New materials and designs for 2D-based infrared photodetectors

Infrared photodetectors have attracted much attention considering their wide civil and military applications. Two-dimensional (2D) materials offer new opportunities for the development of costless, high-level integration and high-performance infrared photodetectors. With the advent of a broad investigation of infrared photodetectors based on graphene and transition metal chalcogenides (TMDs) exhibiting unique properties in recent decades, research on the better performance of 2D-based infrared photodetectors has been extended to a larger scale, including explorations of new materials and artificial structure designs. In this review, after a brief background introduction, some major working mechanisms, including the photovoltaic effect, photoconductive effect, photogating effect, photothermoelectric effect and bolometric effect, are briefly offered. Then, the discussion mainly focuses on the recent progress of three categories of 2D materials beyond graphene and TMDs. Noble transition metal dichalcogenides, black phosphorus and arsenic black phosphorous and 2D ternary compounds are great examples of explorations of mid-wavelength or even long-wavelength 2D infrared photodetectors. Then, four types of rational structure designs, including type-II band alignments, photogating-enhanced designs, surface plasmon designs and ferroelectric-enhanced designs, are discussed to further enhance the performance via diverse mechanisms, which involve the narrower-bandgap-induced interlayer exciton transition, gate modulation by trapped carriers, surface plasmon polaritons and ferroelectric polarization in sequence. Furthermore, applications including imaging, flexible devices and on-chip integration for 2D-based infrared photodetectors are introduced. Finally, a summary of the state-of-the-art research status and personal discussion on the challenges are delivered.