Optically controlled ultrafast terahertz switching in wafer scale PtSe2 thin films

In this study, we have reported a newly ultrafast optically modulated terahertz (THz) switch based on the transition metal dichalcogenide (TMD) material platinum diselenide (PtSe2) with different thicknesses. The high-quality PtSe2 thin films with centimeter scale are fabricated on sapphire substrate by the chemical vapor deposition method. The optical pump and THz probe (OPTP) spectroscopy reveals that the THz response of the thin films is as fast as similar to 2.0 ps after photoexcitation of a 780 nm pulse. Interestingly, we found that the THz response time of the PtSe2 semimetal phase is faster than that of the semiconducting phase. In addition, the THz response time becomes faster when increasing the film thickness for the semimetal phase PtSe2, while for the semiconducting phase, the response time becomes slower with film thickness. Moreover, degenerate optical pump and optical probe spectroscopy (OPOP) demonstrated that the ultrafast photoinduced negative absorption (photoinduced bleaching) occurs after photoexcitation of 780 nm, and the subsequent recovery consists of two relaxation processes: the fast component with more than 85% of weight has a lifetime of similar to 1.5 ps for semiconducting-phase films and less than 1 ps for the semimetal phase, similar to the response time obtained from OPTP measurement. The slow component with less than 15% of weight has a lifetime of a few hundred picoseconds. The subpicosecond response time observed in both OPTP and OPOP is ascribed to the carrier trapping by defect states, and the slow relaxation process appearing in OPOP arises from the defect state relevant relaxation that is insensitive to the THz photoconductivity due to the frozen carrier mobility in defect states. Our experimental results demonstrate a new application of TMD materials such as PtSe2 in THz technology, for instance, the design and fabrication of THz modulators and THz switches. (C) 2021 Optical Society of America

Automated summary

In this study, a newly ultrafast optically modulated terahertz switch based on platinum diselenide (PtSe2) is reported. The response time of the semimetal phase PtSe2 is faster than the semiconducting phase when increasing film thickness. The rapid component after photoexcitation has a lifetime of approximately 1.5 ps for semiconducting-phase films and less than 1 ps for the semimetal phase, while the slow component has a lifetime of a few hundred picoseconds.