Papers by Author: Roberta Nipoti

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Authors: Roberta Nipoti, Antonella Parisini, Salvatore Vantaggio, Giovanni Alfieri, Alberto Carnera, Emanuele Centurioni, Elmi Ivan, Ulrike Grossner
Abstract: This study shows that, after annealing at 1950°C, a 1×1020 cm-3 Al+ implanted 4H-SiC material shows a decreasing resistivity with increasing annealing time in the range 5-25 min. After this, the resistivity remains constant up to an annealing time of 40 min. The estimated minimum time to gain the thermal equilibrium in this implanted material at 1950°C is 12 min. Electrical characterization has been performed in the 20-680 K temperature range.
Authors: Giorgio Lulli, Roberta Nipoti
Abstract: In this work under-mask penetration of Al+ ions implanted in 4H-SiC is investigated by computer simulation based on the Monte-Carlo binary collision approximation (MC–BCA). Results indicate that a small fraction of ions, implanted normal to a (0001) 4H-SiC wafer (8° off-axis towards the {11-20}), is scattered and become channeled in the <1120> directions perpendicular to the <0001> axis. Due to this phenomenon, doped regions with concentration ≤ 10− 4 of the peak value, may extend laterally for a few µm below the edge of a SiO2 mask.
Authors: Francesco La Via, Fabrizio Roccaforte, Antonino La Magna, Roberta Nipoti, Fulvio Mancarella, Peter Wellman, 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.
Authors: Mihai Lazar, Christophe Raynaud, Dominique Planson, Marie Laure Locatelli, K. Isoird, Laurent Ottaviani, Jean-Pierre Chante, Roberta Nipoti, Antonella Poggi, G.C. Cardinali
Authors: R. Pérez, Narcis Mestres, Servane Blanqué, Dominique Tournier, Xavier Jordá, Phillippe Godignon, Roberta Nipoti
Authors: Roberta Nipoti, Alberto Carnera, Giovanni Alfieri, Lukas Kranz
Abstract: The electrical activation of 1×1020 cm-3 implanted Al in 4H-SiC has been studied in the temperature range 1500 - 1950 °C by the analysis of the sheet resistance of the Al implanted layers, as measured at room temperature. The minimum annealing time for reaching stationary electrical at fixed annealing temperature has been found. The samples with stationary electrical activation have been used to estimate the thermal activation energy for the electrical activation of the implanted Al.
Authors: Antonella Parisini, Roberta Nipoti
Abstract: The knowledge of the Hall factor is essential to convert Hall to drift transport data, in order to fit them and reliably evaluate doping and compensation levels of samples. By introducing empirical mass anisotropy factors, reasons were given in favour of a generalized use of the unique experimental evaluation of the Hall factor reported by the literature for p-type 4H-SiC, which has been assessed for an Al acceptor density in the range of 1.8×1015 - 2×1018 cm-3. Using such a curve, carrier transport data, taken in Al+ implanted 4H-SiC for an Al concentration of 5×1019 cm-3 after either 2000°C/30s microwave annealing or 1950°C/300s conventional annealing, were analysed through a standard relaxation time approximation model. A slight difference was evidenced in the compensation level of the samples, also resulting in a different ionization energy of the acceptor.
Authors: Francesco Moscatelli, Andrea Scorzoni, Antonella Poggi, G.C. Cardinali, Roberta Nipoti
Authors: Ulrike Grossner, Francesco Moscatelli, Roberta Nipoti
Abstract: Two families of Al+ implanted vertical p+in diodes that have been processed all by identical steps except the post implantation annealing one have been characterized with current voltage measurements from -100 to +5V at different temperatures. Analysis of the static forward current voltage characteristics shows two different ideality factor regions, which are distinct for each family. The reverse current voltage characteristics reveals corresponding two different activation energies. These are assumed to be correlated to the Z1/2 defect for the one case and another one with an activation energy of 0.25eV.
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