Fig. 6.

The properties of excitons in 2D heterostructures. a EL spectra of the MoSe₂/WSe₂ vertical heterostructure, a small intralayer signal at 1.62 eV was detected, and the inset illustrates the device structure. (Blue and green lines represent the WSe₂ and MoSe₂, respectively.) Reprinted with permission from Ref. [66]. b The optical selection rules in a MoX₂/WX₂ heterostructure with twist angle θ of 0° and 60°, respectively. Reprinted with permission from Ref. [17]. c, d Time-resolved PL (d) of WSe₂/MoSe₂ heterostructure (c) after σ+ pulsed laser excitation, black dots and red dots corresponding to the co-polarized emission (σ+) and cross-polarized emission (σ−), and the blue line shows the degree of polarization, which is tunable by the gate voltage. Reprinted with permission from Ref. [67]. e The trions composed in different ways existing in the MoS₂/WS₂ bilayer. Reprinted with permission from Ref. [68]. (Color figure online)