Tesis y Trabajos de Investigación PUCP
URI permanente para esta comunidadhttp://54.81.141.168/handle/123456789/6
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Ítem Texto completo enlazado Optical and luminiscent properties of terbium / ytterbium doped aluminum oxynitride and terbium doped aluminum nitride thin films(Pontificia Universidad Católica del Perú, 2020-08-06) Tucto Salinas, Karem Yoli; Guerra Torres, Jorge Andrés; Grieseler, RolfIn the present thesis the optical and light emission properties of two systems consisting of Tb3+ and Yb3+ doped amorphous AlOxNy thin films and Tb3+ doped polycrystalline AlN thin films were analyzed. In the two ions system, to obtain an adequate luminescent emission, commonly a significant effort must be made to find a suitable concentration of dopants and elemental composition of the host material. An interesting and highly efficient method is a combinatorial approach, allowing a high velocity screening of a wider range of properties. In the present work a combinatorial gradient based thin film libraries of amorphous AlOxNy:Yb3+, AlOxNy:Tb3+ and AlOxNy:Tb3+:Yb3+ have been prepared by radio frequency co-sputtering from more than one target. In the prepared libraries, the Tb and Yb concentration range spreads along with the oxygen to nitrogen ratio of the host matrix all over the substrate area. Concentrations ranges for each ion were established for producing high emission intensity samples, along with an analysis of the light emission features of Yb3+ ions with Tb3+ ions as sensitizers for cooperative down conversion process. Using different annealing temperatures the activation energy of the rare earth ions and thermal-induced activation mechanisms are evaluated. Here we show that the different oxygen to nitrogen ratios in the host composition affect the light emission intensity. According to experimental results, there is a strong enhancement of the Yb3+ related emission intensity over the Tb3+ emission in codoped films with Tb:Yb concentration ratios near to 1:2, at 850°C. Thus, suggesting the sensitization of Tb3+ ions through an AlOxNy matrix and the cooperative energy transfer between Tb3+ and Yb3+ ions as the driven mechanism for down conversion process with promising applications in silicon solar cells. At the end of this first part, the optimal elemental composition and optimal annealing temperature in the investigated ranges to achieve the highest Yb3+ emission intensity upon sensitization of Tb3+ ions is reported. The second system studied consists of Tb3+ doped AlN layers prepared by reactive magnetron sputtering and analyzed using the conventional one at a time approach. In this work, two types of thermal treatments have been applied: substrate heating during deposition of the films and post deposition rapid thermal annealing, with varying temperature from non intentional heating up to 600°C. The composition, morphology and crystalline structure of the films under different thermal processes and temperatures were investigated along with their optical and light emission properties, with the aim of maximizing the Tb3+ emission intensity. The polycrystalline nature of the films was confirmed by X-ray diffraction under grazing incidence, and the influence of substrate temperature on the crystalline structure was reported. Atomic force microscopy and scanning electron microscopy has revealed the smooth grainy surface quality of the AlN:Tb3+ films. The highest Tb3+ photoluminescence emission intensity was achieved in the film treated with rapid thermal annealing process. For a more detailed study of the post deposition annealing treatments, temperature was further increased up to 900°C, and the influence of annealing temperature on the emission properties was investigated by photoluminescence and photoluminescence decay measurements. An increase in the photoluminescence intensity and photoluminescence decay time was observed upon annealing for the main transition of Tb3+ ions at 545 nm, which was attributed to a decrease of non radiative recombination and increase of the population of excited Tb3+ ions upon annealing. Additionally, using the characterized films as active layer, direct current and alternate current thin film electroluminescence devices were designed and investigated.Ítem Texto completo enlazado On the fundamental absorpion of amorphous semiconductors(Pontificia Universidad Católica del Perú, 2016-06-20) Angulo Abanto, José Rubén; Guerra Torres, Jorge AndrésThe present thesis reviews different models that describe the fundamental absorption of amorphous semiconductors. These models make use of the electronic density of states to shape the absorption coefficient in the fundamental absorption region. The study focuses on the optical absorption of hydrogenated amorphous Silicon (a-Si:H), hydrogenated and non-hydrogenated amorphous silicon carbide (a-SiC:Hx), and silicon nitride (a-SiN) thin films. On the one hand, parameters like the Tauc-gap and Urbach energy are obtained from the absorption coefficient using the traditional models. On the other hand, a recently proposed model based on band thermal fluctuations was assessed [1]. This model allows a determination of the mobility gap and the Urbach energy from a single fit of the absorption coefficient without the need of identifying the Tauc region beforehand. Furthermore, it is able to discriminate the variation of the Urbach energy from the bandgap. The results allow the evaluation of the aforementioned parameters with annealing treatments at different temperatures. The mobility edges are insensitive to the structural disorder by at least one degree lower than the Urbach energy. This work demonstrates that it is possible to obtain the mobility edge through this model. In addition, the measured Tauc-gap and Urbach energy exhibit a strong linear correlation following the Cody model for all three materials. Finally, the Urbach focus concept is evaluated and estimated under different analysis.Ítem Texto completo enlazado Structural, luminescence and Judd-Ofelt analysis to study the influence of post-annealing treatment on the AIN:Tb thin films prepared by radiofrequency magnetron sputtering(Pontificia Universidad Católica del Perú, 2016-06-20) Tucto Salinas, Karem Yoli; Weingärtner, RolandThis thesis investigates the effects of the annealing treatments on the spontaneous emission, radiative lifetime, composition and structure of terbium doped aluminum nitride films deposited on silicon substrates by radio frequency magnetron sputtering. The purpose of this thesis is to determine the Judd-Ofelt intensity parameters from the emission spectrum, in order to calculate the radiative lifetime, branching ratios and spontaneous emission probability. The optimal annealing temperature for the emission of terbium doped aluminum nitride is investigated. The annealing treatment was performed in the temperature range starting from 500 up to 1000°C. Two annealing techniques were investigated: rapid thermal processing and a rather slower quartz tube furnace. Furthermore, two heating approaches were applied: direct heating at 500, 750, 900 and 1000 °C, and multistep heating of 500-750°C, 750-900°C and 900-1000°C. The film was then characterized to determine which conditions resulted in the highest emission of Tb. The film characterization includes the use of X-ray diffraction to study the film’s crystal orientation, Energy dispersive X-ray spectroscopy to determine the film composition, Scanning electron microscopy and Reflection high-energy electron diffraction to resolve the surface morphology and structure of the film respectively. The luminescent intensity and the radiative lifetime were analyzed using cathodoluminescence measurement and Judd-Ofelt analysis. This work shows that the activation of the Tb ions to enhance the emitted cathodoluminescence intensity depends on the structure of the film and the oxygen concentration. The best annealing temperature to produce the highest emitted light intensity in this set of experiments were the single-step heating at 750°C using rapid thermal processing.