Papers by Author: Rositza Yakimova

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Authors: Francesco La Via, Fabrizio Roccaforte, Antonino La Magna, Roberta Nipoti, Fulvio Mancarella, Peter J. Wellmann, Danilo Crippa, Marco Mauceri, Peter Ward, Leo Miglio, Marcin Zielinski, Adolf Schöner, Ahmed Nejim, Laura Vivani, Rositza Yakimova, Mikael Syväjärvi, Gregory Grosset, Frank Torregrosa, Michael Jennings, Philip A. Mawby, Ruggero Anzalone, Salvatore Coffa, Hiroyuki Nagasawa
Abstract: The cubic polytype of SiC (3C-SiC) is the only one that can be grown on silicon substrate with the thickness required for targeted applications. Possibility to grow such layers has remained for a long period a real advantage in terms of scalability. Even the relatively narrow band-gap of 3C-SiC (2.3eV), which is often regarded as detrimental in comparison with other polytypes, can in fact be an advantage. However, the crystalline quality of 3C-SiC on silicon has to be improved in order to benefit from the intrinsic 3C-SiC properties. In this project new approaches for the reduction of defects will be used and new compliance substrates that can help to reduce the stress and the defect density at the same time will be explored. Numerical simulations will be applied to optimize growth conditions and reduce stress in the material. The structure of the final devices will be simulated using the appropriated numerical tools where new numerical model will be introduced to take into account the properties of the new material. Thanks to these simulations tools and the new material with low defect density, several devices that can work at high power and with low power consumption will be realized within the project.
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Authors: T. Paskova, E. Valcheva, Ivan G. Ivanov, Rositza Yakimova, Susan Savage, Nils Nordell, Chris I. Harris
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Authors: P. Råback, Risto M. Nieminen, Rositza Yakimova, M. Tuominen, Erik Janzén
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Authors: Rositza Yakimova, Chariya Virojanadara, Daniela Gogova, Mikael Syväjärvi, D. Siche, Karin Larsson, Leif I. Johansson
Abstract: We are aiming at understanding the graphene formation mechanism on different SiC polytypes (6H, 4H and 3C) and orientations with the ultimate goal to fabricate large area graphene (up to 2 inch) with controlled number of monolayers and spatial uniformity. To reach the objectives we are using high-temperature atmospheric pressure sublimation process in an inductively heated furnace. The epitaxial graphene is characterized by ARPES, LEEM and Raman spectroscopy. Theoretical studies are employed to get better insight of graphene patterns and stability. Reproducible results of single layer graphene on the Si-face of 6H and 4H-SiC polytypes have been attained. It is demonstrated that thickness uniformity of graphene is very sensitive to the substrate miscut.
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Authors: Mikael Syväjärvi, V. Stanciu, M. Izadifard, W.M. Chen, I.A. Buyanova, P. Svedlindh, Rositza Yakimova
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Authors: Antonino La Magna, Ioannis Deretzis, Filippo Giannazzo, Giuseppe Nicotra, Fabrizio Roccaforte, Corrado Spinella, Rositza Yakimova
Abstract: A Kinetic Monte Carlo scheme is applied to simulate with atomic resolution the synthesis of mono (few) layer(s) graphene (Gr) from a silicon carbide (SiC) substrate by selective evaporation of silicon (Si) atoms. The simulation computes the individual dynamics of the residual carbon (C) atoms which diffuse and reconfigure starting from the positions occupied in the SiC hexagonal lattice to the final Gr honeycomb structure. During the transition they gradually modify hybridization (from sp3 to sp2) and bond partners (from Si-C to C-C). We demonstrate that our method is able to recover the complex evolution steps of the epitaxial Gr on SiC in large systems for large time intervals. Moreover, the simulation results can be validated directly by means of comparison with experimental data when varying the material (e.g. initial surface configuration or polarity) or process (e.g. temperature and pressure) conditions.
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Authors: N. Vouroutzis, Rositza Yakimova, Mikael Syväjärvi, Henrik Jacobsson, J. Stoemenos, Erik Janzén
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Authors: Georgios Manolis, Milena Beshkova, Mikael Syväjärvi, Rositza Yakimova, Kęstutis Jarašiūnas
Abstract: We investigated non-equilibrium carrier dynamics in ~20μm thick 3C-SiC layers, grown by sublimation epitaxy directly on 6H-SiC substrate or buffered by a 3C seed layer. Differential transmission and light-induced transient grating techniques were applied to determine the ambipolar diffusion coefficient, carrier lifetime, and thermal activation energy of defects. The temperature dependences of ambipolar mobility and lifetime in 80-700 K range revealed the carrier scattering processes as well the impact of defects on the recombination rate, thus indicating slightly improved photoelectrical parameters of the homoepitaxially grown 3C layer. The determined thermal activation energies of 35 and 57 meV were attributed to the nitrogen impurity.
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Authors: Mads Mikelsen, Ulrike Grossner, Jan H. Bleka, Edouard V. Monakhov, Bengt Gunnar Svensson, Rositza Yakimova, Anne Henry, Erik Janzén, Alexander A. Lebedev
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Authors: A. Kakanakova-Georgieva, Rositza Yakimova, Jie Zhang, L. Storasta, Mikael Syväjärvi, Erik Janzén
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