Ultrafast Auger process in few-layer PtSe

Enhanced many-body interactions due to strong Coulomb interactions and quantum confinement are one of the most prominent features of two-dimensional systems. The Auger process is a representative many-body interaction typically observed in two-dimensional semiconductors, determining important physical properties of materials, such as carrier lifetime, photoconductivity, and emission quantum yield. Recently, platinum dichalcogenides, represented by PtSe 2 and PtS 2 , have attracted great attention due to their superior air stability, thickness-dependent semimetal-to-semiconductor transition, and exotic magnetic characteristics. However, the Auger process in platinum dichalcogenides has not been investigated to date. Here, we utilized ultrafast optical-pump terahertz-probe spectroscopy to explore carrier dynamics in few-layer semiconducting PtSe 2 . Most of the excited carriers are trapped by defects within ∼10 ps after excitation due to high defect density. We overcome this challenge by raising the excitation intensity to saturate trap sites with carriers, and observed a many-body process involving the carriers that survived the rapid trapping. This process is not band-to-band Auger recombination, but rather defect-assisted Auger recombination in which free carriers interact with trapped carriers at defects. Theoretical simulations show that this three-body Auger process can be approximated as bimolecular recombination at the rate of ∼3.3 × 10 −3 cm 2 s −1 . This work provides insights into the interplay between ultrafast many-body processes and defects in two-dimensional semiconductors. Direct observation of the Auger process (representative many-body interaction of carriers) in emerging two-dimensional semiconductor PtSe 2 .