Browsing by Author "Tucto Salinas, Karem Yoli"

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Determinación de las constantes ópticas y el espesor de películas delgadas semiconductoras depositadas por pulverización catódica de radio frecuencia sobre substratos ligeramente abosorbentes en la región visibles
(Pontificia Universidad Católica del Perú, 2013-02-05) Tucto Salinas, Karem Yoli; Weingärtner, Roland
En este trabajo se describe el método de Swanepoel (1983) [1] y el método propuesto por Guerra J A (2010) [2] para caracterizar películas delgadas usando sólo el espectro de transmitancia óptica. La película es caracterizada al quedar determinadas las constantes ópticas y el espesor. Esta tesis presenta una modificación al método de Guerra, a fin de considerar en los cálculos el efecto de la absorción del substrato. La ecuación de transmitancia del sistema película substrato es descrita y obtenida siguiendo la teoría matricial de sistemas multicapas cuya base se encuentra en la teoría electromagnética. Usando el software Wolfram Mathematica v.8.0 se implementa un programa con el método propuesto en el presente trabajo para substratos absorbentes. Este programa es puesto a prueba usando datos de transmitancia óptica simulados y reales. Las medidas son realizadas usando un espectrofotómetro que mide la transmitancia de películas delgadas, en este caso carburo de silicio amorfo hidrogenado (a-SiC:H) depositadas sobre substratos de vidrio ligeramente absorbentes (B270) y fluoruro de calcio (CaF2). Las películas delgadas se fabricaron en el Laboratorio de Ciencias de los materiales de la Sección Física de la Pontificia Universidad Católica del Perú. Las constantes ópticas obtenidas de aplicar el método propuesto por Guerra a la película sobre substrato de CaF2, y aquellas obtenidas aplicando el presente método propuesto para películas sobre substratos de vidrio, son comparadas.
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, Rolf
In 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.
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, Roland
This 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.