The surface termination of In4Se3(001) and the interface of this layered trichalcogenide, with Au, was examined using x-ray photoemission spectroscopy. Low energy electron diffraction indicates that the surface is highly crystalline, but suggests an absence of C2v mirror plane symmetry. The surface termination of the In4Se3(001) is found, by angle-resolved x-ray photoemission spectroscopy, to be In, which is consistent with the observed Schottky barrier formation found with this n-type semiconductor. Transistor measurements confirm earlier results from photoemission, suggesting that In4Se3(001) is an n-type semiconductor, so that Schottky barrier formation with a large work function metal, such as Au, is expected. The measured low carrier mobilities could be the result of the contacts and would be consistent with Schottky barrier formation.

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Theoretical and experimental investigations of various exfoliated samples taken from layered In4Se3 crystals are performed. In spite of the ionic character of interlayer interactions in In4Se3 and hence much higher calculated cleavage energies compared to graphite, it is possible to produce few‐nanometer‐thick flakes of In4Se3 by mechanical exfoliation of its bulk crystals. The In4Se3 flakes exfoliated on Si/SiO2 have anisotropic electronic properties and exhibit field‐effect electron mobilities of about 50 cm2 V−1 s−1 at room temperature, which are comparable with other popular transition metal chalcogenide (TMC) electronic materials, such as MoS2 and TiS3. In4Se3 devices exhibit a visible range photoresponse on a timescale of less than 30 ms. The photoresponse depends on the polarization of the excitation light consistent with symmetry‐dependent band structure calculations for the most expected ac cleavage plane. These results demonstrate that mechanical exfoliation of layered ionic In4Se3 crystals is possible, while the fast anisotropic photoresponse makes In4Se3 a competitive electronic material, in the TMC family, for emerging optoelectronic device applications.

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