Hu Zifan, Wang Hai, Wang Lei, Wang Haiyu
State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China.
Phys Chem Chem Phys. 2024 Mar 20;26(12):9424-9431. doi: 10.1039/d3cp05282f.
Most transition metal dichalcogenide (TMD) heterostructures (HSs) exhibit a type II band alignment, leading to a charge transfer process accompanied by the transfer of spin-valley polarization and spontaneous formation of interlayer excitons. This unique band structure facilitates achieving a longer exciton lifetime and extended spin-valley polarization lifetime. However, the mechanism of charge transfer in type II TMD HSs is not fully comprehended. Here, the ultrafast charge transfer process is studied in MoSe-WSe HS valley-solved broadband pump-probe spectroscopy. Under the conditions of B-excitons of WSe and MoSe being resonantly pumped, a new charge transfer pathway through the higher energy state associated with the B-exciton is found. Meanwhile, the holes (electrons) in the WSe (MoSe) layer of MoSe-WSe HS produce obvious spin-valley polarization even under the condition of B-exciton of WSe (MoSe) being resonantly pumped, and the lifetime can reach tens of ps, which is in stark contrast to the absence of A-exciton spin-valley polarization in monolayer WSe (MoSe) under the same pumping condition. The results deepen the insight into the charge transfer process in type II TMD HSs and show the great potential of TMD HSs in the application of spin-valley electronics devices.
大多数过渡金属二硫属化物（TMD）异质结构（HSs）呈现II型能带排列，导致电荷转移过程伴随着自旋-谷极化的转移和层间激子的自发形成。这种独特的能带结构有助于实现更长的激子寿命和延长的自旋-谷极化寿命。然而，II型TMD HSs中电荷转移的机制尚未完全理解。在此，利用谷分辨宽带泵浦-探测光谱研究了MoSe-WSe HS中的超快电荷转移过程。在WSe和MoSe的B激子被共振泵浦的条件下，发现了一条通过与B激子相关的高能态的新电荷转移途径。同时，即使在WSe（MoSe）的B激子被共振泵浦的条件下，MoSe-WSe HS的WSe（MoSe）层中的空穴（电子）也会产生明显的自旋-谷极化，其寿命可达数十皮秒，这与在相同泵浦条件下单层WSe（MoSe）中不存在A激子自旋-谷极化形成鲜明对比。这些结果加深了对II型TMD HSs中电荷转移过程的理解，并展示了TMD HSs在自旋-谷电子器件应用中的巨大潜力。
