Nonlinear optical absorption and ultrafast carrier's dynamics of ZrTe2 by Transient Absorption (TA) Spectrometer

Abstract

The TMDCs (transition metal di-chalcogenides) family provides a platform to discover novel physical phenomena and exotic electronic properties for various device applications. The ultrafast carrier dynamics of the ZrTe2 sample demonstrate that Transient absorption (TA) signals have (electron-hole) constituents and trap carriers. TA variations depend upon carrier properties and photo-excitation due to spatially localized excitations. In the broadband positive signal obtain from ESA (Excited-State Absorption) and the negative signal from GSA (Ground State Absorption). It is seen that ESA is greater as compared to GSA due to fluence-dependent nonlinear absorption (NLA). To study the TA excitons dynamics of ZrTe2, we attribute positive probe bleach (PB) as hot excitons that are situated at higher excitonic states. The TA from power-dependent decay demonstrates that both types of excitons self-trapped excitons (STE) and free excitons (FE) have three processes, relaxation of ST excitons from F excitons, annihilation process between exciton-exciton and relaxation of the ground state from ST excitons states. The variation in exciton annihilation rate gives the exact information about exciton dynamics, which is the key aspect of transient absorption spectroscopy. The free charge carriers are largely localized and move faster compared to the non-localized trapped charge carriers.