Analytical Study of the Thermal Activation of Tb Doped Amorphous SiC:H Thin Films
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Analytical Study of the Thermal Activation of Tb Doped Amorphous SiC:H Thin Films J. A. Guerra1,2, K. Tucto1, L. M. Montañez1, F. De Zela1, J. A. Töfflinger1, A. Winnaker2, and R. Weingärtner1 1
Departamento de Ciencias, Sección Física, Pontificia Universidad Católica del Perú, Av. Universitaria 1801, Lima 32, Perú 2 Department of Material Science 6, University of Erlangen-Nuremberg, Martenstr. 6, Erlangen 91058, Germany ABSTRACT The luminescence of Tb-doped a-SiC:H thin films with different Tb concentrations under sub-bandgap photon excitation was investigated. Two independent processes were identified. The annealing induced activation of the Tb3+ and the inhibition of host-mediated non-radiative recombination paths. The integrated emission intensity is described by a rate equation model, considering these two. In this study, the luminescence enhancement with increasing annealing temperature is shown. The optimal Tb concentration and annealing temperature for the highest Tb-related light emission intensity is determined. Finally, a parameter proportional to the number of optically active ions is found through the aforementioned model. INTRODUCTION Rare-earth (RE) doped materials have found applications as down and up converters in optoelectronic devices [1-4]. The emission color of the rare earth due to intra f-shell transitions is almost host independent. However, the light emission intensity does. For instance, the optical bandgap and defect states in the host matrix influence excitation mechanisms and the recombination in RE ions affecting the light emission intensity [5-8]. The wide-bandgap semiconductor silicon carbide (SiC) overcomes the RE-related light emission thermal quenching at room temperature [9]. SiC exhibits a large thermal conductivity and excellent chemical and mechanical stability, which makes it suitable for applications in aggressive environments [10-12]. The indirect character of crystalline SiC is not present in the amorphous counterpart. Additionally, hydrogen incorporation into the material passivates dangling bonds and widens the mobility edges. This allows the tailoring of the bandgap of hydrogenated amorphous SiC (a-SiC:H) from 1.8 eV to 3.2 eV by changing the stoichiometry and/or the hydrogen content [13, 15]. Annealing treatments usually enhance the light emission intensity of RE doped materials [6]. These treatments have two effects. First, there is the formation of a suitable crystal-field symmetry surrounding the RE ion. Second, the interaction between the RE and the host can be both, indirect excitation or energy-back-transfer. In the case of energy migration from the RE to the host, the emission intensity decreases due to the presence of non-radiative recombination paths [5, 7]. Non-radiative recombination paths are proportional to the host defect density.
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