Experimental verification of intermediate band formation on titanium-implanted silicon

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García Hemme, Eric
Bailón, L.
Castán, H.
Dueñas, S.
García, H.
Pérez, E.
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American Institute of Physics
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Intermediate band formation on silicon layers for solar cell applications was achieved by titanium implantation and laser annealing. A two-layer heterogeneous system, formed by the implanted layer and by the un-implanted substrate, was formed. In this work, we present for the first time electrical characterization results which show that recombination is suppressed when the Ti concentration is high enough to overcome the Mott limit, in agreement with the intermediate band theory. Clear differences have been observed between samples implanted with doses under or over the Mott limit. Samples implanted under the Mott limit have capacitance values much lower than the un-implanted ones as corresponds to a highly doped semiconductor Schottky junction. However, when the Mott limit is surpassed, the samples have much higher capacitance, revealing that the intermediate band is formed. The capacitance increasing is due to the big amount of charge trapped at the intermediate band, even at low temperatures. Ti deep levels have been measured by admittance spectroscopy. These deep levels are located at energies which vary from 0.20 to 0.28 eV below the conduction band for implantation doses in the range 10(13)-10(14) at./cm(2). For doses over the Mott limit, the implanted atoms become nonrecombinant. Capacitance voltage transient technique measurements prove that the fabricated devices consist of two-layers, in which the implanted layer and the substrate behave as an n(+)/n junction.
© American Institute of Physics. This work was partially supported by VA128A11-2 funded by the Junta de Castilla y León and the Spanish TEC2011 under Grant 27292-C02-01, CSD2006-00004 funded by the Spanish Consolider National Program and the Project NUMANCIA II (Grant No. S-2009/ENE/1477) funded by the Comunidad de Madrid. Research of E. Pérez was supported by a University of Valladolid FPI grant and research of E. García-Hemme by a PICATA predoctoral fellowship of the Moncloa Campus of International Excellence (UCM-UPM). Authors would like to acknowledge the CAI de Técnicas Físicas of the Universidad Complutense de Madrid for the ion implantations and metallic evaporations. J. Olea and D. Pastor thank Professor A. Martí and Professor A. Luque for useful discussions and guidance and acknowledge financial support from the MICINN within the program Juan de la Cierva (JCI-2011-10402 and JCI-2011-11471), under which this research was undertaken.
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