Spatiotemporal Imaging of Thickness-Induced Band-Bending Junctions
van der Waals materials exhibit naturally passivated surfaces and an ability to form versatile heterostructures to enable an examination of carrier transport mechanisms not seen in traditional materials. Here, we report a new type of homojunction termed a "band-bending junction" whose potential landscape depends solely on the difference in thickness between the two sides of the junction. Using MoS₂ on Au as a prototypical example, we find that surface potential differences can arise from the degree of vertical band bending in thin and thick regions. Furthermore, by using scanning ultrafast electron microscopy, we examine the spatiotemporal dynamics of charge carriers generated at this junction and find that lateral carrier separation is enabled by differences in the band bending in the vertical direction, which we verify with simulations. Band-bending junctions may therefore enable new optoelectronic devices that rely solely on band bending arising from thickness variations to separate charge carriers.
Additional Information© 2021 American Chemical Society. Received: April 15, 2021; Revised: June 15, 2021. This work was primarily supported by the Photonics at Thermodynamic Limits Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DE-SC0019140, which supported the sample fabrication, experimental measurements, data analysis, and simulations. J.W. acknowledges additional support from the National Science Foundation Graduate Research Fellowship under grant no. 1144469. Data analysis by A.D. acknowledges support from the UCLA Council on Research Faculty Research Grant. Data analysis by B.L. acknowledges support for this work from the U.S. Army Research Office under the award number W911NF-19-1-0060. Additional Kelvin probe force microscopy measurements and data analysis, performed by D.J. and K.J., acknowledge support for this work by the U.S. Army Research Office under contract number W911NF-19-1-0109. The work at the University of Pennsylvania was carried out at the Singh Center for Nanotechnology, which is supported by National Science Foundation (NSF) National Nanotechnology Coordinated Infrastructure Program grant NNCI-1542153. This research used resources of the Advanced Light Source, a U.S. DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. Author Contributions: J.W., A.D., D.J., and H.A.A. developed the main ideas. J.W., A.D., and D.J. fabricated the samples. B.L. performed SUEM measurements, developed in the laboratory of A.H.Z. A.K. and K.J. performed the Kelvin probe measurements. J.W. performed ARPES measurements with support from D.J., E.R., A.B., and C.M.J. J.W. performed both the time-domain and steady-state simulations with assistance from A.D. H.A.A. supervised all of the data analysis. All authors contributed to the discussion and interpretation of results as well as the presentation and preparation of the manuscript. The authors declare no competing financial interest.
Submitted - 2103.03242.pdf
Supplemental Material - nl1c01481_si_001.pdf