Dresden 2017 – scientific programme

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O: Fachverband Oberflächenphysik

O 32: Focus Session: Charge Transport at Surfaces and Nanostructures with Multi-probe Techniques I

O 32.2: Talk

Tuesday, March 21, 2017, 11:00–11:15, WIL C307

Multi-tip STM analysis of freestanding GaAs-NWs in dependence on surface conditioning — •Andreas Nägelein, Matthias Steidl, Peter Kleinschmidt, and Thomas Hannappel — Photovoltaics Group, Institute of Physics, Technische Universität

Nanostructures e.g. III-V nanowires (NW) are promising candidates for optoelectronic applications. The investigated NWs obtain different doping structures and were grown by MOCVD using the VLS (vapor liquid solid) growth mode. In order to investigate these freestanding nanowires electrically, a multi-tip STM (MT-STM) was used. Here, four-point probe measurements are performed non-destructively by contacting three tips at the nanowire and using the substrate as fourth contact. Besides the investigation of doping profiles, a comparison between nanowires prior to, and after, oxidation was carried out. Therefore, after transferring the NW-samples to the MT-STM in UHV, electrical characterization was performed. Subsequently, the samples were stored at ambient atmosphere and resistance profiles were recorded again. The resistance slope in the intrinsic part of the NW increased drastically with oxidation. In contrast to doped NW-parts where the charge carrier transport mainly happens in the center of a NW, a conductive channel does not exist for intrinsic NWs. Besides contamination-induced band bending, the conductivity is also affected by the surface states themselves. Hence, we consider a changed surface conductivity of the intrinsic nanowire segment as a likely explanation of its increased resistance after exposure to ambient atmosphere.