Photo-Carrier Lifetime in Binary and Ternary Heterostructures of Transition Metal Dichalcogenides

Binary and ternary transition metal dichalcogenide (TMD) heterostructures, MSe₂ and MSeS (where M = Mo or W), are investigated as future building blocks for high-performance device applications with a tailorable electronic bandgap. For light-emitting device applications, investigating the decay time of the material is a prerequisite. Herein, time-resolved photoluminescence (TRPL) of binary and ternary TMD heterostructures is measured. A tri-exponential function is adopted to fit the TRPL data. Short, medium, and long decay times are <50 ps, ≈400 ps, and >400 ps, respectively. Except for monolayer MoSe₂ and MoSeS, only two PL decay time components are observed with a large contribution from short decay time photocarriers (>80%). Bilayer TMDs exhibit a much shorter PL decay time, which could be attributed to the indirect nature of excitons and different dielectric environments, compared with that of monolayer TMDs. Using the center-of-mass (CM) method, a PL decay time map is successfully obtained for binary and ternary TMD heterostructures. This allows the qualitative visualization of the decay time distribution within the heterostructure or among other materials. This technique could be applied to assess the decay time of materials used in high-performance light-emitting devices.