. The results have been interpreted on the basis of an improved mobility of adatoms assisted by the bombardment of the films by fast particles. The optical constants (n, k) and bandgap of the prepared films have been modeled from spectroscopic ellipsometry measurements in transmission and reflection modes. It is found that the refractive index can be tuned with the crystal orientation while keeping constant the bandgap. Our findings suggest that, the optical properties of the AlN films can be tuned via their crystallographic orientation which, in turn, varied by the amount of nitrogen in the gas phase. For doped AlN, crystalline Ce-doped AlN were prepared. The crystal structure of the prepared samples and the compositions have been examined by TEM, RBS, EDS and EELS analyses. It was found that, presence of oxygen in this material is essential for sensitizing the photoluminescence. Oxygen has been found playing major role note only in converting Ce ions from the optically inactive state +4 to the optically active one +3, but also leaded to the formation of defect complexes with Al vacancies. These defect complexes were found contributed in the excitation mechanism of Ce ions. Therefore, an optical excitation and emission mechanisms have been proposed based on the role of oxygen. Based on that, manipulation of the PL was achieved and different colors (blue, and green) were clearly observed by the naked eye. In addition, white light emission approach has been presented and strong eye observed white light was obtained. Yb-doped and (Ce, Yb) co-doped Al(O)N systems are prepared. The crystal structures and compositions of the prepared samples have been investigated. Indirect optical excitation of the NIR emission of Yb ions is achieved. The excitation mechanisms of the NIR and visible emission of single and co-doped samples are discussed. It is found that, the similarity between the PLE spectra of Ce and Yb results in the possibility of achieving energy transfer between the two ions in the co-doping system. The type of energy transfer mechanism is found consistence with the one-to-one down conversion 176 via charge transfer state mechanism. The PL thermal quenching has been studied by following the PL evolution with low temperatures. Keywords: AlN thin films, rare earth doped AlN, optical properties, magnetron sputteringDieses Projekt widmet sich der Untersuchung der Lumineszenzmechanismen von Cerium- (Ce) und Ytterbium-Ionen (Yb), die in Aluminiumnitrid-Dünnschichten (AlN)einzeln und co- dotiert sind. Die reaktive Magnetronsputter-Technik (RMS) wird verwendet, um die undotierten und dotierten AlN-Dünnschichten zu synthetisieren. Die Auswirkung der Prozessbedingungen und der Konzentrationen von Ce und Yb auf die Struktur und die optischen Eigenschaften der hergestellten Proben werden untersucht. Die Struktur- und Zusammensetzungsanalysen wurden mit verschiedenen Methoden wie Transmissionselektronenmikroskopie (TEM), energiedispersive Röntgenspektroskopie (EDS) und Rutherford-Rückstreu-Spektrometrie (RBS) durchgeführt. Die optischen Eigenschaften der Filme wurden durch Spektralphotometrie, Ellipsometrie und Photolumineszenz- Spektroskopie (PL) charakterisiert. Ein vorgeschlagener Mechanismus zur Verbesserung und Löschung der PL wird diskutiert. Zusätzlich wurde ein Energieübertragungsprozess zwischen Ce- und Yb-Ionen erreicht. Basierend auf dem vorgeschlagenen Mechanismus konnten wir die Emission dieses Materials manipulieren, um blaue, grüne und weiße Farben zu erhalten. Unser Befund kann als Richtlinie zum besseren Verständnis des optischen Verhaltens von Seltenerdionen in AlN verwendet werden

Films minces de nitrure d'aluminium dopés par des terres rares pour applications optiques

This project is dedicated to study the optical properties of rare earth-doped aluminum nitride thin films. More particularly, the work is oriented to investigate the luminescence mechanisms of selected RE elements incorporated in AlN thin films to be used as a candidate for lighting devices. During this thesis, reactive magnetron sputtering (RMS) technique is used to synthesize the undoped and doped AlN thin films. The technique and films processing are discussed in details. The effect of sputtering conditions on the structure and optical properties of the prepared films are investigated. The correlation between the sputtering conditions, the crystallographic orientation, the morphology, the microstructure and the optical properties are established. The structure and composition analyses of the prepared samples have been investigated by several means, such as transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS), and Rutherford backscattering spectrometry (RBS). The optical properties of the films are characterized by UV-Visible transmission, Ellipsometry spectroscopy, and Photoluminescence spectroscopyCe projet est consacré à l'étude des propriétés optiques des films minces en nitrure d'aluminium dopé par des terres rares. Plus particulièrement, le travail est orienté pour étudier les mécanismes de luminescence des éléments RE sélectionnés incorporés dans des films minces AlN pour être utilisés comme candidats aux dispositifs d'éclairage. Au cours de cette thèse, la technique de pulvérisation de magnétron réactif est utilisée pour synthétiser les films minces AlN non dopés et dopés. La technique et le traitement des films sont discutés en détail. L'effet des conditions de pulvérisation sur la structure et les propriétés optiques des films préparés est étudié. La corrélation entre les conditions de pulvérisation cathodique, l'orientation cristallographique, la morphologie, la microstructure et les propriétés optiques sont établies. Les analyses de structure et de composition des échantillons préparés ont été étudiées par plusieurs moyens, tels que la microscopie électronique à transmission, la spectroscopie à rayons X à énergie dispersive et la spectrométrie de rétrodiffusion Rutherford. Les propriétés optiques des films sont caractérisées par une transmission UV-Visible, une spectroscopie d'Ellipsometry et une spectroscopie de photoluminescenc

Blue emission of Cerium doped Aluminum (oxy)-nitride thin film prepared by reactive sputtering technique

Recently, blue light emitting solid-state materials received high attention for use in white LEDs and other luminescent applications. In this direction, phosphors- doped nitrides and oxy-nitrides composites attracted much potential due to their thermal, chemical stability and the possibility to tune their electronic structure to adapt to the required applications. In particular, the III-nitrides (e.g. AlN, GaN) have been considered as a suitable host material for phosphors that emit in UV-visible range due to its large bandgap. Thus, the purpose of this study is to sensitize blue emission from rare earth doped AlN as a wide bandgap semiconductor. In the present work, Cerium-doped aluminum nitride (Ce-AlN) thin films were prepared at room temperature using radio frequency (RF) reactive sputtering. X-ray diffraction and high resolution transmission electron microscopy (HRTEM) revealed a well crystalline textured microstructure with single out-of-plane orientation. Strong blue emission from the prepared samples was detected when excited by 325 nm laser. Electron energy loss spectroscopy (EELS) has been used to reveal the dominant oxidation state of Ce atoms, which undergoes a change from of Ce(IV) to Ce(III) ions after annealing. The chemical composition was analyzed by simulation of Rutherford backscattering spectrometry (RBS) and compared to HRTEM images. A clear correlation between microstructure, composition and sample photoluminescence (PL) was established. It was found that surface oxidation during post-deposition annealing plays an important role in the PL response of the samples. We believe that the strong blue emission in this new (oxy)-nitride material holds great potentials for solid state lighting applications due to its thermal and chemical stability as well as the luminescence efficiency. Moreover, the comprehensive approach conducted within this study could serve as a guideline for better understanding and the design of the luminescence behavior in rare earth-doped (oxy)-nitride thin films.Oral presentation given at the Applied Nanotechnology and Nanoscience International Conference 2016, held on November 9-11th, 2016. Session OS1-1: Nanophotonics & Nano-optics (16:00 - Wednesday, 9th November, Room 1).Peer Reviewe

The essential role of oxygen in activation the blue emitting light from cerium doped Aluminum nitride thin films

Oral presentation given at the 2017 E-MRS Spring Meeting, held in Strasbourg (France) on May 22-26, 2017.Rare earth-doped III-nitrides such as GaN and AlN, attract great attention in lightening and optoelectronic applications. Particularly, AlN with large optical bandgap (6.2 eV) can offer an opportunity to cover wide range of light spectrum from UV to IR regions. In addition, AlN with high thermal conductivity (300 W/mK) is a very suitable material for high power working optoelectronic devices. Exploiting the large bandgap and the thermal conductivity features of AlN lead to open the door for generating blue emission with low thermal quenching effect even at high power operation. These are very interesting prerequisites for establishing stable white light emitting diodes (w-LED). Seeking for realization the blue emission from AlN, cerium-doped aluminum nitride (Ce-AlN) thin films were prepared at room temperature using radio frequency (RF) reactive sputtering. X-ray diffraction and high resolution transmission electron microscopy (HRTEM) revealed a well crystalline textured microstructure with single out-of-plane orientation. Strong blue emission from the prepared samples was detected when excited by 325 nm laser. Electron energy loss spectroscopy (EELS) has been used to reveal the dominant oxidation state of Ce atoms, which undergoes a change from of Ce(IV) to Ce(III) ions after annealing. The chemical composition was analyzed by simulation of Rutherford backscattering spectrometry (RBS) and compared to HRTEM images. A clear correlation between microstructure, composition and sample photoluminescence (PL) was established. It was found that surface oxidation during post-deposition annealing plays an important role in the PL response of the samples. The role of oxygen in the excitation mechanism was explained from the photoluminescence excitation measurements. We believe that the strong blue emission in this new (oxy)-nitride material holds great potentials for solid state lighting applications due to its thermal and chemical stability as well as the luminescence efficiency. Moreover, the comprehensive approach conducted within this study could serve as a guideline for better understanding and the design of the luminescence behavior in rare earth-doped (oxy)-nitride thin films

Heavily Doped Si Nanocrystals Formed in P-(SiO/SiO 2 ) Multilayers: A Promising Route for Si-Based Infrared Plasmonics

International audienceAs building blocks of multifunctional materials involving coupling at the nanoscale, highly doped semiconductor nanocrystals are of great interest for potential applications in nanophotonics. In this work, we investigate the plasmonic properties of highly doped Si nanocrystals embedded in a silica matrix. These materials are obtained by evaporation of heavily Phosphorus-doped SiO/SiO2 multilayers in a ultrahigh vacuum chamber followed by rapid thermal annealing. For P contents between 0.7 and 1.9 at%, structural investigations at the nanoscale give clear evidence that P atoms are mainly located in the core of Si nanocrystals with concentrations reaching up to 10 at%, i.e. well beyond the solid solubility limit of P in bulk Si. Alloying and formation of SiP nanoparticles is observed for P contents exceeding 4 at% in the multilayer. Infrared absorption measurements give evidence of a localized surface plasmon resonance located in the 3 to 6 µm range. A core-shell structure was used to model Si nanocrystals embedded in a silica matrix. Based on the Mie theory and the Drude model, both the mobility and the free charge carrier density were extracted from the simulation, with values reaching 27 cm 2 V-1 s-1 and 2.3×10 20 cm-3 , respectively. This results in a dopant activation rate of about 8 %

Heavily Doped Si Nanocrystals Formed in P-(SiO/SiO 2 ) Multilayers: A Promising Route for Si-Based Infrared Plasmonics

International audienceAs building blocks of multifunctional materials involving coupling at the nanoscale, highly doped semiconductor nanocrystals are of great interest for potential applications in nanophotonics. In this work, we investigate the plasmonic properties of highly doped Si nanocrystals embedded in a silica matrix. These materials are obtained by evaporation of heavily Phosphorus-doped SiO/SiO2 multilayers in a ultrahigh vacuum chamber followed by rapid thermal annealing. For P contents between 0.7 and 1.9 at%, structural investigations at the nanoscale give clear evidence that P atoms are mainly located in the core of Si nanocrystals with concentrations reaching up to 10 at%, i.e. well beyond the solid solubility limit of P in bulk Si. Alloying and formation of SiP nanoparticles is observed for P contents exceeding 4 at% in the multilayer. Infrared absorption measurements give evidence of a localized surface plasmon resonance located in the 3 to 6 µm range. A core-shell structure was used to model Si nanocrystals embedded in a silica matrix. Based on the Mie theory and the Drude model, both the mobility and the free charge carrier density were extracted from the simulation, with values reaching 27 cm 2 V-1 s-1 and 2.3×10 20 cm-3 , respectively. This results in a dopant activation rate of about 8 %

Heavily Doped Si Nanocrystals Formed in P-(SiO/SiO 2 ) Multilayers: A Promising Route for Si-Based Infrared Plasmonics

International audienceAs building blocks of multifunctional materials involving coupling at the nanoscale, highly doped semiconductor nanocrystals are of great interest for potential applications in nanophotonics. In this work, we investigate the plasmonic properties of highly doped Si nanocrystals embedded in a silica matrix. These materials are obtained by evaporation of heavily Phosphorus-doped SiO/SiO2 multilayers in a ultrahigh vacuum chamber followed by rapid thermal annealing. For P contents between 0.7 and 1.9 at%, structural investigations at the nanoscale give clear evidence that P atoms are mainly located in the core of Si nanocrystals with concentrations reaching up to 10 at%, i.e. well beyond the solid solubility limit of P in bulk Si. Alloying and formation of SiP nanoparticles is observed for P contents exceeding 4 at% in the multilayer. Infrared absorption measurements give evidence of a localized surface plasmon resonance located in the 3 to 6 µm range. A core-shell structure was used to model Si nanocrystals embedded in a silica matrix. Based on the Mie theory and the Drude model, both the mobility and the free charge carrier density were extracted from the simulation, with values reaching 27 cm 2 V-1 s-1 and 2.3×10 20 cm-3 , respectively. This results in a dopant activation rate of about 8 %