Thickness-dependent optical response and ultrafast carrier dynamics of PtSe2 films

As a novel transition metal dichalcogenide material with high carrier mobility, adjustable band gap and excellent stability, the photocarrier ultrafast dynamics of PtSe2 films with the different thickness is researched by ultrafast transient absorption spectrum and optical pump and terahertz probe spectrum. The experimental results show that the few-layer PtSe2 films present semiconductor phase which exhibits a triple exponential decay process, while multi-layer of PtSe2 films present semi-metallic phase which exhibits a double exponential decay process. And the principle of light response and carrier dynamics of PtSe2 films after excitation is analyzed, one found that the defect state carrier recombination exists in all samples. The carrier relaxation is dominated by Auger exciton–exciton annihilation in few-layer PtSe2 film, and the defect state of multiple-layer PtSe2 film plays a dominant role in the photo carrier relaxation, which is promising to a further application in modulators and detectors for characterizing the transition from semiconductor to semi-metal by controlling its film thickness.