Influence of the magnetron power on the Er-related photoluminescence of AlN:Er films prepared by magnetron sputtering

International audienceThe effect of magnetron power on the room temperature 1.54 µm infra-red photoluminescence intensity of erbium doped AlN films grown by r. f. magnetron sputtering, has been studied. The AlN:Er thin films were deposited on (001) Silicon substrates. The study presents relative photoluminescence intensities of nanocrystallized samples prepared with identical sputtering parameters for two erbium doping levels (0.5 and 1.5 atomic %). The structural evolution of the crystallites as a function of the power is followed by transmission electron microscopy. Copyright line will be provided by the publisher 1 Introduction For some time now, rare-earth (RE)-doped semiconductors represent significant potential applications in the field of opto-electronic technology. Part of this technological interest relies on the shielded 4f levels of the RE ions as they give rise to sharp and strong luminescence peaks [1-5]. Among the RE elements, Er is preferred to its counterparts since the Er ions can produce both visible light at 558 nm (green, one of the primary colours) and IR light at 1.54 µm whose spectrum region coincides with the main low-loss region in the absorption spectrum of silica-based optical fibres, combining so potential applications towards photonic devices and towards optical communication devices operating in the infrared domain. These interesting emissions can however only be exploited when placed into host matrixes. On one side, the shielding of the intra 4f levels prevents the shifting of the RE 3+ energy levels and ensures the frequency emission stability. Moreover the intra 4f transitions are parity forbidden for the isolated ions. Matrixes can render the Er 3+ ions optically active, via a relaxation of selection rules due to crystal field effects. As silicon based materials were tested in the 1960s to the 90s with no clear industrial success it was found that th

Photoluminescence of erbium in SiOxNy alloys annealed at high temperature

Équipe 104 : NanomatériauxInternational audienceAmorphous silicon oxynitride SiOxNy ternary alloys were prepared by reactive evaporation, with stoichiometries varying between Si0.47O0.05N0.48 and Si0.35O0.65. These thin films were doped with erbium during the evaporation process with an effusion cell. The composition and the atomic structure were determined by X-ray photoelectron spectroscopy (XPS), infrared (IR) absorption spectrometry, and Raman spectrometry. Photoluminescence (PL) experiments were carried out in the visible and infrared ranges. The Er signal was maximum for equal amounts of oxygen and nitrogen in the SiOxNy alloys. It disappears for oxygen contents greater than 30%. Photoluminescence excitation (PLE) experiments show that the PL is due to an indirect excitation process from the pure silicon domains

Étude de la photoluminescence de films d'AlN dopé erbium (AlN-Er) déposés par PVD magnétron RF

Ces dernières décennies, les couches minces de semiconducteurs nitrures III-V dopés avec des terres rares ont fait l'objet d'un intérêt grandissant et ont donné lieu à de nombreuses études. En raison de leur bande interdite directe, les nitrures III-V constituent des matrices hôtes adéquates permettant la luminescence des terres rares (TR). Ainsi, en combinant les propriétés des III-V et des TR, il est possible d'envisager des applications prometteuses dans le domaine optoélectronique. Dans cette étude, l'erbium (Er) a été choisi en raison de son émission de photons à la fois dans le visible et dans l'infrarouge. Dans ce travail, les films minces d'AlN dopé à l'Er ont été élaborés avec un réacteur expérimental de pulvérisation cathodique réactive magnétron radiofréquence. Pendant le dépôt, une polarisation négative appliquée sur le substrat a permis d'obtenir des films présentant différents types de morphologies cristallines, qui ont été étudiés par diverses techniques de caractérisation telles que l'AFM, les DRX, l'ellipsométrie, le MEB, le MET. Les propriétés de luminescence des films ont été examinées expérimentalement et à l'aide d'un modèle de simulation optique par spectroscopie de photoluminescence (excitation lumineuse). Des mesures expérimentales par spectroscopie de cathodoluminescence (excitation électronique) ont également été réalisées. Le but de cette thèse était d'optimiser le procédé d'élaboration et le matériau et de mieux comprendre l'influence de la morphologie cristalline de la matrice AlN sur l'efficacité de luminescence de l'erbium. L'AlN-Er représente un système modèle et les résultats obtenus pourront être étendus aux autres TRDuring the last decades, rare-earth-doped III-V thin films have been the subject of growing interest and the topic of many studies. Because III-V nitrides possess a direct gap, they are suitable host matrices to allow rare-earth (RE) luminescence. Thereby, by combining the III-V and the RE characteristics, it becomes possible to consider promising applications in the optoelectronic field. In this study, erbium (Er) was chosen because of its emission both in the visible and in the infrared range. In this work, Er-doped AlN thin films were prepared in an experimental PVD sputtering magnetron radiofrequency reactor. During the deposition, an applied negative bias on the substrate allowed to obtain different kinds of crystalline morphology of the deposited layers, which were studied by several characterization techniques such as AFM, DRX, ellipsometry, MEB, MET. Luminescence properties of the films were investigated both experimentally and with an optical model by photoluminescence (light excitation) spectroscopy. Experimental measurements by cathodoluminescence (electronic excitation) spectroscopy were also performed. This thesis aimed to optimize the elaboration process and the material and to get a better understanding of the influence of AlN host matrix crystalline morphology on the erbium luminescence efficiency. The AlN:Er system stood as a model system and the obtained results could be extended to the other RENANCY-INPL-Bib. électronique (545479901) / SudocMETZ-SCD (574632105) / SudocSudocFranceF

Single step electrodeposition process using ionic liquid to grow highly luminescent silicon/rare earth (Er, Tb) thin films with tunable composition

A one-step method for the electrodeposition of silicon–erbium (Si/Er) and silicon–terbium (Si/Tb) thin films using room temperature ionic liquid (RTIL) has been successfully developed. By playing with the electrochemical parameters, the concentration of incorporated rare earth (RE) ions (Er3+ and Tb3+) in the thin films can be tuned. The obtained thin films have been characterized by electron microscopy and composition analysis techniques. The structural quality of the obtained thin films is characterized by a uniform distribution of Si atoms and RE ions throughout the thickness. The study of the optical properties, carried out by photoluminescence (PL) spectroscopy, demonstrates the efficient optical activity of the films with typical Er and Tb luminescence at room temperature depending on the RE content. The deposition method described is a promising strategy for incorporating RE ions in semiconducting thin films to achieve materials for opto-electronic applications.</p

Structural and optical properties of magnetron-sputtered Er-doped AIN films grown under negative substrate bias

Équipe 104 : NanomatériauxInternational audienceIn seeking suitable host-microstructures enhancing photoluminescent (PL) efficiency of reactively sputtered Er-doped AIN films deposited under varying negative substrate bias, we observed that the films' Er-emitted PL intensity at the wavelength of 1.54 pin builds up with bias up 50 V, before falling sharply and collapsing for U above 90 V. We studied for further insight the bias-induced effects on the film microstructural and optical properties. The transmission electron microscope images of these films biased up to 50 V showed improved film crystallographic quality with wide and long columnar microstructures. The columnar crystallized volumes therein are maximized around a particular bias value around 90V, above which they have finely grained nano-granular microstructures. This film-microstructural evolution concurs well with the film refractive index n and extinction coefficient k obtained from ellipsometry. Both surge for films biased from 50 V to 90V. These correlating evidences point out that adequate adatom mobility gained under low-energy ion bombardment with bias up to 50 V properly configures the AIN Wurzite planes while leaving behind fewer sites for PL-quenching defects. Meanwhile, Urbach tail states associated with other visible-light absorbing defects created by some material disorder in appropriate locations within the columns should have absorb the exciting photon energy and transfer it efficiently to the emitting Er3' ions. These evidences further indicate that the newer defects created under bias above 100 V act as non-radiative centers in putting out the PL. We suggest that these latter defects would be located with a high density, at the numerous grain boundaries of the nano-crystallized volumes

Non-resonance redistribution of electron excitation energy in LiNbO3:Yb3+

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Polaron luminescence in iron-doped lithium niobate

International audiencePhotoluminescence related to the bound polaron Nb 4+Li is investigated as a function of temperature and incident light intensity in iron-doped lithium niobate crystals with various iron concentrations. Experiments are done under constant-wave (CW) and pulsed illumination. Its found that the decay time is always monoexponential. The radiative lifetime, the activation energy of the nonradiative lifetime and the quenching temperature are only weakly sensitive to iron concentration. On the other hand, the magnitude of the photoluminescence signal seems strongly correlated to the Fe2+ concentration, and the superlinear regime evidenced at low CW illumination definitely confirms that polaron excitation in lithium niobate is a two-step process