Spatially\nResolved Persistent Photoconductivity in\nMoS<sub>2</sub>–WS<sub>2</sub> Lateral Heterostructures Article Swipe
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· 2020
· Open Access
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· DOI: https://doi.org/10.1021/acsnano.0c06745.s001
· OA: W4287690987
The\noptical and electronic properties of 2D semiconductors are\nintrinsically linked <i>via</i> the strong interactions\nbetween optically excited bound species and free carriers. Here we\nuse near-field scanning microwave microscopy (SMM) to image spatial\nvariations in photoconductivity in MoS<sub>2</sub>–WS<sub>2</sub> lateral multijunction heterostructures using photon energy-resolved\nnarrowband illumination. We find that the onset of photoconductivity\nin individual domains corresponds to the optical absorption onset,\nconfirming that the tightly bound excitons in transition metal dichalcogenides\ncan nonetheless dissociate into free carriers. These photogenerated\ncarriers are most likely <i>n</i>-type and are seen to persist\nfor up to days. Informed by finite element modeling we reveal that\nthey can increase the carrier density by up to 200 times. This persistent\nphotoconductivity appears to be dominated by contributions from the\nmultilayer MoS<sub>2</sub> domains, and we attribute the flake-wide\nresponse in part to charge transfer across the heterointerface. Spatial\ncorrelation of our SMM imaging with photoluminescence (PL) mapping\nconfirms the strong link between PL peak emission photon energy, PL\nintensity, and the local accumulated charge. This work reveals the\nspatially and temporally complex optoelectronic response of these\nsystems and cautions that properties measured during or after illumination\nmay not reflect the true dark state of these materials but rather\na metastable charged state.
