Unveiling Optoelectronic Properties and Charge Carrier Dynamic Mechanisms in Bi2Se3-Based vdW Heterostructures

Abstract

van der Waals (vdW) heterostructures, combining 2D and topological materials, show strong potential for advancing device performance in optoelectronics and spintronics, offering enhanced charge transport, spin coherence, and optical properties. This study investigates the photoconductivity response of vdW heterostructures fabricated using a wet transfer process, where graphene, fluorographene (FG), molybdenum disulfide (MoS₂), and molybdenum diselenide (MoSe₂) are layered on top of bismuth selenide (Bi₂Se₃), a well-known topological insulator. The integration of these 2D materials with Bi₂Se₃ results in heterostructures with a reduced dark current (I_dark) and improved photodetection performance. Specifically, I_dark was reduced significantly by 32% in graphene/Bi₂Se₃, 48% in MoS₂/Bi₂Se₃, and 31% in MoSe₂/Bi₂Se₃ compared to intrinsic Bi₂Se₃, with significantly decreased noise and enhanced device sensitivity. However, the vdW heterostructures graphene/Bi₂Se₃, FG/Bi₂Se₃, MoS₂/Bi₂Se₃, and MoSe₂/Bi₂Se₃ exhibit an increase in the photoconductive response by 17, 10, 51, and 31%, respectively. This improvement is attributed to the band alignment between Bi₂Se₃ and 2D materials, which suppresses thermally generated carrier flow by creating potential barriers at the interfaces. To understand the underlying charge carrier dynamics, time-resolved transient absorption spectroscopy was employed, revealing distinct charge transfer mechanisms within these heterostructures. The analysis uncovered interfacial phenomena such as exciton transfer, charge accumulation, and the formation of trap states with varying carrier lifetimes. The heterostructure’s MoS₂/Bi₂Se₃ and MoSe₂/Bi₂Se₃ also exhibited tunability in their excitonic energies, further emphasizing their potential for optoelectronic applications. This study establishes vdW heterostructures of 2D and topological materials as a promising strategy for developing highly efficient optoelectronic and spintronic devices.