Inhomogeneous photocarrier dynamics and transport in monolayer MoS2 by ultrafast microscopy
Inhomogeneous photocarrier dynamics and transport in monolayer MoS2 by ultrafast microscopy
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通过超快显微镜研究单层 MoS2 中的不均匀光载流子动力学和传输
DOI：
10.1088/1361-6528/ab3dc2
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发表时间：
2019-09
期刊：
影响因子：
3.5
通讯作者：
Guo Ping Wang
中科院分区：
文献类型：
--
作者：
Kuai Yu;Junzhong Wang;Jing Chen;Guo Ping Wang
单层MoS_2作为二维过渡金属二卤化物(TMDs)的一员，由于其优异的光电性能而引起了人们的广泛关注。了解这些二维系统中的光载流子动力学和输运特性对于从光伏到传感的应用都是有益的。然而，各种结构缺陷强烈地影响着光载流子的动力学和输运。尤其是对TMD中的光载流子输运缺乏精确的测量和了解。本文利用飞秒暂态吸收光谱和显微技术研究了MoS_2单层膜的光载流子动力学和输运特性。在单层MoS_2上观察到缺陷相关的光载流子动力学，其中激子形成和非辐射复合是两个主要的衰减过程。据我们所知，我们首次报道了MoS_2中两种不同的光载流子输运机制，扩散系数分别为D f a S t=8.5±0.4cm2 S−1和D S L o w=1.3±0.6cm2 S−1，利用∼2 0 nm空间精度和∼2 0 0fs时间分辨率的超快显微镜优势。这两个区域分别归因于快速的热载流子扩散和慢的声子限制热扩散。结果表明，与光载流子弛豫动力学相比，初始的快速光载流子输运对结构缺陷的依赖程度较小，这对于热载流子提取应用可能是有用的。
Monolayer MoS2 as a member of two-dimensional transition metal dichalcogenides (TMDs) has attracted considerable attention due to its superior optoelectronic properties. Understanding the photocarrier dynamics and transport in these two dimensional systems is beneficial for applications from photovoltaics to sensing. However, various structural defects strongly impact the dynamics and transport of photocarriers. Especially there lacks a precise measuring and understanding of photocarrier transport in TMDs. Here, femtosecond transient absorption spectroscopy and microscopy were employed to study the photocarrier dynamics and transport in monolayer MoS2. Defect correlated photocarrier dynamics are observed across the monolayer MoS2 where exciton formation and nonradiative recombination are the two dominant decay processes. To the best of our knowledge, we report two distinct photocarrier transport regimes in MoS2 for the first time with diffusion coefficients of D f a s t = 8.5 ± 0.4 cm2 s−1 and D s l o w = 1.3 ± 0.6 cm2 s−1, by taking advantages of ultrafast microscopy with ∼20 nm spatial precision and ∼200 fs temporal resolution. These two regimes are ascribed to fast hot photocarrier diffusion and slow phonon-limited thermal diffusion, respectively. The results indicate that the initial fast photocarrier transport is less dependent on structural defects compared to photocarrier relaxation dynamics which may be useful for hot photocarrier extraction applications.
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