Photoexcited Electron Dynamics in Cd₃As₂ Revealed by Time- and Energy-Resolved Photoemission Electron Microscopy

Abstract

Cd 3 As 2 , as a three-dimensional Dirac semimetal, has attracted considerable research interest because of its distinct optoelectronic and topological properties. However, simultaneous studies on the carrier dynamics in Cd 3 As 2 in spatial, temporal, and energy dimensions are still lacking. Here, we apply photoemission electron microscopy combined with the femtosecond pump− probe technique to reveal the dynamics of the Cd 3 As 2 nanoplate. The photoexcited electrons on the Cd 3 As 2 surface decay fast with an average decay time of 0.68 ps. The electron dynamics are independent of the spatial location by analyzing the decay curves at different positions on the Cd 3 As 2 nanoplate. The effect of boundary states on the relaxation process is negligible. The photoexcited electrons can relax in picoseconds, regardless of the pump or probe power. In the energy-resolved mode, the decay time of nonequilibrium electrons decreases from 7 to 0.25 ps as the energy of hot electrons increases. These results contribute to understanding the photoexcited electron behavior of Cd 3 As 2 .

Reveal Ultrafast Electron Relaxation across Sub-bands of Tellurium by Time- and Energy-Resolved Photoemission Microscopy

“…Diverse carrier dynamics in 2D materials with time scales from tens of femtoseconds to hundreds of picoseconds, such as carrier thermalization, cooling, exciton–exciton annihilation, intervalley scattering, valley depolarization, and defect trapping, − have been characterized by transient absorption or reflection spectroscopy, − time- and angle-resolved photoemission spectroscopy, , time-resolved photoemission electron microscopy (TR-PEEM), − etc. Among these techniques, femtosecond TR-PEEM has advantages in probing the ultrafast carrier dynamics with additional ultrahigh spatiotemporal resolution.…”

“…Among these techniques, femtosecond TR-PEEM has advantages in probing the ultrafast carrier dynamics with additional ultrahigh spatiotemporal resolution. Moreover, time- and energy-resolved photoemission electron microscopy (TR- and ER-PEEM) can reveal the dynamics of excited-state carriers in the energy domain by combining an energy analyzer. ,, TR- and ER-PEEM have been used in revealing the ultrafast carrier dynamics of a number of materials, such as inorganic semiconductors, , graphene, transition metal dichalcogenides, − perovskite, , etc. , …”

Metasurface Enabled Photothermoelectric Photoresponse of Semimetal Cd3As2 for Broadband Photodetection

“…The three-dimensional Dirac semimetal Cd 3 As 2 , a bulk analog of graphene, has attracted widespread attention because of its ultrahigh carrier mobility and gapless Dirac band structure. − Similar to graphene, Cd 3 As 2 can be used in broadband photodetectors with a detection spectrum ranging from ultraviolet to long-wave infrared. , In contrast to monolayer graphene, which has an absorption coefficient of ∼2.3%, the bulk characteristics of Cd 3 As 2 endow it with a strong absorption capability and consequently better photoresponsivity. In addition, similar to graphene, , the Cd 3 As 2 photodetector exhibits an ultrafast response up to the picosecond scale, as revealed by previous femtosecond pump–probe measurements. − Meanwhile, the oxidation layer on the surface of Cd 3 As 2 provides good stability through isolation from the external environment . Therefore, Cd 3 As 2 is a promising material for high-performance photodetectors.…”

“…35,36 The PEEM is a powerful tool for investigating photonic modes, including surface plasmon polaritons, 37,38 dielectric waveguides, 39,40 and QCW modes. 27 In our previous work, 9 we demonstrated that the photoemission intensity of Cd 3 As 2 is proportional to the electric field intensity. The increased electric field contributes to optical absorption.…”

“…■ METHODS Sample Characterization and Device Fabrication. In our previous study, 9,27 the synthesis process, energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry characterizations of the Cd 3 As 2 nanoplates were discussed in detail. The synthesized Cd 3 As 2 nanoplates were transferred to a Si substrate with a 285-nm-thick SiO 2 layer using an XYZ micromanipulator.…”