Probing ultrafast charge transfer in 2D heterostructures of transition-metal dichalcogenides (TMDCs)
Two-dimensional materials field started by initial research on graphene (also awarded by Nobel prize in 2010). Now, this field is extending to other 2D materials which can provide different electronic functionality such as semiconductors, insulators, ferroelectrics, etc. From this respect, transition-metal dichalcogenide (TMDC) class (e.g., MoS2, WS2, WTe2 and etc.) offers broad range of tunability of these physical properties. Furthermore, hetero-structrues of TMDC 2D materials enable novel optoelectronic properties that led to world's thinnest opto-electronic devices such as photo-detectors and solar cells that are only three to four atoms thick.
For designing and developing these devices, it is essential to understand the motion of electrons in these heterostructures. Recently, we demonstrated that 2D heterostructures with Type-II band alignment leads to strong terahertz (THz) radiation analyzing which we can characterize the time-scale of the electron transfer from one layer to another layer in a bilayered system, forming a p-n junction at the atomic scale.
Our measurements enable us for the first time a direct access to the absolute efficiency of this charge transfer process. Within the first several hundered femtosecond following photo-excitation of the heterostructure, at least 70% of the excited state electrons migrate to the layer with lower conduction band energy. This efficient charge separation occuring at ultrafast timescale highlights the potential of these materials for efficient light-detection and photovoltaics systems.
Selected Publications:
E. Y. Ma*, B. Guzelturk*, G. Li, L. Cao, Z. X. Shen, A. M. Lindenberg, T. F. Heinz, “Recording Interfacial Currents on the Sub-Nanometer Length and Femtosecond Time Scale by Terahertz Emission” Science Advances Accepted for publication (2018). * Equal contribution