Semi-metallic Bi2Se3 contact-based interface engineering on monolayer MoS2 for high-performance field-effect transistors and flexible photodetectors

Abstract

The metal–semiconductor junction interface plays a critical role in the performance of a semiconductor optoelectronic device. The high evaporation temperature of conventional metal contacts on ultrathin 2D materials usually induces defects at the metal/semiconductor interface, degrading device performance. This study explores a novel low-temperature deposited semi-metallic topological insulator, Bi₂Se₃, as contacts for monolayer MoS₂ (1L-MoS₂) to fabricate high-performance electronic and optoelectronic devices. It is demonstrated that Bi₂Se₃ contacts on 1L-MoS₂ reduce the interface defect density drastically and also reduce the potential barrier, thereby enhancing the field-effect transistor performance in terms of sub-threshold swings, mobility, and threshold voltage. Notably, the on–off ratio is improved by two orders of magnitude, reaching 10⁸ by reducing the off-state current. We further demonstrate a flexible 1L-MoS₂ photodetector (PD) with Bi₂Se₃ contacts on a PET substrate, achieving an excellent on–off ratio (∼10³), more than twice that of conventional Cr/Au contacts, and it is shown to be sensitive to the bending strain. Various PD performance metrics (e.g., responsivity, detectivity, and external quantum efficiency) also significantly improved owing to contact engineering. These findings emphasize the role of a nearly defect-free contact interface and a lower potential barrier in 2D material devices. This showcases the potential of highly stable ultrathin Bi₂Se₃ for cost-effective and flexible electronics on low-cost flexible substrates.