Enhanced exciton diffusion from interlayer charge-transfer transitions in PtSe₂/MoSe₂ van der Waals heterojunction

Artificial van der Waals (vdWs) heterostructures offer unprecedented opportunities to explore and reveal novel synergistic electronic and optical phenomena, which are beneficial for the development of novel optoelectronic devices at atomic limits. However, due to the damage caused by the device fabrication process, their inherent properties such as carrier mobility are obscured, which hinders the improvement of device performance and the incorporation of vdWs materials into next-generation integrated circuits. Herein, combining pump-probe spectroscopic and scanning probe microscopic techniques, the intrinsic optoelectronic properties of PtSe₂/MoSe₂ heterojunction were nondestructively and systematically investigated. The heterojunction exhibits a broad-spectrum optical response and maintains ultrafast carrier dynamics (interfacial charge transfer ~ 0.8 ps and carrier lifetime ~ 38.2 ps) simultaneously. The in-plane exciton diffusion coefficient of the heterojunction was extracted (19.4 ± 7.6 cm²∙s⁻¹), and its exciton mobility as high as 756.8 cm²∙V⁻¹∙s⁻¹ was deduced, exceeding the value of its components. This enhancement was attributed to the formation of an n-type Schottky junction between PtSe₂ and MoSe₂, and its built-in electric field assisted the ultrafast transfer of photogenerated carriers from MoSe₂ to PtSe₂, enhancing the in-plane exciton diffusion of the heterojunction. Our results demonstrate that PtSe₂/MoSe₂ is suitable for the development of broad-spectrum and sensitive optoelectronic devices. Meanwhile, the results contribute to a fundamental understanding of the performance of various optoelectronic devices based on such PtSe₂ two-dimensional (2D) heterostructures.