Sub‐bandgap activated charges transfer in a graphene‐MoS2‐graphene heterostructure

• Published in: Nano select 2021-10, Vol.2 (10), p.2019-2028
• Main Authors: Kumar, Sunil, Singh, Arvind, Nivedan, Anand, Kumar, Sandeep, Yun, Seok Joon, Lee, Young Hee, Tondusson, Marc, Degert, Jérôme, Oberle, Jean, Freysz, Eric
• Format: Article
• Language: English
• Subjects: Broadband; carrier dynamics; Chalcogenides; Electrons; Energy gap; Experiments; Graphene; Heterostructures; Molybdenum disulfide; Monolayers; Optical activity; Optics; Optoelectronics; Photoexcitation; Photons; Photovoltaic cells; Spectrum analysis; terahertz; Transistors; Transition metal compounds; transition metal dichalcogenides; ultrafast detector
• ISSN: 2688-4011; 2688-4011
• DOI: 10.1002/nano.202000159

Monolayers of transition metal dichalcogenides are semiconducting materials which offer many prospects in optoelectronics. A monolayer of molybdenum disulfide (MoS2) has a direct bandgap of 1.88 eV. Hence, when excited with optical photon energies below its bandgap, no photocarriers are generated and a monolayer of MoS2 is not of much use in either photovoltaics or photodetection. Here, we demonstrate that large size MoS2 monolayer sandwiched between two graphene layers makes this heterostructure optically active well below the band gap of MoS2. An ultrafast optical pump‐THz probe experiment reveals in real‐time, transfer of carriers between graphene and MoS2 monolayer upon photoexcitation with photon energies down to 0.5 eV. It also helps to unravel an unprecedented enhancement in the broadband transient THz response of this tri‐layer material system. We propose possible mechanism which can account for this phenomenon. Such specially designed heterostructures, which can be easily built around different transition metal dichalcogenide monolayers, will considerably broaden the scope for modern optoelectronic applications at THz bandwidth. MoS2 monolayer sandwiched between two graphene layers is found to be optically active well below the band gap of MoS2 down to ∼0.5 eV. The ultrafast optical pump‐THz probe experiments help to unravel an unprecedented enhancement in the broadband THz response of this specially engineered large area 2D heterostructure.