(a) Top: optical image of the photodetector based on a MoS₂–graphene–WSe₂ heterostructure. Bottom: schematic diagram of the device. scale bar, 10 μ m . (b) Responsivity and specific detectivity of the photodetector for wavelengths ranging from 400 nm to 2400 nm with an interval of 100 nm. (c) Top: spectra from ultraviolet to infrared. The bandgap of MoS₂ (E_g1) and WSe₂ (E_g2) and the corresponding wavelengths are plotted on the graph, respectively. Bottom left: for h ν > E g 1 > E g 2 , MoS₂, graphene, and WSe₂ all can generate photogenerated electron–hole pairs. Bottom right: for h ν < E g 1 < E g 2 , only graphene can generate photogenerated electron–hole pairs. (d) The schematic diagram of the device based on graphene–Bi₂Te₃ heterostructure. (e) The dependence of photocurrent of devices based on pure graphene and graphene–Bi₂Te₃ heterostructure on source-drain voltage V_SD. V_G=0 V. (f) Dependence of photocurrent on wavelengths ranging from 400 nm to 1550 nm. Panels (a)–(c) are reproduced from Ref. [79] with permission from the American Chemical Society. Panels (d)–(f) are reproduced from Ref. [82] with permission from the American Chemical Society.