Yue Yuan-Yuan, Wang Zhuo, Wang Lei, Wang Hai-Yu, Chen Yang, Wang Dan, Chen Qi-Dai, Gao Bing-Rong, Wee Andrew T S, Qiu Cheng-Wei, Sun Hong-Bo
State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, People's Republic of China.
International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology of Ministry of Education, Institute of Microscale Optoelectronics, Shenzhen University, Shenzhen 518060, People's Republic of China.
Nanotechnology. 2021 Jan 8;32(13). doi: 10.1088/1361-6528/abcfec.
Band renormalization effects play a significant role for two-dimensional (2D) materials in designing a device structure and customizing their optoelectronic performance. However, the intrinsic physical mechanism about the influence of these effects cannot be revealed by general steady-state studies. Here, band renormalization effects in organic superacid treated monolayer MoS, untreated monolayer MoSand few-layer MoSare quantitatively analyzed by using broadband femtosecond transient absorption spectroscopy. In comparison with the untreated monolayer, organic superacid treated monolayer MoSmaintains a direct bandgap structure with two thirds of carriers populated at K valley, even when the initial exciton density is as high as 2.05 × 10cm(under 400 nm excitations). While for untreated monolayer and few-layer MoS, many-particle induced band renormalizations lead to a stronger imbalance for the carrier population between K and Q valleys inspace, and the former experiences a direct-to-indirect bandgap transition when the initial exciton density exceeds 5.0 × 10cm(under 400 nm excitations). Those many-particle induced band renormalization processes further suggest a band-structure-controlling method in practical 2D devices.
能带重整化效应在二维（2D）材料的器件结构设计和光电性能定制方面发挥着重要作用。然而，这些效应影响的内在物理机制无法通过一般的稳态研究揭示。在此，利用宽带飞秒瞬态吸收光谱对有机超酸处理的单层MoS₂、未处理的单层MoS₂和少层MoS₂中的能带重整化效应进行了定量分析。与未处理的单层相比，即使在初始激子密度高达2.05×10¹²cm⁻²（在400nm激发下）时，有机超酸处理的单层MoS₂仍保持直接带隙结构，且三分之二的载流子分布在K谷。而对于未处理的单层和少层MoS₂，多粒子诱导的能带重整化导致K谷和Q谷之间载流子分布在空间上的不平衡更强，并且当初始激子密度超过5.0×10¹¹cm⁻²（在400nm激发下）时，前者会经历从直接带隙到间接带隙的转变。那些多粒子诱导的能带重整化过程进一步表明了一种在实际二维器件中的能带结构控制方法。
