Rare-earth doped Si nanostructures for Microphotonics
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Rare-earth doped Si nanostructures for Microphotonics D. Pacifici, G. Franzò, F. Iacona,1 A. Irrera,1 S. Boninelli, M. Miritello, and F. Priolo MATIS-INFM and Dipartimento di Fisica e Astronomia, Via S. Sofia 64, I-95123 Catania, Italy 1 CNR-IMM, Sezione di Catania, Stradale Primosole 50, I-95121 Catania, Italy ABSTRACT In the present paper, we will review our work on rare-earth doped Si nanoclusters. The samples have been obtained by implanting the rare-earth (e.g. Er) in a film containing preformed Si nanocrystals. After the implant, samples have been treated at 900°C for 1h. This annealing temperature is not enough to re-crystallize all of the amorphized Si clusters. However, even if the Si nanoclusters are in the amorphous phase, they can still efficiently transfer the energy to nearby rare-earth ions. We developed a model for the Si nanoclusters-Er system, based on an energy level scheme taking into account the coupling between each Si nanocluster and the neighboring Er ions. By fitting the data, we were able to determine a value of 3x10-15 cm3 s-1 for the Si nanocluster-Er coupling coefficient. Moreover, a strong cooperative up-conversion mechanism between two excited Er ions and characterized by a coefficient of 7x10-17 cm3 s-1, is shown to be active in the system, demonstrating that more than one Er ion can be excited by the same nanocluster. We show that the overall light emission yield of the Er related luminescence can be enhanced by using higher concentrations of very small nanoaggregates. Eventually, electroluminescent devices based on rare-earth doped Si nanoclusters will be demonstrated.
INTRODUCTION Among the different approaches developed to overcome the intrinsic low efficiency of silicon as a light emitter, quantum confinement and rare earth doping of silicon have dominated the scientific scenario of silicon-based microphotonics. Recently, Er doping of Si nanocrystals has been recognized as an interesting way of combining the promising features of both the previous methods [1-3]. Indeed, it has been demonstrated that Si nanocrystals can act as efficient sensitizers for Er [4-7]. In particular, the nanocrystal, once excited, transfers quasi-resonantly [8] its energy to the nearby Er ion, which then decays emitting a photon at 1.54 µm. The effective excitation cross section for Er in presence of Si nanocrystals is more than two orders of magnitude higher with respect to the resonant absorption of a photon in a silica matrix [4]. The recent determination of net optical gain at 1.54 µm in Er-doped Si nanocluster sensitized waveguides [9] and the demonstration of efficient room temperature electroluminescence from Er-Si nanoclusters devices [10] opened the route towards the future fabrication of electrically driven optical amplifiers based on this system. Several basic issues remain however to be first addressed, namely i) the role of amorphous Si clusters in exciting the Er3+ ions, ii) the coupling strength between Si nanoclusters and Er ions and the microscopic details of the interaction, ii
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