Berlin 2024 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 46: Transport properties II

HL 46.2: Talk

Thursday, March 21, 2024, 15:15–15:30, ER 325

Direct Observation of Hole Drift and Diffusion in Contacted Nanowires Under Local Illumination — •Moritz Wehrmeister, Daniel Lengle, Carlo Höhmann, Christian Strelow, Alf Mews, and Tobias Kipp — Institute of Physical Chemistry, University of Hamburg, Hamburg, Germany

Kelvin probe force microscopy (KPFM) is a method for measuring the surface potential. Being based on atomic force microscopy, KPFM enables investigating nanostructures, such as nanowires and nanosheets. Combining optical, electrical, and KPFM measurements in one setup enables advanced investigations of the charge-carrier separation in these materials and the properties of semiconductor-metal interfaces. We investigate individual electrically contacted CdS nanowires, by combining scanning photocurrent mapping (SPCM) and KPFM. The charge-carrier mobility information of SPCM extended by KPFM maps gives a more complete picture of the path and hurdles, the charge carriers take inside the nanodevice in operando. We show that upon local optical excitation, differences in charge-carrier mobilities of electrons and holes lead to an imbalance in the surface potential. At the point of illumination, positive charges accumulate, due to their lower mobility. KPFM reveals this imbalance and how it influences the potential drop along the biased CdS nanowire. Furthermore, performing KPFM while optically exciting the probed sample position monitors the excess of positive charge carriers for each position of the illuminated nanowire. A decrease of this excess shows how holes drift and diffuse into the contacts, where they contribute to the measured photocurrent.

Keywords: Semiconductor Nanowires; Charge-Carrier Transport; Kelvin Probe Force Microscopy; Local Illumination