飞秒激光诱导单层二硫化钨的光响应研究

Femtosecond laser-induced optical response of monolayer WS_2

过渡金属硫化物因具有很大的激子束缚能、较强的库仑相互作用以及自旋谷能耦合特性而备受关注,同时该类材料也为研究原子层厚半导体的性质以及开发其在光电器件方向应用的潜力提供机会,研究过渡金属硫化物被激发后的光响应很重要.利用泵浦探测瞬态吸收光谱系统研究单层WS_2中光生载流子的动力学行为,发现激子以俄歇式激子激子湮灭的方式进行无辐射复合,寿命约为27 ps.通过分析不同泵浦光(波长分别为590 nm、580 nm及570 nm)激发条件下位于613 nm的光致漂白信号,证实亚皮秒的衰减组分为激子的形成过程.通过分析A激子共振的漂白和线宽展宽随时间变化,研究导致激子跃迁能发生蓝移和红移的物理过程,结果表明,导致单层WS_2被激发后光响应发生变化的原因有2个,分别是光生载流子导致的多体相互作用以及材料通过声子将热量传递给基底的冷却过程.

The transition metal dichalcogenides(TMDs)have received much attention because of their large exciton binding energy,strong Coulomb interactions and spin-valley coupling.TMDs materials also provide an excellent opportunity to probe properties of atomic-thick semiconductors and develop their potential applications in photoelectronic devices.Therefore,it is important to explore the optical response of TMDs after excitation.In this paper,we study the dynamical behavior of photo-excited carriers in monolayer WS 2 via pump-probe transient absorption spectroscopy.We find that the excitons are recombined in the form of Auger exciton-exciton annihilation,and the lifetime of exciton is about 27 ps.By analyzing the photobleaching signals at 613 nm exited by different pumping wavelengths(590 nm,580 nm and 570 nm,respectively),we conform the formation process of excitons in the sub-picosecond decay component.By analyzing the time-dependent bleaching and broadening of the A-exciton resonance and discussing the physical processes leading to blue-shift and red-shift of the exciton transition energy,it is shown that there are two reasons for the change of the light response after excitation of the monolayer WS 2,which are the multi-body interaction of the photo-excited carriers and the cooling process of material through the heat transfer to substrate by phonon.