Ultrafast carrier dynamics in SnSe thin film studied by femtosecond transient absorption technique

Abstract

The femtosecond transient absorption (TA) technique is used to study the ultrafast carrier dynamics of SnSe thin film prepared by pulsed laser deposition (PLD), which is basically characterized by X-ray diffraction (XRD). The XRD pattern shows pure single-phase of SnSe in term of the diffraction peak of crystalline direction (400), and the indirect bandgap can be estimated by Kubelka-Munk treatment in transmittance spectrum. The TA spectra of SnSe thin film are observed in picosecond timescale, corresponding to the process of carrier scattering, carrier recombination and lattice thermal effects. A triple exponential decay model, including fast (~2 ps), medium (~100 ps), and slow (ns) components, is well fitted to the TA dynamics of SnSe film. There are different dominant processes in the fast, medium and slow components, which are related to the carrier process of scattering, recombination and lattice diffusion, respectively. And these responses are modulated by single pulse energy, the carrier concentration and temperature can affect the microscopic relaxation process. The thickness of SnSe thin films also affect the ultrafast carrier dynamics. And we find there are differences in different probe wavelengths. Our results can improve the comprehension of the relaxation mechanism in SnSe thin film, and provide the important view about the ultrafast optical properties of this layered IV-VI chalcogenide.