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Spatially Resolved Photoconductivity in WS2/MoS2 lateral heterostructures

Published

Author(s)

Samuel Berweger, Hanyu Zhang, Prasana Sahoo, Benjamin Kupp, Jeffrey Blackburn, Elisa Miller, Thomas Mitchell (Mitch) Wallis, Dmitri Voronine, Pavel Kabos, Sanjini Nanayakkara

Abstract

The optical and electronic properties of 2D semiconductors are intrinsically linked via the strong interactions between optically excited bound species and free carriers. Here we use near-field scanning microwave microscopy (SMM) to image spatial variations in photoconductivity in MoS2−WS2 lateral multijunction heterostructures using photon energy-resolved narrowband illumination. We find that the onset of photoconductivity in individual domains corresponds to the optical absorption onset, confirming that the tightly bound excitons in transition metal dichalcogenides can nonetheless dissociate into free carriers. These photogenerated carriers are most likely ntype and are seen to persist for up to days. Informed by finite element modeling we reveal that they can increase the carrier density by up to 200 times. This persistent photoconductivity appears to be dominated by contributions from the multilayer MoS2 domains, and we attribute the flake-wide response in part to charge transfer across the heterointerface. Spatial correlation of our SMM imaging with photoluminescence (PL) mapping confirms the strong link between PL peak emission photon energy, PL intensity, and the local accumulated charge. This work reveals the spatially and temporally complex optoelectronic response of these systems and cautions that properties measured during or after illumination may not reflect the true dark state of these materials but rather a metastable charged state.
Citation
ACS Nano
Volume
14

Keywords

scanning microwave microscopy (smm), scanning microwave impedance microscopy (smim), transition metal dichalcogenide, heterostructure, photoluminescence, persistent photoconductivity

Citation

Berweger, S. , Zhang, H. , Sahoo, P. , Kupp, B. , Blackburn, J. , Miller, E. , (Mitch), T. , Voronine, D. , Kabos, P. and Nanayakkara, S. (2021), Spatially Resolved Photoconductivity in WS2/MoS2 lateral heterostructures, ACS Nano, [online], https://dx.doi.org/10.1021/acsnano.0c06745, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=929606 (Accessed August 9, 2022)
Created April 27, 2021