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Mercredi 20 Fevrier 2013, 14h
Amphi Boreau, Esc C, 1ème etage
Persistent enhancement of the carrier density
in electron irradiated InAs nanowires
B. Grandidier
Institut d’Electronique, de Microélectronique et de Nanotechnologie, IEMN, (CNRS, UMR 8520, Département ISEN, 41 bd Vauban, 59046 Lille Cedex, France.
The advent of nanotechnology requires the development of sophisticated tools capable of investigating the matter at this scale. Since 2010, the Excelsior characterization center at IEMN has successfully operated a multiprobe Scanning Tunneling Microscope (Nanoprobe), working in UHV at variable temperature (30K-530 K), where the unique combination of four STM probe tips and a scanning electron microscope (SEM) allows 4-point contact measurements and function testing of nanodevices within complex structures and integrated circuits. After a detailed description of this instrument, I will report a significant and persistent enhancement of the conductivity in free-standing non intentionnaly doped InAs nanowires upon irradiation in ultra high vacuum.
Outstanding performances or physical effects have been recently demonstrated with semiconductor nanowires. All the experiments require technological steps involving a contact processing or contact through a retrofitted probe that are usually performed with the help of a scanning electron microscope working with an energy beam in the range of 5 to 20 keV. So far no detailed study of the electrical modifications that are caused by electron beam irradiation have been published. Based on four-point probe transport measurements performed with different nanowire surface chemistries, field-effect based measurements and numerical simulations of the electron density, we show that the change of the resistivity is caused by a deepening and a narrowing of the electron surface accumulation layer. Although an electron beam of a few keV, typically used for the inspection and the processing of materials, propagates through the entire nanowire cross-section, the nanowire electrical properties are predominantly affected by radiation-induced defects occuring at the nanowire surface and not in the bulk.