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Wide bandgap semiconductors doped with rare earth ions are of increasing interest for photonic applications. The reasons for this are twofold: firstly, a large bandgap (i.e. >3 eV) allows rare earth emission in the whole visible range, covering the colors blue(Tm3+), green (Tb3+), and red (Eu3+). Secondly, it is well established that conventional semiconductors like silicon quench any rare earth emission at room temperature and therefore are not suitable for technical applications. The wide bandgap semiconductor hosts like SiC, GaN and AlN are known to overcome these problem. Furthermore, bandgap engineering between these materials opens the possibility to tailor the emission properties as it has already been demonstrated in the Al1−xGaxN system. Recently, crystalline and amorphous AlN and SiC hosts have been investigated for some rare earths, showing that they may be a promising candidate to overcome the above mentioned problems. In this context we investigated the terbium doped pseudobinary compound a-(SiC)1-x(AlN)x covering almost the whole composition range x from x=0 to x = 0.94. We obtained optical bandgaps from 2.2 eV to 4.7 eV, derived from optical transmission measurements. The films were produced by radio frequency (rf) triple magnetron sputtering and showed pronounced cathodoluminescence spectra (CL) at room temperature which can be attributed to Tb3+ 4f intrashell transitions. Isochronical annealing steps for a-(SiC)0.83(AlN)0.17 from 300 ◦C to 1100 ◦C by steps of 200 ◦C and at 1150 ◦C were performed in order to activate the Tb3+ emission. At each annealing step CL spectra were recorded and the activation of peak intensity of the Tb3+ 4f intrashell transition was plotted. Considering the variation in composition we observed that at the optimal annealing temperature slightly AlN-richer films (x = 0.55) exhibit the highest CL intensities showing pronounced Tb3+ 4f intrashell transition peaks.
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The present proposal aims to fund the research activities of the group and the laboratory for the next two years, i.e. fund materials, conferences and research stages. These activities are align to the research of rare earth doped widebandgap semiconductors for up and down conversion layers, the study of metalorganic triple cation perovskites and passivation layers for photovoltaic applications, as well as the production and characterization of transparent conductive oxides doped with rare earths and transition metal ions for down shift layers. With exception of the perovskites, the materials are growth by sputtering and characterized by means of FTIR, Raman, PL and CL spectroscopy, Van Der Pauw, capacitance-voltage, XRD and Variable Angle Spectral Ellipsometry (VASE). The materials under study are SiC and AlN doped with Tb and Yb, for up/down conversion layers. AlN for surface passivation of Si wafers as well as Liquid Phased Crystalized Si (LPC-Si) for thin film solar cells. ITO and AZO doped with Tb and Tm, for multifunctional light emitting materials and downshift layers, and doped with Cr for acetone sensing, and perovskites. In particular, the production and part of the characterization of the perovskites and LPC-Si are perform in collaboration with the Helmholz Zentrum Berlin (HZB), Germany, in the framework of a memorandum of understanding. The rest of materials are fully produced and characterized in our laboratories. The main objectives of the project are to study: The thermal activation of rare doped materials and excitation mechanism after thermal annealing treatments. The effect of annealing treatments and doping with rare earths and transition metal ions on the electrical conductivity and optical transparency of ITO and AZO. The passivation capabilities of AlN and other dielectric thin films in order to improve the efficiency of Si based solar cells.
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