Van der Waals SnSe₂₍₁₋<i>_x</i>₎S₂<i>_x</i> Alloys: Composition‐Dependent Bowing Coefficient and Electron–Phonon Interaction

Abstract

Abstract The design of advanced functional materials with customized properties often requires the use of an alloy. This approach has been used for decades, but only recently to create van der Waals (vdW) alloys for applications in electronics, optoelectronics, and thermoelectrics. A route to engineering their physical properties is by mixing isoelectronic elements, as done for the SnSe 2(1− x ) S 2 x alloy. Here, by experiment and first‐principles modeling, it is shown that the value of x can be adjusted over a wide range, indicating good miscibility of the SnS 2 and SnSe 2 compounds. The x ‐dependence of the indirect bandgap energy from E ind = 1.20 eV for SnSe 2 to E ind = 2.14 eV for SnS 2 , corresponds to a large bowing coefficient b ≈ 1 eV, arising from volume deformation and charge exchange effects due to the different sizes and orbital energies of the S‐ and Se‐atoms. This also causes composition‐dependent phonon energy modes, electron–phonon interaction, and temperature dependence of E ind . The alloys are exfoliable into thin layers with properties that depend on the composition, but only weakly on the layer thickness. This work shows that the electronic and vibrational properties of the SnSe 2(1− x ) S 2 x alloy and its thin layers provide a versatile platform for development and exploitation.