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. 2019 Dec 16;10:5736. doi: 10.1038/s41467-019-13713-1

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 2 — a and b Optical microscope image (a) and scanning photocurrent image (b) of a device with irregular shape. c and d, Optical microscope image (c) and scanning photocurrent image (d) of a device with trapezium shape. e, f, g and h Optical microscope image (e) and scanning photocurrent image of different parts (f, g, and h) of a long device with edges along various crystal fracture directions. All measurements were excited with 180-μW 1.96-eV pulse laser. The white arrows in microscopy images mark the crystallographic $\hat{a}$ -axis and the white dashed lines mark the edges that have no photocurrent responses. The red symbols in Figure (a) display the point group symmetries of the crystal lattice. Photocurrents only arise along edges that break the mirror symmetry, in good agreement with the symmetry analysis. The scale bars are all 8 μm.