Ruling out the impact of defects on the below band gap photoconductivity of Ti supersaturated Si

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Mártil de la Plaza, Ignacio
García Hemme, Eric
Prado Millán, Álvaro del
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American Institute of Physics
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In this study, we present a structural and optoelectronic characterization of high dose Ti implanted Si subsequently pulsed-laser melted (Ti supersaturated Si). Time-of-flight secondary ion mass spectrometry analysis reveals that the theoretical Mott limit has been surpassed after the laser process and transmission electron microscopy images show a good lattice reconstruction. Optical characterization shows strong sub-band gap absorption related to the high Ti concentration. Photoconductivity measurements show that Ti supersaturated Si presents spectral response orders of magnitude higher than unimplanted Si at energies below the band gap. We conclude that the observed below band gap photoconductivity cannot be attributed to structural defects produced by the fabrication processes and suggest that both absorption coefficient of the new material and lifetime of photoexcited carriers have been enhanced due to the presence of a high Ti concentration. This remarkable result proves that Ti supersaturated Si is a promising material for both infrared detectors and high efficiency photovoltaic devices.
© 2013 AIP Publishing LLC. he authors would like to acknowledge the C.A.I. de Técnicas Físicas for ion implantation experiments and e-beam evaporations, the Nanotechnology and Surface Analysis Services of the Universidad de Vigo C.A.C.T.I. for ToF-SIMS measurements, Dr. J. Herrero (CIEMAT) for UVVIS-IR measurements facilities, and the Instituto de Nanociencia de Aragón for the TEM images. J. Olea and D. Pastor thanks 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. Research by E. Garcìa-Hemme has been partly supported by a PICATA predoctoral fellowship of the Moncloa Campus of International Excellence (UCM-UPM). This work was partially supported by the projects NUMANCIA II (S-2009/ENE-1477) founded by the Regional Government of Comunidad de Madrid and grant GR35/10-A founded by the Universidad Complutense de Madrid.
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