Study On The Photocarriers Dynamics Of PtSe₂ And Its Van Der Waals Heterostructure

Atomically thin 2D layered crystalline materials are currently attracting much attention in the field of optoelectronics,photonics,and condensed matter physics due to their uniquely controllable properties.Among the 2D material family,platinum diselenide（PtSe₂）,a noble metal dichalcogenide,has emerged as a promising material for investigating quasiparticle interactions and for developing mid-infrared devices.Recent studies have shown some intriguing properties of PtSe₂,such as high charge-carrier mobility,intrinsic patterning,piezoresistivity,and spin-layer locking.Despite a number of reports addressing the synthesis,electrical properties,and prototype devices,there is still a lack of understanding regarding the carrier dynamics in PtSe₂ and its van der waals heterostructure on an ultrafast time scale.Through carrier injection by ultrafast laser pulses,understanding ultrafast dynamical processes in 2D materials is essential for exploring many-body phenomena and light–matter coupling from a fundamental physics point of view.Here,photocarrier spatiotemporal dynamics of PtSe₂ and ultrafast interlayer charge transfer in the heterostructure formed by PtSe₂ and WS₂ are studied by transient absorption microscopy.The energy band structures of monolayer,bilayer and bulk materials PtSe₂ are calculated by using interactive correlation functional（GGA-PBE）and Heyd-Scuseria-Ernzerhof（HSE）methods.The state densities of monolayer and bilayer PtSe₂ are calculated by using tetrahedron method with Bl?chl corrections.The absorption,reflection and transmission spectra of PtSe₂ are obtained by studying its linear response function.The excitonic dynamics in monolayer PtSe₂ synthesized by chemical vapor deposition（CVD）is studied by spatiotemporally resolved transient absorption microscopy.A direct transition at about 1.85 e V in monolayer PtSe₂ is experimentally established.Diffusion of excitons in the monolayer plane is directly resolved.An exciton diffusion coefficient of 48 cm²/s is obtained,which several times to one-order-of-magnitude larger than most previously studied monolayer semiconductors.For comparison,the diffusion coefficient in bilayer PtSe₂ is about 6-7 cm²/s.Other aspects of the exciton dynamics,such as their recombination lifetime and diffusion length,are also measured.In particular,the unusually large exciton diffusion coefficient makes monolayer PtSe₂ a good candidate for developing practical room-temperature excitonic devices.We study,for the first time,the ultrafast interlayer charge transfer between bilayer PtSe₂ and monolayer WS₂,as an example to establish PtSe₂ as a valuable member of the material library for developing novel 2D heterostructures.Although interlayer charge transfer has been observed in other 2D heterostructures,most studied combined 2D materials of the same lattice structure（2H/2H）.This is one of the few examples of（1T/2H）heterostructure that show such highly efficient interlayer charge transfer properties.Combining layer-selective pump-probe with photoluminescence quenching measurements,we establish their formation of a type-II band alignment.The charge transfer facilitates formation of the interlayer excitons with a long lifetime of about 400ps,a diffusion coefficient of 0.9 cm²/s,and a diffusion length of 200 nm.The information revealed here is useful for developing fundamental understanding on the performance of various optoelectronic devices based on heterostructures involving PtSe₂.