Fig. 1. (Color online) (a) XRD patterns of the SnSe₂, SnS, and SnSe crystals. The insets are the corresponding optical microscopy images. (b) XPS spectra of the SnS, SnS, and SnSe crystals.

Fig. 2. (Color online) (a) AFM results of the SnS/SnSe₂ and SnSe/SnSe₂ heterostructures. The insets are the corresponding height profile. (b) Raman spectra of the SnS/SnSe₂ and SnSe/SnSe₂ heterostructures.

Fig. 3. (Color online) (a) and (b) Output characteristics of the SnS/SnSe₂ and SnSe/SnSe₂ photodetectors. The insets: the schematic diagrams and the optical images of the photodetectors. (c) and (d) Transfer characteristics on linear (left) and semi-logarithmic (right) scales of the SnS/SnSe₂ and SnSe/SnSe₂ photodetectors.

Fig. 4. (Color online) (a) and (b) The semi-logarithmic current−voltage curves of the SnS/SnSe₂ and SnSe/SnSe₂ photodetectors. (c) and (d) Transient photoresponse of the SnS/SnSe₂ and SnSe/SnSe₂ photodetectors. (e) and (f) Response time and photocurrent−power density plots of the two types of photodetectors.

Fig. 5. (Color online) (a) Photocurrent−power density plots of the SnS/SnSe₂ and SnSe/SnSe₂ photodetectors under different wavelengths. (b) Transient photoresponse under different wavelengths. (c) Responsivity and normalized detectivity as a function of wavelength. (d) Comparison of normalized detectivity and response time of our devices with photodetectors based on other heterostructures under different wavelengths.

Fig. 6. (Color online) (a) and (b) Planar-averaged charge density difference of the SnS/SnSe₂ and SnSe/SnSe₂ heterostructures. (c) and (d) Band alignments of the SnS/SnSe₂ and SnSe/SnSe₂ heterostructures.