【作者】 王琳；

【导师】 张汉壮； 王英惠；

【作者基本信息】 吉林大学 ， 光学， 2020， 硕士

【摘要】 由于单层石墨烯在光电场的广泛应用,原子性的二维薄膜材料受到了广泛关注。半导体过渡金属二元化物（TMDCs）家族包括MoS₂,WS₂,MoSe₂和MoTe₂,由于其亚纳米级的厚度,以及较强的光学吸收特性,和约1-2 eV的相当大的带隙等重要的物理特性使它的重要作用日益增加。单层TMDCs作为直接带隙半导体更是有着更高的发光效率,因此本文选用单层WS₂薄膜作为研究对象。在本篇论文中我们制作了一个基于单层WS₂的简单的大面积的光电器件,由于单层WS₂的特殊的载流子动力学,器件显示出了较高的光灵敏度和快速响应速率。而且由于激发的单层WS₂的时间依赖性演化过程的确定有助于器件的研究,对基于二维过渡金属二硫化物的光电子器件的合理设计提供基础十分重要,因此我们使用瞬态吸收（TA）来测试激发态单层WS₂薄膜的弛豫特性。研究发现,当泵浦光子密度增加至3.45×10¹⁴cm^-2时,激子之间会发生多体相互作用。激子解离（带电激子的产生）会参与光致弛豫过程可能是导致器件性能良好的原因。通过比较WS₂激发至A,B激子态的弛豫特性,得到高能激子有利于载流子的产生和器件的性能的结论。然而,由缺陷态俘获过程产生的束缚激子弛豫是真实存在的并且这一过程不利于器件的性能。为了进一步研究单层WS₂中的激子动力学,我们利用瞬态吸收（TA）探测了单层WS₂膜的时间分辨光学响应,确定了其激子弛豫机制。我们发现通过改变泵浦光和探测光的强度,对A激子之间的多体相互作用可以得到进一步的研究。具体来说,我们发现激子的俘获过程和激子的辐射复合在A激子的弛豫过程中占主导地位,然而随着泵浦光强增高,激子-激子湮灭逐渐占据主要衰变通道。更多还原

【Abstract】 Since the monolayer of graphene has been applied extensively in the optoelectronic fields,the atomically thin materials have been received much attention.The family of semiconducting transition metal dichalcogenides（TMDCs）,involving MoS₂,WS₂,MoSe₂,and MoTe₂,have highlighted an increasingly important role,owing to their intriguing physical properties,such as their sub-nanometer thickness,large optical absorbance and sizable bandgaps around 1-2 eV.As a direct band gap semiconductor,single-layer TMDCs has a higher luminous efficiency,so in this paper,single-layer WS₂ film is selected as the research objective.Here,we made a simple and large-area photodetector based on monolayer WS₂with high light sensitivity and fast response,benefiting from the special dynamics of carrier.Also it is important to determine the time-dependent evolution of the excited monolayer WS₂,which will provide a basis for reasonable design of optoelectronic devices based on two-dimensional transition metal dichalcogenides,thus,we tested the relaxation behavior of excited monolayer WS₂ by employing transient absorption（TA）.It is found that the multi-body interaction among exciton would occur after the density of pump photon increases to 3.45×10¹⁴ photons cm^-2.The exciton dissociation accompanying with the generation of trion would appear in the photo-induced relaxation process,which would be benefit for the operation of this photodetector.The high energy exciton transition is good for the generation of carrier through comparing the relaxation behavior of WS₂ excited into A and B exciton state originated from the splitting of valence band.However,the bound exciton relaxation originated from capture process of defect state would exist and play an unfavorable role during the working of devices.In order to further study the exciton dynamics in the monolayer WS₂,we use transient absorption（TA）to detect the time-resolved optical response of the monolayer WS₂ film and identify its exciton relaxation mechanism.We find that the multi-body interaction between A exciton is further clarified through changing the intensity of pump and probe laser.Specifically,we find the trapping process of exciton and the exciton radiative recombination would be dominant in the relaxation process of A exciton,besides the exciton-exciton annihilation will also occupy the decay channel at high pump intensity.更多还原